DETERMINATION OF HERBICIDES BY GAS-CHROMA TOGRAPHY NEGATIVE-ION CHEMICAL-IONIZATION MASS-SPECTROMETRY WITH AUTOMATED SAMPLE PREPARATION INSTRUMENT

A method for the automatic analysis of 8 chlorinated phennoxy acid her bicides was developed using an automated sample preparation instrument in combination with a GC/MS with negative ion chemical ionization (NC I). The instrument can automate many sample preparation steps, such as solid phase extraction (SPE) and derivatization. All of the following steps were automated. 1) A sample of 10 ml was injected into the SPE cartridge (THC) where 8 herbicides were retained. 2) The cartridge was then washed with dichloromethane. 3) The 8 herbicides were then eluat ed from the washed cartridge using 0.1% sulfuric acid-methanol (1 ml). 4) The eluate was evaporated to dryness. 5) A derivatizing reagent, 2 % pentafluorobenzyl bromide (PFBBr) in toluene and triethylamine, was added to the eluate. 6) And finally, the reaction mixture-sample solut ion was injected into the GC/MS by high pressure pulsed splitless inje ction. The total analysis time for 4 samples was approximately 4 hrs. The detection limits of the 8 herbicides ranged from 10 ppt to 50 ppt. The overall recoveries of the herbicides except for picloram were fro m 82 to 102% {RSD (n = 5) were from 4.1 to 9.1%} for river water and f rom 96 to 116% {RSD (n = 5) were from 4.3 to 7.3%} for wine, respectiv ely. The recovery of picloram was about 50%, but we could get good res ults by using a standard calibration curve.