The expansion dynamics achieved under these conditions were found to be fairly slow whereas the degree of aerosol dispersion for NIR-ns-LA using helium drastically increased due to its lower viscosity. It could, for instance, be shown that NIR-ns-LA under quiescent argon atmosphere provokes the formation of a dense aerosol confined within a radially propagating vortex ring. In order to achieve adequate temporal and spatial resolution a pulsed laser source was utilized for illuminating a 0.5 mm-wide cross section of the expanding aerosol. The expansion of aerosols generated by near infrared (NIR) nanosecond (ns) and femtosecond (fs) laser ablation (LA) of metals at atmospheric pressures was explored by laser-induced scattering.
The potential of this prototype was evaluated through fundamental analyses such as elemental fractionation and characterization of the aerosol produced by laser ablation and through the development of different applications such as analysis of soils and sediments by in-cell isotope dilution, detection of selenoproteins in gel electrophoresis, and determination of uranium isotopic composition of micrometric particles. Its unusual characteristics (high repetition rate and scanning beam device) allow to perform some new ablation strategies and open encouraging analytical perspectives in terms of sensitivity and quantification. Through a collaboration between the LCABIE (Laboratoire de Chimie Analytique Bio-Inorganique et Environnement) of Pau and Novalase SA (a company specialized in optical and laser integration), the first integrated femtosecond laser ablation system was designed in 2003. The use of femtosecond laser sources permit to improve analytical performances of the coupling thanks to the non-thermal ablation obtained in comparison with the more conventional nanosecond laser used. Laser ablation inductively coupled plasma mass spectrometry is more and more considered as a tool of choice for solid analysis. It promises to have a significant impact on numerous applications, such as imaging of biological samples or trace element determinations on climate archives (e.g., stalagmites). The evaluation of the ablation cell demonstrates high resolution capabilities on large solid samples. To demonstrate the potential of the ablation cell, p-(hydroxymercuri)benzoic acid (pHMB) derivatised ovalbumin was ablated from polyacrylamide gels after electrophoretic separation. Gas flow patterns in the cell were modeled by computational fluid dynamics (CFD) and validated by measurements on two reference materials.
The washout of the new ablation cell is 70% faster when compared to the standard ablation cell previously applied in our laboratory and provides washout times within 2.6 s for 99.9% of the signal. To obtain high resolution profiles of trace element distributions, the ablation cell must offer fast washout of the aerosol to decrease mixing of the particles from different laser pulses. The performance of the cell was tested using silicate glass NIST SRM 610 and steel CRM JK-2D. The profiles presented in this article suggest a seasonal variation, revealing some new aspects of Norway spruce (PICEA ABIES) metabolism.Īn ablation cell was developed to host large or several small samples (up to dimensions 230 mm × 34 mm × 16 mm, L × W × D) for high spatial resolution analysis. Potassium, the third element measured, seems to be especially accumulated in the latewood. This was unexpected, because it was previously assumed that the distribution of phosphorus remains constant throughout the year.
A similar seasonal pattern was also found for phosphorus, another crucial element in tree nutrition. Despite its low quantity in wood, sulphur is an important macronutrient for plants and seems to display seasonal variations of its concentration, which correspond to actual theories of sulphur metabolism in plants. This technique combines excellent spatial resolution with superior detection power, and makes it possible to measure low element concentrations even in relatively narrow annual rings. This became possible by using a novel laser ablation system coupled to HR-ICP-MS for measuring these elements in Norway spruce drill cores. Seasonal profiles of sulphur, phosphorus, and potassium content in the wood of trees have been established for the first time.
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