How to detect azide group on a primer? I bought azide-labeled primer for click chemistry, but it didn't work. So I want to prove the existence of azide group. How could I achieve this? I found a method to add PPh3 to Kaiser test reagents, but the concentration of the primer is too low (the protocol needs the solution be higher than 0.1M) and I cannot see the reaction.
One possibility would be to check the IR spectrum.  If there's any azide in there the azide band should show up as a strong band at around 2150 cm-1.  The trouble is of course that this isn't quantitative, you can only prove the absence of azide, not how much is present.

The Staudinger reaction might be a viable option.  PPh3 won't go up in aqueous solution, but sulfonated PPh3 will.  One should be able to distinguish starting material and product by 31P NMR.  With a known quantity of TPPTS you can even determine % azide in the starting material.