Gas Chromatography - Tandem Techniques - Examples of GC/MS Spectrometry Applications > Determination of Pesticides in Biological Matrixes > Page 82

The second portion was dissolved in 0.5 ml of methanol, added to 0.5 ml of diazomethane in diethyl ether and then allowed to stand for 1 hour at room temperature. The excess of diazomethane was decomposed with 0.1 ml of acetic acid, 0.3 ml of the anthracene standard added and the mixture shaken vigorously. 3 ml samples were used for analysis. The detection limit was estimated to be 14 to 180 pg per ml for a 1 liter water sample. The recover from the water was projected (statistically) to range between 2.6 and 22.6% and the recovery process obviously requires some further investigation.

The second portion was dissolved in 0.5 ml of methanol, added to 0.5 ml of diazomethane in diethyl ether and then allowed to stand for 1 hour at room temperature. The excess of diazomethane was decomposed with 0.1 ml of acetic acid, 0.3 ml of the anthracene standard added and the mixture shaken vigorously. 3 ml samples were used for analysis. The detection limit was estimated to be 14 to 180 pg per ml for a 1 liter water sample. The recover from the water was projected (statistically) to range between 2.6 and 22.6% and the recovery process obviously requires some further investigation.

 

Determination of Pesticides in Biological Matrixes

 

GC separations followed by negative ion chemical ionization mass spectrometry has been shown to be a very sensitive method for monitoring pesticide contamination of vegetable foodstuff (28). The procedure used was as follows. 15 g of the material was extracted with 60 ml of ethyl acetate and 13 g of anhydrous sodium sulfate and separated. The residue was then extracted with a further 30 ml of ethyl acetate and the two extracts combined. A 30 ml aliquot was evaporated to dryness in a rotary evaporator at 60 C. The residue was then dissolved in 5 ml of ethyl acetate and was used directly for analysis. The technique was tested using pepper extracts spiked with chlorothalonil and procymidone. 2 ml samples were injected onto a capillary column 30 m long, 0.25 mm I.D. carrying a film 0,25 mm thick of crosslinked 5% diphenyl-95% dimethylsiloxane Initially the column was held at 70 C for 1 minute and then programmed to 180 C at 35 C per minute, then to 240 C at 10 C per minute with a final hold at 240 C for 5 minutes. The eluted materials were passed to the mass spectrometer and ionized by negative ion chemical ionization. Chromatograms and spectra obtained from the pesticides are show in figure 67.