United States
                     Environmental Protection
                     Agency
Environmental Monitoring Systems
Laboratory
Research Triangle Park NC 27711
                     Research and Development
EPA/600/S4-85/062  Jan. 1986
ŁEPA         Project Summary
                    Direct Calibration of  GC/MS
                    Systems  Using  SRM
                    Gas  Cylinders

                    G. D. Byrd, K. L. Richie, L. T. Sniegoski, and E. White V
                      A cryogenic trapping system has been
                     developed for use in calibrating GC/MS
                     systems  for the analysis of volatile
                     organic compounds. This system pro-
                     vides for direct Standard Reference
                     Material  (SRM) traceability  on data
                     generated on gaseous samples. The
                     cryogenic trap is a coil of stainless steel
                     tubing immersed in a cryogen to trap
                     and preconcentrate organic  species
                     present in a gaseous sample. The trap
                     also contains a heated injection port for
                     the addition of isotopically labeled com-
                     pounds for  use in isotope dilution
                     measurements.  The first part of this
                     research is concerned with the develop-
                     ment of isotope dilution mass spectrom-
                     etry (IDMS) as an independent method
                     for the quantification of analytes in
                     gaseous samples to be used as stand-
                     ards.  Results are presented  for the
                     determination of bromobenzene in nitro-
                     gen at nominal concentrations of 1 and
                     25 ppb. In the second part of the re-
                     search, a  calibration curve method was
                     developed for using these standards in
                     auditing the  performance of GC/MS
                     systems.  This method is demonstrated
                     on multicomponent aromatic  mixtures
                     in the 10 to 200 ppb concentration
                     range. The system using the calibration
                     curve  method  was evaluated at an
                     independent  laboratory and compared
                     with a static  dilution bottle calibration
                     curve method.
                      This Project Summary was developed
                     by  EPA's Environmental Monitoring
                     Systems Laboratory, Research Triangle
                     Park,  NC, to announce key findings of
                     the research project that is fully docu-
                     mented in a separate report of the same
                     title (see Project Report ordering infor-
                     mation at back).
Summary
  The goal of this project was to develop a
trapping system that can  be  used  to
introduce volatile  organic  compounds
(VOCs) at low concentrations (ppb) from a
gas cylinder into a combined gas chromato-
graph/mass spectrometer (GC/MS) in-
strument. A trap has been  constructed
that condenses the gaseous  sample from
the cylinder using a small coil immersed
in a dry ice-ethanol bath. The coil is then
electrically heated to revolatize the sam-
ple. The gas is introduced into the GC/MS
with a syringe needle  that is silver
soldered to the coil tubing  so that the
effluent can be injected directly into the
instrument. A heated injection port also
allows  introduction of liquid solutions
into the GC/MS. The performance of the
trap was evaluated  using isotope dilution
mass spectrometer  (IDMS) measure-
ments on samples that had been well
characterized by  other  methods. Re-
sponse factor determinations were made
using isotopically labeled analytes.
  A GC/MS method based on establish-
ing a calibration curve was developed
that permits a direct comparison of the
concentrations of trace components from
two gas sources. This provided a means
of linking data from different laboratories
to a common SRM. The  cryogenic trap
was used for this method, since it can be
employed with any GC system that con-
tains a septum inlet. The principle of the
calibration curve is to establish a plot of
response versus amount for a particular
analyte. From a measured  volume of a
sample with an unknown concentration
of the  analyte and  its  response, the
concentration can  be calculated. SRV
gas cylinders containing the analytes of
interest  are well  suited as calibrant

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  samples because of their certified values
  for analytes. In order for this method to
  work properly, a known relationship, pref-
  erably linear, must be established over
  the desired concentration range. This, in
  turn, requires that reproducible amounts
  of the sample be trapped and delivered to
  the GC/MS for analysis. The procedure
  was validated by measurements at an
  independent laboratory on two cylinders
  containing "unknown" concentrations of
  benzene, chlorobenzene, and bromoben-
  zene. A cylinder containing known con-
  centrations of the same compounds was
  used for calibration. All of the cylinders
  had been previously prepared and ana-
  lyzed at the National Bureau of Standards
  (NBS)  using the trapping system.  The
  combined average values for  all the
  measurements made on these cylinders
  at  both  laboratories  were within  two
  standard deviations of the preoared value
  for all  analytes except bromobenzene in
  one cylinder. This value was slightly more
  than three standard deviations outside of
  the prepared concentration.
   The  components of  the gas cylinders
  were also analyzed by GC/MS  using a
  calibration curve generated by injections
  of pure gaseous compounds from static
  dilution flasks. This was the usual method
  of calibration of the independent labor-
  atory and afforded a way to compare the
  results of the two ways to calibrate the
  analytical system. The differences in the
  relative standard deviations for the two
  sets of measurements were not signif-
  icant, indicating similar precision for both
  laboratories. The average percent differ-
  ence between  delivered and measured
  amounts-for the analytes was biased on
  all cases with 11% to 35% more of the
  compounds detected than was delivered.
        G. D. Bryd, K. L. Richie. L T. Sniegoski. andE. White are with the National Bureau
          of Standards, Gaithersburg, MD 20899.
        Howard Crist is the EPA Project Officer (see below).
        The complete report, entitled "Direct Calibration of GC/MS Systems Using SRM
          Gas Cylinders."(Order No. PB86-110 715/AS; Cost: $9.95. subject to change)
          will be available only from:
                National Technical Information Service
                5285 Port Royal Road
                Springfield, VA 22161
                Telephone: 703-487-4650
        The EPA Project Officer can be contacted at:
                Environmental Monitoring Systems Laboratory
                U.S. Environmental Protection Agency
                Research Triangle Park, NC 27711
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Official Business
Penalty for Private Use $300

EPA/600/S4-85/062
           0000329   PS
                           PROTECTION

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