A spectrofluorimetric technique was applied to the determination of compounds in samples with unknown background fluorescence, consisting of performing synchronous scans through a trajectory joining points of equal intensity of a fluorescence matrix three-dimensional spectrum, which is called ‘matrix isopotential synchronous fluorescence’. This technique can be improved by application of derivatives. The determination of pyridoxamine in urine was performed using this technique and the validity, applicability and simplicity of the method were demonstrated. With first-derivative matrix isopotential synchronous fluorescence the maximum sensitivity was 12.5 mg l–1 for pyridoxamine in real urine samples. The measurements were performed in aqueous medium at pH 7.0, adjusted by adding 0.05 mol l–1 phosphate buffer, and without any previous derivatization reactions. A complete statistical analysis of the experimental data was performed. Pyridoxamine in urine was determined by this method with good results and without the need for tedious prior separation.
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