Thermogravimetric analyzers (TGA) are widely applied for studies of coal conversion as a function of process parameters. However, weight change of fuel samples as a function of temperature is not always sufficient for detailed identification of volatilized or reacted species. Coupling TGA with various gas analyzers could provide useful additional information for understanding mechanisms of trace element release and reaction kinetics. Until now, coupling of TGA with gas analysis has mostly been carried out by extraction of gas samples from the hot reaction zone followed by time-delayed and external analysis in a separate measurement cell. Changes of sample composition during gas analysis often cannot be avoided due to temperature and pressure reduction and filtering of hot reaction gas. Additionally, effects of local gas phase change on sample surfaces due to displacement of purge gas by evolved components cannot be determined. Compared to external analysis, in situ measurement of gas composition immediately in the hot reaction zone would provide inherent advantages. In this paper, the application of three optical in situ measurement techniques for a high temperature TGA is shown. Therefore, a TGA standard setup was redesigned and equipped with sapphire windows and optical ports. Transmission behavior of sapphire against wavelength and temperature is presented. Coal and char gasification and alkali release were examined with thermogravimetric methods and complemented with optical techniques. The release of gaseous sodium compounds was investigated with Excimer Laser Induced Fragmentation Fluorescence Spectroscopy (ELIF). The main gasification products (H(2), CO(2), CO, H(2)O) were detected with Raman and Fourier Transformation Infrared Spectroscopy (FTIR). Various experiments demonstrate that in situ spectroscopy is applicable up to 1300 C even in an optically difficult accessible TGA and results give useful additional input to further evaluation of TGA data. (C) 2011 Published by Elsevier Ltd.