Column liquid chromatography determination of vitamins A and E in powdered milk and local flour: a validation procedure

Some remarks on characterization and application of stationary phases for RP-HPLC determination of biologically important compounds

Biologically active compounds such as vitamins, steroids, nucleosides, peptides and proteins play a very important role in coordinating living organism functions. Determination of those substances is indispensable in pathogenesis. Their complex structure and physico-chemical properties cause many analytical problems. Chromatography is the most common technique used in pharmaceutical and biomedical analysis. The interaction between analyte and stationary phase plays a major role in the separation process. The structure of the packing has a significant influence on the results of the separation process. Various types of spectroscopic techniques, such as nuclear magnetic resonance spectroscopy, infrared spectroscopy, fluorescence spectroscopy and photoacoustic spectroscopy can be useful tools for the characterization of packings. Surface area measurements, elemental analysis, thermal analysis and microcalorimetric measurements are also helpful in this field. Part of the paper contains a description of chromatographic tests used for the determination of column properties. The description of the possibilities of surface characterization is not complete, but is focused on the most popular techniques and practical chromatographic tests. All the presented methods made possible the design and quality control of a new generation stationary phases, which are the future of high-performance liquid chromatography.

Determination of liposoluble vitamins in cooked meals, milk and milk products by liquid chromatography

A method for the simultaneous determination of liposoluble vitamins in cooked meals was established. Saponification was performed with 50% (w/v) KOH at 80 degrees C, and ascorbic acid was added as antioxidant. The subsequent extraction was carried out with diethyl ether. This was followed by a liquid chromatographic separation on a reversed-phase C18 column with methanol-water (94:6, v/v as the mobile phase. Retinyl acetate was used as the internal standard. The analytical parameters linearity, detection limit (0.19 and 8.33 microg/100 g for retinol and alpha-tocopherol, respectively), precision of the method (RSD=5.24 and 6.99% for retinol and alpha-tocopherol, respectively) and recovery assays (95.6 and 96.5% for retinol and alpha-tocopherol, respectively) show that the method studied is useful for measuring these compounds in foods and cooked meals.

Qualitative and quantitative liquid chromatographic determination of natural retinoids in biological samples

Liquid chromatography continues to be the preferred method for determining retinoids in biological samples. The highly unstable nature of retinoids and the real possibility of artifacts or erroneous results have led to the development of rapid and highly automated protocols for retinoid extraction, separation and detection. Due to strong light absorbance in the ultraviolet region, UV detectors still predominate although mass spectrometric detection is gaining increased popularity. This paper reviews recent advances and provides major guidelines for using liquid chromatography to identify and quantify retinoids in biological samples.

Simultaneous determination of fat-soluble vitamins and provitamins in milk by microcolumn liquid chromatography

The fat-soluble vitamins A, D2, D3, E and K1, retinyl acetate, retinyl palmitate, tocopherol acetate, ergosterol and 7-dehydrocholesterol in milk were separated on a packed reversed-phase fused-silica microcolumn, and determined with UV detection. Conventional liquid chromatographic equipment was adapted for such purposes, providing a highly efficient and sensitive analytical system. The vitamins could be separated in gradient mode with detection limits comprised between 0.02 ng/ml for retinol and 2 ng/ml for vitamin E. All vitamins were separated in less than 17 min. Recovery studies showed good results for all solutes (89-107%) and the intra-day coefficients of variations ranged from 2 to 8%. Application of the proposed method to the quantification of fat-soluble vitamins in milk is reported.