Simultaneous determination of levodopa and carbidopa by synchronous fluorescence spectrometry using double scans

A synchronous fluorescence spectrometric method is described for the simultaneous determination of binary mixtures of levodopa and carbidopa in pharmaceutical formulation and urine sample, without prior separation steps, using two scans. At Delta lambda = 30 nm, only carbidopa yields a detectable signal that is independent of the presence of levodopa. Similarly, at Delta lambda = 65 nm the signal of levodopa is not influenced by the presence of carbidopa. Signals at two wavelengths, 288 nm (Delta lambda = 30 nm) and 281 nm (Delta lambda = 65 nm), vary linearly with carbidopa and levodopa concentrations over the range 0.019-1.971 microg mL(-1) (for levodopa) and 0.022-2.262 microg mL(-1) (for carbidopa), respectively. The correlation coefficients for the standard calibration graphs were 0.9962 and 0.9951 (n=10) for carbidopa and levodopa, respectively. The limits of detection (LOD estimated as per IUPAC recommendations) were 0.01 and 0.006 microg mL(-1) for carbidopa and levodopa, respectively. The method was successfully applied to the determination of levodopa and carbidopa in pharmaceutical formulation and urine sample. The recovery results were satisfactory.