Proton sponge: a novel and versatile MALDI matrix for the analysis of metabolites using mass spectrometry.

ABSTRACT

Here, we show the usefulness of a strong base, 1,8-bis(dimethyl-amino)naphthalene (DMAN; proton sponge), as a novel matrix for MALDI-TOF/MS analysis of anions. Several strong and weakly acidic low-molecular-weight analytes (fatty acids, amino acids, fatty acid-amino acid conjugates, plant and animal hormones, vitamins, and short peptides) were measured at physiologically relevant concentrations. Clear negative-mode MALDI-TOF/MS spectra of all analytes using DMAN as the matrix show only deprotonated analyte signals at a low picomole/femtomole limit-of-detection. Moreover, the spectra were totally devoid of any matrix-related signals. Standard calibration curves gave good linearity over the entire picomole range over two concentration orders in most cases and over three orders for peptides. Using this method, the crude regurgitate of the tobacco hornworm caterpillars (Manduca sexta, Lepidoptera, Sphingidae) was analyzed. As many as 11 different components were identified from a single spot, including 160, 182, 183, and 210 free acids and 50-Glu, 60-Glu, 182-Glu, 183-Glu, 160-Glu, and 163-Glu fatty acid-amino acid conjugates (FACs) in complete qualitative agreement with previously reported anion exchange-HPLC analyses. The identity of these components was confirmed by negative ion collision-induced dissociation (CID) MS2 spectra.