Abstract
100mg of sample (mixture of calcium oxalatemonohydrate and magnesium oxalate dihydrate) was analyzed with a differential thermal analyser under heating rate of 4°C/min. DTA curve exhibited four peaks, including a peak of endothermic reaction with liberation of crystalling water from the two compounds (220°C, peak I), another peak of exothermic reaction with liberation and oxidation of CO from calcium oxalate (480°C, peak II), another peak of endothermic reaction with liberation of CO and CO2 from magnesium oxalate (510°C, peak III), and the last peak of endothermic reaction with liberation of CO2 from calcium compound (850°C, peak IV).
Determination of calcium was run by an analysis of the relationship between the ratio of peak area (peak IV/peak I or peak IV/peak III) and weight percentage of calcium oxalate. That of magnesium was run by the same method as calcium, where the ratio of peak area to be used was peak III/ peak I or peak III/peak IV. Ten to 80% of calcium oxatate in magnesium oxalate or the reverse was determined within -7% error. An internal standard method with KH-phthalate was also studied.
