Amino acid analysis with LCMS

[bpatro]

Hi!
We are trying to establish a method for amino acid analysis of feed ingredients and plasma using an LC-MS in our lab but so far no luck. For some of the amino acids such as arginine, histidine, threonine and cystine, the SD is more than 15% using reference amino acids. I was hoping someone may already have figured out how to get robust data.

The instrumentation we have are Agilent 1100 LC and Bruker amaZon SL iontrap MS. We are using dansyl chloride for precolumn derivatization with carbonate buffer to control the pH. After derivatization, the reaction mixture is made up to volume with methanol and 0.1% formic acid. The mobile phases are: 1:1 MeOH:ACN with 0.1% formic acid (A) and 0.1% formic acid (B). We use C18 column and operate the MS on positive scanning mode in the 303-444 m/z. It seems that we may have some solubility issues. I would appreciate any inputs to solve the problem. Thank you.

Best regards,
BPatro

[MSCHemist]

I do Amino acids on the GC with ethyl chloroformate and can do every one but Arginine because the guanidino group doesn't react with the chloroformate and from what I understand with most other techniques the guanadino group hydrolyzes off from the high temperature to differing extents each run and with silylation there are multiple derivatives.

I have seen some pretty good capillary electrophoresis applications.

[lmh]

I've used Waters AccQ tag reagent and found it very reliable, although not cheap