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,Comparisonof Manual and Automated Analysis Methods for :.$hlftir b9Qxfde .+ In Manually Impinged Ambient Air Samples
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JStm Logardon il* and Mark J. Carter Cbhtral #e;tidtIal Laboratory, Environmental Protection Agency, Vc)r
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Data were compared from the analysis of manually imtyinged 24-hr ambient air samples for sulfur dioxide by two commonly used automated methods and the Environment i l Protection Agency reference method. The automated analytical methods, both adaptations of the West-Gaeke pararosanaline method to Technicon AutoAnalyzer systems, yielded results that were not significantly biased from and wete more precise than the reference method.
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Protection Agency (EPA) has proanalytical procedure as the reference hethod.for the determination of sulfur dioxide in manually 'Impinged ambient air samples ( I ) . Many air pollution con8 trol agencies that analyze large numbers of samples find the reference method tedious and slow when compared to Available automated methods and therefore routinely use , the automated analysis techniques. Also, there is no SAROAD (Storage and Retrieval of h r o m e t r i c Data) method code number for data generated mtomated analysis of manually impinged samples so \ ,data have been processed and stored under the refer.*' ehce me!hod code numb@ ( 2 ) .Once in the data bank, data fFom both manual and automated methods are indistin, , guishable and therefore used interchangeably. If biases , exist in the methods used to analyze manually impinged xide, then erroneous conclusions may q from the data. es analytical data from the analysis of ambient air samples by the three paiarosanaline methods in common use. The EPA manual reference method is compared to the West-Gaeke ( 3 )method adapted to a Technicon AutoAnalyzer I system ( 4 ) and to a Technicon AutoAnalyzer I1 system ( 5 ) .The automated methods were modified to use the reference-method absbrbing solution (6).
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1819 West Pershing Road, Chicago, 111. 60609
aniline in 11.8 M phosphoric acid. The formaldehyde solution was prepared by diluting 5 ml of 40% formaldehyde to 1 1. with distilled water. The sulfamic acid solution was prepared by dissolving 2.0 g of sulfumic acid in distilled water and diluting to 1 1. The sulfamic acid solution used here is 0.2%. Reference 4 uses 0.17%. This difference was not considered significant. Automated I1 Pararosaniline Method. This automated system is a modification of the West-Gaeke method ( 2 ) .The method is adapted to a Technicon AutoAnalyzer I1 and was used as described in Reference 5. Figure 2 shows the manifold diagram. The pararosaniline solution used in this procedure is 0.016% pararosaniline in 1.84 M phosphoric acid. Formaldehyde solution was prepared by diluting 5 ml of 40% formaldehyde to 1 1. with distilled water and adding 0.5 ml of Aerosol 22 wetting agent. The Aerosol 22 smooths the flow of the solution through the manifold and colorimeter flow cell and does not affect the analysis. Two-tenths percent sulfamic acid solution was prepared by dissolving 2 g of sulfamic acid in distilled water and diluting to 1 1.
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Reperence Methdd. This method of analysis of manually ifipinged sulfur dioxide samples was used as described in the Federal Register ( I ) . Briefly, 5 ml of SO2 absorbed in potassium tetrachloromercurate (TCM) are placed in a 25-ml volumetric flask. One ml of 0.6% sulfamic acid in distilled water is added and the solution allowed to stand for 10 min. Two ml of 0.2% formaldehyde in distilled water and 5 ml of 0.016% purified pararosanaline in 0.3 M phosphoric acid are pipetted in. The solution is diluted to volume with distilled water and the absorbance read against a distilled watet blank at 548 nm with 1-cm cells after 30 min. Aatomated I Pararosaniline Method. This automated system is the West-Gaeke method adapted to a Technicon AutoAnalyzer I and was used as described in Reference 4. T h e manifold diagram in Figure 1 shows the analysis scheme. The pararosaniline is 0.016% purified (99-100%) pararos1172
Environmental Science & Technology
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Figure 1. Automated I sulfur dioxide manifold diagram. Compatible with AutoAnalyzer I components and equipment
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Figure 2. Automated II sulfur dioxide manifold diagram. Assembled from AutoAnalyzer II components and equipment
Table I . Comparison of the Analysis Solutions a t the Time the Sample Absorption Is Determined Auto-
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Reference Method
Automated I
method
TCM, M
Sulfamic acid, Yo Formaldehyde, YO Par a r osa na I i ne, O h PH
X m a x , nm Extinction coefficient,a x lo4 Solution detection iimit,b 1.1g/ml Air detection limit,c p g / m 3
mated
II
0.016 0.024 0.008 0.0032 1.56 547 5.13
0.020 0.01 1 0.014 0.0027 0.85 580 4.06
0.020 0.054 0.017 0.0022 1.11 560 4.8
0.075
0.030
0.02 1
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a Expressed as absorbance liters/centimeter mole etermined f r o m the difference of the Sample and blank absorbance. #Determined f r o m t w o standard deviations of the blank. CAssuming 300 I o f air sa rnpled.
Results a n d Discussion Table I shows the concentrations of the reagents added
Methods Comparison In all of the analytical procedures, sulfur dioxide in absorbing reagent is determined as sulfite ion by the addition of formaldehyde and acid bleached pararosaniline to form a colored species, pararosaniline methyl sulfonic acid (7,8). The absorbance of the colored solution is determined at
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some point between 540 and 570 nm. Scaringelli et al. have shown that the A max is pH dependent (7). Figure 3 shows the absorption spectra of a reagent blank and a sample containing sulfur dioxide as determined by each method. Thirty-six samples for the comparison of the reference method and the Automated TI method were collected. Most wete 24-hr ambient air samples collected using referencemethod sampling procedures ( I , 9). These samples were collected from National Air Surveillance Network monitoring sites in Illinois, Indiana, Michigan, Minnesota, Ohio, and Wisconsin where the average ambient sulfur dioxide concentration is generally less than 80 pg per cubic meter (less than 0.5 pg of sulfur dioxide per milliliter (pg SOz/ml) in absorbing reagent). To broaden the range of available sample concentrations, four sample? from the field were spiked with SO2 in absorbing reagent and two samples were collected from test atmospheres generated with a petmeation tube apparatus ( I , IO). In addition, 17 similar samples were collected for comparison of the Automated I method to the Automated I1 method. A number of samples were analyzed in duplicate to determine the precision of each method.
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for each method in the analysis solution a t the time the absorbance is determined. The apparent higher sensitivity of the automated methods in Figure 3 is due to the use of 2.5 times more sample than in the reference method. The extinction coefficients in Table I show that the reference method is most sensitive in fact. The detection limits based on twice the standard deviation of the blank are also shown. The Automated I1 method has the highest sulfamic acid concentration (used to reduce interferences from nitrogen oxides) of the three methods. However, the analytical results indicated no significant differences between methods due to this. The nitrogen dioxide (NOz) concentrations corresponding to each sample were between 5 and 150 pg NOz/m3, and each method appears able to cope with these levels. Nitric oxide (NO) concentrations were not determined.
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Reloreno Mothod 600 nm
550 nm
Figure 3. Absorption spectra of the analysis solutions from each method. The sample contained approximately 1 pg S02/ml
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lug SO2/mrIa~l
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Flgure 4. Plot of comparison data for the reference and Automated I1 methods Equation of the line: y
= 0.959 X
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Volume 9, Number 13, December 1975
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the variance of the Automated I1 system to be significantly less than that of the reference method. The data from samples analyzed with the Automated I and Automated I1 systems are plotted in Figure 5. The slope of 0.97 f 0.02 is not significantly different from 1.0 and the correlation coefficient is 0.998. Duplicate analyses with the Automated I system yielded a standard deviation of 0.023 pg SOz/l. (N = 17, mean concentration = 0.50 pg SOz/ml) which is significantly greater than that of the Automated I1 procedure. This precision is, however, better than the reference method. The results from the Automated I1 system were on the average 0.012 pg SOz/ml (2 pg/m3) higher than the reference method results. The Automated I system results were on the average 0.006 pg SOJml (1 pg/m3) higher than the Automated I1 system results or 0.018 pg SOz/ml (3 pg/m3) higher than the reference method. These biases are not significant when considering the variations in duplicate analysis by each method. References ~utomrtrdII system [ut S O ~ / m e t d j
Figure 5. Plot of comparison data for the Automated II and Automated I methods Equation of the line: y = 0.972 X
+ 0.013
Each method contains sufficient formaldehyde and pararosaniline and gives linear plots of absorbance vs. concentration for samples in the range of 0-1 pg SOz/ml (0-167 1g/m3). Any samples higher than 1 pglml are routinely diluted with absorbing reagent. Figure 4 shows the data plot from the reference method and the Automated I1 procedure comparison. The slope was calculated to be 0.96 f 0.03, which is not significantly different from 1.0 (t-test a = 0.05); the correlation coefficient was 0.992. The analysis of duplicate samples yielded standard deviations of 0.037 pug SOz/ml ( N = 7, mean concentration = 0.26 pg SOz/ml) and 0.013 pg SOz/ml (N = 16, mean concentration = 0.42 pg SOz/ml) for the reference and Automated I1 methods respectively. An F-test showed
(1) Fed. Regist., 36,22385 (1971). (2) “Users Manual: SAROAD (Storage And Retrieval of Areometric Data)”, U.S. Environmental Protection Agency, Office of Air Programs, No. ADTD-0663, November 1971. (3) West, P. W., Gaeke, G. A., Anal. Chem., 28,1816 (1956). (4) “Determination of Sulfur Dioxide: Automated Para-Rosaniline Method As Used by AQALB, 1972” from Analytical Quality Assurance Laboratory Branch, 1972 (Environmental Protection Agency). (5) “Industrial Method No. 169-72AP”, Technicon Instruments Corp., Tarrytown, N.Y., 1973. (6) Scaringelli, F. P., Elfers, L., Norris, D., Hochheiser, S., Anal. Chem., 42,1818 (1970). ( 7 ) Scaringelli, F. P., Saltzman, B. E., Frey, S. A,, ibid., 39, 170918 (1967). (8) Cedergren, A., Wikby, A., Bergner, K., ibid., 47,100-6 (1975). (9) Morgan, G. B., Golden, G., Tabor, E k . in “Automation in Analvtical Chemistrv. Technicon Svmuosia “ . 1966”. Mediad. Inc.. Tarrytown, N.Y., i967. (10) O’Keefee, A. E., Ortman, G. C., Anal. Chem., 38,760 (1966).
Received for review May 5, 1975. Accepted October 1, 1975. Mention of commercial products is for identification only and does not constitute endorsement by the Environmental Protection Agency of the U.S. Government.
Correction B. J. Dowty, D. R. Carlisle, and J. L. Laseter point out an error in their paper, “New Orleans Drinking Water Sources Tested by Gas Chromatography-Mass Spectrometry. Occurrence and Origin of Aromatics and Halogenated Aliphatic Hydrocarbons” [Environ. Sci. Technol., 9 (8), 762-5 (1975)) “Closer examination of the spectrum of compound number 58, reported in Table I as (2- or 1-Napthy1)dichloromethane, reveals this compound to be dichloroiodomethane. Although both of these compounds share common spectral features such as their isotope ratios of the molecular ion and the presence of the -CHC12 fragment, comparison of the spectrum of our compound with that of the recently synthesized dichloroiodomethane reveals our initial interpretation to be in error. Spectrum of the dichloroiodomethane was furnished by Robert Kleopfer, USEPA, Region VII.” 1174
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