Selective determination of pyridoxine in the presence of hydrosoluble vitamins using a continuous-flow solid phase sensing device with UV detection.

A very simple, inexpensive and highly selective flow injection UV spectrophotometric method for the determination of vitamin B(6) is presented. The native absorbance of the analyte is continuously monitored at 290 nm when it is transiently retained on Sephadex SP C-25 cation exchanger gel beads placed in the detection area of a flow cell. The preconcentration on the active solid phase provides by itself a high increase in sensitivity compared with the same procedure carried out without a solid support. The analytical response is linear in the concentration ranges 1-10 and 2-20 microg ml(-1) using 600 and 1250 microl of sample, respectively. The R.S.D. (%) are 0.65 (600 microl) and 0.84 (1250 microl) and the detection limits 0.08 and 0.02 microg ml(-1), respectively. The procedure was successfully applied to the determination of vitamin B(6) in pharmaceuticals containing (among other active principles) hydrosoluble vitamins in much higher concentrations than that tolerated by the method if performed in aqueous solution. Nevertheless they were tolerated using the proposed sensor due to the selective retention of the analyte.