Determination of Chlorophenoxy Acid Herbicides by Liquid Chromatography Using Carbon-14 Tracers

摘要

The extractive recovery of 2,4-dichlorophenoxyacetic acid (2,4-D) and 2-(2,4,5-trichloro)phenoxypropionic acid (Silvex) from environmental samples was evaluated using carbon-14 tracers of the acid form of both herbicides. Recoveries using methylene chloride or 1:1 methylene chloride:acetone for solids exceeded 75% when the material being extracted was maintained at an acid pH (pH less than or equal to2). Following extraction, the extract is taken to dryness and then dissolved in the solution being used for HPLC elution. Two slightly different isocratic elutions with reversed phase columns were studied. In the first system studied a heavily loaded (18% carbon by weight), completely endcapped C18 reversed phase column was eluted with an aqueous solution of 30% (v/v) acetonitrile that contained 0.001 M concentration of a pH 4.6 acetate buffer. The effluent from this column was monitored at 280 nm. The minimum amount detected, when monitoring at 280 nm, is 100 ng of either Silvex or 2,4-D in the injected sample. A second isocratic elution system avoided the use of a buffered eluent by utilizing a high performance reversed phase column and an aqueous methanol (20% v/v) eluent. This second column has been monitored at multiple wavelengths with a diode array detector. The sensitivity of detection can be greatly increased at wavelengths below 240 nm; however, any real sample must be very ''clean'' in order to avoid interferences when monitoring below 230 nm. Thus monitoring at 280 nm is probably optimal for real environmental samples. At this wavelength the detectable concentration of either herbicide in the solution being injected is 5 ppM for a 20 mu l injection. (ERA citation 12:037372)