Thermogravimetric-Fourier transform infrared (TG-FTIR) studies, using a ramp rate of 30 degrees C/min, have been used to determine the total acidity and carboxylic acid contents for a range of lignites from the Latrobe Valley coal fields, Vic., Australia, some of which were also studied in water- and acid-washed form. The results are compared with values determined by barium ion-exchange. Total acidities from barium ion-exchange showed good agreement with those determined from the total amount of CO + CO2 evolved. The carboxylic acid content determined from the amount Of CO2 evolved in pyrolysis showed a good correlation with the concentration of stronger acid functional groups determined by barium ion-exchange, but was lower. The effect of ion-exchange with Na, Mg, Ca and Al on CO, CO2, pyrolysis H2O and hydrocarbon gas production, as well as on the relative yields of these different gases, was similar to that observed by earlier workers for pyrolysis over much longer run times. (c) 2005 Elsevier Ltd. All rights reserved.