Detection of native protein ions in aqueous solution under ambient conditions by electrospray laser desorption/ionization mass spectrometry.

Liquid electrospray laser desorption/ionization (ELDI) mass spectrometry allows desorption and ionization of proteins directly from aqueous solutions and biological fluids under ambient conditions. Native protein ions such as those of myoglobin, cytochrome c, and hemoglobin were obtained. A droplet (ca. 5 microL) containing the protein molecules and micrometer-sized particles (e.g., carbon graphite powder) is irradiated with a pulsed UV laser. The laser energy adsorbed by the inert particles is transferred to the surrounding solvent and protein molecules, leading to their desorption; the desorbed gaseous molecules are then postionized within an electrospray (ESI) plume to generate the ESI-like protein ions. With the use of this technique, we detected only the protonated protein ions in various biological fluids (including human tears, cow milk, serum, and bacterial extracts) without interference from their corresponding sodiated or potassiated adduct ions. In addition, we rapidly quantified the levels of glycosylated hemoglobin present in drops of whole blood obtained from diabetic patients without the need of sample pretreatment.

Characterization of the chemical components on the surface of different solids with electrospray-assisted laser desorption ionization mass spectrometry.

In this study we demonstrate that electrospray-assisted laser desorption ionization (ELDI) mass spectrometry (MS) can be used to rapidly characterize major chemical components on the surfaces of different solids under ambient conditions. The major chemical components in (a) dried milks with different fat contents, (b) different color-regions of a painting, (c) the thin coating on a compact disc, (d) drug tablets, and (e) porcine brain tissue were rapidly characterized as protonated molecules [M+H](+) or sodiated molecules [M+Na](+) by ELDI-MS with minimum sample pretreatment. The ionized ions of synthetic polymer and dye standards were detected directly from dried sample solutions using either positive or negative ion mode. Further structural information for the FD&C Red dye was obtained through tandem mass spectrometric (MS/MS) analysis using an ion trap mass analyzer attached to the ELDI source.