Direct Analysis of Aqueous Solutions and Untreated Biological Samples Using Nanoelectrospray Ionization Mass Spectrometry with Pipette Tip in Series with High-Ohmic Resistor as Ion Source.

Abstract

Commercially available disposable plastic pipette tip with the inner diameter of ca. 120μm in series with a high-ohmic resistor (10GΩ) was adapted as a low-cost alternative ion source for high-throughput nanoelectrospray mass spectrometry (nESI-MS) analysis of a variety of samples, especially aqueous solutions, without sample pretreatment. The use of high-ohmic resistor enabled the formation of stable electrospray of aqueous solutions at ambient conditions. In addition, corona discharge was avoided even with a high voltage applied. Quantitative analysis of vitamin B in water was successfully conducted by tip-ESI. The results exhibited a good linearity (R ˃0.9983), a low detection limit (0.25ng/mL), and a wide dynamic response range (0.25-1000ng/mL). Our study revealed that tip-ESI not only performed equally well to capillary nESI in terms of flow rate (˂100nL/min), signal sensitivity, and sample consumption, but also offered a number of additional advantages, including better signal duration, tolerance to high analyte concentration (> 100μg/mL) and high ionizing voltage (up to 6kV), and obviation of tip clogging and corona discharge. High compatibility of tip-ESI with various kinds of samples (aqueous, viscous, solid, or bulk biological samples) makes it a promising tool for direct MS analysis.