Ninhydrin amino acid assay
I am trying to implement a colorimetric assay using ninhydrin for analysis of glycine. I know from student time that we did this in biochemistry basic training, and I remember that it was quite sensitive.
So I googled a bit and found several protocols that state a sensitivity of about 10 µM amino acid (= 750 µg/L glycine).
I tried it in the lab, but I just can't get it to work.
I have tested several protocols that I found in the web, some with sodium acetate buffer (pH 5.2 - 5.6), some with acetic acid added to the ninhydrin reagent, concentration of ninhydrin ranges from 0.1 to 2 % in ethanol or acetone, incubation times from 30 °C to boiling water bath, ...
To make a long story short: I am not able to see any colour development unless I use at least 200 mg/L glycine, which is 2.7 mM.
And yes, I tried two different batches of ninhydrin and two different batches of glycine.
Can anybody assist with a working protocol?
(or any other assay for glycine...)