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

Abstract

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, 2.00–50.0 mg l −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 μmol l −1) ascorbic acid, 0.8 mg l −1 (2 μmol l −1) thiamine, 0.2 mg l −1 (0.5 μmol l −1) riboflavine and 0.1 mg l −1 (0.9 μmol 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.