Fuelquest,
I haven't personally used it and the only problem I have heard of had to do with the purity of the mobile phase additives used, i.e. you need to use very high purity ammonium formate (if memory serves).
As a matter of fact, I have made a comparative study of detectors that are able to detect underivatized amino acids (see Petritis et al. J. Chromatogr. A 961, 2002, 9-21) where I compared with the same LC conditions almost all the detectors that can detect the amino acids in their underivatized form (UV 210, ELSD, CLND, NMR, RI, CD, MS, MS-MS). At that point I had asked Dionex to loan me their amperometric detector but they refused.
Anyway, my preferable method is by LC-MS-MS, where you can do simultaneously more than 70 underivatized amino acids in virtually any matrix in less than 20 minutes. The LC part of the method is very robust and has been validated in conjuction with ELSD (see Petritis et al. Chromatographia 2004, 60, 293-298). The LC-MS-MS method has been developed for the screening of inborn errors of metabolism of newborns (matrix is urine and blood/plasma/serum).
You may see:
Petritis and co-workers:
Rapid Commun. Mass Spectrom. 2003, 17, 1297-1311 and
Rapid Commun. Mass Spectrom. 2005, 19, 1587-1602
