Development and optimization of a solid-phase microextraction gas chromatography-tandem mass spectrometry methodology to analyse ultraviolet filters in beach sand.

A methodology based on solid-phase microextraction (SPME) followed by gas chromatography-tandem mass spectrometry (GC-MS/MS) has been developed for the simultaneous analysis of eleven multiclass ultraviolet (UV) filters in beach sand. To the best of our knowledge, this is the first time that this extraction technique is applied to the analysis of UV filters in sand samples, and in other kind of environmental solid samples. Main extraction parameters such as the fibre coating, the amount of sample, the addition of salt, the volume of water added to the sand, and the temperature were optimized. An experimental design approach was implemented in order to find out the most favourable conditions. The final conditions consisted of adding 1 mL of water to 1 g of sample followed by the headspace SPME for 20 min at 100 °C, using PDMS/DVB as fibre coating. The SPME-GC-MS/MS method was validated in terms of linearity, accuracy, limits of detection and quantification, and precision. Recovery studies were also performed at three concentration levels in real Atlantic and Mediterranean sand samples. The recoveries were generally above 85% and relative standard deviations below 11%. The limits of detection were in the pg g level. The validated methodology was successfully applied to the analysis of real sand samples collected from Atlantic Ocean beaches in the Northwest coast of Spain and Portugal, Canary Islands (Spain), and from Mediterranean Sea beaches in Mallorca Island (Spain). The most frequently found UV filters were ethylhexyl salicylate (EHS), homosalate (HMS), 4-methylbenzylidene camphor (4MBC), 2-ethylhexyl methoxycinnamate (2EHMC) and octocrylene (OCR), with concentrations up to 670 ng g.