A screening method for analyzing environmental waters contaminated with UV filters using direct analysis in real-time mass spectrometry (DART-MS) was developed. To demonstrate the suitability of DART-MS a test set of seven organic UV filters, namely benzophenone-3 (BP-3), ethylhexyl dimethyl p-aminobenzoate (OD-PABA), 4-t-butyl-4'-methoxydibenzoylmethane (BM-DBM), homomethyl salicylate (HMS), 2-(ethylhexyl) salicylate (EHS), octocrylene (OC), and 4-methylbenzylidene camphor (4-MBC), was defined. In the first step, standard solutions of the analytes prepared in methanol were investigated in order to determine optimum parameters for the DART-MS. Because of the very low concentrations of UV filters expected in environmental water samples, a pre-concentration step using stir bar sorptive extraction was performed. DART-MS allows the direct, simple and rapid semi-quantitative analysis of the analytes enriched on the surface of the polydimethylsiloxane-coated stir bars. The optimized method provided calibration curves with correlation coefficients R > 0.959, repeatability from 5% (for 4-MBC) to 30% (for BM-DBM) relative standard deviation and limits of detection lower than 40 ng L(-1) for all analytes. Finally, real lake water samples from locations with typical leisure activities were analyzed. Results obtained with the developed DART-MS method were cross-checked by confirmatory analysis using thermodesorption gas chromatography mass spectrometry (TD-GC-MS). Thereby, it could be demonstrated that both analytical methods provide comparable concentrations for the UV filters in the lake water samples.
In the present paper we report, for the first time, the successful on-line coupling of microemulsion electrokinetic chromatography (MEEKC) with mass spectrometric (MS) detection using an atmospheric pressure photoionization interface. Microemulsions (MEs) including mostly volatile ingredients and classical MEs based on nonvolatile buffer components and sodium dodecyl sulfate (SDS) as surfactant were compared with respect to their compatibility with MS detection. The investigations performed revealed that MEs with up to 3% SDS and buffers containing sodium borate can be employed without significant suppression of the MS signals. A test mixture of nine substances could be separated by MEEKC using a ME consisting of 0.8% octane, 2% SDS, 6.6% butanol, and 90.6% of 20-mmol ammonium hydrogencarbonate buffer (pH 9.5). Operating the MS instrument in the MS(2) mode provided improved signal/noise ratios for analytes leading to characteristic MS-MS transitions. Thereby, limits of detection ranging between 0.5 (carbamazepine) and 5 microg mL(-1) (phenacetin) could be obtained.
A method for analysing plastic samples without any sample pretreatment using direct analysis in real time mass spectrometry (DART-MS) was developed. DART-MS allows the direct, simple and rapid identification of polymer additives in plastic products. To demonstrate the suitability of DART-MS for the detection of a wide range of commonly employed stabilising agents, a test set of 21 stabilisers was selected. In a first step standard solutions of these stabilisers in toluene as well as toluene-extracts from polymer samples were analysed. Subsequently, to prove the applicability of the developed DART-MS method also for the direct analysis of plastic products, samples of polypropylene containing a range of stabilisers were prepared using a lab-scale compounder. Polymer samples were cut into 0.5 cm wide pieces and directly placed into the DART ion source. Focusing on the DART ionisation, several parameters like discharge needle potential, potential of the grid electrode and the discharge electrode, the heater temperature and the gas flow had to be varied to guarantee optimum results. Both positive and negative ionisation was tested, whereby the positive ion mode led to higher signal intensities for all analytes. Determination of accurate masses to improve the certainty in signal assignment could be achieved by using PEG 600 as an internal standard for mass calibration. The developed method allowed the detection of all selected additives (including some of their degradation products) in real polymer samples.
An easy to employ method for the determination of melamine in milk powder samples using CZE with either UV or MS detection is presented. The separation capabilities of CZE allowed keeping sample preparation rather simple. Before analysis, milk powder samples were dissolved in water, de-fatted with dichloromethane and diluted with ACN to precipitate the protein, filtrated and injected without further pretreatment. The developed CZE method allowed the determination of melamine in milk powder down to a level of 0.50 mg/kg using UV detection and 0.25 mg/kg when ESI quadrupole/TOF MS was employed for detection.
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