I've synthesised 15-azido pentadecanoic acid from the corresponding 15-bromo derivative using classical approach: reflux with NaN3 in dry acetone or nitromethane. The conversion works quite well, however, after work-up the H-NMR of the product tells me that some bromo derivative is left. Unfortunately, both substances seem to have a very similar chromatographic behavior since I cannot distinguish between both using TLC and different solvent mixtures.

Any idea how to separate both components?

Thanks in advance,