The most common derivatization procedure is that using ninhydrin with subsequent determination of optical density. These derivatives, after emerging from the column, are then quantified by various detection devices. GLC and HPLC procedures are frequently more rapid than ion exchange procedures, but their major limitations often lie in the preparation of the derivatives rather than in the chromatography as such. Pre-column derivatization is required for amino acid analysis. These are then detected and measured by a fluorescence detector, which can provide detection limits in the picogram range.
Procedures can, however, be extremely rapid and sensitive.
Thus, while the procedure currently suffers from some limitations, it seems highly likely that the method will develop into a rapid and sensitive routine procedure for amino acid analysis. One major advantage of HPLC over all other chemical procedures lies in its ability to distinguish D and L forms of amino acids. Therefore, for certain research purposes, its use is already essential. With recent advances, such as the use of lithium instead of sodium buffers, higher pressures, narrow columns with fine spherical resin particles, and fluorescamine reagents replacing ninhydrin, the newer commercial equipment will give good separation of the common amino acids in picogram quantities in two hours or less. It is essential to introduce an internal standard into each hydrolysate to check the potency of ninhydrin solutions.