Figure 2. Schematic of Nd: YAG LA system (fifth harmonic: 213 nm) for ICP-MS.
LA-ICP-MS as a Sampling Technique Quadrupole inductively coupled plasma mass spectrometry (ICP-MS) enables the analysis of elements across the periodic table with very low detection limits. Typically, samples are introduced into an ICP-MS by aspirating a solution of the sample. Often, liquid samples require little preparation, but without a solid sampling accessory, solid samples need to be dissolved. This process is time-consuming and often requires the use of acid-dissolution reagents and additional sample preparation apparatus. Adding chemicals such as hydrofluoric acid to dissolve the sample can give rise to matrix-based interferences forming in the plasma, as well as being a potential source of contamination. Additionally, aqueous analysis typically has minimum requirements for sampling mass. A 200-µm glass shard, entangled in clothing, is an insufficient quantity for reliable aqueous results of the trace elements. In contrast, combining ICP-MS with the direct solid-sample introduction technique of laser ablation (LA) requires minimal sample preparation. LA-ICP-MS provides an excellent and relatively nondestructive technique for elemental analysis of forensic samples that are difficult to digest, or where small fragments or inclusions must be analyzed. LA-ICP-MS is amenable particularly to time-resolved analysis (TRA); enabling direct comparison of samples in three dimensions. Combining such flexible data-handling capabilities with in-situ solid sampling enhances the discriminating power of samples with similar visual, physical, and chemical characteristics, strengthening the analyst's ability to determine the similarities and differences within large data sets. These attributes, combined with low levels of detection and high precision, explain the increasing acceptance of LA-ICP-MS for investigation of forensic samples.