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• 6 • 2008 vol. 3
As labs operate in an extremely competitive market, the demand for more sensitive multiresidue pesticide methods is increasing. A
GC/MS method is a logical choice, as this instrument provides a high degree of specificity, yet is relatively inexpensive and easy to
operate, compared to LC/MS/MS, high resolution MS, or GC/MS/MS. However, to take full advantage of GC/MS, careful column
selection is critical. The column used must be of the proper selectivity to separate compounds that share common spectra, and also
exhibit a high degree of inertness and minimal bleed. Here we demonstrate the effectiveness of an Rxi®-5Sil MS column for low level
analysis of a wide variety of pesticides differing in volatility, compound class, and degree of activity.
Excellent Response for Difficult Active Compounds
Column inertness, selectivity, and bleed are key considerations and often determine the success or failure of analytical runs. Inertness
can be assessed through the behavior of active compounds, which often exhibit disproportionately poor responses at low concen-
trations. Although the compound list analyzed here contains many compounds with a high degree of activity, low level linearity
(10-1,000ng/mL) was established with an r2 value of 0.990 or above for many of these challenging compounds (Table I). In addition,
the notoriously problematic compounds of EPA Method 8081, endrin and 4,4'-DDT, were among the least troublesome tested here,
attaining values of 0.997 and 0.998, respectively. Note that standards were analyzed for this study and some compounds with r2
Environmental
Reliably Detect Pesticides Down to 10pg with
Sensitive SIM GC/MS Multiresidue Method
Market demands are increasing for multiresidue pesticide methods that are both sensitive and effective
across a broad range of compound chemistries. The Rxi®-5Sil MS column gives accurate low level
results for a wide variety of analytes in a single run.
By Jason Thomas, Environmental Innovations Chemist
Table I The Rxi®-5Sil MS column provides excellent linearity, and thus more accurate results,
for a wide range of pesticide chemistries down to 10pg.
Retention Quant. Qual. Qual. r2
Compound time (min.) ion ion 1 ion 2 IS (10-1,000 ppb)
methamidophos 5.77 141 95 94 BNB 0.997
dichlorvos 6.02 185 79 109 BNB 0.998
bromonitrobenzene (IS) 7.21 203 201 157 IS —
mevinphos 8.26 192 127 109 BNB 0.995
acephate 8.30 136 95 94 BNB 0.982
o-phenylphenol 9.44 170 169 141 BNB 0.997
omethoate 10.23 156 110 109 BNB 0.976
dimethoate 11.77 125 143 93 BNB 0.981
pentachloronitrobenzene (IS) 12.13 295 249 237 IS —
diazinon 12.45 179 304 137 PCNB 0.994
chlorothalonil 12.55 266 264 268 PCNB 0.983
vinclozin 13.48 285 198 212 PCNB 0.998
carbaryl 13.65 144 116 115 PCNB 0.996
metalaxyl 13.69 206 160 132 PCNB 0.997
dichlofluanid 14.17 123 167 224 PCNB 0.954
malathion 14.19 173 125 127 PCNB 0.992
thiabendazole I 15.34 201 202 174 PCNB 0.958
captan 15.34 79 119 149 PCNB 0.987
folpet 15.46 260 130 104 PCNB 0.964
imazalil 16.10 215 175 173 PCNB 0.982
myclobutanil 16.34 206 179 150 PCNB 0.973
endrin 16.82 265 279 317 PCNB 0.997
fenhexamid 17.79 177 179 97 PCNB 0.969
4,4'-DDT 17.79 237 235 165 PCNB 0.998
propargite 18.04 173 150 135 PCNB 0.999
triphenylphosphate (IS) 18.09 325 215 326 IS —
iprodione 18.47 314 316 187 TPP 0.991
bifenthrin 18.64 181 166 165 TPP 0.998
fenpropathrin 18.82 265 208 181 TPP 0.985
dicofol 18.89 139 251 253 TPP 0.788
permethrin I 20.41 183 165 163 TPP 0.998
permethrin II 20.54 183 163 165 TPP 0.995
deltamethrin 22.87 253 251 181 TPP 0.995
Standard curve: 10, 25, 75, 150, 500, and 1,000 ng/mL mixed standards, single 1µL injections.
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