Gas Chromatographic Analysis of Dalapon in Water P. A. Frank and R. J. Demint Crops Research Division, Agricultural Research Service, U. S. Department of Agriculture, in cooperation with the Division of Research, Bureau of Reclamation, Denver, Colo.
An efficient and sensitive procedure for extraction and analysis of dalapon (2,2-dichloropropionic acid) in water was developed. Acidified and NaC1-saturated samples containing dalapon were extracted with diethyl ether. After partitioning the extract through bicarbonate and back t o ether. the dalapon was converted to its methyl ester. Analysis was by electroncapture gas chromatography. Recoveries of dalapon from water averaged 9 6 z . and the minimum level of detection was 0.1 ng.
S
everal methods for analysis of 2,2-dichloropropionic acid (dalapon) residues have been reported. The spectrophotometric method of Smith et at. (1957), which involves the hydrolysis of dalapon to pyruvic acid and its conversion t o 2,4-dinitrophenylhydrazone,has been used extensively, but requires a great deal of time. Abbott et of. (1964) described paper and thin-layer chromatographic systems for determining dalapon. In addition to being timeconsuming, these systems also lack the sensitivity required for most present-day residue analysis. The gas-chromatographic method of Getzendaner (1963) was developed to analyze dalapon acid directly and it permits more rapid analysis than other procedures. However, the anomalous behavior of the chromatographic column used would make it unsatisfactory to many analysts. The present studies on dalapon residues in water involved analysis of a large number of samples. The method reported here was developed for that purpose, and is rapid. reliable, and highly sensitive.
collected and combined in an accurately graduated 15-ml. centrifuge tube. If the analysis for dalapon was delayed, the tubes were covered and held in a freezer to retard evaporation. The dalapon samples were prepared for analysis by evaporating ether from the centrifuge tubes at room temperature under a gentle stream of dry air. After reducing the ether volume t o 2 ml., an equal volume of 0 . 5 z diazomethane in ether was added to each tube. The tubes were rotated during addition of the diazomethane to wash down any dalapon adhering to the tube. Ten minutes were allowed for esterification. The volume of ether in each tube was adjusted t o exactly 4 ml. with additional ether, and the samples were ready for analysis. Analysis of Dalapon. The gas chromatograph used for analysis of dalapon was a n Aerograph Model 204. The instrument was equipped with a n electron capture detector and a 5-foot by ','&-inchstainless steel column packed with 60- t o 80-mesh Chromosorb P treated with hexamethyldisilane. The solid phase was coated with 10% F F A P (the esterification product of Carbowax 20-M and 2-nitroterephthalic acid). Column, detector, and injection port temperatures were 140°, 195", and 215" C., respectively. Nitrogen purified with a molecular sieve was used as the carrier gas at 30 ml. per min. The instrument range and attenuation were modified as required by the size of the dalapon sample analyzed. In most instances, an injection volume of 1 pl. was adequate for analysis of the samples. However, for very dilute solutions of dalapon, volumes as large as 5 p l . could be injected. Standard curves were prepared by injecting known quantities of dalapon into the gas chromatograph and plotting peak heights cs. sample weights in micrograms or nanograms.
Methods arid Materials Dalapon Extraction and Esterification. All water samples containing dalapon were brought to near-saturation with NaCl by addition of 34 grams of NaCl for each 100-ml. sample. HC1 diluted 1-to-1 with distilled water was used to adjust the water to p H 1. Water volumes of 500 ml. were extracted three times with 50-, 2 5 , and 25-ml. volumes of diethyl ether. Smaller volumes of water were extracted with correspondingly less ether. The combined ether extracts were extracted three times with 20, 10, and 10 ml. of 0 . 1 N N a H C 0 3 solution saturated with NaCl and adjusted to p H 8 with NaOH. The ether phase was discarded, and the combined buffer extracts were acidified to p H 1 with 1-to-1 HCI. The final extractions of dalapon acid from the acidified buffer were made with 5 , 4. and 4 ml. of ether. The ether phase was
Table I. Recovery of Dalapon from Water. Dalapon,
Dalapon
Concn., P.P.B.
Recoveryb
98 100 97 96 91 91
0.5 2.5 5
10 20 1000 b
Water volume of 500 ml. Average of three or more replicates
Volume 3, Number 1, January 1969 69
80. injection containing 5ng o f dalapon
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Figure 1. Chromatogram of dalapon extracted from distilled water showing peak configuration and retention time
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The two peaks immediately following the solvent peak are due t o the diazomethane used in esterification of dalapon
Figure 3. Chromatogram of dalapon extracted from 500 ml. of irrigation water
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Figure 2. Dalapon standard curve showing peak height quantity of dalapon injected 70 Environmental Science & Technology
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Figure 4. Chromatogram of dalapon extracted from a water sample containing 2,4-D, 2,4,5-T, and silvex I n addition to dalapon, the injected sample contained 5 ng. each of the three phenoxq herbicides
Results and Discussion Because of the sensitivity of the method, it should rarely be necessary t o work with samples larger than 1 liter. Recovery of dalapon from known samples of distilled water was very efficient and ranged from 91 to 100%. with an average recovery of 96% (Table I). Recovery from spiked samples of canal water ranged from 91 t o 99% and averaged 95.4%. Extracting solvents tested were benzene, hexane, carbon tetrachloride, chloroform and diethyl ether. Ether gave the most complete extraction, provided the water was saturated or near saturation with NaCI. To saturate the samples completely with NaCl required considerable time. Approximately 90 % saturation could be achieved more rapidly without reducing the efficiency of the ether extraction. The p H of the water affected the extractions. Extractions with ether at p H levels of 1 or below were satisfactory. However, a slight loss of dalapon was observed at p H 2 and almost complete loss at pH 3.5. Partitioning dalapon from the original ether extract through bicarbonate and back to ether served as additional cleanup of the samples and also reduced the volume of ether that had to be evaporated prior to esterification. Dalapon was converted t o the methyl ester with diazomethane, which was prepared as described by Erickson and Hield (1962). Synthesis of diazomethane by this procedure resulted in an ether solution of approximately 1 % diazomethane, which was safe t o handle and could be stored in a freezer for many weeks. Esterification with diazomethane was simple and rapid at room temperature. Dalapon in acid form was quite volatile, and care was taken in evaporating ether from the final extract. Evaporations were made without heat. and the ether volume was not reduced to less than 2 ml. Losses of 2 to 355 were observed when the final ether extracts were evaporated t o 2 ml. Reducing the volume to 1 and 0.5 ml. resulted in losses of 7 and IO%, respectively. Dalapon losses of 48% occurred when evaporation was discontinued just as the tubes reached dryness. Attempts to evaporate ether from the solution of the methyl ester of dalapon invariably caused large losses of dalapon. The 5-foot column with 10% F F A P as the stationary phase was selected as optimum for analysis of dalapon. A number of other stationary phases commonly used for analysis of chlorinated pesticides was examined with little success. The
peak configuration of dalapon was satisfactory and free of major interferences. After analyzing several hundred dalapon samples, no loss in efficiency of either column or detector was observed. The retention time was slightly more than 4 minutes, and the minimum level of detection was 0.1 ng. Precision of the method is +5%. A trace of dalapon extracted from distilled water is shown in Figure 1. The curve for dalapon concentration cs. peak height is shown in Figure 2. Water from a number of natural sources was extracted and analyzed for dalapon. N o substances that interfere with the analysis were encountered. Figure 3 shows a typical trace of dalapon extracted from irrigation water flowing through an agricultural area. Herbicides such as 2,4-D (2,4-dichlorophenoxyacetic acid) are extracted and converted to the methyl ester along with dalapon. However, these d o not interfere in the analysis and never appear on the chromatogram. Figure 4 shows the trace of an injection containing 5 ng. each of dalapon. 2,4-D, 2,4,5-T (2,4,5-trichlorophenoxyacetic acid), and silvex [2-(2,4,5-trichlorophenoxy)propionic acid], all in the form of their methyl esters. TCA (trichloroacetic acid) was present in some samples of irrigation water. This herbicide was also carried through the extraction and methylation procedures. In contrast to the phenoxy herbicides, it did appear on the chromatogram with dalapon and was analyzed very effectively. Retention time for TCA was 5.5 minutes. The analytical procedure reported here was developed and used exclusively for analysis of dalapon in water. Using the methods reported by others (Abbott et a[., 1964; Getzendaner, 1963; Smith et al., 1957) for extraction of dalapon, this procedure, because of its sensitivity and simplicity, should be useful in analysis of dalapon in soils and plant tissues. Literature Cited Abbott, D. C., Egan, H., Hammond, E. W., Thomson, J., Analysr 89, 480 (1964). Erickson, L. C., Hield, H. A,, J. Agr. Food Chem. 10, 204 (1962). Getzendaner, M. E., J . Assoc. Offic. Agr. Chemists 46, 269 (1963). Smith, G . N., Getzendaner, M. E., Kutschinski, A. H., J. Agr. Food Chem. 5,675 (1957). Receiced for reciew May 14,1968. Accepted November 8, 1968.
Volume 3. Number 1. January 1969 71
