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Utrecht, Netherlands

Pirman D.A.,University of Florida | Kiss A.,FOM Institute for Atomic and Molecular Physics | Kiss A.,Netherlands Proteomic Center | Heeren R.M.A.,FOM Institute for Atomic and Molecular Physics | And 2 more authors.
Analytical Chemistry | Year: 2013

Generating analyte-specific distribution maps of compounds in a tissue sample by matrix-assisted laser desorption/ionization (MALDI) mass spectrometric imaging (MSI) has become a useful tool in numerous areas across the biological sciences. Direct analysis of the tissue sample provides MS images of an analyte's distribution with minimal sample pretreatment. The technique, however, suffers from the inability to account for tissue-specific variations in ion signal. The variation in the makeup of different tissue types can result in significant differences in analyte extraction, cocrystallization, and ionization across a sample. In this study, a deuterated internal standard was used to account for these signal variations. Initial experiments were performed using pure standards and optimal cutting temperature compound (OCT) to generate known areas of ion suppression. By monitoring the analyte-to-internal-standard ratio, differences in ion signal were taken into account, resulting in images that better represented the analyte concentration. These experiments were then replicated using multiple tissue types in which the analyte's MS signal was monitored. In certain tissues, including liver and kidney, the analyte signal was attenuated by up to 90%; however, when the analyte-to-internal-standard ratio was monitored, these differences were taken into account. These experiments further exemplify the need for an internal standard in the MSI workflow. © 2012 American Chemical Society. Source

Pirman D.A.,University of Florida | Reich R.F.,University of Florida | Kiss A.,FOM Institute for Atomic and Molecular Physics | Kiss A.,Netherlands Proteomic Center | And 3 more authors.
Analytical Chemistry | Year: 2013

Mass spectrometric imaging (MSI) is an analytical technique used to determine the distribution of individual analytes within a given sample. A wide array of analytes and samples can be investigated by MSI, including drug distribution in rats, lipid analysis from brain tissue, protein differentiation in tumors, and plant metabolite distributions. Matrix-assisted laser desorption/ionization (MALDI) is a soft ionization technique capable of desorbing and ionizing a large range of compounds, and it is the most common ionization source used in MSI. MALDI mass spectrometry (MS) is generally considered to be a qualitative analytical technique because of significant ion-signal variability. Consequently, MSI is also thought to be a qualitative technique because of the quantitative limitations of MALDI coupled with the homogeneity of tissue sections inherent in an MSI experiment. Thus, conclusions based on MS images are often limited by the inability to correlate ion signal increases with actual concentration increases. Here, we report a quantitative MSI method for the analysis of cocaine (COC) from brain tissue using a deuterated internal standard (COC-d3) combined with wide-isolation MS/MS for analysis of the tissue extracts with scan-by-scan COC-to-COC-d 3 normalization. This resulted in significant improvements in signal reproducibility and calibration curve linearity. Quantitative results from the MSI experiments were compared with quantitative results from liquid chromatography (LC)-MS/MS results from brain tissue extracts. Two different quantitative MSI techniques (standard addition and external calibration) produced quantitative results comparable to LC-MS/MS data. Tissue extracts were also analyzed by MALDI wide-isolation MS/MS, and quantitative results were nearly identical to those from LC-MS/MS. These results clearly demonstrate the necessity for an internal standard for quantitative MSI experiments. © 2012 American Chemical Society. Source

Kiss A.,FOM Institute for Atomic and Molecular Physics | Kiss A.,Netherlands Proteomic Center | Heeren R.M.A.,FOM Institute for Atomic and Molecular Physics | Heeren R.M.A.,Netherlands Proteomic Center
Analytical and Bioanalytical Chemistry | Year: 2011

Size, weight and position are three of the most important parameters that describe a molecule in a biological system. Ion mobility spectrometry is capable of separating molecules on the basis of their size or shape, whereas imaging mass spectrometry is an effective tool to measure the molecular weight and spatial distribution of molecules. Recent developments in both fields enabled the combination of the two technologies. As a result, ion-mobility-based imaging mass spectrometry is gaining more and more popularity as a (bio-) analytical tool enabling the determination of the size, weight and position of several molecules simultaneously on biological surfaces. This paper reviews the evolution of ion-mobilitybased imaging mass spectrometry and provides examples of its application in analytical studies of biological surfaces. © The Author(s) 2011. Source

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