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??OBJECTIVE To establish an HPLC-UV-ESI-MSⁿ method for the study of impurity profile of amoxicillin and clavulanate potassium tablets. METHODS Agilent 1100 LC/MSD Trap liquid chromatography-mass spectrometry was used, and the column was Shim pack CLC-ODS RP18(4.6 mm??250 mm, 5 ??m). The mobile phase A was 20 mmol??L^-1 ammonium acetate (pH adjusted to 6.0), and the mobile phase B was 20 mmol??L^-1 ammonium acetate-acetonitrile (20??80) (pH adjusted to 6.0). Gradient elution was performed at a flow rate of 1.0 mL??min^-1. ESI source was used. Positive and negative ion scan was conducted with a scanning range of m/z 100-1 500. The nebulizing pressure was 275.8 kPa, dry gas flow was 9 L??min^-1, and post-column diversion ratio was 1??5. Some related substances were identified by comparing the retention time in the chromatography, [M+H]⁺ spectrum and MS² spectrum with those of the reference substances, while the others which do not have reference substances were deduced or speculated by analyzing the MS² or MSⁿ fragmentation with the help of a rule summarized from the MS² fragmentation of amoxicillin, clavulanic acid and system suitability impurity reference substances. RESULTS A total of 15 related substances were separated and characterized including nine known impurities like amoxicilloic acid, amoxicillin dimer, etc. and six unknown impurities. CONCLUSION The method can be applied in the identification and qualitative analysis of the related substances in amoxicillin and clavulanate potassium tablets and is helpful for the quality control and optimization of the synthetic process.     

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??OBJECTIVE To establish a method for quantitative analysis of the impurities in vardenafil hydrochloride orally disintegrating tablets.METHODS Gradient elution at the flow rate of 1.0 mL??min^-1 was used for the determination of known impurities A-E and the unknown impurities simultaneously. The separation was performed on Athena C₁₈-WP column (4.6 mm??250 mm,5 ??m) with acetate solution containing 0.8 g ammonium acetate in 900 mL of water-acetonitrile (90??10) as mobile phase A and acetate solution containing 0.8 g ammonium acetate in 100 mL of water-acetonitrile (10??90) as mobile phase B. The UV detection was carried out at 245 nm, and the column temperature was maintained at 40 ??. RESULTS After being treated with oxidation, heat, and light, vardenafil underwent more or less degradation. The degradation products were effectively separated and detected using this method.Meanwhile, the method showed good specificity, linearity, and ruggedness. CONCLUSION The method is selective, sensitive, and accurate, and it is suitable for the quality control of vardenafil hydrochloride orally disintegrating tablets.     

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??OBJECTIVE To establish an improved LC method combined with pulsed electrochemical detection for the analysis of etimicin sulfate. METHODS The mobile phase was composed of 40 mL of acetonitrile and 960 mL of an aqueous solution containing 15 mL??L^-1 of trifluoroacetic acid,500 ??L??L^-1 of pentafluoropropionic acid, 8 mL??L^-1of sodium hydroxide (50%) and 1.5 g??L^-1of sodium sulfate. The pH of the aqueous solution was adjusted to 3.5 with 50% NaOH solution. A pulsed electrochemical detector, which was kept at 35 ?? in a hot air oven was adopted. The electrochemical cell consisted of a working electrode, a pH-Ag/AgCl reference electrode and a titanium counter electrode. The working electrode was a gold electrode (diameter 3 mm)and a quadruple-potential waveform (QPW) was selected as detection waveform. The 0.8 mol??L^-1 NaOH solution was added post column at a flow rate of 0.4 mL??min^-1. RESULTS In total, 22 impurities could be separated. The LOD and LOQ of etimicin were found to be 2 ng and 6 ng respectively. The linearity of the calibration curve for etimicin ranged from 0.24 to 45 ??g??mL^-1 with a coefficient of correlation equal to 0.999 7. The repeatability RSDs (n=6) of the content and total impurities in one sample were 0.7% and 1.72% respectively. The inter-day repeatability RSDs (n=18) of the content and total impurities in one sample were 0.98% and 1.71% respectively. The sample solution was stable within 12 h. CONCLUSION Compared with previously published methods, this improved method shows higher sensitivity, better separation ability and robustness and has been incorporated by the Chinese Pharmacopoeia (Ch.P.) 2015 for analysis of etimicin sulfate.     

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??OBJECTIVE To establish the self contrast and correction factor method for the content determination of the related substances in compound ezetimibe and rosuvastatin calcium tablets simultaneously. METHODS RP-HPLC method was adopted. The determination was performed on Kromasil 100-5 C₁₈ Dimensions column (4.6 mm??250 mm, 5 ??m) with mobile phase A consisting of methanol-acetonitrile-0.05 mol??L^-1 potassium dihydrogen phosphate (adjusted to pH 4.0 with phosphoric acid) (10??30??60) and mobile phase B consisting of tetrahydrofuran-acetonitrile-0.05 mol??L^-1 potassium dihydrogen phosphate (adjusted to pH 4.0 with phosphoric acid) (10??50??40) at a flow rate of 1.0 mL??min^-1. The detection wavelength was set at 242 nm. The injection volume was 20 ??l. The slope of linear equation was used to determine the correction factors between ROS impurities 1, 2, 3, EZT impurities 1, 2, 3, 4, 5, 6, 7 and ezetimibe or rosuvastatin calcium. The relative retention time was used to determine the positions of impurities. RESULTS The relative retention time of ROS impurities 1, 2, 3, 4 and EZT impurities 1, 2, 3, 4, 5, 6, 7 to rosuvastatin calcium was 1.5, 1.9, 2.1, 1.1, 1.7, 2.5, 2.6, 2.8, 2.9, 3.0, and 4.0, respectively.The correction factors of ROS impurities 1, 2, 3, 4 and EZT impurities 1, 2, 3, 4, 5, 6, 7 were 1.1, 1.1, 1.0, 1.0, 1.3, 1.1, 1.0, 1.3, 1.4, 0.5, and 1.0,respectively.The content of ROS impurity 4 was 0.15% in three batches of samples, the other impurities were less than 0.1%, and the contents of total impurities were 0.27%, 0.27%, and 0.26%, respectively. CONCLUSION The method is simple,efficient, and accurate for analyzing the related substances in compound ezetimibe and rosuvastatin calcium tablets.     

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??OBJECTIVE To establish an LC/MSⁿ method for identification of the related substances in etimicn sulfate detected under the chromatographic condition described in Chinese Pharmacopoeia 2010.METHODS The HPLC separation was carried out on a Welch Ultimate LP-C₁₈ column(4.6 mm??300 mm,5 ??m)with mobile phase consisting of 0.2 mol??L^-1trifluoroacetic acid(containing 0.1% propionic acid )-methanol(84??16) at a flow rate of 1.0 mL??min^-1. Thirty percent of the eluent was detected by ion trap mass spectrometry, and the parent ions and the corresponding product spectra of all the related substances in etimicin sulfate were determined and elucidated.RESULTS Addition of 0.1% propionic acid into the mobile phase significantly enhanced the sensitivity of MS detector without altering the chromatographic behavior such as retention time and elution order of the related substances. Twenty-eight related substances were separated and detected by the LC/MSⁿ method in a typical sample. Nine of them were identified with the help of corresponding impurity reference substances and 14 of them were elucidated by MS fragment information, while the other five were not identified due to limitated information. CONCLUSION The established method can be applied to the identification of the related substances in etimicn sulfate detected under the chromatographic condition described in Chinese Pharmacopoeia 2010, which is helpful to the quality improvement and process optimization of etmicin sulfate.     

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??OBJECTIVE To rapidly identify the related substances in doxycycline hyclate tablets and investigate the possible degradation pathways of doxycycline hyclate solution by 2D-LC-IT-TOF/MS. METHODS Firstly,the chromatography was carried out using the 1stD InertSustain^TM C₁₈(4.6 mm??150 mm,5 ??m) column and a mobile phase containing a mixture of buffer solution(0.25 mol??L^-1 ammonium acetate solution-0.1 mol??L^-1 ethyldiaminetetraacetic acid disodium: triethyiamine=100??10??1)-acetonitrile(85??15). Solution pH was adjusted to 8.8 with glacial acetic acid. Then a InertSustain^TM C₁₈(2.1 mm??50 mm,2 ??m) column was used with 0.1% formic acid-water as mobile A and 0.1% formic acid-acetonitrile as mobile B in a gradient elution mode in 2ndD. Electrospray ionization (ESI) source was tested in both positive and negative ion modes. Nebulized gas flow was 1.5 L?? min^-1. Dry gas flow was 10 L?? min^-1. The desolvation tube temperature was kept at 200 ??. Related substances were characterized according to multi-level MS behaviors. The 2D-LC-IT-TOF/MS method was employed to identify the structures of impurities in forced degradation solutions and illuminate the degradation pathways of doxycycline hyclate solution. RESULTS A total of eight related substances were detected in doxycycline hyclate tablets. Four of them had a content of more than 0.1%, and their structures were identified to be 4-epidoxycycline, metacycline, ??-epidoxycycline and 2-acetyl-2-decarbamoyldoxycycline. The solution of doxycycline hyclate easily degraded under alkaline condition and generated an open loop compound taken off the keto group. The solution was sensitive to heat, and generated 4-epidoxycycline with a little amount of 4-epi-6-epidoxycycline; but the solution was stable under illumination and acidic condition. CONCLUSION The established method is suitable for rapid identification of impurities in doxycycline hyclate, which can be applied as a useful analytical tool for quality control and drug process optimization of doxycycline hyclate.     

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??OBJECTIVE To discuss whether the difference in dissolution profile in vitro may cause different bioavailability in vivo and investigate the effects of the key quality parameters of leflunomide on bioavailability.METHODS Using SANOFI product as the reference preparation and domestic product as the test preparation, the disintegration solution of leflunomide tablets was analyze by Morphologi G3-ID automated measurement to get the paricile size and size distribution of the API; using pH 6.5 FaSSIF solution without adding ox-gall sulfonic acid sodium and lecithin as the dissolution medium, the dissolution and permeation profiles of the reference and test preparations and raw material were compared at 37 ?? with rotate speed of 150 r??min^-1. The influence of quality parameters on the process of API??s release and absorption was investigated, then the difference between the reference and test preparations were compared to preliminarily predict the bioavailability and bioequivalence.RESULTS The particle size Dv(50)of domestic leflunomide tablets was 79.80 ??m, while the particle size Dv(50)of the reference product was 17.60 ??m; the dissolution rate and penetration rate of the test preparation were about 70% of the the reference preparation, the t_max was basically identical,but the ??_max and AUC_0-t were lower than the reference preparation. The bioavailability of the test preparation was about 90% of the reference preparation.CONCLUSION Though the dissolution profile of domestic leflunomide tablets is not identical to the reference preparation, but the two products were predicted to be bioequivalent.     

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??OBJECTIVE To establish a gradient elution method for determination of related substances of azithromycin for injection. METHODS Gradient elution was used for the analysis. A C₁₈ (CAPCELL PAK MG??, 4.6 mm??250 mm,5 ??m)column was used. The mobile phase A consisted of 0.05 mol??L^-1 K₂HPO₄ solution (pH 8.2, adjusted with 20% phosphoric acid)-acetonitrile (45??55), and the mobile phase B was methanol. The flow rate was 1.2 mL??min^-1, and the detection wavelength was set at 210 nm. The column temperature was maintained at 30 ??. The gradient elution program was as follows: 0-35 min, A:75%??95%; 35-64 min, A:75%; 64-65 min, A:95%??75%; 65-71 min, A:75%. RESULTS Azithromycin, near peaks and known impurities were well separated from each other. All acid radicals of azithromycin for injection did not influence the determination of related substances of azithromycin. CONCLUSION This method is more specific than the exising method for determination of related substances of azithromycin, which can more effectively control the quality of the drug.