A New Equation for Solute Retention in Liquid Chromatography

In consideration of the adsorption of solvent,diluent and solute molecules on the surface of a stationary phase,a new equation for solute retention in liquid chromatography is presented. This equation includes three parameters: the displacement equilibrium constant( K _ sd ) between the solvent and diluent molecules on the surface of the stationary phase,the total number( N ) of the solvent and diluent molecules released from the stationary phase after one solute molecule being adsorbed,and the parameter( I ) related to the thermodynamic equilibrium constant for the solute adsorption on the stationary phase. Over the whole concentration range of the solvent in the mobile phase,the experimental retention data can be well described by this equation,parameters K _ sd ,N and I can be obtained by the regression analysis of the experimental retention data,and consequently the number of the solvent and the diluent molecules displaced by one solute molecule from the stationary phase can also be derived at different solvent concentrations in the mobile phase.

Impacts of Land-use and Land-cover Changes on River Runoff in Yellow River Basin for Period of 1956–2012

River runoff is affected by many factors, including long-term effects such as climate change that alter rainfall-runoff relationships, and short-term effects related to human intervention(e.g., dam construction, land-use and land-cover change(LUCC)). Discharge from the Yellow River system has been modified in numerous ways over the past century, not only as a result of increased demands for water from agriculture and industry, but also due to hydrological disturbance from LUCC, climate change and the construction of dams. The combined effect of these disturbances may have led to water shortages. Considering that there has been little change in long-term precipitation, dramatic decreases in water discharge may be attributed mainly to human activities, such as water usage, water transportation and dam construction. LUCC may also affect water availability, but the relative contribution of LUCC to changing discharge is unclear. In this study, the impact of LUCC on natural discharge(not including anthropogenic usage) is quantified using an attribution approach based on satellite land cover and discharge data. A retention parameter is used to relate LUCC to changes in discharge. We find that LUCC is the primary factor, and more dominant than climate change, in driving the reduction in discharge during 1956–2012, especially from the mid-1980 s to the end-1990 s. The ratio of each land class to total basin area changed significantly over the study period. Forestland and cropland increased by about 0.58% and 1.41%, respectively, and unused land decreased by 1.16%. Together, these variations resulted in changes in the retention parameter, and runoff generation showed a significant decrease after the mid-1980 s. Our findings highlight the importance of LUCC to runoff generation at the basin scale, and improve our understanding of the influence of LUCC on basin-scale hydrology.