598
ANALYTICAL CHEMISTRY, VOL. 51, NO. 6, MAY 1979
from the literature. Further, this equation requires no further adoption of a new system of reporting data in terms of partition coefficients which would be necessary for Purnell's system.
LITERATURE CITED (1) S.T. Preston, J . Chromatogr. Sci., 11, 201 (1973). (2) J. H. Purnell and J. M. Vargas Andrade, J. Am. Chem. Soc., 97,3585 (1975). (3) 6.J. 'Laub and J. H. Purnell, J . Am. m e m . soc., 98, 30 (1976). (4) R . J. Laub and J. H. Purnell, Anal. Chem., 48, 799, 1720 (1976). (5) R . J. Laub and J. H. Purnell, J. Chromatogr., 112, 71 (1975).
(6) R. J. Laub, J. H. Purnell, and P. S. Williams, J . Chromatogr., 134,249 (1977). (7) R. J. Laub, J. H. Purnell, D. M. Summers, and P. S. Williams, J. Chromatog., 155, 1 (1978). (8) R. J. Laub and R. L. Pecsok, "Physiochemlcal Appllcatlons of Gas Chromatography", John Wlley and Sons, New York, 1978. (9) J. F. Parcher and P. Urone, J . Gas Chromatogr., June 1984.
(10) W. R. Supina, "The Packed Column in Gas Chromatography", Supelco
Inc., Bellefonte, Pa., 1974.
RECEIVED
for review September 11, 1978. Accepted January
25, 1979.
SimuIta neous Determination of 4- ChI oro-2- methy Iphenoxyacetic Acid and Its Metabolites in Soil by Gas Chromatography Mohammad A. Sattar and Jaakko Paasivirta" Department of Chemistry, University of Jyvaskyla, SF 40 100 Jyvaskyla 10, Finland
Analysis of MCPA (4-chloro-2-methylphenoxyacetlc acid) and two of Its main metabolites 4 chloro-o-cresol and J-chloro3-methylcatechol have been studied by gas chromatography of their pentafluorobenzyl derlvatives simultaneously in four different soil materials. After derivatlration of the residue extract, three dlfferent clean-up procedures were tried. The best recoveries of compounds from soils were obtained when the extraction was performed by shaking with ether-acetone-heptane-hexane (2:l:l:l) from acidified soil and when the cleanup was done by TLC.
Phenoxyalkanoic acid herbicides prevent direct gas chromatographic determination because of the high polarity or low volatility of the compounds and must be converted to their more volatile derivatives. The sensitivity of the EC detector toward alkyl esters of MCPA (4-chloro-2-methylphenoxy acetic acid (I)), MCPB (4-chloro-2-methylphenoxy butyric acid) etc. is very poor. The methyl ester of MCPA was 100 times less sensitive to electron affinity detection than 2,4-D methyl ester ( I ) . Chau and Terry ( 2 ) reported the formation of pentafluorobenzyl derivatives of 10 herbicidal acids including MCPA (I). They found that 5 h was an optimum reaction time at room temperature with pentafluorobenzyl bromide in the presence of potassium carbonate solution. Agemian and Chau (3) studied the residue analysis of MCPA (I) and MCPB from water samples by making the pentafluorobenzyl derivatives. Bromination ( 4 ) , nitrification (5), and esterification with halogenated alcohol ( 1 ) have also been used to study the residue analysis of MCPA (I) and MCPB. Recently pentafluorobenzyl derivatives of phenols and carboxylic acids (6, 7 ) were prepared for detection by ECD a t very low levels. Pentafluorobenzyl bromide has also been used for the analytical determination of organophosphorus pesticides (8). MCPA (I) is one of the most effective hormone herbicides. 4-Chloro-o-cresol (11),5-chloro-3-methyl catechol (111) and cis,cis-4-chloro-a-methyl muconic acid (IV) were first identified as metabolites of MCPA (I) by Gaunt and Evans (9). Several other investigators have also studied the microbial degradation of MCPA (10-14). The technical product of 0003-2700/79/0351-0598$01 .OO/O
Table I. Physical and Chemical Characteristics of the Finnish (i and ii, Kemira Co.)and Bangladesh (iii and iv) Soils
soil types
moisture, % field capacity, % ignition loss, % PH organic carbon, % organicmatter, % coarse sand, % fine sand, % silt, % clay, %
sandy
clay
sandy
clay, i
loam,
loam, iii
clay,
13.9 28.1 33.2
14.8
2.0 12.1 2.2 6.6 0.6 1.1 5.1 20.7 58.5 15.7
2.3 15.5 2.0 7.5 0.7 1.2
4.6 10.3 17.8 19.7 31.1 30.1 18.7
ii
34.0 36.0 4.8 12.2 21.1 10.8 24.2 25.3 39.5
iv
4.9 32.7 18.9
42.4
MCPA in Finland contains approximately 4% of I1 as a n impurity (15). MCPA (I) is a widely used pesticide in Finland especially against herbs in the grain field (16). This is due to the confirmation of MCPA (I) as a safe compound (17, 18). Analysis of MCPA (I) from soil material has not been described in detail in the literature. We met with difficulties in efforts t o apply bromination (19)to detect the substance by ECD. Our determinations of MCPA methyl ester using FID were also not readily applicable to soil samples because of numerous interfering compounds. Thus we developed a n improved analysis method using the pentafluorobenzyl derivative of MCPA (20). In the present study, derivatization with pentafluorobenzyl bromide and clean-up processes are extended to the residue model compounds of I1 and I11 with four typical soils. The formulas of I-IV and the pentafluorobenzyl derivatives VI-VI1 are illustrated in Figure 1. The structures of the derivatives VI-VI11 were also verified by us with NMR spectra.
EXPERIMENTAL Two Finnish (Kemira Co., Helsinki) and two typical Bangladesh (Soil Science Department, Agriculture University, Bangladesh) soils were used for the experiment. The soils were dried at room temperature, ground to pass through a 2-mm sieve and stored in plastic containers. The physical and chemical characteristics 0 1979 American Chemical Society
ANALYTICAL CHEMISTRY, VOL. 51, NO.
I
FF&:
1 C8F5-CH2Br or V
61
Ill
IV
I
I
K2C03
I CI
ACETONE
c
I F
eCH3 Ll
Flgure 1. Structures of MCPA (4-chloro-2-methylphenoxyacetic acid, (I)), its metabolites 4-chloro-o-cresol (II), 5-chloro-3-methyl catechol (III), 4-chloro-2-methyl muconic acid (IV), reagent pentafluorobenzyl bromide (V), and the derivatives VI-VI11 from 1-111
of the soils are presented in Table I. Soil Analysis. The moisture content, field capacity, and the particle size distribution (sand, salt, and clay) of the soils were determined by the method of Piper (21) and the ignition loss by Ball's method (22). Soil pH was determined with a pH (23) and organic carbon by wet oxidation method (24). The textural classification of the soils was made using the triangular coordinate (25). Soil Extraction Experiment. Five or ten grams of soil was taken in a 250-mL beaker. Then 250, 250, and 250 pL or 500, 500, and 500 pL of 0.1% solution of compounds I (MCPA-Na salt in water, Kemira Co.), I1 (4-chloro-o-cresol in ether, synthesized in our laboratory) and I11 (5-chloro-3-methyl catechol in ether, synthesized in our laboratory) were added (1:l:l) to the soil, respectively, and mixed well with a glass rod. Water, 1 or 2 mL, was added to make the soil about field condition and stirring was continued until the mixture was uniform, then 1-3 g anhydrous sodium sulfate was added, again mixed well, and allowed to stand for an hour. The experiment was continued either by shaking or Soxhlet extraction with different solvent systems. The shaking extraction was performed by transferring the soil sample to a shaking flask with 50 mL of solvent and shaking for 40 min with a Griffin flask shaker under a tight cork. The mixture was filtered through paper with 1 g of anhydrous sodium sulfate and the shaking procedure repeated with another 50 mL of solvent. The combined filtrates were evaporated and transferred with diethyl ether to a volumetric flask to make 10 mL. of ether solution. The solvent systems selected in the previous study (20) were (1) ether-acetone-hexane-heptane (2:l:l:l) for fresh and acidified soils and (2) ether-chloroform (l:l), adjusted to pH 3.0 by 5 N HCl or 1 N NaOH solution for fresh soils only. The soil acidification was performed by using 3 or 5 mL of 1 N H3P04or 30% H 8 O 4solution after transferring the soil to the shaking flask and mixed uniformely for 10-15 min before the addition of the solvent mixtures. Soxhlet extraction was applied to both fresh and acidified soils for 24 h with chloroform. The soil acidification was done before transferring the sample to the extraction thimble. The extract was evaporated and transferred with ether to a volumetric flask to make 20 mL of ether solution. Similar extractions were also carried out with all the four soils under study. The blank experiments were performed with soils. Derivatization Experiments. Next 100 pL or 200 pL or 400 pL or 500 pL of 0.1% solution of compounds I or I1 or I11 was transfered to a 15-mL centrifuge tube with 200 pL pentafluorobenzyl bromide (1% solution in acetone), 50 pL 30% potassium carbonate solution, and 4 mL of acetone, shaken vigorously, and allowed to stand at room temperature for 3 h. Then 2 mL of n-heptane was added and the solution was evaporated by a nitrogen gas stream and transferred with ether to a volumetric flask to make 10 mL of a crude model compound
6,MAY 1979
599
derivative solution (model samples). Similar derivatizations were performed with the soil samples using 100 pL or 200 pL from 10 mL of the shaking or soxhlet extract. The blank soil extract was also treated. Clean-up Experiments. (i) Water/Toluene Shaking. Next 100 pL or 200 yL from 10 mL of the crude derivative of model compounds or soil samples was taken to a 15-mL glass-stoppered centrifuge tube and evaporated by a nitrogen gas stream. Then 3 mL distilled water and 10 mL toluene were added and the stoppered tube was shaken vigorously. The layers were separated and the toluene layer was dried over anhydrous sodium sulfate. The 100-pL blank solution was also treated. (ii) TCL Cleanup. Standard glass chromatoplates (20 X 20 cm) were prepared with a Desaga-Brinkmann model S-11 applicator to make a 1-mm layer of silica gel G (type 60, Merck) using slurry with water (1:2 w/v). The plates were activated at 110 "C for 12 h. The plates were divided by vertical lines into 5 sections leaving 1 cm from the side of the layer. Two sections were for the soil samples (100 and 200 pL) and three for the standards I, 11, and I11 samples (50 pL each). The model soil samples and standards were spotted (100- or 200-pL pipets, H. E. Pedersen, Denmark) to a starting line 1 cm from the bottom and eluted with dichloromethane (Merck) for 40 min. The air-dried plates were partly covered (sample section) with aluminum foil and the noncovered standard sections were sprayed with 0.5% diphenyl amine solution in ethanol. Then the standard (1-111) could be seen in UV light as a brown spot at the same distance from the bottom of the plate. Each sample fraction was scraped as a 2-cm high zone from the level of the standard spots, inserted into a glass tube (10 X 1 cm) on a cotton stopper, and packed to form a tight column with the aid of a glass rod. The column was then eluted with diethyl ether to a measuring flask to make 10 mL. Cleanup of the blank soil derivative solution was also performed. (iii) Column Cleanup. The silica gel used (60-200 mesh, Merck) was activated by heating at 130 "C for 14 h and then deactivated by adding 5% (w/w) of distilled water and shaking (Griffin) for an hour. The material was poured to a 10 x 1 cm glass tube on a cotton stopper to form a 4-cm high column. Then 100 or 200 pL from 10 mL of crude model or soil sample derivative solutions or 100 pL of the blank derivatization solution was pipetted to a 15-mL centrifuge tube, evaporated by a nitrogen gas stream and dissolved in 5 mL of hexane. n-Hexane, 5 mL, was added to drain on the top of the silica gel column. Then the sample in hexane was added by rinsing the centrifuge tube with hexane. Excess of the pentafluorobenzyl bromide and contaminants were removed by eluting with 10 mL of toluene-hexane 1:3 mixture (v/v). Then the purified derivative was collected by eluting with 3:l toluene-hexane mixture to a volumetric flask to make 10 mL. Gas Chromatographic Determinations. A Varian Model 600 gas chromatograph with 3H ECD was used. The column was a glass coil 1.5 m long, inside diameter 1.5 mm filled with 6% of the 4:l mixture of QF-1 and SF 96 silicon phases on Chromosorb W (acid washed, silanized) 100/200 mesh. Temperatures applied were 200 "C for column and detector, 225 "C for injector. Nitrogen was used as carrier gas, 30 mL/min. For determination of the recovery in each experiment, pure 1, 2, and 3 pL of the soil after clean-up procedure and 1 and 2 pL of model samples were injected. The areas of the peaks of the derivatives VI, VII, and VI11 of the compounds 1-111 were measured and compared to the peak area of the respective standard. Standard Solution. Next 100 mg each of compound I or I1 or 111,200 pL pentafluorobenzyl bromide, 1 mL of 30% potassium carbonate, and 4 mL of acetone were shaken vigorously in a 50-mL glass-stoppered flask and then allowed to stand for 3 h; 2 mL of n-heptane was added and evaporated with a nitrogen stream. Then 5 mL distilled water and 20 mL toluene were added and the mixture was shaken well. The toluene layer was separated and dried over anhydrous sodium sulfate. After evaporation with a nitrogen gas stream, the reside was verified by GLC, infrared, and 'H NMR spectra to be a pure pentafluorobenzyl derivative of VI, VII, or VIII. A weighed amount of the residue was diluted to form a standard solution which contained 100 pg each of the derivative VI of I, VI1 of 11, or VI11 of I11 in 1pL. This corresponds to 58.47 pg of I, 44.19 pg of 11, and 30.51 pg of I11 in the original
600
ANALYTICAL CHEMISTRY, VOL. 51, NO. 6, MAY 1979
Table 11. Clean-up Experiments of the Pentafluorobenzyl Derivatives: V I from MCPA (I), V I 1 from 4-Chloro-o-cresol (11) and VI11 from 5-Chloro-3-methylcatechol (1II)O shaking with water/toluene
a
compound
N
I I1 I11
16 16 16
Results as averages
-
column
TLC
X
s
N
94.7 91.9 79.0
2.06 2.15 1.77
16 16 16
X
s
N
97.6 94.7 80.3
1.25 1.40 1.10
16 16 16
X
S
85.3 82.9 70.7
5.25 5.96 4.89
(x)of the % recoveries of N experiments with standard deviations s.
samples in wL. A mixed solution was prepared to form a standard for simultaneous determination of I, 11, and 111. The limit of detection in gas chromatography was found to be 21 pg of I, 22 pg of 11, and 24 pg of I11 as their derivatives. This proved to be sufficiently low for the present analyses where the expected peaks in the resulting gas chromatograms corresponded to 100 pg amounts of 1-111.
RESULTS AND DISCUSSION Clean-up methods were tested using the model sample solutions of the pentafluorobenzyl derivatives VI-VI11 of the compounds 1-111. For each of the model samples, 16 experiments were done by each of the three clean-up procedures. T h e recoveries of I, 11, and I11 as derivatives were calculated and averaged for each set of 16 gas chromatograms obtained. The results are collected in Table 11. The differences between the methods for each compound and between the compound recoveries for each method were investigated by t-tests and found to be very significant (p < 0.1%) with two exceptions: for catechol 111, the difference between water/toluene shaking and T L C clean-up methods was only slightly significant ( p < 10%) and for column cleanup, there was no significant difference between the recoveries of MCPA (I) and cresol 11. TLC cleanup proved to give the highest recoveries of all three compounds. Water-toluene shaking gave somewhat and column cleanup considerably lower recoveries. T h e pilot analysis experiments resulted in 48 gas chromatograms for each combination of soil type, extraction, and clean-up method. T h e recoveries of I, 11, and I11 were calculated for each chromatogram and then averaged (N= 48) to yield results which are collected in Table 111. Our preliminary results from the analysis of MCPA (I) from fresh soil (20) had indicated that water/toluene shaking was a slightly more effective cleanup than TLC. Table I11 shows t h e same result for the recovery of I from fresh soil in most cases. However, the results for compounds I1 and I11 and also for MCPA (I) when the soil is acidified clearly show that the TLC cleanup generally is the most effective one. Water/ toluene shaking gives nearly as good results and thus could be the best choice for routine determinations because of its simplicity. Acidification, preferably with phosphorus acid, of the soil before the extraction increases the recoveries regardless of the method of extraction or cleanup used. The shaking extraction was generally more effective than Soxhlet but the Soxhlet extraction of the soils after acidification with H3P04also gave satisfactory results. The mixed solvent ether-acetone-hexane-heptane (2:l: 1:l) which had been selected in the preliminary study (20) for the optimal extraction of MCPA (I) proved to be a n excellent solvent system for the residue analysis of all three compounds 1-111 with the shaking method. The experiments from fresh soil with ether-chloroform (1:l) p H 3.0 showed slightly lower recoveries (Table 111). Soxhlet extraction with chloroform, on the contrary, gave quite satisfactory results if the soil was acidified with phosphorus acid. This method is most convenient for routine analyses. Generally, the recoveries were far below 100%. Obviously the extractions were not complete because of the properties
of the soils studied. Yip (26)reported that the binding of the soil particles and organic matter with the herbicide residues prevented the complete extraction of them with an organic solvent. Upchurch and Mason (27) found that the extent of adsorption of herbicides is highly dependent on the type of organic matter and clay as well as on the amounts of their constituents in a soil. The present results (Table 111) allow us to compare the possible influence of the characteristics of the four soils studied (Table I) on the recoveries. The results of fresh soil treatments show that the p H has no significant effect in the area 4.6-7.8. Also, one could conclude that the soil texture (especially the differences in clay contents) has no significant influence on the amounts of the residues 1-111 recovered. The present results support a general conclusion that organic matter is the main factor which influences to the fate of herbicides and their analyses in the soil. T h e present Finnish soils (i, ii) had high but Bangladesh (iii, iv) very low organic matter contents (Table I). Consequently, significantly higher recoveries of the residues 1-111 were generally obtained from the latter soil materials than from soils i and ii. In addition, the Finnish soils gave selectively lower 5-chloro3-methyl catechol (111) recoveries related to recoveries of I and 11. This can be clarified by calculating ratios of the average recoveries of different residues 1-111. The overall average ratio of MCPA (I) recovery from Bangladesh soil to Finnish soil was 1.044 & 0.031. T h e corresponding ratios for 4-chloro-o-cresol (11) and 5-chloro3-methyl catechol (111) were 1.051 f 0.028 and 1.139 f 0.024, respectively. Recovery ratios II/I and III/I were calculated for each soil and analysis combination. The former ratios were found to be independent but the latter dependent on the soil type from the results of the t-tests between the different means. For example, the mean II/I value from 42 ratios (from Table 111) of Finnish soils i and ii was % = 0.9439 with standard deviation s = 0.0234, and the corresponding mean II/I from 42 ratios of Bangladesh soils iii and iv was f = 0.9390 with s = 0.0234 (difference insignificant). These results show that MCPA (I) and 4-chloro-o-cresol (11) behave very similarly in the analysis procedures regardless of the soil type. On the contrary, the ratio III/I average from Finnish soils was % = 0.8022 with s = 0.0174 but from Bangladesh soils 5 = 0.8704 with s = 0.0364 (a very significant difference, p < 0.170). Thus, organic matter seems to have a very strong degreasing efect on the recovery of 5-chloro-3-methyl catechol (111) from soil. The nature of the effect is uncertain, thus far. It might rise from stronger binding of I11 to organic matter substances or faster metabolism of I11 in live soil than I or 11. The future field experiments planned by us might shed further light on this question. For routine multicomponent residue analysis of 1-111 from soil, we recommend, based on the present experience, extraction of the acidified (H3P04)soil by chloroform with Soxhlet, derivatization with pentafluorobenzyl bromide and cleanup by water/toluene shaking for determination with gas chromatography using EC detection.
ANALYTICAL CHEMISTRY. VOL. 51, NO. 6, MAY 1979
P
97% C???
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aww
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mat-
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601
002
ANALYTICAL CHEMISTRY, VOL. 51, NO. 6, M A Y 1979
LITERATURE CITED ( I ) W. H. Gutenmann and D. J. Lisk, J. Assoc. Off. Anal. Chem.. 47, 353
(1964). (2) A. S. Y. Chau and K. Terry, J. Assoc. Off. Anal. Chem., 58. 1294 (1975). (3) H. Agemian and A. S. Y. Chau, Analyst (London), 101, 732 (1976). (4) W. H. Gutenmann and D. J. Lisk, J . Assoc. Off. Anal. Chem., 46, 859 (1963). (5) C. A. Bache, D. J. Lisk, and M. A. Loos. J. Assoc. Off. Anal. Chem., 47, 348 (1964). (6) F. K. Kawahara, Anal. Chem., 40, 1009 (1968). (7) F. K. Kawahara, Envlron. Sci. Technoi., 5 , 235 (1971). (8) J. Coburn and A. S. Y. Chau, J. ASSOC.Off. Anal. Chem., 5 7 , 1272 (1974). (9) J. K. Gaunt and W. C. Evans, Biochem. J., 122, 519 (1971). (10) T. I. Steenson and M. Walker, J. Gen. Microbiol., 16, 146 (1957). (11) J. M. Bollag, C. S. Helling, and M. Alexander, Appl. Microbiol., 15, 1393 (1967). (12) J. K. Gaunt, Ph.D. Thesis, University of Wales, Bangor, 1962. (13) J. K. Gaunt and W. C. Evans, Biochem. J., 122, 533 (1971). (14) M. A. Loos, J. M. Bollag, and M. Alexander, J. Agric. Food Chem., 15, 858 (1967). (15) L.Rashen, M. L. Hattuh, and A. U. Arstih, Bull. Environ. Contam. Toxicoi., 18, 565 (1977). (16) K. Tiittanen and H. Blomqvist. Kern.-Kemi, 3, 424 (1976). (17) M. R. Gurd, G. L. M. Harmer, and B. Lessei, Food Cosmet. Toxicol., 3, 883 (1965). (18) H. G. Verschuuren. R. Kroes, and E. M. Den Tonkelaar, Toxicol.. 3, 349 (1975).
(19) V. Mattinen. H. Siltanen, and A. L. VaRa, "Investigations of the Pesticide Residues", State Institute of Agricultural Chemistry, No. 7, Helsinki, 1972, p 40. (20) M. A. Sattar, M. L. Hattuh, M. Lahtipera, and J. Paasivirta, Chemosphwe, 11, 747 (1977). (21) C. S. Piper, "Soil and Phnt Analysis", Adehide University Press, Adelaide, Australia, 1950. (22) D. F. Ball, J. Soil Sci., 15, 84 (1964). (23) M. L. Jackson, "Soil Chemical Analysis", hentice-Hall, Englewood Cliffs, N.J., 1962. (24) A. Walkey and I.A. Black, Soil Scl., 37, 29 (1934). (25) J. A. Prescott, J. K. Tayor, andT. J. Marshall, Trans. 1st. Comm. Inst. SOC. Soil Sci. Versallles, 143 (1934). (26) G. Yip, J. Chromarogr. Scl., 13, 225 (1975). (27) R. P. Upchurch and D. D. Mason, Weeds, IO, 9 (1962).
RECEIVED for review October 10, 1978. Accepted January 15, 1979. This work has been supported by the Department of International Developement Co'operation, Ministry of Foreign Affairs, Finland, and by Kemira Company, Finland. T h e results have been presented by M.A.S. in an oral communication at the EUROANALYSIS I11 congress in Dublin, Ireland, Aug. 19-25, 1978.
Gas Chromatographic Determination of Benzene and Toluene in Crude Oils Patrick L. Grizzle" and Harold J. Coleman
U.S. Department of Energy, Bartlesville Energy Technology Center, P.0. Box
A gas chromatographic method for the determination of benzene and toluene In crude oils has been developed and utilized In the analysis of 102 crude-oil samples. The method, which is readily adaptable to most chromatographs, uses a simple backflushing technique with nonpolar (OV-1) and polar ( 1,2,3-tris( 2-cyanoe1hoxy)propane) columns in series. Repeatability and accuracy of the method are better than f 2 % and f4% of the measured values for benzene or toluene. The Importance of such data for the identification of crude oils from a common geological origln is demonstrated. For predictive purposes, correlations of benzene and toluene weight percents with routinely measured physical properties of crude oils have been developed. Reasonable estimates of benzene and toluene concentrations can be obtained from these correlatlons.
Recent federal environmental regulations have prompted the determination of known or possible carcinogenic compounds in many commercial products. Of these compounds, benzene has probably received the greatest attention. Occupational exposure to benzene from industrial and laboratory environments as well as exposure from commercial petroleum products such as gasoline and from crude oils is currently being carefully monitored and controlled. Although benzene levels in crude oils, gasoline, and other petroleum-based products have been periodically measured for many years, rapid and accurate methods of analysis are now of major importance. In addition to tedious physical separation methods ( I ) , benzene contents in crude oils and gasolines have been determined by various analytical methods. These include in-
1398, Bartlesville, Oklahoma 74003
frared ( 2 , 3 ) , Raman ( 4 ) , and ultraviolet spectroscopy ( 5 ) , polarography (6), and gas chromatography (7-11). Of these methods, gas chromatography provides both a rapid and reliable quantification of benzene. For gasoline, standard gas chromatographic methods (ASTM D 2267 and D 3606) have been established (7, 11). Although ASTM D 2267 has an upper temperature limit of 300 O F , this limit has been extended (8). Alternatively, ASTM D 3606 is directly applicable t o the determination of benzene in motor and aviation gasolines. However, no standard method for the determination of benzene in crude oils has been established. This paper presents a rapid and reliable gas chromatographic method for the determination of benzene and toluene in crude oils and other fossil fuels. The method can be easily adapted to any gas chromatograph with flame ionization detection capabilities. The method was developed concurrently with ASTM D 3606 and the data were obtained prior to acceptance of D 3606. Although, in principle, D 3606 should be applicable to the analysis of petroleum products other than gasoline, the presented method can be viewed as an extension of this standard method to allow for analysis of a wider range of petroleum products. In addition, this investigation both correlates the benzene and toluene data obtained on 102 samples with routinely measured physical properties of crude oils for predictive purposes and demonstrates the importance of such data to the identification of crude oils from a common geological origin.
EXPERIMENTAL Apparatus. A Hewlett-Packard model 5830A gas chromatograph equipped with a heated injector block, dual flameionization detectors, and a temperature programmer was used.
This article not subject to U S . Copyright. Published 1979 by the American Chemical Society
