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

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 +/- 0.6 mu 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.