Interpreting Chromatograms
- The less polar components travel further up the TLC plate
- Their Rf values are higher than those closer to the baseline
- They are more soluble in the mobile phase and get carried forwards with the solvent
- More polar components do not travel far up the plate
- They are more attracted to the polar stationary phase
- The extent of separating molecules in the investigated sample depends on the solubility in the mobile and stationary phases
- Knowing the Rf values, of compounds being analysed, helps to compare the polarity of various molecules
Worked example
A mixture of amino acids is analysed by thin layer chromatography (TLC). The TLC plate produced is shown below. Identify the amino acids in the sample using the table of values for Rf.
Answers:
Blue spot Rf value = 2.82 ÷ 4.63= 0.61 = Leucine
Green spot Rf value = 2.45 ÷ 4.63= 0.536 = Isoleucine
Red spot Rf value = 2.04 ÷ 4.63= 0.44 = Valine
