Electrospray ionization Fourier transform mass spectrometry quantification of enkephalin using an internal standard

Abstract

Fourier transform mass spectrometry (FTMS), long-known for its capabilities in structural characterization of molecules, is an emerging tool in quantification, and quantification methods using external and internal standards with electrospray ionization (ESI) FTMS have recently been demonstrated. Here, commercial ESI-FTMS is used to quantify the opioid pentapeptide methionine enkephalin using an internal standard. Linear working curves over three orders of magnitude are obtained using the internal standard, an improvement of one order of magnitude over the previous external standard ESI-FTMS quantification method for enkephalins. Low coefficients of variation (generally <6%) are observed, and inter-day and intra-day assays are compared and found to possess similar linearity and precision. The high mass accuracy advantage of FTMS can be exploited to give molecular specificity. Efforts to improve mass accuracy using internal mass calibration generally provide mass accuracies within 2.5 ppm.

Use of the filter diagonalization method in the study of space charge related frequency modulation in Fourier transform ion cyclotron resonance mass spectrometry

“…Current FTMS instruments are capable of routinely producing measurements with ϳ1 ppm accuracy internally calibrated [6][7][8] and ϳ5 ppm externally calibrated [9,10]. Recent studies in proteomics show that determination of amino acid composition of tryptic peptides requires at least 0.1 ppm mass accuracy [11,12].…”