Application of single-drop microextraction combined with in-microvial derivatization for determination of acidic herbicides in water samples by gas chromatography–mass spectrometry

A single-drop microextraction (SDME) method and gas chromatography with mass spectrometry detection have been developed for the determination of acidic herbicides in water. The analytes were extracted from a 3 mL sample solution using 4 μL of hexyl acetate. After extraction, derivatization was carried out inside a glass microvial (1.1 mm i.d.) using pentafluorobenzyl bromide (PFBBr). Triethylamine (TEA) was used as the reaction catalyst. The influence of derivatization reagent volume, catalyst amount, derivatization time and temperature on the yield of the in-microvial derivatization was investigated. Derivatization reaction was performed using 0.3 μL of PFBBr and 0.4 μL of TEA (10%, v/v in toluene) at 100 °C during 5 min. Also, the effects of different experimental SDME parameters such as selection of organic solvent, sample pH, addition of salt, extraction time and temperature of extraction were studied. Analytical parameters such as enrichment factor, precision, linearity and detection limits were also determined. The enrichment factors were between 83 and 157. The limits of detection (LOD) were in the range 1.2–7 ng/L (S/N = 3). The relative standard deviations obtained were below 10.1% (n = 5).