Problem 5: An aqueous sample contained traces of the compounds TABLE 15.1: Octan

Question

Problem 5: An aqueous sample contained traces of the compounds TABLE 15.1: Octanol-Water Distribution listed in the table. The octanol-water distribution coefficients are tabulated as pKD values. Assume you analyzed an aliquot of the aqueous sample using high-performance LC with a mobile phase that Coefficients: pk -log(k pk, 3.45 3.11 3.60 3.82 3.85 COMPOUND NAME n-Pentane 2.2-Dimethylpropane 3-Methylpropane 2,2-Dimethylbut 2,3-Dimethylbutane was 75% methanol and 25% water on a cellulose column. Predict the elution order and explain your answer. ane

Explanation / Answer

In HPLC with 75% methanol and 25% water, we know that stationary phase is polar and mobile phase is non-polar. Hence the elution order is most non-polar analytes elutes first.

Therefore the elution order according to pKD is as follows.

2,3-dimethylbutane, 2,2-Dimethylbutane , 3-Methylpropane ,n-Pentane ,2,2-Dimethylpropane

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