The determination of protein, oligonucleotide and peptide molecular weights by ion‐spray mass spectrometry

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Abstract
The mass spectra of several compounds with molecular weights in the 2500–20 000 Da range were obtained with a quadrupole mass spectrometer equipped with an atmospheric pressure ion source. Average molecular weight determinations of mellitin (2846.4 Da), a synthetic oligonucleotide (4262.8 Da), myoglobin (16 950.4 Da) and on the subunits of β-lactoglobulin (18 277.1 Da) requiring as little as 1 pmol of material were achieved with accuracies and precisions of ± 1 Da. An ion-spray interface was used to produce ions via the ion evaporation process, producing mass spectra containing a series of multiply-charged molecular species. A simple method for calculating the molecular weight of unknown compounds from the spectra containing multiply-charged ions is described.