Determination of Chlorophenoxy Acids in Formulations by Gas-Liquid Chromatography of Their Trimethylsilyl Derivatives

Abstract

Abstract A rapid, precise, and specific method for the analysis of free acid and amine salt formulations of chlorophenoxy acids has been developed. Samples containing the amine salts are prepared by addition of dioxane and removal of the water/dioxane azeotrope by rotary evaporation. The trimethylsilyl esters are prepared by incubation of free acids or the above dry residues with N,O-his (trimethylsilyl) acetamide. The esters are chromatographed on 5% SE-30 on 80–100 mesh Chromosorb W with column temperature programming, using pyrene as an internal standard. The method has undergone a ruggedness test which showed very little sensitivity to changes in many of the chromatographic and derivatization conditions. The method was compared to the official final action infrared method for 2,4-D amine salt formulations, 6.A15–6.A19, and to a modified infrared method using the C–CI stretching band at 15.6 μm for measurement. The official method gave a relative standard deviation of 9%, while the modified infrared method and the gas chromatographic method gave relative standard deviations of 1.2 and 1.0%, respectively. The gas chromatographic method resulted in values not significantly different from those of the official method. With the modified infrared method, high results were obtained for some samples, presumably due to the presence of chlorine-containing compounds other than 2,4-D. Recovery of acids and amine salts for the gas chromatographic method is 100.5±1.0%. The method distinguishes between MCPA, MCPP, 2,4-D, 2,4- 5-T, silvex, and 2,4-DB.