Liquid chromatographic determination of Vitamin D3 in infant formulas and fortified milk

Differential Thermal Isomerization: Its Role in the Analysis of Vitamin D3 in Foods

Background

For nutritional purposes, the measurement of vitamin D3 (defined as the sum of vitamin D3 and previtamin D3) is required to obtain an accurate and reliable estimate of its content in foods. An often neglected aspect in the development of methods for the analysis of vitamin D3 is accounting for any potential analytical bias in the results associated with differential thermal isomerization between previtamin D and vitamin D.

Conclusions

For LC-UV methods using a vitamin D2 internal standard, cold saponification, or direct lipid extraction techniques should be avoided, unless chromatographic separation of vitamin D2, vitamin D3, and their previtamin forms is achieved so that UV absorbance corrections can be made. For both LC-UV and LC-MS methods using calciferol internal standards, the simplest solution to avoid analytical bias due to the presence of previtamin D is to utilize heating conditions (typically during saponification) such that previtamin D and vitamin D in the sample and the internal standard reach an equivalent equilibrium state prior to instrumental analysis. Only under such circumstances is the integration of previtamin D unnecessary to obtain accurate results for vitamin D3.

Highlights

A detailed discussion of the quantitation of vitamin D3 in food with concise recommendations for avoiding measurement bias as a consequence of differential thermal isomerization.

Surfactant enhanced flow injection chemiluminescence method for vitamin D3 determination in pharmaceutical formulations

A flow injection based chemiluminescence process has been reported for vitamin D₃ determination without using especial chemiluminescence reagent. Vitamin D₃ shows enhancement on the CL intensity of diperiodatocuprate(III) with surfactant (Triton X-100) solution. The calibration curve was found to be linear over the concentration range 0.01-40 mg/L (R² = 0.9997, n = 8) tested. A limit of detection (S/N = 3), limit of quantification (S/N = 10) and sample injection throughput of 2.5 × 10^-3, 8.3 × 10^-3 mg/L and 150 h^-1 respectively were obtained. Various experimental variables were tested to get most suitable response, e.g., the concentrations of reagents, and their flow rates, sample injection volume and photomultiplier tube voltage. The effect of potential interferences was also examined. Vitamin D₃ determination was successfully carried out in pharmaceutical formulations. The recoveries from the formulations were obtained in the range of 96 ± 4-108 ± 2%. The reaction mechanism discussion for diperiodatocuprate(III) complex-Triton X-100-vitamin D₃ was also included.