Stability-indicating method for determination of oxyphenonium bromide and its degradation product by high-performance liquid chromatography

A high-performance liquid chromatographic (HPLC) method was developed for determination of oxyphenonium bromide (OX) and its degradation product. The method was based on the HPLC separation of OX from its degradation product, using a cyanopropyl column at ambient temperature with mobile phase of acetonitrile-25 mM potassium dihydrogen phosphate, pH 3.4 (50 + 50, v/v). UV detection at 222 nm was used for quantitation based on peak area. The method was applied to the determination of OX and its degradation product in tablets. The proposed method was also used to investigate the kinetics of the acidic and alkaline degradation of OX at different temperatures, and the apparent pseudo first-order rate constant, half-life, and activation energy were calculated. The pH-rate profile of the degradation of OX in Britton-Robinson buffer solutions within the pH range 2-12 was studied.     

Chromatographic determination of itopride hydrochloride in the presence of its degradation products

Two sensitive and reproducible methods are described for the quantitative determination of itopride hydrochloride (IH) in the presence of its degradation products. The first method is based on HPLC separation on a reversed phase Kromasil column [C18 (5-microm, 25 cm x 4.6 mm, ID)] at ambient temperature using a mobile phase consisting of methanol and water (70:30, v/v) adjusted to pH 4.0 with orthophosphoric acid with UV detection at 258 nm. The flow rate was 1.0 mL per min with an average operating pressure of 180 kg/cm2. The second method is based on HPTLC separation on silica gel 60 F254 using toluene:methanol:chloroform:10% ammonia (5.0:3.0:6.0:0.1, v/v/v/v) as mobile phase at 270 nm. The analysis of variance (ANOVA) and Student's t-test were applied to correlate the results of IH determination in dosage form by means of HPLC and HPTLC methods. The drug was subjected to acid and alkali hydrolysis, oxidation, dry heat, wet heat treatment, UV, and photodegradation. The proposed HPLC method was utilized to investigate the kinetics of the acidic, alkaline, and oxidative degradation processes at different temperatures and the apparent pseudo-first-order rate constant, half-life, and activation energy were calculated. In addition the pH-rate profile of degradation of IH in constant ionic strength buffer solutions in the pH range 2-11 was studied.     

Stability-Indicating HPLC Method for the Determination of Metadoxine as Bulk Drug and in Pharmaceutical Dosage Form

A sensitive and reproducible method is described for the quantitative determination of metadoxine in the presence of its degradation products. The method was based on high performance liquid chromatographic separation of the drug from its degradation products on the reversed phase, kromasil column [C₁₈ (5-micron, 25 cm × 4.6 mm, i.d.)] at ambient temperature using a mobile phase consisting of methanol and water (50: 50, v/v). Flow rate was 1.0 mL min^?1 with an average operating pressure of 180 kg cm^?2 and t _R was found to be 2.85 ± 0.05 min. Quantitation was achieved with UV detection at 286 nm based on peak area with linear calibration curves at concentration range 10–100 μg mL^?1. This method has been successively applied to pharmaceutical formulation. No chromatographic interference from the tablet excipients was found. The method was validated in terms of precision, robustness, recovery and limits of detection and quantitation. Drug was subjected to acid, alkali and neutral hydrolysis, oxidation, dry heat, wet heat treatment and photo and UV degradation. As the proposed method could effectively separate the drug from its degradation products, it can be employed as stability indicating one. Moreover, the proposed HPLC method was utilized to investigate the kinetics of the acidic, alkaline and oxidative degradation processes at different temperatures and their respective apparent pseudo first order rare constant, half-life and activation energy was calculated with the help of Arrhenius plot. In addition the pH-rate profile of degradation of metadoxine in constant ionic strength buffer solutions with in the pH range 2–11 was studied.     

High-performance liquid chromatographic mass spectrometric identification of the photoproducts of cymoxanil

The photochemical degradation of the fungicide cymoxanil {2-cyano-N-[(ethylamino)carbonyl]-2-(methoxyimino) acetamide} was studied in aqueous buffer solution (pH 5.9+/- 0.1) under UV light and in laboratory conditions. The degradation followed a pseudo- first-order kinetic with significant correlation coefficient. The main photoproducts were separated and tentatively identified by HPLC/UV and HPLC/MS data, as 3-ethyl-4-(methoxyamino)-2,5-dioxo-4-imidazolidinecarbonitrile, 1-ethyl-5-(methoxyimino)-2,4-imidazolidin-2,4-dione, ethylimidazolidinetrione and {[(ethylamino)carbonyl]-amino}oxoacetic acid. A photolysis pathway of cymoxanil is proposed.     

New approach for determination of the degradation products of fenspiride hydrochloride found in oral liquid formulations

Fenspiride hydrochloride (FNS) is used in treating chronic inflammatory diseases, most commonly as a liquid oral solution. FNS produces degradation products along with fenspiride N‐oxide (FNO) and 1‐phenylethyl‐4‐hydroxy‐4‐aminomethyl piperidine hydrochloride (PHAP). We aimed to develop and validate a chromatographic method in order to identify the main degradation products in the presence of other compounds from a liquid preparation. The method used a dual gradient using two buffer solutions: the first with pH 4.5 (buffer 1, pH 4.5–MeOH 90:10%, v/v) and the second with pH 2.9 (buffer 2, pH 2.9–acetronitrile–methanol, 65:15:10%, v/v/v). As mentioned, there was a modification of the organic mixture, starting with 10% methanol and ending with a mixture of acetonitrile–methanol (15:10%, v/v). The flow‐rate was 1.5 mL/min. According to the elution program, experimental conditions started with 100% solution S1, which decreased to 0% and, simultaneously, solution S2 increased to 100% during the first 10 min and was maintained for a further 5 min. After 15 min, initial conditions were re‐established. The linearity interval was 0.5–2 μg/mL and the minimum correlation coefficient was 0.999. The recovery factor was 100.47–103.17% and the limit of quantification was 0.19–0.332 μg/mL. Intra‐day maximum precision was 4.08% for FNS and 2.65% for PHAP. This double‐gradient mobile phase produced good specificity in relation to the degradation products of FNS and other constituents of the oral liquid formulation. Forced degradation studies revealed other related substances that were confirmed in mass balance analyses. Degradation products were confirmed in acidic, basic and oxidative media.     

Stability in aqueous solution of two monocyclic beta-lactam antibiotics: aztreonam and nocardicin A.

The catalytic effect of various buffer systems (citrates, acetates, phosphates, borates and carbonates) on the degradation of aztreonam and nocardicin A in aqueous solution was studied at 35 degrees C and a constant ionic strength of 0.5 mol.dm-3 over a pH range of 3.50 to 10.50. The observed degradation rates, obtained by measuring the remaining intact antibiotic, were shown to follow pseudo-first-order kinetics with regard to antibiotic concentrations and to be influenced by general acid and general base catalysis. The changes in the concentration of intact beta-lactam antibiotic in the solutions were established by reverse-phase HPLC with UV-detection. In general the buffer systems employed in the kinetic studies showed a very weak catalytic effect on the degradation of aztreonam and nocardicin A. The pH-rate profiles for these antibiotics showed degradation minimums at pH 5.38 and 6.13, respectively. Aztreonam is slightly more reactive with hydrogen ions than nocardicin A and is much more reactive with hydroxide ions. In comparison with other beta-lactamic antibiotics, aztreonam and nocardicin A are much more stable in aqueous solution, except for aztreonam in a base solution, which is just as unstable as penicillins and cephalosporins. The Arrhenius activation energies were determined for aztreonam and nocardicin A at pH's 4.23, 6.59 and 8.60.     

Enamines. 7. kinetics of the hydrolysis of 1-methyl-2-benzoylmethylenehexahydroazepine in acidic media

The dependence of the hydrolysis of 1-methyl-2-benzoylmethylenehexahydroazepine on the pH of the solution was studied. It is shown that the dependence of the observed rate constant (k_obs) on the pH is represented by a bell-shaped curve. At pH 3–6, k_obs depends on the acetic acid concentration in an acetate buffer with the same pH value. The addition of potassium acetate to a 0.1 N HCl solution gives rise to a statistically reliable increase in k_obs. It was shown by means of a model compound that the O-protonated form of the enamino ketones is resistant to hydrolysis. A mechanism for the hydrolysis of 1-methyl-2-benzoylmethylenehexahydroazepine in which the rate-determining step at pH 0–6 is C protonation is proposed.See [1] for communication 6.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1678–1682, December, 1979.Original article submitted February 7, 1979.     

The mechanism of the sonochemical degradation of benzoic acid in aqueous solutions

The sonolytic degradation of benzoic acid in aqueous solution was investigated at an ultrasonic frequency of 355 kHz. The degradation rate was found to be dependent upon the solution pH and the surface activity of the solute. The degradation rate was favoured at a solution pH lower than the pK _a of benzoic acid. At pH < pK _a, HPLC, GC and ESMS analysis showed that benzoic acid could be degraded both inside the bubble by pyrolysis and at the bubble/solution interface by the reaction with OH radicals. At higher pH (> pK _a) benzoic acid could only react with OH radicals in the bulk solution. During the sonolytic degradation of benzoic acid, mono-hydroxy substituted intermediates were observed as initial products. Further OH radical attack on the mono-hydroxy intermediates led to the formation of di-hydroxy derivatives. Continuous hydroxylation of the intermediates led to ring opening followed by complete mineralization. Mineralization of benzoic acid occurred at a rate of < 40μM/h.     

Application of a validated stability-indicating densitometric thin-layer chromatographic method to stress degradation studies on moxifloxacin

A simple, sensitive, selective, precise and stability-indicating high-performance thin-layer chromatographic (HPTLC) method for densitometric determination of moxifloxacin both as a bulk drug and from pharmaceutical formulation was developed and validated as per the International Conference on Harmonization (ICH) guidelines. The method employed TLC aluminium plates pre-coated with silica gel 60F-254 as the stationary phase and the mobile phase consisted of n-propanol-ethanol-6 M ammonia solution (4:1:2, v/v/v). Densitometric analysis of moxifloxacin was carried out in the absorbance mode at 298 nm. Compact spots for moxifloxacin were found at R_f value of 0.58 ± 0.02. The linear regression analysis data for the calibration plots showed good linear relationship with r = 0.9925 in the working concentration range of 100-800 ng spot⁻¹. The method was validated for precision, accuracy, ruggedness, robustness, specificity, recovery, limit of detection (LOD) and limit of quantitation (LOQ). The LOD and LOQ were 3.90 and 11.83 ng spot⁻¹, respectively. Drug was subjected to acid and alkali hydrolysis, oxidation, dry heat, wet heat treatment and photodegradation. All the peaks of degradation products were well resolved from the standard drug with significantly different R_f values. Statistical analysis proves that the developed HPTLC method is reproducible and selective. As the method could effectively separate the drug from its degradation products, it can be employed as stability-indicating one. Moreover, the proposed HPTLC method was utilized to investigate the kinetics of the acidic and alkaline degradation processes at different temperatures. Arrhenius plot was constructed and apparent pseudo-first-order rate constant, half-life and activation energy were calculated. In addition the pH-rate profile for degradation of moxifloxacin in constant ionic strength buffer solutions within the pH range 1.2-10.8 was studied.     

Tuning the release rate of acidic degradation products through macromolecular design of caprolactone-based copolymers

Macromolecular engineering is presented as a tool to control the degradation rate and release rate of acidic degradation products from biomedical polyester ethers. Three different caprolactone/1,5-dioxepan-2-one (CL/DXO) copolymers were synthesized: DXO/CL/DXO triblock, CL/DXO multiblock, and random cross-linked CL/DXO copolymer. The relation of CL and DXO units in all three copolymers was 60/40 mol %. The polymer discs were immersed in phosphate buffer solution at pH 7.4 and 37 degrees C for up to 364 days. After different time periods degradation products were extracted from the buffer solution and analyzed. In addition mass loss, water absorption, molecular weight changes, and changes in thermal properties were determined. The results show that the release rate of acidic degradation products, a possible cause of acidic microclimates and inflammatory responses, is controllable through macromolecular design, i.e., different distribution of the weak linkages in the copolymers.     

Determination of Benzocaine Using HPLC and FIA with Amperometric Detection on a Carbon Paste Electrode

A new method for benzocaine determination employing FIA and HPLC with electrochemical detection on a carbon paste electrode was developed. The optimum conditions for the determination were found. Carrier solution for FIA consisted of B–R buffer pH 4 (80 % methanol, v/v) and used flow rate was 1.0 mL min^?1. Mobile phase for HPLC consisted of B–R buffer pH 4 (75 % methanol, v/v) with flow rate 0.4 mL min^?1. Working potential of +1.2 V was employed. Practical applicability of the methods was tested on the determination of benzocaine in selected pharmaceuticals. The results were in agreement with results obtained using spectrophotometric detection and with one exception also with the content declared by the manufacturer.     

CE as orthogonal technique to HPLC for alprazolam degradation product identification

The control of degradation products is currently a critical issue to the pharmaceutical industry. A degradation product that appeared in alprazolam tablets during their stability assay, 7-chloro-1-methyl-5-phenyl-[1,2,4]triazolo[4,3-a]quinolin-4-amine, also named triazolaminoquinoline, was tested as possible candidate in the HPLC method employed for the study. The impurity showed the same retention time and spectra as the degradation product; but as all these compounds are very closely related, a confirmation with an independent technique was necessary, and CE was chosen for that purpose. Problems related to the adsorption of the analytes to the negatively charged silica surface were solved by employing a new polymeric capillary coating consisting of poly(3-aminopropylmethylsiloxane). The polymer provided EOF towards the anode, and the two compounds were separated in less than 8 min in a 60 cm total-length capillary, 75 microm id capillary with a BGE containing 50 mM phosphate buffer at pH 2.0 with 20% ACN. When the sample containing the degradation product was injected, the presence of triazolaminoquinoline was confirmed.     

Kinetic Study of the Hydrolysis of Schiff Bases Derived from 2-Aminothiophenol

The kinetics of the hydrolysis of Schiff bases derived from 2-aminothiophenol have been studied in aqueous sodium hydroxide media containing 40?% (v/v) methanol in the temperature range 22?C45?°C. The Schiff base molecular structure-hydrolysis reactivity relationship has been investigated and discussed. Suitable reaction mechanisms have been suggested. From the effect of temperature on the rate constant, various activation parameters have been evaluated. The work has been extended to study the hydrolysis mechanism in buffer solutions of pH?=?2?C13 at 22?°C for Schiff base I (H). A rate profile diagram of pH-rate constant has been proposed.     

Enzymatic fluorination using fluoride ion generated from degradation of fluorinated materials

The recycle of fluoride ion generated from the degradation of 1-methyl-3-butylimidazolium tetrafluoroborate, diethyl methyl methoxyethylammonium tetrafluoroborate in the presence of Tris-HCl buffer solution and/or the biodegradation of fluorobenzene and benzotrifluoride, was described. The generated fluoride ion was reused to produce 5′-fluoro-5′-deoxyadenosine (5′-FDA), fluoroacetate and/or 4-fluorothreonine.     

Voltammetric behaviour of bromhexine and its determination in pharmaceuticals

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 E_P versus pH plot revealing a protonation–deprotonation (pK_a) equilibrium of bromhexine was observed. Spectrophotometrically, an apparent pK_a 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.     

CCl4 对左旋氧氟沙星超声降解的影响

研究了CCl4对超声降解喹诺酮类抗生素左旋氧氟沙星(Levofloxacin)的影响, 考察了CCl4添加量、 超声功率、 溶液初始pH值及左旋氧氟沙星初始浓度等影响因素, 并采用HPLC和LC-MS/MS对超声降解产物进行了初步分析. 结果表明, CCl4增强了左旋氧氟沙星的超声降解, 当反应液体积为50 mL, 超声35 min时, 随着CCl4体积分数的增大(0~0.06%), 左旋氧氟沙星的降解率由1.9%增至69.2%; 超声功率为100~200 W时, 降解率随着功率的升高而增大, 功率为200~400 W时降解率有所降低; pH值对左旋氧氟沙星的超声降解影响很大, pH =7.14时容易超声降解, pH过低或过高均导致降解率显著减小; CCl4的体积分数一定时, 左旋氧氟沙星的降解率随其初始浓度的增大而降低; 左旋氧氟沙星的降解率在33~49 ℃时最大. CCl4强化超声降解左旋氧氟沙星过程主要是由·OH和一系列氯自由基参与的反应. HPLC分析发现, 降解过程中同时生成了2个产物, 并通过LC-MS/MS对其进一步鉴定.     

Kinetic study of the degradation of forskolin in aqueous systems by stability-indicating HPLC method and identification of its degradation products

The degradation kinetics of forskolin in aqueous solution was investigated qualitatively and quantitatively. Two degradation products were isolated and identified as isoforskolin and forskolin D by liquid chromatography–tandem mass spectrometry (LC–MS/MS) and nuclear magnetic resonance (NMR) spectroscopy. A stability-indicating high-performance liquid chromatography (HPLC) method was developed and validated for the quantification of forskolin and its degradation products. Chromatographic separation was performed on a Luna C₁₈ column with acetonitrile–water (65:35, v/v) as the mobile phase. The flow rate was kept at 1 mL/min, and the detection wavelength was 210 nm. The kinetic study of forskolin was carried out in aqueous solutions of pH 1.5–8.5 at 37, 50, 65, and 80°C. The degradation rate of forskolin increases with increasing temperature. Forskolin is relatively stable in the pH range 3.5–6.5, but its stability decreases when the pH is outside this range. In the pH range 6.5–8.5, the forskolin degradation follows pseudo-first-order kinetics. Based on the structural identification and quantitative analysis of the degradation products, a possible pathway for forskolin degradation is proposed. Forskolin can be converted to isoforskolin rapidly, and both forskolin and isoforskolin can further decompose to forskolin D.     

Degradation kinetics of fluvoxamine in buffer solutions: In silico ADMET profiling and identification of degradation products by LC-MS/ESI

The kinetics of hydrolysis of fluvoxamine maleate (FLV) has been investigated over the pH range 1.0–12.0 at 40, 60 and 80 °C. FLV degradation follows pseudo-first-order kinetics which is consistent with the kinetics of drugs that are not readily dissolved in aqueous medium. The hydrolytic degradation rate constant (k_obs) range from 0.92 (pH 6.0) to 13.8 × 10⁻⁴ min⁻¹ (pH 1.0). The k_obs represents the sum of six different degradation rate constants; the k_H has been found to be higher than k_OH. The FLV exhibits a typical rate- pH profile with a flat bottom over the pH range 3.0–6.0 which indicates its maximum stability at pH 6.0. Ten FLV degradants have been predicted by Zeneth software and among them four degradation products (D1, D2, D3 and D4) have been identified in degraded samples. The in-silico pharmacokinetics and toxicity of degradation products have been determined using Swiss ADME and admetSAR software. The toxicity profile reveals that D2 is both AMES toxic and carcinogenic while the rest of the products are non-AMES toxic and non-carcinogenic. All of the degradation products are high in causing fish toxicity thus their presence in pharmaceutical waste is alarming for environmental safety.     

Plasma-induced Degradation of Chlorobenzene in Aqueous Solution

Liquid-phase degradation of chlorobenzene (CB), induced by contact glow discharge electrolysis under various reaction conditions, such as, the initial solution pH, current intensity, volume of solution and iron salts was investigated. Experimental results indicated that, in the absence of catalysts, the depletion of CB followed first-order kinetics, where the observed value of the first-order rate constant ‘k’ is directly proportional to the applied current intensity and inversely proportional to the solution volume. Initial solution pH had little effect on the value of k. HPLC and IC analyses showed that the major intermediate products were chlorophenols, phenol, organic acids and chloride ions. During the treatment, a lot of hydrogen peroxide was formed. Role of Fenton’s reaction was examined. A reaction pathway is proposed based on the degradation kinetics and the distribution of intermediate products.     

Aspects of Degradation Kinetics of Azithromycin in Aqueous Solution

The chemical stability of azithromycin (AZM) in aqueous solution has been investigated utilizing a stability-indicating LC assay with ultraviolet detection. The degradation kinetics were studied as functions of pH (4–7.2), buffer composition (phosphate, acetate, and citrate), buffer concentration, ionic strength, drug concentration and temperature. The observed rate obtained by measuring the remaining intact AZM was shown to follow pseudo-first-order kinetics. The maximum stability of AZM occured at an approximate pH 6.3 in 0.05 M potassium phosphate. The observed degradation rate increased with ionic strength, buffer concentration and obeyed the Arrhenius equation over the temperature range investigated (70–100 °C). The apparent energy of activation (E _a) for AZM in solution was found to be 96.8 kJ mol^?1 and by application of the Arrhenius equation the stability at 25 °C (k ₂₅) and 40 °C (k ₄₀) had been predicted. Moreover, the degradation rate of AZM was independent on its initial concentration. Trace metal ions are unlikely to be involved in the degradation of AZM in aqueous solution. The major degradation product of AZM in aqueous solution was isolated and identified by LC–MS–MS and ¹H and ¹³C NMR spectra.