Further investigation into ICP-induced elemental fractionation in LA-ICP-MS using a local aerosol extraction strategy

Abstract

The source and degree of elemental fractionation is one of the remaining challenges in LA-ICP-MS. In this study, the ICP-induced fractionation behavior of 63 elements was studied using a local aerosol extraction strategy while using a 193 nm excimer laser ablation system for sampling. We found that the sampling distance between the ablation site and the gas outlet nozzle tip positively correlated with the size of the laser ablation produced aerosol particles or agglomerates in the local aerosol extraction strategy.Therefore, the local aerosol extraction strategy allowed detailed studies of the ICP-induced fractionation behaviors for different elements. At a low makeup gas flow rate of 0.6 L min À1 (hot plasma conditions), the increase in the size of aerosol agglomerates or particles because of the increased sampling distance from 1 mm to 10 mm does not affect the ionization efficiency of the sample aerosol in ICP. In contrast, at a high makeup gas flow rate of 0.9 L min À1 , the normalized signal intensities of the elements significantly differ when the sampling distance increases from 1 mm to 10 mm. These experimental results suggest that the changes in the size of aerosol particles or agglomerates under our given conditions do not affect the transport efficiency of aerosol particles but affect the vaporization of aerosol particles in ICP. The mass load effect is more significant in the presence of large amounts of large aerosol particles and agglomerates, which deteriorates the vaporization of aerosol particles. Our experimental results also show that the sample position in the normal ablation cell affects the size of laser ablation produced aerosol particles or agglomerates. The high velocity of the carrier gas flow rate on the ablation site facilitates the production of small aerosol agglomerates or particles. To reduce the ICP-induced fractionation behaviors in LA-ICP-MS, hot plasma conditions and high velocity of the carrier gas flow rate on the ablation site are required.

Impact of ablation cell design in LA-ICP-MS quantification

“…As such, it offers the closest approximation to the behavior of particles before entering the ICP. 45 As previous works recognized a sample position dependent effect on quantification within the ablation cell, 27,29,46 this work reassesses these findings in the context of particle agglomeration within two ablation cell geometries caused by gas dynamics. Special focus was put into experimental data for fast washout cells (in this case, a tube cell variation), which is shown and compared to data acquired on more common cylindrical ablation cells.…”

“…This transformation is then reversed through adiabatic expansion to recombine into mostly neutral particles due to ambient pressure. [25][26][27][28][29] Several particle formation mechanisms during laser irradiation have been described previously in the literature, 25 but this work will focus on the dominant generation of nanoparticles and their transport and vaporization within the ICP. During and after LA, the ablated material is vaporized and forms the laser plasma plume.…”

Online, Absolute Quantitation of Propranolol from Spatially Distinct 20- and 40-μm Dissections of Brain, Liver, and Kidney Thin Tissue Sections by Laser Microdissection–Liquid Vortex Capture–Mass Spectrometry

“…For example, laser ablation of a surface is known to preferentially segregate elements based on ablation conditions, a process termed chemical fractionation. This has been a long-standing problem in the LA/ICP-MS field. − In direct liquid extraction techniques, complete extraction of drug from the sample is usually not achieved, and extraction efficiencies can vary across different tissue types complicating quantitative analysis. ,, For more detail on the challenges of quantitative mass spectrometry methods we recommend the reader to several reviews covering the subject. ,,,,− …”

Influence of temperature on laser ablation fractionation during ICP-MS analysis for 213 nm and 266 nm laser wavelength micro-sampling

“…Fractionation effects can be assessed by the evaluation of the U/Th ratio calculated for signals registered during NIST 610 ablation allowing for comparison of the performance of various laser wavelengths used during the ablation of solids for ICP-MS analysis. 27,45 They are more pronounced for the 266 nm laser wavelength compared with 213 nm or shorter laser wavelengths. 27 Fast heating of samples is also related to the use of the 266 nm laser wavelength during ablation and was found to be a remarkable limitation for microsampling of biological samples.…”

“…21,22 Fractionation can occur not only during the ablation process, 14,23,24 but also during aerosol transport or ionization in the plasma. 3,23,[25][26][27] It was oen described in the literature that laser parameters (laser wavelength, pulse duration, and uence) 19,20,22,25,28,29 as well as elemental/matrix composition and properties (melting and boiling points, vapor pressure, ionization potential, etc.) 30 of ablated materials inuence the intensity of fractionation.…”