Water-soluble and fat-soluble vitamins are very different in their physicochemical properties, but are often found together in multivitamin products. Our main goal was to develop simple procedures for the simultaneous extraction and separation of water- and fat-soluble vitamins, because such sample of preparation for the analysis of both vitamin groups cannot be found in the other literature. We evaluated ten hydrophilic vitamins (ascorbic acid, thiamine hydrochloride, riboflavin, niacinamide, calcium pantothenate, pyridoxine hydrochloride, biotin, folic acid, cyanocobalamin and tetrahydrofolic acid) and five lipophilic vitamins (retinyl acetate, retinyl palmitate, D3, K1, alpha tocopheryl acetate) in their forms, most commonly found in multivitamin products.
Two previously developed chromatographic methods (HPLC method for fat-soluble and UHPLC method for water-soluble vitamins) were verified in accordance with ICH guidelines, before the development of extraction procedures, confirming their selectivity, linearity, accuracy, repeatability and sample stability for both vitamin groups. The development of the extraction procedures was first performed on aqueous standards mixtures and later also on selected commercial products in different dosage forms. For this purpose, three different extraction procedures were developed for each dosage form (capsules, tablets and oral solutions). During extraction procedure optimization, the following parameters were verified: solvent addition order, choice of aqueous and organic solvent, their volumes and ratios, number of extraction cycles, mixing and shaking time, sampling and others.
The developed final extraction procedures were suitable for vitamins extraction from each tested dosage forms. It was then confirmed by high extraction efficiency (100 ± 10%) and low variability of the results (RSD < 5%) for most analytes. The determined vitamin contents in the tested products were typically higher than the labeled contents, but were seldom beyond the acceptable USP limits for dietary supplements.
The developed extraction procedures were further compared with established extraction procedures of the separate vitamin groups. The obtained results were equivalent or even better. Therefore it can be concluded that the developed extraction procedures are suitable for the analysis of both vitamin groups in multivitamin products, with a single sample preparation as the main advantage, thus reducing the time and sample usage as well as solvents for analysis.
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