Vitamins form a heterogeneous chemical group having different stability. In foodstuffs some of them might be bound to matrix components. In the case of vitamin supplemented food products, since the vitamins are not strongly embedded in the matrix a general extraction method could be fit for purpose. The aim of this study was the simultaneous determination of the most common water-soluble vitamins, i.e. ascorbic acid (C), riboflavin (B ₂), niacin (B ₃), pyridoxine (B ₆), folic acid (B ₉) in enriched food products. Sample preparation based on the European Standard (CEN, 2003) was optimised for further LC-MS compatible chromatography. The separation of the vitamins was achieved by reversed-phase liquid chromatography. Detection was carried out with a photodiode array detector at four different wavelengths. The chromatographic method and the sample preparation were successfully applied for vitamin-enriched cereal, instant cacao powder and fruit juice samples.

The separation and determination of the ten water-soluble vitamins by using capillary electrophoresis in the micellar electrokinetic chromatography in a single run are proposed. The method uses low toxicity and cost solvent (ethanol) as modifier of background electrolyte (BGE) attending to the Green Chemistry principles. The electrophoretic method uses 10.0 % (v/v) ethanol, 2.0 % (w/v) SDS, 0.02 mol L⁻¹borate at pH 8.70 as BGE. The standard and real sample solutions were injected in the eletrophoretic system by hydrodynamic injection under pressure of 0.80 psi for 8 s, and the separation was carried out in a fused silica capillary under a potential of 28 kV at 25 °C; the analytical signals were monitored at 214 nm. The analytical method is precise (r.s.d. < 6 %), accurate (better than 9 %), selective, sensitive, robust, simple, and presents high analytical frequency as ten water-soluble vitamins were separated in only 18 min, with migration times of 5.75 ± 0.02, 6.81 ± 0.02, 8.13 ± 0.04, 8.80 ± 0.07, 8.98 ± 0.06, 11.10 ± 0.08, 11.34 ± 0.05, 13.85 ± 0.15, 14.82 ± 0.04, and 17.85 ± 0.30 min. Detection and quantification limits of 0.34, 0.32, 0.27, 0.20, 2.50, 4.98, 4.92, 0.30, 0.86 and 0.28 mg L⁻¹and 1.02, 0.97, 0.83, 0.62, 7.56, 15.09, 14.91, 0.90, 2.59 and 0.83 mg L⁻¹, for vitamins PP (nicotinamide), B₁₂(cyanocobalamin), B₂(riboflavin), B₆(pyridoxine), B₈(biotin), C (ascorbic acid), B₅(pantothenic acid), B₃(nicotinic acid), B₁(thiamine), and B₉(folic acid), respectively. Excellent recoveries (intra and inter-day) were obtained and, when the method was applied to food supplement analyses the results were in agreement with the conventional HPLC methods.