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.
Analitičke primene oscilatornih hemijskih reakcija: određivanje nekih
Izvod U poslednjih dvadesetak godina razvijene su brojne analitičke primene oscilatornih hemijskih reakcija realizovanih u otvorenom reaktoru. Predložene kinetičke metode se zasnivaju na sposobnosti analiziranih supstancija da menjaju kinetičke parametre hemijskih reakcija, pri čemu eksperimentalno dobijeni signal odražava reakcionu brzinu koja zavisi od koncentracije ispitivanog analita. Razvoju ovih metoda poklanja se sve veća pažnja zbog jednostavne eksperimentalne procedure, velikog linearnog opsega regresione jednačine (10−10 mol L) i niskog limita detekcije (10−10 mol L, u nekim slučajevima, ≤ 10 mol L), a njihovo korišćenje je vrlo pogodno za rutinske analize različitih neorganskih i organskih jedinjenja, kao i gasova. Ovaj rad ima za cilj da dâ kratki pregled primene takozvane pulsne perturbacione tehnike za kvantitativna određivanja nekih farmaceutski i biološki važnih jedinjenja u periodu od druge polovine 2005. godine do prve polovine 2011. godine.
Simultaneous determination of ascorbic acid, caffeine and paracetamol in drug formulations by differential-pulse voltammetry using a glassy carbon electrode.
A simple, rapid and accurate method for the simultaneous determination of ascorbic acid, caffeine and paracetamol in drug formulations has been developed. Peak currents were measured with a glassy carbon electrode at +0.350, +0.618 and +1.425 V versus a saturated calomel electrode for ascorbic acid, paracetamol and caffeine, respectively. Perchloric acid (0.1 M) - methanol (1 + 1) was used both as a solvent and supporting electrolyte. The optimum modulation amplitude, pulse repeat time and scan rate of the polarographic analyser were found to be 50 mV, 0.5 s and 5 mV s-1, respectively and the linear calibration ranges for ascorbic acid, caffeine and paracetamol were 0-35, 0-50, and 0-55 micrograms ml-1, respectively. The relative standard deviations for 9.30 micrograms ml-1 of ascorbic acid, 8.50 micrograms ml-1 of caffeine and 7.30 micrograms ml-1 of paracetamol were 1.3, 2.5 and 0.7%, respectively. Results are reported for several commercially available drugs.