Increasing detection sensitivity in gas chromatography by cooling a nano-gravimetric detector

Response of nanogravimetric detector is based on adsorption of molecules on the surface of a vibrating beam. For any compound, NGD temperature (originally from 40 to 200°C) is the main operating parameter to control its sensitivity. Introduction of a cooling unit to enlarge the operating temperature range (down to -100°C) led to a substantial improvement in detection sensitivity and a significant reduction in quantification limits. The response of tetrahydrothiophene (THT) over a wide temperature range was deeply investigated: peak height increased exponentially as temperature decreased, while noise was slightly lowered. Consequently, the limit of quantification (LOQ) of THT can be reduced from 22 ppm at 50°C to 0.16 ppm at -65°C. However, significant peak tailing was observed at very low temperatures, which may compromise the separation of complex mixtures. THT chromatographic peaks were successfully modeled using an Exponentially Modified Gaussian (EMG) function, and the temperature dependence of the EMG adjusted parameters has been discussed.