Capillary Chromatography - The Analysis of Pesticides
The Analysis of Pesticides
Pesticide analysis is important in optimizing crop protection, in a wide range of tests for pollution control (involving soils samples, water samples, food samples etc.), environmental studies and under certain circumstances for forensic purposes.
|1. Dichlorvos||8. Disulfoton||15. Stirophos|
|2. Mevinphos||9. Methyl Chlorpyriphos||16. Tokuthion|
|3. Unknown||10. Methyl Parathion||17. Merphos|
|4. Ethoprop||11. Ronnel||18. Fensulfothion|
|5. Phorate||12. Chlorpyriphos||19. Sulprophos|
|6. Demeton||13. Fenthin||20. Azinphos Methyl|
|7. Diazinon||14. Trichloronate||21. Coumaphos|
Courtesy of SGE Ltd.
Figure 31. The USEPA Method 22 for the GC Analysis of Organophosphorous Pesticides
Due to the large number of pesticides that might be present in any sample, high column efficiencies are necessary to provide the required resolution. An example of a separation is shown in figure 31. The stationary phase used was BPX5 which is a proprietary product of SGE Ltd. and consists of a dimethyl silicone polymer containing 5% of a phenyl derivative. The phenyl group provides some polarizable character to the stationary phase which will offer significant polar interaction with strong polar groups on any solute. This stationary phase can be operated at relatively high temperatures (up to 320ûC or more) with very low column bleed. The column was 30 m long, 0.22 mm I.D. and carried a film of stationary phase 0.25 mm thick. The initial temperature was 50ûC which was raised to 150ûC at 30ûC/min., The temperature gradient was then reduced to 6ûC/min. and heated to 320ûC. A splitless injector was used and 1 ml of sample was placed on the column. helium was used as the carrier gas at an exit flow velocity of 30 cm/sec.
It is seen that an excellent separation is achieved and the analysis was complete in little over 25 minutes. The concentration of the sample was not reported so the actual mass sensitivity is not known. However, as on column injection was employed with no split flow a few fentogram of material would, without doubt, be detectable.