title: Application of the fast-evaporation sample preparation method for improving quantification of angiotensin II by matrix-assisted laser desorption/ionization.
abstract: The fast-evaporation method of sample preparation has been applied for quantitative analysis using matrix-assisted laser desorption/ionization (MALDI) mass spectrometry. An instrumental protocol focusing on improvement of shot-to-shot repeatability and compensation for signal degradation has been developed for quantification of angiotensin II using the fast-evaporation technique and an internal standard. The fast-evaporation method was compared to the standard method of sample preparation (using a multicomponent matrix) in the quantitative analysis of angiotensin II, and found to be superior in several respects. Improvement in sample homogeneity using the fast-evaporation method enhanced both point-to-point repeatibility and sample-to-sample reproducibility. The relative standard deviations of the analyte/internal standard ratios (point RSD) were decreased by a factor of three compared to those obtained using the multicomponent matrix method. The average point RSD was found to be ca. 5% for the fast-evaporation technique. Two internal standards were evaluated for quantification of angiotensin II. The better one, 1-SAR-8-Ile angiotensin II, yielded a relative standard deviation of the standard curve slope of ca. 2.2% over two orders of magnitude of concentration (45 nM to 3000 nM), an improvement by a factor of two over the standard preparation method. Renal microdialysate samples, spiked with angiotensin II and the internal standard 1-SAR-8-Ile angiotensin 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 angiotensin II concentration in these samples was found to be 13.9% with a relative error of 8.19%.
authors.affiliation: Department of Chemistry, University of Pittsburgh, PA 15260, USA.
authors.forename: A J
authors.initials: AJ
authors.lastname: Nicola
authors.forename: A I
authors.initials: AI
authors.lastname: Gusev
authors.forename: A
authors.initials: A
authors.lastname: Proctor
authors.forename: E K
authors.initials: EK
authors.lastname: Jackson
authors.forename: D M
authors.initials: DM
authors.lastname: Hercules
mesh_terms: D015059:1-Sarcosine-8-Isoleucine Angiotensin II / Q000032:analysis; D000804:Angiotensin II / Q000032:analysis* / Q000737:chemistry; D000818:Animals; D007668:Kidney / Q000737:chemistry; D051381:Rats; D012015:Reference Standards; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
chemical_list: D000804:Angiotensin II; D015059:1-Sarcosine-8-Isoleucine Angiotensin II