Advantage of zero-crossing-point first-derivative spectrophotometry for the quantification of calcium oxalate crystalline phases by infrared spectrophotometry.

The main component of urinary calculi in industrialized countries is calcium oxalate. Its detection in stones is easily performed by infrared spectrophotometry. However its two crystalline forms calcium oxalate monohydrate (COM) and calcium oxalate dihydrate (COD), which are linked to different aetiologies, provide similar patterns, with overlapping vibrations leading to difficulties in differentiation and quantitation of both the phases in mixtures. Some minor but characteristic bands of each crystalline species are emphasized for analytical purposes. The method of zero-crossing-point first-derivative spectrophotometry was applied to calcium oxalate species quantitation and revealed to be easy, accurate, precise and very well adapted to routine laboratories.