Development of Sample Preparation Methods for Vitamin-Mineral Complexes and Determination of their Elemental Composition Using Total Reflection X-Ray Fluorescence Analysis

Techniques to prepare samples of vitamin-mineral complexes (VMCs) for total reflection x-ray fluorescence (TXRF) analysis are described. Sample preparation of slightly soluble VMCs as suspensions in ethylene glycol is proposed because this method avoids complicated sample digestion and simplifies and accelerates the analytical procedure. The internal standard technique is used for quantitative determination. The results of TXRF determination are compared to those of inductively coupled plasma atomic emission spectrometry (ICP-AES) and to data provided by the manufacturers. Nickel in Multimax VMC was not detected by TXRF at the level declared by the manufacturer. Nickel detected by ICP-AES may be caused by its introduction during lengthy sample preparation where solutions contact stainless-steel equipment. Low contents of chromium and nickel are found in Duovit VMC by ICP-AES. These elements are not declared by the manufacturer and are not found by TXRF. Although TXRF has lower agreement factors than widely used ICP-AES, it uses a much simpler sample preparation technique (dissolution and suspension) and shortens the analysis time by several times.