Environ. Sci. Technol. 1991, 25, 878-883
is part of the doctoral dissertation of L.S. a t the University of Mainz. Registry No. MeSn3+, 16408-15-4; Me2Sn2+,16408-14-3; Me3Sn+,5089-96-3;Bu2Sn2+,14488-53-0;BuSn3+,78763-54-9;Sn, 7440-31-5.
Literature Cited Blunden, S. J.; Chapman,A. In Organometallic Compounds in the Environment; Craig, P. J., Ed.; Longman: Essex, U.K., 1986; pp 111-159. Clark, E. A.; Sterrit, R. M.; Lester, J. N. Environ. Sci. Technol. 1988, 22, 600. Maguire, R. J.; Thacz, R. J.; Chau, Y. K.; Bengert, G. A.; Wang, P. T. S. Chemosphere 1986, 15, 253. Walkirs, A. 0.;Seligman, P. F.; Stang, P. M.; Homer, V.; Lieberman, S. H.; Vafa, G.; Dooley, C. A. Mar. Pollut. Bull. 1986, 17, 319. Cleary, J. J.; Stebbing, A. R. D. Mar. Pollut. Bull. 1987, 18, 238. Thompson, J. R. J.; Scheffer, M. G.; Pierce, R. C.; Chau, Y. K.; Cooney, J. J.;Cullen, W. R.; Maguire, R. J. Organotin compounds in the aquatic environment: Scientific criteria f o r assessing their effectson enuironmental quality; NRCC
No. 22494; National Research Council Canada: Ottawa, Canada, 1985. Hall, L. W. CRC Crit. Rev. Toxicol. 1985, 14, 159. Boyer, I. J. Toxicology 1989, 55, 253. Schumann, H.; Schumann, I. Gmelin Handbook o f Inorganic Chemistry, 8th ed.; Sn Organotin Compounds, Part 5 : Organotin Fluorides. Triorganotin Chlorides; Part 6:
(10) Mueller, M. D. Anal. Chem. 1987, 59, 617. (11) Byrd, J. T.; Andreae, M. 0. Science 1982, 218, 565. (12) Matthias, C. L.; Olson, G. J.; Brinckman, F. E.; Bellama, J. M. Enuiron. Sci. Technol. 1986, 20, 609. (13) Malle. K. G , 2,Wasser-Forsch. 1984, 17, 75. (14) Randall, L.; Donard, 0. F. X.; Weber, J. H. Anal. Chim. Acta 1986, 184, 197. (15) Matthias, C. L.; Bellama, J. M.; Olson, G. J.; Brinckman, F. E. Int. J . Enuiron. Anal. Chem. 1989, 35, 61. (16) Cooney, J. J.; Kronick, A. T.; Olson, S. J.; Blair, W. R.; Brinckman, F. E. Chemosphere 1988, 17, 1795. (17) Schebek,L. Ph.D. Dissertation, University of Mainz, F.R.G., 1990. (18) Mueller, M. D. Fresenius Z. Anal. Chem. 1984, 317, 32. (19) Stang, P. M.; Goldberg, E. D. Appl. Organomet. Chem. 1989, 3, 183.
(20) Waldock, M. J.; Thain, J. E.; Waite, M. E. Appl. Organomet. Chem. 1987, 1 , 187. (21) Schebek, L.; Andreae, M. 0.;Tobschall, H. J. Znt. J . Enuiron. Anal. Chem., submitted. (22) Hellmann, H. Analytik uon Oberflachengewassern; Thieme: Stuttgart/New York, 1986. (23) Randall, L.; Weber, J. H. Sei. Total Enuiron. 1986,57, 191. (24) Champ, M. A,; Lowenstein, F. L. Oceanus 1987, 30, 68. (25) Seligman, P. F.; Valkirs, A. 0.; Lee, R. F. Environ. Sci. Technol. 1986, 20, 1229. (26) Dai, S.; Huang, G.; Cai, Y. Appl. Organomet. Chem. 1989, 3, 437-441. (27) Ritchie, L. S.; Lopez, V. A.; Cora, J. M. In Molluscicides in Schistosomiasis Control; Cheng, T. H., Ed.; Academic Press: New York, 1974; pp 77-78.
Diorganotin Dichlorides. Organotin Trichlorides;Springer
Verlag: Berlin, 1978/1979.
Received f o r reuieu: June 19, 1990. Accepted December 4, 1990.
Quantitative Determination of Acrylonitrile in an Industrial Effluent by Ambient-Temperature Purge and Trap Capillary GC-MS and by Heated Purge and Trap GC-FID Daniel L. Vassilaros" and Thomas J. Bzik Air Products and Chemicals, Inc., 720 1 Hamilton Boulevard, Trexlertown, Pennsylvania 18195-150 1
Carol A. Cara
Bio Rad Laboratories, 3726 East Miraloma Avenue, Anaheim, California 92806 EPA priority pollutant method 603 for determining acrylonitrile (AN) in water could not be used t o analyze an effluent containing primary and secondary amines. Matrix effects including thermal decomposition of Michael addition products of amines and AN and coelution of isopropyl alcohol with AN precluded the use of the method 603 heated purge cell and Porapak QS column. The samples were then analyzed by a modified 624 method using capillary GC-MS and an ambient-temperature purge cell. Method validation data and a statistical analysis of data from calibration standard solutions analyzed over a 6month period show that the method is linear and has good sensitivity. The method precision determined from a series of standards yielded a l u relative standard deviation of 22%.
Introduction The commitment of regulatory agencies t o minimize exposure to acrylonitrile (AN) has prompted the development of analytical methods to determine AN in water. 878
Environ. Sci. Technol., Vol. 25, No. 5, 1991
Many literature methods for quantifying AN in aqueous matrices were developed around packed column gas chromatography (GC) with purge and trap preconcentration. Ramstad and Nicholson (1) reported a method for determining sub-parts-per-billion levels of AN in aqueous solutions by combining steam distillation, elevated temperature purge and trap of the distillate, packed column GC analysis, and nitrogen-specific detection. However, the authors pointed out that they had not applied their method to highly contaminated matrices. The Environmental Protection Agency (EPA) priority pollutant methods ( 2 , 3 ) on , the other hand, were designed to analyze aqueous waste streams. Method 603, specifically developed for the determination of AN, requires a heated purge cell, a packed column, and flame ionization detection. Acrylonitrile was also listed in 1979 as a parameter for method 624, which employs an ambient-temperature purge cell, a packed column, an internal standard, and mass spectrometric detection of the analytes. In the 1979 proposed Guidelines Establishing Test Procedures for the Analysis of Pollutants, (2) the EPA stated that method 624
0013-936X/91/0925-0878$02.50/0
0 1991 American Chemical Society
Table I Comparison of Analytical Methodsn anal. param cell temp trap material
603
EPA method 624
85 +Z 2 "C 23 cm of Tenax and 1 cm of 3% OV-1
624 modified
ambient 15 cm of Tenax, 8 cm of silica gel, 1 cm of 3% OV-1 180 OC desorb temp 180 "C column 10-ft packed column 6-ft packed column inlet on column, 220 "C on column, 220 "C temp program 90 "C for 1.5 min, 30 "C/min to 120 "C, 45 "C for 3 min, 8 "C/min to 220 "C, hold 20 min, 30 "C/min to 210 "C for hold for 15 min 10 min detector flame ionization quadrupole mass spectrometer
ambient 16 cm of Tenax and 8 cm of silica gel 100 "C 30-m FSOT column split 10:1, 100 "C 4 min a t -196 "C (liquid N2 trap), 25 "C for 2 min, 30 "C/min to 250 "C for 1 rnin quadrupole mass spectrometer
Critical differences are purge cell temperature, analytical column, and detector t,ype.
was useful for AN analyses but cautioned that purging efficiencies at room temperature were low and erratic; thus, method 603 with the heated purge cell was the preferred method. The 1984 edition (3)underscored the preference for method 603 by stating that 624 could be used to "screen" samples for AN. Although the EPA methods stipulate packed GC columns, capillary columns have also been applied to analyzing water for organic volatiles. Dreisch and Munson ( 4 ) used capillary column gas chromatography-mass spectrometry (GC-MS) for purge and trap analysis of volatile organic compounds in water. They suggested that advantages of the capillary column include extending the range of compounds that can be effectively analyzed by purge and trap, handling samples of excessive complexity and those samples with components a t a broad range of concentrations, and resolving late-eluting peaks. Trussell et al. (5) analyzed AN and other volatiles, base /neutral and acid extractables, and pesticides in a single chromatographic run by a purge and trap capillary GC-MS method. The target analytes were recovered from water at low parts-per-trillion levels. The authors found the technique suitable for drinking and river waters and tertiary effluents but were less certain of its applicability to the complex organic matrices found in raw sewage and industrial wastes. In this paper, we evaluate the application of EPA method 603 to the routine determination of AN in a specific industrial waste effluent. This wastewater contained a complex mixture of nitrogen- and oxygen-substituted aliphatic and alicyclic hydrocarbons; its chemical composition was significantly different from the effluent used in the single laboratory evaluation of method 603 (6). The consequent matrix effects forced fundamental modification of 603 instrumentation. In addition, a purge and trap capillary GC-MS system (hereafter referred to as "modified 624") was evaluated and shown to be less sensitive to the matrix effects. Modified 624 method validation data and a statistical analysis of standards data collected over 6 months of routine analyses are presented. The intent of this paper is to show first that the standard 603 method cannot reliably identify and quantify AN in this effluent, and second that the modified 624 method provides consistent, definitive identification of AN in a complex sample with equivalent precision of quantitative results.
Experimental Section Instrumentation. Method 603. Experimental details are described in Ref 6. Modified 624. A Finnigan OWA mass spectrometer with a Perkin-Elmer Sigma 3B gas chromatograph was
interfaced with a Tekmar LSC-2 purge and trap device. The temperature of the Tekmar purge cell was maintained a t ambient temperature during the purge cycle. The Tekmar adsorbent trap was packed with 15 cm of Tenax, 1 cm of 3% SP-2100 on Chromosorb WAW, and 8 cm of silica gel. The trap was desorbed a t 100 "C for 4 min. The sample was split a t a ratio of 1 O : l in the injection port. The chromatographic column was a J & W DB-5 fused-silica capillary column (30 m X 0.25 mm i.d., 1-ym df). A loop of the column in a Dewar of liquid nitrogen served to cryofocus the volatile organic compounds (VOC) released from the adsorbent trap during the desorption cycle. At the end of the desorption cycle the column was removed from the liquid nitrogen Dewar. After 2 min at ambient temperature, the oven door was closed and the GC oven was heated rapidly to 250 "C and held 1 min a t the final temperature. Calibration. Method 603. Calibration standards of AN in water were prepared in the range of 10-1000 ppb (ng mL-I). Appropriate calibration standards, spiked samples, and blanks were included in each set of samples. Modified 624. The mass spectrometer was tuned daily by using perfluorotributylamine. Concentrated calibration standards of AN in methanol were prepared such that a 1000-fold dilution in water would generate solutions in the range of 4-1612 ppb (ng mL-', 2-800 ng on the capillary column). An internal standard solution was prepared from the Supelco purgeables internal standard mix for EPA method 624 [containing bromochloromethane (BCM), l-chloro-2-bromopropane, and 1,4-dichlorobutane] at 200 ppm and added to all calibration standards, blanks, and samples at the 200 ppb level. A blank of 5 mL of deionized water was analyzed daily before analyzing a low-concentration (40.3 ppb) AN standard. A high-concentration (806 ppb) AN standard was the last daily injection. Sample Analysis. Samples of aqueous effluent were acidified with phosphoric acid, filtered with Rainin Nylon 66 filters, and refrigerated until analysis. All other details of sample handling and analysis are described in the documentation of EPA methods 603 and 624. Acrylonitrile was quantified by GC-MS by the internal standard method using the extracted ion current profile of the m / z 53 ion of AN and the m f z 128 ion of BCM.
Results and Discussion Table I shows a comparison of the instrumentation required for EPA methods 603 and 624 and the modified 624. The significant differences between 603 and the 624 methods are the temperature of the purge cell and the detection techniques. Method 603 includes a heated purge cell and flame ionization detection, while 624 requires an ambient-temperature purge cell and a quadrupole mass Environ. Sci. Technol., Vol. 25, No. 5, 1991
879
100
RIC
CN
SCAN:
400
500
600
700
800
900
1000
TIME: 1O:OO
12:30
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Figure 1. Portion of reconstructed ion chromatogram of effluent spiked with AN. Molecular weights confirmed by NH, chemical ionization. Marked peaks appeared after spiking wastewater with AN. Electron ionization conditions: Finnigan 4500, 30 m X 0.259 mm i.d., l.O-fim df, DB-5; 1O:l split; 2 minl90 O C / 8 O C min-'1280 O C / 5 min; 29-450 amu at 1.5 s/scan; 70 eV. CI conditions: Finnigan 4500; similar column and oven temperature program; 0.31 Torr NH, (Pirani); 100 eV; 90-450 amu at 1.5 s/scan.
spectrometer for analyte detection. Method 624 was further modified by substituting a capillary column for the packed column and adding a liquid nitrogen trap to the capillary column. Method 603. Method 603 was specifically developed for determining AN, acrolein, and acetonitrile in aqueous matrices. The 603 heated purge cell increases the purge efficiency of AN to approximately 10070 at 85 "C (6) and improves the reproducibility of the purging process. In studies of the target effluent, however, we found that the heated purge cell generated extraneous AN. Effluent samples that were shown by a high-pressure liquid chromatographic (HPLC) method to contain low levels of AN appeared to produce extremely large amounts of AN by the 603 method. Room-temperature purging, on the other hand, gave results that matched the HPLC data. The high levels of AN were thus thought to be due to thermal decomposition of AN derivatives in the wastewater. This hypothesis was confirmed when addition products of AN with primary and secondary amines were detected by the GC-MS analysis of an aliquot of the effluent, which had been spiked with excess AN (Figure 1). Thermally labile Michael addition products could decompose during the heated purging process and thereby generate extraneous AN. Confirmation of our hypothesis forced us to modify the method: All samples were subsequently purged at ambient temperature. Even after lowering the temperature of the purge cell, some samples contained surprisingly large amounts of AN. Purge and trap GC-MS analysis of these samples showed the seemingly high levels of AN as interference from isopropyl alcohol (IPA),which coelutes with AN on the 603 Porapak QS column. 880
Environ. Sci. Technol., Vol. 25, No. 5, 1991
Therefore, the modified 603 monitoring method cannot reliably identify and quantify AN when IPA is present in the effluent. This problem may be resolved by replacing the FID with a nitrogen-specific detector. In summary, matrix compounds decomposed to form extraneous AN in the method 603 heated purge cell, and IPA interfered with flame ionization detection of AN. Thus, the unmodified 603 method is not appropriate for the routine determination of AN in this sample matrix. Modified 624. Mass spectrometric detection provided unambiguous identification of the target analyte under all conditions because of the unique molecular weight and mass spectral fingerprint of AN. Quantitation, however, was affected by a matrix component that occasionally interfered with the ion peak of the internal standard against which AN was quantified, and by the irregular purging behavior of AN at ambient temperature. Tetrahydrofuran (THF) eluted on the DB-5 column near the BCM peak and appeared to suppress the ionization of BCM. The response of the m / z 128 ion of BCM was degraded approximately 9070 in the presence of large amounts of THF. When interfering levels of T H F were present, AN was quantified with respect to 1-chloro-2bromopropane, a less volatile internal standard. The balance of this paper describes the quality assurance and validation data for the modified 624 method. (a) Method Uncertainty. The observed uncertainty of individual measurements is shown in the control charts provided in Figures 2 and 3. These figures illustrate the results of statistically analyzing the same series of identical 40.3 ppb standards of AN under differing quantitative assumptions (Figure 2, absolute areas of mlz 53 ion; Figure 3, normalized AN response) over a 6-month period. Each control chart shows an upper control limit (UCL), the total mean, and a lower control limit (LCL). These
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OBSERVATION NUMBER Figure 2. Individuals control chart of raw peak areas of extracted ion profile of ion m l z 53, over 6 months. UCL and LCL are upper and lower "30" control limits, respectively. 0.161 0
UCL
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OBSERVATION NUMBER Figure 3. Individuals control chart of ratioed areas of extracted ion profiles of ions m l z 53 and 128 (area of m l z 5 3 l a r e a of m l z 128), over 6 months. UCL and LCL are upper and lower "30" control limits, respectively.
upper and lower limits were estimated by overall mean f 2.66(R bar), where R bar is the average of the ranges between neighboring measurements. "Neighboring" is defined without regard to the elapsed time between consecutive calibrations; thus, the time between neighbors could be one or several hours, overnight, or a weekend.
The scale factor, 2.66, provides the equivalent to 3 standard deviation limits on an individuals control chart. The range-based estimate of the standard deviation used in the construction of a moving range control chart for individual observations is not calculated in the usual manner for an overall standard deviation but rather as the standard deEnviron. Sci. Technol., Vol. 25, No. 5, 1991
881
to a series of three analyses that identified the best time frame for Calibration. The first analysis applied the response factor from a single calibration to the subsequent measurement of a standard in order to obtain a predicted concentration of AN. This approach approximates the actual process of daily calibration and sample quantitation against a single calibration and shows the time variations inherent in a one-to-one (calibration-to-sample)processing mode. This approach implicitly assumes calibration is a relatively short-lived phenomenon. The following method statistics were generated from the 40.3 ppm standards:
Table 11. Matrix Spiking Experiments sample
bkgdn
1 2 3 4 5 6
16 65 53 65 62 25
spiken 32 32 32 16 32 32
reca
70 rec
46 92 90 76 103 63
96 95 106 94 110 111
av 70rec SD 2 ' rec O/c RSD
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OAmounts in Dab i n r mL-').
x
viation of neighboring measurements. Figure 2 graphs the absolute areas of the m / z 53 ion. The observed range was 570-9500 area counts, and the overall mean and standard deviation based on 101 observations were 4100 and 1846 area counts, respectively. The percent relative standard deviation ('70RSD) was 45. The magnitude of the standard deviation reflects the inherent uncertainty in an ambient-temperature purge of AN from water. Figure 3 graphs the AN response normalized to the response of BCM. This normalization decreased the '70 RSD by almost 50% (from 45 to 24). The observed range for the normalized data was 0.036-0.154, and the overall mean and standard deviation based on 101 observations were 0.083 and 0.020, respectively. Normalization decreased the range from approximately 20-fold to 4-fold and improved the precision of the data. Although BCM is similar in volatility to AN, its solubility is significantly different, and it cannot fully compensate for the irregular purging behavior of AN in water. Given the small proportion of results that fall near or exceed the control limits, one would conclude the system underlying either figure is in statistical control. No strong statistical evidence was found to indicate that the overall (long-term) variability in the data was larger than the short-term variability between neighboring results. A set of 10 replicate 40.3 ppb calibration solutions was analyzed in duplicate at the beginning of the project. The overall average and standard deviation of the normalized responses from this limited set of data (which is included in the figures) are 0.085, and 0.024, respectively. The '70 RSD was 28. The lack of a statistically significant difference between the mean of the normalized data collected at the beginning of a 6-month analysis period and the overall mean of all analyses over 6 months strongly suggests the following: (1) The analytical system was relatively constant in performance in spite of daily tuning, calibration, and other daily, standard operations. (2) The initial calibration exercise accurately characterized the response of the analytical system. (b) Time-Frame Analysis of 40.3 ppm Standards Data. The normalized data from Figure 3 were subjected
__
S -
70RSD
n -
42.0
11.4
27
100
where X is the average of the n = 100 predictions of AN possible from using the 101 observations in such a manner, s is the standard deviation of the 100 predictions, and the 7% RSD is s / X expressed as a percentage. The second analysis applied the average response factor from the previous five measurements of the standard to the subsequent measurement of a standard. This approach assumes a calibration remains in effect for some period of time (days). The following method statistics were generated from the 40.3 ppb standards: __
x
--S
% RSD
n -
41.6
9.9
24
96
The third analysis assumes that the calibration was in effect for the entire 6-month period. This analysis used the average response factor from all 101 measurements of the 40.3 ppb standard to obtain
X -
-.
S
% RSD
n -
40.3
8.8
22
101
Comparing the three averages to 40.3 shows the bias observed from using these three calibration methods. The exact match (third analysis) is an artifact of how the same data were used in both establishing and evaluating calibration. The comparison of the averages, by itself, does not establish which method of calibration is best. The more critical number is s, the standard deviation. It is a measure of the precision of the data about each observed average. The smallest s (best precision) was obtained through use of the overall response factor average as the calibration method/model. This value is equivalent to published data from a 603 method validation study. An analyst can use the one-to-one calibration method (or other short-term methods) as data are being collected. As more and more calibration data become available, one can determine whether calibration has changed over a longer time frame. If it has not, the accuracy and precision of data acquired over a period of time can be improved by reprocessing that data with the average response factor
Table 111. Stability Studies sample
1
3
1 2
