Non-specific, on-probe cleanup methods for MALDI-MS samples

I. Introduction 429 II. Decontamination with Films of Commercial Polymers 431 A. Polyvinylidenedifluoride and Nitrocellulose 431 B. Nylon 431 C. Nafion 432 D. Polyethylene (PE) and Polypropylene (PP) 432 E. Polyurethane 432 F. Paraffin and Teflon 432 G. Ion‐Exchange Materials 433 III. Decontamination with Thin Layers of Matrix Crystals 433 A. Mechanism of Adsorption to Matrix Crystals 434 B. Preparation of Desalting Matrix Crystals 434 1. Thin Layers of Matrix Crystals 434 2. Hydrophilic Spots of Matrix in Hydrophobic Polymer Layers 435 IV. Decontamination with SAMs and Ultrathin Polymer Films 435 A. Decontamination with Hydrophobic Interactions 435 B. Decontamination with Electrostatic Interactions 436 C. Patterned SAM/Polymer Films 437 V. Conclusions 438 Acknowledgments 438 References 438 High concentrations of contaminants such as salts and surfactants are often present in biological samples to solubilize or stabilize analytes such as proteins. Unfortunately, the presence of those contaminants often precludes direct analysis by MALDI‐MS. Selective adsorption of analytes directly on modified MALDI probes, followed by rinsing to remove contaminants, overcomes this problem. This review focuses on various modifications of MALDI probes to allow the adsorption of proteins and DNA, even in a large excess of salt or surfactant. Interfaces deposited on the MALDI probes to adsorb analytes include films of commercial polymers, thin layers of matrix crystals, self‐assembled monolayers, and ultrathin polymer films. Hydrophobic and ionic interactions both effect analyte adsorption on those interfaces, and patterned interfaces allow the concentration and purification of analyte molecules. © 2003 Wiley Periodicals, Inc., Mass Spec Rev 22:429–440, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mas.10064