Anal. Chem. 1903, 55, 1775-7778 (12) Hammers, W. E.; Janseen, R. H. A. M.; Baare, A. G.; DeLlgny, C. L. J . Chromatogr. 1978, 167, 273-289. (13) Eksborg, S. J . Chromnfogr. 1978, 149, 226-232. (14) Crommen, J. J . Chronlatogr. 1979, 186, 705-724. (15) Sugden, K.; Cox, G. 6.; Loscombe, C. R. J . Chromatogr. 1978, 149, 337-390. (16) Nelis, H. J. C . F.; DeLeenheer, A. P. J . (;hromatogr. 1980, 195, 35-42. (17) Hill, R. E. J . Chromatogr. 1977, 135, 419-425. (18) Gelijkens, C. F.; DeLeenheer, A. P. J . CWomatogr. 1980, 194, 305-3 14. (19) Crommen, J.; Fransson, 6.; Schlll, G. J . (:hromatogr. 1977, 142, 283-297. (20) Crombeen, J. P.; Kraak, J. C.; Poppe, H. J . Chromatogr. 1978, 167, 219-230. (21) Sokolowskl, A,; Wahlund, K. G. J . Chromato!gr. 1980, 189, 299-316. (22) Bidlingmeyer, 8.;DelRlos, J. K.; Korpi, J. Anal. Chem. 1982, 5 4 , 442-447. (23) Svendsen, H.; Grelbrokk, T. J . Chromatogr. 1981, 212, 153-166. (24) Van Der Houwen, 0. A. G. J.; Sorel, R. H. A.; Halshoff, A,; Teeuwsen, J.; Indemans, A. W. MI. J . Chromatogr. lSE,l, 209, 393-404. (25) Mackey, D. J. J . Chromatogr. 1982, 242. 275-267. (26) Smith, P. A.; Frank, S. J . Am. Chem. SOC.1952, 74, 509-513. (27) Clint, J. H. J . Co/lo/dInterface Scl. 1973, 43, 132-143. (28) Bates, R. G. "Determination of pH-Theory arid Practlce"; Wiley-lnterscience: New York, 1973; pp 248-249.
132) i33j (34) (35) (36) (37) (38) . , (39) (40)
1775
Tietz, N., Ed. "Fundamentals of Clinical Chemistry", 2nd ed.; W. B. Saunders: Philadelphia, PA, 1976; pp 915-917. Thurman, E. M. J . Chromatogr. 1979, 165, 625-634. Verzele, M.; DePotter, M.; Ghyseis, J. HRC CC, J . High Resolut. Chromatogr. Chromatogr. Commun. 1978, 3 , 151-153. Dunin, R. "Ion Exchange Reslns"; Wlley: New York, 1958; pp 47-54. Helffrich, F. "Ion Exchange"; McGraw-Hill: New York, 1962; pp 424-426. Helffrich, F. "Ion Exchange"; McGraw-HIII: New York, 1962; pp 168-1 69. Knox, J. H.; Hartwick, R. A. J . Chromatogr. 1981, 204, 3-21. Gregor, H. P.; Collins, F. C.; Pope, M. J . Colloid Sc/. 1951, 6 , 323-347. Unpublished results, this laboratory. Kirchenerova. J.: Farrell. P. G.: Edward, J. T. J . Phvs. Chem. 1976, 8 0 , 1974-1980. Kirkwood, J. G. J . Chem. Phys. 1934, 2 , 351-361. Gostling, L. J.; Albrlght, P. S. J . Am. Chem. SOC. 1946, 6 8 , 106 1- 1063.
RECEIVED for review December 7 , 1982. Resubmitted June 20,1983. Accepted June 20,1983. This work was supported by the National Institutes of Health, through Grant GM28112, and by Research Corporation.
Determination of Halogens in Organic Compounds by Ion Chromatography after Sodium Fusion Chung-Yu Wang and James G . Tarher*
Department of Chemistry, North Texas State University, Denton, Texas 76203
A Na fusion-ion chromatographic ( I C ) method for determination of F, Ci, Br, andl I is described. Seventeen organic halo compounds and eleven mixtures wc?re decomposed by Na fumes at 280-290 'IC for 1 h or longer. These products were absorbed by 250 mL of standard eluent and the absorbing solutions were then injected for I C analysis using a combination of electrochemlcal and conductometric detectors. The average recoverie!s were from 91.38 to 96.56% for F, 93.56 to 98.79% for Ci, 97.57 to 101.04% for Br, and 92.50 to 99.13% for I. The rcslative standard deviations for all four halogen analyses were less than 3%. This Na fusion-IC method provides a mechanism for compiiete analysis for all four halogen elements in one ion chroniatographlc sample injection. Reproducibiliity is excellent and iiquld sample handling is also mentloned.
There is a wide range of published methods for the determination of organicallybound halogens. The decomposition methods which have bleen developed include closed flask combustion ( I ) , oxygen combustion tube) (2-4), metal bomb ( 1 , 5 ) , Carius ( 6 ) ,and alkali metal or coinpound suspended in liquid system (7-11). The reported detection systems include gravimetric methods (4),visual titrimetric methods ( I ) , electrometric methods ( 1 , 4 ) ,and other methods for specific halide determination, such as thorium nitrate titrimetry (12) and fluoride-sensitive ellectrodes (13,14)for fluorine and an iodometric method for iodine and/or bromine (4). All of the methods mentioned above are subject to one or more of the following: problems involved in the analysis of low boiling organic fluoro compounds, problems arising from the unique behavior of the fluoride Eon, and/or problems arising from the
interference of one halide ion upon the detection of a second halide ion. Ion chromatography (IC) (15) has been proven to be a highly accurate technique for determination of halide ions by using conductometric detection to measure fluoride, chloride, and bromide ions and electrochemical detection to measure iodide ion to the parts-per-million range. None of the conventional methods for the simultaneous titrations of fluoride, chloride, bromide, and iodide is entirely satisfactory, particularly on the microchemical scale (1,4, 12), for all four halides in the presence of each other. The alkali fusion method for decomposition of organic halo compounds has been chosen to use with ion chromatography for the determination of halide ions. The advantages are the following: (i) Most organic halo compounds can be successfully destroyed by alkali fumes ( 4 ,and the fusion method is also readily applied to samples which exhibit a high vapor pressure. (ii) The chemical reaction taking place for releasing the organically bound halogens is a reduction reaction. The halogens are converted to the lowest valence state; hence the resulting products are all in the form of halides (5). Therefore, no other treatment of the absorbing solution is needed before using ion chromatographic analysis. (iii) The reaction time and temperature can be controlled easily. Because potassium is more sensitive to oxygen and moisture than sodium and because sodium can be cut and weighed in the open air, sodium is considered preferable to potassium in the alkali fusion-IC method. The sodium fusion-IC method described in this paper provides an inexpensive but efficient mechanism for the routine analysis of the halides in organic samples. Seventeen compounds containing either one or two halogens and eleven mixtures prepared by combining sodium difluorochloroacetate,
0003-27C~0/83/0355-1775$01.50/0 @ 1983 American Chemical Society
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ANALYTICAL CHEMISTRY, VOL. 55, NO. 11, SEPTEMBER 1983
Table I. Ion Chromatographic Parameters eluent flow rate precolumn separator column suppressor column injection volume working electrode working potential electrochemical full scale conductance full scale
0.003 mol/L NaHCO, and 0.0024 mol/L Na,CO, 156 mL/h 50 mm fast run 100 mm fast run 150 mm fast run 100 mm anion suppressor column 100 pL Ag 0.2 V 1.5 pA/V 30 or 50 pmho
p-chlorobromobenzene, and o-iodophenol in different weight fractions were analyzed by this method. No difficulty was found in handling the fluoro and/or liquid compounds.
EXPERIMENTAL SECTION Apparatus. The decomposition vessel consists of 2-mL untreated ampules (Kimble), a 1-L thick-wall glass bottle (Wheaton 219180), an oven, a Bunsen burner, and an analytical balance (Mettler H30). The determination equipment includes an ion chromatograph (Dionex Model-10) and 25 mm diameter, 0.2-llm pore-size membrane filters for filtration. The operating conditions with all parameters are shown in Table I. Reagents and Materials. Metallic sodium weighing approximately 30-40 mg was used for each sample decomposition. Seventeen organic halo compounds were obtained from the following manufacturers: Aldrich Chemical Co., Inc. (2-chloroacetophenone and 2,3-dichlorophenol); Eastman Kodak Co. (2chloroacetamide,p-chlorobromobenzene,p-dichlorobenzene,and naphthalene tetrachloride); Eastman Organic Chemicals (2bromopropane and o-iodophenol); Fisher Scientific Co. (p-iodotoluene); J. T. Baker Chemical Co. (p-bromoaniline and 1chloronaphthalene);Matheson Coleman & Bell (bromophenolblue and bromotrichloromethane); Pfaltz Bauer, Inc. (N-chlorosuccinimide); Pierce Chemical Co. (chlorodifluoroacetamide); Sigma Chemical Co. (2,4-dinitrofluorobenzene). Sodium difluorochloroacetate was not in the original bottle. All solutions were prepared from distilled-deionized water, and standard solutions of each halide were prepared for at least five different concentrations to construct calibration curves for the determination of each halide in the absorbing solution. The concentration ranges of the standards were 5-25 ppm for F-,10-50 ppm for C1-, 20-80 ppm for Br-, and 10-90 ppm for I-. Procedure. Between 5 and 35 mg of sample was weighed into the ampule with an accuracy of &O.l mg. A piece of sodium metal about 30-40 mg was cut until it was no longer covered with mineral oil. The piece of sodium was then cut into 15 or 20 pieces and these pieces were put into the ampule immediately. The top of ampule was sealed by Bunsen burner as quickly as possible (generally it would take 15-20 s for this step). If the sample is liquid and/or might react with sodium at room temperature, place the sodium pieces in the middle of the ampule $0keep the sodium away from the sample and seal the top of ampule. After the ampule was sealed, it was heated in an oven at 280-290 "C for approximately 1h or longer. If the ampule was not sealed completely before heating, a white or light color product, probably sodium oxide, would be formed on the wall during the heating. If the ampule is cracked during heating, it might be necessary to reduce sample size. No explosions occurred during this procedure. In several instances, however, a small crack developed near the top of the ampule allowing gas to escape. Two-hundred-fifty milliliters of the standard eluent was transferred into a clean, dry, 1-L thick-wall glass bottle equipped with a cap having a piece of parafilm inside. The heated ampule, after cooling to room temperature, was placed into the glass bottle and the top of the bottle was capped. The bottle and contents were shaken vigorously by hand for several minutes to make sure that the ampule was broken and the sodium halide was dissolved by the eluent.
A clean, 5-mL syringe and a filter with a membrane filter were flushed with the absorbing solution several times; the syringe was then reloaded and injected into the sample loop of the ion chromatograph by passing through the filter. Thus, the sample loop was charged with the clear absorbing solution which eliminated the solid residue products. The procedure of ion chromatographic analysis for determination of halogens in the absorbing solution by using the two detection system has been described previously (16). The sodium fusion-IC analysis of halogens in organic compounds is an efficient method of analysis. The length of time necessary for the analysis of one sample is less than 3 h of which 1 h is the heating time and 10-40 min is for the ion chromatographic analysis. The variation in time is due to the additional time necessary for the determination of the iodide ion. Since numerous samples can be heated simultaneously and a second set of samples can be prepared while the first set is in the oven, the time necessary for a series of samples is relatively short. A single set of eight to ten samples containing the iodide ion can be analyzed in approximately 6-8 h without much difficulty. One problem might occur during the chloride concentration determination from chromatograms using the normal eluent. This problem is caused by a large amount of sodium in excess of that needed to decompose the sample. The high concentration of hydroxide ion produced by the decomposition of the excess sodium creates a small response in the conductivity detector that is not totally separated from the chloride ion peak. However, a small amount of excess sodium is necessary to make sure all the sample can be decomposed. Usually, 30 to 40 mg of sodium cut into many very small pieces will minimize this error. Caution. The sodium metal must be handled with extreme caution at all times. All normal safety precautions such as proper eye protection and protective clothing should be worn.
RESULTS AND DISCUSSION Fluoride, chloride, and bromide ions can be easily detected by the conductivity detector following the suppressor column in the ion chromatograph. Therefore, a 300-mm fast run anion separator column with a suppressor and a conductivity detector are suitable to determine these three halogen ions simultaneously in the absorbing solution. If the absorbing solution contains only the iodide ion, the electrochemical detector should be placed immediately after a 50-mm precolumn. An optimum potential, 0.2 V, is applied to the silver electrode for iodide detection (17). One important result which must be noted is that the response of the relative peak height a t high iodide concentrations yields a curved rather than a linear relationship. The quantitative results are obtained by the following calculation: mg of halogen found in sample = p p m halide found in absorbing solution(mg/L) X volume of absorbing solution (mL) 1000 m L / L (1) The volume of absorbing solution need not be 250 mL, it may be 100 mL or 500 mL depending on convenience and the concentration of halide analyzed. The results of the halogen analysis of these organic compounds are presented in Table T 1
11.
There were three reasons for choosing the heating temperature in the range of 280-290 "C. (i) All the compounds studied will melt under this temperature range, the highest melting point compound in Table I1 is bromophenol blue (270 "C). (ii) Most ovens can reach this temperature range without difficulty. (iii) I t will prevent the 2-mL ampule from exploding if the sample is not suitable for reacting with sodium fumes at higher temperatures or if too large a sample was used (over 30 mg). Most of the compounds studied can be successfully decomposed at this temperature range in 1h of heating. A few organic compounds require longer heating to yield good results, for instance, 2,3-dichlorophenol and bromophenol blue
ANALYTICAL CHEMISTRY, VOL. 55, NO. 11, SEPTEMBER 1983
1777
Table 11. Results of Analysis of Organic Halogen Compounds no.
rmp, "C
46.45 (Br) 47.71 (Br)
3 4 5
2-chloroacetamide 2-chloracetop~henone p-chlorobromobenzene
117-119 56 67
6
chlorodifluoroacetamide
83.42
7 8
p-dichlorobenzene 2,3-dichlorophenol
53.5 57
37.91 (Cl) 22.93 (Cl) 18.52 (Cl) 41.74 (Br) 29.34 ( F ) 27.38 (Cl) 48.23 (CI) 43.50 (Cl)
o-iodophenol p-iodotoluene naphthalene tetrachloride N-chlorosuccinimide
93-94 3 E; 187-189
57.68 (I) 58.20 (I) 53.32 (CI)
148-149
26.55 (CI)
13 14 15
sodium difluorochloroacetate 2-bromopropanee bromotrichloromethanee
16 17
1-chloronaphthalenee (263) 2,4-dinitroflu~robenzene~(178)
24.92 ( F ) 23.25 (Cl) 64.96 (Br) 53.64 (Cl) 40.29 (Br) 21.80 (Cl) 10.21 ( F )
(59.4) (104)
std devC % RSDd
1
5 5 6 5 6 19
13.3-30.8
3.
5
15.3-35.3 10.1-21.9 7.2-1 8.3 7.1-16.3 9.8-14.4 4.9-21.9 7.1-16.7
3 3 6
7 5 8 6 5 6 6
45.39 (Br) 31.21 (Br) 47.20 (Br) 37.45 (Cl) 22.31 (Cl) 18.09 (Cl) 41.20 (Br) 28.33 (F) 26.30(C1) 46.55 (Cl) 25.82 (Cl) 38.25 (Cl) 41.83 (Cl) 57.09 (I) 56.82(1) 50.22 (Cl)
0.76 4.26 1.23 0.94 0.48 0.29 0.64 0.18 0.34 0.95 2.55 3.07 0.75 0.77 0.98 0.71
1.67 13.65 2.61 2.52 2.16 1.63 1.56 0.62 1.28 2.05 9.88 8.03 1.79 1.35 1.71 1.42
25.19 (Cl) 24.84 (Cl) 23.45 (F) 22.80 (Cl) 65.63 (Br) 51.70 (CI) 40.44 (Br) 20.44 (Cl) 9.33 ( F )
0.34 0.47 0.58 0.60 0.89 0.70 0.62 0.37 0.17
1.35 1.89 2.48 2.65 1.36 1.35 1.53 1.80 1.79
15.3-34.5 18.1-28.6 11.2-22.2 15.3-32.4 18.3-32.9 17.3-47.2
66.4 270
12
av %found
wt range, mg
p-bronioaniline bromophenol blue
9 10 11
nb
%theory
2
1
e
compound
to 1 31
6 I! 3.
10 3. 3. 3.
12.3-29.4 12.7-26.5 10.1-18.0
3 1
6 6 6
6.9-17.2 9.5-13.7
1. 1
7 7
11.7-29.2 15.4-31.0
1.
6 6
std dev = standard deviation. a t = heating time. b n = number of analyses. These compounds are liquids and their lboiling points are shown in parentheses. --
6
1
RSD = relative standard deviation.
l____l_l_-_-
___-
Table 111. Results of Analysis of Mixtares components,a mg B C
-___
no. 1
2 3 4 5 6 7 8 9 10 11
a
A
6.0 7.9 8.3 8.0 7.9 10.0 4.4 6.7 12.5 15.1 3.3 11.4 11.7 11.5 5.2 7.1 11.8 5.5 8.3 8.4 6.6 12.5 % av recovery std dev % re1 std d w
5.4 9.9 7.0 11.9 11.7 6.2 10.4 6.7 10.6 6.6 6.3
-
%
theory
Ffound
7.75 7.72 7.89 7.29 7.91 7.36 4.77 4.43 9.57 8.88 3.94 3.86 8.68 8.26 6.82 6.50 9.79 10.54 8.74 8.03 6.48 6.40 94.84 2.82 2.98
% c1-
theory
found
14.81 13.92 13.02 12.46 14.82 13.78 9.34 8.63 14.83 15.02 13.78 12.19 14.43 14.27 13.29 12.37 13.49 13.06 14.89 14.49 15.16 14.15 94.93 3.53 3.71
theory
Brfound
17.09 17.14 12.75 12.19 16.77 16.39 12.16 11.48 13.28 13.02 22.78 22.76 14.29 14.05 15.61 15.38 8.23 8.45 15.18 15.14 20.54 19.42 98.17 2.55 2.60
% I'
theory
found
16.14 15.75 21.79 19.93 16.21 14.75 29.85 28.54 17.17 15.78 17.11 15.47 17.85 15.48 20.34 18.75 21.92 20.27 16.48 15.47 14.31 13.50 92.50 2.87 3.10
Component A, sodium difluorochloro'acetate; component B, p-chlorobromobenzene; component C, o-iodophenol.
in Table 11. After complete decomposition, the relative standard deviation should be very small; if not, a longer heating time will be required. Eleven individual mixtures were prepared from sodium difluorochloroacetate, p-chlorobromobenzene, and o-iodophenol. Table I11 shows the variations of each components' weight in the mixtures and the results of halogen analysis of' mixtures. By use of the sodium fusion-IC method, a complete analysis of all four halogens in the organic sample was performed. The chromatograms of the first mixture analysis are shown in Figure I as an example. Four liquid organic halo compounds have been analyzed. These are 2,4-dinitrofluorobenzene, 1-chloronaphthalene, 2-bromopropane, and bramotrichloromethane. The chemical reactivity and the high vapor pressure of liquid compounds presented an interesting problem in sampling. The time required for sealing the ampule must be minimized. In addition, the sodium should be placed in the middle of the ampule, as discussed earlier, during sealing to minimize
-
premature reactions. These four liquid compounds have proved amenable to the sodium fusion method. Nitrite and nitrate were thought to be potential interferents because their retention times on the ion chromatograph are similar enough to that of chloride and bromide, respectively, that the peaks could overlap to some extent a t high nitrite ion or nitrate ion concentrations (18). However, the nitrite and nitrate ions have never been observed after using sodium fusion to decompose the organic samples containing nitrogen, even for 2,3-dinitrofluorobenzeneafter being decomposed by sodium fumes. The average recoveries of halogens in these completely decomposed organic compounds ranged from 91.38 to 96.56% for fluorine, 93.56 to 98.79% for chlorine, 97.57 to 101.04% for bromine, and 92.50 to 99.13% iodine. All these compounds have been analyzed at least five times with different sample weights. The relative standard deviations are lower than 3% for each analysis. Incomplete decomposition is evident from the precision obtained in multiple analyses of the same sample.
1778
Anal. Chem. 1983, 55, i m - 1 7 8 1
1
I
matographic detection limit (19), and a more accurate weighing device and a torch that can supply a higher sealing temperature flame than a Bunsen burner would be needed for more rapid sealing of the ampule. Registry No. Flourine, 7782-41-4;chlorine, 7782-50-5; bromine, 7726-95-6; iodine, 7553-56-2.
Br-
LITERATURE CITED
I
0 2 4 6 8 IO 12
22 24 26 28 30 32 34 36 38
RETENTION TIME (MINUTE)
~
Figure 1. Chromatograms of analysis of mixture 1.
High relative standard deviations are indicative that longer heating times may be required.
CONCLUSION Since these compounds have been analyzed on a semimicroscale, it is also believed that a microscale analysis can be accomplished by the sodium fusion-IC method. Under these conditions, it must be noted that pump noise and temperature drift are the major factors affecting the ion chro-
(1) Ma, T. S.; Rittner, R. C. "Modern Organlc Elemental Analysis"; Marcel Dekker: New York, 1979; pp 158-206. (2) Cottrell, M. R.; Cottrell, F. H. "Instrumental Organic Elemental Analysis"; Belcher, R., Ed.;Academic Press: New York, 1977; p 26. (3) Belcher, R.; Spooner, C. E. J . Chem. SOC. 1943, 313. (4) Olson, E. C. "Treatlse on Analytlcal Chemistry"; Kolthoff, I.M., Elving, P. J., Eds.; Wiley: New York, 1971; Part 11, Vol. 14, pp 1-22. (5) Lohr, L. J.; Bonsteln, T. E.; Frauenfelder, L. J. Anal. Chem. 1953, 25, 1115-1 1 17. (6) Steyermark, A. "Quantltative Organic Microanalysis", 2nd ed.; Academic Press: New York, 1961; p 316. (7) Vaughn, T. H.; Nieuwland, J. A. I n d . Eng. Chem., Anal. E d . 1931, 3 , 274-275. (8) Strahm, R. D. Anal. Chem. 1959, 37,615-616. (9) Liggett, L. M. Anal. Chem. 1954, 26, 748-750. (IO) Benton, F. L.;Hamiil, W. H. Anal. Chem. 1948, 20, 269-270. (11) Egll, R. A. Helv. Chim. Acta 1968, 51,2090. (12) Ma, T. S. "Treatlse on Analytical Chemlstry"; Kolthoff. I.M., Elving, P. J., Eds.; Wlley: New York 1965; Part 11, Vol 12, pp 117-168. (13) Francis, H. J., Jr.; Deonarlne, J. H.; Persing, D. D. Microchem. J . 1969, 1 4 , 580-592. (14) Light, T. S.; Mannlon, R. F. Anal. Chem. 1989, 47, 107-111. (15) Small, H.; Stevens, T. S.; Bauman, W. C. Anal. Chem. 1975, 4 7 , 1801-1809. (16) Wang, C. Y.; Bundy, S. D.; Tarter, J. G. Anal. Chem. 1983, 55, 1617-1619. (17) Rocklin, R. D.; Johnson, E. L. Anal. Chern. 1963, 55, 4-7. (18) Slemer, D. D. Anal. Chem. 1980, 52, 1874-1877. (19) Evans, K. L.; Moore, C. B. Anal. Chem. 1980, 52, 1908-1912.
RECEIVED for review May 2, 1983. Accepted June 13, 1983. This work was funded by a Grant from the North Texas State University Faculty Research Fund.
Microbore Liquid Chromatography with Electrochemical Detection for Determination of Nitro-Substituted Polynuclear Aromatic Hydrocarbons in Diesel Soot Zuliang Jin' and Stephen M. Rappaport* Department of Biomedical and Environmental Health Sciences, School of Public Health, University of California, Berkeley, California 94720
Synthetlc mlxtures of reference nltro-PAHs and extracts of diesel soot were subjected to HPLC wlth mlcrobore columns and reductive electrochemlcal detection. By use of two 50 cm by 1.0 mm 1.d. reversed-phase columns In serles and a thin-layer flow cell wlth an internal volume of 0.91 pL, HETP values ranged between 33.6 pm (k' = 3.1) and 38.0 pm (k' = 7.2) at a mobile phase velocity of 0.085 cm/s (flow rate = 40 pL/mln). Sensltlvltles of measurement were typlcally less than 0.1 ng lndlcatlng, at comparable slgnal to noise ratlos, an Increase of between 3 and 7 tlmes over those observed prevlously with 4 mm i.d. columns. The voltammetrlc behavlor of peaks observed In extracts of diesel soot were conslstent wlth those of reference nitro-PAHs. However, the only compound whose presence was lndlcated was l-nitropyrene at concentratlons in four samples of between 0.45 and 14.7 ng/mg of soot.
It has been demonstrated that engine exhausts (1-7) and urban air (8,9) contain nitro-substituted polynuclear aromatic hydrocarbons (nitro-PAHs) adsorbed in soot particles. Because many nitro-PAHs have been shown to be mutagenic and carcinogenic, there is considerable interest in measuring these compounds in environmental samples. This has proven to be a difficult task, however, because these samples contain a myriad of potentially interfering compounds. One analytical technique (7)has coupled reductive electrochemical detection (RED) with high-performance liquid chromatography (HPLC) to measure several nitro-PAHs in synthetic mixtures and to quantify 1-nitropyrene in extracts of diesel soot. That work demonstrated the use of hydrodynamic voltammetry to differentiate nitro-PAHs from other reducible species, such as quinones of PAHs. We report here the use of microbore HPLC columns with RED to enhance both the resolution and the sensitivity of analysis.
On leave from Institute of Environmental Chemistry, Chinese Academy of Sciences, Beijing, The People's Republic of China.
EXPERIMENTAL SECTION Apparatus. A HPLC system, constructed as shown in Figure
0 1983 American Chemical Society 0003-2700/83/0355-1778$01.50/0
