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Laser ablation coupled to inductively coupled plasma mass spectrometry has become a versatile and powerful analytical method for direct solid analysis. The applicability has been demonstrated on a wide variety of samples, where major, minor, and trace element concentrations or isotope ratio determinations have been of interest. The pros and cons of UV-nsec laser ablation have been studied in detail, and indicate that aerosol generation, aerosol transport, and aerosol excitation-ionization within the ICP contribute to fractionation effects, which prevent this method from a more universal application to all matrices and all elements. Recent progresses in IR-fs and UV-fs laser ablation coupled to ICP-MS have been reported, which increase the inter-matrix and multi-element quantification capabilities of this method. These fundamental improvements in LA-ICP-MS are of significant importance for entering new applications in material science and related research fields. In particular, because coatings (conducting and non-conducting) consist of single or multilayers of various elemental composition and of different thickness (nm-mm range), significant progress in the field of depth profiling with fs-laser ablation can be expected. Therefore, in-depth profile analysis of polymers, semiconductors, and metal sample investigations, using ultra-fast laser ablation for sampling and the currently achievable figures of merit, are discussed. In this review manuscript, the enhanced capabilities of fs-LA-ICP-MS for direct solid sampling are highlighted, and it is discussed about current methods used for quantitative analysis and depth profiling, the ablation process of UV-ns and UV-fs, the influence of the laser beam profile, aerosol structure and transport efficiency, as well as the influence of the ICP-MS (e.g., vaporization and ionization efficiency in the plasma, and type of mass analyzer).

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The capabilities of ultraviolet femtosecond laser ablation inductively coupled plasma mass spectrometry (UV-fs-LA-ICPMS) for depth profile analysis of thin metal coatings were evaluated. A standard sample consisting of a single Cr thin layer of 500 nm +/- 5% on a Ni substrate was used. A fast washout was obtained by a high-efficiency aerosol dispersion ablation cell (V approximately 1 cm3), which allowed single-shot analysis with increased depth resolution. Laser ablation was performed in helium at atmospheric pressure conditions. A laser repetition rate of 1 Hz and low laser fluence (<0.5 J/cm2) were used. Very low ablation rates (<10 nm/pulse) were determined by atomic force microscopy (AFM). Information about the crater geometry and morphology was investigated using scanning electron microscopy and AFM. The depth resolution, calculated via the maximum slope of the tangent in the layer interface region, was smaller than 300 nm. Our data indicate that UV-fs-LA-ICPMS represents a powerful combination of high lateral and depth resolution for the analysis of thin metal coatings. Moreover, an overall ion yield, defined as the ratio of detected ions and ablated atoms, of approximately 5 x 10-5 was estimated for the chromium layer under the operating conditions chosen. The absolute amount of ablated material per laser pulse was approximately 1 pg, which corresponds to a detection limit of 180 microg/g.

A novel ablation cell for laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) was developed. The ''high efficiency aerosol dispersion'' (HEAD) ablation cell is based on the use of a directed gas flow expansion of the laser generated aerosol at the ablation site and a venturi effect created by two nozzles to extract the aerosol into the main make up gas stream, which finally transports the particles into the ICP. The figures of merit were evaluated based on the ablation of glass SRM NIST 610 using two different cell gases (Ar and He). The investigation of the capabilities of this type of aerosol extraction (using a Nd:YAG laser, l ¼ 266 nm) demonstrates that a laser generated aerosol can be modified (HEAD effect) by shifting the original particle size distribution towards smaller particle sizes. This effect was obtained for both gases (Ar and He) for increasing cell gas flows and showed an optimum at a flow rate of 100 ml min À1 . In comparison with standard cell results, elemental ratios (e.g. U/Th) showed reduced elemental fractionation effects attributed to reduced agglomeration and, therefore, an improved vaporization of the aerosol within the ICP. Most importantly, stability and reproducibility of the ion-signals were significantly improved without compromising sensitivity. In addition to the glass analysis, the HEAD ablation cell was also used for the ablation of brass samples, as this matrix is known to show pronounced elemental fractionation effects due to the thermal volatility difference of Cu and Zn. The temporal stability of element ratios (e.g. Cu/Zn) achievable using such an extraction approach (5%) was significantly improved in comparison with previously reported Cu/Zn ratios (30%) measured using standard cell configurations.

The analytical potential of a radiofrequency glow discharge orthogonal time-of-flight mass spectrometer (RFGD-TOFMS) has been evaluated in both pulsed and non-pulsed modes. A certified reference steel was selected for this study. The operating conditions of the GD plasma (pressure and applied power) were optimized in terms of sensitivity. Additionally, duty cycle and pulse width parameters were investigated in the pulsed RF mode. In this case, high analyte ion signals and improved signal to background ratios were measured after the end of the pulse, in the so-called afterglow domain. The analyte ion signals were normalized to sputtering rates to compare different operating conditions. It was found that the sensitivity in the pulsed mode was improved in comparison to the non-pulsed mode; however, the factor of enhancement is element dependent. Moreover, improved analytical performance was obtained in terms of ion separation capabilities as well as in terms of accuracy and precision in the evaluation of the isotopic ratios, using the pulsed RFGD-TOFMS. Additionally, depth profile analyses of a Zn/Ni coating on steel were performed and the non-pulsed and pulsed RFGD-TOFMS analytical performances were compared.

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