Column chromatographic separations of amino acids, peptides, and protein in normal human urine

Profiling of amino acids in body fluids and tissues by means of liquid chromatography

The needs of urgent diagnoses and the needs emerging from acute forms of diseases have directed progress in amino acid profiling to modern, rapid, automated analyses that can be done at reasonable cost. The first step in this direction was the short programmes of classical ion-exchange chromatography. At the beginning of this review we attempted to survey methods of sample preparation and sample treatment, as these are frequently neglected stages where artefacts or erroneous results may arise. There are basically the following approaches in amino acid profiling by liquid chromatographic techniques. For preliminary screening of a large number of samples in clinical routine planar procedures are the methods of choice, as they allow large numbers of samples to be handled with minimum effort and at very reasonable cost. For more precise profiling, particularly where quantitative data are essential, one can choose between some of the modern procedures for separating underivatized amino acids using modern equipment for cation-exchange chromatography, by making use of a stepped series of lithium citrate buffers with ninhydrin, o-phthalaldehyde or 4-fluoro-7-nitrobenzo-2,1,3-oxadiazole detection. Ninhydrin detection is preferred in those situations where the demands on sensitivity are not high. Where, however, only small amounts of samples are available or high sensitivity is required, one of the latter two methods is preferred. The o-phthalaldehyde procedure is not suitable for the detection of secondary amines and, if these are of interest, then diazole derivatization is to be preferred. At present, however, the ninhydrin and o-phthalaldehyde detection procedures are the most popular. The other choice is to use one of the sophisticated HPLC systems equipped with fluorescence detection and to separate amino acids as derivatives. Here o-phthalaldehyde and 4-fluoro-7-nitrobenzo-2,1,3-oxadiazole derivatives offer the most versatile possibilities. Automation and computerization have penetrated both categories of liquid column separation and are applied to automated sample delivery, automated and computerized gradient formation and quantitation of the data obtained. The tables of metabolic disorders of amino acids and the roles of different amino acids in these disorders should provide preliminary information for clinical chemists.

High-pressure liquid chromatography of amino acids and dipeptides on a tripeptide bonded stationary phase

A bonded tripeptide (L-valyl-L-phenylalanyl-L-valine) phase has been used as a stationary phase in liquid chromatography. Unique retention orders and retention variations are shown for phenylthiohydantoin (PTH) derivatives of amino acids and isomeric dipeptides using acidic and basic mobile phases. It is shown that the 25 PTH-amino acids studied here have different capacity ratios when 1% citric acid in water (ca. pH 2.5) is used as the mobile phase. The analysis time for these amino acid derivatives could be shortened without a loss in the resolution by adding 5% methanol to the above mobile phase. Of particular importance is the fact that the basic amino acids are eluted first. Isomeric dipeptides have been resolved by using deionized water (pH 5.5), and 1% sodium citrate in water (pH 7.9), as mobile phases. The data show that the nature of the mobile phases, the pH, and the ionic strength are the important factors affecting the selectivity and efficiency of the separations of amino acids and dipeptides.

Bonded peptide stationary phases for the separation of amino acids and peptides using liquid chromatography

Bonded optically active tripeptides have been applied as stationary phases for liquid chromatography. Significant retention variations are shown for some UV absorbing amino acids when compared to a silica gel column using the same mobile phase. The separation of certain isomeric dipeptides has been accomplished using the bonded optically active tripeptide stationary phases. It is shown that these separations are superior to those possible on silica gel, although the efficiencies of the column are low. Phenylthiohydatoin (PTH)-amino acids have also been analyzed using the bonded tripeptide L-Val-L-Ala-L-Ser on silica gel CT and 1% citric acid-water as the mobile phase. No two PTH-amino acids showed the same capacity ratio out of 25 tested and the separation of 15 in one isocratic run is presented. The implications and future for the use of bonded opitcally active peptides as stationary phases for liquid chromatography are discussed.

The mass spectrometric identification of dipeptides in the urine of a patient suffering from chronic skin ulceration and oedema

The identification of a complex ninhydrin positive mixture present in the urine of a child suffering from chronic skin ulceration and oedema by direct chemical ionisation mass spectrometric analysis is described. The compounds were shown to be dipeptides, of which glycylproline was the major constituent. At least 15 dipeptides were identified in the urine, most of which contained proline or hydroxyproline in the carboxy terminal position. The results suggested that the patient suffered from a defect in collagen metabolism. This hypothesis was subsequently confirmed by a grossly diminished level of prolidase in cultured fibroblasts and erythrocytes.