Determination of ascorbic acid in pharmaceutical dosage forms and urine by means of an oscillatory reaction system using the pulse perturbation technique
A simple and reliable method for the determination of ascorbic acid (AA) is proposed and validated. It is based on potentiometric monitoring of the concentration perturbations of an oscillatory reaction system in a stable nonequilibrium stationary state close to the bifurcation point. The response of the Bray–Liebhafsky (BL) oscillatory reaction as a matrix, to the perturbation by different concentrations of AA, is followed by a Pt electrode. The linear relationship between maximal potential shift and the logarithm of the amount of AA is obtained between 0.01 and 1.0 μmol. The sensitivity of the proposed method (as the limit of detection) is 0.009 μmol and the method has excellent sample throughput (30 samples per hour). The procedure was used for AA determination in pharmaceutical formulations and urine. The results are in agreement with those obtained using the official method. Some aspects of the possible mechanism of AA action on the BL oscillating chemical system are discussed.
1,10-Phenanthroline-H2O2-KSCN-CuSO4-NaOH oscillating chemiluminescence system.
In this paper, oscillating chemiluminescence (CL), 1,10-phenanthroline H2O2-KSCN-CuSO4-NaOH system, was studied in a batch reactor. The system described is a novel, slowly damped oscillating CL system, generated by coupling the well-known Epstein-Orban, H2O2-KSCN-CuSO4-NaOH chemical oscillator reaction with the CL reaction involving the oxidation of 1,10-phenanthroline by hydrogen peroxide, catalyzed by copper(II) in alkaline medium. In this system, the CL reaction acts as a detector or indicator system of the far-from-equilibrium dynamic system. Narrow and slightly asymmetric light pulses of 1.2 s half-width are emitted at 440 nm with an emitted light time of 200-1000 s, induction period of 3.5-357 s and oscillation period of 28-304 s depending on the reagent concentrations. In this report the effect of the concentration variation of components involved in the oscillating CL system on the induction period, the oscillation period and amplitude was investigated and the parameters were plotted with respect to reagent concentrations. Copper concentration showed a significant effect on the oscillation period. The possible mechanism for the oscillating CL reaction was also discussed.
Quantitative in situ thin-layer chromatography of quinidine and salicylic acid in capillary blood.
A micro-method based on in situ thin-layer chromatography has been developed for the determination of quinidine and salicylic acid in 10-mu 1 samples of serum or plasma. The sample is applied directly to the silica gel layer without extraction, the proteins being precipitated on the chromatogram origin by means of ethanol. The chromatogram can be evaluated quantitatively by fluorescence scanning. Different pre-coated plates were investigated.