Development of a gas chromatography-mass spectrometry method for the determination of ultraviolet filters in beach sand samples

An analytical method for the determination of eight fat-soluble ultraviolet (UV) filters in beach sand samples is presented for the first time. The method is based on a leaching process of the target compounds from sand samples using vortex mixer agitation and further centrifugation, followed by dispersive liquid-liquid microextraction (DLLME) of the supernatant and gas chromatography-mass spectrometry (GC-MS) analysis of the DLLME extract. The variables involved in the leaching and in the DLLME processes were studied to provide the best enrichment factors. In the first case, the leaching solvent type and volume, and the vortex mixer agitation time were studied. In the case of the DLLME, the type and volume of both disperser and extraction solvent and the influence of the pH and the ionic strength of the supporting aqueous solution were studied. Under the selected conditions, the method was successfully validated showing good linearity (R-2 > 0.995), method limits of detection at the pg g(-1) level, enrichment factors in the range of 8 to 50 (depending on the analyte) and good intra- and inter-day precision. No significant matrix effects were found, thus external calibration can be used. However, internal calibration was recommended to improve the repeatability in both the DLLME and the GC-injection. Moreover, in order to correct losses during the leaching process, the surrogate was added to the samples before the leaching step. The validated method was successfully applied to the analysis of several beach sand samples of different origin.