An open, non-contact cell for laser ablation-inductively coupled plasma-mass spectrometry† Dhinesh Asogan, ab Barry L. Sharp, * a Ciaran J. P. O’ Connor, c Damon A. Green c and Robert W. Hutchinson c Received 10th March 2009, Accepted 15th April 2009 First published as an Advance Article on the web 13th May 2009 DOI: 10.1039/b904850b A novel, open, non-contact cell for laser ablation, capable of sampling: large planar samples, embedded planar samples, or samples of less than 2 mm mounted on a planar platform, without an outer containment enclosure, is described. This cell, when tested on NIST-613 CRM, exhibited rapid wash- out (<3.6 s for 99% signal reduction), low limits of detection and good signal precision in LA-ICP-MS. The cell uses a dual, annular, micro-jet gas flow array to exclude atmospheric gases and to entrain the ablated sample aerosol. The micro-jet array employed enabled a sampling height, between the sample surface and the lowest plane of the cell, of up to 200 mm. The micro-jet array has the facility to be electrically biased if the application demands it, e.g. extracting a charged plume in Matrix-Assisted Laser Desorption/Ionisation (MALDI) or Desorption Electrospray Ionisation (DESI) experiments. This particular implementation of the cell featured dual sample output channels, which could enable connection of the cell to more than one analyser. A micro jet-pump was coupled to the cell to extract the ablated aerosol from the low-volume inner ablation chamber, provide mixing of the aerosol with the injector flow of the ICP and to isolate the cell from downstream conditions in the injector flow. Potential applications of this cell include: analysis of silicon wafers, gel-plates/membranes, tissue samples, multiple sample analysis in high throughput facilities; and toxic fume removal and analysis in laser scribing, cutting and etching. Introduction Laser ablation-inductively coupled plasma (LA-ICP) optical- and mass-spectrometry are currently limited by the size of the samples they can analyse. Ingress of atmospheric gases can make an ICP unstable, leading to extinction of the plasma, and the presence of these gases greatly enhances the abundance of unwanted molecular ions when mass spectrometric detection is employed. This has meant that samples have had to be enclosed in a sample chamber filled with argon or helium. To avoid difficulties with sample transport and excessive wash-in and wash-out times, the sample cells have tended to be relatively small. In 2007, Bleiner and Bogaerts 1 studied a range of cell designs using computer simulations to assess gas flow patterns and the entrainment of the aerosol. The various cells were categorised into ‘closed’ and ‘open’ cells. The ‘closed’ cell was defined as a sample chamber which fully enclosed the sample, requiring little to no sample preparation, and the ‘open’ cell used the sample as a final, closing wall; this normally requires the sample to be polished to provide adequate sealing. The ‘open’ cells offer advantages in terms of shortened washout times (as most have small internal volumes) and increased flexibility in sample size. However, alteration of the sample surface by polishing is not viable for many samples; it may introduce contamination or remove features that could otherwise be studied by the LA technique. Custom cells have been described for a variety of applications including closed cells for: low pressure ablation, 2 ablation of gel plates and membranes 3 and radionuclides; 4 and open cells for: continuous sampling, 5 flat plates, 6 solutions, polymers and steel, 7 antiques 8 and large sample handling. 9–11 A key feature of all the cells described to date is that ultimately the sample is either contained in a box or contacts the sample for a final seal; this limits the sample size and complicates multi- sample or high throughput operation. An open, ‘non-contact’ cell 12 that does not physically touch the sample would overcome many of the problems associated with existing cell designs and enable LA to be applied directly to samples of any arbitrary size or number. This paper describes such a cell. LA cells using annular gas flows Annular gas flows can be used to reduce the effective volume of an ablation cell and to entrain ablated material from the ablation site. Further, by maintaining a stable geometry relative to the laser beam, the ablation site remains in a reproducible gas flow environment. A cell design, incorporating an annular flow of argon, intended for quasi-continuous sampling was patented by Barringer in a Centre for Analytical Science, Department of Chemistry, Loughborough University, Loughborough, Leicestershire, UK LE11 3TU. E-mail: B.L. Sharp@lboro.ac.uk b Centre for Innovative and Collaborative Engineering, Department of Civil and Building Engineering, Loughborough University, Loughborough, Leicestershire, UK LE11 3TU c Electro Scientific Industries, New Wave Research Division, 8 Avro Court, Ermine Business Park, Huntingdon, Cambridgeshire, UK PE29 6XS † Presented at the 2009 European Winter Conference on Plasma Spectrochemistry, Graz, Austria, February 15–20, 2009. This journal is ª The Royal Society of Chemistry 2009 J. Anal. At. Spectrom., 2009, 24, 917–923 | 917 PAPER www.rsc.org/jaas | Journal of Analytical Atomic Spectrometry Downloaded by Loughborough University on 16 May 2011 Published on 13 May 2009 on http://pubs.rsc.org | doi:10.1039/B904850B View Online