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Laser-generated aerosols in helium, argon and nitrogen were directly compared using a nitrogen microwave inductively coupled plasma in combination with a mass spectrometer. An increased surface darkening of the sample was observed during ablation in nitrogen, suggesting a more pronounced particle deposition in comparison to helium, but only 30% lower sensitivities were obtained for nitrogen. Crater depth measurements proved that these variations were not the consequence of a difference in ablation rate (271 ± 17 nm per pulse for He vs. 267 ± 12 nm per pulse for N2). Particle size measurements and electron microscopy images indicated that the aerosol generated in nitrogen or argon tends to form smaller agglomerates in comparison to helium. This dependence in agglomeration however appeared to be dependent on the ablation cell used. Furthermore, the fluence of the 193 nm laser system used for the experiments significantly influenced the temporal stability of the signals (e.g.238U+/232Th+). Finally, the quantification capabilities of nitrogen as an ablation environment and carrier gas were studied and compared to helium generated aerosols transported in nitrogen. A selection of samples (NIST SRM 612, USGS BCR-2G, USGS GSD-1G and GSE-1G) were quantified using NIST SRM 610 as an external standard. The potential of nitrogen as an alternative carrier gas was highlighted with deviations from the reference values calculated between −13% and +16% in comparison to the deviations between −15% and +17% obtained with helium in a cylindrical ablation cell for most elements in the different reference materials analyzed. [ABSTRACT FROM AUTHOR]

The analytical capabilities of a nitrogen-sustained high-power microwave inductively coupled atmospheric-pressure plasma mass spectrometer (N2 MICAP-MS) were investigated using solution nebulization with and without aerosol desolvation. The reduced solvent load for the desolvated aerosol and the increased aerosol transfer resulted in a signal enhancement of ten times for most elements in samples without a significant amount of dissolved solids. An exception was boron, whose signal decreased by a factor of seven when a desolvator was used. To compare the accuracy, reproducibility, and matrix susceptibility of the N2 MICAP-MS, the mass fractions of 30 elements were determined in two certified water reference materials using external calibration and standard addition. The results were generally found to agree within 10% of the certified reference values with a maximum deviation of 17% in the case of 64Zn. Comparing external calibration and standard addition provided comparable results regardless of the sample introduction method. To assess the extent of matrix effects, multi-element standard solutions were doped with amounts of up to 100 mg kg−1 calcium. This resulted in a signal suppression of up to 30% and 70% for conventional nebulization and aerosol desolvation, respectively. This substantially reduced the improvement in sensitivity observed for the desolvated aerosol. To further investigate the fundamental characteristics of the N2 MICAP-MS, the plasma gas temperature was estimated using three methods. The determined temperatures for the two most reliable methods were in the range of ∼5000–6000 K and were found to be independent of the sample introduction method and similar to those of an Ar ICP. [ABSTRACT FROM AUTHOR]

Lithium isotope measurement in spodumene by femtosecond LA‐MC‐ICP‐MS was investigated and the influence of plasma operating conditions and data reduction strategy on accuracy and precision was studied. It was found that "hot" plasma conditions led to an unstable baseline signal and substantial variations in the Li isotope ratios. By adding a constant amount of water to the carrier gas, a stable baseline was achieved and isotope ratios became reproducible and were consistent with data from solution‐based MC‐ICP‐MS. The resulting biases were within ± 0.51‰ and the reproducibility was better than 0.09‰. Comparison of Li isotope ratios resulting from different data evaluation schemes showed that the mean of the transient intensity ratios, integration of the entire or a user‐defined period of the ion signals resulted in good agreement with solution‐based data, while linear regression underestimated the Li isotope ratios. It was also found that "cool" plasma operation produced a stable baseline signal, but the Li isotope results were biased by up to ‐4.3%, irrespective of water introduction and the data evaluation scheme. With the optimised "hot‐wet" conditions, the Li isotope ratios in eleven spodumene materials were determined which successfully allowed distinguishing regional deposits and partially veins of the available samples. [ABSTRACT FROM AUTHOR]

The forensic analysis of glass fragments is often limited by the size of objects found during investigation. Many of the glass fragments found on suspects are too small to be analysed with the established laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) method, and alternative methods like refractive index measurements show significantly higher error rates. This work builds on a previous method which used resolved laser pulses and a time of flight mass spectrometer (single pulse ICP-TOFMS) to analyse glass fragments pulse by pulse and get more information from one sample while requiring 25× less material. Resolved signals of individual laser pulses are achieved by using low dispersion ablation cells, of which two were compared: The parallel flow ablation cell (PFAC) designed for fast washouts using small spot sizes and a modified version (MPFAC) specifically made for using larger spot sizes. The signal durations of each laser pulse showed a narrow Gaussian distribution for the MPFAC compared to a wide bimodal distribution of the PFAC. Due to the significantly improved aerosol transport using the MPFAC, smaller and more reproducible relative standard deviations were observed. When applying standard interval matching procedures for forensic glass fragments, the PFAC achieved a success rate of up to 95%, while the MPFAC achieved 98%, which are comparable to the established LA-ICPMS method used by forensic institutes. Using multivariate statistics for matching requires significantly higher amounts of data points than dimensions, which previous methods did not allow. Using single pulse LA-ICP-TOFMS data, it was possible to use Hotelling's T2-test for matching. Direct application of the statistical tests resulted in unusable high amounts of error rates. However, closer investigation into the resulting F-values revealed a significant difference between the values of matching pairs and mismatching pairs. Increasing the F-value threshold for matching resulted in success rates around 99% for both ablation cell designs. This work validates the value of single pulse LA-ICP-TOFMS for the analysis of small samples which are commonly found in forensic applications. Furthermore, it showed the advantages of multivariate statistics and the necessary corrections that are required when used with real case samples. [ABSTRACT FROM AUTHOR]

A high-power nitrogen-based microwave inductively coupled atmospheric-pressure plasma was coupled to a quadrupole mass spectrometer to investigate its characteristics as an ion source for element mass spectrometry. The influence of operating conditions on analyte sensitivity, plasma background, and polyatomic ion formation was investigated for conventional solution-based analysis. By varying the forward power and the nebulizer gas flow rate, the plasma background ions were found to decrease with increasing gas flow rates and decreasing operating power. Analyte ions showed different trends, which could be related to the physical–chemical properties of the elements. We could identify three groups based on the location of maximum intensity in the power vs. flow rate contour plot. Atomic ions of elements with low first ionization energy and low oxygen bond strength were found to maximize at a high nebulizer gas flow rate and lower microwave power. Elements with intermediate ionization energy and higher oxygen bond strength required higher power settings for optimum sensitivity, while elements with the highest ionization energies required the highest power and lowest gas flow rates for their optimization. The latter group showed a substantial suppression in sensitivity compared to elements of similar mass, which is considered to result from the high abundance of NO in the plasma source, whose ionization energy is close to that of these elements. Metal oxide ions were found at similar or higher abundances than in the conventional argon-based ICP and could be minimized only by using a low gas flow rate and high power settings. These general trends were also observed when the vacuum interface was modified. To change the dynamics of the supersonic expansion, different sampler cone orifice sizes and sampler–skimmer distances were investigated and the interface pressure was lowered through an additional pump. These modifications did not yield significant differences in ion transmission but lowering the interface pressure reduced the relative abundance of metal oxide ions. The limits of detection were evaluated for optimized plasma conditions and found comparable to those of an argon ICP source with the same mass spectrometer. [ABSTRACT FROM AUTHOR]