Solvent-minimized extraction for determining halonitromethanes and trihalomethanes in water

Halonitromethanes (HNMs) are a class of nitrogenous disinfection by-products (N-DBPs) that have so far received little attention and focused largely on trichloronitromethane. By contrast, trihalomethanes (THMs) are the most commonly regulated DBPs and have been the subject of much study. This paper reports the first miniaturized system for the simultaneous determination of the nine known HNMs and four THMs in tap and swimming pool water. Micro liquid–liquid extraction (MLLE) is an adaptation of EPA Method 551.1 using ethyl acetate instead of methyl tert-butyl ether as extractant and large injected sample volumes (30 μL) in combination with programmed temperature vaporizer–gas chromatography–mass spectrometry for improved sensitivity and selectivity. Because extraction is done with a few microlitres of organic solvent (200 μL) and practically all extract is injected into the instrument, MLLE can be regarded as a virtually solvent-free sample preparation technique. The proposed method provided an extraction efficiency of ∼85%, average limits of detection (tribromonitromethane excluded) of 30 ng/L and relative standard deviations of ∼6.0%. The influence of various dechlorinating agents on the stability of the thirteen target analytes in treated water was evaluated; the only salt allowing both types of compounds to be efficiently preserved was (NH4)2SO4, but only for 1 day at 4 °C. Therefore, acidifying the sample at pH ∼3.4—the optimum value for MLLE—at the time of collection is recommended in order to ensure that both HNMs and THMs retain their integrity for 2 days during storage at 4 °C.