Liquid Chromatography Questions and Answers

Answer: A

Lengthening the column increases both the retention time and the back pressure, so the run takes longer. The other three all shorten it, at some cost in resolution or in column life. Because every route to speed spends something - resolution, pressure or the column's lifetime - choosing between them means deciding which of those is most readily afforded.

Answer: B

The layer is about 0.2 mm thick.

Commercial analytical TLC plates carry a layer of adsorbent (silica gel or alumina) about 0.2 to 0.25 mm thick. That is thin enough to give sharp, well-separated spots from small samples.

50 microns (0.05 mm) is much thinner than standard plates. 600 microns and 0.1 cm (1 mm) are the thicknesses of preparative plates, used to separate larger amounts of material.

Answer: C

The best way is Reverse-phase chromatography.

Each method separates by one property. With identical molecular weight, gel filtration (size) cannot separate the two proteins. With identical isoelectric points, the methods that rely on charge, ion exchange chromatography and chromatofocusing (which separates by pI), also fail.

Reverse-phase chromatography separates by hydrophobicity, a property that depends on the amino acids exposed and is very unlikely to be the same in two different proteins, so it can resolve them.