Technical note: Common glitch affecting the EC/OC split point determination in the Sunset Thermal-Optical Analyzerand recommendations to reduce its occurrence

Abstract. We identified a common and relatively frequent glitch in the light transmittance/reflectance measurement during thermal-optical analysis in the Sunset Laboratory bench top thermal-optical analyzer models. In the instrument studied, the glitch is observed for one in three punch analyses when using the default analysis parameters. The occurrence of this glitch can invalidate the split point and thus the OC and EC fractions and absolute quantities reported. The glitch was observed in data from at least three independent laboratories using different thermal protocols. We describe this glitch as a “discontinuity” (rapid increase or decrease occurring over a few seconds) in the laser transmittance or reflectance which happens relatively frequently and whose behaviour varies in amplitude, timing and direction. We use over 2,200 filter-punch analyses to expose the factors that contribute to the risk of such a discontinuity occurring. We demonstrate that these discontinuities are due to the movement of filter punches within the instrument, and can therefore be minimized by decreasing the blower speed of the instrument and, if possible, by ensuring a tighter fit of the filter punch in its holder (by testing different spoons). The decrease in blower speed has a negligible effect on the measured temperature program during analysis and is the single most effective way to reduce the risk of discontinuity occurrence. We recommend these modifications for all Sunset instruments.