Detection and quantification of aromatic contaminants in water and soil samples by means of laser desorption laser mass spectrometry.
The combination of laser desorption of untreated soil samples and subsequent selective laser ionization followed by time-of-flight mass analysis results in an ultrafast technique for the quantitative detection of aromatic contaminants in soil samples. The method allows for high sample throughput, because the complete measurement is finished within about 1 min. Although the different types of soil investigated (sand, humus, clay) showed differences in the desorption efficiency, none of them produced mass spectrometric interferences when an ionization laser wavelength of 266 nm was used. Quantification was carried out by relative measurement with respect to an internal standard and gave satisfactory results over 4 orders of magnitude of analyte concentration. Although the detection of polycyclic aromatic hydrocarbons could successfully be carried out using nanosecond laser pulses, the quality of the mass spectra obtained for labile substances, for example, nitrotoluenes, could be greatly improved by the use of ultrashort pulses in the subpicosecond range. With the preliminary setup, detection limits in the low micrograms-per-gram range were achieved. The identical setup can be used for the analysis of liquids, in particular, water, when the soil sample is replaced by a solid, porous adsorber medium onto which the sample is applied. Activated carbon proved to be a useful adsorber for IR laser desorption, whereas for the UV, granular clay or lime/sand mixtures are preferable.