Analysis of fat-soluble vitamins. XXV. High performance liquid chromatographic determination of vitamin D in multivitamin preparations: collaborative study.

The HPLC method for determining vitamin D in multivitamin preparations was studied collaboratively. Samples were distributed to 43 laboratories in 10 countries. Twenty-four laboratories gave their results.

Analysis of fat-soluble vitamins. XXIV. High performance liquid chromatographic determination of vitamin D in vitamin D resin containing powders: collaborative study.

Further study of vitamin D methodology solved the discrepancy between the AOAC chemical method, 43.068-43.078, and the HPLC assay for vitamin D3 in resin containing dry powders.

Analysis of fat-soluble vitamins. XXIII. High performance liquid chromatographic assay for vitamin D in vitamin D3 and multivitamin preparations.

Vitamin D is determined in preparations containing other fat-soluble vitamins by high performance liquid chromatography (HPLC). The unsaponifiable residue is extracted and separated from interferences by reverse phase chromatography; the fraction corresponding to vitamin D3 is collected and quantitated using normal phase chromatography (amylalcohol-n-hexane as mobile phase) by measuring the vitamin D3 and pre-vitamin D3 peaks at 254 nm. Previtamin D3 content is calculated as vitamin D3 with a conversion factor (determined on the equipment used).

Analysis of fat-soluble vitamins. XXII. High performance liquid chromatographic determination of vitamin D in concentrates. Collaborative study.

A collaborative study was carried out which compared the official chemical method (43.B14-43.B24), the HPLC method according to Hofsass et al.

Analysis of fat-soluble vitamins. XXI. High pressure liquid chromatographic assay methods for vitamin D in vitamin D concentrates.

Two high pressure liquid chromatographic methods, a straight and a reverse phase system, were developed and compared with the official (chemical) AOAC method for vitamin D concentrates. The effects of the systematic error and the reproducibility of using an internal or external standard were studied, as well as the effect of using peak height or peak height X retention time for calculating the potential vitamin D content. A method is given for determining the conversion factor to calculate previtamin D as vitamin D.

Analysis of fat-soluble vitamins. XX. Determination of vitamin D in multivitamin preparations. Second collaborative study.

The official first action method for determining vitamin D in multivitamin preparations was modified. The method was collaboratively studied by 7 laboratories, using 6 preparations in oil. The preparations consisted of vitamin D at various levels and at various ratios (in w/w) in vitamin A.

Analysis of fat-soluble vitamins. XIX. Collaborative studies on the chemical assay for vitamin D concentrates.

In 1971, a chemical method for the assay of vitamin D in concentrates containing only vitamin D was collaboratively studied by 14 laboratories, using 6 different samples from 2 European manufacturers. On the basis of these results, the laboratories were divided into 2 groups: 5 with significant laboratory biases of greater than or equal to 2%, and 9 laboratories with nonsignificant bias. The 9 laboratories were subdivided into 2 groups which differed significantly as to reproducibility within laboratories.

Analysis of fat-soluble vitamins. XV. Confirmation of isotachysterol in vitamin D concentrates.

The reaction with maleic anhydride yielding Diels-Alder adducts is used to distinguish vitamin D isomers. Treatment at 100 degrees C for 3 hr eliminates the fast-reacting (tachysterol and trans-vitamin D) and slow-reacting (cis-vitamin D and previtamin D) isomers. However, isotachysterol is not eliminated.