A multicommuted flow system for sequential spectrophotometric determination of hydrosoluble vitamins in pharmaceutical preparations

A multicommuted flow system is proposed for spectrophotometric determination of hydrosoluble vitamins (ascorbic acid, thiamine, riboflavine and pyridoxine) in pharmaceutical preparations. The flow manifold was designed with computer-controlled three-way solenoid valves for independent handling of sample and reagent solutions and a multi-channel spectrophotometer was employed for signal measurements. Periodic re-calibration as well as the standard addition method was implemented by using a single reference solution. Linear responses (r = 0.999) were obtained for 0.500-10.0 mg l(-1) ascorbic acid, 2.00-50.6 mgl(-1) thiamine, 5.00-50.0 mg l(-1) riboflavine and 0.500-8.00 mg l(-1) pyridoxine. Detection limits were estimated as 0.08 mg l(-1) (0.5 mumol l(-1)) ascorbic acid, 0.8 mg l(-1) (2 mumol l(-1)) thiamine, 0.2 mg l(-1) (0.5 mumol l(-1)) riboflavine and 0.1 mg l(-1) (0.9 mumol l(-1)) pyridoxine at 99.7% confidence level. A mean sampling rate of 60 determinations per hour was achieved and coefficients of variation of 1% (n = 20) were estimated for all species. The mean reagent consumption was 25-fold lower in relation to flow-based procedures with continuous reagent addition. Average recoveries between 95.6 and 100% were obtained for commercial pharmaceutical preparations. Results agreed with those obtained by reference methods at 95% confidence level. The flow system is suitable for application in quality control processes and in dissolution studies of vitamin tablets. (C) 2002 Elsevier Science B.V. All rights reserved.