Optimised extraction of folic acid from multivitamin-mineral preparations for liquid chromatographic analysis

A comprehensive approach for the simultaneous analysis of all main water-soluble vitamins in multivitamin preparations by a stability-indicating HPLC-DAD method

A stability-indicating HPLC-DAD method for simultaneous determination of all nine main water-soluble vitamins, in addition to two commonly used vitamers, was developed and fully validated in analytical ranges, adjusted to their recommended dietary allowance values. An XSelect CSH C18 column with gradient elution using phosphate buffer and methanol was used for their optimal separation. The results from forced degradation studies along with peak purity tests and response ratios at dual wavelengths for the individual vitamins in all tested samples confirmed the method's stability-indicative nature. The complete developed methodology, including a single sample preparation for the vitamins simultaneous analysis, was applied to their assay in 13 commercial multivitamin preparations, revealing mostly higher amounts than the label claims. The developed method is applicable for stability testing, multivitamin products shelf-life determination as well as routine assay analysis of all water-soluble vitamins in their most common forms, including the analytically most demanding flavin mononucleotide.

Determination of folic acid in milk, milk powder and energy drink by an indirect immunoassay

BACKGROUND

Folic acid (FA) is essential for healthy people (reference daily intake 400 µg day⁻¹) and pregnant women (600 µg day⁻¹). Insufficient intake of FA will increase the risk of neural tube defects in newborns. In this study an indirect enzyme-linked immunosorbent assay was developed for rapid and convenient detection of FA in vitamin-fortified foods.

RESULTS

A carbodiimide-modified active ester method was used to synthesise the immunogen (FA-bovine serum albumin (BSA) conjugate) to raise polyclonal antibodies for FA. The coupling ratio of FA with BSA was determined to be 14:1 (molar ratio). The detection limit of the immunoassay was 3.0 ng mL⁻¹ in buffer, 3.52 ng mL⁻¹ in energy drink, 11.91 ng mL⁻¹ in milk and 16.50 ng mL⁻¹ in milk powder. Intra- and inter-assay variability ranged from 6.6 to 15.1%. Analytical recoveries of FA-spiked samples were 88.3-108.9%.

CONCLUSION

The immunoassay developed in this study can be used as a simple, rapid and accurate method for fast semi-quantitative and quantitative on-site analysis of FA in food products.

Quantitative determination of folic acid in multivitamin/multielement tablets using liquid chromatography/tandem mass spectrometry

Two different isotope-dilution liquid chromatography/tandem mass spectrometry (LC/MS/MS) methods for the quantitative determination of folic acid (FA) in multivitamin/multielement tablets are reported. These methods represent distinct improvements in terms of speed and specificity over most existing microbiological and chromatographic methods for the determination of FA in dietary supplements. The first method utilizes an aqueous/organic-based extraction solvent combined with positive-ion mode LC/MS/MS detection of protonated [M + H]+ FA molecules and the second method utilizes a pure aqueous-based extraction solvent combined with negative-ion mode LC/MS/MS detection of deprotonated [M - H]- FA molecules. The LC/MS/MS methods exhibit comparable linear dynamic ranges (> or =3 orders of magnitude), limits of detection (0.02 ng on-column) and limits of quantification (0.06 ng on-column) for FA. Two methods employing different extraction and different MS detection modes were developed to allow method cross-validation. Successful validation of each measurement procedure supports the use of either method for the certification of FA levels in dietary supplements. The accuracy and precision of each measurement procedure were evaluated by applying each method to the quantitative determination of FA in a NIST standard reference material (NIST SRM 3280 multivitamin/multielement tablets). The FA measurement accuracy for both methods was > or =95% (based on the manufacturer's assessment of the FA level in SRM 3280) with corresponding measurement precision values (% RSD) of approximately 1%.