Determination of amino acids and carbohydrates

Two approaches have been adopted for the study of natural organic compounds in seawater. compound class reactions based on the chemical reactivity of specific functional groups, i.e., here the amine or aldehyde functionalities, and detailed investigations of individual compounds after chromatographic separation. 

The techniques presented below are restricted to determinations of carbohydrates and amino acids by methods that have been found to be reproducible and suitable for use in field work. While the less specific techniques generally do not require sophisticated equipment and hence are adapted easily to shipboard work, chromatographic techniques are, from an instrumentation point of view, more complex. However, modem instruments are usually rugged enough to withstand conditions at sea, at least for some time. 

Natural organic compounds occur in seawater at levels in the pico- to low nanomolar range exceeded by several orders of magnitude by the concentrations of inorganic salts. To determine these compounds with a minimum amount of pre-treatment should be the ultimate aim of the marine analytical chemist. This in turn requires highly sensitive techniques employing small amounts of seawater. 

Filtration not only may contribute to sample contamination, but may also lead to other more or less systematic and quantifiable errors such as cell rupture or adsorption on filter materials. If possible, filtration should therefore be avoided. Filtration is usually unnecessary, when methods are employed which require small volumes of seawater ( 1 mL). In other cases, simple gravity Qtration through a pre-combusted glass fibre filter appears to be the method of choice. 

The methods described here advocate the determination of free amino acids in unfiltered samples whenever possible and soon after sampling. J0rgensen et al. (1981) suggested that deep-frozen (- 20 °C) the amino acid composition remains unaltered for short periods of time. 

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Yu, H., Ding, Y.S., Mou, S.F. et al. (2002) Simultaneous determination of amino acids and carbohydrates by anion-exchange chromatography with integrated pulsed amperometric detection. J. Chromatogr. A, 966, 89-97. 

Copper electrodes have been used to determine amino acids and carbohydrates [10]. Metal oxide electrodes (including thin-film semiconductors) show some promise, but nothing of substance has yet been published with regard to LCEC. Pulsed amperometric detection (PAD) takes advantage of metal oxides formed in situ. This approach is discussed later. 

Soga, T. and Ross, G.A. 1999. Simultaneous determination of inorganic anions, organic acids, amino acids and carbohydrates by capillary electrophoresis. Journal of Chromatography A 837 231-239. 

Freeman and Daniel 226) one of 124,000 both being based on sedimentation-equilibrium studies, and in addition, the amino acid and carbohydrate composition suggest a molecular weight near 130,000 119). These studies appear to establish the molecular weight of ceruloplasmin to be near 124,000—134,000. Morell et al. 134) have carefully determined the Cu content and dry weight of the protein finding a value of 0.275 0.009%, w/w Cu which for a molecular weight of... 

Since biological value is dependent primarily upon essential amino acid constitution, it would seem logical to assess the nutritive value of a protein by determining its essential amino acid constitution and then comparing this with the known amino acid requirements of a particular class of animal. Application of modern chromatographic techniques coupled with automated procedures allows relatively quick and convenient resolution of mixtures of amino acids. However, the acid hydrolysis used to produce such mixtures from protein destroys practically all the tryptophan and a considerable proportion of the cystine and methionine. Tryptophan has to be released by a separate alkaline hydrolysis, and cystine and methionine have to be oxidised to cysteic acid and methionine sulphone to ensure their quantitative recovery. Losses of amino acids and the production of artefacts, which are greater with foods of high carbohydrate content, are reduced if the hydrolysis is carried out in vacuo. Evaluations of proteins in terms of each individual amino acid would be laborious and inconvenient, and several attempts have been made to state the results of amino acid analyses in a more useful and convenient form. 

The relationship, if any, between the secondary metabolism of L-phenylalanine and carbohydrate degradation during brown-rot wood decay processes has not yet been determined. However, we suspect that the secondary metabolism of this aromatic amino-acid plays an important role in converting monomeric sugars to nitrogen-free metabolites (Shimada, M., and Takahashi, M., In Handbook of Wood and Cellulosic Materials Hon,... 

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