Breakthrough and desorption characteristics of a microtrap

Microtraps have been used as a concentrator cum injector in on-line gas chromatography, mass spectrometry, and in continuous nonmethane organic carbon (CNMOC) analysis. It is made by packing a narrow bore metal capillary with one or more adsorbents. The microtrap is heated with a pulse of electric current of 1-5 s duration depending upon the size of the trap. The concentration pulse desorbed from it is sharp enough to serve as an injection for high resolution gas chromatography (GC) separation. It has low thermal mass that allows it to be heated and cooled very rapidly. Breakthrough of volatile compounds, and quantitative desorption of large molecules are the major issues related to the microtrap. Parameters that effect breakthrough have been studied before, and variation in breakthrough volume as a function of analyte concentration is presented in this paper. Since the heating-cooling cycle is of the order of a few seconds, it is not easy to measure the microtrap temperature. An infrared thermocouple was used in this research to measure the microtrap temperature during its desorption. Desorption profiles and desorption efficiencies were studied under various conditions.