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.

Enantiomeric Ratio of Amino Acids as a Tool for Determination of Aging and Disease Diagnostics by Chromatographic Measurement

“…Chiral selector S-(-)-t-Leu-cyclooctylamide proved to be applicable for the age estimation from the Asp racemization extent in human dentin [25]. Increased detection sensitivity for the determination of polar AAs was achieved by the selective ion monitoring (SIM) mode (m/z 134) with zero needle potential [35]. The utility of zero needle voltage electrospray ionisation (ESI) was demonstrated on the age determination of human teeth by the Asp racemization method.…”

Formation of [nM−nH+(n+1)Na]+ cluster ions from amino acid by electrospray ionization

“…Zhan and coworkers [15] reported re-solvation of bare electrospray-generated peptide ions in the lens region of the mass spectrometer that resulted from nucleation within the supersonic expansion jet. Analysis of amino acids using liquid chromatography/mass spectrometry (LC/MS) has been studied [16][17][18][19][20][21][22][23]. Some researchers [17,18] anaylzed underivatized amino acids for the diagnosis and therapy assessment.…”

Wood typification by Venturi easy ambient sonic spray ionization mass spectrometry: the case of the endangered Mahogany tree

“…Net charges in these very tiny droplets are created by the statistical imbalance distribution in solution of cations and anions . The main advantages of EASI are its very simple apparatus and the use of no heating, radiation or voltages hence its freedom from electrical, discharge, thermal or oxidation interferences and much reduced solvent noise with improved signal‐to‐noise ratios . More recently, an even simpler and more versatile self‐pumping version of EASI using the Venturi effect was introduced and termed Venturi EASI (V‐EASI) .…”