Research Article Received: 12 June 2014

Revised: 12 September 2014

Accepted: 13 September 2014

Published online in Wiley Online Library

Rapid Commun. Mass Spectrom. 2014, 28, 2627–2635 (wileyonlinelibrary.com) DOI: 10.1002/rcm.7054

Rapid cell mode switching and dual laser ablation inductively coupled plasma mass spectrometry for elemental bioimaging Christoph A. Wehe1, Ann-Christin Niehoff1,2, Georgina M. Thyssen1, Michael Sperling1,3 and Uwe Karst1* 1

University of Münster, Institute of Inorganic and Analytical Chemistry, Corrensstr. 28–30, 48149 Münster, Germany NRW Graduate School of Chemistry, University of Münster, Wilhelm-Klemm-Str. 10, 48149 Münster, Germany 3 European Virtual Institute for Speciation Analysis (EVISA), Mendelstr. 11, 48149 Münster, Germany 2

RATIONALE: Two different approaches to improve the limits of detection (LODs) in elemental bioimaging have been developed. They both consider the fact that for the widely applied quadrupole-based instruments, metals in the mass range 30, before tuning of the lenses. Typical cell gas flow rates were in the range of 4.8–5.0 mL/min with a bias potential of 3 V between the CRC and the quadrupole mass analyzer. For the CCT mode, using a mixture of O2 and He, the optimum settings of the lenses were adjusted automatically by applying different voltages on every second lens and finding the optimum sensitivity for a solution containing 1 μg/L of Bi in 2% (w/w) HNO3. The cell gas flow rate was adjusted automatically by finding the point of maximum sensitivity vs blank intensities, i.e., the value which provides the best LODs. Under KED conditions, the following isotopes were recorded with dwell times according to the natural abundance: 55Mn (0.08 s), 56Fe (0.08 s), 57Fe (0.2 s), 58Ni (0.04 s), 59Co (0.08 s), 60Ni (0.1 s), 63Cu (0.04 s), 65Cu (0.08 s), 66 Zn (0.15 s) and 68Zn (0.15 s). For CCT mode studies, 31 16 P O (0.2 s) and 32S16O (0.8 s) were acquired. The macro instruction file (see Supporting Information) was written for Microsoft (Redmond, WA, USA) Excel 2013 VBA using Microsoft Visual Studio Professional 2013. The LA unit was controlled using DigiLaz II software (Teledyne

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these settings. The scan speed of the laser beam onto the sample surface was set to produce one pixel per second of the final image, i.e., 50 and 25 μm/s, respectively. The ICP-MS units were equipped with a novel, low-volume CRC with RF-only driven bent, flat rods (QCell). During all the studies, the instruments were operated at a power of 1550 W (free-running generator) and a cooling gas flow rate of 14 L/min Ar. A sampling depth of 7 mm and an auxiliary gas flow rate of 0.5 L/min Ar were used for the ICP-MS instrument running under KED settings for the LA-dualICP-MS studies; otherwise 5 mm and 0.8 L/min Ar provided the best sensitivity. Coupling of LA and ICP-MS was performed using a homebuilt perfluoroalkoxy polymer (PFA) sample inlet, in which the dry aerosol from the laser ablation is mixed with the wet tertiary aerosol, generated by a μFlow-PFA nebulizer (Elemental Scientific Inc., Omaha, NE, USA). The nebulizers were operated within a Peltier-cooled cyclonic quartz glass spray chamber at 2.7 °C. Tuning of the instruments was possible without any further hardware modifications under LA conditions. The x- and y-positions of the torch, the nebulizer gas flow rate, and the potential of the second extraction lens and the lens in front of the QCell were tuned on a daily basis by the introduction of a multi-element standard with a sensitivity for 1 μg/L In of at least 350 000 counts per second (cps), an oxide ratio