Determination of organothiophosphorus pesticides in water by liquid chromatography and post-column chemiluminescence with cerium(IV)

• HPLC—chemiluminescence detection of organothiophosphorus pesticides.
• High selectivity and sensitivity thanks to the post-column chemiluminescence reaction.
• Successful simultaneous determination of organothiophosphorus pesticides in water samples in a short analysis time.

A new, fast, selective and sensitive method has been developed for the simultaneous determination of nine organothiophosphorus (OTP) pesticides, namely omethoate, dimethoate, disulfoton-sulfoxide, methidathion, phosmet, malathion, diazinon, pirimiphos-methyl and chlorpyrifos. The pesticides were separated on a Kinetex C18 column by gradient elution with acetonitrile:water. A post-column basic hydrolysis of the pesticides and later a chemiluminescence (CL) reaction with cerium (IV) in acid medium was carried out. Hexadecylpyridinium chloride highly enhanced the CL emission. Under optimized conditions, linearity, precision, limits of detection and quantification, and accuracy were determined. Both selectivity and sensitivity were compared with those obtained with UV detection. In combination with SPE, limits of detection in the range 15–80 ng/L and 5–30 ng/L were obtained when 250 mL and 1000 mL of solution were treated, respectively. When applied to 250 mL of sample the inter-day precision of the method was between 3.5% and 7.3% and the intra-day precision between 2.9% and 6.0%. The method was applied to determine OTP pesticides in spiked water samples from different origins: irrigation, river, sea, ground, spring, mineral and tap waters, being the percentage of recovery of added amounts near 100% form most of the pesticides.