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 spectroph otometric method for the determination of vitamin B-6 is presented. The nat ive absorbance of the analyte is continuously monitored at 290 nm when it i s transiently retained on Sephadex SP C-25 cation exchanger gel beads place d 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 res ponse is linear in the concentration ranges 1-10 and 2-20 mu g ml(-1) using 600 and 1250 mu l of sample, respectively. The R.S,D. (%) are 0.65 (600 mu l) and 0.84 (1250 mu l) and the detection limits 0.08 and 0.02 mu g ml(-1) , respectively. The procedure was successfully applied to the determination of vitamin B-6 in pharmaceuticals containing (among other active principle s) hydrosoluble vitamins in much higher concentrations than that tolerated by the method if performed in aqueous solution. Nevertheless they were tole rated using the proposed sensor due to the selective retention of the analy te. (C) 2000 Elsevier Science B.V. All rights reserved.