title: Determination of D/L-amino acids by zero needle voltage electrospray ionisation.
abstract: Ion formation may be made more efficient than in normal electrospray ionization (ESI) for certain classes of compounds, such as the polar amino acids Glu, Asn, His, Ser, Asp, Arg, Tyr and Lys, by adjusting the voltage of a normal ESI interface needle to zero voltage. For aspartic acid (Asp) the gain in signal-to-noise (S/N) ratio of the liquid chromatography/mass spectrometry (LC/MS) chromatograms obtained in the selective ion monitoring (SIM) mode (m/z 134) with zero needle potential was 40-50 times higher than detection at 4 kV. Ion formation at zero potential is likely to follow a mechanism related to sonic spray ionization. The utility of the zero needle voltage ESI was illustrated by determining the age of a human tooth by the aspartic acid epimerization method. The procedure involved separating the D- and L-aspartic acid of a tooth extract on a chiral HPLC column and detection by zero voltage ESI-MS3.
authors.affiliation: Department of Nature, Systems and Models, Roskilde University, DK-4000 Roskilde, Denmark.
authors.forename: Morten B
authors.initials: MB
authors.lastname: Sørensen
authors.forename: Per
authors.initials: P
authors.lastname: Aaslo
authors.forename: Helge
authors.initials: H
authors.lastname: Egsgaard
authors.forename: Torben
authors.initials: T
authors.lastname: Lund
mesh_terms: D000366:Age Determination by Teeth / Q000379:methods*; D000596:Amino Acids / Q000032:analysis* / Q000737:chemistry*; D004563:Electrochemistry / Q000379:methods*; D005553:Forensic Dentistry / Q000379:methods*; D006801:Humans; D066298:In Vitro Techniques; D007536:Isomerism; D009339:Needles; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*; D014070:Tooth / Q000737:chemistry*
chemical_list: D000596:Amino Acids