United States
               Environmental Protection
               Agency
               Research and Development
  Atmospheric Research and
  Exposure Assessment Laboratory
  Research Triangle Park, NC 27711

  EPA/600/SR-92/050 April 1992
EPA       Project  Summary

                Evaluation of the  Fourier
                Transform  Infrared Spectrometer
                for  Particle-Associated
                Ammonium  Sulfate
                Determination
               Kenneth John Krost
                A commercial Fourier transform In-
               frared (FTIR) spectrometer, modified for
               automated analysis of particle-associ-
               ated sulfate, was used to obtain trans-
               mission spectra of samples of partlcu-
               late matter collected from the ambient
               air onto Teflon filters. An evaluation of
               this Instrumentation was undertaken to
               determine its applicability for measur-
               ing sulfate and the correlation of re-
               sults with those of ion chromatogra-
               phy and X-ray fluorescence. Particle
               samples from six geographical areas
               were evaluated in this study. Results
               from different filter sets, for which Indi-
               vidual filter blanks were used, show
               values of the coefficient of determina-
               tion of 0.90 or higher using any  two
               analytical techniques, with one notable
               exception. This exception Is due to dis-
               placement of sulfate absorption from
               the wavelength Interval used for analy-
               sis, and it apparently indicates the ef-
               fect  of  co-collected  compounds in
               chemically shifting the spectra. For the
               best analytical results, the spectrum of
               Individual Teflon filters should be used
               for subtracting the contribution of Te-
               flon absorption. Orientation of the filter
               in the FTIR system must be maintained
              to avoid errors In determining the zero
               loading values of sulfate. The detec-
              tion limit of 1.2 ng/cm2was determined
              by establishing the  uncertainty  (3o)
              value for replicate measurements of
              blank filters. This corresponds to  the
              sample  loading  obtained by sampling
              an ambient air concentration of approxi-
              mately 0.4 jig/m3 of ammonium sulfate
 collected over 24 hours as the fine par-
 ticulate fraction in a dlchotomous sam-
 pler.

   This Project Summary was developed
 by EPA's Atmospheric Research and
 Exposure Assessment Laboratory, Re-
 search Triangle Park, NC, to announce
 key findings of the research project
 that Is fullly documented In a separate
 report of the same title (see Project
 Report ordering Information at back).


 Introduction
  There are  several techniques available
 to measure or estimate sulfate concentra-
 tions of the  various particulate species
 collected on air filters. Among these tech-
 niques  are Ion chromatography (1C), X-
 ray fluorescence (XRF) and Fourier trans-
 form infrared (FTIR) transmission  spec-
 trpmetry. Of  these three the FTIR tech-
 nique is the only one that can provide an
 unambiguous, nondestructive analysis of
 sulfate. For this reason and because other
 functional groups can also be measured,
 EPA has a continuing interest in this tech-
 nique and  has pursued the development
 and evaluation of instrumentation and pro-
 cedures appropriate for  optimization. In
 particular, a: commercially available FTIR
 spectrometer  was previously modified and
 demonstrated for the automated analysis
 of particle-associated sulfate by transmis-
 sion spectrometry. In the current report,
 sample analysis results for sulfate by the
 FTIR technique are compared with those
 using XRF and 1C analysis for samples
obtained at six different field sites.
                                                             Printed on Recycled Paper

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Procedure
  A commercial (FTIR)  spectrometer,
modified with the addition of an automatic
sample-changing  compartment, was ap-
plied to the measurement of sulfate in the
form of ammonium sulfate. The sample
compartment directly accepts  the sample
carousel from  a Sierra/Anderson,  Inc.
Model 245* dtehotomous air sampler. To
perform an analysis, the  spectrum of  a
blank Teflon filter is recorded  and subse-
quently subtracted from the spectrum ob-
tained after loading the filter with particu-
lato matter. This results in a spectrum due
solely to absorption by substances in the
partfculate matter. Software was written to
analyze ambient air samples by automati-
cally  providing  an absorbance spectrum
with optimal background subtraction of the
blank Teflon filter contribution  and inte-
gration of the absorbance peak over the
595- to 635-cnv1  spectral  range used for
sulfate detection and quantitation.  The
sample filters were  37-mm  diameter,  2
u.m pore size PTFE  Teflon (Gelman Sci-
ences, Incorporated, Ann  Arbor,  Ml),
mounted on a polypropylene ring holder.

Results and Discussion
   The inherent detection sensitivity for the
current instrumentation and procedure was
determined to be 1.2 ng/cm2of particle -
associated ammonium sulfate. The error
in ammonium sulfate measurement result-
ing from a rotation of  blank filters by 90°
averaged  0.7 ng/cm2for  six  filters while
slight vertical displacement of the filters
had negligible effect.
   Sets of 10-11 particulate  (<2.5-u.m)
 samples wore  collected from five sites in
 fivo states in the eastern U.S.A. and ana-
 lyzed for sulfate concentrations by FTIR,
 XRF, and IC. For the most part, good
 agreement among the three systems was
 achieved. For four of  the state sites, the
 linear least squares fitting (y=mx+b)  of
 data between FTIR-determined values (Y)
 and IC-determined values (X) gave slopes
 at ±95% uncertainty values of 1.04 ± 0.08
 (NY), 1.08 ± 0.04 (VA), 0.77 ± 0.13 (TN)
 and 0.93 ± 0.07 (KY),  while the coefficient
 of determination exceeded 0.90 in each
 case and averaged  0.97. Figure  1 shows
 a typical comparison using samples taken
 at a NY site. Figure 2 shows the equiva-
 lency obtained for four of the five sites
 when the values from FTIR measurements
were plotted against 1C values. As seen
the agreement is  quite good. The one
noticeable exception to good agreement
existed for the samples collected at a site
in Massachusetts for which the slope val-
ues were 0.19 ± 0.23 with a coefficient of
determination  of 0.18.  In this set FTIR
results were often significantly different
from those obtained from the IC and XRF
analyses. The FTIR spectra for this set of
filters were  closely  examined.  In  every
instance where a  major discrepancy ex-
isted in the reported sulfate values, a dis-
placed and skewed sulfate absorption band
was evident. Similar spectral effects have
been produced in the laboratory when high
humidity samples were collected, exposed
to water vapor and analyzed. There was a
noticeable loss of peak symmetry and lack
of absorption  at 870 cm'1. The presence
of bisulfate in the sample can also cause
a change in the spectral features being
used for sulfate  determination; however
bisulfate was  not present in the samples
from Massachusetts. Intercept values other
than the Massachusetts filter set for the
FTIR/IC comparative studies were all less
than 6.50 u.g/cm2, and averaged -2.02 u.g/
cm2.


Conclusions
   FTIR transmission  spectrometry was
shown to be a viable technique for mea-
surement of sulfate in  the form of ammo-
 nium sulfate, such  as that occurring  in c
collected  ambient air  particulate matter.
The detection limit of 1.2 ug/cm2 is equiva-
 lent to the  loading obtained by sampling
 an ambient air concentration of approxi-
 mately 0.4,u,g/m3 of  ammonium  sulfate
 collected over 24 hours as the fine par-
 ticulate fraction in a dichotomous sampler.
 This detection limit is low enough to allow
 measurement of background  ammonium
 sulfate concentrations (these are routinely
 above 3  u.g/m3).  Intercomparison of  the
 FTIR method with X-ray fluorescence and
 ion chromatography show values of  the
 coefficient of variations of 0.90 or better
 using any two analytical techniques, with
 one exception. This exception is  due to
 shifting of absorption features caused by
 co-collected compounds or to the pres-
 ence of ammonium bisulfate. In either case
 this problem  is easily  identified by exami-
 nation of the individual spectra.
                Intercept =7.38 ± 1.44 -
                Slope = 0.85±0.05   _
                Pf = 0.985
!
       0 5 10 15 20 25 30 35 40 45 50
                Intercept = -2.93 ± 2.23 -
                Slope » 1.22 ±0.10
                Ff = 0.985
     -5 0 5 10 15 20 25 30 35 40 45 50

                XRF-pg/crr?
50
45
40
35
30
25
20
15
10
 5
 0
                Intercept = -1.37 ± 2.05-
                 Slope= 1.04 ±0.08   _
                 P? = 0.985
      -505 10 15 20 25 30 35 40 45 50

                 IC—^g/crrf
Figure 1.  New York intercomparative
          analysis of particulate sulfate.
          Calculated for± two standard
          errors.
 ' Mffttbn of trtcSa names or common:!*! products does not
 cootltut* •odoreoment or rocommondalkxi for use.

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                    Kentucky

              O   New York

                    Tennessee

                    Virginia
                                                                                 Intercept = 0.12 ± 1.05
                                                                                 Slope = 0.91 ± 0.05
                                                                                 Ff = 0.962
                                                                                 Calculated for ± Two Standard Errors
Figure 2.  Results from sulfate analysis for samples from composite of Kentucky, New York, Tennessee, and Virginia.
                                                                               •fru.S. GOVERNMENT PRINTING OFFICE: 1992 - 648-080/40234

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 The EPA author Kenneth J. Krost (also the EPA Project Officer, see below) is
     with tho Atmospheric Research and Exposure Assessment Laboratory,
     Triangle Park, NC 27711
 The complete report, entitled "Evaluation of the Fourier Transform Infrared
     Spectrometer for Particle-Associated Ammonium Sulfate Determination,"
     (Order No. PB92-160084/AS; Cost: $19.00,  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:
        Atmospheric Research and Exposure Assessment Laboratory
        U.S. Environmental Protection Agency
        Research Triangle Park, NC 27711
United States
Environmental Protection
Agency
Center for Environmental
Research Information
Cincinnati, OH 45268
      BULK RATE
POSTAGE & FEES PAID
         EPA
   PERMIT No. G-35
Official Business
Penalty for Private Use $300
EPA/600/SR-92/050

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