Interlaboratory Trial for Measurement of Vitamin D and 25-Hydroxyvitamin D [25(OH)D] in Foods and a Dietary Supplement Using Liquid Chromatography-Mass Spectrometry.

Assessment of total vitamin D intake from foods and dietary supplements (DSs) may be incomplete if 25-hydroxyvitamin D [25(OH)D] intake is not included. However, 25(OH)D data for such intake assessments are lacking, no food or DS reference materials (RMs) are available, and comparison of laboratory performance has been needed. The primary goal of this study was to evaluate whether vitamin D3 and 25(OH)D3 concentrations in food and DS materials could be measured with acceptable reproducibility. Five experienced laboratories from the United States and other countries participated, all using liquid chromatography tandem-mass spectrometry but no common analytical protocol; however, various methods were used for determining vitamin D3 in the DS. Five animal-based materials (including three commercially available RMs) and one DS were analyzed. Reproducibility results for the materials were acceptable. Thus, it is possible to obtain consistent results among experienced laboratories for vitamin D3 and 25(OH)D3 in foods and a DS.

Comparison of various dilutions and solid-phase extraction cleanup on the determination of ephedrine-type alkaloids and internal standard recovery in ephedra botanical raw material and powdered extract.

A study was conducted to determine the effect of 3 dilution levels on the precision of the ephedra alkaloid method when used in conjunction with a solid-phase extraction (SPE) column. For the dilutions studied, SPE column cleanup is necessary because it promotes a greater recovery of the internal standard. However, overall, target precision values were not obtained on the test materials. It was determined that the SPE column is not the cause of the lower recovery in the more concentrated solutions. Significant signal suppression of the internal standard occurs in more concentrated solutions within the mass spectrometer. It is hypothesized that this lack of performance on the part of the SPE column may be linked to its inability to fully clean contaminants from the higher concentration solutions and/or a mass spectrometer overload, which resulted in the internal standard not fully correcting for signal suppression in more concentrated solutions. An internal standard is necessary, especially for accuracy, for the determination of all alkaloids, and only dilute solutions can be accurately analyzed. Due to the sensitivity of the mass spectrometer, it is recommended that the determination of ephedrine alkaloids in dietary supplements and botanicals should be studied using a standard graph at a level 10 x less than the current method. It is also recommended that the SPE column used should be evaluated on its need for the sample dilutions made to fit the newly recommended standard graph.