QUANTIFICATION OF BIOMOLECULES BY EXTERNAL ELECTROSPRAY-IONIZATION FOURIER-TRANSFORM MASS-SPECTROMETRY

Fourier transform mass spectrometry (FTMS) is well-known for its capab ilities in structural characterization of molecules, Recent developmen ts in radio frequency excitation, linearized trapping, and accumulatio n of ions generated from external sources have improved the potential of FTMS for quantitative analysis, Here, a commercial external electro spray ionization ETMS, employing a linearized ion trap (the Infinity C ell) and an ion accumulation procedure in which ions are deflected off -axis and injected into the trap, is evaluated as an analytical method for quantifying amino acids, peptides, and proteins. Linear response over similar to 2-3 orders of magnitude is observed for singly-charged ions with low coefficients of variation (generally <10%), and the cal ibration curves generated can be used to quantify structurally similar analytes with <4% relative error, as shown here for quantification of leucine enkephalin from curves generated by methionine enkephalin, Si milar precision is obtained for multiply-charged lysozyme, but over on ly 1.5 orders of magnitude, Some mit discrimination is observed as a f unction of trap accumulation potential for a two-component cytochrome c/lysozyme mixture, The results are promising because they suggest tha t quantification using liquid chromatography coupled to electrospray F TMS is possible.