Determination of amino acids in sea water — Recent chromatographic developments and future directions

In the past, the determination of dissolved free amino acids in seawater has proven to be analytically challenging mainly because these compounds are present in low concentrations (typically low nanomolar or less). Thus, lengthy and potentially contaminating desalting/concentration steps were usually required prior to chromatography. Recently, these problems have been largely overcome with the introduction of a simple, highly sensitive method based on precolumn fluorescence derivatization using an o-phthalaldehyde/thiol reagent. The reagent is simply added to a seawater sample which is then injected without further treatment into the liquid chromatograph. In this review, applications and improvements of this method for the trace analysis of amino acids in seawater (and related samples) are described. Emphasis is placed on addressing: (1) problems with the derivatization technique; (2) problems related to sample handling, especially sample filtration and short-term sample storage; and (3) questions as to whether chromatographically determined concentrations may be considered as biologically available concentrations in seawater.