The determination of α-amino acids in seawater using a fluorimetric analyser

A method is described for the detection of free α-amino acids in the picomole range in seawater samples of less than 100 ml volume. The modifications made to a standard amino acid analyser to incorporate a fluorimetric detection system are described in detail, together with the methods for desalting the seawater samples on cation exchange resin and the concentration procedures prior to analysis. A complete analysis of up to 30 amino acids requires around 3 h with a detection limit of around 0.05 μg of an individual acid per litre. Twenty samples of seawater from different depths in the open Baltic have been analysed for their FAA contents together with 3 samples taken from the Kiel Fjord. The total FAA content of the samples ranges from 4.5 to 84 μg/l with a mean of around 25 μg/l. Five samples were hydrolysed prior to analysis in order to estimate the CAA content of the seawater. The values lay in the range 438–805 μg/l.