Georgia Tech | EPICS Lab

Analysis of Selenium Metabolites by Laser Desorption Single Photon Ionization Mass Spectrometry

SALDI is particularly valuable in the identification of small organic molecules because of the low level of background chemical noise in the mass region of m/z < 500. However, this approach requires specific procedures to prepare substrates with optimum properties for reproducible results. Two-step laser desorption photoionization mass spectrometry is a powerful analytical technique for characterizing a wide range of molecular systems which does not require as rigorous substrate preparation. This technique uses one laser to stimulate desorption of intact neutral molecules and a second laser to ionize the desorbed neutral molecules. The analysis of organoselenium and organic acid metabolites using laser desorption from graphite surfaces coupled to vacuum ultraviolet single photon ionization mass spectrometry (LD/SPI MS) has been studied. It was found to have a 1-10 fmol sensitivity and linear dynamic range which allows quantitative detection of organoselenium metabolites in complex biological samples such as human urine. In addition, common urinary metabolites are readily detected. Screening and quantitative detection of these organoselenium and organic acid metabolites is achieved within minutes. These results are also consistent with those obtained using high-performance liquid chromatography tandem mass spectrometry techniques. The study demonstrates the viability of matrix-free LD/SPI MS for molecular characterization and quantitive analysis of biological metabolites in the m/z 10-500 range that are present in complex biological fluids.