ChromatographyEdexcel A-Level Chemistry: Mind map

Exam questions on Chromatography

1. A forensic analyst separates the dyes in a sample of black ink using thin-layer chromatography (TLC). The plate is coated with a thin layer of silica gel, and a solvent rises up the plate. When the plate is removed, the solvent front has travelled 8.0 cm from the baseline and the centre of one dye spot is 3.2 cm from the baseline.
   Explain why the dyes in the ink separate on the plate.2 marks
2. A laboratory tests urine samples from athletes for banned drugs using gas chromatography coupled with mass spectrometry (GC–MS). The sample is vaporised and carried through a long column by a gas.
   Explain why the gas chromatograph is coupled to a mass spectrometer.2 marks
3. A student separates a mixture of two amino acids by one-way thin-layer chromatography. After development, the solvent front is 12.5 cm from the baseline. Spot 1 has its centre 4.5 cm from the baseline and spot 2 has its centre 9.0 cm from the baseline. Under identical conditions, a reference sample of leucine has an Rf value of 0.72.
   Calculate the Rf value of each spot and deduce which spot is leucine.3 marks