By not explicitly specifying the type of solvent strength model,the features of ladder-like gradient elution were studied based on the general retention time formula that was derived in our previous work.For the case where the solute is eluted at the slope of the ladderlike gradient,we derived the expression that connects the mobile phase composition (φR),at which the solute is eluted from the column,with the gradient slope (B).It was shown that φR will increase with the increase of B in this case.For the case where the solute is eluted at the last isocratic segment of the ladder-like gradient,it was proven that the retention time (tR) will correlate linearly with the reciprocal of the gradient slope (1/B) when the initial and final mobile phase compositions are set to be constant.In experiments,by taking biphenyl as the sample,the values of retention time in isocratic and gradient elution were measured on a C18 column by using a mixture of methanol and water as the mobile phase.The experimental values were found to be well consistent with the theoretical values that were calculated from the expressions.These expressions will be helpful to understand the features of the ladder-like gradient in practice.%根据前期得到的梯度液相色谱保留时间计算公式,在不指定溶剂强度模型形式的前提下,探讨了梯形梯度洗脱的一些特点.对于溶质在梯形梯度坡度上流出时的情形,推导得到溶质流出色谱柱所对应的流动相组成(φR)随梯度斜率(B)变化的表达式.该公式表明,在该情形中φR将会随着B值的增加而增加.对于溶质在梯形梯度最后一个等度区间流出时的情形,如果初始和终止流动相组成保持不变而仅有梯度的斜率发生变化时,从理论上证明了溶质保留时间(tR)与梯度斜率的倒数(1/B)之间呈线性关系.实验中以C18色谱柱为固定相,甲醇-水为流动相,联苯为样品,测定了不同流动相组成以及梯形梯度条件下的保留时间,所得到的实验值与理论值吻合,从而验证了理论方法的正确性.
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