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Resumo:
Separation of the acidic compounds in the ion-exchange capillary electrochromatograph (IE-CEC) with strong anion-exchange packing as the stationary phase was studied. It was observed that the electroosmotic flow (EOF) in strong anion-exchange CEC moderately changed with increase of the eluent ionic strength and decrease of the eluent pH, but the acetonitrile concentration in the eluent had almost no effect on the EOF. The EOF in Strong anion-exchange CEC with eluent of low pH value was much larger than that in RP-CEC with Spherisorb-ODS as the stationary phase. The retention of acidic compounds on the strong anion-exchange packing was relatively weak due to only partial ionization of them, and both chromatographic and electrophoretic processes contributed to separation. It was observed that the retention values of acidic compounds decreased with the increase of phosphate buffer and acetonitrile concentration in the eluent as well as the decrease of the applied voltage, and even the acidic compounds could elute before the void time. These factors also made an important contribution to the separation selectivity for tested acidic compounds, which could be separated rapidly with high column efficiency of more than 220 000 plates/m under the optimized separation conditions. (C) 2000 Elsevier Science BN. All rights reserved.
Resumo:
Separation of small peptides on ion-exchange capillary electrochromatography (IE-CEC) with strong cation-exchange packing (SCX) as stationary phase was investigated. It was observed that the number of theoretical plates for small peptides varied from 240 000 to 460 000/m, and the relative standard deviation for t(0) and the migration time of peptides were less than 0.57% and 0.27%, respectively for ten consecutive runs. Unusually high column efficiency has been explained by the capillary electrophoretic stacking and chromatofocusing phenomena during the injection and separation of positively charged peptides. The sample buffer concentration had a marked effect on the column efficiency and peak area of the retained peptides. The influences of the buffer concentration and pH value as well as the applied voltage on the separation were investigated. It has been shown that the electrostatic interaction between the positively charged peptides and the SCX stationary phase played a very important role in IE-CEC, which provided the different separation selectivity from those in the capillary electrophoresis and reversed-phase liquid chromatography. A fast separation of ten peptides in less than 3.5 min on IE-CEC by adoption of the highly applied voltage was demonstrated. (C) 2000 Elsevier Science B.V. All rights reserved.
Resumo:
A novel mode of capillary electrochromatography (CEC), called dynamically modified strong cation-exchange CEC (DMSCX-CEC), is described in this paper. A column packed with a strong cation-exchange (SCX) packing material was dynamically modified with a long-chain quaternary ammonium salt, cetyltrimethylammonium bromide (CTAB), which was added to the mobile phase. CTAB ions were adsorbed onto the surface of the SCX packing material, and the resulting hydrophobic layer on this packing was used as the stationary phase. Using the dynamically modified SCX column, neutral solutes were separated with the CEC mode. The highest number of theoretical plates obtained was about 190 000/m, and the relative standard deviations (RSD's) for migration times and capacity factors of alkylbenzenes were less than 1.0% and 2.0% for five consecutive runs, respectively. The effects of CTAB and methanol concentrations and the pH value of the mobile phase on the electroosmotic flow and the separation mechanism were investigated. Excellent simultaneous separation of the basic and neutral solutes in DMSCX-CEC with a high-pH mobile phase was obtained, A mixture containing the acidic, basic, and neutral compounds was well separated in this mode with a low-pH mobile phase; however, peak tailing for basic compounds was observed in this mobile phase.
Resumo:
Fuel of proton exchange membrane fuel cells (PEMFC) mostly comes from reformate containing CO. which will poison the fuel cell electrocatalyst. The effect of CO on the performance of PEMFC is studied in this paper. Several electrode structures are investigated for CO containing fuel. The experimental results show that thin-film catalyst electrode has higher specific catalyst activity and traditional electrode structure can stand for CO poisoning to some extent. A composite electrode structure is proposed for improving CO tolerance of PEMFCs. With the same catalyst loading. the new composite electrode has improved cell performance than traditional electrode with PtRu/C electrocatalyst for both pure hydrogen and CO/H-2. The EDX test of composite anode is also performed in this paper, the effective catalyst distribution is found in the composite anode. (C) 2002 Elsevier Science B.V. All rights reserved.
Resumo:
P-J Fit and P-O Fit are focus problems in the investigation field of industry and organization psychology. They have distinct influences on staff job performance and job attitude. In a certain extend,these influences are moderated by some variables. LMX(Leader-member Exchange) and TMX(Team-member exchange) are two most important personal relationship types in job scene. Post investigations indicated that they are equal to forecasting variables and moderating variables of staff job performance and job attitude. From actualities, although there are many investigations about the relationships between P-J Fit, P-O Fit, LMX, TMX and job attitude, these investigations only focused on some aspects, and they discussed little about four aspects at one time and mutual influences. Using hierarchical regression analysis to analyze the survey data collected from 592 employees in a big governmental telecom company, we got some results as follows: (1)After controlling demography variables, standardized regression coefficients on P-J Fit, P-O Fit, LMX, TMX and job satisfaction, organization commitment are all positive, and reach distinct levels. (2) LMX could distinctly moderate the influences of P-J Fit, P-O Fit on job satisfaction, but couldn’t distinctly moderate the influences of the two on organization commitment. Specifically, as LMX increased,the effect of P-J on job satisfaction decreased gradually,while the effect of P-O increased. (3) TMX could not distinctly moderate the relationships between P-J Fit, P-O Fit, job satisfaction and organization commitment. The theoretical implication of this investigation lies in enriching and developing investigations in these fields in a certain extend, through conforming the influences of P-J Fit, P-O Fit, LMX, and TMX on job satisfaction and organization commitment. The practical implication lies in revealing these aspects for corporation governors: When selecting applications for a job, they should try their best to realize the best fit of personal ability and the job requirements, personal value and organization culture. They should enhance staff job satisfaction and organization commitment through furthering the relationship between the leader and members, team members each other. They should cushion disadvantage influences of non-P-J Fit on staff job satisfaction and enhance positive influences of P-O Fit. 【Key words】 person-job fit; person-organization fit; leader-member exchange; team member exchange; job attitude
Resumo:
Although the research into coworker relationship quality has been recognized one of key factors related to organization performance, and has been thought a new trend in organization behavior research with the flatting of organization structure and complication of task assignment, there is relatively little empirical research on the mechanism between coworkers’ interaction, contraring to the fruitful results on member exchange research based on social network theory, say nothing of the influence of cultural differences such as GUANXI. This research developed the scale for the assessment of Coworker Relationship Quality by literature review, deep interview, and questionnaires, compared the predictable ability of Coworker Relationship Quality (CRQ) scale and Coworker Exchange (CWX) scale on employees’ work attitudes and behaviors. Finally, the mediating effect of Coworker Relationship Quality between employees’ similarities on personality and their work attitudes and behaviors was investigated. Following are main results. Firstly, we found that the interpersonal communication, trust, and mutual support are the key factors of coworker relationship quality, which is similar to the result getting from western samples. But Chinese people are more GUANXI ORIENTATION, means they want to build longtime relationship with others, not only when they are coworkers, but also when one of them left the organization. Secondly, though the core meaning of CRQ and CWX are same, their predictable ability on organization outcomes is different. CRQ is more powerful than CWX, especially on turnover intention. The result showed that after controlling the effect of demographic variables and CRQ, CWX cannot predict turnover intention significantly, but CRQ can still predict turnover intention significantly after controlling demographic variables and CWX. Thirdly, the partial mediating effect of CRQ between positive affectivity similarity and organizational citizenship behavior, coworker satisfaction, organizational commitment and turnover intention are validated, but we did not find the mediating effect of CRQ between demographic variable similarity and workers’ attitudes and behaviors. The Similarity Attraction Paradigm, Social Identity Theory, and Self Category Theory were supported.