Toxicological applications of cryogenic laser ablation inductively coupled plasma time of flight mass spectrometry (CLA-ICP-TOF-MS)

Abstract

The analysis of acid digested bulk tissue samples by ICP-MS is a primary method for toxicologists when trying to characterize the uptake and storage of a trace metal by an organism. This approach is sensitive, reliable and reproducible but requires the homogenization of the tissue for analysis. This procedure does not provide any information on the distribution of the analyte of interest within the tissue sample. Sub-sampling is a possible alternative method for preserving distribution data but in many cases sub-sampling on the scale necessary for useful information is not an option due to sample size limitations. By coupling a laser ablation system equipped with a cryogenic cell to an Inductively Coupled Plasma Mass Spectrometer (CLA-ICP-MS), it is possible to achieve high-resolution trace metal distribution data on toxicological tissue samples. A cryo-cell is critical for proper ablation of soft tissue samples by LA-ICP-MS. The system used for the work presented is a commercially available cryo cell from GeoMed Analytical capable of temperatures as low as −30 °C, coupled to a GBC Scientific ICP-Time of Flight-MS (ICP-TOF-MS). The speed of the TOF system is an ideal platform for the analysis of the transient signal produced by laser ablation and has detection limits that are comparable to traditional ICP-MS (i.e. low ppb range). This system is suitable for the ablation of a range of tissues with a spatial resolution of 25 microns for most elements. Results will be presented that identify the optimal ablation settings for obtaining accurate and precise Zn and Cu isotope ratios in tissue samples. A demonstration of the potential toxicological application of the CLA-ICP-TOF-MS system using a Zn stable isotope tracer in the earthworm Lumbricus terrestris will also be presented.