Investigations of Some Liquid Matrixes for Analyte Quantification by MALDI

Quantitative Approach Using Matrix-Assisted Laser Desorption/Ionization Time-of-Flight (MALDI-ToF) Mass Spectrometry

Quantitation using mass spectrometry (MS) is a routine approach for multiple analytes, including small molecules and peptides. Electrospray-based MS platforms are typically employed, as they provide highly reproducible outputs for batch processing of multiple samples. Quantitation using matrix-assisted laser desorption/ionization (MALDI) time-of-flight (ToF) mass spectrometry, while less commonly adopted, offers the ability to monitor analytes at significantly higher throughput and lower cost compared with ESI MS. Achieving accurate quantitation using this approach requires the development of appropriate sample preparation, spiking of appropriate internal standards, and acquisition to minimize spot-to-spot variability. Here we describe the preparation of samples for accurate quantitation using MALDI-ToF MS. The methodology presented shows the ability to quantitate perfluorooctanesulfonic acid (PFOS) from contaminated water.

Ionic Liquid-Assisted Laser Desorption/Ionization-Mass Spectrometry: Matrices, Microextraction, and Separation

Ionic liquids (ILs) have advanced a variety of applications, including matrix-assisted laser desorption/ionization-mass spectrometry (MALDI-MS). ILs can be used as matrices and solvents for analyte extraction and separation prior to analysis using laser desorption/ionization-mass spectrometry (LDI-MS). Most ILs show high stability with negligible sublimation under vacuum, provide high ionization efficiency, can be used for qualitative and quantitative analyses with and without internal standards, show high reproducibility, form homogenous spots during sampling, and offer high solvation efficiency for a wide range of analytes. Ionic liquids can be used as solvents and pseudo-stationary phases for extraction and separation of a wide range of analytes, including proteins, peptides, lipids, carbohydrates, pathogenic bacteria, and small molecules. This review article summarizes the recent advances of ILs applications using MALDI-MS. The applications of ILs as matrices, solvents, and pseudo-stationary phases, are also reviewed.

Gain Switching for a Detection System to Accommodate a Newly Developed MALDI-Based Quantification Method

In matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF), matrix-derived ions are routinely deflected away to avoid problems with ion detection. This, however, limits the use of a quantification method that utilizes the analyte-to-matrix ion abundance ratio. In this work, we will show that it is possible to measure this ratio by a minor instrumental modification of a simple form of MALDI-TOF. This involves detector gain switching. Graphical Abstract ᅟ.

Quantitative transfer of polar analytes on a solid surface to a liquid matrix in MALDI profiling

In profiling of a specimen by matrix-assisted laser desorption ionization (MALDI) using a solid matrix, the solvent of the matrix solution extracts an analyte(s). A quantitative profiling cannot be achieved if the solvent evaporates before the complete extraction of the analyte. The extraction can become more quantitative when a liquid matrix dissolved in a solvent is used, which remains a liquid even after the evaporation of the solvent. To check this, radii of an analyte circle (r_A ), a matrix solution drop (r_D ) and a liquid matrix (r_M ) remaining after the solvent evaporation were controlled. Three types of samples were prepared, case A (r_A , r_D  < r_M ), case B (r_D  ≤ r_M  < r_A ) and case C (r_M  < r_D  < r_A ). In case A, the analyte amount in the matrix layer determined by MALDI was the same as the prepared amount inside the analyte circle. In case B, the analyte amount was the same as the amount inside the matrix circle. Only the analytes in contact with the liquid matrix layer, not more and not less, are transferred to the matrix layer. In case C, the analyte amount was greater than the amount inside the matrix circle, presumably because some of the analyte outside the matrix circle was dissolved by the solvent of the matrix solution. Copyright © 2016 John Wiley & Sons, Ltd.