Hollow fibre liquid-phase microextraction of functionalised carboxylic acids from atmospheric particles combined with capillary electrophoresis/mass spectrometric analysis

A method was developed to enrich various mono- and dicarboxylic acids from aqueous extracts of atmospheric particles by three-phase hollow fibre liquid-phase microextraction. Analysis was performed by capillary electrophoresis/electrospray ionisation mass spectrometry applying a previously reported separation method. Several extraction parameters (pH of donor and acceptor phase, composition of supported liquid membrane, shaking speed, and extraction time) were tested for their influence on analyte recovery. A strong dependence of the recovery on the acceptor phase pH was observed. The final method consisted of 10% (w/v) trioctylphosphine oxide in dihexylether as supported liquid membrane, 1.8 ml aqueous particle extract, acidified by sulfuric acid to a pH of 2 as donor phase, and 15 μl of 50 mM aqueous ammonia solution as acceptor phase. The extraction devices were shaken at 2200 rpm for 2 h. With this method, the recoveries from aqueous standards were between 10 and 80% with a repeatability of 4–14% for most compounds. Generally, more polar compounds were extracted less efficient than less polar ones. A few of the most polar compounds showed recoveries <10% with a repeatability of 20–55%. The enrichment factor was typically 10–100. The analyte recovery from real samples was found to strongly depend on the sample matrix due to co-extraction of mineral acids and organic acidic material present in atmospheric particles. Quantification was achieved by the method of standard addition. The easy handling of the hollow fibre devices, the low costs per extraction and the possibility to do many extractions in parallel allowed for an application of the developed method to a large set of real samples.

► An extraction method based on HF-LPME for various carboxylic acids from atmospheric particles was developed.
► Satisfactory recoveries and enrichment factors were obtained with best results for less polar compounds.
► Atmospheric detection limits were comparable to the ones of more established GC/MS methods.
► The method allowed for a simple, repeatable, and low-cost determination of the analytes with reasonable effort.