Simultaneous Quantitation of Amino Acid Mixtures using Clustering Agents

Abstract

A method that uses the abundances of large clusters formed in electrospray ionization to determine the solution-phase molar fractions of amino acids in multi-component mixtures is demonstrated. For solutions containing either four or 10 amino acids, the relative abundances of protonated molecules differed from their solution-phase molar fractions by up to 30-fold and 100-fold, respectively. For the four-component mixtures, the molar fractions determined from the abundances of larger clusters consisting of 19 or more molecules were within 25% of the solution-phase molar fractions, indicating that the abundances and compositions of these clusters reflect the relative concentrations of these amino acids in solution, and that ionization and detection biases are significantly reduced. Lower accuracy was obtained for the 10-component mixtures where values determined from the cluster abundances were typically within a factor of three of their solution molar fractions. The lower accuracy of this method with the more complex mixtures may be due to specific clustering effects owing to the heterogeneity as a result of significantly different physical properties of the components, or it may be the result of lower S/N for the more heterogeneous clusters and not including the low-abundance more highly heterogeneous clusters in this analysis. Although not as accurate as using traditional standards, this clustering method may find applications when suitable standards are not readily available. Electronic supplementary materialThe online version of this article (doi:10.1007/s13361-011-0081-4) contains supplementary material, which is available to authorized users.

Simultaneous quantitation of nucleosides, nucleobases, amino acids, and alkaloids in mulberry leaf by ultra high performance liquid chromatography with triple quadrupole tandem mass spectrometry

“…Other reagent solutions, such as ammonium formate (Lingfeng Chemical Reagent, Shanghai, China) and ammonium acetate (Sinopharm Chemical Reagent), were of analytical grade. Chemical standards of adenine (1), guanine (2), xanthine (3), thymine (10), inosine (13), arginine (15), histidine (16), lysine (17), tyrosine (20), valine (21), proline (22), glutamate (24), serine (27), threonine (28), alanine (29), tryptophan (31), phenylalanine (32), leucine (34), isoleucine (35), aspartic acid (37), 1-deoxynojirimycin (DNJ) (39), and fagomine (40) were purchased from the National Institute for the Control of Pharmaceutical and Biological Products, Beijing, China. Reference compounds of cytidine-5 -monophosphate (4), 2 -deoxyguanosine (5), 2 -deoxyuridine (8), 2 -deoxyinosine (9), cytidine (11), 2 -deoxyadenosine-5 monophosphate (12), thymidine (14), ornithine (18), hydroxyproline (19), citrulline (23), glutamine (25), asparagine (26), glycine (30), ␥-aminobutyric acid (36), and cysteine (38) were obtained from Sigma (St. Louis, MO).…”

“…High sensitivity and high throughput can be obtained by using triple quadrupole mass detection and multiple reaction monitoring (MRM), which use one transition each from the precursor to the reporter ions for every compound, respectively. To our knowledge, unfortunately, there are just quantitative methods for each particular class of the compounds, but no published analytical methods are available for the quantification of nucleosides, nucleobases, amino acids, and alkaloids together. Thus, the UHPLC–triple quadrupole MS (TQ‐MS) method, with which the 40 analytes were completely separated and detected, was established and applied to ten mulberry leaf samples.…”

Formation of deaminated dimer species of amino acids by atmospheric pressure chemical ionization

“…When AA concentration is high enough to form cluster in aqueous solution or aerosol phase, intracluster ion‐molecule reactions can occur. Heteroclusters of Ser (Ser n Ala, Ser n Arg, Ser n ArgHis, Ser n Gly, Ser n His, and Ser n Leu) and Trp (Trp n His and Trp n Lys) formed by ESI were reported . However, deaminated AA dimer species have not been reported.…”