Two-dimensional liquid chromatography is increasingly being used to address challenging separations in fields ranging from pharmaceutical analysis to the food industry. A significant impediment to development of more methods is the lack of a complete theoretical foundation upon which sound development decisions can be made. One parameter that is currently not fully understood is the extent of filling of sampling loops in the case where effluent from the first dimension separation is transferred to the second dimension separation through this type of open loop interface. This is a highly important parameter because it is connected to several other variables in a 2D-LC system, including the first dimension flow rate, the sampling (modulation) time, and the loop volume. In this study we have used both numerical simulation methods and experimental measurements to understand the extent to which sampling loops can be filled before a significant fraction of the analyte is lost from the end of the loop. Variables included in the study are the analyte diffusion coefficient (D_mol), loop filling rate (F_fill), loop inner diameter or radius (R_loop) and loop volume (V_loop). For a straight loop capillary we find that analyte breakthrough curves (as measured at the loop outlet) depend only on a single the dimensionless parameter $t^{*}=\frac{V_{loop}}{F_{fill}}·\frac{D_{mol}}{R_{loop}^2}$ . As a function of this parameter, the fraction of analyte lost from the loop outlet for different extents of loop filling could be calculated, allowing to develop guidelines for the maximum permissible extent of filling before a specified level of analyte loss is reached. Breakthrough measurements using a coiled loop capillary show that less breakthrough is observed compared to the straight capillary at high filling flow rates, presumably due to secondary flows that increase radial dispersion. These measurements enabled the calculation of apparent radial diffusion coefficients for use with coiled capillaries such that the same relation for t* can be used to predict analyte loss due to breakthrough. These results should be very useful to practitioners of 2D-LC, enabling them to make rational decisions about the extent of loop filling on the basis of experimental conditions and analyte type.

二维液相色谱法越来越多地用于解决从药物分析到食品工业等领域的挑战性分离。开发更多方法的一个重大障碍是缺乏可以做出合理的开发决策的完整理论基础。目前尚不完全了解的一个参数是在通过这种类型的开环接口将第一维分离的流出物转移到第二维分离的情况下，采样环的填充程度。这是一个非常重要的参数，因为它与2D-LC系统中的其他几个变量有关，包括一维流速，采样（调制）时间和定量环体积。在这项研究中，我们同时使用了数值模拟方法和实验测量方法，以了解在定量分析物从定量分析循环末端损失掉之前可以填充定量分析循环的程度。研究中包括的变量是分析物扩散系数（D_mol），回路填充率（F _fill），回路内径或半径（R _loop）和回路体积（V _loop）。对于直管毛细管，我们发现分析物的穿透曲线（在环管出口处测量）仅取决于单个无量纲参数${Ť}^{*}=\frac{V_{升ØØp}}{F_{F\mathrm{一世}升升}}·\frac{d_{米Ø升}}{{\mathrm{[R}}_{升ØØp}^2}$。作为该参数的函数，可以计算出不同程度的定量环充填从定量环出口流失的分析物分数，从而允许在达到指定水平的分析物损失之前制定最大允许填充量的指导原则。使用盘绕毛细管的穿透测量结果表明，与直毛细管相比，在高填充流速下观察到的穿透较少，这大概是由于二次流动增加了径向扩散。这些测量使得能够计算用于卷曲毛细管的表观径向扩散系数，从而可以使用与t *相同的关系来预测由于突破而导致的分析物损失。这些结果对2D-LC的从业者非常有用，