v-xEPA
                                 United States
                                 Environmental Protection
                                 Agency
                                 Industrial Environmental Research
                                 Laboratory
                                 Research Triangle Park NC 27711
                                 Research and Development
                                 EPA-600/S7-82-033  August 1982
Project  Summary
                                 Interpretation  of Low
                                 Resolution  Mass  Spectra  for
                                 Level  1  Analysis of
                                 Environmental  Mixtures
                                 James L. Stauffer
                                  This report is a set of guidelines for
                                 interpreting the low resolution mass
                                 spectra (LRMS) of complex chemical
                                 mixtures, within the context of EPA's
                                 Level 1  Environmental Assessment
                                 Program1.  It discusses principles
                                 underlying direct mass spectrometric
                                 analysis of complex mixtures, tech-
                                 niques for optimizing the  analyses,
                                 and interpreting and evaluating the
                                 results.  A  chapter presents some
                                 interpretive aids for LRMS analysis of
                                 environmental  mixtures. The guide-
                                 lines are illustrated by a step-by-step
                                 detailed analysis of the mass spectra
                                 of four representative samples.  The
                                 final  chapter gives  direction for
                                 reporting the results in the EPA Level
                                 1 LRMS report format.
                                  LRMS plays an important  role in
                                 determining the chemical  composi-
                                 tion of environmental mixtures.  The
                                 other components of the Level  1
                                 organic analysis scheme,  liquid
                                 chromatography (LC) fractionation
                                 and infrared analysis (IR),  also con-
                                 tribute significantly to the overall
                                 analysis. The LC and  IR procedures
                                 are described elsewhere1. This report
                                 is limited to a  detailed discussion of
                                 the LRMS  component of the Level 1
                                 scheme.
                                  This Project  Summary was devel-
                                 oped by EPA's Industrial Environ-
                                 mental Research Laboratory, Research
                                 Triangle Park, NC, to announce key
                                 findings of the research project that is
                                 fully documented in a separate report
                                 of the same title (see Project Report
                                 ordering information at back).


                                 Summary
                                   Requirements for mass spectrometric
                                 analysis of the environmental samples
                                 obtained in the EPA Level 1 program are
                                 for identification of chemical class, and
                                 order of magnitude quantitation. These
                                 standards are met through the com-
                                 bination of complementary analysis
                                 methods: (1) a liquid chromatographic
                                 (LC) fractionation of the environmental
                                 mixture,  followed by (2)  mass  spec-
                                 trometric and infrared spectrometric
                                 (IR) analysis of each LC fraction. The LC
                                 fractionation  narrows the range of
                                 chemical classes that can be present in
                                 any of the individual fractions to a level
                                 which is  manageable  by  LRMS; the
                                 mass spectrometric analysis of each LC
                                 fraction establishes the molecular
                                 weight range  of the fraction, and the
                                 chemical classes present.  To eliminate
                                 the chemical discrimination effects that
                                 are likely to be encountered when gas
                                 chromatography  is used for LRMS
                                 sample introduction, the samples in this
                                 program are introduced in the LRMS via
                                 the direct probe. This provides the most
                                 representative aliquot of the sample to
                                 the  LRMS source, but  also yields
                                 spectra that, typically, contain the
                                 superimposed spectra of several chem-
                                 ical components. A batch  inlet is used

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for  samples that are too volatile for
successful  introduction via the probe
inlet.
  Complementary sources of informa-
tion available in the EPA Level  1
program that may be useful in interpret-
ing the mass spectra  include the IR
spectra that are obtained on all of the LC
fractions. These  support (confirm) the
assignments obtained via LRMS,  and
signal  the presence of  chemical func-
tional groups that may not be recogniz-
able solely on the  basis  of the mass
spectra.
  The LC f ractionation scheme provides
an  initial polarity separation of  the
mixture into seven fractions that range
from  non-polar  (fraction 1) to most
polar  (fraction 7). Table  1 shows the
types of separations that are obtained.
  The  analysis  results  obtained by
LRMS  are reported primarily as chemi-
cal classes  and molecular weight
ranges of those classes, with subcate-
gory or specific compound or composi-
tion designation whenever possible.
The categories defined for reporting
LRMS  data are shown in Table 2.


Direct Analysis of  Mixtures
by LRMS

  The detail that may be obtained from
the mass spectrum of multi-component
mixtures depends both on the complexity
of the spectrum itself,  and on  the
amount of supplemental information
that is available. The precision of the
identification that may be  obtained will
vary accordingly, ranging  from specific
compound or composition assignments
for  all  of the  spectrum, to simply an
indication of the  chemical classes that
are present. The task confronting the
analyst of the mass spectra of multi-
component mixtures is  to discover the
correct combination  of individual
spectra that will adequately account for
the experimentally observed spectrum.
The additive  nature of superimposed
mass  spectra ensures  that this is
possible,  and the multi-peak nature of
electron impact mass spectra makes it
practical in most cases. The combina-
tion of the two aspects  ensures that, if
the observed  mass spectrum  is fully
accounted  for by the combined indi-
vidual  assignments,  then those assign-
ments are an accurate indication of the
chemical class makeup  of the sample.
  Two principal  techniques  provide
clues  to  the analyst for tentative
individual chemical class or compound
 Table 1.    Representative Checmical class Distribution by LC Fraction*

LC Fraction
 1. aliphatic hydrocar-
bons, sulfur
2.  aromatic hydrocar-
bons

3.  PAH species
4.  carbazoles
5.
6.
7.
                           halogenated aliphatics
                           halogenated aromatics
aromatic hydrocarbons


nitroaromatics
       carbolic acids
       phenols
       sulfonic acids
heterocyclic sulfur, PAH
                         heterocyclic N
                         heterocyclic O
                         ketones
                         esters
*This list represents the type of partitioning that may be expected to occur, but it
 should not be taken as definitive.
   Many conditions could cause compound class distribution to vary from that shown
 here. The illustrated overlap between fractions similarly is representative, rather
 than definitive.
assignments. The first and  most im-
portant Off  these is the fractional
distillation'of the sample that occurs as
the direct insertion probe  is slowly
taken through its complete temperature
cycle from cool to hot. The second is the
use of both high (70 eV) and low (10 - 2O
eV) electron  impacts or chemical
ionization  modes, at or near  the same
probe temperature. The thermal disti Na-
tion  provides  a separation  into suc-
cessive  molecular weight ranges, and
the change of ionization mode differen-
tiates between  parent and  fragment
ions. All of the data, taken in combina-
tion, provide enough information for
overall spectral interpretation.
  Tentative assignments made on the
basis of the  above information are
confirmed or modified in the confirma-
tion phase of the analysis. In the first
phase of confirmation, standard spectra
obtained either from the literature2"3 or
from reference compounds are used to
evaluate how completely  the experi-
mentally observed mass spectrum is
accounted for by the combined tentative
individual  assignments. The second
phase is to make a similar comparison
against  the data obtained  in the IR
analysis, to see  if all fractional groups
and IR  spectral features have been
recognized and  accounted  for  in the
mass spectral analysis. An accurate set
of assignments will account for  all
              spectral features of both the MS and the
              IR data.
               Several  interpretation  aids can  be
              helpful in analyzing the LRMS data. The
              first of these is a table of mass numbers
              and associated Z values, where the Z
              value is given by the relationship:

                        mW = CnH(2n + Zl
              A Z value  for any ion  in  the spectrum
              can be correlated with a limited range of
              possible chemical classes, and a very
              limited  range of possible  chemical
              compositions. Mass values for PAH
              species  can be correlated to specific
              chemical compositions and numbers of
              rings, although not to specific isomers.
              In most cases, similarily specific chemi-
              cal  composition  assignments can  be
              made to individual mass values for aza-
              arenes,  and  for  oxygen- or  sulfur-
              containing polycyclic species.
                Several  step-by-step  examples of
              analyses are included in the report. The
              samples used for examples are:
               (1) A  synthetic mixture  of polar
                   materials (LC fractions 5, 6, 7).
               (2) A simple PAH mixture (LC fraction
                   3).
               (3) A complex  hydrocarbon mixture
                   (without LC chromatographic
                   separation).
               (4) A  set of potentially confusing
                   spectra, obtained from cigarette
                   tar (LC fractions 3 and 4).

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 Table 2.    Categories for Reporting LRMS Data
Category
  (Subcategory)
    Most probable
     LC fraction*
Category
  (Subcategory}
Most probable
 LC fraction*
Aliphatic hydrocarbons
  (Alkanes)
  (Alkenes)
  (Alkynes)
Halogenated aliphatics
  (Saturated)
  (Unsaturated)

Aromatic hydrocarbons
  (Benzenes}
Halogenated aromatic hydrocarbons
Nitro aromatic hydrocarbons

Fused alternate,  nonalternate hydrocarbons
MW<216 (methyl pyrene)
MW<216

Ethers
  (Halogenated ethers)
Epoxides

Aldehydes
Heterocyclic oxygen compounds
Nitrites
  (Aliphatic)
  (Aromatic)

Alcohols
  (Primary, secondary, tertiary)
  (Glycols)
           1
           1
           1
           1
          1,2
          1,2
          1,2

          2,3
          2,3
          2,3
          4,5

          2.3
          2,3
          2,3

          4
          4
          4

          4
          3.4
          4
          4
          4

          6
          6
          6
Phenols
  (Alkyl, etc.)
  (Halogenated phenols)
  (Nitrophenols)
Esters
  (Phthalates)
Ketones
Amines
  (Primary, secondary, tertiary)
  (Hydrazines, azo compounds)
  (Nitrosoamines)

Heterocyclic nitrogen compounds
  (Indoles, carbazoles)
  (Quinolines, acridines)

Alkyl sulfur compounds
  (Mercaptans)
  (Sulfides. disulfides)
Heterocyclic sulfur compounds
  (Benzothiophenes)

Sulfonic acids, sulfoxides
Amides
Carboxylic acids

Silicones

Phosphates
      6
      6
      6
      6
      6
      6
      6
      6
      6
      6
      6
      4
      6

      6
      6
      6
      7
      6
     6,7

    2,3,4

    5.6.7
  *Possible assignments. Fractions 4-5, 5-6, 6-7 generally overlap to a considerable extent. Also, additional components of a
   particular molecule may cause it to elute in an LC fraction other than that expected. For example, a short-chain ester would
   probably elute in LC Fraction 5 or 6, whereas a long-chain ester would elute in Fraction 3 or 4.
  The several examples are designed to
illustrate:
  (1)  The  establishment of mass
      spectral peak associations.
  (2)  The use of reference spectra for
      identification assignments in a
      complex spectral matrix.
  (3)  The principle of  total spectrum
      accounting.
  (4)  Utilization of the LC fractionation
      scheme  for  interpreting LRMS
      spectra.
  (5)  Chemical class assignments in a
      complex spectral matrix.
  The spectra utilized in the analysis
examples are  then used as reporting
examples to  illustrate the use of the
standard EPA Level 1  Environmental
Assessment Program LRMS report
form.
References

 1. Lentzen, D.E., Wagoner, D.E., Estes,
   E.D., and  Gutknecht,  W.F., "IERL-
   RTP Procedures Manual: Level 1
   Environmental Assessment (2nd
   edition)," EPA-600/7-78-201, NTIS
   PB 293-795.(1978).
 2. "Eight Peak Index of Mass Spectra,"
   4 volumes, 2nd edition, published by
   Mass Spectrometry  Data Centre,
   AWRE, Aldermaston, Reading, RG7
   4PR, United Kingdom, 1974.

 3. Heller, S.R.,  and  Milne, G.W.A.,
   "EPA/NIH Mass Spectral Data
   Base," 5 volumes, U.S. Department
   of Commerce/National  Bureau of
   Standards, NSRDS-NBS 63 (1978).
* U.8.30VEHNMEWTPHIKT1NQOFFICE:HtS-559-017/0787

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       James L. Stauffer is with Arthur D. Little, Inc.. Cambridge, MA 02140.
       Larry D. Johnson is the EPA Project Officer (see below).
       The complete report, entitled "Interpretation of Low Resolution Mass Spectra for
         Level 1 Analysis of Environmental Mixtures, "(Order No. PB 82-232 455; Cost:
         $15.00, 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:
               Industrial Environmental Research Laboratory
               U.S. Environmental Protection Agency
               Research Triangle Park, NC 27711
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Postage and
Fees Paid
Environmental
Protection
Agency
EPA 335
Official Business
Penalty for Private Use $300
           CHICAGO

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