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Summary. The effects of sunlight and ultraviolet light (253.7 nm) on 4‐amino‐3,5,6‐trichloropicolinic acid (picloram) in a basic aqueous solution were investigated. Electron‐capture gas chromatography determinations showed that approximately 20% of a 2 × 10−2 M concentration of picloram was degraded for each 48‐hr exposure to ultraviolet light of an intensity of 200 μW/cm2. Decomposition by sunlight was slower and more variable. Precipitation of the degradation products with AgNO3 indicated that two chloride ions were liberated for each molecule of picloram that was degraded. Titrations indicated that acids were formed in the degradation process, and ultraviolet spectra showed that the pyridine nucleus was destroyed. Chromatograms of the methylated decomposition products showed that at least five products were formed. The effect of the addition of a free radical scavenger, hydroquinone, on the rate of decomposition was investigated but no definite conclusions could be drawn. La dégradation photolytique du piclorame

THE NEED for simple and sensitive methods for residue analysis of herbicides and other pesticides is apparent. Gas chromatography is often employed, but compounds containing an acid group must be esterified before injection into the chromatograph. Diazomethane or BF3-methanol is usually employed in the esterification process (1-4). The esterification of picloram (4-amino-3,5,6-trichloropicolinic acid) in soil, water, or forage samples has several disadvantages including the handling of toxic reagents, cumbersome extraction procedures and, most importantly, the predominance of interfering peaks, causing a lack of usable sensitivity.This paper describes an improved analytical technique based on the on-column decarboxylation of picloram, and the determination of the decarboxylated product by electroncapture gas chromatography. EXPERIMENTAL Apparatus. A Barber-Coleman gas chromatograph Model 5630 equipped with an electron capture detector and a 6-foot spiral glass ( 5 mm i.d.) column was modified to include a flow-through high temperature pyrolysis unit. The pyrolysis unit was constructed of vycor glass tubing (5 mm i.d.) packed with vycor chips (2-4 mm squares) and was connected ahead of the chromatographic column. The first 6 inches of the column were packed with 2 to 4 mm vycor chips, the next 3.5 feet with 3 Z SE-30 on 60-to 80-mesh Chromosorb W and the last 2 feet with 10% DC-200 on 60-to 80-mesh Gaschrom Q. The injector, pyrolysis, column, and detector temperatures were 290, 385, 165, and 240 "C, respectively. The carrier gas was nitrogen at an inlet pressure of 28 psi and a flow rate of 110 ml per minute. Further details on the construction of the pyrolysis unit have been described (5).Procedure. The appropriate amounts of picloram were dissolved in diethyl ether which had been saturated with water at 25 "C. Two microliters of this solution were injected into the pyrolysis chamber with an ice-cold syringe. The retention time and the concentration of the decarboxylated product were compared with those of a sample prepared in a preparative hot-tube reactor under conditions identical to those employed in gas chromatography. The decarboxylated product was found to be 4-amino-2,3,5-trichloropyridine; it had a melting point (149-149.5 "C), a mixed melting point undepressed, and NMR spectrum identical to those of a sample obtained by an unambiguous synthesis (6).

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