Improved gas chromatography methods for micro-volume analysis of haloacetic acids in water and biological matrices

Abstract

A fast headspace solid-phase microextraction gas chromatography method for micro-volume (0.1 mL) samples was optimized for the analysis of haloacetic acids (HAAs) in aqueous and biological samples. It includes liquid–liquid microextraction (LLME), derivatization of the acids to their methyl esters using sulfuric acid and methanol after evaporation, followed by headspace solid-phase microextraction with gas chromatography and electron capture detection (SPME-GC-ECD). The derivatization procedure was optimized to achieve maximum sensitivity using the following conditions: esterification for 20 min at 80 °C in 10 μL methanol, 10 μL sulfuric acid and 0.1 g anhydrous sodium sulfate. Multi-point standard addition method was used to determine the effect of the sample matrix by comparing with internal standard method. It was shown that the effect of the matrix for urine and blood samples in this method is insignificant. The method detection limits are in the range of 1 μg L⁻¹ for most of the HAAs, except for monobromoacetic acid (MBAA) (3 μg L⁻¹) and for monochloroacetic acid (MCAA) (16 μg L⁻¹). The optimized procedure was applied to the analysis of HAAs in water, urine and blood samples. All nine HAAs can be separated in <13 min for biological samples and <7 min for drinking water samples, with total sample preparation and analysis time <50 min. Analytical uncertainty can increase dramatically as the sample volume decreases; however, similar precision was observed with our method using 0.1 mL samples as with a standard method using 40 mL samples.