APPLICATION OF THE FAST-EVAPORATION SAMPLE PREPARATION METHOD FOR IMPROVING QUANTIFICATION OF ANGIOTENSIN-II BY MATRIX-ASSISTED LASER-DESORPTION IONIZATION

The fast-evaporation method of sample preparation has been applied for quantitative analysis using matrix-assisted laser desorption/ionizati on (MALDI) mass spectrometry. An instrumental protocol focusing on imp rovement of shot-to-shot repeatability and compensation for signal deg radation has been developed for quantification of angiotensin II using the fast-evaporation technique and an internal standard. The fast-eva poration method was compared to the standard method of sample preparat ion (using a multicomponent matrix) in the quantitative analysis of an giotensin II, and found to be superior in several respects, Improvemen t In sample homogeneity using the Past-evaporation method enhanced bot h point-to-point repeatibility and sample-to-sample reproducibility. T he relative standard deviations of the analyte/internal standard ratio s (point RSD) were decreased by a factor of three compared to those ob tained using the multicomponent matrix method, The average point RSD w as found to be ca. 5% for the fast-evaporation technique. Two internal standards were evaluated for quantification of angiotensin II. The be tter one, 1-SAR-8-Ile angiotensin II, yielded a relative standard devi ation of the standard curve slope of ca. 2.2% over two orders of magni tude of concentration (45 nM to 3000 nM), an improvement by a factor o f two over the standard preparation method. Renal microdialysate sampl es, spiked with angiotensin II and the internal standard 1-SAR-8-Ile a ngiotensin II, were also analyzed using the fast-evaporation technique . The detection limit was calculated to be in the high attomole range (675 amol). Furthermore, the accuracy for a single determination of an giotensin II concentration in these samples was found to be 13.9% with a relative error of 8.19%.