Rapid cell mode switching and dual laser ablation inductively coupled plasma mass spectrometry for elemental bioimaging

Wehe C., Niehoff A., Thyssen G., Sperling M., Karst U.

Abstract

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 <100 u are analyzed with the best figures of merit in the kinetic energy discrimination (KED) mode; much better LODs are achieved for some metalloids and nonmetals by the introduction of more reactive gases, e.g., oxygen, into the collision/reaction cell (CRC). METHODS: While the first approach simultaneously utilizes two inductively coupled plasma mass spectrometry (ICP-MS) detectors hyphenated to one laser ablation (LA) system, the second is based on a single ICP-MS instrument with fast cell mode switching (CMS) of the CRC between individual line scans. RESULTS: Both methods were evaluated concerning their respective improvements by the analysis of rat brain samples. The utilization of two detectors showed improved LODs compared with conventional KED-only analysis in dependency on the gas flow splitting ratio, e.g., for sulfur by about 3.5 orders of magnitude. CMS provided even better results with a further improvement by a factor of 1.6. CONCLUSIONS: As a CRC with a small inner volume was used, fast cell gas switches at the end of every line prevented issues related to the reproducibility of the laser ablation stage for the CMS approach. Linear interpolation was found to be a valuable tool without affecting the spatial resolution of the images. In addition, a software macro is presented, which facilitates data evaluation.