A small high‐irradiance laser ionization time‐of‐flight mass spectrometer

Abstract

A small high-irradiance laser ionization time-of-flight mass spectrometer (LI-TOFMS) with orthogonal sample introduction was described. High irradiance of 6 × 10 10 W/cm 2 at 532 nm from a Nd : YAG laser was applied in the experiment to get a high ionization degree in plasma and to dissociate the interferential polyatomic ions. Meanwhile, the interferential multiply charged ions resulted by high-irradiance were nearly eliminated in the spectrum by utilizing helium as the buffer gas in the ion source due to three-body recombination, which resulted in a relatively clean background. Improved signal stability was obtained by automated step moving of the sample stage in short time intervals. By using two sets of Einzel lens in transport system, nearly uniform relative sensitivity coefficients (RSCs) were achieved for most of metal elements including light ions which were detected in extremely low sensitivity in previous hexapole transportation instrument. The resolving power reaches 2200, and the detection limits (DLs) are 10 −6 g/g for metal elements in the steel standard.

On Applicability of a Miniaturised Laser Ablation Time of Flight Mass Spectrometer for Trace Elements Measurements

“…It is well known that at the irradiances used in this study, the ion yield of most elements will depend on laser irradiance [1,21]. The saturation of the ion yield for most of the elements is observed for irradiances larger than few dozens of GW/cm 2 which corresponds to temperature of the plasma about ∼50 000 K [26]. Although sharp changes of the laser irradiance at the sample surface may explain our observation, other effects can also contribute, for example, the appearance of the melting rim.…”

“…Improvements of the design and functionality were also reported after a miniaturisation of laser ablation TOF mass analyser initiated in 1990s by filtering ions of specific energies (energy windowing) [17], or by just applying appropriate ion optics and reflectron combined with ring-shaped detector [13]. Significant improvements of the instrumental performance have been recently achieved by application of novel laboratory LIMS instrument utilising collisional cooling of ions in He buffer gas combined with an orthogonal extraction [26]. The quantitative analysis of the sample composition is, however, not straightforward and requires a careful control of experimental conditions for laser ablation and additional studies of appropriate standard reference materials.…”

Improved detection sensitivity of elements in solids via laser postionization in laser desorption time‐of‐flight mass spectrometry

“…In this geometry, relatively high resolution can be achieved at high laser irradiance, but 1 issue to consider is the elemental fractionation due to the selection of a certain part of the generated plasma. Additionally, introducing helium into LI source and employing repelling pulse trains offer the elevated performance in terms of mass resolution and multiply charged interferences . Another alternative strategy refers to the laser postionization of sputtered neutral atoms generated by primary laser ablation.…”

“…Due to the high sensitivity, isotopic information, and simplified spectrum, mass spectrometry has proven to be a broadly applicable tool for trace elemental analysis in solids, such as secondary ion mass spectrometry (SIMS), [9][10][11] laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), [12][13][14] glow discharge mass spectrometry (GD-MS), [15][16][17] and high irradiance laser ionization mass spectrometry (LI-MS). [18][19][20] SIMS is capable of achieving LOD down to ng/g and an analytical volume of nanoscale, whereas hard to quantify due to severe matrix effects. 21 Laser postionization secondary neutral mass spectrometry (Laser-SNMS) was proposed to mitigate severe matrix effects and improve ionization efficiency of SIMS, whereas the high cost of SIMS and laser-SNMS cannot be ignored.…”

“…Additionally, introducing helium into LI source and employing repelling pulse trains offer the elevated performance in terms of mass resolution and multiply charged interferences. 18 Another alternative strategy refers to the laser postionization of sputtered neutral atoms generated by primary laser ablation. It is of vital importance to separate both the ablation and ionization events temporally as well as spatially, because of the poor spectral resolution under a high irradiance and relatively high LOD at a low irradiance.…”