Article pubs.acs.org/ac
High-Speed, High-Resolution, Multielemental Laser AblationInductively Coupled Plasma-Time-of-Flight Mass Spectrometry Imaging: Part I. Instrumentation and Two-Dimensional Imaging of Geological Samples Alexander Gundlach-Graham,*,† Marcel Burger,† Steffen Allner,† Gunnar Schwarz,† Hao A. O. Wang,† Luzia Gyr,† Daniel Grolimund,‡ Bodo Hattendorf,† and Detlef Günther*,† †
Laboratory of Inorganic Chemistry, ETH Zurich, Vladimir-Prelog-Weg 1, CH-8093 Zurich, Switzerland microXAS Beamline Project, Swiss Light Source, Paul Scherrer Institute, 5232 Villigen PSI, Switzerland
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ABSTRACT: Low-dispersion laser ablation (LA) has been combined with inductively coupled plasma-time-of-flight mass spectrometry (ICP-TOFMS) to provide full-spectrum elemental imaging at high lateral resolution and fast imageacquisition speeds. The low-dispersion LA cell reported here is capable of delivering 99% of the total LA signal within 9 ms, and the prototype TOFMS instrument enables simultaneous and representative determination of all elemental ions from these fast-transient ablation events. This fast ablated-aerosol transport eliminates the effects of pulse-to-pulse mixing at laser-pulse repetition rates up to 100 Hz. Additionally, by boosting the instantaneous concentration of LA aerosol into the ICP with the use of a low-dispersion ablation cell, signalto-noise (S/N) ratios, and thus limits of detection (LODs), are improved for all measured isotopes; the lowest LODs are in the single digit parts per million for single-shot LA signal from a 10-μm diameter laser spot. Significantly, high-sensitivity, multielemental and single-shot-resolved detection enables the use of small LA spot sizes to improve lateral resolution and the development of single-shot quantitative imaging, while also maintaining fast image-acquisition speeds. Here, we demonstrate simultaneous elemental imaging of major and minor constituents in an Opalinus clay-rock sample at a 1.5 μm laser-spot diameter and quantitative imaging of a multidomain Pallasite meteorite at a 10 μm LA-spot size.
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ince its introduction in 1985 by Gray,1 laser ablationinductively coupled plasma mass spectrometry (LAICPMS) has become a routine and widely used procedure for the qualitative and quantitative elemental characterization of solid materials. LA-ICPMS allows for the determination of elemental composition over a broad dynamic range, from trace to major elements, with little to no sample preparation.2 Typically, LA-ICPMS is applied in a targeted-analysis mode, in which the laser beam is focused on a region of interest of the sample and fired repeatedly while ICPMS signal is acquired. However, more and more, LA-ICPMS is used for twodimensional (2D) elemental imaging.3,4 In LA-ICPMS imaging, the laser beam is scanned across a sample surface and ICPMS signals are acquired as a function of laser-beam position. In particular, elemental mapping enables the characterization of microstructures and elemental distributions across multiphase and heterogeneous samples in fields such as geology,5 biology and medicine,4,6−10 and archeology.11,12 LA-ICPMS is complementary with other elemental imaging methods, such as micro synchrotron X-ray fluorescence spectroscopy (μ-SR-XRF), micro proton-induced X-ray emis© XXXX American Chemical Society
sion spectroscopy (μ-PIXE), energy-dispersive X-ray spectrometry (EDXS), electron-probe X-ray micro analysis (EPMA), and secondary-ion mass spectrometry (SIMS). More detailed comparison of elemental surface imaging techniques can be found in a number of recent books and reviews.13−16 Of the Xray-based methods, LA-ICPMS generally offers better detection limits and access to a broader range of elements as well as isotopic information. μ-SR-XRF and μ-PIXE can achieve excellent lateral resolution (10−0.1 μm) with moderate sensitivity but require access to large synchrotron and particle-accelerator facilities, respectively; whereas benchtop EDXS instruments can provide moderate lateral resolution (
