Untersuchungen über freie gelöste Aminosäuren in Meerwasser

In the literature concerning the determination of free dissolved amino acids in sea water, the evaluation of the various methods employed varies considerably. During our experiments, a two-stage preparatory method—evaporation of sea water to a small volume and desalination of the solution by ion exchange — which in principle was first used by Palmork (1963a), proved satisfactory. Recovery was about 80%, and reproduction of results sufficiently good. Following this preparatory method, and using the Beckman-Amino acid analyzer “Unichrom” for final analysis, a series of aged seawater samples was submitted to amino acid determination. The water samples always contained very small amounts of amino acids. A larger number of samples was collected in April and May, 1969, near Helgoland (54°11.3′ N, 7°54.0′ E). The samples were immediately filtered through a membrane filter (pore size 0.45 μ) and stored at-20°C until processed. Of the total amino acid content, glycine and serine were present regularly in the largest amounts, followed at some distance by lysine, glutamic acid, proline, and threonine. Quantitative determinations of aspartic acid were not usually possible, as it could not be separated sufficiently from another substance, probably methioninsulfoxide. Particular attention was paid to the danger of contamination of the samples by ninhydrinpositive compounds. The ion exchange resins used proved to be a considerable source of such foreign substances.