Use of chlorpyrifos as an evaluation standard for gas chromatographic detectors

Abstract The performance of a range of element-selective detectors was studied using chlorpyrifos (O,O-diethyl-O-3,5,6-trichloro-2-pyridyl phosphorothioate) as a standard. It involved determination of the minimum detectable amount and linearity of the response of the flame photometric, alkali flame ionization, Hall electrolytic conductivity and electron capture detectors. The minimum detectable amount varied with both the model and type of detector, with the electron capture detector (frequency-modulated mode) being the most sensitive and the flame photometric detector (S-mode) the least. A study of various models of electron capture detector demonstrated the superior performance of the frequency-modulated type to the d.c. or d.c. pulse mode in both sensitivity and linearity. The responses of various types of alkali flame ionization detector were similar and ca. 10 times more sensitive than the flame photometric detector (P-mode). The N/P response of the alkali flame ionization detector was dependent on the hydrogen flow-rate. The multi-element response of the detector is suppressed by using a flame energized source. The response of the flame photometric detector to chlorpyrifos analogues showed a variation in the minimum detectable amout of 2.1–4.5 for the PO/PS ratio, which indicated it to be a detector effect. The results obtained warrant the consideration of chlorpyrifos as a common evaluation standard for the sensitivity and linearity data of gas chromatographic detectors used in pesticide residue analysis.