The reference method to quantify mixing ratios of the criteria air pollutant nitrogen dioxide(NO_(2)) is NO-O_(3) chemiluminescence(CL), in which mixing ratios of nitric oxide(NO) are measured by sampling ambient air ...The reference method to quantify mixing ratios of the criteria air pollutant nitrogen dioxide(NO_(2)) is NO-O_(3) chemiluminescence(CL), in which mixing ratios of nitric oxide(NO) are measured by sampling ambient air directly, and mixing ratios of NO_(x)(= sum of NO and NO_(2))are measured by converting NO_(2) to NO using, for example, heated molybdenum catalyst or,more selectively, photolytic conversion(P-CL).In this work, the nitrous acid(HONO) interference in the measurement of NO_(2) by P-CL was investigated.Results with two photolytic NO2 converters are presented.The first used radiation centered at 395 nm, a wavelength region commonly utilized in P-CL.The second used light at 415 nm, where the overlap with the HONO absorption spectrum and hence its photolysis rate are less.Mixing ratios of NO_(2),NO_(x) and HONO entering and exiting the converters were quantified by Thermal Dissociation Cavity Ring-down Spectroscopy(TD-CRDS).Both converters exhibited high NO_(2) conversion efficiency(CF_(NO2);> 90%) and partial conversion of HONO.Plots of CF against flow rate were consistent with photolysis frequencies of 4.2 s^(-1) and 2.9 s^(-1) for NO_(2) and 0.25 s^(-1) and 0.10 s^(-1) for HONO at 395 nm and 415 nm, respectively.CFHONOwas larger than predicted from the overlap of the emission and HONO absorption spectra.The results imply that measurements of NO2 by P-CL marginally but systematically overestimate true NO_(2) concentrations,and that this interference should be considered in environments with high HONO:NO_(2) ratios such as the marine boundary layer or in biomass burning plumes.展开更多
Acitretin is a photosensitive oral retinoid with very limited data available on its degradation.The official HPLC method for acitretin determination was insufficient to resolve the degradation products generated durin...Acitretin is a photosensitive oral retinoid with very limited data available on its degradation.The official HPLC method for acitretin determination was insufficient to resolve the degradation products generated during stability studies.Therefore,an isocratic RP-HPLC-UV method was developed for the determination of acitretin in the presence of its related impurities and degradation products.Efficient chromatographic separation was achieved on a Thermo beta-basic column C18(100 mm4.6 mm,5μm)with mobile phase containing 0.3%(v/v)glacial acetic acid with acetonitrile(ACN)and isopropyl alcohol(IPA)in an isocratic ratio of 70:30 at a flow rate of 1.0 mL/min with the eluent monitored at 360 nm.The method was validated for specificity,linearity,precision,accuracy and robustness.The calibration plot was linear over the concentration range of 50-150μg/mL with a correlation coefficient(r2)of 0.999.The proposed method was used to investigate the degradation kinetics of acitretin under the different degradative conditions.The degradation rate constant(K),half-life(t1/2),and t90 were calculated.Degradation of acitretin followed pseudo-first-order kinetics.The drug was found to be less stable under acidic and photolytic degradation conditions:the photolytic degradation constants for acitretin in sunlight and UV light were 0.002698%and 0.0008402%min1,respectively.The LOD for acitretin and the known impurities were at a level below 0.02%.The method shows consistent recoveries for ACTR(99.8%-101.2%)and also for its known impurities(97.2-101.3%).The method was found to be accurate,precise,linear,specific,sensitive,rugged,robust,and useful for characterizing the stability of this chemical.展开更多
The radical intermediates, the crosslink microstructures, and the reaction mechanism of benzophenone (BP)-photoinitiated crosslinking of low-density polyethylene (LDPE) and model compounds (MD) have been reviewed in d...The radical intermediates, the crosslink microstructures, and the reaction mechanism of benzophenone (BP)-photoinitiated crosslinking of low-density polyethylene (LDPE) and model compounds (MD) have been reviewed in detail. The spin-trapping electron spin resonance (ESR) spectra obtained from the LDPE/BP systems with spin-trap agents show that two kinds of polymer radical intermediates are mainly formed: tertiary carbon and secondary carbon radicals. The spin-trapping ESR studies of MD/BP systems give further evidence that photocrosslinking reactions of PE predominantly take place a sites of tertiary carbon, secondary carbon, and especially allylic carbon when available. The high resolution C-13-NMR spectra obtained from LDPE and MD systems show that the crosslink microstructures have H- and Y-type links and that their concentrations are of the same order. The fluorescence, ESR, C-13 and H-1-NMR spectra from the PE and MD systems demonstrate that the main photoreduction product of BP (PPB) is benzpinacol formed by the recombination of two diphenylhydroxymethyl (K-.) radical intermediates. Two new PPB products: an isomer of benzpinacol with quinoid structure, 1-phenylhydroxymethylene-4-diphenylhydroxymethyl-2,5-cyclobexadiene and three kinds of alpha-alkyl-benzhydrols have been detected and identified. These results provide new experimental evidence for elucidating the reaction mechanism in the BP-photoinitiated crosslinking of polyethylene.展开更多
基金by the Natural Sciences and Engineering Research Council of Canada (NSERC) through a Discovery grant (to H.D.O.)support by an Alberta Graduate Excellence Scholarship (AGES) awardGlobal Analyzer Systems for the loan of PhoNOTM photolytic converters。
文摘The reference method to quantify mixing ratios of the criteria air pollutant nitrogen dioxide(NO_(2)) is NO-O_(3) chemiluminescence(CL), in which mixing ratios of nitric oxide(NO) are measured by sampling ambient air directly, and mixing ratios of NO_(x)(= sum of NO and NO_(2))are measured by converting NO_(2) to NO using, for example, heated molybdenum catalyst or,more selectively, photolytic conversion(P-CL).In this work, the nitrous acid(HONO) interference in the measurement of NO_(2) by P-CL was investigated.Results with two photolytic NO2 converters are presented.The first used radiation centered at 395 nm, a wavelength region commonly utilized in P-CL.The second used light at 415 nm, where the overlap with the HONO absorption spectrum and hence its photolysis rate are less.Mixing ratios of NO_(2),NO_(x) and HONO entering and exiting the converters were quantified by Thermal Dissociation Cavity Ring-down Spectroscopy(TD-CRDS).Both converters exhibited high NO_(2) conversion efficiency(CF_(NO2);> 90%) and partial conversion of HONO.Plots of CF against flow rate were consistent with photolysis frequencies of 4.2 s^(-1) and 2.9 s^(-1) for NO_(2) and 0.25 s^(-1) and 0.10 s^(-1) for HONO at 395 nm and 415 nm, respectively.CFHONOwas larger than predicted from the overlap of the emission and HONO absorption spectra.The results imply that measurements of NO2 by P-CL marginally but systematically overestimate true NO_(2) concentrations,and that this interference should be considered in environments with high HONO:NO_(2) ratios such as the marine boundary layer or in biomass burning plumes.
文摘Acitretin is a photosensitive oral retinoid with very limited data available on its degradation.The official HPLC method for acitretin determination was insufficient to resolve the degradation products generated during stability studies.Therefore,an isocratic RP-HPLC-UV method was developed for the determination of acitretin in the presence of its related impurities and degradation products.Efficient chromatographic separation was achieved on a Thermo beta-basic column C18(100 mm4.6 mm,5μm)with mobile phase containing 0.3%(v/v)glacial acetic acid with acetonitrile(ACN)and isopropyl alcohol(IPA)in an isocratic ratio of 70:30 at a flow rate of 1.0 mL/min with the eluent monitored at 360 nm.The method was validated for specificity,linearity,precision,accuracy and robustness.The calibration plot was linear over the concentration range of 50-150μg/mL with a correlation coefficient(r2)of 0.999.The proposed method was used to investigate the degradation kinetics of acitretin under the different degradative conditions.The degradation rate constant(K),half-life(t1/2),and t90 were calculated.Degradation of acitretin followed pseudo-first-order kinetics.The drug was found to be less stable under acidic and photolytic degradation conditions:the photolytic degradation constants for acitretin in sunlight and UV light were 0.002698%and 0.0008402%min1,respectively.The LOD for acitretin and the known impurities were at a level below 0.02%.The method shows consistent recoveries for ACTR(99.8%-101.2%)and also for its known impurities(97.2-101.3%).The method was found to be accurate,precise,linear,specific,sensitive,rugged,robust,and useful for characterizing the stability of this chemical.
基金The project was successively supported by the National Natural Science Foundation of China (No. 50073022, No 59773030, No. 59543002 and No. 5880104).
文摘The radical intermediates, the crosslink microstructures, and the reaction mechanism of benzophenone (BP)-photoinitiated crosslinking of low-density polyethylene (LDPE) and model compounds (MD) have been reviewed in detail. The spin-trapping electron spin resonance (ESR) spectra obtained from the LDPE/BP systems with spin-trap agents show that two kinds of polymer radical intermediates are mainly formed: tertiary carbon and secondary carbon radicals. The spin-trapping ESR studies of MD/BP systems give further evidence that photocrosslinking reactions of PE predominantly take place a sites of tertiary carbon, secondary carbon, and especially allylic carbon when available. The high resolution C-13-NMR spectra obtained from LDPE and MD systems show that the crosslink microstructures have H- and Y-type links and that their concentrations are of the same order. The fluorescence, ESR, C-13 and H-1-NMR spectra from the PE and MD systems demonstrate that the main photoreduction product of BP (PPB) is benzpinacol formed by the recombination of two diphenylhydroxymethyl (K-.) radical intermediates. Two new PPB products: an isomer of benzpinacol with quinoid structure, 1-phenylhydroxymethylene-4-diphenylhydroxymethyl-2,5-cyclobexadiene and three kinds of alpha-alkyl-benzhydrols have been detected and identified. These results provide new experimental evidence for elucidating the reaction mechanism in the BP-photoinitiated crosslinking of polyethylene.
