Recent Advances in the Analysis of Vitamin D and Its Metabolites in Food Matrices

Applications of Chromatographic Techniques in Food and Environmental Analysis

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Assessment of Regulatory Compliance Testing for Vitamin D in Infant Formula—Impact of Delegated Regulation (EU) 2019/828

Background

Since the publication of Standard Method Performance Requirements (SMPR®) for vitamin D in infant formula (SMPR 2011.004) by AOAC INTERNATIONAL, revised vitamin D limits have been recommended by the European Food Safety Authority (EFSA) for infant formula and adopted in Commission Delegated Regulation (EU) 2019/828. The vitamin D range introduced, 2–2.5 μg/100 kcal, is significantly narrower than previous limits specified by Codex Standard 72–1981 and requires lower method reproducibility metrics to adequately assess regulatory compliance. The narrower limits for vitamin D present a significant challenge for current-generation reference analytical methods that comply with SMPR 2011.004.

Objective

We evaluate the impact of Delegated Regulation (EU) 2019/828 on the demonstrated performance of AOAC Method 2016.05/ISO 20636:2018 to assess the likelihood that vitamin D results produced by the method would be found outside the EU limits when testing infant formula that is compliant as manufactured.

Methods

AOAC Method 2016.05/ISO 20636:2018, specifically data generated during multi-laboratory study, was used as a basis for statistical evaluation of the impact of the narrower EU vitamin D limits.

Results

The review of AOAC Method 2016.05/ISO 20636:2018 method performance against the vitamin D regulatory range introduced in (EU) 2019/828 indicates methods capable of performing in alignment with SMPR 2011.004 are likely to produce results that fail to meet EU requirements.

Conclusions

Our assessment illustrates the high probability that a well-manufactured product with vitamin D levels within the EU regulatory range would fail to meet the regulatory requirements due to analytical method variability when tested using fit-for-purpose methods. Further, required method performance cannot be expected with the future development of new methods. To avoid this, consideration should be given to aligning proposed regulatory limits with method performance metrics of current-generation compendial methods.

Highlights

Current, state-of-the-art methods cannot consistently verify infant formula product compliance for vitamin D in accordance with (EU) 2019/828.

Simultaneous Determination of Vitamin D and Its Hydroxylated and Esterified Metabolites by Ultrahigh-Performance Supercritical Fluid Chromatography-Tandem Mass Spectrometry

In this study, an analytical method has been developed that, for the first time, allows simultaneous determination of vitamin D₂ and vitamin D₃ along with their hydroxylated and esterified forms. A group of 12 vitamin D analogues including vitamin D₂ and vitamin D₃, seven hydroxylated metabolites, and three ester forms were separated in a single 8.0 min run using ultrahigh-performance supercritical fluid chromatography coupled with triple quadrupole tandem mass spectrometry. Electrospray ionization and atmospheric pressure chemical ionization were investigated as ion sources, of which the latter showed a higher ionization efficiency. Chromatographic conditions were thoroughly evaluated by a step-by-step method, whereas an experimental design was applied for the optimization of the ionization parameters. Calibration and repeatability studies were carried out to validate the instrumental methodology showing determination coefficients higher than 0.9992 and good intra- and interday precision with relative standard deviations for areas and retention times lower than 10 and 2.1%, respectively, for all target analytes. Limits of quantification were below 3.03 μg/L for all compounds. The methodology was then validated and applied for the evaluation of human plasma samples in order to demonstrate its applicability to the analysis of vitamin D analogues in biological samples. Samples of five individuals were analyzed. Results show that linoleate-D₃, vitamin D₂, vitamin D₃, 25-hydroxyvitamin D₂, 24,25-dihydroxyvitamin D₃, and 1,25-dihydroxyvitamin D₃ could be detected in most samples, while the two latter also were quantified in all analyzed samples.

Analysis of vitamin D metabolic markers by mass spectrometry: Recent progress regarding the "gold standard" method and integration into clinical practice

Liquid chromatography/tandem mass spectrometry is firmly established today as the gold standard technique for analysis of vitamin D, both for vitamin D status assessments as well as for measuring complex and intricate vitamin D metabolic fingerprints. While the actual mass spectrometry technology has seen only incremental performance increases in recent years, there have been major, very impactful changes in the front- and back-end of MS-based vitamin D assays; for example, the extension to new types of biological sample matrices analyzed for an increasing number of different vitamin D metabolites, novel sample preparation techniques, new powerful chemical derivatization reagents, as well the continued integration of high resolution mass spectrometers into clinical laboratories, replacing established triple-quadrupole instruments. At the same time, the sustainability of mass spectrometry operation in the vitamin D field is now firmly established through proven analytical harmonization and standardization programs. The present review summarizes the most important of these recent developments.