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RECEIVED for review June 23,1982. Accepted August 18,1982. The support of this work by NSF (Neurobiology Section) via Grant BNS 7914226 and NIH via Grant NS 16364 is gratefully acknowledged. G.G. also received partial support from an Analytical Division Fellowship from the American Chemical Society.
Determination of Temperature Rise Time and Temperature Profiles for Three Commercial Pyrolyzer Sample Holders John J. R. Mertens‘ VUB-Cyclotron, Vrije Unlversiteit Brussel, Plelnlaan 2, 1050 Brussels, Eelgium
Eddy Jacobs, Andr6 J. A. Callaerts, and A. Buekens Dlenst Industriele Scheikunde, Vrue Unlverslteit Brussel, Pleinlaan 2, 1050 Brussels, Belgium
The importance of various physical parameters in pyrolysis gas chromatography (Py GC) has been mentioned by several authors (1-5) but has only been investigated by a few who developed a pyrolysis system (6-9). Wells et al. (10) report the heating profile curves obtained for a CDS Pyroprobe ribbon pyrolyzer (Chemical Data Systems, Inc., Oxford, PA). This paper describes a simple method of determining the temperature rise time (TRT) and the temperature profile of the three types of sample holders of this commercially available CDS Pyroprobe pyrolyzer, both in the presence and absence of sample (polystyrene). The Pyroprobe system is provided with electronic feedback control of the preset temperaturs which corrects for all heat effects, e.g., the heat consumed by endothermic thermal degradation processes. In this setup it is no longer possible to measure a “true pyrolysis temperature” neither by means of a thermocouple, as described by Levy et al. (6), nor by monitoring the T R T on that place of the filament where the sample has been applied, as described by Wolf at al. (7). The pyrolysis time and temperature thus are to be measured indirectly.
EXPERIMENTAL SECTION The temperature of the heated sample holder is measured by means of a phototransistor provided with a focusing lens mounted on a movable set. The sensor-head is directed perpendicular to the axis of the coil (or strip). The correct position of the phototransistor along this axis can be adjusted with a micrometer probe incorporated in the setup. The coil (or strip) is inserted intoa Pyrex-glass tube with the same dimensions as the pyroprobe interface chamber. Both the tube and the nitrogen gas flowing through the tube are heated at 200 OC to simulate the temperature contribution due to heat flux from the filament toward the wall of the interface chamber. The intensity of the wire radiation is measured as a voltage over a 1 kn resistance in series with the phototransistor and recorded on a high impedance input X.B. recorder (Kipp & Zonen-BD11) or a storage oscilloscope (Tektronix). The part of the coil taken into account by the phototransistor is one winding, so that small displacementa to the left or the right result in a clear drop in output voltage. For both the ribbon and coil, the manufacturer provides a correction factor tabulated as a function of the preset temperature. The sensitivity of the phototransistor is given as a plot of the output voltage vs. the equilibrium temperature (Figure la). The calibration curve originaly used was a straight line fitted on the
logarithim of the voltage as a function of the preset temperature in the region 420-800 OC. At higher temperatures a slight deviation from linearity is observed, probably due to the change of the light frequencies in the emitted spectrum and/or saturation of the phototransistor at higher intensities. A lower temperatures (
