Abstract
Traditional analytical methods for determining soil samples rely on decomposition procedure, typically through microwave or acid digestion and analysis of resulting solution by ICP-AES or ICP-MS. These analytical methods based on dissolving the sample are easily calibrated but suffer from the time and difficulty needed to bring the sample into dissolution as well as from dilution and contamination induced by the digestion procedure. Solid sample introduction into an ICP-MS by laser ablation (LA) is a very attractive alternative to the nebulization of aqueous sample solutions. In addition to the usual analytical advantages of ICP-MS, LA offers reduced sample preparation, rapid sample exchange and throughput, reduced spectral interferences and the possibility of situ spatially resolved analysis. There are also a number of concerns and problems that have prevented LA-ICP-MS from becoming a general technique for analysis of materials. Practical concerns include the difficulty of obtaining or making matrix-matched standards that contains all the elements of interest and the accuracy of the resulting calibration. We try to propose two mehtods of preparing standard for analysis of LA-ICP-MS and overcome the above problems. Standard soil samples are mixed with a polyethene-based binding agent and press into pellets for direct solid sampling by the laser. It is found that the correlation coefficient of the calibration curves based on 9 standards (10-90% of soil) in three different soil sample are better than 0.9 when appropriate elements are chosen as the internal standard. A simultaneous dried solution aerosol (supersonic nebulizer) and laser-induced aerosol introduction system is also used to investigate the calibration capabilities of dried solution for LA-ICP-MS. In most cases, the measure concentrations are within ±20% of the certified value if 208Pb as the internal standard. The lower results obtained for Sr and Ba may be partially due to matrix effects resulting from the high levels of efficiently ionized element (EIEs).