Microfabrication of low thermal mass heated nebulizer chips for mass spectrometry

Abstract

A low thermal mass Si-glass heated nebulizer chip for mass spectrometry is presented. The chips are used to mix a liquid sample (ca. 10 µL/min) and with a nebulizer gas (N 2 at ca. 100 mL/min) and vaporize the mixture. They are suited to work with multiple atmospheric pressure ionization methods. Miniaturization of heated nebulizer chips increases sensitivity, performance and flexibility for mass spectrometry. The microsystem includes a sample channel with an in-plane converging exit nozzle and a resistive copper heater, located on the channel roof, enabling operation temperatures above 450 °C. Excessive Si is etched away for reduction of heat losses due to conduction, and improvement of the heater efficiency. The chip is designed to ensure low temperatures at the side of fluidic inlet, allowing an easy connection of nebulizer gas with a polymeric sealant. The jets are characterized by scanning with a miniature thermocouple perpendicularly to the stream direction. Jet temperatures and shape can be evaluated with the acquired cross-sectional 2dimensional temperature maps. Jets are found to stream without spreading, creating small spot sizes depending on nozzle dimensions.