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【求助放弃】翻译一篇文献的摘要和前言两段
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取消求助翻译一篇文献的摘要和前言两段 要求：1 语序必须通顺 2 专业一点，专业词汇可用英文单词代替 3 可借助金山词霸，但大意还需一致。 4 []内是参考文献，可以不翻，简写词也可不翻 Abstract Advances in the theory of gradient liquid chromatography and their practical impacts are reviewed. Theoretical models describing retention in reversed-phase, normal-phase and ion-exchange modes are compared. Main attention is focused on practically useful models described by twoor three-parameter equations fitting the experimental data in the range of mobile phase composition utilized for sample migration during gradient elution. The applications of theory for gradient method development, optimization and transfer are addressed. The origins and possibilities for overcoming possible pitfalls are discussed, including the effects of the instrumental dwell volume, uptake of mobile phase components on the column and size of the sample molecules. Special attention is focused on gradient separations of large molecules. 前言 Gradient elution versus isocratic elution The profile of the gradient, i.e., the gradient steepness, the initial and the final mobile phase composition, and in some cases the shape of the gradient (curved or multi-segmented linear) affects the retention of solutes in similar way as the elution strength in a binary mobile phase under isocratic conditions [1,5–9]. This is illustrated by the example of reversed-phase (RPC) separation of lower n-alkylbenzenes under isocratic and gradient conditions. Under isocratic conditions (Fig. 1), the retention times decrease as the concentration of acetonitrile increases from 60 to 80% in aqueous–organic mobile phases. Similar effect have increasing gradient steepness (defined as the concentration change of the strong solvent B in the gradient time from the start to the end of the gradient, see Eq. (12)) and increasing initial concentration of the solventB(acetonitrile) at the start of the gradient (see Fig. 2). Both increasing gradient steepness and the initial concentration of B decrease the retention times and result in narrower peaks more regularly spaced in the chromatogram. This effect is more apparent with gradients covering a broader concentration range (cf. the separations in Fig. 2A, 60–100% acetonitrile, and Fig. 2C, 80–100% acetonitrile. For comparison, see the isocratic separation in 80% acetonitrile, Fig. 1C. Many workers try to avoid gradient elution, as this technique requires some additional time for column re-equilibration between subsequent runs and because the selection of an optimumgradient program and transfer of gradient methods between the instruments and columns are less straightforward than the development and transfer of isocratic separation methods, as there are more parameters to be fixed. Further, higher-purity solvents than in isocratic elution should be used in gradient-elution to achieve high sensitivity in trace analysis [1]. Some detectors are not compatible with gradient elution, such as most electrochemical detectors or the refractometric detector. The latter one is a universal detector, which gives a response for almost all sample compounds, but also for the mobile phase components. The only universal detector useful for gradient elution is the evaporative light-scattering (ELS) detector, but it is approximately two orders of magnitude less sensitive than the UV detector [1,8]. As the ELS detector gives response to the stray light on solid particles of analytes after evaporation of the solvent from the nebulized column effluent, its use is restricted to volatile mobile phases and nonvolatile analytes. [ Last edited by telomerase on 2009-1-12 at 14:25 ] |
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