Polyalanine - a practical polypeptide mass calibration standard for matrix-assisted laser desorption/ionization mass spectrometry and tandem mass spectrometry in positive and negative mode.

ABSTRACT

RATIONALE Mass calibration in matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) is currently obtained using mixtures of individual peptides. This procedure has several drawbacks, including laborious preparation, limited shelf life and unequal calibration mass spacing. Polyalanine, a simple to prepare polydisperse molar mass standard, alleviates these problems. METHODS: Polyalanine is prepared by the typical protocols for biological sample analytics. RESULTS: Polyalanine is the first polymeric standard providing abundant signals in both, positive and negative polarity mode with the typical matrices DHB and HCCA. CONCLUSIONS: Facile MS as well as MS/MS calibration is thus enabled for the first time in both polarity modes by employing this polydisperse standard.