[Analysis of chemically synthesized peptides by liquid secondary ion mass spectrometry (LSIMS)].

Liquid secondary ion mass spectrometry (LSIMS) was proven to have advantage for analysis of chemically synthesized peptides. The molecular weights of large peptides were determined accurately, without difficulty in spite of only small sample quantities (50 pmol-10 nmol). This approach was also useful in comparing actual isotopic cluster-distribution of protonated molecular-ion with that derived theoretically for ascertaining peptide integrity. Sometimes LSIMS spectra showed abundant fragment ions from which partial peptide sequences were determinable and unexpected synthetic product could be easily identified from informative fragment ions in LSIMS spectra. The analytical procedure combining LSIMS and high performance liquid chromatography (HPLC) was very beneficial for detecting impurities having slight structural differences. Moreover, LSIMS proved excellent for use in analysis of tyrosine-O-sulfate [Tyr(SO3H)] containing peptides. Constant neutral loss (80 amu) spectra, measured in view of the specific fragmentation (-SO3), showed the complete sequence of a Tyr(SO3H) containing peptide. These results document the usefulness of LSIMS for analysis of peptide samples where difficulty is encountered in evaluation by traditional analytical methods.