A complete electrochemical study and a novel electroanalytical procedure for bromhexine quantitation are described. Bromhexine in methanol/0.1 mol L−1 Britton–Robinson buffer solution (2.5/97.5) shows an anodic response on glassy carbon electrode between pH 2 and 7.5. By DPV and CV, both peak potential and current peak values were pH-dependent in all the pH range studied. A break at pH 5.5 in EP versus pH plot revealing a protonation–deprotonation (pKa) equilibrium of bromhexine was observed. Spectrophotometrically, an apparent pKa value of 4.3 was also determined.
An electrodic mechanism involving the oxidation of bromhexine via two-electrons and two-protons was proposed. Controlled potential electrolysis followed by HPLC–UV and GC–MS permitted the identification of three oxidation products: N-methylcyclohexanamine, 2-amino-3,5-dibromobenzaldehyde and 2,4,8,10-tetrabromo dibenzo[b,f][1,5] diazocine.
DPV at pH 2 was selected as optimal pH for analytical purposes. Repeatability, reproducibility and selectivity parameters were adequate to quantify bromhexine in pharmaceutical forms. The recovery was 94.50 ± 2.03% and the detection and quantitation limits were 1.4 × 10−5 and 1.6 × 10−5 mol L−1, respectively. Furthermore, the DPV method was applied successfully to individual tablet assay in order to verify the uniformity content of bromhexine. No special treatment of sample were required due to excipients do not interfered with the analytical signal. Finally the method was not time-consuming and less expensive than the HPLC one. 相似文献
Melatonin was determined in pharmaceutical preparations by means of two simple and reliable analytical methods based on micellar electrokinetic chromatography (MEKC) and spectrofluorimetry. The fluorescence emission values were measured at λ=350 nm when exciting at λ=275 nm. The MEKC analysis was achieved using a system consisting of 40 mM SDS in phosphate buffer (20 mM, pH 7.5). The extraction of melatonin from the tablets was achieved by means of a simple one-step dissolution with methanol/water. Both methods were applied for the determination of melatonin in commercial formulations and galenic preparations. The MEKC procedure allows the quantitative determination of melatonin in all pharmaceutical preparations tested. On the contrary, the spectrofluorimetric method is not suitable for tablets which also contain tryptophan; this interference can be eliminated by a suitable liquid-liquid extraction procedure. The results obtained with the two methods are in good agreement and satisfactory in terms of precision and accuracy. 相似文献
A validated kinetic spectrophotometric method has been developed for the determination of losartan potassium in pure and dosage forms. The method is based on oxidation of the losartan potassium with alkaline potassium permanganate at room temperature (25 ± 1 °C). The reaction is followed spectrophotometrically by measuring the increase in absorbance with time at 603 nm, and the initial rate, fixed time (at 12.0 min) and equilibrium time (at 90.0 min) methods are adopted for constructing the calibration graphs. All the calibration graphs are linear in the concentration range of 7.5–60.0 μg mL?1 and the calibration data resulted in the linear regression equations of n? = ?6.422 × 10?7 + 1.173 × 10?5 C, A =3.30 × 10?4 + 5.28 × 10?3 C and A = ?2.09 × 10?2 + 1.05 × 10?1 C for initial‐rate, fixed time and equilibrium time methods, respectively. The limits of detection for initial rate, fixed time and equilibrium time methods are 0.71, 0.21 and 0.19 μg mL?1, respectively. The activation parameters such as Ea, ΔH?, ΔS?, and ΔG? are also determined for the reaction and found to be 87.34 KJ mol?1, 84.86 KJ mol?1, 50.96 JK?1 mol?1 and ?15.10 KJ mol?1, respectively. The variables are optimized and the proposed methods are validated as per ICH guidelines. The method has been applied successfully to the estimation of losartan potassium in commercial tablets. The performance of the proposed methods was judged by calculating paired t‐ and F‐ values. The analytical results of the proposed methods when compared with those of the reference method show no significant difference in accuracy and precision and have acceptable bias. 相似文献
A highly sensitive liquid chromatography tandem mass spectrometry (LC–MS/MS) method for simultaneous determination of glycyrrhizin (GL) and its active metabolite, glycyrrhetinic acid (GA), from human plasma was validated and applied to a human pharmacokinetic study. The analytes were extracted from human plasma using an Oasis MAX cartridge and chromatographic separation was performed on an Inertsil ODS‐3 column. The detection was performed using an API 4000 mass spectrometer operating in the positive electrospray ionization mode. Selected ion monitoring transitions of m /z 823 → 453 for GL and m /z 471 → 149 for GA were obtained. The response was a linear function of concentration over the ranges of 0.5–200 ng/mL for GL and 2–800 ng/mL for GA (both R 2 > 0.998). Using this method, the pharmacokinetics of GL after single oral administration of a clinical dose (75 mg) to six healthy male Japanese volunteers were evaluated. GL was detected in the plasma of all subjects and the average peak concentration was 24.8 ± 12.0 ng/mL. In contrast, peak concentration of GA was 200.3 ± 60.3 ng/mL, i.e. ~8‐fold higher than that of GL. This is the first report clarifying pharmacokinetic profiles of GL and GA simultaneously at a therapeutic oral dose of a GL preparation. 相似文献