Abstract

A simplistic model was formulated to show the effects of pulsed heating upon a flow of gas through an ETV. Using this model, a significant change in flow was predicted with a profile that increased sharply during the initial stages of heating, but then tapered off. Experimentally, pressure and flow increases were shown to be coincident to the pulsed heating of an ETV, by using both a direct and an indirect method of determination. Direct measurement of both pressure and flow increases were acquired through the use of a probe that contained pressure, flow and temperature sensors. An indirect measurement of the pressure/flow pulse was obtained by monitoring the Ar₂⁺, which is sensitive to the carrier gas flow rate. The pressure increase was determined to be minimal (<0.5 Torr) while the flow increase was much more substantial (>100 ml min⁻¹). The magnitudes of both pressure and flow increases were determined to be dependent upon the initial carrier gas flow rates. Due to the envisioned deleterious effects of the pressure/flow pulse, an attempt was made to separate the arrival of the pulse at the plasma from the analyte signal by lengthening the transport tubing. In this manner, it was determined that the analyte signal traveled at a velocity which was much less than that of the pressure pulse which propagates at the speed of sound in Ar. However, increased transport tubing lengths resulted in lower sensitivities and no significant gain in precision.