Liquid–liquid–liquid microextraction of degradation products of nerve agents followed by liquid chromatography–tandem mass spectrometry

Alkyl alkylphosphonic acids (AAPAs) are important environmental markers of nerve agents. A simple hollow fiber-based liquid–liquid–liquid microextraction (HFLLLME) technique has been developed to enrich the AAPAs from water. AAPAs were extracted from acidified aqueous phase to organic phase present in pores of the hollow fiber, and then back extracted into the alkaline acceptor phase present in the lumen of the hollow fiber. Variables affecting the HFLLLME process were optimized using a Plackett–Burman design and a Doehlert design. Optimal experimental conditions were: organic solvent, 1-octanol; pH of acceptor phase, 14; extraction time, 60 min; pH of donor phase, 1; and NaCl concentration, 10% (w/v). Depending upon the alkyl substituent, lower limits of detection varied from 0.1 to 100 ng mL⁻¹ (S/N ≥ 5). Repeatability of the method was observed with relative standard deviation of 1.49–9.83% (n = 3). After validation, the method was applied to detect AAPAs present in the water sample provided by the Organization for Prohibition of Chemical Weapons (OPCW) during the 23rd official proficiency test. The added advantage of this method is that several successive extractions of AAPAs from the same water sample can be performed.