Photodegradation Kinetics of Fexofenadine Hydrochloride Using a LC Method

The kinetics of photodegradation of the antihistamine fexofenadine hydrochloride using a stability-indicating high performance liquid chromatography (HPLC) method is demonstrated. The degradation was carried out in methanol and in water solutions, prepared from coated tablets, in quartz cells under UV light at 254 nm. The kinetics parameters of order of reaction and the rate constants of the degradation were determined for both solvents. The degradation process of fexofenadine hydrochloride in solutions can be described by second-order kinetics under the experimental conditions used in this study. The obtained results show that the HPLC method is satisfactory in the determination of the kinetics of degradation of fexofenadine hydrochloride in the presence of its photolytic degradation products.     

A study of photodegradation of quetiapine by the use of LC-MS/MS method

Photodegradation of quetiapine under UVC irradiation in methanol solution was investigated and structural elucidation of its photodegradation products was performed with the use of the reversed phase UHPLC system coupled with accurate mass hybrid ESI-Q-TOF mass spectrometer. During one run all essential data for the determination of photodegradation kinetics and for the structural elucidation of the products was collected with the use of auto MS/MS mode. Five degradation products were found and their masses and formulas were obtained with high accuracy (0.26–5.02 ppm). For all the analyzed compounds, MS/MS fragmentation spectra were also obtained allowing structural elucidation of the unknown degradation products and indicating photodegradation pathways of quetiapine. The main photodegradation product was identified as 2-[2-[4-(5-oxidodibenzo[b,f][1,4]thiazepin-11-yl)-1-piperazinyl]ethoxy]-ethanol and the photodegradation reaction yields the first-order kinetics with the rate constant k = 0.1094 h⁻¹.     

β-Cyclodextrin as a photostabilizer of the plant growth regulator 2-(1-naphthyl) acetamide in aqueous solution

The plant growth regulator 2-(1-naphthyl) acetamide (NAAm) is susceptible to degradation by sunlight and UV light in aqueous solution. Its inclusion complex with β-cyclodextrin (β-CD) was characterized by absorption and fluorescence spectroscopy and its photodegradation was compared with that of aqueous solutions of NAAm. The complex was formed with a stoichiometric ratio of 1:1 with a binding constant of 651 M^?1. The photodegradation behavior of NAAm in the inclusion complex NAAm:β-CD was investigated using both UV (λ = 254 nm) and simulated solar light (Suntest) irradiation. It was found that the NAAm:β-CD complex increases NAAm photostability towards photochemical degradation markedly. In addition, an influence of β-CD concentration was also observed on NAAm degradation rate: higher β-CD concentrations lead to a slower photoinduced transformation. Moreover, some differences were found in the photoproducts in the presence and absence of the cyclodextrin, indicating inhibition of some of the mechanistic pathways. β-CD stabilizes NAAm photodegradation towards sunlight and UV irradiation, enhancing its efficient application on formulations for the treatment of fruits and vegetables.     

Forced degradation studies of clobetasol 17‐propionate in methanol,propylene glycol,as bulk drug and cream formulations by RP‐HPLC

A rapid, simple, stability‐indicating forced degradation study of clobetasol 17‐propionate was conducted using RP‐HPLC. The method was used to analyze clobetasol 17‐propionate in methanol, propylene glycol, and a cream formulation. Isocratic elution of clobetasol and its degradation products was achieved using a Nova‐Pak® 4 μm C₁₈ 150 mm × 3.9 mm id cartridge column and a mobile phase of methanol: water (68:32 v/v) at a flow rate of 0.9 mL min^?1. Quantitation was achieved with UV detection at 239 nm. Nondegraded clobetasol was eluted at a retention time of 6.0 min. Clobetasol 17‐propionate was subjected to different stress conditions viz., acidic, basic, heat, oxidation, light, and neutral hydrolysis. The greatest degradation occurred under strong base and oxidative conditions. Strong base‐degraded clobetasol produced additional peaks at retention times of 1.8, 4.0, 5.0, and 8.0 min and clobetasol oxidation degradation peaks eluted at 2.2 and 24 min. Complete validation was performed for linearity, accuracy, and precision over the concentration range 0.15–15 μg mL^?1. All data were analyzed statistically and this RP‐HPLC method proved to be accurate, precise, linear, and stability indicating for the quantitation of clobetasol 17‐propionate in methanol, propylene glycol, and cream formulations.     

LC/MS/MS study for identification of entacapone degradation product obtained by photodegradation kinetics

Entacapone is indicated for clinical use as an adjunct to levodopalcarbidopa to treat patients with idiopathic Parkinson's Disease who experience the signs and symptoms of end-of-dose wearing-off. The aim of this study was to determine the photodegradation kinetics and to elucidate the structure of the main degradation product. The stability of entacapone was studied in order to investigate the degradation kinetics of this drug using LC as a stability indicator. Entacapone was subjected to accelerated photodegradation. This study was carried out with methanolic solutions, prepared from coated tablets, in quartz cells under UV light at 254 nm. The degradation process of entacapone in solutions can be described by second-order kinetics under the experimental conditions used in this study. The LC/MS/MS determinations revealed that in the above conditions the photodegraded product formed the geometric isomer of entacapone (Z-entacapone). The obtained results show the importance of appropriate light protection during the drug development process, storage, and handling.     

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.     

Photodegradation of Rhodamine B over unexcited semiconductor compounds of BiOCl and BiOBr

This study reported, for the first time systematically, photodegradation of Rhodamine B (RhB) in aqueous solution over BiOCl and BiOBr semiconductors. Under visible light irradiation (λ>400 nm, λ>420 nm and λ=550±15 nm), RhB adsorbed on the surface of BiOCl and BiOBr was photosensitized and decomposed effectively over unexcited BiOCl and BiOBr. The degradation of Methyl Orange (MO) and Methylene Blue (MB) over BiOCl and BiOBr was investigated as well, and the results were compared with RhB photodegradation. It was found that MB molecules having the lowest LUMO could not be degraded by this process. Utilizing the quantum chemical calculation (Gaussian 03 program), the relationship between frontier orbital energy of selected dye molecules and photodegradation rate was established for the first time in this study.     

A common method for the determination of several calcium channel blockers using an HPLC system with ultraviolet detection

We report a common HPLC method for the single or simultaneous determination of four calcium channel blockers (CCB), namely diltiazem (DTZ), verapamil (VER), nifedipine (NIF) and nitrendipine (NIT) and their active metabolites demetildiltiazem and deacetildiltiazem (MA and M1), norverapamil (NOR), and dehydronifedipine (DHN). DHN was first synthesised in our laboratory and different pH values of the mobil phase were subsequently prepared and tested for chromatographic separation. The detection system and the environmental light conditions were optimised. The best separations of all analytes were obtained using a C₁₈ column and a mobile phase of methanol, 0.04 M ammonium acetate, acetonitrile and triethylamine (2:2:1:0.04 v/v). Quantitation was performed using imipramine (IMI) as the internal standard. For DTZ and its metabolites (M1 and MA), the wavelength chosen was 237 nm; for VER and its metabolite NOR, it was 210 nm; and, finally for NIF and its metabolite DHN and NIT it was 216 nm. When a simultaneous analysis was carried out the wavelength was of 230 nm. The optimum pH were 7.90 and 7.10 when the separation of NIT and DTZ or VER and NIF were carried out, respectively, and 7.90 when a simultaneous separation was carried out. The detection limit of the assay was less than 8 ng ml⁻¹ for all compounds, with coefficients of variation less than 7% (for inter- and intra-day) over the concentration range of 1–1000 ng ml⁻¹. The retention times were less than 11 min. When NIF or NIT were studied, it was necessary to use a sodium vapour lamp in order to avoid the photodegradation which takes place under daylight conditions.     

HOMOGENEOUS PHOTOBLEACHING OF CHLOROPHYLL HOLOCHROMES IN A PHOTOSYSTEM I REACTION CENTER COMPLEX

Chlorophyll (Chl) photobleaching and P700 photodegradation were followed simultaneously in a P700 Chi a-protein complex (Chl a /P700 < 35). During strong illumination, the photobleaching kinetics of the bulk Chl corresponded with that of P700 photodegradation. The absence of a blue shift of the absorption maximum at 678 nm after photobleaching indicated the simultaneous degradation of all Chl holochromes and the absence of long wavelength-absorbing energy traps that would protect P700 against excess light energy. It was deduced that in the P700 reaction center core complex, the excitons are uniformly distributed amongst the Chl holochromes, which decreases the deleterious effects of excess light energy on P700 and protects the photosystem against photoinhibition.     

Degradation kinetics of telithromycin determined by HPLC method

The degradation kinetics of the antibiotic telithromycin using a stability-indicating high-performance liquid chromatography (HPLC) method is demonstrated. The photodegradation is performed by UVC lamp-254 nm (15W), installed in a chamber internally coated with mirrors, where telithromycin solutions prepared from coated tablets are placed in quartz cells. To promote oxidation, the reaction between the telithromycin solution and 3% hydrogen peroxide solution is carried out. The kinetics parameters of order of reaction and the rate constants of the degradation are determined for both conditions. The degradation process of telithromycin can be described by first-order kinetics under both experimental conditions used in this study. The results reveal the photo and oxidation lability of the drug and confirm the reliability of HPLC method for telithromycin in the presence of its degradation products.     

Characterization of paliperidone photodegradation products by LC‐Q‐TOF multistage mass spectrometry

The photodegradation of paliperidone in aqueous and methanol media under UVA and UVC irradiation was investigated. The identification and structural elucidation of its photodegradation products were performed by the use of the reversed‐phase liquid chromatography coupled with accurate mass hybrid Q‐TOF mass spectrometry and an atmospheric pressure chemical ionization source. Five degradation products were found and their masses were obtained with high accuracy (1.10–5.26 ppm) based on the TOF (MS) spectra. For the structural elucidation of unknown degradation products MS/MS spectra were also registered. However, for the identification of the main photodegradation product (3‐{2‐[4‐(6‐fluoro‐1,3‐benzoxazol‐2‐yl)piperidin‐1‐yl]ethyl}‐9‐hydroxy‐2‐methyl‐6,7,8,9‐tetrahydro‐4H‐pyrido[1,2‐a]pyrimidin‐4‐one) in‐source fragmentation connected with collision‐induced dissociation was used and MS³ spectra were finally performed. The photodegradation of paliperidone yields the first‐order kinetics in all tested conditions. The aqueous medium was in this case much less stable than the methanol solvent regardless of the irradiation source. Additionally, the toxicity of the analyzed photodegradation products was predicted by the use of ECOSAR software and comparable values of LC₅₀ for the main degradants and the parent compound were obtained. Copyright © 2015 John Wiley & Sons, Ltd.     

A Stress Stability Behavior and Development of an LC Assay Method for Anastrozole

This present work narrates the stress stability behavior and development of a liquid chromatographic method for the quantitative determination of anastrozole. Anastrozole is appropriately used when using substantial amounts of aromatizing steroids, or when one is prone to gynecomastia and using moderate amounts of such steroids. A chromatographic separation was achieved on a Hichrom RPB18 (250 × 4.6 mm, 5 μ) column using water and mixture of acetonitrile and methanol (1:1 ratio) as mobile phase. Forced degradation studies were performed on bulk samples of anastrozole using acid, base, hydrogen peroxide, heat and UV light. Degradation of the drug substance was observed in base hydrolysis. Degradation product formed under base hydrolysis was found to be Imp-C. The sample solution and mobile phase were found to be stable up to 48 h. The developed method was validated with respect to linearity, accuracy, precision, robustness and forced degradation studies prove the stability indicating power of the method.     

Stability indicating LC method to determination of sodium montelukast in pharmaceutical dosage form and its photodegradation kinetics

Reversed-phase high performance liquid chromatography (LC) method is developed for the assay of sodium montelukast in coated tables and its photodegradation kinetics. An isocratic LC separation is performed on a Zorbax XDB C18 column using a mobile phase of acetonitrile-methanol-water (pH 3.8) (75:10:15, v/v/v) at a flow rate of 0.8 mL/min and detection at 280 nm. The detector response for sodium montelukast is linear over the concentration range from 5-35 μg/mL (r = 0.9999). The specificity of the method is proved using stress conditions. The solutions are exposed to UV radiation (352 nm), alkaline and acid hydrolysis, oxidation, and temperature (80 °C). The intra- and inter-day precision show suitable results (RSD < 0.49%). The accuracy of analytical method is 100.04% (RSD = 0.44%). Detection and quantification limits are 0.10 and 0.32 μg/mL respectively. The robustness of the method is assured after small changes in chromatographic conditions. The kinetic of photodegradation using a LC method is established and it can be described by zero-order kinetics. This developed method show to be viable for the determination of sodium montelukast in pharmaceutical dosage form and satisfactory in the determination of the kinetics of degradation.     

Photoinduced degradation of orange II on different iron (hydr)oxides in aqueous suspension: rate enhancement on addition of hydrogen peroxide, silver nitrate, and sodium fluoride

Photoinduced organic oxidation with iron (hydr)oxides in aqueous suspension has been argued with respect to two principal mechanisms: (a) photoinduced ligand-to-metal charge transfer within a surface complex and (b) semiconductor photocatalysis. In this work, the photodegradation of azo dye orange II with UV light (lambda > or = 320 nm) in the aerated aqueous suspensions of haematite, maghemite, magnetite, goethite, lepidocrocite, and feroxyhite at an initial pH of 6.5 has been examined. The results showed that (1) all of the catalysts were effective at initiating dye photodegradation but the iron oxides appeared to be more active than the iron hydroxides; (2) the photodissolution of different iron phases and the dye photolysis in the dissolved iron solutions were very slow; (3) the initial rate of dye loss was proportional to the initial amount of adsorption, implying dye photodegradation on the catalyst surface; and (4) upon addition of H2O2, AgNO3, and NaF to the suspension, the rate of dye photodegradation was significantly enhanced with all the catalysts. In the presence of H2O2, less than 50% of the total rate enhancement was ascribed to the photo-Fenton reaction in solution and the dark Fenton reactions in solution and on the catalyst. In the presence of AgNO3, about 1 mole of silver particles was produced by consuming 3 moles of the dye substrate. In the presence of NaF, hydroxyl radicals were detected by an ethanol scavenger, whereas such radicals were not found in the absence of NaF. Moreover, under visible-light irradiation (lambda > or = 450 nm), the dye degradation was much slower than that under UV irradiation, but the reaction was also accelerated by the addition of NaF and AgNO3. The results suggest that mechanism b, not mechanism a, is operative for dye photodegradation occurring on the iron (hydr)oxides. A detailed discussion of all possible pathways is given in the text.     

Photooxidation of phenol in aqueous nanodispersion of humic acid

Photooxidation of phenol sensitized by Aldrich humic acid (AHA) has been studied in an aqueous solution at neutral and basic pH. Solutions containing phenol and AHA of various concentrations were irradiated with monochromatic light at 253.7 nm or with polychromatic light within the wavelength range of 310–420 nm. The quantum yields of phenol photodegradation under these conditions were determined. At the wavelength of 253.7 nm direct degradation of phenol was much more effective than that sensitized by AHA. With polychromatic light the photooxidation was found to be strongly dependent on pH of aqueous solution and independent on AHA concentration.     

UV–vis photodegradation of dyes in the presence of colloidal Q-CdS

The interaction of the dyes Safranin-O (SO) and Orange II (OII) with aqueous colloidal Q-CdS clusters, which emit single fluorescence bands with maximum wavelengths at 481 nm (excitonic band) or 559 nm (trapped band), has been studied. This was carried out by monitoring both the photodegradation of the dye in the presence of the clusters and the quenching of the clusters fluorescence by the dyes. The photolysis experiments were carried out by excitation either at 520 nm (the wavelength at which the dyes, but not the clusters absorb light) or at 350 nm (the wavelength at which the clusters strongly absorb light, and the dyes have absorbance minima). At 520 nm, photodegradation of SO could be observed, which follows a first-order kinetics (for trapped-band clusters) and a second-order kinetics (for excitonic-band clusters). For the excitation wavelength of 350 nm, photodegradation of either of the dyes could not be observed. The Stern–Volmer plots for the quenching of the excitonic band-clusters fluorescence by SO show an upward curvature, pointing to the occurrence of more than one species acting as the fluorescence quencher, whereas the Stern–Volmer plots for the quenching of the trapped band-clusters fluorescence by SO are linear, indicating that only one species acts as a fluorescence quencher. Lambert–Beer type plots (absorbance vs. concentration) are linear for SO in water and in trapped band-clusters solutions, but a similar study of SO in excitonic band-clusters solution show the occurrence of a new band, which can be assigned to a ground-state dimer of the dye. The latter can be used to explain both the upward curvature of the Stern–Volmer plots and the second-order kinetics observed for SO photodegradation in the SO-excitonic band-clusters system. The Stern–Volmer plots for the quenching of both fluorescence bands by OII are linear.     

Photostability and solubility improvement of β-cyclodextrin-included tretinoin

In this work, we investigated the influence of β-cyclodextrin on the photostability of tretinoin and compared the photo-chemical stability of tretinoin, either in methanol or complexed with β-cyclodextrin, when exposed both to UV and fluorescent light. The physico-chemical characterization of tretinoin-β-cyclodextrin complexes, prepared by the freeze-drying process, using different tretinoin:β-cyclodextrin molar ratios (1:1 and 1:3), was carried out in solution by phase solubility studies, ¹H-NMR spectroscopy, and in solid state by infrared spectroscopy (FT-IR); these analyses confirmed the existence of an inclusion compound. Solubility study results showed that tretinoin solubility was enhanced by inclusion in β-cyclodextrin as a function of increasing concentrations of β-cyclodextrin in aqueous solution at different pH values (i.e., 3.0, 5.5, and 7.0). Moreover, the complexation of the tretinoin with β-cyclodextrin effectively protected the photolabile drug and reduced the degradation of tretinoin induced by UV and fluorescent light, improving its photo-chemical stability in comparison with free drug in methanol. Indeed, dissolved tretinoin in methanol degraded very quickly and completely, while β-cyclodextrin-included tretinoin decomposition was delayed and, after 30 days under UV exposure, the percentage of remaining drug was about 20–25% (depending on the tretinoin concentration). The photodegradation of tretinoin in methanol under fluorescent light was slower: after 5 days of irradiation it reached a photostationary state and intact tretinoin remained constant (6.6%). In conclusion, the β-cyclodextrin complexation always led to a reduction of degradation, depending on the tretinoin:β-cyclodextrin molar ratio and on the drug concentration (0.2 mg/ml or 0.4 mg/ml).     

Validation of an HPLC Method for the Determination of Valdecoxib and its Degradation Product: a Mixture of α- and β-n-Lactosyl Sulfonamide Anomers

An HPLC method has been developed for the separation of valdecoxib and a degradation product consisting of α and β-N-lactosyl sulfonamide, i.e. α and β anomers (SC-77852). Best results were achieved with a Chromolith Performance RP-18e column (100 mm × 4.6 mm), macropore size 2 μm, mesopore size 13 nm, with an eluent of methanol:water containing a 1% solution of TEA (36:64 v/v), pH 7.4 (adjusted with 85% orthophosphoric acid), at 22 °C. Detection was at 220 nm. The method was validated for its selectivity, linearity, precision (repeatability) and robustness. Quantitation and detection limits were determined for both valdecoxib and SC-77852. Method robustness was further evaluated by performing 2³ full factorial design experiments. The final step, optimisation of the variables, was performed using response surface design. The validated method was used for assay of valdecoxib and SC-77852 in Bextra^® film-coated tablets.     

Highly Efficient Photodegradation of Organic Pollutants Assisted by Sonoluminescence

The mechanism of the photodegradation of azo dyes via ultrasonication is studied using a combination of the high‐performance liquid chromatography and UV–vis spectroscopy with detailed analysis of the kinetics. Based on the kinetics studies of the sonodegradation, it was proposed that the degradation of azo dyes was a multistage process that involved: (1) the direct attack of azo bonds and phenyl rings of dyes by the sonochemically formed reactive oxygen species; (2) the activation of semiconductor particles by the light emitted during cavitation and the triggering of the photocatalytic pathways of dye degradation and (3) increase of the adsorption capacity of the semiconductor particles due to the sonomechanically induced interparticle collisions. The detailed kinetics study can help in following an effective process up‐scaling. It was demonstrated that extremely short pulses of light flashes in a cavitated mixture activated the surface of photocatalysts and significantly enhanced dye degradation processes.     

Ag@AgBr光催化剂的制备及其可见光催化降解亚甲基蓝反应性能

采用沉积-沉淀及光还原法制备了Ag@AgBr等离子体光催化剂,利用X射线衍射、扫描电镜和紫外-可见漫反射光谱对其进行了表征,并考察了该等离子体光催化剂在可见光(λ420nm)下的催化性能,探讨了催化剂用量、pH值、亚甲基蓝初始浓度、H2O2添加量、循环使用及捕获剂对Ag@AgBr催化性能的影响.结果表明,当亚甲基蓝的初始浓度为10mg/L,催化剂用量为1g/L,pH=9.8时,光照12min后,亚甲基蓝的降解率高达96%,且样品经5次循环使用后活性基本保持不变;而少量H2O2的添加对光催化活性影响不大,过量的H2O2会降低光催化活性;乙二胺四乙酸捕获空穴后比异丙醇捕获·OH后的光催化活性降得更低.同时,对Ag@AgBr等离子体光催化剂可见光降解亚甲基蓝的催化机理进行了分析.