Identification and characterization of stress degradation products of sumatriptan succinate by using LC/Q‐TOF‐ESI‐MS/MS and NMR: Toxicity evaluation of degradation products

Sumatriptan succinate, a selective 5‐HT1B receptor agonist, was subjected to forced degradation studies as per to International Conference on Harmonization‐specified conditions. The drug exclusively showed its degradation under basic, photolytic, and oxidative stress conditions, whereas it was found to be stable under acidic, thermal, and neutral conditions. Eight (DP‐1 to DP‐8) degradation products were identified and characterized by UPLC‐ESI/MS/MS experiments combined with accurate mass measurements. The effective chromatographic separation was achieved on Hibar Purospher STAR, C18 (250 × 4.6 mm, 5 μm) column using mobile phase consisting of 0.1% formic acid and methanol at a flow rate of 0.6 mL/minute in gradient elution method. It is noteworthy that 2 major degradation products DP‐3 and DP‐7 were isolated using preparative HPLC and characterized by advanced NMR experiments. The degradation pathway of the sumatriptan was established, which was duly justified by mechanistic explanation. In vitro cytotoxicity of isolated DPs was tested on normal human cells such as HEK 293 (embryonic kidney cells) and RWPE‐1 (normal prostate epithelial cells). This study revealed that they were nontoxic up to 100 μm concentration. Further, in silico toxicity of the drug and its degradation products was determined using ProTox‐II prediction tool. This study revealed that DP‐4 and DP‐8 are predicted for immune toxicity. Amine oxidase A and prostaglandin G/H synthase 1 are predicted as toxicity targets for DP‐3, DP‐4, and DP‐6 whereas DP‐1 and DP‐2 are predicted for amine oxidase A target.     

Synthesis of ZnO photocatalyst modified with activated carbon for a perfect degradation of ciprofloxacin and its secondary pollutants

The proposed research, presents the synthesis, characterization, and photocatalytic accomplishment of ZnO nanoplate (ZnOs) modified with activated carbon derived from Konar bark. The obtained nanocomposite (photocatalyst) was characterized by scanning electron microscopy (SEM), X‐ray diffraction (XRD), Raman spectroscopy, X‐ray photoelectron spectroscopy (XPS), and Brunauer–Emmett–Teller (BET). First, the ZnO photocatalyst and activated carbon (AC) were prepared separately; then, the ZnO photocatalyst was modified with activated carbon. Various parameters namely pH, degradation time, and photocatalyst dose were optimized and studied in multivariate method by design expert7 software. The synergic efficiency of ZnO‐AC (adsorbent/photocatalyst) exhibited a good rate of ciprofloxacin (CIP) removal under visible irradiation. In addition, first pseudo order kinetic and isotherms equations were calculated. Moreover, the identification of degradation products was performed by ultra performance liquid chromatography‐tandem mass spectrometer (UPLC‐MS/MS). It is for the first time that a ZnO photocatalyst modified with activated carbon (ZnO‐AC) applied for CIP degradation.     

Identification of degradation products in stressed tablets of Rabeprazole sodium by HPLC‐hyphenated techniques

Three unknown impurities of Rabeprazole, a proton pump inhibitor, were formed in the formulated drug under the stress conditions, [40 °C/75% relative humidity (RH) for 6 months] with relative retention times (RRTs) 0.17, 0.22 and 0.28. The Impurity‐I (0.17 RRT) was isolated using preparative HPLC and characterized by NMR and MS. The other two impurities, Impurity‐II (RRT 0.22) and Impurity‐III (RRT 0.28) could not be isolated, hence they are characterized by HPLC‐hyphenated techniques, LC–NMR and high‐resolution LC–MS. On the basis of the spectral data, the Impurity‐I, Impurity‐II and Impurity‐III were characterized as 1‐(1H‐benzo[d]imidazol‐2‐yl)‐3‐methyl‐4‐oxo‐1,4‐dihydropyridine‐2‐carboxylic acid, 1H‐benzo [d] imidazole‐2‐sulfonic acid and 4‐(3‐methoxy propoxy)‐3‐methyl‐2‐pyridine carboxylic acid, respectively. Copyright © 2009 John Wiley & Sons, Ltd.     

A rapid assay for angiotensin‐converting enzyme activity using ultra‐performance liquid chromatography–mass spectrometry

Angiotensin‐converting enzyme (ACE) plays an important role in the renin–angiotensin system and ACE activity is usually assayed in vitro by monitoring the transformation from a substrate to the product catalyzed by ACE. A rapid and sensitive analysis method or ACE activity by quantifying simultaneously the substrate hippuryl–histidyl–leucine and its product hippuric acid using an ultra‐performance liquid chromatography coupled with electrospray ionization‐mass spectrometry (UPLC‐MS) was first developed and applied to assay the inhibitory activities against ACE of several natural phenolic compounds. The established UPLC‐MS method showed obvious advantages over the conventional HPLC analysis in shortened running time (3.5 min), lower limit of detection (5 pg) and limit of quantification (18 pg), and high selectivity aided by MS detection in selected ion monitoring (SIM) mode. Among the six natural products screened, five compounds, caffeic acid, caffeoyl acetate, ferulic acid, chlorogenic acid and resveratrol indicated potent in vitro ACE inhibitory activity with IC₅₀ values of 2.527 ± 0.032, 3.129 ± 0.016, 10.898 ± 0.430, 15.076 ± 1.211 and 6.359 ± 0.086 mm , respectively. A structure–activity relationship estimation suggested that the number and the situation of the hydroxyls on the benzene rings and the acrylic acid groups may play the most predominant role in their ACE inhibitory activity. Copyright © 2009 John Wiley & Sons, Ltd.     

Stability of doripenem in reconstituted solution – thermal and oxidative decomposition kinetics and degradation products by LC–MS

A ultra‐fast liquid chromatography method applied to quantitation of doripenem in powder for injection was validated. Validation parameters were assayed and a rapid analysis was established by a reversed‐phase system comprising a C₁₈ column endcapped (50 × 4.0 mm, 2.0 μm), mobile phase consisting of phosphoric acid 0.01% (pH 3.8) and acetonitrile (98:02, v /v) and a flow rate of 0.4 mL min⁻¹. Drug stability was studied through submission to forced conditions, allowing the major degradation products to be detected and the kinetics parameters to be established. Thermal and oxidative degradation were determined, and indicated a kinetic decomposition following first and second order, respectively. The main degradation products were identified by LC–MS analysis, and the results were evaluated in order to suggest the chemical structures corresponding to respective masses and fragmentations. Six compounds were identified, with m/z 411, 427, 437, 634, 650 and 664. All of them resulted from cleavage of β ‐lactam ring and alcoholic chain and/or dimerization. These experimental results provide valuable information about the stability of doripenem reconstituted solution and procedures for its handling and storage.     

Easy conversion of nitrogen‐rich silk cocoon biomass to magnetic nitrogen‐doped carbon nanomaterial for supporting of Palladium and its application

In this study, magnetic nitrogen‐doped carbon (MNC) was fabricated through facile carbonization and activation of natural silk cocoons containing nitrogen and then combined with Fe₃O₄ nanoparticles to create a good support material for palladium. Palladium immobilization on the support resulted in the formation of magnetic nitrogen‐doped carbon‐Pd (MNC‐Pd). The prepared heterogeneous catalyst was well characterized using FT‐IR, TGA, EDX, FE‐SEM, XRD, VSM, and ICP‐OES techniques. Thereafter, the synthesis of biaryl compounds was conducted to investigate the catalyst performance via the reaction of aryl halides and phenylboronic acid. Further, the catalyst could be used and recycled for six consecutive runs without any significant loss in its activity.     

Enantioseparation of N‐acetyl‐glutamine enantiomers by LC–MS/MS and its application to a plasma protein binding study

A novel chiral method was developed and validated to determine N‐acetyl‐glutamine (NAG) enantiomers by liquid chromatography–tandem mass spectrometry (LC–MS/MS). Enantioseparation was achieved on a Chiralpak QD‐AX column (150 × 4.6 mm i.d., 5 μm) using methanol–water (50 mm ammonium formate, pH 4.3; 70:30, v/v) at a flow rate of 500 μL/min. The detection was operated with an electrospray ionization source interface in positive mode. The ion transition for NAG enantiomers was m/z 189.0 → 130.0. The retention time of N‐acetyl‐l ‐glutamine and N‐acetyl‐d ‐glutamine were 15.2 and 17.0 min, respectively. Calibration curves were linear over the range of 0.02–20 μg/mL with r > 0.99. The deviation of accuracy and the coefficient of variation of within‐run and between‐run precision were within 10% for both enantiomers, except for the lower limit of quantification (20 ng/mL), where they deviated <15%. The recovery was >88% and no obvious matrix effect was observed. This method was successfully applied to investigate the plasma protein binding of NAG enantiomers in rats. The results showed that the plasma protein binding of NAG enantiomers was stereoselective. The assay method also exhibited good application prospects for the clinical monitoring of free drugs in plasma.     

Determination and quantification of astragalosides in Radix Astragali and its medicinal products using LC–MS

In the present study, a liquid chromatography–tandem mass spectrometry method was developed for the separation and simultaneous quantification of astragalosides I–IV in samples of Radix Astragali and a medicinal product thereof (Jinqi Jiangtang tablets). Chromatographic separation was achieved on an Agilent Eclipse XDB (ODS)‐C18 column with a mobile phase consisting of acetonitrile and 0.05% formic acid aqueous solution by use of an efficient 17‐min program. A triple quadrupole mass spectrometer was operated in positive ionization mode with multiple reaction monitoring for the detection of four astragalosides. The saponin ginsenoside Rg1 (similar structure to astralagosides) was used as an internal standard. All calibration curves showed excellent linear regressions (r² ? 0.9912) within the range of tested concentrations. The intra‐ and inter‐day variations were below 4.57% in terms of RSD. The recoveries were 94.38–103.53% with RSD of 1.39–3.58% for spiked Radix Astragali samples. The method was successfully used for the analysis of samples of Radix Astragali and Jinqi Jiangtang tablets. In conclusion, we have developed a rapid, efficient, and accurate LC–MS/MS method for the detection of astragalosides, which can be applied for quality control of Radix Astragali and related medicinal products.     

Synthesis of CuS nanoparticles loaded on activated carbon composite for ultrasound‐assisted adsorption removal of dye pollutants: Process optimization using CCD‐RSM,equilibrium and kinetic studies

In this study, the CuS nanoparticles loaded on activated carbon (CuS‐NPs‐AC) composite was synthesized and then, characterized by XRD and FE‐SEM analyses. The prepared composite was used as a potential adsorbent for the simultaneous ultrasound‐assisted removal of Indigo Carmine (IC) and Safranin‐O (SO). The CuS‐NPs‐AC dose (0.01‐0.03 g), sonication time (1‐5 min), initial SO concentration (5‐15 mg L^‐1) and initial IC concentration (5‐15 mg L^‐1) as expectable effective parameters were studied by central composite design (CCD) under response surface methodology (RSM) to obtain an useful knowledge about the effect of simultaneous interaction between IC and SO on their removal percentage. The optimum SO and IC removal percentages were determined to be 98.24 and 97.15% at pH = 6, 0.03 g of the CuS‐NPs‐AC, 3 min sonication time, 12 and 10 mg L^‐1 of IC and SO. The values of coefficient of determination (R²) for SO and IC were 0.9608 and 0.9796, respectively, indicating the favorable fitness of the experimental data to the second order polynomial regression model. The isotherm data were well correlated with Freundlich model. The maximum monolayer adsorption capacities of 87.5 and 69.90 mg g^‐1 at room temperature for IC and SO in the investigated binary system expressed the high efficiency of the novel adsorbent for water cleanup within a short time. The investigation of correlation between time and rate of adsorption revealed that IC and SO adsorption onto the CuS‐NPs‐AC followed pseudo‐second‐order and intra‐particle diffusion simultaneously.     

Determination of toosendanin in rat plasma by ultra‐performance liquid chromatography–electrospray ionization–mass spectrometry and its application in a pharmacokinetic study

Toosendanin (TSN) is a major triterpenoid existing in Melia toosendan, which has been used as a digestive tract parasiticide and insecticide but with serious hepatotoxicity. An ultra‐performance liquid chromatography–electrospray ionization–mass spectrometry method was developed for determination of TSN in rat plasma. Plasma samples were separated on Acquity UPLC^TM BEH C₁₈ column with acetonitrile and water as flow phase by gradient elution and determined by quadrupole mass spectrometer in negative selective ion monitoring mode. Usolic acid was used as internal standard. The calibration curves were linear over 0.02–3.0 µg/mL for TSN with a lower limit of quantification (LLOQ) of 20 ng/mL in rat plasma. The extraction recoveries of TSN were within 74.3–80.7% with an accuracy of 94.5–108.9%. The intra‐ and inter‐day precision values of the assay at three quality control levels were 8.8–13.8% and <13.9% at LLOQ level, respectively. The method was successfully applied to a pharmacokinetic study of TSN in rats after a single intravenous and oral administration of 2 and 60 mg/kg. The shorter T_max, higher V_d and Cl of TSN after oral administration indicated that TSN could be absorbed, distributed and eliminated quickly in rats in vivo. The absolute bioavailability of TSN after oral administration was 9.9%. Copyright © 2012 John Wiley & Sons, Ltd.     

Au‐ and Ag‐loaded MnO2 nanostructures supported on nitrogen‐ and nitrogen–sulfur‐doped pyroproteins: Synthesis and catalytic activity in organic transformations

Four novel Au‐ and Ag‐loaded MnO₂ nanostructures supported on nitrogen‐doped pyroprotein of natural silk (Au–MnO₂@PPNS and Ag–MnO₂@PPNS) and nitrogen–sulfur‐doped pyroprotein of natural wool (Au–MnO₂@PPNW and Ag–MnO₂@PPNW) have been synthesized. Nitrogen‐ and nitrogen–sulfur‐doped pyroproteins were prepared by carbonization of natural silk and wool proteins, respectively. The catalysts were investigated for the aerobic oxidation of aromatic hydrocarbons of petroleum naphtha and the aerobic oxidative synthesis of 2‐phenylbenzo[d ]thiazoles, 2‐phenyl‐1H ‐benzo[d ]imidazoles and 2‐phenyl‐4‐quinazolinones in the absence of any co‐promoter and additional oxidizing reagent. The prepared catalytic systems showed higher catalytic activity in comparison to aggregated catalysts.     

A simple LC–MS/MS method facilitated by salting‐out assisted liquid–liquid extraction to simultaneously determine trans‐resveratrol and its glucuronide and sulfate conjugates in rat plasma and its application to pharmacokinetic assay

A simple LC–MS/MS method facilitated by salting‐out assisted liquid–liquid extraction (SALLE) was applied to simultaneously investigate the pharmacokinetics of trans‐ resveratrol (Res) and its major glucuronide and sulfate conjugates in rat plasma. Acetonitrile–methanol (80:20, v /v) and ammonium acetate (10 mol L⁻¹) were used as extractant and salting‐out reagent to locate the target analytes in the supernatant after the aqueous and organic phase stratification, then the analytes were determined via gradient elution by LC–MS/MS in negative mode in a single run. The analytical method was validated with good selectivity, acceptable accuracy (>85%) and low variation of precision (<15%). SALLE showed better extraction efficiency of target glucuronide and sulfate conjugates (>80%). The method was successfully applied to determine Res and its four conjugated metabolites in rat after Res administration (intragastric, 50 mg kg⁻¹; intravenous, 10 mg kg⁻¹). The systemic exposures to Res conjugates were much higher than those to Res (AUC_0–t , i.v., 7.43 μm h; p.o., 8.31 μm h); Res‐3‐O‐β ‐d ‐glucuronide was the major metabolite (AUC_0–t , i.v., 66.1 μm h; p.o., 333.4 μm h). The bioavailability of Res was estimated to be ~22.4%. The reproducible SALLE method simplified the sample preparation, drastically improved the accuracy of the concomitant assay and gave full consideration of extraction recovery to each target analyte in bio‐samples.     

Elucidation of stress‐induced degradation products of mangiferin: Method development and validation

The degradation behavior of mangiferin, under various ICH Q1A(R2) recommended stress conditions, was studied using an isocratic elution with mobile phase (pH 2.4), composed of acetonitrile and 1% orthophosphoric acid (12:88 v/v) at a flow rate of 1.0 mL/min, with λ _max 262 nm. It was suitably adapted for LC–MS studies by replacing with 1% acetic acid (ACN–1% acetic acid; 18:82) and the pH was adjusted to 3.0. Extensive degradation was found to occur during alkaline medium stress studies at 2.31 min of retention time at λ _max of 235 nm. The mass spectrum of mangiferin, 3 h after treatment with 0.1 M NaOH, clearly shows the rupture of the tricyclic ring, indicating that a fragment at m /z − 269 was formed. Furthermore, the results were supported by nuclear magnetic resonance as well. However, no degradation was observed in other stress conditions.     

Validated UPLC‐MS/MS method for determination of moclobemide in human brain cell supernatant and its application to bidirectional transport study

A simple and sensitive analytical method based on ultraperformance liquid chromatography–tandem mass spectrometry (UPLC‐MS/MS) has been developed for determination of moclobemide in human brain cell monolayer as an in vitro model of blood–brain barrier. Brucine was employed as the internal standard. Moclobemide and internal standard were extracted from cell supernatant by ethyl acetate after alkalinizing with sodium hydroxide. The UPLC separation was performed on an Acquity UPLC^TM BEH C₁₈ column (50 × 2.1 mm, 1.7 µm, Waters, USA) with a mobile phase consisting of methanol–water (29.5:70.5, v/v); the water in the mobile phase contained 0.05% ammonium acetate and 0.1% formic acid. Detection of the analytes was achieved using positive ion electrospray via multiple reaction monitoring mode. The mass transitions were m/z 269.16 → 182.01 for moclobemide and m/z 395.24 → 324.15 for brucine. The extraction recovery was 83.0–83.4% and the lower limit of quantitation (LLOQ) was 1.0 ng/mL for moclobemide. The method was validated from LLOQ to 1980 ng/mL with a coefficient of determination greater than 0.999. Intra‐ and inter‐day accuracies of the method at three concentrations ranged from 89.1 to 100.9% for moclobemide with precision of 1.1–9.6%. This validated method was successfully applied to bidirectional transport study of moclobemide blood–brain barrier permeability. Copyright © 2013 John Wiley & Sons, Ltd.     

Simultaneous determination of nalbuphine and its prodrug sebacoly dinalbuphine ester in human plasma by ultra‐performance liquid chromatography–tandem mass spectrometry and its application to pharmacokinetic study in humans

A rapid, simple, sensitive and selective ultraperformance liquid chromatography–tandem spectrometry (UPLC‐MS/MS) method for the determination of nalbuphine and its prodrug sebacoly dinalbuphine ester (SDE) was developed and validated in human plasma. The sample pretreatment involves basification and iterative liquid–liquid extraction with ethyl‐ether–dichloromethane (7:3, v/v) solution, followed by LC separation and positive electrospray ionization (ESI) API‐3000 mass spectrometry detection. The chromatography was on a Waters Acquity UPLC BEH HILIC column (2.1 × 100 mm, 1.7 µm). The mobile phase was composed of acetonitrile and water (83:17, v/v) that contained 0.2% formic acid and 4 mm ammonium formate at a flow rate of 0.25 mL/min. Ethylmorphine and naloxine were selected as the SDE and nalbuphine internal standard (IS), respectively. The calibration curve for both was linear over the range from 0.05 to 20 ng/mL, with correlation coefficients ≥0.995. The lower limit of quantification was set at 0.05 ng/mL. The intra‐ and inter‐day precision values for nalbuphine and SDE were acceptable as per FDA guidelines. The method was applied successfully to determine nalbuphine concentration in human plasma samples obtained from four Taiwanese volunteers receiving intramuscularly administration of sebacoyl dinalbuphine ester. The method is sensitive, selective and directly applicable to human pharmacokinetic studies involving nalbuphine. Copyright © 2013 John Wiley & Sons, Ltd.     

Stability‐indicating validation of acitretin and isoacitretin in human plasma by LC‐ESI‐MS/MS bioanalytical method and its application to pharmacokinetic analysis

LC‐ ESI‐ MS/MS simultaneous bioanalytical method was developed to determine acitretin and its metabolite isoacitretin in human plasma using acitretin‐d3 used as the internal standard for both analytes. The compounds were extracted using protein precipitation coupled with liquid–liquid extraction with flash freezing technique. Negative mass transitions (m/z) of acitretin, isoacitretin and acitretin‐d3 were detected in multiple reactions monitoring (MRM) mode at 325.4 → 266.3, 325.2 → 266.1 and 328.3 → 266.3, respectively, with a turbo ion spray interface. The chromatographic separation was achieved on an Ascentis‐RP amide column (4.6 × 150 mm, 5 µm) with mobile phase delivered in isocratic mode. The method was validated over a concentration range of 1.025–753.217 ng/mL for acitretin and 0.394–289.234 ng/mL for isoacitretin with a limit of quantification of 1.025 and 0.394 ng/mL. The intra‐day and inter‐day precisions were below 8.1% for acitretin and below 13.8% for isoacitretin, while accuracy was within ±7.0 and ±10.6% respectively. For the first time, the best possible conditions for plasma stability of acitretin and isoacitretin are presented and discussed with application to clinical samples. Copyright © 2010 John Wiley & Sons, Ltd.     

A UPLC–MS/MS approach for simultaneous determination of eight flavonoids in rat plasma,and its application to pharmacokinetic studies of Fu‐Zhu‐Jiang‐Tang tablet in rats

The purpose of this study is to establish and validate a UPLC–MS/MS approach to determine eight flavonoids in biological samples and apply the method to pharmacokinetic study of Fu‐Zhu‐Jiang‐Tang tablet. A Waters BEH C₁₈ UPLC column was employed with methanol/0.1% formic acid–water as mobile phases. The mass analysis was carried out in a triple quadrupole mass spectrometer using multiple reaction monitoring with negative scan mode. A one‐step protein precipitation by methanol was used to extract the analytes from blood. Eight major flavonoids were selected as markers. Our results showed that calibration curves for 3′‐hydroxypuerarin, mirificin, puerarin, 3′‐methoxypuerarin, daidzin, rutin, astragalin and daidzein displayed good linear regression (r ² > 0.9986). The intra‐day and inter‐day precisions (RSD) of the eight flavonoids at high, medium and low levels were <8.03% and the bias of the accuracies ranged from −5.20 to 6.75%.The extraction recoveries of the eight flavonoids were from 91.4 to 100.5% and the matrix effects ranged from 89.8 to 103.8%. The validated approach was successfully applied to a pharmacokinetic study in Sprague–Dawley rats after oral administration of FZJT tablet. Double peaks were emerged in curves of mean plasma concentration for 3′‐methoxypuerarin, which was reported for the first time.     

Simultaneous quantification of imatinib and its main metabolite N‐demethyl‐imatinib in human plasma by liquid chromatography–tandem mass spectrometry and its application to therapeutic drug monitoring in patients with gastrointestinal stromal tumor

The aim of this study was to improve and validate a more stable and less time‐consuming method based on liquid chromatography and tandem mass spectrometry (LC‐ MS/MS) for the quantitative measurement of imatinib and its metabolite N‐ demethyl‐imatinib (NDI) in human plasma. Separation of analytes was performed on a Waters XTerra RP₁₈ column (50 × 2.1 mm i.d., 3.5 μm) with a mobile phase consisting of methanol–acetonitrile–water (65:20:15, v /v/v) with 0.05% formic acid at a flow‐rate of 0.2 mL/min. The Quattro MicroTM triple quadruple mass spectrometer was operated in the multiple‐reaction‐monitoring mode via positive electrospray ionization interface using the transitions m /z 494.0 → 394.0 for imatinib, m /z 479.6 → 394.0 for NDI and m /z 488.2 → 394.0 for IS. The method was linear over 0.01–10 μg/mL for imatinib and NDI. The intra‐ and inter‐day precisions were all <15% in terms of relative standard deviation, and the accuracy was within ±15% in terms of relative error for both imatinib and NDI. The lower limit of quantification was identifiable and reproducible at 10 ng/mL. The method was sensitive, specific and less time‐consuming and it was successfully applied in gastrointestinal stromal tumor patients treated with imatinib.     

Determination of itraconazole and its photodegradation products with kinetic evaluation by ultra‐performance liquid chromatography/tandem mass spectrometry

A simple and reproducible UPLC‐MS/MS method for the determination of itraconazole (ITZ) and its photodegradation products formed during exposure to UV‐A radiation was developed. Chromatographic separations were carried out using an Acquity UPLC BEH C₁₈ column (2.1 × 100 mm, 1.7 μm particle size). The column was maintained at 40°C, and eluted under gradient conditions from 100% to 50% of eluent A over 13 min, at a flow rate of 0.3 mL min^?1. Eluent A was 0.1% (v/v) formic acid in water; eluent B was 0.1% (v/v) formic acid in acetonitrile. The linear regression analysis for the calibration curve showed a good linear correlation over the concentration range 0.0066–0.15 mg mL^?1 with determination coefficient > 0.99. The activities of some photocatalysts during degradation process of ITZ were compared. It was found that indirect photodegradation of ITZ was more effective than direct photolysis. Under our experimental conditions the photodegradation rate constant depended on the applied catalysts with catalytic activity decreasing in the following pattern: FeCl₃ > TiO₂/FeCl₃ > TiO₂. The kinetic analysis of the photodegradation data revealed that the degradation of the ITZ follows first‐order kinetics. The photodegradation products of ITZ were identified, and their fragmentation pathways, derived from MS/MS data, were proposed. Copyright © 2016 John Wiley & Sons, Ltd.     

Comparative pharmacokinetic studies of andrographolide and its metabolite of 14‐deoxy‐12‐hydroxy‐andrographolide in rat by ultra‐performance liquid chromatography–mass spectrometry

Andrographolide (AND), one of the major diterpenoids from Andrographis paniculata (Burm. f.) Nees, can be metabolized as a phase two metabolite of 14‐deoxy‐12‐hydroxy‐andrographolide‐19‐O‐β‐d ‐glucuronide in human. The aim of this study is to characterize and synthesize the phase one metabolite of 14‐deoxy‐12‐hydroxy‐andrographolide (DEO‐AND) after gavage feeding of AND in rats, and to compare the pharmacokinetics of AND and DEO‐AND after intravenous administration. DEO‐AND was first discovered existing in rat serum by HPLC‐MSⁿ after administration of AND. Furthermore, the target metabolite was synthesized and elucidated by NMR. In addition, a rapid, selective and sensitive UPLC‐ESI/MS method was developed for the first time to determine the content of AND and DEO‐AND in rats serum. The method was successfully applied to a pharmacokinetic study in rats after a single intravenous dose of 5 mg/kg AND and DEO‐AND, respectively. In comparison, the pharmacokinetic parameters of metabolite DEO‐AND, including distribution rate constant, elimination rate constant, half‐life and mean residence time, were significantly less than those of AND (p < 0.05). However, the AUC_{0→720 min} value after intravenous administration of DEO‐AND was 781.59 ± 81.46 µg min/mL, which was 17.71 times higher than that of AND (44.13 ± 10.45 µg min/mL; p < 0.05). These results show the pharmacokinetic profile of AND to be significantly different from that of DEO‐AND by intravenous administration. Copyright © 2013 John Wiley & Sons, Ltd.