Thermal Conductivity Detector for Gas Chromatography: Very Wide Gain Range Acquisition System and Experimental Measurements

Abstract

The aim of this paper is to present an acquisition system featuring a very wide gain range and experimental measurements of a new micromachined thermal conductivity detector ( $\mu$ TCD), applied downstream of a gas-chromatography (GC) system. We describe a simple and innovative electronics for $\mu$ TCD control and data acquisition, outlining its resistance control, native imbalance compensation, and automatic gain control (AGC) algorithm. The acquisition electronics features two parallel amplification stages with programmable gain: a high-gain stage (gain: 70–1280) and a low-gain or attenuating stage (gain: 0.6–30). The resulting detection range turns out to be very wide, with full scales ranging between 3.9 mV and 6.5 V while voltage is acquired with a 10-b-resolution analog-to-digital converter. Measurements and sensitivity tests have been carried out by connecting our $\mu$ TCD and acquisition system downstream of the microfluidic section and GC column of a commercial GC system. Sensitivity measurements on several toluene masses gave very good results, having observed a system sensitivity of $15.2 \pm 0.6 \mu\hbox{Vs/ng}$ . This high sensitivity will enable the $\mu$ TCD to be used in many portable applications like in-line quality control, and industrial security and safety. We also show the good operation of the AGC algorithm.