Determination of Organophosphorus Pesticides in Vegetables by ...

Alvin Chai Lian Kuet & Lau Seng
118.3% with CV of 0.6% to 6.1 %. Statistical analysis showed that there was a
significant difference between these two methods as the t-value obtained was
higher than the critical value.
TABLE 4
Recovery of organophosphorus pesticides from spiked green mustard
samples with and without SAX/NH 2 cleanup
SAX/NH 2
No cleanup
Pesticide Recovery(a) % CV% Recovery(a) % CV%
Methamidophos* 15.3 4.5 74.3 1.5
Dimethoate 102.0 9.9 118.3 6.1
Diazinon 88.3 6.5 92.3 1.5
Tolcofos-methyl 92.0 4.6 89.7 1.5
Fenitrothion 91.3 4.7 93.3 5.9
Chlorpyrifos 94.0 5.2 96.7 2.1
Phenthoate 89.7 4.5 93.3 3.2
Prothiofos 90.7 704 97.3 0.6
Triazofos 86.0 2.7 89.7 4.0
Cyanofenfos 88.0 5.3 91.3 3.2
Azinphos-ethyl 82.0 4.6 92.3 6.1
AV 9004 95.5
SD 5.3 804
AV
SD
CV
(a)
Average mean excluding *
Standard deviation excluding *
Coefficient of variation
n=3
The chromatograms for SPE cleanup and without cleanup are shown in Figs.
5 and 6. The extract obtained after SPE cleanup was light green as compared
to dark green without cleanup. The SPE cleanup removed a substantial amount
of coloured compounds from the sample. As discussed earlier, cleaner extracts
are preferred as less GC maintenance is required. No interfering peaks were
observed in either chromatogram.
CONCLUSION
The results from this study show that SAX/NH 2 is suitable for cleanup of
vegetable extracts for most of the OP pesticides tested. Their recoveries were
within the acceptable range. However, SPE is not suitable for polar pesticides
such as methamidophos. As the use of methamidophos is prohibited on most
food crops including vegetables, this method can still be used for routine
pesticide analysis in vegetables. This initial study has shown that the SPE
method has potential as an alternative to the conventional method for OP
pesticide analysis in vegetable and fruit crops. The SPE method affords a
cleaner extract and as such it reduces GC maintenance, especially on capillary
columns and the injector inlet. This clean extract may also be suitable for ECD
102 PertanikaJ. Sci. & Technol. Vol. 11 No.1, 2003