Gas Chromatography - Tandem Techniques - Examples of GC/MS Spectrometry Applications > Analysis of Waxes and Lipid Type Materials > Page 81

Okumyura et al., (27) also developed an alternative type of extraction procedure to determine carbamate pesticides in water samples. The extraction and analysis procedure, is shown as a block diagram in figure 66.

It is seen that the herbicide peaks are clearly and unambiguously revealed. The individual mass spectra of Atrazine (retention time 16.30 minutes) and Simazine (retention time 16.36 minutes) are shown in figures 65, C and D, The spectra are clear and more than adequate to confirm the identity of the two herbicides.

 

Okumyura et al., (27) also developed an alternative type of extraction procedure to determine carbamate pesticides in water samples. The extraction and analysis procedure, is shown as a block diagram in figure 66.

Figure 66. Extraction Procedure for Determining Carbamate Pesticides in Water

 

The modus operandi was as follows. A sample of water 1 litre in volume was extracted for a period of 5 minutes with a 100 ml portion of dichloromethane for. This was repeated three times and the extracts combined and concentrated on a water bath at 70-80ūC. The concentrate was then divided into two equal portions and each portion evaporated to dryness in a stream of nitrogen.

 

One portion which was used to determine the following six types of carbamate, 3-(sec-butyl)phenyl N-methylcarbamate, 2-isopropoxyphenyl N-methyl-carbamate, 3,5-xylyl N-methyl-carbamate, 3-methylphenyl N-methyl-carbamate, 2-isopropyl-phenyl N-methyl-carbamate and 1-naphthyl N-methyl-carbamate. This portion was dissolved in 0.2 ml ethyl acetate and treated for 2 hours at 50ūC with 0.2 ml of trifluoroacetic anhydride. 5 ml of a n-hexane-ether mixture (94+6), together with 0.2 ml of an external standard solution of anthracene (1.0 ppm in n-hexane) was then added. The mixture was washed three times with 5 ml of water, and concentrated to a volume of 2 ml. 3 ml of this solution was used for analysis by GC/MS employing the single ion monitoring (SIM) mode.