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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 compare and optimize the analytical methods for detection of related substances of etimicin sulfate injection. METHODS For the HPLC-CAD (charge aerosol detector)method, the mobile phase was 0.2 mol·L^-1 trifluoroacetic acid aqueous solution-methanol (95:5), the flow rate was 1.0 mL·min^-1 and the column temperature was maintained at 30 ??. The nebulization temperature for the CAD was maintained at 30 ?? and the gas pressure was 0.24 MPa.The HPLC-ELSD and HPLC-PAD methods adopted by the Ch.P 2015 were also used to detect the related substances of etimicin sulfate injection for the purpose of comparison. RESULTS Compared with the HPLC-ELSD method, the HPLC-CAD method showed higher selectivity and sensitivity; compared with the HPLC-PAD method, the results of the determination of the impurities were more accurate for the HPLC-CAD method. CONCLUSION The separation capability of the new HPLC-CAD method for detection of the related substances of etimicin sulfate injection is superior to HPLC-PAD and HPLC-ELSD methods and can detect more impurities, which is suitable for the quality control of etimicin sulfate injection.     

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??OBJECTIVE To establish an HPLC-MS/MS method to identify the unknown impurities in polymyxin B sulfate. METHODS The analysis was performed on Agilent 1260-6550 Q/TOF-MS with a Diamonsil Plus C₁₈ column(4.6 mm??250 mm, 5 ??m). Mobile phase A was 0.01 mol??L^-1 trifluoroacetic acid-acetonitrile(95??5), and mobile phase B was acetonitrile containing 0.1% formic acid. Mobile phase A and B were set at the volume ratio of 79??21 at a flow rate of 1 mL??min^-1 under isocratic elution. The detection wavelength was set at 254 nm. ESI source was used. Positive ion scanning was conducted in the range of m/z 50-1 700 for MS and MS/MS. The unknown components were identified by comparing the MS and MS/MS with the known reference standards like polymyxin B₁ and B₂. The photochemical Paterno-B??chi reaction was performed using a low-pressure mercury lamp as the light source at emission wavelength of 254 nm with acetone/water(50/50, V/V) as the reaction solvent. RESULTS The structures of seven unknown related substances in polymyxin B sulfate were identified. The most abundant impurity was identified to be vinyl polymyxin B₁, for which the double bond was at the end of the fatty acyl residue. CONCLUSION Vinyl polymyxin B₁ is reported for the first time. The method provides a good idea for the identification of related substances in drugs.     

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??OBJECTIVE To establish an HPLC-MS method for the analysis of the impurity profile of cefotaxime sodium. METHODS Shimadzu-LCMS-IT-TOF was used with Waters XBridge Shield (RP18,4.6 mm??250 mm, 5 ??m) column. Mobile phase A was 20 mmol??L^-1 ammonium acetate (pH adjusted to 6.25)-methanol (92:8), and mobile phase B was set at 20 mmol??L^-1 ammonium acetate-methanol (60:40) (pH adjusted to 6.25).Gradient elution was performed at a flow rate of 1.0 mL??min^-1. ESI source was used.Positive and negative ion scanning was conducted in the range of m/z 150-900.The heating temperature was 200 ??, CDL temperature was maintained at 200 ??, atomization gas flow rate was 1.5 L??min^-1, dry gas pressure was 94.0 kPa, and the post-column diversion ratio was 1:4.Some related substances in cefotaxime sodium were identified by comparing the retention time in chromatography,[M+H]⁺ spectrum and MS² spectrum with those of reference substances, the others which haven't 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 cefotaxime sodium and the reference substances of system suitability impurities. RESULTS Twenty-six related substances were separated and detected in the sample, all of which were identified or deduced. They were cefotaxime sodium isomeric compounds and homologs generated during the production process or degradation products. CONCLUSION The method can be applied in the identification and qualitative analysis of the related substances of cefotaxime sodium and the quality control and optimization of the synthesis of cefotaxime sodium.     

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??OBJECTIVE To establish an HPLC-PAD method to determine the related substances of sisomicin sulfate injection and compare with the statutory method. METHODS IonPac AMG C₁₈(4.0 mm??150 mm, 3 ??m)chromatographic column was used with acetonitrile-0.1 mol??L^-1 trifluoroacetic acid (containing 0.025% of pentafluoropropionic acid, 5 mL of 50% NaOH solution without carbonate, pH of the aqueous solution adjusted to 2.3 with 50% NaOH solution.)as mobile phase at a flow rate of 0.7 mL??min^-1. NaOH solution of 0.76 mol??L^-1 was added post column at a flow rate of 0.35 mL??min^-1. The column temperature was maintaine at 30 ??. PAD detector was operated with the cell temperature set at 35 ??. The working electrode was a gold electrode (diameter of 3 mm)and a quadruple-potential waveform was selected as detection waveform. The reference electrode was Ag/AgCl, the detection potential was four potential. The determination result of the related substances of sisomicin sulfate injection was compared with that of the statutory method. RESULTS The peaks of sisomicin sulfate, gentamicin C_1a and netilmicin could be completely separated, and other impurities could also be effectively separated. The blank sample had no interferences. The LOD and LOQ of etimicin were found to be 2 and 6 ng respectively, and the RSD of precision test (n=6) was 0.9%. Paired-samples t-test showed significance levels of P=0.034, P=0.364 and P=0.605 for total amount of impurities (%), the biggest single impurity (%)and content (%)respectively between the statutory method and the method of HPLC-PAD. CONCLUSION Compared with the statutory method, this HPLC-PAD method shows higher sensitivity, and is accurate and reliable. It can be applied to the determination of related substances in sisomicin sulfate injection.     

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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 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 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 establish an analytical method for simultaneous determination of scutellarin ethyl ester and its related substances by RP-HPLC and identify the main related substances by UPLC-MS.METHODS The assay was performed on a Kromasil C₁₈ column(4.6 mm??250 mm,5 ??m),and gradient elution was used with methanol-water containting 0.2% formic acid. The flow rate was 1.0 mLmin^-1and the detection wave length was set at 335 nm.The structure of the main related substance was identified by high resolution MS.RESULTS Under the separation condition,the related substances were completely separated from the principal components.The calibration curve of scutellarin ethyl ester showed good linearity in the concentration range of 5.005-1 001 mgL^-1(r²=0.999 9). The average recovery was 99.6%. The main related substance was identified as scutellarin by LC-MS. The contents of total impurities and scutellarin were 1.14% and 0.89%, respectively.CONCLUSION The method is simple, efficient and accurate, and can be used for the quality control of scutellarin ethyl ester.     

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??OBJECTIVE To establish a UPLC-MS method for the separation and detection of principal component isomers and related substances in ioversol bulk drug. METHODS The separation was performed on a Waters ACQUITY UPLC^TM BEH C₈ column (2.1 mm??100 mm,1.7 ??m), the mobile phase consisted of acetonitrile-0.1% formic acid in water (3:97),and the detection wavelength was set at 254 nm. The identification of isomers and impurities in ioversol bulk drug was performed with a triple-quadrupole mass spectrometer, with an electrospray ionization (ESI) source in the positive ion mode, and the cone voltage was set at 80 V. RESULTS The four optical isomers and related substances were seperated well, and their structures were confirmed by MS,UV, and RP-UPLC.The linear ranges of ioversol, impurity??, and impurity ?? were 0.5-52.8, 0.2-9.3, and 0.5-28.4 ??g??mL^-1, respectively (r=0.999 9); the detection limits of ioversol, impurity??, and impurity?? were 0.2, 0.08, and 0.2 ??g??mL^-1, respectively.CONCLUSION The method is simple, sensitive, and accurate, can be used to separate and determine the principal component isomers and related substances in ioversol bulk drug.