5546                       905R80114
                   Measurement of Trihalomethanes in Drinking Water
                     with Gas Chromatography/Mass Spectrometry and
                                Selected Ion Monitoring
                                     Method 501.3
     1.   Scope  and Application                                                        *
         1.1  This method  (501.3) provides procedures for identification and         *
             measurement  of the four regulated  trihalomethanes (chloroform,
             bromoform, bromodichloromethane, and chlorodibromomethane) in
             finished drinking water, raw source water, or drinking water in 'any
                                                              2
             treatment stage.  Previously promulgated methods, , 501.1 and
             501.2,  involve gas chromatographic separation, identification, and
             measurement  of these specific trihalomethanes after they are
             removed from the sample matrix.  Method 501.2 is an extraction
             procedure; Methods 501.1 and 501.3 involve removal of trihalo-
             methanes with purge and trap procedures.  In Method 501.3, selected
             ion monitoring with a mass spectrometer is substituted for the
             hali de-specific gas chromatographic detector specified in Method
             501.1.  Any  one of these methods may be used to analyze drinking
             water for these four trihalomethanes, whose total concentration is
             called  total trihalomethanes.
         1.2  With Method  501.3, method detection limits (MDLs) for trihalo-
             methanes are:
                  chloroform,           0.06 ug/L;
                                                                                     t
                  bromodichloromethane, 0.07 ug/L;
                  chlorodibromomethane, 0.05 ug/L; and
                                              w             .
                  bromoform,            0.04 ug/L;     r :•  ,:   :
                                                       23 j sj .;.;„•
                                                       Chicago, iiimois  6u6v4
                                                                          v

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sncy

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         where MDL is the minimum amount that can be measured with 99%
         confidence that the reported value  is greater than zero.
2.  Summary of Method
    2.1  Trihalomethanes are removed (purged) from the sample matrix by
         bubbling helium through the aqueous sample.  Purged trihalomethanes
         and other sufficiently volatile sample components with sufficiently
                                                      P
         low water solubility are sorbed onto Tenax-GC   (a porous polymer
         based on 2,6-diphenyl-p_-phenylene oxide) contained in a stainless
         steel tube.  When purging is complete, the sorbent tube is heated
         and backflushed with helium to desorb purged sample components  into
         a gas chromatograph (GC) interfaced to a mass spectrometer (MS).
         Trihalomethanes eluting from the GC column are  identified and
         measured by acquiring mass spectral data for selected ions that are
         characteristic of individual trihalomethanes.
3.  Interferences and Contamination Sources
    3.1  With selected ion monitoring, the mass spectrometer is essentially
         a compound-selective detector, and  interferences are minimal.  GC
         retention time and relative ion abundance data for the four
         trihalomethanes provide reliable identifications.  No known com-
         pounds that are purged with the conditions used in this method have
         the same GC retention times and also produce the same fragment  ions
         in the same relative abundances as the four trihalomethanes.
    3.2  With selected-ion monitoring, interfering contamination is only
         likely to occur when a sample containing low concentrations of
         trihalomethanes is analyzed immediately after a sample containing
         relatively high concentrations of trihalomethanes.  A preventive

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         technique is between-sample rinsing of the purging apparatus and
         sample syringes with two portions of reagent water.  After analysis
         of a sample containing high concentrations of trihalomethanes, the
         system should be baked for 10 min by passing helium through the
         sample purging chamber into the heated (180°) sorbent trap.  One
         or .more method blanks should be analyzed to ensure that accurate
         values are obtained for the next sample.
    3.3  Samples may be contaminated during shipment or storage'by diffusion
         of volatile organics through the sample bottle septum seal.  Field
         blanks must be analyzed to determine when sampling and storage
         procedures have not prevented contamination.
    3.4  During analysis, major contaminant sources are impurities in the
         inert purging gas and in the sorbent trap.  Analysis of field
         blanks and method blanks provides information about the presence of
         contaminants.
4.  Safety
    4.1  The toxicity or carcinogenicity of chemicals used in this method
         has not been precisely defined; each chemical should be treated as
         a potential health hazard, and exposure to these chemicals should
         be minimized.  Each laboratory is responsible for maintaining
         awareness of OSHA regulations regarding safe handling of chemicals
         used in this method.  Additional references to laboratory safety
         are cited.
    4.2  Primary standards of trihalomethanes should be handled in a hood.
5.  Equipment and Materials
    5.1  Sample containers — 25-mL or larger glass bottles, equipped with a
         screw cap with center hole (Pierce #13075 or equivalent) and a
         Teflon** faced silicone septum.

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5.2  Purge and trap device (Figures 1-2) consisting of sample purging
     chamber, sorbent trap and desorber.  (Acceptable devices are
     commercially available.)
     5.2.1  The all glass sample purging chamber (Figure 1) holds 5-mL
            samples with < 15 ml of gaseous headspace between the water
            column and the trap.  The helium purge gas passes through
            the water column as finely divided bubbles (optimum diameter
            of <3 mm at the origin).  The purge gas must be introduced
            at a point <5 mm from the base of the water column.
     5.2.2  The stainless steel sorbent trap (Figure 3) is 25 cm long by
            2.5 mm ID and is packed with 1 cm of methyl-silicone coated
                                      R
            packing, 15 cm of Tenax-GC , and 8 cm of silica gel, in
            that order with respect to the inlet end of the trap.
            Silica gel is not necessary for efficient trapping of
            trihalomethanes but does not hinder trapping; therefore,
                                                               P
            silica gel may be replaced with additional Tenax-GC .  A
            trap with different dimensions can be used if it has been
            evaluated and found to perform satisfactorily.  Before
            initial use, the trap should be conditioned overnight at
            180°C by backflushing with helium flow of at least 20
            mL/min.  Each day the trap should be conditioned for 10 min
            at 180°C with backflushing.
     5.2.3  The desorber (Figure 3) should be capable of rapidly heating
            the trap to 180°C.  The trap section containing
            Tenax-GC  should not be heated to higher than 180°C, and
            the temperature of the other sections should not exceed
            200°C.

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5.3  Syringes and syringe valves
     5.3.1  Two 5-mL glass hypodermic syringes with Luerlok tip (if
            applicable to the purging device being used).
     5.3.2  One 5-mL gas-tight syringe with shutoff valve.
     5.3.3  Two two-way syringe valves with Luer ends (if applicable to
            the purging device being used).
     5.3.4  One 25-uL micro syringe with 0.006 in. ID needle.
     5.3.5  One 100-uL micro syringe.
5.4  Miscellaneous
     5.4.1  Standard solution storage containers — 10 ml bottles with
                  o
            Teflon -lined screw caps.
     5.4.2  Analytical balance capable of weighing 0.0001 g accurately.
     5.4.3  Helium purge gas, as contaminant free as possible.
5.5  Sorfaent trap packing materials
     5.5.1  Polymer based on 2,6-diphenyl-p_-phenylene oxide ~ 60/80
                         o
            mesh Tenax-GC , chromatographic grade, or equivalent.
     5.5.2  Methyl silicone coated packing — 3% OV-1 on 60/80 mesh
            Chromosorb W, or equivalent.
     5.5.3  Silica gel — 35/60 mesh, Oavison Chemical grade 15, or
            equivalent.
5.6  Reagents
     5.6.1  Sodium thiosulfate or sodium sulfite — granular, ACS
            reagent grade.
     5.6.2  Methanol — pesticide quality or equivalent.
     5.6.3  Reagent water — water in which an interferent is not

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            observed at the method detection limit of the compound of
            interest. Reagent water may be prepared by passing tap water
            through a filter bed containing about 0.5 kg of activated
            carbon (Calgon Corp. Filtrasorb 300 or equivalent), by using
            a water purification system (Millipore Super Q or equiva-
            lent), or by boiling distilled water for 15 min followed by
            a 1 h purge with inert gas while the water temperature is
            held at 90°C.  Reagent water should be stored in clean,
                                            o
            narrow-mouth bottles with Teflon -lined septa and screw
            caps.
5.7  Stock standard solutions — These solutions may be purchased as
     certified solutions or prepared from pure standard materials using
     the following procedures:
     5.7.1  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 min or until all alcohol-wetted
            surfaces have dried.  Weigh the flask to the nearest 0.1
            mg.  With a 100-uL syringe, immediately add two or more
            drops of assayed reference compound to the flask.  (The
            liquid must fall directly into the alcohol without contact-
            ing the flask.)  Reweigh the flask, dilute to volume,
            stopper, and mix by inverting several times.
     5.7.2  From the net weight gain, calculate the concentration in
            micrograms per microliter.  When assayed compound purity is
            > 96%, the uncorrected weight may be used to calculate
            concentration.

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     5.7.3  Stock standard solutions should be stored with minimal head-
                           is
            space in Teflon -lined screw-capped bottles.
5.8  Secondary dilution standard — Stock standard solutions are used to
     prepare a secondary dilution standard solution that contains the
     four trihalomethanes in methanol.  The secondary dilution standard
     should be prepared at a concentration that can be easily diluted to
     prepare aqueous calibration solutions (Section 8.2.3) at concentra-
     tions that will bracket the working concentration range.  (For this
     method, the concentration of each trihalomethane in the secondary
     dilution standard solution should be about 1 to 25 ug/mL.)  The
     solution should be stored with minimal headspace and should be
     checked frequently for signs of deterioration or evaporation,
     especially just before preparing calibration standards from it.
5.9  Internal standard spiking solution and surrogate compound spiking
     solution — A spiking solution of fluorobenzene in methanol should
     be prepared at a concentration of 0.5 ug/mL.  When 10 uL of this
     solution is added to 5 ml of sample or standard calibration
     solution, the fluorobenzene concentration will be 1 ug/L. If the
     internal standard technique is used, fluorobenzene serves as the
     internal standard.  If the external standard technique is used,
     fluorobenzene is a surrogate compound added to each sample to
     monitor method efficiency.  The measured efficiency for fluoro-
     benzene is considered to be indicative of method efficiency for the
     four trihalomethanes being measured with this method.
5.10 Gas Chromatograph/Mass Spectrometer/Data System (GC/MS/DS)

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5.10.1 The GC, which must be capable of temperature programming,
       should be interfaced to the MS with an all-glass enrichment
       device and an all-glass transfer line.  Any enrichment
       device or transfer line can be used, however, if performance
       specifications described in this method can be demonstrated
       with it.  The recommended GC column is 1.3 m long by 2 mm ID
       glass packed with 1% SP-1000 on 60/80 mesh Carbopack B.
       Helium carrier gas flow rate is 30 mL/min.  The column
       temperature program is initial 3 min period at 45°C,
       increased to 200°C at a rate of 8°C/min, and isothermal
       at 200°C for 15 min.  Other columns may be used if they
       provide data with adequate accuracy and precision as
       specified in this method.  An alternative column is 1.8 m
       long by 2 mm ID glass or stainless steel packed with 0.2%
       Carbowax 1500 on 80/100 mesh Carbopack C.
5.10.2 Mass spectral data are to be obtained with electron-impact
       iom'zation at a nominal electron energy of 70 eV.  The mass
       spectrometer must produce a mass spectrum that meets all
       criteria in Table 1 when 50 ng or less of p_-bromofluoro-
       benzene (8FB) is introduced into the GC.
5.10.3 An interfaced data system (OS) is required to acquire,
       store, reduce and output mass spectral data.  The data
       system must be equipped with a program to acquire data for
       only a few selected ions that are characteristic of the

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  Table 1.  Ion Abundance Criteria for _p-Bromofluorobenzene
  Mass	Ion Abundance Criteria	
_15  to  40% of  mass  95
  75                            30  to  60% of  mass  95
  95                            Base Peak,  100% Relative Abundance
  96                            5 to 9% of  mass 95
 173                            < 2% of mass  174
 174                            > 50%  of mass 95
 175                            5 to 9% of  mass 174
 176                            > 95%  but < 101% of mass -174
 177                            5 to 9% of  mass 176
        internal  standard  and  the trihalomethanes being analyzed.
        As  compounds  elute from  the GC,  mass  spectral  data are
        acquired  continuously, but only  for a few masses rather than
        for a  broad mass range that would  provide a complete mass
        spectrum  of each sample  component.  This  is known as
        selected  ion  monitoring  (SIM).
5.10.4  SIM is used because it provides  lower detection limits than
        does full-spectrum data  acquisition.   Although identifica-
        tions  based on  SIM data  are less reliable than those based
        on  full-spectrum data, identifications of the  four trihalo-
        methanes  are  more  reliable with  SIM than  with  the most
        selective conventional chromatographic detectors.  This
        identification  reliability is obtained by using relative
        retention time  information,  by selecting  appropriate
        characteristic  ions to be monitored,  and  by checking
        relative  abundances of naturally occurring isotopes of
        chlorine  and  bromine.

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         5.10.5 Increased sensitivity is achieved with SIM because more time
                is dedicated to acquiring abundance data for each mass when
                only a few masses (ions) are monitored rather than every
                mass in the full-spectrum mass range.  For example, if 4 s
                are required for full-spectrum data acquisition, approxi-
                mately 17 ms will be dedicated to each mass from 20 to 260
                atomic mass units (amu).  If only eight masses are
                monitored, however, approximately 500 msec can be dedicated
                to each mass during a 4 s data acquisition period.  This
                relatively long data acquisition time with SIM improves
                detection limits by averaging random noise, which improves
                the signal-to-noise ratio.
         5.10.6 For SIM of trihalomethanes, the data system must be capable
                of monitoring at least four ions; the capability to monitor
                eight ions is highly desirable.  When less than eight ions  .
                can be monitored simultaneously, this disadvantage can be
                overcome if the ions being monitored can be changed as a
                function of time.  With knowledge of trihalomethane reten-
                tion times, the operator can then change ions being
                monitored as different compounds elute.
6.  Selection of Ions
    6.1  The four trihalomethanes are distinguished from one another and
         from other sample components by acquiring abundance information
         about characteristic ions and by using GC retention time data.
         Mass spectra of the four trihalomethanes (Figures 4-7) contain
         characteristic patterns caused by chlorine and bromine isotopes.

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     For example, the chloroform mass spectrum contains an ion cluster
     at
     37,
at m/z 83, 85, and 87 with known relative abundances of   Cl and
       Cl isotopes.  Similar isotope clusters are produced by fragmen-
     tation of molecules containing bromine or chlorine and bromine.
6.2  Because two ions are monitored for each trihalomethane, relative
     abundances of isotope cluster ions provide corroborating identifi-
     cation information.  To achieve maximum sensitivity, monitored ions
     (Table 2) are the two most abundant ions in a trihalomethane mass
     spectrum.  Because chloroform and bromodichloromethane produce
     identical isotope clusters at m/z 83, 85, and 87 (produced by loss
     of chlorine and bromine, respectively), m/z 83 and 85 are used to
     monitor both compounds.  (They are distinguished from each other by
     differences in retention time.)  Two ions each are needed to
     identify and measure dibromochloromethane and bromoform; one ion is
     required for fluorobenzene.  Therefore, the capability to monitor a
     total of seven ions is needed to measure simultaneously all four
     trihalomethanes and fluorobenzene.
                Table  2.   Ions  Selected  to Detect  and
                        Measure  Trihalomethanes
                                                              Theoretical
Compound
CMC 13

CHCl2Br

CHC18r2

C6H5F
CHBr3

Ion
CHCl2+

CHC12+

CHClBr+

C6H5F+
CHBr2+

m/z
83
85
83
85
127
129
96
171
173
Rel. Abun.
100
65
100
65
77
100
100
51
100
(X)










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6.3  If only four ions can be monitored simultaneously but the set of
     ions can be changed with only a brief interruption of data
     acquisition, different compounds can be monitored as they elute
     from the GC.  For example, an ion current profile similar to that
     obtained when seven ions were monitored (Figure 8) can be obtained
     by sequentially monitoring two sets of ions, one set of four ions
     and one of three ions.  Monitoring m/z 83, 85, 127 and 129 until
     after chlorodibromomethane elutes would permit detection of chloro-
     form, bromodichloromethane, and chlorodibromomethane.  Changing the
     set of monitored ions to m/z 96, 171 and 173 would then permit
     detection of fluorobenzene and bromoform.
6.4  Although some purgeable organohalides have the same retention times
     as trihalomethanes with the recommended columns, these compounds
     are not observed because they do not produce ions being monitored.
     A representative chromatogram of halogenated organic compounds
     (Figure 9) shows no components coeluting with chloroform or bromo-
     dichloromethane.  Chlorodibromomethane, however, coelutes with
     1,1,2-trichloroethane and cis-l,3-dichloropropene.  Because neither
     of the latter two compounds produces ions at m/z 127 or 129 (which
     are the ions used to detect and measure chlorodibromomethane),
     neither will be observed.  A similar situation exists with the
     coelution of bromoform (monitored with m/z 171 and 173) and
     1,1,1,2-tetrachloroethane, which produces neither m/z 171 nor 173.
5.5  Non-halogenated compounds will not be falsely identified as
     trihalomethanes, because two ions are monitored to detect isotope
     clusters produced by trihalomethanes, but not by non-halogenated
     comoounds.

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    5.6  The length of time to be spent acquiring data for each  ion must be
         selected with consideration of several factors, such as the number
         of ions monitored, total data acquisition time for the  set of
         monitored ions, GC resolution of sample components, ion counting
         statistics, and dynamic range of ion detection and data storage
         devices.  Sufficient.time must be spent on each ion to  acquire
         reliable data about changes in ion abundance as a function of time.
         If too much time is spent on any one ion, however, other sample
         components will not be detected as they elute from the GC column.
         At least five data points must be acquired for each GC peak.  The
         same data acquisition time need not be used for all ions monitored;
         the data acquisition time used to monitor a sample component,
         however, must be the same as the time used to prepare the cali-
         bration curve for that trihalomethane or to calculate its relative
         response factor.
7.  Sample Collection, Preservation and Handling
    7.1  All samples should be collected in duplicate.  Sample bottles must
         be filled to overflowing.  No air bubbles should pass through the
         sample as the bottle is filled, or be trapped in the sample when
         the bottle is sealed.  Samples must be kept sealed from collection
         time until analysis; this storage period should not exceed 14 days,
         because significant biodegradation may occur after this period.
         7.1.1   When sampling from a water tap, open the tap and allow the
                system to flush until the water temperature has stabilized.
                Adjust the flow to about 500 mL/min and collect  duplicate
                samples from the flowing stream.
         7.1.2   When sampling from an open body of water, fill a 1-qt
                wide-mouth bottle with sample from a respresentative area,

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                and carefully fill duplicate sample bottles from the  1-qt
                bottle.
    7.2  If a sample is expected to contain residual chlorine, a reducing
         agent, sodium thiosulfate or sodium sulfite (10 mg per 40-mL sample
         for up to 5 ppm chlorine) should be added to the empty sample
         bottle before it is shipped to the sampling site.  (The reducing
         agent is not added to samples to be analyzed to determine maximum
         trihalomethane potential.)
    7.3  Duplicate field blanks must be collected along with each sample
         set, which is composed of the samples collected from the same
         general sample site at approximately the same time.  Field blanks
         are prepared by filling sample bottles with reagent water at the
         laboratory and shipping the sealed bottles to the sampling site
         along with empty sample bottles and back to the laboratory with
         filled sample bottles.  (If reducing agent is added to sample
         bottles, it must also be added to blanks.)
8.  Calibration
    8.1  The analytical system is calibrated each 8 h period by analyzing
         standard solutions with the same procedures that will be used to
         analyze samples (Section 9).  Either the external standard or
         internal standard technique may be used.  With either technique,
         however, fluorobenzene must be added (Section 5.9) to all cali-
         bration solutions, because it will be used either as an internal
         standard or as a surrogate compound.
    8.2  External Standard Technique
         3.2.1  An external standard is a known amount of a pure compound
                that is analyzed with the same procedures and conditions
                that are used to analyze samples containing that compound.

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       From measured detector responses to known amounts of the
       external standard, a concentration of that same compound can
       be calculated from measured detector response to that
       compound in a sample analyzed with the same procedures.
8.2.2  Calibration curves are prepared by analyzing at least three
       calibration solutions, each containing a standard of each of
       the four trihalomethanes.  One solution should contain each
       trihalomethane at a concentration approaching but greater
       than the method detection limit (Table 4) for that compound;
       the other two solutions should contain trihalomethanes at
       concentrations that bracket the range expected in samples.
       For example, if the detection limit for a particular
       trihalomethane is 0.06 yg/L, and a 5-mL sample expected to
       contain approximately 5 ug/L is analyzed, aqueous solutions
       of standards should be prepared at concentrations of 0.1
       ng/mL, 1 ng/mL, and 10 ng/mL.
8.2.3  Three calibration solutions are prepared by adding 20.0 uL
       of the secondary dilution standard solution to 50 ml, 250
       ml, and 500 ml aliquots of reagent water.  (A 25-yL syringe
       with a 0.006 in. ID needle is recommended for this
       transfer.)  Aqueous standard solutions may be stored for up
       to 24 hr in sealed vials with zero headspace.
8.2.4  Because the surrogate, fluorobenzene, will be spiked into
       all samples by adding 10 yL of the surrogate spiking solu-
       tion, this technique should also be used to add the
       surrogate to calibration solutions.  The surrogate spiking
       solution should be added to the syringe containing 5 ml of
       calibration solution immediately before the syringe is

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            attached to the purging device.
     8.2.5  Each calibration solution is analyzed with the procedures to
            be used to analyze samples.  For each trihalomethane,
            integrated abundances of the ion characteristic of that
            compound are plotted as a function of the concentration.
            The primary (most abundant) characteristic ion should be
            used (Table 2).  If the ratio of ion abundance to amount of
            trihalomethane is constant (< 10% relative standard
            deviation) throughout the concentration range, the average
            ratio may be used instead of a calibration curve.
     8.2.6  Calibration data must be checked each day by measurement of
            one or more external standard calibration solutions.  If the
            absolute ion abundance measured for any trihalomethane
            varies from expected abundance by more than 10%, a fresh
            calibration solution must be prepared and analyzed.  Prepar-
            ation of a new calibration curve may be necessary, because
            detector response may have changed.
8.3  Internal standard technique
     8.3.1  An internal standard is a pure compound added to a sample in
            known amounts and used to calibrate concentration measure-
            ments of other compounds that are sample components.  The
            internal standard must be a compound that is not contained
            in the sample.  Fluorobenzene was selected as the internal
            standard because it:
            o  is stable in aqueous solutions,
            o  is efficiently purged from aqueous solutions,

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       o  does not occur naturally;
       o  is not commercially produced in bulk quantities but is
          available as a laboratory reagent chemical,
       o  does not coelute with any of the trihalomethanes being
          monitored but elutes among them (Figure 8), and
       o  can be monitored with one ion.
8.3.2  A calibration curve should be prepared by analyzing at least
       three aqueous solutions containing a known amount of each of
       the four trihalomethanes and the internal standard, fluoro-
       benzene.  One of the solutions should contain trihalomethane
       standards at concentrations near the limit of detection; in
       the other solutions, trihalomethane concentrations should
       bracket the range of concentrations expected in samples.
       The internal standard concentration must be constant in all
       calibration solutions.
8.3.3  Because the internal standard will be spiked into all
       samples by adding 10 yL of the internal standard spiking
       solution, this technique must also be used to add the
       internal standard to calibration solutions.  The internal
       standard spiking solution is added to the syringe containing
       5 ml of calibration solution immediately before the syringe
       is attached to the purging device.
3.3.4  Trihalomethane measurements are calibrated by calculating
       the mass spectrometer response to each compound relative to
       fluorobenzene, the internal standard.  The response factor
       (RF) is calculated with the equation,

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                           RF =  V QS  .
                                 V "x
                where   A  =   integrated abundance of the selected ion for
                         A
                               the trihalomethane standard;
                        A  =   integrated abundance of the selected ion for
                               the internal standard;
                        Q  =   quantity of internal standard; and
                        Q  =   quantity of trihalomethane standard.
                         ^
                RF is a unitless number; units used to express quantities of
                trihalomethane and internal standard must be equivalent.
         8.3.5  For each trihalomethane, the response factor should be
                independent of trihalomethane quantity for the working range
                of the calibration.  Each day, one or more standards must be
                analyzed to verify that response factors have not changed.
                When changes occur (> 10% relative standard deviation), new
                standard solutions must be prepared and analyzed to deter-
                mine new response factors.
9.  Sample Analysis
    9.1  Analysis procedures
         9.1.1  Initial conditions — Adjust the helium purge gas flow rate
                to 40 ± 3 mL/min.  Attach the sorbent trap to the purging
                device, and set the device to the purge mode.  Open the
                syringe valve located on the sample introduction needle of
                the purging chamber.
         9.1.2  Sample introduction and purging — Remove the plunger from a
                5-mL syringe and attach a closed syringe valve.  Open the

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       sample or standard bottle, which has been allowed to come to
       ambient temperature, and 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 to
       5.0 ml.  (Because this process of taking an aliquot impairs
       the integrity of the remaining sample, a second syringe
       should be filled at the same time, in case a second analysis
       is required.)  Add 10.0 uL of the spiking solution (Section
       5.9) of fluorobenzene in methanol through the syringe valve
       and close the valve.  Attach the syringe and its valve
       assembly to the syringe valve on the purging device.  Open
       the syringe valves and slowly inject the sample into the
       purging chamber.  Close both valves and purge the sample for
       11.0 ± 0.1 min at ambient temperature.
9.1.3  Desorption and data acquisition — At the conclusion of
       purging, attach the sorbent trap to the GC, adjust the
       purging device to the desorb mode, and initiate the GC
       temperature programming (Section 5.10.1), trap heating,
       (Section 5.2) and MS data acquisition (Section 6).  Trapped
       sample components are transferred into the GC column by
       heating the trap to 180°C rapidly (within 4 min) while it
       is backflushed with helium flowing at 20 to 60 mL/min.  (If
       the trap cannot be heated rapidly, the GC column may be used
       as a secondary trap by cooling the column to < 30°C during
       desorption.)

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     9.1.4  Sample chamber rinsing — During desorption empty the
            purging chamber with the sample introduction syringe, and
            rinse the chamber with two 5-mL portions of reagent water.
     9.1.5  Trap reconditioning — After desorfaing the sample for 4 min,
            reset the purging device to the purge mode.  After 15 s,
            close the syringe valve on the purging device to begin gas
            flow through the trap.  After approximately 7 min, turn off
            the trap heater and open the syringe valve to stop gas flow
            through the trap.  When cool, the trap is ready for the next
            sample.
     9.1.6  Termination of data acquisition — When sample components
            have eluted from the GC, terminate MS data acquisition and
            store data files on the data system storage device.  Use
            appropriate data output software to display selected ion
            abundance profiles.  If any ion abundance exceeds the system
            working range, dilute the sample aliquot in the second
            syringe with reagent water and analyze the diluted aliquot.
9.2  Identification criteria
     9.2.1  The GC retention time of the sample component trihalomethane
            must be within £ s of the time observed for that same
            compound when the standard solution was anaTyzed.  The value
            of Jt is calculated with the equation:
                    t =VRT    ,
            where RT = observed retention time (in seconds) of the
            compound when standard solution was analyzed.
     9.2.2  Relative abundances of naturally occurring isotopes must

-------
            agree with theoretical values within ± 10%  (Table 3).
     Table 3.   Relative Abundance Criteria for Trihalomethane Ions
Compound
CHC13
CHCl2Br
CHC1 Br2
CHBr3
Selected Ions
33
83
127
171
&
&
&
&
85
85
129
173
m/z
m/z
m/z
m/z
Abundance
85
85
127
171
= 58
= 58
* 69
= 46
to
to
to
to
Criteria
72%
72%
85%
56%
of
of
of
of
m/e
m/e
m/e
m/e
83
83
129
173
9.3  Concentration calculations
     9.3.1  With either the internal or external standard technique,
            concentrations are calculated with the equation:
                  Cx
                         AS .  RF
            where C  =   analyte concentration in micrograms per liter;
                   ^
                  AX =   integrated ion abundance of the primary charac-
                         teristic ion of the sample analyte;
                  AS =   integrated ion abundance of the primary charac-
                         teristic ion of the standard (either internal
                         or external), in units consistent with those
                         used for the analyte ion abundance;
                  RF   = response -factor (With an external standard,
                         RF = 1, because the standard is the same
                         compound as the measured analyte.);
                  Q  =   quantity of internal standard added or external
                         standard analyzed, in micrograms; and
                  V    = purged sample volume in liters.
     9,3.2  The concentration of total trihalomethanes is the sum of

-------
                concentrations of the four individual trihalomethanes.
10.  Quality Control
    10.1  Minimum quality control  requirements consist of initial demonstra-
         tion of laboratory analytical capability (efficiency, accuracy and
         precision procedures, Sections 10.2.7-10.2.9), analysis of labora-
         tory control  standards as a continuing performance check, quarterly
         analysis of a quality control check sample (Section 10.2.11), and
         maintenance of performance records to define the quality of gene-
         rated data.
    10.2  Quality control  analyses
         10.2.1  Field blanks — A field blank must be analyzed along with
                each sample set.   If a field blank contains trihalomethanes
                at concentrations above the method detection limits, a
                method blank must be analyzed.  If trihalomethanes are not
                detected in the method blank but are detected in the field
                blank, sampling or storage procedures have not prevented
                sample contamination, and the sample set must be discarded.
         10.2.2  Method blanks —  A method blank is a 5-mL portion of reagent
                water placed in the purging apparatus and analyzed as if it
                were a drinking water sample.  A reagent water blank must be
                analyzed each day to demonstrate acceptable levels of inter-
                ferences  and contaminants in the analytical system.  No
                sample is to be analyzed until no trihalomethanes are
                detected  in method blanks at concentrations above method
                detection limits.
         10.2.3  Laboratory duplicates — To determine precision associated

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       with laboratory techniques, analyze two aliquots (Section
       9.1.2) of at least 5% of the samples in which trihalo-
       methanes were observed at concentrations above method
       detection limits.  Calculate percent deviation (D) of
       duplicate analyses using the formula:
             D  =  —^—  .  100
                     C
       where  R = range of concentrations observed, and
              C~ = mean concentration observed.
       If D is greater than 30%, precision is inadequate, and
       laboratory techniques must be improved.
10.2.4 Field duplicates — At least 10% of samples should be
       analyzed in duplicate to determine precision limitations
       imposed by sampling, transport and storage techniques.
10.2.5 MS performance standard — Near the beginning of each 8 h
       work period day that trihalomethanes are to be measured, the
       mass spectrum produced by £ 50 ng of £-bromofluorobenzene
       (BFB) must be measured to ensure that it meets performance
       criteria (Table 1).  BFB may be introduced into the MS
       either by syringe injection or through the purge and trap
       system.  The entire mass spectrum (mass range 35 to  260
       amu) should be obtained at an MS scan rate that produces at
       least five spectra for the BFB GC peak but does not exceed
       7 s per spectrum.  If the BFB spectrum is unacceptable,
       GC/MS operating parameters must be adjusted until an accept-
       able spectrum is produced before samples are analyzed.

-------
10.2.5 Laboratory control standard — To demonstrate ability to
       produce data within acceptable accuracy and precision
       limits, a laboratory control standard must be analyzed
       during each 8 h work period.  A laboratory control standard
       is reagent water spiked with known amounts of trihalo-
       methanes.
       10.2.S.I  For each trihalomethane to be measured, select a
                 concentration representative of its occurrence in
                 drinking water samples.  From stock standard
                 solutions, prepare a laboratory control standard
                 concentrate in methanol.  This solution should
                 contain all four trihalomethanes at concentrations
                 500 times those selected as representative
                 concentrations.  (Laboratory control standard
                 concentrates, which are also called QC check
                 sample concentrates, are available from the U. S.
                 Environmental Protection Agency, Environmental
                 Monitoring and Support Laboratory, Quality
                 Assurance Branch, Cincinnati, Ohio 45268.)
       10.2.6.2  Add 10 uL of the laboratory control standard
                 concentrate to a 5-mL aliquot of reagent water,
                 and analyze according to procedures in Section 9.
10.2.7 Method efficiency - For each trihalomethane, method
       efficiency is calculated by comparing the detector response
       when the compound is introduced by syringe injection with

-------
the detector response when the same amount is introduced by
purging, trapping, and desorption.  Because of the calibra-
tion technique used in this method, high efficiency is not
required for acceptable precision and accuracy but is
required for acceptable sensitivity.  Low method efficiency
will cause unacceptably high detection limits.  Method
efficiency for each trihalomethane must be recalculated when
the analytical system undergoes major modification, such as
replacement of trap packing.
10.2.7.1  At least five laboratory control standards are
          analyzed with the purge, trap, desorption and
          GC/MS SIM detection procedures.  Interspersed
          among these five or more analyses, three or more
          aliquots of the secondary dilution standard
          solution (Section 5.8) are injected directly into
          the GC to introduce each trihalomethane in an
          amount equivalent to that introduced by purge and
          trap procedures.  The recommended amount is 5 ng
          of each trihalomethane.  The same MS data acquisi-
          tion parameters are used for SIM of injected
          trihalomethanes as are used for those introduced
          with the purge and trap procedures.
10.2.7.2  Calculate the method efficiency (E) for each
          trihalomethane in each aliquot of the laboratory
          control standard with the equation:

-------
                                  100
                 where A  =   ion abundance of compound introduced
                              with purge and trap techniques, and
                       A.. =   ion abundance produced by an equal
                              amount of the same compound when
                              injected.
                 For this calculation, use data obtained from an
                 injection either closely preceding or following
                 the purge and trap analysis from which data are
                 used.
       10.2.7.3  Calculate the mean method efficiency for each
                 compound and the mean of the mean method efficien-
                 cies for all four trihalomethanes.  Acceptable
                 detection limits can be achieved if the mean of
                 the mean method efficiencies is j> 60%; the minimum
                 required effficiency for any individual trihalo-
                 methane is 30 %.
10.2.8 Accuracy — Accuracy can be calculated from the same set of
       data acquired to determine efficiency.  One aliquot of the
       laboratory control standard analyzed with purge and trap
       techniques is selected to be treated as a standard with
       known component concentrations, and the other aliquots are
       treated as samples.  (Data obtained from direct injections
       are not used in accuracy calculations.)  Data acquired for
       the aliquot chosen to be the standard may be treated as an

-------
external standard or may be used to calculate response
factors relative to fluorobenzene used as an internal
standard.
10.2.8.1  When using the external standard procedure, data
          obtained from the solution selected as a standard
          are assumed to be true values, and accuracy is the
          ion abundance found in the sample solution
          expressed as a percentage (P) of the ion abundance
          found in the external standard solution:
                         A..
                         As
                                . 100
          where A  =   abundance of ion used to monitor
                 A
                       trihalomethane treated as an unknown,
                       and
                A  =   abundance of ion used to monitor the
                       same trihalomethane treated as an
                       external standard.
10.2.8.2  When using the internal standard procedure,
          fluorobenzene in the solution of trihalomethane
          standards is selected as an internal standard, and
          response factors are calculated (Section 8.3.4)
          for each trihalomethane relative to fluorobenzene.
          With these response factors, SIM data acquired for
          the other solutions analyzed are used to calculate
          accuracy:

-------
                            Ax  .   100
                 where A  =   abundance of ion used to monitor a
                        /\
                              trihalomethane in the laboratoary
                              control standard solution,
                      A  = abundance of ion used to monitor
                         fluorobenzene in the same solution, and
                      RF * response factor of the particular
                           trihalomethane relative to fluorobenzene.
       10.2.8.3  For each of the four trihalomethanes, the mean
                 accuracy is calculated; the mean of these four
                 means is the method accuracy and must be in the
                 range of 90 to 110%.
10.2.9 Precision
       10.2.9.1  For each trihalomethane, method precision is
                 expressed as the standard deviation(s) of the
                 percentages of the true values (?) obtained in the
                 accuracy calculations:
                                                  'J2
                                       n (n-1)
                 where n = number of measurements for each trihalo-
                 methane.
       10.2.9.2  The dispersion of the set of means for each
                 trihalomethane is expressed as the relative
                 standard deviation (RSD):

-------
                              RSD =  _s_  .  100
                                      P
                          where s - standard deviation, and
                                P - mean percentage of true value.
                10.2.9.3  Adequate precision is obtained when the relative
                          standard deviation is _< 15%.
         10.2.10   Monitoring the surrogate compound ^- If the external
                   standard technique is used, f1uorobenzene is a surrogate
                   compound used to monitor method performance.  Each day
                   method efficiency is determined for fluorobenzene by
                   analyzing a laboratory control standard and comparing
                   results obtained with purge and trap procedures to those
                   obtained with direct injection.  If for any sample,
                   method efficiency (Section 10.2.7) and accuracy (Section
                   10.2.8) values obtained for fluorobenzene fall below
                   acceptable values, trihalomethane values obtained for
                   that sample should not be reported.
         10.2.11   At least quarterly, a quality control check sample
                   obtained from the U.S. Environmental Protection Agency,
                   Environmental Monitoring and Support Laboratory, Quality
                   Assurance Branch, Cincinnati, must be analyzed.  If
                   measured trihalomethane concentrations are not within
                   ±20% of true values, the entire analytical procedure must
                   be checked to locate and correct the problem source.
11.  Method Performance
    11.1  The method detection limit is defined  as the minimum
         concentration of analyte that can be measured and reported with 99%

-------
confidence that the value is above zero.  Method detection limits
and single laboratory accuracy and precision data (Table 4) were
obtained from seven replicate analyses (using the external standard
technique) of reagent water spiked with trihalomethanes.  For the
four trihalomethanes, individual mean method accuracies were
calculated, and a mean method accuracy for all four was calculated
to be 102.4%.

-------
REFERENCES

1.  "National Interim Primary Drinking Water Regulations; Control of
    Trihalomethanes in Drinking Water," Federal Register, Volume 44, No.
    231, p. 68624 (November 29, 1979).

2.  "Appendix C.  Analysis of Trihalomethanes in Drinking Water," Federal
    Register, Volume 44, No. 231, p. 68672-68690 (November 29, 1979).

3.  "Definition and Procedure for the Determination of the Method Detection
    Limit," U. S. Environmental Protection Agency, Office of Research and
    Development, Environmental Monitoring and Support Laboratory,
    Cincinnati, OH, July 1981, Revision 1.12.

4.  "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, Aug. 1977.

5.  "OSHA Safety and Health Standards, General Industry," (29CFR1910),
    Occupational Safety and Health Administration, OSHA 2206, (Revised,
    January 1976).

6.  "Safety in Academic Chemistry Laboratories," American Chemical Society
    Publication, Committee on Chemical Safety, 3rd Edition, 1979.

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-------
100-
 80-
 60-
 40-
 20-
         li
        50
   100
     Figure 4 Mass Spectrum of Chloroform
  100-
   80-
  60-
  20
      li__ L '-:!
                          il
        30
100
150
     Figure 5 Mass Spectrum of Bromodichioromethane

-------
   100-r
       |
    30-
    20-i
                    100
                           ISO
   200
     Figure 6 Mass Spectrum of Chlorodibromomethane
.COT
bu-

40 -j

20-i
I .!«.
                                                  1!
                100
                       150
200
250
      Figure 7 Mass Spectrum of Bromoform

-------
           50
100
150
Figure 8 Selected Ion Current Profile of Trihalomethanes
         and Internal Standard

-------
U.S. r         t^ Protection Agency
               60604

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-------