Development of probe electrospray using a solid needle

Electrospray using a solid needle probe for the analysis of liquid samples was developed. The needle was moved up and down a vertical axis by a motor-driven system. At the lowest position of the needle, the tip of the needle touched the surface of the liquid sample and a small amount of liquid was picked up by the needle. At the highest position, a high voltage of approximately 3 kV was applied to the needle and the sample loaded on the tip of the needle was electrosprayed. The ions formed were measured by an orthogonal time-of-flight mass spectrometer. A single sample loading by the needle gave reasonably strong ion signals for amino acids, peptides, proteins and polyethylene glycol (PEG) in aqueous solution. The addition of salts or acids to aqueous solution led to dramatic enhancement of the ion signals.