MICRO-ELECTROSPRAY MASS-SPECTROMETRY - ULTRA-HIGH-SENSITIVITY ANALYSIS OF PEPTIDES AND PROTEINS

A ''micro-electrospray'' ionization source has been developed that mar kedly increases the sensitivity of the conventional electrospray sourc e. This was achieved by optimization of the source to accommodate nano liter flow rates from 300 to 800-nL/min spraying directly from a capil lary needle that, for the analysis of peptides, contained C18 liquid c hromatography packing as an integrated concentration-desalting device. Thus, a total of 1 fmol of methionine enkephalin was desorbed from th e capillary column spray needle, loaded as a 10-muL injection of 100-a mol/muL solution. The mass spectrum showed the [M + H]+ ion at m/z 574 .2 with a signal-to-noise ratio of better than 5:1 from a chromatograp hic peak with a width of about 12 s. A narrow range (15-u) tandem mass spectrum was obtained for methionine enkephalin from the injection of 500 amol, and a full-scan tandem-mass spectrum was obtained from 50 f mol. For proteins, the average mass measurement accuracy was approxima tely 100-200 ppm for the injection of 2.5 fmol of apomyoglobin and 20- 40 ppm for 200 fmol. Carbonic anhydrase B and bovine serum albumin sho wed similar mass measurement accuracies.