The advantage of the above described method is in the determination of sulfide or organic thiols in sediments or turbid solutions t h a t are not amenable t o other procedures. The method would be extremely useful for determining any organic sulfide if it is known to be the only one present, which is true for many industrial effluents. We have analyzed 2 core samples from the nearby salt marsh for "organic sulfur" and found t h a t it varies from 2 to 8 times the inorganic sulfide content. Extraction tech-
niques are now being used to determine the nature of these compounds. Received for review December 26, 1973. Accepted April 22, 1974. This research was partially supported by Grant GX39141 from the National Science Foundation (Office for the International Decade of Ocean Exploration) and is part of the Controlled Ecosystem Pollution experiment, Grant GX-39148.
Derivatization and Gas Chromatographic Measurement of Some Thermally Unstable Ureas Donald G. Saunders and Lynn E. Vanatta Eli Lilly and Company, Greenfield Laboratories, Greenfield, Ind. 46 140
Analytical methods for trisubstituted urea herbicides usually involve acidic or basic hydrolysis of the urea to the corresponding amines. One or both of the hydrolysis products can then be measured colorimetrically after diazotization and coupling ( I ) or alternately by gas chromatography (GC) either directly (2) or after derivatization ( 3 , 4 ) . Direct GC methods for intact trisubstituted ureas are usually not analytically feasible because of the thermal decomposition reaction shown in the equation: 0
R,-S--C--SH-R I
I
It
-& R,-NH
I
+ O=C=h-R,
R. This thermal reaction usually does not go quantitatively to completion during GC, thus preventing reproducible measurement of the products formed. Attempts have been made to overcome this problem by employing special GC column techniques, either to prevent the thermal decomposition ( 5 , 6) or to assure complete decomposition to measurable products ( 7 ) . Some carbamate insecticides also undergo thermal decomposition during GC to yield a phenol and isocyanate ( 8 ) .Their analytical measurement usually involves hydrolysis followed by determination of the liberated phenol. Recently, several workers have reported on the derivatization of intact carbamates followed by determination by GC. Carbaryl (1-naphthyl N-methyl-carbamate) was reacted with acetic anhydride to give the N-acetyl derivative which was thermally stable during analysis by GC (9). Many carbamates have also been converted to stable perfluoroacylated derivatives which have been utilized in sensitive assays employing GC with electron capture (EC) detection (10,lI). (1) W. E. Bieidner, H. M. Baker, M. Levitsky, and W. K. Lowen, J. Agr. Food Chem., 2, 476 (1954). (2) J. J. Kirkland, Anal. Chem., 34, 428 (1962). (3) W. H. Gutenrnann and D. J. Lisk. J. Agr. FoodChem., 12, 46 (1964). (4) I. C. Cohen and B. 8. Wheals, J. Chromatogr., 43, 233 (1969). (5) C. E. McKone and R . J. Hance, J. Chromatogr., 36, 234 (1968). (6) C. E. McKone, J. Chromatogr., 44, 60 (1969). (7) D. Spengler and 8. Harnroll, J. Chrornatogr., 49, 205 (1970). (8) W. L. Zielinski, Jr., and L. Fishbein, J. Gas Chromatogr., 3, 333 (1965). (9) L. J. Sullivan, J. M. Eldridge, and J. B. Knaak, J. Agr. Food Chem., 15, 927 (1967). (10) S. C. LauandR. L. Marxmiller, J. Agr. FoodChem., 18,413 (1970). (1 1) J. N. Seiber, J. Agr. Food Chem.. 20, 443 (1972).
The necessity to develop a sensitive and selective method of detection for an experimental trisubstituted urea herbicide prompted an investigation into the possibility of preparing derivatives of ureas stable during GC. Other workers have shown that the treatment of some urea herbicides with silylation reagents produced derivatives with increased thermal stability (12). I t seemed reasonable t h a t other ureas would react with different reagents to form products amenable to sensitive assay by GC. We have successfully prepared a number of thermally stable derivatives of 1-(5-tert-butyl-1,3,4-thiadiazo1-2-y1)1,3-dimethylurea (I), a compound with promising herbicidal activity. Methods of preparation and GC data for these derivatives are presented. In addition, some of the derivatizing reagents are shown to be useful for preparing thermally stable products of the herbicides diuron (3-(3,4-dichloropheny1)-1,l-dimethylurea),fenuron (3-phenyl-1,ldimethylurea), and monuron (3-(p-chlorophenyl)-l,l-dimethylurea).
11
I
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