vvEPA
   United States
   Environmental Protection
   Agency
Method 624.1 - Purgeables by GC/MS
December 2014

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                 U.S. Environmental Protection Agency
                           Office of Water
                   Office of Science and Technology
               Engineering and Analysis Division (4303T)
                   1200 Pennsylvania Avenue, NW
                       Washington, DC 20460
                         EPA-821-R-14-014
Method 624.1                           i                         December 2014

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                         METHOD 624.1 - PURGEABLES BY GC/MS
1.    Scope and Application

1.1   This method is for determination of purgeable organic pollutants in industrial discharges and other
      environmental samples by gas chromatography combined with mass spectrometry (GC/MS), as
      provided under 40 CFR 136.1.  This revision is based on previous protocols (References 1 - 3), on
      the revision promulgated October 26,  1984 (49 FR 43234), and on an interlaboratory method
      validation study (Reference 4). Although this method was validated through an interlaboratory
      study conducted more than 29 years ago, the fundamental chemistry principles used in this method
      remain sound and continue to apply.

1.2   The analytes that may be qualitatively and quantitatively determined using this method and their
      CAS Registry numbers are listed in Table  1.  The method may be extended to determine the
      analytes listed in Table 2; however, poor purging efficiency or gas chromatography of some of
      these analytes may make quantitative  determination difficult. For example, an elevated temperature
      may be required to purge some analytes from water.  If an elevated temperature is used, calibration
      and all quality control (QC) tests must be performed at the elevated temperature. EPA encourages
      the use of this method to determine additional compounds amenable to purge-and-trap GC/MS.

1.3   The large number of analytes in Tables 1 and 2 of this method makes testing difficult if all analytes
      are determined simultaneously.  Therefore, it is necessary to determine and perform QC tests for
      "analytes of interest" only.  Analytes of interest are those required to be determined by a
      regulatory/control authority or in a permit, or by a client. If a list of analytes is not specified, the
      analytes in Table 1 must be determined, at a minimum, and QC testing must be performed for these
      analytes. The analytes in Table 1 and some of the analytes in Table 2 have been identified as Toxic
      Pollutants (40 CFR 401.15), expanded to a list of Priority Pollutants (40 CFR 423, appendix A).

1.4   Method detection limits (MDLs; Reference 5) for the  analytes in Table 1 are listed in that table.
      These  MDLs were determined in reagent water (Reference 6). Advances in analytical technology,
      particularly the use of capillary (open-tubular) columns, allowed laboratories to routinely achieve
      MDLs for the analytes in this method  that are 2 - 10 times lower than those in the version
      promulgated in 1984 (40 FR 43234).  The MDL for a specific wastewater may differ from those
      listed,  depending on the nature of interferences in the  sample matrix.

      1.4.1    EPA has promulgated this method at 40 CFR Part 136 for use in wastewater compliance
             monitoring under the National Pollutant Discharge Elimination System (NPDES). The data
             reporting practices described in Section 13.2 are focused on such monitoring needs and
             may not be relevant to other uses of the method.

      1.4.2   This method includes "reporting limits" based on EPA's "minimum level" (ML) concept
             (see the glossary in Section 20). Table 1 contains MDL values and ML values for many of
             the analytes. The MDL for an analyte in a specific wastewater may differ from that listed
             in Table 1, depending upon the nature of interferences in the sample matrix.

1.5   This method is performance-based. It may be modified to improve performance (e.g., to overcome
      interferences or improve the accuracy of results) provided all performance requirements are met.

      1.5.1    Examples of allowed method  modifications are described at 40 CFR 136.6. Other
             examples of allowed modifications specific to this method are described in Section 8.1.2.
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      1.5.2   Any modification beyond those expressly allowed at 40 CFR 136.6 or in Section 8.1.2 of
             this method shall be considered a major modification that is subject to application and
             approval of an alternate test procedure under 40 CFR 136.4 and 136.5.

      1.5.3   For regulatory compliance, any modification must be demonstrated to produce results
             equivalent or superior to results produced by this method when applied to relevant
             wastewaters (Section 8.3).

1.6   This method is restricted to use by or under the supervision of analysts experienced in the operation
      of a purge-and-trap system and a gas chromatograph/mass spectrometer and in the interpretation of
      mass spectra.  Each analyst must demonstrate the ability to generate acceptable results with this
      method using the procedure in Section 8.2.

1.7   Terms and units of measure used in this method are given in the glossary at the end of the method.
2.    Summary of Method

2.1   A gas is bubbled through a measured volume of water in a specially-designed purging chamber
      (Figure 1). The purgeables are efficiently transferred from the aqueous phase to the vapor phase.
      The vapor is  swept through a sorbent trap where the purgeables are trapped (Figure 2). After
      purging is completed, the trap is heated and backflushed with the gas to desorb the purgeables onto
      a gas chromatographic column (Figures 3 and 4).  The column is temperature programmed to
      separate the purgeables which are then detected with a mass spectrometer.

2.2   Different sample sizes in the range of 5 - 25 mL are allowed in order to meet differing sensitivity
      requirements. Calibration and QC samples must have the same volume as field samples.
3.    Interferences

3.1   Impurities in the purge gas, organic compounds outgassing from the plumbing ahead of the trap,
      and solvent vapors in the laboratory account for the majority of contamination problems. The
      analytical system must be demonstrated to be free from contamination under the conditions of the
      analysis by analyzing blanks as described in Section 8.5.  Fluoropolymer tubing, fittings, and thread
      sealant should be used to avoid contamination.

3.2   Samples can be contaminated by diffusion of volatile organics (particularly fluorocarbons and
      methylene chloride) through the septum seal into the sample during shipment and storage. Protect
      samples from sources of volatiles during collection, shipment, and storage.  A reagent water field
      blank carried through sampling and analysis can serve as a check on such contamination.

3.3   Contamination by carry-over can occur whenever high level and low level samples are analyzed
      sequentially. To reduce the potential for carry-over, the purging device and sample syringe must be
      rinsed with reagent water between sample analyses. Whenever an unusually concentrated sample is
      encountered, it should be followed by an analysis of a blank to check for cross contamination. For
      samples containing large amounts of water-soluble materials, suspended solids, high boiling
      compounds or high purgeable levels, it may be necessary to wash the purging device with a
      detergent solution, rinse it with distilled water, and then dry it in a 105C oven between analyses.
      The trap and other parts of the system are also subject to contamination; therefore, frequent bakeout
      and purging of the entire system may be required.  Screening samples at high dilution may prevent
      introduction of contaminants into the system.

Method 624.1                                     2                                    December 2014

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4.    Safety

4.1   The toxicity or carcinogenicity of each reagent used in this method has not been precisely defined;
      however, each chemical compound should be treated as a potential health hazard. From this
      viewpoint, exposure to these chemicals must be reduced to the lowest possible level. The
      laboratory is responsible for maintaining a current awareness file of OSHA regulations regarding
      the safe handling of the chemicals specified in this method. A reference file of safety data sheets
      (SDSs, OSHA, 29 CFR  1910.1200[g]) should also be made available to all personnel involved in
      sample handling and chemical analysis. Additional references to laboratory safety are available and
      have been identified (References 7-9) for the information of the analyst.

4.2.   The following analytes covered by this method have been tentatively classified as known or
      suspected human or mammalian carcinogens: benzene; carbon tetrachloride; chloroform; 1,4-
      dichlorobenzene; 1,2-dichloroethane; 1,2-dichloropropane; methylene chloride; tetrachloroethylene;
      trichloroethylene; and vinyl chloride. Primary standards of these toxic compounds should be
      prepared in a chemical fume hood, and a NIOSFi/MESA approved toxic gas respirator should be
      worn when handling high concentrations of these compounds.

4.3   This method allows the use of hydrogen as a carrier gas in place of helium (Section 5.3.1.2). The
      laboratory should take the necessary precautions in dealing with hydrogen, and should limit
      hydrogen flow at the source to prevent buildup of an explosive mixture of hydrogen in air.
5.   Apparatus and Materials

     Note:   Brand names, suppliers, and part numbers are cited for illustration purposes only.  No
             endorsement is implied. Equivalent performance may be achieved using equipment and
             materials other than those specified here. Demonstration of equivalent performance that
             meets the requirements of this method is the responsibility of the laboratory. Suppliers for
             equipment and materials in this method may be found through an on-line search.

     5.1     Sampling equipment for discrete sampling.

     5.1.1   Vial - 25 or 40 mL capacity, or larger, with screw cap with a hole in the center (Pierce
             #13075 or equivalent). Unless pre-cleaned, detergent wash, rinse with tap and reagent
             water, and dry at 105C before use.

     5.1.2   Septum - Fluoropolymer-faced silicone (Pierce #12722 or equivalent). Unless pre-cleaned,
             detergent wash, rinse with tap and reagent water, and dry at 105  5C for one hour before
             use.

5.2  Purge-and-trap system - The purge-and-trap system consists of three separate pieces of equipment:
     A purging device, trap, and desorber. Several complete systems are commercially available. Any
     system that meets the performance requirements in this method may be used.

     5.2.1   The purging device should accept 5- to 25-mL samples with a water column at least 3 cm
             deep.  The purge gas must pass though the water column as finely divided bubbles. The
             purge gas must be introduced no more than 5 mm from the base of the water column.  The
             purging device illustrated in Figure 1 meets these design criteria.  Purge devices of a
             different volume may be used so long as the performance requirements in this method are
             met.
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      5.2.2   The trap should be at least 25 cm long and have an inside diameter of at least 0.105 in.  The
             trap should be packed to contain the following minimum lengths of adsorbents:  1.0 cm of
             methyl silicone coated packing (Section 6.3.2), 15 cm of 2,6-diphenylene oxide polymer
             (Section 6.3.1), and 8 cm of silica gel (Section 6.3.3). The minimum specifications for the
             trap are illustrated in Figure 2. A trap with different dimensions and packing materials is
             acceptable so long as the performance requirements in this method are met.
      5.2.3   The desorber should be capable of rapidly heating the trap to the temperature necessary to
             desorb the analytes of interest, and of maintaining this temperature during desorption. The
             trap should not be heated higher than the maximum temperature recommended by the
             manufacturer. The desorber illustrated in Figure 2 meets these design criteria.

      5.2.4   The purge-and-trap system may be assembled as a separate unit or coupled to a gas
             chromatograph as illustrated in Figures 3 and 4.

5.3   GC/MS system

      5.3.1   Gas chromatograph (GC) - An analytical system complete with a temperature
             programmable gas chromatograph and all required accessories, including syringes and
             analytical columns. Autosamplers designed for purge-and-trap analysis of volatiles also
             may be used.

             5.3.1.1   Injection port - Volatiles interface, split, splitless, temperature programmable
                      split/splitless (PTV), large volume, on-column, backflushed, or other.

             5.3.1.2   Carrier gas - Data in the tables in this method were obtained using helium carrier
                      gas.  If another carrier gas is used, analytical conditions may need to be adjusted
                      for optimum performance, and calibration and all QC tests must be performed
                      with the alternate carrier gas. See Section 4.3 for precautions regarding the use
                      of hydrogen as a carrier gas.

      5.3.2   GC column - See the footnote to Table 3. Other columns or column systems may be used
             provided all requirements in this method are met.

      5.3.3   Mass spectrometer - Capable of repetitively scanning from 35-260 Daltons (amu) every 2
             seconds or less, utilizing a 70 eV (nominal) electron energy in the electron impact
             ionization mode, and producing a mass spectrum which meets all criteria in Table 4 when
             50 ng or less of 4-bromofluorobenzene (BFB) is injected through the GC inlet. If acrolein,
             acrylonitrile, chloromethane, and vinyl chloride are to be determined, it may be necessary
             to scan from below 25 Daltons to measure the peaks in the 26-35 Dalton range for reliable
             identification.

      5.3.4   GC/MS interface - Any GC to MS interface that meets all performance requirements in this
             method may be used.

      5.3.5   Data system - A computer system must be interfaced to the mass spectrometer that allows
             continuous acquisition and storage of mass spectra throughout the chromatographic
             program. The computer must have software that allows searching any GC/MS data file for
             specific m/z's (masses) and plotting m/z abundances versus time or scan number. This type
             of plot is defined as an extracted ion current profile (EICP).  Software must also be
             available that allows integrating the abundance at any EICP between specified time or scan
             number limits.
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5.4   Syringes - Graduated, 5-25 mL, glass hypodermic with Luerlok tip, compatible with the purging
      device.

5.5   Micro syringes - Graduated, 25 - 1000 uL, with 0.006 in. ID needle.

5.6   Syringe valve - Two-way, with Luer ends
5.7   Syringe - 5 mL, gas-tight with shut-off valve.

5.8   Bottle - 15 mL, screw-cap, with Teflon cap liner.

5.9   Balance - Analytical, capable of accurately weighing 0.0001 g.


6.    Reagents

6.1   Reagent water - Reagent water is defined as water in which the analytes of interest and interfering
      compounds are not detected at the MDLs of the analytes of interest. It may be generated by passing
      deionized water, distilled water, or tap water through a carbon bed, passing the water through a
      water purifier, or heating the water to between 90 and  100C while bubbling contaminant free gas
      through it for approximately 1  hour. While still hot, transfer the water to screw-cap bottles and seal
      with a fluoropolymer-lined cap.

6.2   Sodium thiosulfate - (ACS) Granular.

6.3   Trap materials

       6.3.1   2,6-Diphenylene oxide polymer- Tenax, 60/80 mesh, chromatographic grade, or
               equivalent.

       6.3.2   Methyl silicone packing - 3%  OV-1 on Chromosorb-W, 60/80 mesh, or equivalent.

       6.3.3   Silica gel - 35/60 mesh, Davison, Grade-15  or equivalent.

               Other trap materials  are acceptable if performance requirements in this method are met.

6.4   Methanol - Demonstrated to be free from the target analytes and potentially interfering compounds.

6.5   Stock standard solutions - Stock standard solutions may be prepared from pure materials, or
      purchased as certified solutions. Traceability must be  to the National Institute of Standards and
      Technology (NIST) or other national standard.  Stock  solution concentrations alternate to those
      below may be used. Prepare stock standard solutions in methanol using assayed liquids or gases as
      appropriate.  Because some of the compounds in this method are known to be toxic, primary
      dilutions should be prepared in a hood, and a NIOSH/MESA approved toxic gas respirator should
      be worn when high concentrations of neat materials are handled.  The following procedure may be
      used to prepare standards from neat materials:

      6.5.1   Place about 9.8 mL of methanol  in a 10-mL ground-glass-stoppered volumetric flask.
             Allow the flask to stand, unstoppered, for about 10 minutes or until all alcohol wetted
             surfaces have dried.  Weigh the flask to the nearest 0.1 mg.

      6.5.2   Add the assayed reference material.
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             6.5.2.1   Liquids - Using a 100 uL syringe, immediately add two or more drops of assayed
                      reference material to the flask. Be sure that the drops fall directly into the
                      alcohol without contacting the neck of the flask. Reweigh, dilute to volume,
                      stopper, then mix by inverting the flask several times.  Calculate the
                      concentration in ug/uL from the net gain in weight.

             6.5.2.2   Gases - To prepare standards for any of compounds that boil below 30C, fill a
                      5-mL valved gas-tight syringe with reference standard vapor to the 5.0 mL mark.
                      Lower the needle to 5 mm above the methanol meniscus. Slowly introduce the
                      vapor above the surface of the liquid (the vapor will rapidly  dissolve in the
                      methanol). Reweigh, dilute to volume, stopper, then mix by inverting the flask
                      several times. Calculate the concentration in ug/uL from the net gain in weight.

      6.5.3   When compound purity is assayed to be 96% or greater, the weight may be used without
             correction to calculate the concentration of the stock standard.  Commercially prepared
             stock standards may be used at any concentration if they are certified by the manufacturer
             or by an independent source.

      6.5.4   Prepare fresh standards weekly for the gases and 2-chloroethylvinyl ether.  All standards
             should be replaced after one month, or sooner if the concentration of an analyte changes by
             more than 10 percent.

      Note:  2-Chloroethylvinyl ether has been shown to be stable for as long as one month if prepared
             as a separate standard, and the other analytes have been shown to be stable for as long as
             2 months if stored at less  than -10C with minimal headspace in sealed, miniature  inert-
             valved vials.

6.6   Secondary dilution standards - Using  stock solutions, prepare secondary dilution standards in
      methanol that contain the compounds  of interest, either singly or mixed.  Secondary dilution
      standards should be prepared at concentrations such that the aqueous calibration standards prepared
      in Section 7.3.2 will bracket the working range of the analytical system.

6.7   Surrogate standard spiking solution -  Select a minimum of three surrogate compounds from Table
      5. The surrogates selected should match the purging characteristics of the analytes of interest as
      closely as possible. Prepare a stock standard solution for each surrogate in methanol as described in
      Section 6.5, and prepare a solution for spiking the surrogates into all blanks, LCSs, and MS/MSDs.
      The spiking solution should be prepared such that spiking a small volume will  result in surrogate
      concentrations  near the mid-point of the calibration range.  For example, adding 10 uL of a spiking
      solution containing the surrogates at a concentration of 15 ug/mL in methanol to a 5-mL aliquot of
      water would result in a concentration of 30  ug/L for each surrogate. Other surrogate concentrations
      may be used.

6.8   BFB standard - Prepare a solution of BFB in methanol as described in Sections 6.5 and 6.6. The
      solution should be prepared such that  an injection or purging from water will result in introduction
      of < 50 ng into the GC. BFB may be included in a mixture with the internal standards and/or
      surrogates.

6.9   Quality control check sample concentrate - See Section 8.2.1.

6.10  Storage - When not being used, store  standard solutions (Sections 6.5 - 6.9) at -10 to -20C,
      protected from light, in fluoropolymer-sealed glass containers with minimal headspace.
Method 624.1                                      6                                    December 2014

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7.    Calibration

7.1   Assemble a purge-and-trap system that meets the specifications in Section 5.2. Prior to first use,
      condition the trap overnight at 180C by backflushing with gas at a flow rate of at least 20 mL/min.
      Condition the trap daily prior to use.

7.2   Connect the purge-and-trap system to the gas chromatograph. The gas chromatograph should be
      operated using temperature and flow rate conditions equivalent to those given in the footnotes to
      Table 3. Alternative temperature and flow rate conditions may be  used provided that performance
      requirements in this method are met.

7.3   Internal standard calibration

      7.3.1   Internal standards

             7.3.1.1   Select three or more internal standards similar in chromatographic behavior to
                      the compounds of interest. Suggested internal standards are listed in Table 5.
                      Use the base peak m/z as the primary m/z for quantification of the standards.  If
                      interferences are found at the base peak, use one of the next two most intense
                      m/z's for quantitation. Demonstrate that measurement of the internal standards
                      are not affected by method or matrix interferences.

             7.3.1.2   To assure accurate analyte identification, particularly when selected ion
                      monitoring (SIM) is used, it may be advantageous to include more internal
                      standards than those suggested in Section 7.3.1.1. An analyte will be located
                      most accurately if its retention time relative to an internal standard is in the range
                      of 0.8 to 1.2.

             7.3.1.3   Prepare a stock standard solution for each internal standard surrogate in methanol
                      as described in Section 6.5, and prepare a solution for spiking the internal
                      standards into all blanks, LCSs, and MS/MSDs. The spiking solution should be
                      prepared such that spiking a small volume will result in internal standard
                      concentrations near the mid-point of the calibration range. For example, adding
                      10 uL of a spiking solution containing the internal standards at a concentration of
                      15 ug/mL in methanol to a 5-mL aliquot of water would result in a concentration
                      of 30 ug/L for each internal standard.  Other concentrations may be used. The
                      internal standard solution and the surrogate standard spiking solution (Section
                      6.7) may be combined, if desired. Store the solution at <6C in fluoropolymer-
                      sealed glass containers with a minimum of headspace. Replace the solution after
                      1 month, or more frequently if comparison with QC  standards indicates a
                      problem.

      7.3.2   Calibration

             7.3.2.1   Calibration standards

                      7.3.2.1.1    Prepare calibration  standards at a minimum of five concentration
                                  levels for each analyte of interest by adding appropriate volumes of
                                  one or more stock standards to a fixed volume (e.g., 40 mL) of
                                  reagent water in volumetric glassware. Fewer levels may be
                                  necessary for some analytes based on the sensitivity of the MS. The
                                  concentration of the lowest calibration standard for an analyte should

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                                 be at or near the ML value in Table 1 for an analyte listed in that
                                 table. The ML value may be rounded to a whole number that is more
                                 convenient for preparing the standard, but must not exceed the ML
                                 values listed in Table 1 for those analytes which list ML values.
                                 Alternatively, the laboratory may establish the ML for each analyte
                                 based on the concentration of the lowest calibration standard in a
                                 series of standards obtained from a commercial vendor, again,
                                 provided that the ML values does not exceed the MLs in Table 1,
                                 and provided that the resulting calibration meets the acceptance
                                 criteria in Section 7.3.4, based on the RSD, RSE, or R2.

                                 The concentrations of the higher standards should correspond to the
                                 expected range of concentrations found in real samples, or should
                                 define the working range of the GC/MS system for full-scan and/or
                                 SIM operation, as appropriate. A minimum of six concentration
                                 levels is required for a second order, non-linear (e.g.,  quadratic; ax2 +
                                 bx + c) calibration. Calibrations higher than second order are not
                                 allowed.

                      7.3.2.1.2   To each calibration standard or standard mixture, add a known
                                 constant volume of the internal standard spiking solution (Section
                                 7.3.1.3) and surrogate standard spiking solution (Section 6.7) or the
                                 combined internal standard solution and surrogate spiking solution
                                 (Section 7.3.1.3). Aqueous standards may be stored up to 24 hours,
                                 if held in sealed vials with zero headspace as described in Section
                                 9.1. If not so stored, they must be  discarded after one hour.

             7.3.2.2   Prior to analysis of the calibration standards, analyze the BFB standard (Section
                      6.8) and adjust the scan rate of the MS to produce a minimum of 5 mass spectra
                      across the BFB GC peak, but do not exceed 2 seconds per scan. Adjust
                      instrument conditions until the BFB criteria in Table 4 are met.

             Note:    The BFB spectrum may be evaluated by summing the intensities of the m/z 's
                      across the GC peak, subtracting the background at each m/z in a region of the
                      chromatogram within 20 scans of but not including any part of the BFB peak.
                      The BFB spectrum may also be evaluated by fitting a Gaussian to each m/z and
                      using the intensity at the maximum for each Gaussian, or by integrating the area
                      at each m/z and using the integrated areas.  Other means may be used for
                      evaluation of the BFB spectrum so long as the spectrum is not distorted to meet
                      the criteria in Table 4.

             7.3.2.3   Analyze the mid-point standard and enter or review the retention time, relative
                      retention time, mass spectrum, and quantitation m/z in the data system for each
                      analyte of interest, surrogate, and internal standard. If additional analytes (Table
                      2) are to be quantified, include these analytes in the standard. The mass spectrum
                      for each analyte must be comprised of a minimum of 2 m/z's; 3 to 5 m/z's assure
                      more reliable analyte identification.  Suggested quantitation m/z's are shown in
                      Table 6 as the primary m/z.  For analytes in Table 6 that do not have a secondary
                      m/z, acquire a mass spectrum and enter one or more secondary m/z's for more
                      reliable identification.  If an interference occurs at the primary m/z, use one of
                      the secondary m/z's or an alternate m/z.  A single m/z only is required for
                      quantitation.

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             7.3.2.4   For SIM operation, determine the analytes in each descriptor, the quantitation
                      m/z for each analyte (the quantitation m/z can be the same as for full-scan
                      operation; Section 7.3.2.3), the dwell time on each m/z for each analyte, and the
                      beginning and ending retention time for each descriptor. Analyze the verification
                      standard in scan mode to verify m/z's and establish retention times for the
                      analytes. There must be a minimum of two m/z's for each analyte to assure
                      analyte identification. To maintain sensitivity, the number of m/z's in a
                      descriptor should be limited. For example, for a descriptor with 10 m/z's and a
                      chromatographic peak width of 5 sec, a dwell time of 100 ms at each m/z would
                      result in a scan time of 1  second and provide 5 scans across the GC peak. The
                      quantitation m/z will usually be the most intense peak in the mass spectrum.  The
                      quantitation m/z and dwell time may be optimized for each analyte. However, if
                      a GC peak spans two (or more) descriptors, the dwell time and cycle time
                      (scans/sec) should be  set to the same value in both segments in order to maintain
                      equivalent response.  The acquisition table used for SIM must take into account
                      the mass defect (usually less than 0.2 Dalton) that can occur at each m/z
                      monitored.

             7.3.2.5   For combined scan and SIM operation, set up the scan segments and descriptors
                      to meet requirements in Sections 7.3.2.2 - 7.3.2.4.

      7.3.3   Analyze each calibration standard according to Section 10 and tabulate the area at the
             quantitation m/z against concentration for each analyte of interest, surrogate, and internal
             standard. Calculate the response factor (RF) for each compound at each concentration
             using Equation 1 .
                                           Equation 1

                                               (AsxCis)
               where:
               As =   Area of the characteristic m/z for the analyte to be measured.
               A1S=   Area of the characteristic m/z for the internal standard.
               Cjs=   Concentration of the internal standard (ug/L).
               Cs =   Concentration of the analyte to be measured (ug/L).

      7.3.4   Calculate the mean (average) and relative standard deviation (RSD) of the response factors.
             If the RSD is less than 35%, the RF can be assumed to be invariant and the average RF can
             be used for calculations. Alternatively, the results can be used to fit a linear or quadratic
             regression of response ratios, AS/A1S, vs. concentration ratios CS/C1S. If used, the regression
             must be weighted inversely proportional to concentration (1/C). The coefficient of
             determination (R2)  of the weighted regression must be greater than 0.920 (this value
             roughly corresponds to the RSD limit of 35%). Alternatively, the relative standard error
             (Reference 10) may be used as an acceptance criterion. As with the RSD, the RSE must be
             less than 35%.  If an RSE less than 35% cannot be achieved for a quadratic regression,
             system performance is unacceptable, and the system must be adjusted and re-calibrated.

      Note:  Using capillary columns and current instrumentation, it is quite likely that a laboratory can
             calibrate the target analytes in this method and achieve a linearity metric (either RSD or
             RSE) well below 35%. Therefore,  laboratories are permitted to use more stringent
             acceptance criteria for calibration than described here, for example, to harmonize their
             application of this method with those from other sources.

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7.4   Calibration verification - Because the analytical system is calibrated by purge of the analytes from
      water, calibration verification is performed using the laboratory control sample (LCS). See Section
      8.4 for requirements for calibration verification using the LCS, and the Glossary for further
      definition.
8.      Quality Control

8.1   Each laboratory that uses this method is required to operate a formal quality assurance program.
      The minimum requirements of this program consist of an initial demonstration of laboratory
      capability and ongoing analysis of spiked samples and blanks to evaluate and document data quality
      (40 CFR 136.7). The laboratory must maintain records to document the quality of data generated.
      Results of ongoing performance tests are compared with established QC acceptance criteria to
      determine if the results of analyses meet performance requirements of this method. When results of
      spiked samples do not meet the QC acceptance criteria in this method, a quality control check
      sample (laboratory control sample; LCS) must be analyzed to confirm that the measurements were
      performed in an in-control mode of operation.  A laboratory may develop its own performance
      criteria (as QC acceptance  criteria), provided such criteria are as or more restrictive than the criteria
      in this method.

      8.1.1   The laboratory must make an initial demonstration of capability (DOC) to generate
             acceptable precision and recovery with this method.  This demonstration is detailed in
             Section 8.2.

      8.1.2   In recognition of advances that are occurring in analytical technology, and to overcome
             matrix interferences, the laboratory is permitted certain options (Section 1.5 and 40 CFR
             136.6(b)) to improve separations or lower the costs of measurements. These options may
             include an alternate purge-and-trap device, and changes in both column and type of mass
             spectrometer (see 40 CFR 136.6(b)(4)(xvi)). Alternate determinative techniques, such as
             substitution of spectroscopic or immunoassay techniques, and changes that degrade method
             performance, are not allowed. If an  analytical technique other than GC/MS is used, that
             technique must have a specificity equal to or greater than the specificity of GC/MS  for the
             analytes of interest. The laboratory  is also encouraged to participate in inter-comparison
             and performance evaluation studies (see Section 8.9).

             8.1.2.1   Each time a modification is made to this method, the laboratory is required to
                      repeat the procedure in Section 8.2.  If the detection limit of the method will be
                      affected by the change, the laboratory must demonstrate that the MDLs (40 CFR
                      Part 136, Appendix B) are lower than one-third the regulatory compliance limit, or
                      at least as low as the MDLs listed in this method, whichever are greater.  If
                      calibration will be affected by the change, the instrument must be recalibrated per
                      Section 7. Once the modification is demonstrated to produce results equivalent or
                      superior to results produced by this method, that modification may be used
                      routinely thereafter, so long as the other requirements in this method are met
                      (e.g., matrix spike/matrix  spike duplicate recovery and relative percent difference).

                      8.1.2.1.1    If a modification is to be applied to a specific discharge, the
                                  laboratory must prepare and analyze matrix spike/matrix spike
                                  duplicate (MS/MSD) samples (Section 8.3) and LCS samples
                                  (Section 8.4). The laboratory must include internal standards and
                                  surrogates (Section 8.7) in each of the samples.  The MS/MSD and
                                  LCS samples must be fortified with the analytes of interest (Section

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                                  1.3.)  If the modification is for nationwide use, MS/MSD samples
                                 must be prepared from a minimum of nine different discharges (See
                                 Section 8.1.2.1.2), and all QC acceptance criteria in this method
                                 must be met. This evaluation only needs to be performed once, other
                                 than for the routine QC required by this method (for example it could
                                 be performed by the vendor of the alternate materials) but any
                                 laboratory using that specific material must have the results of the
                                 study available.  This includes a full data package with the raw data
                                 that will allow an independent reviewer to verify each determination
                                 and calculation performed by the laboratory (see Section 8.1.2.2.5,
                                 items a-1).

                      8.1.2.1.2   Sample matrices on which MS/MSD tests must be performed for
                                 nationwide use of an allowed modification:

                                 (a) Effluent from a POTW
                                 (b) ASTMD5905 Standard Specification for Substitute Wastewater
                                 (c) Sewage sludge, if sewage sludge will be in the permit
                                 (d) ASTM Dl 141 Standard Specification for Substitute Ocean
                                     Water, if ocean water will be in the permit
                                 (e) Untreated and treated wastewaters up to a total of nine matrix
                                     types (see
                                     http:water.epa.gov/scitech/wastetech/guide/industry.cfm) for a
                                     list of industrial categories with existing effluent guidelines).

                                     At least one  of the above wastewater matrix types must have at
                                     least one of the following characteristics:
                                     (i) Total suspended solids greater than 40 mg/L
                                     (ii) Total dissolved solids greater than 100 mg/L
                                     (iii) Oil and grease greater than 20 mg/L
                                     (iv) NaCl greater than 120 mg/L
                                     (v) CaCO3 greater than 140 mg/L

                                 The interim acceptance criteria for MS, MSB recoveries that do not
                                 have recovery limits specified in Table 7, and recoveries for
                                 surrogates that do not have recovery limits specified in Table 7, must
                                 be no wider than 60-140 %, and the relative percent difference
                                 (RPD) of the concentrations in the MS and MSB that do not have
                                 RPD limits specified in Table 7 must be less than 30%.
                                 Alternatively, the laboratory may use the laboratory's  in-house limits
                                 if they are tighter.

                                 (f)  A proficiency testing (PT) sample from a recognized provider, in
                                     addition to tests of the nine matrices (Section 8.1.2.1.1).

             8.1.2.2   The laboratory is required to maintain records of modifications made to this
                      method. These records include the following, at a minimum:

                      8.1.2.2.1   The names, titles, street addresses, telephone numbers, and e-mail
                                 addresses of the analyst(s) that performed the analyses and
                                 modification, and of the quality control officer that witnessed and will
                                 verify the analyses and modifications.

Method 624.1                                     11                                   December 2014

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                       8.1.2.2.2    A list of analytes, by name and CAS Registry Number.

                       8.1.2.2.3    A narrative stating reason(s) for the modifications.

                       8.1.2.2.4    Results from all quality control (QC) tests comparing the modified
                                  method to this method, including:

                                  a)  Calibration (Section 7).
                                  b)  Calibration verification/LCS (Section 8.4).
                                  c)  Initial demonstration of capability (Section 8.2).
                                  d)  Analysis of blanks (Section 8.5).
                                  e)  Matrix spike/matrix spike duplicate analysis (Section 8.3).
                                  f)  Laboratory control sample analysis (Section 8.4).

                       8.1.2.2.5    Data that will allow an independent reviewer to validate each
                                  determination by tracing the instrument output (peak height, area, or
                                  other signal) to the final result. These data are to include:

                                  a)  Sample numbers and other identifiers.
                                  b)  Analysis dates and times.
                                  c)  Analysis sequence/run chronology.
                                  d)  Sample volume (Section 10).
                                  e)  Sample dilution (Section 13.2).
                                  f)  Instrument and operating conditions.
                                  g)  Column (dimensions, material, etc).
                                  h)  Operating conditions (temperature program, flow rate, etc).
                                  i)  Detector (type, operating conditions, etc).
                                  j)  Chromatograms, mass spectra, and other recordings of raw data.
                                  k)  Quantitation reports,  data system outputs, and other data to link
                                     the raw data to the results reported.
                                  1)  A written Standard Operating Procedure (SOP).

                       8.1.2.2.6    The individual laboratory wishing to use a given modification must
                                  perform the start-up tests in Section 8.1.2 (e.g., DOC, MDL), with
                                  the modification as an integral part of this method prior to applying
                                  the modification to specific discharges. Results of the DOC must
                                  meet the QC acceptance  criteria in Table 7 for the analytes of interest
                                  (Section 1.3), and the MDLs must be equal to or lower than the
                                  MDLs in Table3 for the analytes of interest

      8.1.3   Before analyzing samples, the laboratory must analyze a blank to demonstrate that
             interferences from the analytical system, labware, and reagents are under control. Each
             time a batch of samples is analyzed or reagents are changed, a blank must be analyzed as a
             safeguard against laboratory contamination.  Requirements for the blank are given in
             Section 8.5.

      8.1.4   The laboratory must, on an ongoing basis, spike and analyze a minimum of one sample, in
             duplicate, with the batch of samples run during a given 12-hour shift (see the note at
             Section 8.4). The laboratory must also spike and analyze, in duplicate, a minimum of 5%
             of all samples  from a given site  or discharge to  monitor and evaluate method and laboratory
             performance on the sample matrix. The batch and site/discharge samples may be the same.
             The procedure for spiking and analysis is given in Section 8.3.

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      8.1.5   The laboratory must, on an ongoing basis, demonstrate through analysis of a quality control
             check sample (laboratory control sample, LCS; on-going precision and recovery sample,
             OPR) that the measurement system is in control.  This procedure is given in Section 8.4.

      8.1.6   The laboratory should maintain performance records to document the quality of data that is
             generated. This procedure is given in Section 8.8.

      8.1.7   The large number of analytes tested in performance tests in this method present a
             substantial probability that one or more will fail acceptance criteria when many analytes are
             tested simultaneously, and a re-test is allowed if this situation should occur.  If, however,
             continued re-testing results in further repeated failures, the laboratory should document the
             failures (e.g., as qualifiers on results) and either avoid reporting results for analytes that
             failed or report the problem and failures with the data. Failure to report does not relieve a
             discharger or permittee  of reporting timely results.  Results for regulatory compliance must
             be accompanied by QC results that meet all acceptance criteria.

8.2   Initial demonstration of capability (DOC) - To establish the ability to generate  acceptable recovery
      and precision, the laboratory must perform the DOC in Sections 8.2.1 through 8.2.6 for the analytes
      of interest. The laboratory must also establish MDLs for the analytes of interest using the MDL
      procedure at 40 CFR 136, Appendix B. The  laboratory's MDLs must be equal to or lower than
      those listed in Table  1 for those analytes which list MDL values,  or lower than  one-third the
      regulatory compliance limit, whichever is greater.  For MDLs not listed in Table 1, the laboratory
      must determine the MDLs using the MDL procedure at 40 CFR 136, Appendix B under the same
      conditions used to determine the MDLs for the analytes listed in Table 1.  All procedures used in
      the analysis must be  included in the DOC.

      8.2.1   For the DOC, a QC check sample concentrate containing each analyte of interest (Section
             1.3) is prepared in methanol. The QC check sample concentrate must be prepared
             independently from those used for calibration, but may be from the same source as the
             second-source standard used for calibration verification/LCS (Sections 7.4 and 8.4). The
             concentrate should produce concentrations of the analytes of interest in water at the mid-
             point of the calibration range, and may be  at the same concentration as  the LCS (Section
             8.4).

      Note:   QC check sample concentrates are no longer available from EPA.

      8.2.2   Using a pipet or micro-syringe, prepare four LCSs by adding an appropriate volume of the
             concentrate to each of four aliquots of reagent water. The volume of reagent water must be
             the same as the volume that will be used for the sample, blank (Section 8.5), and MS/MSD
             (Section 8.3). A volume of 5 mL and a concentration of 20  ug/L were  used to develop the
             QC acceptance criteria in Table 7. An alternative volume and sample concentration may be
             used, provided that all QC tests are performed and all QC acceptance criteria in this method
             are met. Also add an aliquot of the surrogate spiking solution (Section 6.7) and internal
             standard spiking  solution (Section 7.3.1.3) to the reagent-water aliquots.

      8.2.3   Analyze the  four LCSs according to the  method beginning in Section 10.

      8.2.4   Calculate the average percent recovery (X) and the standard deviation of the percent
             recovery (s)  for each analyte using the four results.

      8.2.5   For each analyte, compare s and X with the corresponding acceptance criteria for precision
             and recovery in Table 7. For analytes in Tables  1 and 2  not listed in Table 7, DOC QC

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             acceptance criteria must be developed by the laboratory.  EPA has provided guidance for
             development of QC acceptance criteria (References 11 and 12). If s and X for all analytes
             of interest meet the acceptance criteria, system performance is acceptable and analysis of
             blanks and samples may begin. If any individual s exceeds the precision limit or any
             individual X falls outside the range for recovery, system performance is unacceptable for
             thatanalyte.

     Note:  The large number of analytes in Tables 1 and 2 present a substantial probability that one
             or more will fail at least one of the acceptance criteria when many or all analytes are
             determined simultaneously.  Therefore, the analyst is permitted to conduct a "re-test" as
             described in Sec. 8.2.6.

     8.2.6   When one or more of the analytes tested fail at least one of the acceptance criteria, repeat
             the test for only the analytes that failed. If results for these analytes  pass, system
             performance is acceptable and analysis of samples and blanks may proceed.  If one or more
             of the analytes again fail, system performance is unacceptable for the analytes that failed
             the acceptance criteria. Correct the problem and repeat the test (Section 8.2). See Section
             8.1.7 for disposition of repeated failures.

     Note:  To maintain the validity of the test and re-test, system  maintenance and/or adjustment is not
             permitted between this pair of tests.

 .3  Matrix spike and matrix spike duplicate (MS/MSD) - The laboratory must, on an ongoing basis,
     spike at least 5% of the samples from each sample site being monitored in duplicate to assess
     accuracy (recovery and precision). The data user should identify the sample and the analytes of
     interest (Section  1.3) to be spiked. If direction cannot be obtained, the laboratory must spike at
     least one sample  per batch of samples analyzed on a given 12-hour shift with the analytes in Table
      1.  Spiked sample results should be reported only to the data user whose sample was spiked, or as
     requested or required by a regulatory/control authority, or in a permit.

     8.3.1   If, as in compliance monitoring, the concentration of a specific analyte will be checked
             against a regulatory concentration limit, the concentration of the spike should be at that
             limit; otherwise, the concentration of the spike should be one to five times higher than the
             background concentration determined in Section 8.3.2, at or near the midpoint of the
             calibration range, or at the concentration in the LCS (Section 8.4) whichever concentration
             would be larger.

     8.3.2   Analyze  one sample aliquot to determine the background concentration (B) of the each
             analyte of interest. If necessary, prepare a new check  sample concentrate (Section 8.2.1)
             appropriate for the background concentration. Spike and analyze two additional sample
             aliquots,  and determine the concentration after spiking (Ai and A2) of each analyte.
             Calculate the percent recoveries (Pi and P2) as 100 (A] - B) / T and 100 (A2  - B)  / T, where
             T is the known true value of the spike. Also calculate the relative percent difference (RPD)
             between the concentrations (Ai and A2) as 200 |Ai - A2| / (Ai + A2).  If necessary, adjust the
             concentrations used to calculate the RPD to account for differences in the volumes of the
             spiked aliquots.

     8.3.3   Compare the percent recoveries (Pi and P2) and the RPD for each analyte in the MS/MSD
             aliquots with the corresponding QC acceptance criteria in Table 7. A laboratory may
             develop and apply QC acceptance criteria more restrictive than the criteria in Table 6, if
             desired.
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             8.3.3.1   If any individual P falls outside the designated range for recovery in either
                      aliquot, or the RPD limit is exceeded, the result for the analyte in the unspiked
                      sample is suspect and may not be reported or used for permitting or regulatory
                      compliance purposes. See Section 8.1.7 for disposition of failures.

             8.3.3.2   The acceptance criteria in Table 7 were calculated to include an allowance for
                      error in measurement of both the background and spike concentrations, assuming
                      a spike to background ratio of 5:1. This error will be accounted for to the extent
                      that the spike to background ratio approaches 5:1 (Reference 13). If spiking is
                      performed at a concentration lower than 20 ug/L, the laboratory must use either
                      the QC acceptance criteria in Table 7, or optional QC acceptance criteria
                      calculated for the specific spike concentration. To use the optional acceptance
                      criteria: (1) Calculate recovery (X') using the equation in Table 8, substituting
                      the spike concentration (T) for C; (2) Calculate overall precision (S') using the
                      equation in Table 8, substituting X' for X ; (3) Calculate the range for recovery
                      at the spike concentration as (100 X'/T)  2.44(100 SVT)%  (Reference 4). For
                      analytes of interest in Tables 1 and 2 not listed in Table 7, QC acceptance criteria
                      must be developed by the laboratory. EPA has provided guidance for
                      development of QC  acceptance criteria (References 11 and 12).

      8.3.4   After analysis of a minimum of 20 MS/MSD samples for each target analyte and surrogate,
             the laboratory must calculate and apply in-house QC limits for recovery and RPD of future
             MS/MSD samples (Section 8.3). The QC limits for recovery are calculated as the mean
             observed recovery  3 standard deviations, and the upper QC limit for RPD is calculated as
             the mean RPD plus 3 standard deviations of the RPDs . The in-house  QC limits must be
             updated at least every two years and re-established after any major change in the analytical
             instrumentation or process. At least 80% of the analytes  tested in the MS/MSD must have
             in-house QC acceptance criteria that are tighter than those in Table 7.  If an in-house QC
             limit for the RPD is greater than the limit in Table 7, then the limit in Table 7 must be used.
             Similarly, if an in-house lower limit for recovery is below the lower limit in Table 7, then
             the lower limit in Table 7 must be used, and if an in-house upper limit for recovery is above
             the upper limit in Table 7, then the upper limit in Table 7 must be used. The laboratory
             must evaluate surrogate recovery data in each sample against its in-house surrogate
             recovery limits. The laboratory may use 60 -140% as interim acceptance criteria for
             surrogate recoveries until in-house limits are developed.

8.4   Calibration verification/laboratory control sample (LCS) - The working calibration curve or RF
      must be verified at the beginning of each 12-hour shift by the measurement of an LCS.

      Note:   The 12-hour shift begins after  analysis of the blank that follows the LCS and ends 12 hours
             later.  The blank is outside of the 12-hour shift. The MS andMSD are treated as samples
             and are analyzed within the 12-hour shift.

      8.4.1   Prepare the LCS by adding QC check sample concentrate (Section 8.2.1) to reagent water.
             Include all analytes of interest (Section 1.3) in the LCS.  The LCS may be the same sample
             prepared for the DOC (Section 8.2.1).  The volume of reagent water must be the same as
             the volume used for the sample, blank (Section 8.5), and  MS/MSD (Section 8.3).  Also add
             an aliquot of the surrogate solution (Section 6.7) and internal standard solution (Section
             7.3.1.3). The concentration of the analytes in reagent water should be the same as the
             concentration in the DOC (Section 8.2.2).
Method624.1                                     15                                   December 2014

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      8.4.2   Analyze the LCS prior to analysis of field samples in the batch of samples analyzed during
             the 12-hour shift (see the Note at Section 8.4).  Determine the concentration (A) of each
             analyte. Calculate the percent recovery (Q) as  100 (A/T) %, where T is the true value of
             the concentration in the LCS.

      8.4.3   Compare the percent recovery (Q) for each analyte with its corresponding QC acceptance
             criterion in Table 7. For analytes of interest in Tables 1 and 2 not listed in Table 7, use the
             QC acceptance criteria developed for the MS/MSD (Section 8.3.3.2). If the recoveries for
             all analytes of interest fall within their respective QC acceptance criteria,  analysis of blanks
             and field samples may proceed.  If any individual Q falls outside the range, proceed
             according to Section 8.4.4.

      Note:  The large number of analytes in Tables 1 - 2 present a substantial probability that one or
             more will fail the acceptance criteria when all analytes are tested simultaneously.  Because
             a re-test is allowed in event of failure  (Sections 8.1.7 and 8.4.3), it may be prudent to
             analyze two LCSs together and evaluate results of the second analysis against the QC
             acceptance criteria only if an analyte fails the first test.

      8.4.4   Repeat the test only for those analytes that failed to meet the acceptance criteria (Q). If
             these analytes now pass, system performance is acceptable and analysis of blanks and
             samples may proceed. Repeated failure, however, will confirm a general  problem with the
             measurement system. If this occurs, repeat the test using a fresh LCS (Section 8.2.2) or an
             LCS prepared with a fresh QC check sample concentrate (Section 8.2.1),  or perform and
             document system repair. Subsequent to repair, repeat the calibration verification/LCS test
             (Section 8.4). If the acceptance criteria for Q cannot be met, re-calibrate the instrument
             (Section 7). If failure of the LCS indicates a systemic problem with samples analyzed
             during the 12-hour shift, re-analyze  the samples analyzed during that 12-hour shift. See
             Section 8.1.7  for disposition of repeated failures.

      Note:  To maintain the validity of the test and re-test, system maintenance and/or adjustment is not
             permitted between this pair of tests.

      8.4.5 After analysis of 20 LCS samples, the laboratory must calculate and apply in-house QC limits
           for recovery  to future LCS samples (Section 8.4).  Limits for recovery in the LCS are
           calculated as the mean recovery 3 standard deviations. A minimum of 80% of the analytes
           tested for in the LCS must have QC acceptance criteria tighter than those in Table 7. Many
           of the analytes and surrogates may not contain recommended acceptance criteria.  The
           laboratory should use 60 -140% as interim acceptance criteria for recoveries of spiked
           analytes and surrogates that do not have recovery limits specified in Table 7, until in-house
           LCS and surrogate limits are developed.  If an in-house lower limit for recovery is lower than
           the lower limit in Table 7, the lower limit in Table 7 must be used, and if an in-house upper
           limit for recovery is higher than the upper limit in Table 7, the upper limit in Table 7 must be
           used.

 .5   Blank - A blank must be analyzed at the beginning of each  12-hour shift to demonstrate freedom
      from contamination. A blank must also be analyzed after a sample containing a high concentration
      of an analyte or potentially interfering compound to demonstrate freedom from carry-over.

      8.5.1   Spike the internal  standards and surrogates into the blank. Analyze the blank immediately
             after analysis of the LCS (Section 8.4) and prior to analysis of the MS/MSD and samples to
             demonstrate freedom from contamination.
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      8.5.2   If any analyte of interest is found in the blank: 1) at a concentration greater than the MDL
             for the analyte, 2) at a concentration greater than one-third the regulatory compliance limit,
             or 3) at a concentration greater than one-tenth the concentration in a sample analyzed
             during the 12-hour shift (Section 8.4), whichever is greater; analysis of samples must be
             halted and samples affected by the blank must be re-analyzed. Samples must be associated
             with an uncontaminated blank before they may be reported or used for permitting or
             regulatory compliance purposes.

8.6   Surrogate recoveries - Spike the surrogates into all samples, blanks, LCSs, and MS/MSDs.
      Compare surrogate recoveries against the QC acceptance criteria in Table 7. For surrogates in
      Table 5 without QC acceptance criteria in Table 7, and for other surrogates that may be used by the
      laboratory, limits must be  developed by the laboratory. EPA has provided guidance for
      development of QC acceptance criteria (References 11 and 12). If any recovery fails its criteria,
      attempt to find and correct the cause of the failure. Surrogate recoveries from the blank and LCS
      may be used as pass/fail criteria by the laboratory or as required by a regulatory authority, or may
      be used to diagnose problems with the analytical system.

8.7   Internal standard responses

      8.7.1   Calibration verification/LCS - The responses (GC peak heights or areas) of the internal
             standards in the calibration verification/LCS must be within 50% to 200% (1/2 to 2x) of
             their respective responses in the  mid-point calibration standard.  If they are not, repeat the
             LCS test using a fresh QC check sample (Section 8.4.1) or perform and document system
             repair. Subsequent to repair, repeat the calibration verification/LCS test (Section 8.4). If
             the responses are still not within 50% to 200%, re-calibrate the instrument (Section 7) and
             repeat the calibration verification/LCS test.

      8.7.2   Samples, blanks, and MS/MSDs - The responses (GC peak heights or areas) of the internal
             standards in each sample, blank, and MS/MSD must be within 50% to 200% (1/2 to 2x) of
             its respective response in the most recent LCS. If, as a group, all internal standard are not
             within this range, perform and document system repair, repeat the calibration verification/
             LCS test (Section 8.4), and re-analyze the affected samples. If a single internal  standard is
             not within the 50% to 200% range, use an alternate internal standard for quantitation of the
             analyte referenced to the affected internal standard.

8.8   As part of the QC program for the laboratory, control charts or statements of accuracy for
      wastewater samples must be assessed and records maintained periodically (see 40 CFR
      136.7(c)(l)(viii)). After analysis of five  or more spiked wastewater samples as in Section 8.3,
      calculate the average percent recovery (X) and the standard deviation of the percent recovery (sp).
      Express the accuracy assessment as a percent interval from X -2spto X +2sp. For example,
      if X  = 90% and sp = 10%, the accuracy interval is expressed as  70 - 110%. Update the accuracy
      assessment for each analyte on a regular basis (e.g., after each 5-10 new accuracy measurements).

8.9   It is recommended that the laboratory adopt additional quality assurance practices for use with this
      method. The specific practices that are most productive depend upon the needs of the laboratory
      and the nature of the samples. Field duplicates may be analyzed to assess the precision of
      environmental measurements. Whenever possible, the laboratory should analyze standard reference
      materials and participate in relevant performance evaluation studies.
Method 624.1                                     17                                   December 2014

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9.    Sample Collection, Preservation, and Handling

9.1   Collect the sample as a grab sample in a glass container having a total volume of at least 25 mL.
      Fill the sample bottle just to overflowing in such a manner that no air bubbles pass through the
      sample as the bottle is being filled.  Seal the bottle so that no air bubbles are entrapped in it.  If
      needed, collect additional sample(s) for the MS/MSD (Section 8.3).

9.2   Ice or refrigerate samples at <6 C from the time of collection until analysis, but do not freeze. If
      residual chlorine is present, add sodium thiosulfate preservative (10 mg/40 mL is sufficient for up
      to 5 ppm C12) to the empty sample bottle just prior to shipping to the sampling site. Any method
      suitable for field use may be employed to test for residual chlorine (Reference 14). Field test kits
      are also available for this purpose. If sodium thiosulfate interferes in the determination of the
      analytes, an alternate preservative (e.g., ascorbic acid or sodium sulfite) may be used. If
      preservative has been added, shake the sample vigorously for one minute.  Maintain the hermetic
      seal on the sample bottle until time of analysis.

9.3   If acrolein is to be determined, analyze the sample within 3 days. To extend the holding time to  14
      days, acidify a separate sample to pH 4-5  with HC1 using the procedure in Section 9.7.

9.4   Experimental evidence indicates that some aromatic compounds, notably benzene, toluene, and
      ethyl benzene are susceptible to rapid biological degradation under certain environmental
      conditions (Reference 3). Refrigeration alone may not be adequate to preserve these compounds in
      wastewaters for more than seven days. To extend the holding time for aromatic compounds to 14
      days, acidify the sample to approximately pH 2 using the procedure in Section 9.7.

9.5   If halocarbons are to be determined, either use the acidified aromatics sample in Section 9.4 or
      acidify a separate sample to a pH of about 2 using the procedure in Section 9.7.  Aqueous samples
      should not be preserved with acid if the ethers in Table 2, or the alcohols that they would form upon
      hydrolysis, are of analytes of interest.

9.6   The ethers listed in Table 2 are prone to hydrolysis at pH 2 when a heated purge is used. Aqueous
      samples should not be acid preserved if these ethers are of interest, or if the alcohols they would
      form upon hydrolysis are of interest and the ethers are anticipated to present.

9.7   Sample acidification - Collect about 500 mL of sample in a clean container and adjust the pH of the
      sample to 4 - 5 for acrolein (Section 9.3), or to about 2 for the aromatic compounds (Section 9.4) by
      adding  1+1 HC1 while swirling or stirring.  Check the pH with narrow range pH paper.  Fill a
      sample container as described in Section 9.1.  Alternatively, fill a precleaned vial (Section 5.1.1)
      that contains approximately 0.25 mL of 1+1 HC1 with sample as in Section 9.1.  If preserved using
      this alternative procedure, the pH of the sample can be verified to be <2 after some of the sample is
      removed for analysis. Acidification will destroy 2-chloroethylvinyl ether; therefore, determine
      2-chloroethylvinyl ether from the unacidified sample.

9.8   All samples must be analyzed within 14 days of collection (Reference 3), unless specified otherwise
      in Sections 9.3 - 9.7.
10.   Sample Purging and Gas Chromatography

10.1  The footnote to Table 3 gives the suggested GC column and operating conditions.  Included in
      Table 3 are retention times and MDLs that can be achieved under these conditions.  Sections 10.2
      through 10.7 suggest procedures that may be used with a manual purge-and-trap system.  Auto-

Method624.1                                      18                                   December 2014

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      samplers and other columns or chromatographic conditions may be used if requirements in this
      method are met.

10.2  Attach the trap inlet to the purging device, and set the purge-and-trap system to purge (Figure 3).
      Open the syringe valve located on the purging device sample introduction needle.

10.3  Allow the sample to come to ambient temperature prior to pouring an aliquot into the syringe.
      Remove the plunger from a syringe and attach a closed syringe valve. Open the sample bottle (or
      standard) and carefully pour the sample into the syringe barrel to just short of overflowing. Replace
      the syringe plunger and compress the sample. Open the syringe valve and vent any residual air
      while adjusting the sample volume.  Since this process of taking an aliquot destroys the  validity of
      the sample for future analysis, the analyst should fill a second syringe at this time to protect against
      possible loss of data.  Add the surrogate spiking solution (Section 6.7) and internal standard spiking
      solution (Section 7.3.1.3) through the valve bore, then close the valve.  The surrogate and internal
      standards may be mixed and added as a single spiking solution.  Autosamplers designed for purge-
      and-trap analysis of volatiles also may be used.

10.4  Attach the syringe valve assembly to the syringe valve on the purging device. Open the  syringe
      valve and inject the sample into the purging chamber.

10.5  Close both valves and purge the sample at a temperature, flow rate, and duration sufficient to purge
      the less-volatile analytes onto the trap, yet short enough to prevent blowing the more-volatile
      analytes through the trap.  The temperature, flow rate, and time should be determined by test. The
      same purge temperature, flow rate, and purge time must be used for all calibration, QC,  and field
      samples.

10.6  After the purge, set the purge-and-trap system to the desorb mode (Figure 4), and begin  to
      temperature program the gas chromatograph. Introduce the trapped materials to the GC column by
      rapidly heating the trap to the desorb temperature while backflushing the trap with carrier gas at the
      flow rate and for the time necessary to desorb the analytes of interest. The optimum temperature,
      flow rate, and time should be determined by test. The same temperature,  desorb time, and flow rate
      must be used for all calibration, QC, and field samples. If heating of the trap does not result in
      sharp peaks for the early eluting analytes, the GC column may be used as a secondary trap by
      cooling to an ambient or subambient temperature. To avoid carry-over and interferences, maintain
      the trap at the desorb temperature and flow rate until the analytes, interfering compounds, and
      excess water are desorbed. The optimum conditions should be  determined by test.

10.7  Start MS data acquisition at the start of the desorb cycle and stop data collection when the analytes
      of interest, potentially interfering compounds, and water have eluted (see the footnote to Table 3 for
      conditions).

10.8  Cool the trap to the purge temperature and return the trap to the purge mode (Figure 3).  When the
      trap is cool, the next sample can be analyzed.
11.   Performance Tests

11.1  At the beginning of each 12-hour shift during which analyses are to be performed, GC/MS
      performance must be verified before blanks or samples may be analyzed (Section 8.4). Use the
      instrument operating conditions in the footnotes to Table 3 for these performance tests. Alternate
      conditions may be used so as long as all QC requirements are met.
Method624.1                                     19                                    December 2014

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11.2  BFB - Inject 50 ng of BFB solution directly on the column. Alternatively, add BFB to reagent
      water or an aqueous standard such that 50 ng or less of BFB will be introduced into the GC.
      Analyze according to Section 10.  Confirm that all criteria in Section 7.3.2.2 and Table 4 are met.
      If all criteria are not met, perform system repair, retune the mass spectrometer, and repeat the test
      until all criteria are met.

11.3  GC resolution - There must be a valley between 1,2-dibromoethane and chlorobenzene, and the
      height of the valley must not exceed 25 percent of the shorter of the two peaks. For an alternate GC
      column, apply this valley height criterion to two representative GC peaks separated by no more
      than 7 seconds.

11.4  Verify calibration with the LCS (Section 8.4) after the criteria for BFB are met (Reference 15) and
      prior to analysis of a blank or sample.  After verification, analyze a blank (Section 8.5) to
      demonstrate freedom from contamination and carry-over at the MDL.
12.   Qualitative Identification

12.1  Target analytes are identified by comparison of results from analysis of a sample or blank with data
      stored in the GC/MS data system (Section 7.3.2.3).  Identification of an analyte is confirmed per
      Sections 12.1.1 through 12.1.4.

      12.1.1  The signals for all characteristic m/z's stored in the data system (Section 7.3.2.3) for each
             analyte of interest must be present and must maximize within the same two consecutive
             scans.

      12.1.2  Based on the relative retention time (RRT), the RRT for the analyte must be within 0.06
             of the RRT of the analyte in the LCS run at the beginning of the shift (Section 8.4).
             Relative retention time is used to establish the identification window because it
             compensates for small changes in the GC temperature program whereas the absolute
             retention time does not (see Section 7.3.1.2).

      Note:  RRT is a unitless quantity (see Sec. 20.2), although some procedures refer to "RRT units"
             in providing the specification for the agreement between the RRT values in the sample and
             the LCS or other standard.

      12.1.3  Either (1) the background corrected EICP areas, or (2) the corrected relative intensities of
             the mass spectral peaks at the GC peak maximum, must agree within 50% to 200% (1/2 to
             2 times) for all m/z's in the reference mass spectrum stored in the data system (Section
             7.3.2.3), or from a reference library. For example, if a peak has an intensity of 20% relative
             to the base peak, the analyte is identified if the intensity of the peak in the sample is in the
             range of 10% to 40% of the base peak.

      12.1.4  The m/z's present in the acquired mass spectrum for the sample that are not present in the
             reference mass spectrum must be accounted for by contaminant or background m/z's.  A
             reference library may be helpful to identify  and account for background or contaminant
             m/z's. If the acquired mass spectrum is  contaminated, or if identification is ambiguous, an
             experienced spectrometrist (Section 1.6) must determine the presence or absence of the
             compound.

12.2  Structural isomers that have very similar mass spectra can be identified only if the resolution
      between authentic isomers in a standard mix is acceptable. Acceptable resolution is achieved  if the

Method 624.1                                     20                                   December 2014

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      baseline to valley height between the isomers is less than 50% of the height of the shorter of the two
      peaks.  Otherwise, structural isomers are identified as isomeric pairs.
13.   Calculations

13.1  When an analyte has been identified, quantitation of that analyte is based on the integrated
      abundance from the EICP of the primary characteristic m/z in Table 5 or 6. Calculate the
      concentration using the response factor (RF) determined in Section 7.3.3 and Equation 2. If a
      calibration curve was used, calculate the concentration using the regression equation for the curve.
      If the concentration of an analyte exceeds the calibration range, dilute the sample by the minimum
      amount to bring the concentration into the calibration range, and re-analyze. Determine a dilution
      factor (DF) from the amount of the dilution.  For example, if the extract is diluted by a factor of 2,
      DF = 2.
                                           Equation 2

                                               As x Cis x DF
                                     C' WL)   AuRF
       where:
       Cs =  Concentration of the analyte in the sample, and the other terms are as defined in Section
             7.3.3.

13.2  Reporting of results

      As noted in Section 1.4.1, EPA has promulgated this method at 40 CFR Part 136 for use in
      wastewater compliance monitoring under the National Pollutant Discharge Elimination System
      (NPDES).  The data reporting practices described here are focused on such monitoring needs and
      may not be relevant to other uses of the method.

      13.2.1  Report results for wastewater samples in ug/L without correction for recovery.  (Other units
             may be used if required by in a permit.) Report all QC data with the sample results.

      13.2.2  Reporting level

             Unless otherwise specified in by a regulatory authority or in a discharge permit, results for
             analytes that meet the identification criteria are reported down to the concentration of the
             ML established by the laboratory through calibration of the instrument (see Section 7.3.2
             and the glossary for the derivation of the ML).  EPA considers the terms "reporting limit,"
             "quantitation limit," and "minimum level" to be synonymous.

              13.2.2.1  Report a result for each analyte in each sample, blank, or standard at or above the
                      ML to 3 significant figures. Report a result for each analyte found in each
                      sample below the ML as "
-------
             13.2.2.3  Report a result for an analyte found in a sample that has been diluted at the least
                      dilute level at which the area at the quantitation m/z is within the calibration
                      range (i.e., above the ML for the analyte) and the MS/MSD recovery and RPD
                      are within their respective QC acceptance criteria (Table 7).  This may require
                      reporting results for some analytes from different analyses.

      13.2.3  Results from tests performed with an analytical system that is not in control (i.e., that does
             not meet acceptance criteria for all of QC tests in this method) must not be reported or
             otherwise used for permitting or regulatory compliance purposes, but do not relieve a
             discharger or permittee of reporting timely results.  If the holding time would be exceeded
             for a re-analysis of the sample, the regulatory/control authority should be consulted for
             disposition.
14.   Method Performance

14.1  This method was tested by 15 laboratories using reagent water, drinking water, surface water, and
      industrial wastewaters spiked at six concentrations over the range 5 - 600 ug/L (References 4 and
      16). Single operator precision, overall precision, and method accuracy were found to be directly
      related to the concentration of the analyte and essentially independent of the sample matrix.  Linear
      equations to describe these relationships are presented in Table 8.

14.2  As noted in Sec. 1.1, this method was validated through an interlaboratory study conducted more
      than 29 years ago. However, the fundamental chemistry principles used in this method remain
      sound and continue to apply.
15.   Pollution Prevention

15.1  Pollution prevention encompasses any technique that reduces or eliminates the quantity or toxicity
      of waste at the point of generation. Many opportunities for pollution prevention exist in laboratory
      operations.  EPA has established a preferred hierarchy of environmental management techniques
      that places pollution prevention as the management option of first choice. Whenever feasible, the
      laboratory should use pollution prevention techniques to address waste generation.  When wastes
      cannot be reduced at the source, the Agency recommends recycling as the next best option.

15.2  The analytes in this method are used in extremely small amounts and pose little threat to the
      environment when managed properly.  Standards should be prepared in volumes consistent with
      laboratory use to minimize the disposal of excess volumes of expired standards.

15.3  For information about pollution prevention that may be  applied to laboratories and research
      institutions, consult Less is Better: Laboratory Chemical Management for Waste Reduction,
      available from the American Chemical  Society's Department of Governmental Relations and
      Science Policy,  1155 16th Street NW, Washington DC 20036, 202/872-4477.
16.   Waste Management

16.1  The laboratory is responsible for complying with all Federal, State, and local regulations governing
      waste management, particularly the hazardous waste identification rules and land disposal
      restrictions, and to protect the air, water, and land by minimizing and controlling all releases from
      fume hoods and bench operations. Compliance is also required with any sewage discharge permits

Method 624.1                                     22                                    December 2014

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     and regulations.  An overview of requirements can be found in Environmental Management Guide
     for Small Laboratories (EPA 233-B-98-001).

16.2 Samples at pH <2, or pH >12, are hazardous and must be neutralized before being poured down a
     drain, or must be handled and disposed of as hazardous waste.

16.3 Many analytes in this method decompose above 500 C. Low-level waste such as absorbent paper,
     tissues, and plastic gloves may be burned in an appropriate incinerator. Gross quantities of neat or
     highly concentrated solutions of toxic or hazardous chemicals should be packaged securely and
     disposed of through commercial or governmental channels that are capable of handling these types
     of wastes.

16.4 For further information on waste management, consult The Waste Management Manual for
     Laboratory Personnel and Less is Better-Laboratory Chemical Management for Waste Reduction,
     available from the American Chemical Society's Department of Government Relations and Science
     Policy, 1155  16th Street NW, Washington, DC 20036, 202/872-4477.
17.  References

1.    Bellar, T.A. and Lichtenberg, J.J. "Determining Volatile Organics at Microgram-per-Litre Levels
     by Gas Chromatography," Journal American Water Works Association, 66, 739 (1974).

2.    "Sampling and Analysis Procedures for Screening of Industrial Effluents for Priority Pollutants,"
     U.S. Environmental Protection Agency, Environmental Monitoring and Support Laboratory,
     Cincinnati, Ohio 45268, March  1977, Revised April 1977.

3.    Bellar, T.A. and Lichtenberg, J.J. "Semi-Automated Headspace Analysis of Drinking Waters and
     Industrial Waters for Purgeable Volatile Organic Compounds," Measurement of Organic Pollutants
     in Water and Wastewater, C.E. Van Hall, editor, American Society for Testing and Materials,
     Philadelphia, PA. Special Technical Publication 686, 1978.

4.    "EPA Method Study 29 EPA Method 624-Purgeables," EPA 600/4-84-054, National Technical
     Information Service, PB84-209915, Springfield, Virginia 22161, June 1984.

5.    40 Code of Federal Regulations  136, Appendix B

6.    "Method Detection Limit for Methods 624 and 625," Olynyk, P., Budde, W.L., and Eichelberger,
     J.W. Unpublished report, May 14, 1980.

7.    "Carcinogens-Working With Carcinogens," Department of Health, Education, and Welfare, Public
     Health Service, Center for Disease Control, National Institute for Occupational Safety and Health,
     Publication No. 77-206, August  1977.

8.    "OSHA Safety and Health Standards, General Industry," (29 CFR Part 1910), Occupational Safety
     and Health Administration, OSHA 2206 (Revised, January 1976).

9.    "Safety in Academic Chemistry Laboratories," American Chemical Society Publication, Committee
     on Chemical Safety, 7th Edition, 2003.

10.  40 Code of Federal Regulations  136.6(b)(5)(x)
Method 624.1                                    23                                  December 2014

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11.  40 Code of Federal Regulations 136.6(b)(2)(/)

12.  Protocolyfor EPA Approval of New Methods for Organic and Inorganic Analytes in Wastewater and
     Drinking Water (EPA-821-B-98-003) March 1999

13.  Provost, L.P. and Elder, R.S.  "Interpretation of Percent Recovery Data," American Laboratory, 15,
     58-63 (1983).

14.  40 CFR 136.3(a), Table IB, Chlorine - Total residual

15.  Budde, W.L. and Eichelberger, J.W. "Performance Tests for the Evaluation of Computerized Gas
     Chromatography/Mass Spectrometry Equipment and Laboratories," EPA-600/4-80-025, U.S.
     Environmental Protection Agency, Environmental Monitoring and Support Laboratory, Cincinnati,
     Ohio 45268, April 1980.

16.  "Method Performance Data for Method 624," Memorandum from R. Slater and T. Pressley, U.S.
     Environmental Protection Agency, Environmental Monitoring and Support Laboratory, Cincinnati,
     Ohio 45268, January 17, 1984.
Method 624.1                                   24                                  December 2014

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18.   Tables
Table 1 - Purgeables1
Analyte
Acrolein
Acrylonitrile
Benzene
Bromodichloromethane
Bromoform
Bromomethane
Carbon tetrachloride
Chlorobenzene
Chloroethane
2-Chloroethylvinyl ether
Chloroform
Chloromethane
Dibromochloromethane
1 ,2-Dichlorobenzene
1 , 3 -Dichlorobenzene
1 ,4-Dichlorobenzene
1 , 1 -Dichloroethane
1 ,2-Dichloroethane
1 , 1 -Dichloroethene
fras-l,2-Dichloroethene
1 ,2-Dichloropropane
cis-\,3 -Dichloropropene
fra5-l,3-Dichloropropene
Ethyl benzene
Methylene chloride
1 , 1 ,2,2-Tetrachloroethane
Tetrachloroethene
Toluene
1,1,1 -Trichloroethane
1 , 1 ,2-Trichloroethane
Trichloroethene
Vinyl chloride
CAS Registry No.
107-02-8
107-13-1
71-43-2
75-27-4
75-25-2
74-83-9
56-23-5
108-90-7
75-00-3
110-75-8
67-66-3
74-87-3
124-48-1
95-50-1
541-73-1
106-46-7
75-34-3
107-06-2
75-35-4
156-60-5
78-87-5
10061-01-5
10061-02-6
100-41-4
75-09-2
79-34-5
127-18-4
108-88-3
71-55-6
79-00-5
79-01-6
75-01-4
MDL (M/L)2


4.4
2.2
4.7

2.8
6.0


1.6

3.1



4.7
2.8
2.8
1.6
6.0
5.0

7.2
2.8
6.9
4.1
6.0
3.8
5.0
1.9

ML (M.g/L)3


13.2
6.6
14.1

8.4
18.0


4.8

9.3



14.1
8.4
8.4
4.8
18.0
15.0

21.6
8.4
20.7
12.3
18.0
11.4
15.0
5.7

    All the analytes in this table are Priority Pollutants (40 CFR 423, Appendix A)
    MDL values from the 1984 promulgated version of Method 624
    ML = Minimum Level - see Glossary for definition and derivation
Method 624.1
25
December 2014

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Table 2 - Additional Purgeables
Analyte
Acetone :
Acetonitrile 2
Allyl alcohol l
Allyl chloride
t-Amy\ ethyl ether (TAEE)
t-Amy\ methyl ether (TAME)
Benzyl chloride
Bromoacetone 2
Bromobenzene
Bromochloromethane
1,3 -Butadiene
-Butanol :
2-Butanone (MEK) l'2
t-Butyl alcohol (TEA)
-Butylbenzene
sec-Butylbenzene
^-Butylbenzene
t-Buty\ ethyl ether (ETBE)
Carbon disulfide
Chloral hydrate 2
Chloroacetonitrile :
1-Chlorobutane
Chlorodifluoromethane
2-Chloroethanol 2
bis (2-Chloroethyl) sulfide 2
1 -Chlorohexanone
Chloroprene (2-chloro-l,3-butadiene)
3-Chloropropene
3 -Chloropropionitrile
2-Chlorotoluene
4-Chlorotoluene
Crotonaldehyde 1>2
Cyclohexanone
1 ,2-Dibromo-3 -chloropropane
1 ,2-Dibromoethane
Dibromomethane
c/s-l,4-Dichloro-2-butene
fra5-l,4-Dichloro-2-butene
c/5-l,2-Dichloroethene
Dichlorodifluoromethane
CAS Registry
67-64-1
75-05-8
107-18-6
107-05-1
919-94-8
994-058
100-44-7
598-31-2
108-86-1
74-97-5
106-99-0
71-36-3
78-93-3
75-65-0
104-51-8
135-98-8
98-06-6
637-92-3
75-15-0
302-17-0
107-14-2
109-69-3
75-45-6
107-07-3
505-60-2
20261-68-1
126-99-8
107-05-1
542-76-7
95-49-8
106-43-4
123-73-9
108-94-1
96-12-8
106-93-4
74-95-3
1476-11-5
110-57-6
156-59-2
75-71-8
Method 624.1
26
December 2014

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Table 2 - Additional Purgeables
Analyte
1,3-Dichloropropane
2,2-Dichloropropane
l,3-Dichloro-2-propanol 2
1 , 1 -Dichloropropene
cis- 1 , 3 -Dichloropropene
1 :2,3:4-Diepoxybutane
Diethyl ether
Diisopropyl ether (DIPE)
1,4-Dioxane2
Epichlorohydrin 2
Ethanol 2
Ethyl acetate 2
Ethyl methacrylate
Ethylene oxide 2
Hexachlorobutadiene
Hexachloroethane
2-Hexanone 2
lodomethane
Isobutyl alcohol :
Isopropylbenzene
/>-Isopropyltoluene
Methacrylonitrile 2
Methanol 2
Malonitrile 2
Methyl acetate
Methyl acrylate
Methyl cyclohexane
Methyl iodide
Methyl methacrylate
4-Methyl-2-pentanone (MIBK) 2
Methyls-butyl ether (MTBE)
Naphthalene
Nitrobenzene
N-Nitroso-di--butylamine 2
2-Nitropropane
Paraldehyde 2
Pentachloroethane 2
Pentafluorobenzene
2-Pentanone 2
2-Picoline 2
CAS Registry
142-28-9
590-20-7
96-23-1
563-58-6
10061-01-5
1464-53-5
60-29-7
108-20-3
123-91-1
106-89-8
64-17-5
141-78-6
97-63-2
75-21-8
87-63-3
67-72-1
591-78-6
74-88-4
78-83-1
98-82-8
99-87-6
126-98-7
67-56-1
109-77-3
79-20-9
96-33-3
108-87-2
74-88-4
78-83-1
108-10-1
1634-04-4
91-20-3
98-95-3
924-16-3
79-46-9
123-63-7
76-01-7
363-72-4
107-19-7
109-06-8
Method 624.1
27
December 2014

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Table 2 - Additional Purgeables
Analyte
1-Propanol1
2-Propanol :
Propargyl alcohol 2
fteto-Propiolactone 2
Propionitrile (ethyl cyanide) :
-Propylamine
-Propylbenzene
Pyridine 2
Styrene
1,1,1 ,2-Tetrachloroethane
Tetrahydrofuran
o-Toluidine 2
1,2,3-Trichlorobenzene
Trichlorofluoromethane
1,2,3-Trichloropropane
1,2,3-Trimethylbenzene
1 ,2,4-Trimethylbenzene
1 , 3 ,5 -Trimethylbenzene
Vinyl acetate
w -Xylene 3
o-Xylene 3
/-Xylene 3
m+o- Xylene 3
m+p- Xylene 3
o+p- Xylene 3
CAS Registry
71-23-8
67-63-0
107-19-7
57-58-8
107-12-0
107-10-8
103-65-1
110-86-1
100-42-5
630-20-6
109-99-9
95-53-4
87-61-6
75-69-4
96-18-4
526-73-8
95-63-6
108-67-8
108-05-4
108-38-3
95-47-6
106-42-3
179601-22-0
179601-23-1
136777-61-2
                         Determined at a purge temperature of 80C
                         May be detectable at a purge temperature of 80C
                         Determined in combination separated by GC column. Most
                         GC columns will resolve o-xylene from/w+p-xylene.
                         Report using the CAS number for the individual xylene or
                         the combination, as determined.
Method 624.1
28
December 2014

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Table 3 - Example Retention Times
Analyte
Chloromethane
Vinyl chloride
Bromomethane
Chloroethane
Trichlorofluoromethane
Diethyl ether
Acrolein
1 , 1 -Dichloroethene
Acetone
lodomethane
Carbon disulfide
3-Chloropropene
Methylene chloride
Acrylonitrile
trans- 1 ,2 -Dichloroethene
1 , 1 -Dichloroethane
Vinyl acetate
Allyl alcohol
2-Chloro- 1 ,3 -butadiene
Methyl ethyl ketone
cis- 1 ,2-Dichloroethene
Ethyl cyanide
Methacrylonitrile
Chloroform
1,1,1 -Trichloroethane
Carbon tetrachloride
Isobutanol
Benzene
1 ,2-Dichloroethane
Crotonaldehyde
Trichloroethene
1 ,2-Dichloropropane
Methyl methacrylate
/>-Dioxane
Dibromomethane
Bromodichloromethane
Chloroacetonitrile
2-Chloroethylvinyl ether
cis- 1 ,3 -Dichloropropene
4-Methyl -2 -pentanone
Retention time (min)
3.68
3.92
4.50
4.65
5.25
5.88
6.12
6.30
6.40
6.58
6.72
6.98
7.22
7.63
7.73
8.45
8.55
8.58
8.65
9.50
9.50
9,57
9.83
10.05
10.37
10.70
10.77
10.98
11.00
11.45
12.08
12.37
12.55
12.63
12.65
12.95
13.27
13.45
13.65
13.83
Method 624.1
29
December 2014

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Table 3 - Example Retention Times
Analyte
Toluene
trans- 1 ,3 -Dichloropropene
Ethyl methacrylate
1 , 1 ,2-Trichloroethane
1 ,3 -Dichloropropane
Tetrachloroethene
2-Hexanone
Dibromochloromethane
1 ,2-Dibromoethane
Chlorobenzene
Ethylbenzene
1,1,1 ,2-Tetrachloroethane
w+p-Xylene
o-Xylene
Bromoform
Bromofluorobenzene
1 , 1 ,2,2-Tetrachloroethane
1,2,3-Trichloropropane
trans- 1 ,4-Dichloro-2-butene
Retention time (min)
14.18
14.57
14.70
14.93
15.18
15.22
15.30
15.68
15.90
16.78
16.82
16.87
17.08
17.82
18.27
18.80
18.98
19.08
19.12
                         Column:
75 m x 0.53 mm ID x 3.0 um wide-bore DB-624
                         Conditions:   40C for 4 min, 9C/min to 200C, 20C/min (or
                                      higher) to 250C, hold for 20 min at 250C to remove
                                      water

                         Carrier gas flow rate:  6-7 mL/min at 40C
                         Inlet split ratio:       3:1
                         Interface split ratio:   7:2
Method 624.1
            30
December 2014

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Table 4 - BFB Key m/z Abundance Criteria 1
m/z
50
75
95
96
173
174
175
176
177
Abundance criteria
15 -40% of m/z 95.
30 -60% of m/z 95.
Base Peak, 100% Relative Abundance.
5 -9% of m/z 95.
<2%ofm/zl74.
>50%ofm/z95.
5 -9% of m/z 174.
>95 % but < 1 0 1 % of m/z 1 74 .
5 -9% of m/z 176.
                            Abundance criteria are for a quadrupole mass
                            spectrometer; contact the manufacturer for criteria for
                            other types of mass spectrometers
Table 5 - Suggested Surrogate and Internal Standards
Analyte
Benzene -d6
4-Bromofluorobenzene
Bromochloromethane
2-Bromo-l -chloropropane
2-Butanone-d5
Chloroethane-ds
Chloroform-13C
l,2-Dichlorobenzene-d4
1 ,4-Dichlorobutane
1 ,2-Dichloroethane-d4
1 , 1 -Dichloroethene-d2
1 ,2-Dichloropropane-de
fra5-l,3-Dichloropropene-d4
1 ,4-Difluorobenzene
Ethylbenzene -di 0
Fluorobenzene
2-Hexanone-d5
Pentafluorobenzene
1 , 1 ,2,2-Tetrachloroethane-d2
Toluene -ds
Vinyl chloride -d3
Retention time (min)1
10.95
18.80
9.88
14.80
9.33
4.63
10.00

18.57
10.88
6.30
12.27
14.50

16.77

15.30

18.93
14.13
3.87
Primary m/z
84
95
128
77
77
71
86
152
55
102
65
67
79
114
98
96
63
168
84
100
65
Secondary m/z's

174, 176
49, 130,51
79, 156




90,92




63,88

70





  For chromatographic conditions, see the footnote to Table 3.
Method 624.1
31
December 2014

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Table 6 - Characteristic m/z's for Purgeable Organics
Analyte
Chloromethane
Bromomethane
Vinyl chloride
Chloroethane
Methylene chloride
Trichlorofluoromethane
1 , 1 -Dichloroethene
1 , 1 -Dichloroethane
trans- 1 ,2 -Dichloroethene
Chloroform
1 ,2-Dichloroethane
1,1,1 -Trichloroethane
Carbon tetrachloride
Bromodichloromethane
1 ,2-Dichloropropane
trans- 1 ,3 -Dichloropropene
Trichloroethene
Benzene
Dibromochloromethane
1 , 1 ,2-Trichloroethane
cis- 1 ,3 -Dichloropropene
2-Chloroethylvinyl ether
Bromoform
1 , 1 ,2,2-Tetrachloroethane
Tetrachloroethene
Toluene
Chlorobenzene
Ethyl benzene
1 ,3 -Dichlorobenzene
1 ,2-Dichlorobenzene
1 ,4-Dichlorobenzene
Primary m/z
50
94
62
64
84
101
96
63
96
83
98
97
117
83
63
75
130
78
127
97
75
106
173
168
164
92
112
106
146
146
146
Secondary m/z's
52
96
64
66
49, 51, and 86
103
61 and 98
65, 83, 85, 98, and 100
61 and 98
85
62, 64, and 100
99, 117, and 119
119 and 121
127, 85, and 129
112, 65, and 114
77
95, 97, and 132

129, 208, and 206
83, 85, 99, 132, and 134
77
63 and 65
171, 175, 250, 252, 254, and 256
83,85, 131, 133, and 166
129, 131, and 166
91
114
91
148 and 111
148 and 111
148 and 111
Method 624.1
32
December 2014

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Table 7 - LCS (Q), DOC (s and X ), and MS/MSD (P and RPD) Acceptance Criteria l
Analyte
Benzene
Benzene-d6
Bromodichloro methane
Bromoform
Bromomethane
2-Butanone-ds
Carbon tetrachloride
Chlorobenzene
Chloroethane
Chloroethane-ds
2-Chloroethylvinyl ether
Chloroform
Chloroform-1^
Chloromethane
Dibromochloromethane
,2 -Dichlorobenzene
,2-Dichlorobenzene-d4
,3 -Dichlorobenzene
,4 -Dichlorobenzene
, 1 -Dichloroethane
,2 -Dichloroethane
,2-Dichloroethane-d4
,1-Dichloroethene
, 1 -Dichloroethene-d2
trans- 1 ,2 -Dichloroethene
,2 -Dichloropropane
,2-Dichloropropane-de
cis- 1 , 3 -Dichloropropene
/ra5-l,3-Dichloropropene
/ra5-l,3-Dichloropropene-d4
Ethyl benzene
2-Hexanone-ds
Methylene chloride
1 , 1 ,2,2-Tetrachloroethane
1 , 1 ,2,2-Tetrachloroethane-d2
Tetrachloroethene
Toluene
Toluene-d8
1,1,1 -Trichloroethane
1 , 1 ,2-Trichloroethane
Trichloroethene
Trichlorofluoromethane
Vinyl chloride
Vinyl chloride-d3
Range for Q
(%)
65-135

65-135
70-130
15-185

70-130
65-135
40-160

D-225
70-135

D-205
70-135
65-135

70-130
65-135
70-130
70-130

50-150

70-130
35-165

25-175
50-150

60-140

60-140
60-140

70-130
70-130

70-130
70-130
65-135
50-150
5-195

Limit for s
(%)
33

34
25
90

26
29
47

130
32

472
30
31

24
31
24
29

40

27
69

79
52

34

192
36

23
22

21
27
29
50
100

Range for
X(%)
75-125

50-140
57-156
D-206

65-125
82-137
42-202

D-252
68-121

D-230
69-133
59-174

75-144
59-174
71-143
72-137

19-212

68-143
19-181

5-195
38-162

75-134

D-205
68-136

65-133
75-134

69-151
75-136
75-138
45-158
D-218

Range for
P (%)
37-151
70-130
35-155
45-169
D-242
60-140
70-140
37-160
14-230
60-140
D-305
51-138
70-130
D-273
53-149
18-190
70-130
59-156
18-190
59-155
49-155
70-130
D-234
70-130
54-156
D-210
60-140
D-227
17-183
70-130
37-162
60-140
D-221
46-157
70-130
64-148
47-150
70-130
52-162
52-150
70-157
17-181
D-251
70-130
Limit for
RPD
61

56
42
61

41
53
78

71
54

60
50
57

43
57
40
49

32

45
55

58
86

63

28
61

39
41

36
45
48
84
66

  1 Criteria were calculated using an LCS concentration of 20 (ig/L
  Q =  Percent recovery in calibration verification/LCS (Section 8.4)
  s =  Standard deviation of percent recovery for four recovery
      measurements (Section 8.2.4)

  X = Average percent recovery for four recovery measurements
      (Section 8.2.4)
  P =  Percent recovery for the MS or MSB (Section 8.3.3)
  D =  Detected; result must be greater than zero
        Notes:
        1. Criteria for pollutants are based upon the method
          performance data in Reference 4.  Where necessary,
          limits for recovery have been broadened to assure
          applicability to concentrations below those used to
          develop Table 7.

        2. Criteria for surrogates are from EPA CLP
          SOM01.2D
Method 624.1
33
December 2014

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Table 8 - Recovery and Precision as Functions of Concentration
Analyte
Benzene
Bromodichloromethane
Bromoform
Bromomethanea
Carbon tetrachloride
Chlorobenzene
Chloroethane
2-Chloroethylvinyl ethera
Chloroform
Chloromethane
Dibromochloromethane
1 ,2-Dichlorobenzeneb
1 ,3 -Dichlorobenzene
1 ,4-Dichlorobenzeneb
1 , 1 -Dichloroethane
1 ,2-Dichloroethane
1 , 1 -Dichloroethene
trans- 1 ,2,-Dichloroethene
1 ,2-Dichloropropanea
cis- 1 ,3 -Dichloropropenea
trans- 1 ,3 -Dichloropropenea
Ethyl benzene
Methylene chloride
1 , 1 ,2,2-Tetrachloroethane
Tetrachloroethene
Toluene
1,1,1 -Trichloroethane
1 , 1 ,2-Trichloroethane
Trichloroethene
Trichlorofluoromethane
Vinyl chloride
Recovery, X'
(Hi/L)
0.93C+2.00
1.03C-1.58
1.18C-2.35
l.OOC
1.10C-1.68
0.98C+2.28
1.18C+0.81
l.OOC
0.93C+0.33
1.03C+0.81
1.01C-0.03
0.94C+4.47
1.06C+1.68
0.94C+4.47
1.05C+0.36
1.02C+0.45
1.12C+0.61
1.05C+0.03
l.OOC
l.OOC
l.OOC
0.98C+2.48
0.87C+1.88
0.93C+1.76
1.06C+0.60
0.98C+2.03
1.06C+0.73
0.95C+1.71
1.04C+2.27
0.99C+0.39
l.OOC
Single analyst
precision, sr'
(Hi/L)
20.26 X-1.74
0.15 X+0.59
0.12 X+0.36
0.43 X
0.12 X+0.25
0.16 X-0.09
0.14 X+2.78
0.62 X
0.16 X+0.22
0.37 X+2.14
0.17 X-0.18
0.22 X-1.45
0.14 X-0.48
0.22 X-1.45
0.13 X-0.05
0.17 X-0.32
0.17 X+1.06
0.14 X+0.09
0.33 X
0.38 X
0.25 X
0.14 X+1.00
0.15 X+1.07
0.16 X+0.69
0.13 X-0.18
0.15 X-0.71
0.12 X-0.15
0.14 X+0.02
0.13 X+0.36
0.33 X-1.48
0.48 X
Overall
precision,
S' (ug/L)
0.25 X-1.33
0.20 X+1.13
0.17 X+1.38
0.58 X
0.11 X+0.37
0.26 X-1.92
0.29 X+1.75
0.84 X
0.18 X+0.16
0.58 X+0.43
0.17 X+0.49
0.30 X-1.20
0.18 X-0.82
0.30 X-1.20
0.16 X+0.47
0.21 X-0.38
0.43 X-0.22
0.19 X+0.17
0.45 X
0.52 X
0.34 X
0.26 X-1.72
0.32 X+4.00
0.20 X+0.41
0.16 X-0.45
0.22 X-1.71
0.21 X-0.39
0.18 X+0.00
0.12 X+0.59
0.34 X-0.39
0.65 X
       X'  = Expected recovery for one or more measurements of a sample containing a concentration of C, in (ig/L.
       Sr'  = Expected single analyst standard deviation of measurements at an average concentration found of X , in (ig/L.
       S'   = Expected interlaboratory standard deviation of measurements at an average concentration found of X , in (xg/L.
       C   = True value for the concentration, in (ig/L.
       X  = Average recovery found for measurements of samples containing a concentration of C, in ng/L.
       a Estimates based upon the performance in a single laboratory (References 4 and 16).
       bDue to coelutions, performance  statements for these isomers are based upon the sums of their concentrations.
Method 624.1
34
December 2014

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19.  Figures
                  OPTIONAL
                  FOAM
                  TRAP
-EXIT % in.
     0, D.
                                 1-14IBIW O. D.
                                  INLET % M.
                                       O. D.
              O. D, EXIT
    SAMPLE INLET

    2-WAV SYRINGE VALVE
    17CM. 20 GAUGE SYRINGE NEEDLE

    6MM. 0,  O, RUBBEB SEPTUM

        10MM. 0, D.     1/16 IN, 0.0.
                   y STAINLESS STEEL
                                           INLET
                                             IN. 0. D,
                                                        133C MOLECULAR
                                                        SIEVE PURGE
                                                        GAS FILTER
                                                          PURGE GAS
                                                          FLOW
                                                          CONTROL
                  1GMM GLASS FRIT
                  MEDIUM POROSITY
                              Figyre 1, Pyrging dvica.
Method 624.1
       35
December 2014

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                   PACKING PROCEDURE

                 GLASS
                       SIM

                    15
              SILICA casci

                     15C1
               3% OV-1
                      SMM
               WOOL      TRAPINLET
   CONSTRUCTION
               COMPRESSION
               FITTING NUT
               AND FERRULES
                14FT.7A/FOOI
                RESISTANCE WIRE

                THERUGCQUPLE/
               _ CONTROLLER
                                                       TUBING 25CM
                                                       0.101 IN, t.D,
                                                       0.121 IN, 0,D.
                                                                sna
                   Figure 2. Trap packings and construction to include
                           desorb capability.
Method 624.1
36
December 2014

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                 CARRIER GAS FLOW CONTROL
                PRESSURE REGULATOR
  LIQUID INJECTION PORTS
                     COLUMN OVEN
                PURGE GAS     	.
                FLOW CONTROL \j
                              Lj
                13X MOLECULAR
                SIEVE FILTER
                                                              CONFIRMATORY COLUMN
                                                            TO DETECTOR
                                                               ANALYTICAL COLUMN
          OPTIONAL 4-PORT COLUMN
          SELECTION VALVE
                 |NLET
              RESISTANCE WIRE
                                                                CHEATER CONTROL
                                                    PURGING
                                                    DEVICE
                    Nota:ALL LINES BETWEEN
                        TRAP AND GC
                        SHOULD BE HEATED
                        TO 80*C
                         Figure 3. Purge and trap system - purge mode.
                          CARRIER GAS
                          FLOW CONTROL
                   PRESSURE
                   REGULATOR
LIQUID INJECTION PORTS
                   COLUMN OVEN
          JIPJL-L .^CONFIRMATORY COLUMN
                PURGE GAS
                FLOW CONTROL S ,
                 13X MOLECULAR
                 SIEVE FILTER"
                                                JLTJl
               _O TO DETECTOR
                  ""-ANALYTICAL COLUMN
       OPTIONAL 4-PQRT COLUMN
       SELECTION VALVE
  6-PORT TRAP INLET
  VALVE  I RESISTANCE WIRE
                                                   PURGING
                                                   DEVICE
                                                                  HEATER
                                                                  CONTROL
                      Note:
                      ALL LINES BETWEEN
                      TRAP AND GC
                      SHOULD BE HEATED
                      TO 95 C.
                       Figure 4,  Purge and trap system - desorb mode.
Method 624.1
       37
December 2014

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20.   Glossary

These definitions and purposes are specific to this method, but have been conformed to common usage to
the extent possible.

20.1  Units of weight and measure and their abbreviations

      20.1.1  Symbols

             C   degrees Celsius
             ug   microgram
             uL   microliter
             <    less than
             >    greater than
             %   percent

      20.1.2  Abbreviations (in alphabetical order)

             cm   centimeter
             g    gram
             h    hour
             ID   inside diameter
             in.   inch
             L    liter
             M   Molecular ion
             m   mass
             mg  milligram
             min minute
             mL  milliliter
             mm millimeter
             ms   millisecond
             m/z mass-to-charge ratio
             N   normal; gram molecular weight of solute divided by hydrogen equivalent of solute, per
                  liter of solution
             ng   nanogram
             pg   picogram
             ppb part-per-billion
             ppm part-per-million
             ppt  part-per-trillion
             psig pounds-per-square inch gauge
             v/v  volume per unit volume
             w/v weight per unit volume

20.2  Definitions and acronyms (in alphabetical order)

Analyte - A compound tested for by this method. The analytes are listed in Tables 1 and 2.

Analyte of interest - An analyte of interest is an analyte required to be determined by a regulatory/control
authority or in a permit, or by a client.

Analytical batch - The set of samples analyzed on a given instrument during a 12-hour period that begins
and ends with analysis of a calibration verification/LCS.  See Section 8.4.

Method 624.1                                      38                                   December 2014

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Blank - An aliquot of reagent water that is treated exactly as a sample including exposure to all glassware,
equipment, solvents, reagents, internal standards, and surrogates that are used with samples. The blank is
used to determine if analytes or interferences are present in the laboratory environment, the reagents, or the
apparatus.  See Section 8.5.

Calibration - The process of determining the relationship between the output or response of a measuring
instrument and the value of an input standard.  Historically, EPA has referred to a multi-point calibration
as the "initial calibration," to differentiate it from a single-point calibration verification.

Calibration standard - A solution prepared from stock solutions and/or a secondary standards and containing
the analytes of interest, surrogates, and internal standards. The calibration standard is used to calibrate the
response of the GC/MS instrument against analyte concentration.

Calibration verification standard - The laboratory control sample (LCS) used to verify calibration. See
Section 8.4.

Descriptor - In SIM, the beginning and ending retention times for the RT window, the m/z's sampled in
the RT window, and the dwell time at each m/z.

Extracted ion current profile (EICP) - The line described by the signal at a given m/z.

Field duplicates - Two samples collected at the same time and place under identical conditions, and
treated identically throughout field and laboratory procedures.  Results of analyses of field duplicates
provide an estimate of the precision associated with sample collection, preservation, and storage, as well
as with laboratory procedures.

Field blank - An aliquot of reagent water or other reference matrix that is placed in a sample container in
the field, and treated as a sample in all respects, including exposure to sampling site conditions, storage,
preservation, and all analytical procedures. The purpose of the field blank is to determine if the field or
sample transporting procedures and environments have contaminated the sample.

GC - Gas chromatograph or gas chromatography

Internal standard - A compound added to a sample in a known amount and used as a reference for
quantitation of the analytes of interest and surrogates. Internal standards are listed in Table 5.  Also see
Internal standard quantitation.

Internal standard quantitation - A means of determining the concentration of an analyte of interest (Tables 1
and 2) by reference to a compound added to a sample and not expected to be found in the sample.

DOC - Initial demonstration of capability (DOC; Section 8.2); four aliquots of reagent water spiked with
the analytes of interest and analyzed to establish the ability of the laboratory to generate acceptable
precision and recovery. A DOC is performed prior to the first time this method is used and any time the
method or instrumentation is modified.

Laboratory control sample (LCS; laboratory fortified blank (LFB); on-going precision and recovery sample;
OPR) - An aliquot of reagent water spiked with known quantities of the analytes of interest and surrogates.
The LCS is analyzed exactly like a sample. Its purpose is to assure that the results produced by the
laboratory remain within the limits specified in this method for precision and recovery. In this method, the
LCS is synonymous with a calibration verification sample (See Sections 7.4 and 8.4).

Laboratory fortified sample matrix - See Matrix spike

Method 624.1                                     39                                    December 2014

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Laboratory reagent blank - See Blank

Matrix spike (MS) and matrix spike duplicate (MSB) (laboratory fortified sample matrix and duplicate) -
Two aliquots of an environmental sample to which known quantities of the analytes of interest and
surrogates are added in the laboratory.  The MS/MSD are prepared and analyzed exactly like a field
sample. Their purpose is to quantify any additional bias and imprecision caused by the sample matrix.
The background concentrations of the analytes in the sample matrix must be determined in a separate
aliquot and the measured values in the MS/MSD corrected for background concentrations.

May - This action, activity, or procedural step is neither required nor prohibited.

May not - This  action, activity, or procedural step is prohibited.

Method blank (laboratory reagent blank) - See Blank.

Method detection limit (MDL) - A detection limit determined by the procedure at 40 CFR 136, Appendix
B. The MDLs determined by EPA in the original version of the method are listed in Table 1.  As noted in
Sec.  1.4, use the MDLs in Table  1 in conjunction with current MDL data from the laboratory actually
analyzing samples to assess the sensitivity of this procedure relative to project objectives and regulatory
requirements (where applicable)

Minimum level (ML) - The term "minimum level" refers to either the sample concentration equivalent to
the lowest calibration point in a method or a multiple of the method detection limit (MDL), whichever is
higher. Minimum levels may be obtained in several ways: They may be published in a method; they may
be based on the lowest acceptable calibration point used by a laboratory;  or they may be calculated by
multiplying the  MDL in a method, or the MDL determined by a laboratory, by a factor of 3. For the
purposes of NPDES compliance monitoring, EPA considers the following terms to be synonymous:
"quantitation limit," "reporting limit," and "minimum level."

MS - Mass spectrometer or mass spectrometry

Must - This action, activity, or procedural step is required.

m/z - The ratio  of the mass of an ion (m) detected in the mass spectrometer to the charge (z) of that ion.

Quality control  sample (QCS) - A sample containing analytes of interest at known concentrations. The
QCS is obtained from a source external to the laboratory or is prepared from standards obtained from a
different source than the calibration standards.

The purpose is to check laboratory performance using test materials that have been prepared independent
of the normal preparation process.

Reagent water - Water demonstrated to be free from the analytes of interest and potentially interfering
substances at the MDLs for the analytes in this method.

Regulatory compliance limit (or regulatory concentration limit) - A limit on the concentration or amount
of a pollutant or contaminant specified in a nationwide standard, in a permit, or otherwise established by a
regulatory/control authority.

Relative retention time (RRT) - The ratio of the retention time of an analyte to the retention time of its
associated internal standard. RRT compensates for small changes in the GC temperature program that can
affect the absolute retention times of the analyte and internal standard. RRT is a unitless quantity.

Method 624.1                                     40                                   December 2014

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Relative standard deviation (RSD) - The standard deviation times 100 divided by the mean.  Also termed
"coefficient of variation."

RF - Response factor. See Section 7.3.3.

RSD - See relative standard deviation

Safety Data Sheet (SDS) - Written information on a chemical's toxicity, health hazards, physical
properties, fire, and reactivity, including storage, spill, and handling precautions that meet the
requirements of OSHA, 29 CFR 1910.1200(g) and Appendix D. United Nations Globally Harmonized
System of Classification and Labelling of Chemicals (GHS), third revised edition, United Nations, 2009.

Selected Ion Monitoring (SIM) - An MS technique in which a few m/z's are monitored. When used with
gas chromatography, the m/z's monitored are usually changed periodically throughout the
chromatographic run to correlate with the characteristic m/z's for the analytes, surrogates, and internal
standards  as they elute from the chromatographic column.  The technique is often used to increase
sensitivity and minimize interferences.

Signal-to-noise ratio (S/N) - The height of the signal as measured from the mean (average) of the noise to
the peak maximum divided by the width of the noise.

SIM - See Selection Ion Monitoring

Should - This action, activity, or procedural step is suggested but not required.

Stock solution - A solution containing an analyte that is prepared using a reference material traceable to
EPA, the National Institute of Science and Technology (NIST), or a source that will attest to the purity and
authenticity of the reference material.

Surrogate  - A compound unlikely to be found in a sample, and which is spiked into sample in a known
amount before purge-and-trap.  The surrogate is quantitated with the same procedures used to quantitate
the analytes of interest. The purpose of the surrogate is to monitor method performance with each
sample.
Method 624.1                                     41                                    December 2014

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