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Figure 1.1 A concise visual reference of most of the ring analytical techniques to compare the detection limits and analytical resolutions for materials characterization.

      Source: Reproduced from Ref. [3] with the kind permission and copyright of © Eurofins Scientific (www.eurofinseag.com).

In contrast to traditional AAS that can detect only one element at a time, ICP‐MS instruments have ability to measure all the elements present in the sample material even at once. However, advanced AAS systems (AnalyticJena) are also available, which is of the scan variety (not independent hollow cathode lamp) and can measure the elements sequentially (http://www.analytik‐jena.com). ICP‐MS is widely used in forensic and biomedical science, in particular toxicology [3]. Depending on the specific parameters in the patient, the collection of samples taken for the analysis process can vary from blood, serum, plasma, urine, to even packed red blood cells. This instrument is also used in the environmental field. The applications include testing of water samples in the soil for municipalities water and for industrial purposes.

      The ICP‐MS instrument should be free of obstruction. Even the smallest obstruction can disturb the flow of the sample, which can clog the sample tips within the spray chamber. Also, high concentrations of NaCl in samples such as sea or ocean water can lead to obstruction. These blockages can be overcome by dilution of the samples wherever a high concentration of salt has been observed and compensated for. This process comes at the cost of detection limits. ICP‐MS has been used for glass analysis in forensic applications [3, 4]. It is capable of tracing the elements on the glass. The elements detected on the glass can be utilized in order to match the sample materials observed at the crime scene.

Laser ablation ICP‐MS (LA‐ICP‐MS) uses a high‐power pulsed laser beam (typically ns) to ablate a small amount of material (picograms to femtograms) from the surface of the sample [3]. A plume of atomic particles and ions are generated which are then carried to an ICP‐MS detector with the help of a constant flow of argon (Ar) or helium (He) gas. The sample is subsequently ionized in an IC plasma, and its atomic species are transported in the form of ions, which are further separated and analyzed using their mass/charge ratio. It is used to measure major and trace elemental composition of samples at the level of parts‐per‐billion (ppb). It is considered a versatile technique due to its high analytical performance for various kinds of unprepared solid samples. A very small amount of the sample (solid and liquid) quantities (picograms to femtograms) is sufficient to produce highly sensitive results up to the ppb level, depending on the measurement system. The laser beam can be focused up to 5–200 μm range and thus allows a single spot analysis and line scanning over the surface of the samples. It is recognized as a good analytical technique that can be used for the analysis of a variety of sample materials detected in forensic applications [3]. It has already proven its potential in the forensic analysis of bone, tooth, car paint, printing ink, metals, glasses, trace fingerprints, soil, and paper fields [3].

A comparative study of LA‐ICP‐MS and micro‐XRF by Gholap et al. [12] was performed in order to compare their detection limits and spatial resolution. The experiment for elemental imaging was performed on Daphnia magna, which is typically used as an indicator of aquatic ecosystem health and is ascribed as a model organism in ecotoxicology. The authors used sections of the freshwater crustacean D. magna (typical thickness of 10‐20 μm) for the analysis and obtained the elemental localization of elements in particular Ca, P, S, and Zn which allowed elemental correlation with the tissues. The authors plotted the RGB maps (as shown in Figure 1.2) to conceptualize the simultaneous presence of metallic elements in the sample. Figure 1.2 shows the RGB representation of the distribution of Ca, Fe, P using μ‐XRF and Ca, P, Zn using LA‐ICP‐MS in the sagittal and dorsoventral parts of D. magna. The results reveal the concomitant presence of Ca/P in thoracic appendages, P/Zn in the gut and Ca/Zn in the exoskeleton. The co‐existence of Ca/P and Zn/P is ascribed to the formation of intracellular and membrane‐bound phosphate granules, which can be a reason for the storage of metallic ions Ca²⁺ and Zn²⁺ in living tissues [12, 13]. Both the techniques provide comparable limits of detection (LOD) for Ca and P which validated the imaging results. LA‐ICP‐MS was found to be sensitive in determining Zn (LOD 20 ppm, 15 μm spot size) in D. magna, but the detection power of μ‐XRF was found inadequate. On the other hand, LA‐ICP‐MS was found inadequate for the distribution analysis of S, which could be better examined and visualized using μ‐XRF (LOD 160 ppm, five seconds life time).