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RESEARCH PROFILE The best of both worlds with LC/FTMS With MS, you generally can’t have your cake and eat it too. You can use a MALDI time-of-flight (TOF) mass spectrometer to get high mass accuracy, or you can opt for the superior MS/MS capabilities of a triple-quadrupole or a quadrupole ion trap instrument. Achieving high performance in both realms is a much more difficult task. In the September 15 issue of Analytical Chemistry (pp 4266–4274), Jarrod A. Marto, Donald F. Hunt, and colleagues at the University of Virginia describe a new approach that may provide the best of both worlds: They couple microcapillary HPLC columns, which have been fabricated with integrated nanoelectrospray emitter tips, to a Fourier transform (FT) ion cyclotron resonance mass spectrometer. For MS analysis, the researchers report the generation of accurate mass (±0.010 Da) tryptic peptide maps with high sequence coverage (20–60%), using as little as 10 amol of sample. They also report high resolution (m/D m > 5000) and accurate mass (5–10 ppm) MS/MS analysis for peptides present at levels as low as 400 amol. Although other researchers have obtained peptide and protein sequence information using electrospray ionization (ESI) with FTMS, they have typically infused samples directly. Acquiring data on a chromatographic timescale was difficult because the instruments used pulsed gas-assisted ion accumulation inside the Penning trap, and the time needed to restore the vacuum was not compatible with LC analysis. But that changed with the advent of external ion accumulation about 3 years ago. “The use of external ion accumulation allows us to acquire several mass spectral scans across a chromatographic peak,” Marto explains. In addition, the microcapillary HPLC column/ESI emitter has a low postcolumn dead volume, resulting in LC peak widths of
split to transfer excess eluent into a 6-port, 2-position valve. Fused-silica restrictors in opposing valve ports allow real-time selection of either highflow (~120 nL/min) or low-flow (
