Kinetic study on the degradation of indomethacin in alkaline aqueous solutions by derivative ultraviolet spectrophotometry

A fourth-order derivative method for monitoring a degradation product is proposed for the kinetic investigation of the alkaline hydrolysis of indomethacin, where indomethacin co-exists with its degradation products. A second-order derivative approach for monitoring the parent compound itself was also examined but showed limitations. Detection limits for the second-and fourth-order derivative methods, defined as b + 3sb, are 4 × 10-6 and 2 × 10-6 mol dm-3, respectively. In this work the kinetic investigation of the alkaline hydrolysis of indomethacin was carried out at pH levels of 8.0, 9.0 and 10.0. Two sets of recovery studies, in order to calculate one substance in the presence of the other, gave us 104.0 ± 0.3% and 96.8 ± 9.7% (for the second-order derivatization) and 100.9 ± 0.9% and 101.4 ± 1.5% (for the fourth-order derivative approach) showing that only the latter method can be considered free of interference and is analytically useful. Accelerated studies at higher temperatures have been employed that enable rapid prediction of the long-term stability of this drug at pH 8.0 (90 °C), 9.0 (35, 40 and 45 °C) and 10.0 (20, 26 and 30 °C). At pH 9.0 and 10.0 enough data were produced to draw Arrhenius plots and calculate the activation energies for drug decomposition: Ea = 17 ± 1 kcal mol-1 (1 cal = 4.184 J) and 14 ± 1 kcal mol-1, respectively. Kinetic results for kobs and t1/2 at room temperature (25 °C) were estimated from the Arrhenius plots: kobs = 7.7 × 10-4 min-1 and t1/2 = 900 min at pH 9.0 and kobs = 7.3 × 10-3 min-1 and t1/2 = 95 min at pH 10.0. Measurements of absorbance at a wavelength of 360 nm in the zero-order spectrum of indomethacin were included in our study for the purpose of comparison, as well as literature results

Development and validation of a reversed-phase high-performance liquid chromatographic method for the determination of ethyl-3-(N-n-butyl-N-acetyl)aminopropionate in an insect repellent semi-solid formulation

A reversed-phase high-performance liquid chromatographic method with detection at 220 nm was developed and validated for the determination of ethyl-3-(N-n-butyl-N-acetyl)aminopropionate, IR 3535, in an insect repellent semi-solid product. A Hypersil ODS RP-C18 column (250×4.6 mm), 5 μm particle size, was equilibrated with a mobile phase consisted of water-acetonitrile (60:40, v/v). Its flow-rate was 1.0 ml/min. Excipients did not interfere with the determination of IR 3535 (Rs=8.663). Intra- and inter-day relative standard deviations for samples were not higher than 0.61 and 1.2%, respectively. Mean recovery was found not lower than 98.5% and not higher than 100.3%. The method of external standard was adopted. Calibration curves were linear in the concentration range between 1.0×10-6 and 5.0×10-4 M. Limits of detection and quantitation were 65 and 196 ng/ml, respectively. © 2002 Elsevier Science B.V. All rights reserved

Development and optimization of a reversed-phase high-performance liquid chromatographic method for the determination of piperacillin and tazobactam in tazocin injectable powder

A reversed phase high-performance liquid chromatographic method with detection at 220 nm was developed and validated for the determination of piperacillin, I, and tazobactam, II, in Tazocin injectable powder. Acetaminophen was used as internal standard. A Hypersil BDS RP-C18 column (250×4.6 mm), 5 μm particle size, was equilibrated with a mobile phase composed of aqueous solution of sodium dihydrogenphosphate-dihydrate (20 mM)-acetonitrile-methanol (70:15:15, v/v/v) and pH 5.0. Its flow rate was 1.0 ml/min. Calibration curves were linear for I and II in the concentration ranges of 3.0×10-7-2.0×10-4 M and 7.0×10-7-2.0×10-4 M, respectively. Limits of detection and quantitation were 1×10-7, 3×10-7 M for I and 2×10-7, 7×10-7 M for II, respectively. Relative standard deviation, for I and II was less than 0.40 and 0.75%, respectively. Extensive recovery studies were also performed. © 2002 Elsevier Science B.V. All rights reserved

Development and validation of a non-aqueous reversed-phase high-performance liquid chromatographic method for the determination of four chemical UV filters in suncare formulations

A non-aqueous reversed-phase high performance liquid chromatographic method (RP-HPLC) with UV detection at 313nm was developed and validated for simultaneous determination of methylene bis-benzotriazolyl tetramethylphenol (Tinosorb M) along with three other chemical UV filters, octocrylene (Eusolex OCR), octyl methoxycinnamate (Eusolex 2292) and octyl salicylate (Eusolex OS) in suncare products. An isocratic elution was performed on a Hypersil BDS RP-C18 column (250mm x 4.6mm), 5μm particle size, using a mobile phase consisted of methanol-acetonitrile (90:10, v/v) with a flow-rate of 1.5ml/min. The determination of the four UV filters was not interfered by the excipients in the products. The method of external standard, as well as the standard addition method was used for the determination. The external standard calibration curves were linear for Eusolex OCR, Eusolex 2292, Eusolex OS, and Tinosorb M in the concentration ranges of 0.5-100μM, 0.5-100μM, 0.5-200μM, and 0.2-100μM, respectively. Day-to-day relative standard deviation of the determination was within 3%. Limits of detection and quantitation of the above compounds were found equal to 36 and 110nM, 220 and 660nM, 170 and 520nM, 44s and 130nM, respectively. The recovery of these four chemical UV filters from the spiked samples was 96-103%. © 2003 Elsevier B.V. All rights reserved

Estimation of chromatographic parameters on two silica-based columns connected in series under nonaqueous reversed phase liquid chromatographic conditions

Empirical equations were produced to relate important chromatographic parameters on two silica-based columns serially linked, in isocratic nonaqueous RP HPLC, to retention times and peak widths of the separated compounds on the individual columns. These equations were derived because the experimental data seemed to deviate from the values expected, applying basic chromatographic theoretical equations. The chromatographic parameters studied were retention time, peak width, resolution, number of theoretical plates, capacity factor, and separation factor. In addition, empirical linear relationships were produced for the estimation of the above mentioned parameters of the serial systems, in direct and reverse order, relating them to those obtained on each column, separately. The experimentally obtained values were in good agreement with those estimated by the derived equations. © 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

C18 columns for the simultaneous determination of oxytetracycline and its related substances by reversed-phase high performance liquid chromatography and UV detection

Simultaneous determination of oxytetracycline, 4-epioxytetracycline, α-apooxytetracycline, tetracycline and β-apooxytetracycline on C18 columns has been accomplished using a high performance liquid chromatographic method with UV detection. Separation was achieved on a Hypersil BDS RP-C18 column (250 mm × 4.6 mm) and on a Waters C18 Symmetry column (150 mm × 3.9 mm), 5 μm particle size each. These columns were equilibrated with mobile phases consisted of methanol-acetonitrile-0.1 M phosphate buffer pH 8.0 (12.5:12.5:75, v/v/v) and (15:15:70, v/v/v), respectively. The flow rate was 1.0 ml/min and the total elution time was 15 and 5 min, respectively. Both methods were applied to oxytetracycline raw material, human and veterinary formulations, where the excipients did not interfere. External standard calibration curves were linear for 4-epioxytetracycline, oxytetracycline, α-apooxytetracycline, tetracycline and β-apooxytetracycline in the concentration range of 0.27-200 μM, 0.05-200 μM, 0.03-200 μM, 0.35-200 μM and 0.20-200 μM on column A and 0.08-200 μM, 0.15-200 μM, 0.09-200 μM, 0.25-200 μM and 0.47-200 μM on column B, respectively. Day-to-day relative standard deviation of the determination for every component was less than 3%. Concerning the first column, limits of detection and quantification of the above compounds were in the concentration ranges of 10-106 nM and 30-352 nM, respectively, whereas on the second column these ranges became 27-144 nM and 81-475 nM, respectively. Recovery of the separated compounds was 95-105%. © 2006 Elsevier B.V. All rights reserved

Semi-automated kinetic determination of phenolic compounds using a fluoride-selective electrode and based on their micellarcatalysed reaction with 1-fluoro-2,4-dinitrobenzene

A kinetic - potentiometric method is described for the determination of phenol and phenolic drugs based on monitoring their reaction with 1-fluoro-2,4-dinitrobenzene, catalysed by cetyltrimethylammonium bromide micelles, using a fluoride-selective electrode. The measurement step was automated by interfacing a digital electrometer to a microcomputer. By measuring the initial slopes (ΔE/Δt), kinetic parameters (reaction order and rate constants) were obtained and kinetic determinations in the range 6 × 10-6-7 × 10-4 M were performed for phenol, acetaminophen, isoxsuprine, nylidrin, isoproterenol and metaraminol. Micellar catalysis was found to enhance the reaction rate of the various phenolic compounds tested by between 37 and 290 times. The proposed method did not suffer any interference from excipients or from cloudy and coloured solutions and was evaluated by assaying acetaminophen in commercial formulations. The results showed good agreement with those obtained using established methods

Kinetics and mechanism of acidic hydrolysis of nordazepam studied by high-performance liquid chromatography and fourth-order derivative ultraviolet spectrophotometry

A reversed-phase HPLC method was developed to study the acid-catalysed hydrolysis of nordazepam in hydrochloric acid solutions of 0.01, 0.1 and 1.0 M. One intermediate was observed, which was isolated and identified. The mechanism of hydrolysis appeared to be biphasic, showing a consecutive reaction with a reversible first step. Initial breakage of the azomethine bond, followed by a slow hydrolysis of the amide bond resulted to creation of the benzophenone product in strongly acidic solutions. A fourth-order derivative method for monitoring the parent compound itself was also proposed and evaluated, as well. Relative standard deviation was less than 2% for the HPLC and less than 5% for the derivative method. Detection limits for nordazepam, intermediate and final degradation product were 1.8 x 10-9 M, 2.1 x 10-9 M and 2.0 x 10-9 M, respectively, in the former method and 7.0 x 10-7 M for nordazepam in the latter. Estimation of k1, k-1 and k2 values was tried and results of HPLC and fourth-order derivative methods were compared

Kinetic study on the acidic hydrolysis of lorazepam by a zero-crossing first-order derivative UV-spectrophotometric technique

A zero-crossing first-order derivative UV-spectrophotometric technique for monitoring the main degradation product, 6-chloro-4-(2-chlorophenyl)-2- quinazoline carboxaldehyde, was developed to study the acidic hydrolysis of lorazepam in hydrochloric acid solutions of 0.1 M. Due to the complete overlap of the spectral bands of the parent drug and the hydrolysis product (the range between their spectral maxima was only 3 nm), the graphical methods of derivative spectrophotometry were not efficient. The relative standard deviation of the proposed technique was less than 2.4% and the detection limit was 6.6 x 10-8 M. Accelerated studies at higher temperatures have been employed that enable rapid prediction of the long- term stability of this drug. Pseudo-first order reaction kinetics was observed kinetic parameters, k(obs) and t(1/2), were calculated, which were similar to those estimated by an HPLC method developed in our laboratory