The most perfect method for the determination of the amino

acid composition of pure protein, feeds or biological fluids is still the

ion exchange column chromatography (IEC). By the help of the lithium

buffer system most of the problems on the field of free amino acid analysis

of biological fluids can be solved. At IEC most contaminants move

rapidly through the post-column system and are discarded before separation

of amino acids begins, resulting in better performance. The time of

the sample preparation is minimal compared to pre-column methods, and

the detection (with ninhydrin or OPA) is chemically specific for aminoacids. Nowadays a new off-line sample preparation method was introduced

before analysis by anion-exchange chromatography and integrated

amperometric detection, which eliminates carbohydrates from amino acid

samples. The major problems remained the hydrolysis of the protein, the

deproteinization of the biological fluids and the partial decomposition of

methionine, cysteine and tryptophan during the sample preparation for

analysis. At the moment the traditional IEC with postcolumn ninhydrin

derivatization seems to be the best for both pure proteins and feeds

and complex mixtures, but in some comparison the HPLC methods were

found to be similar to that of the IEC

common column