Optimization and validation of an analytical method for the determination of macro and micro elements in multivitamin/multimineral formulations

Abstract

The goal of the study was to optimize microwave decomposition conditions (Acid mixture, sample weight, radiation power, radiation period) to determine several minerals (Fe, Mg, Zn, Cu Mn, Cr and Se) in multivitamin/multimineral formulations. Optimum conditions were found to be 0.1 g of sample powder, acid mixture 5 ml of nitric acid, 0.5 ml of hydrochloric acid and 1 ml of hydrogen peroxide H2O2 and microwave conditions. A pretreatment, using a three-steps heating program: starting irradiation from 10 minutes at 500W, for 16 minutes at 600W and then cooling at room temperature. A reagent of the oxidizing acids mixture was suitable for determining the seven minerals studied without subsequent manipulation of the digestion product. The accuracy of the procedure was verified, and recoveries of iron, zinc, manganese, magnesium, copper, chromium and selenium were found to be in the percentage range 98.59 ± 0.36-100.91 ± 0.61, 99.05 ± 0.46-101.19 ± 0.56, 97.30 ± 0.1-100.57 ± 0.09, 97.50 ± 5.63-99.10 ± 3.62, 98.93 ± 0.05-100.12 ± 0.057, 99.136 ± 0.01-100.13 ± 0.02, and 98.54 ± 0.07-99.85 ± 0.03, respectively. The optimized method was validated and applied to the determination of iron, zinc, manganese, magnesium, copper, chromium and selenium in eight available multivitamin/multimineral capsules obtained from the local pharmacies. The developed microwave digestion procedure was used to determine thirteen macro and micro elements Ca, Co, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, Se, V and Zn in the multivitamin/multimineral formulations, employing ICP-MS, and optimized by factorial design 33, The microwave digestion conditions, temperature, acid mixture volume and radiation period were selected as factors. Moreover, a multiple response was built to establish a compromise condition between the elements. The optimum conditions were found to be 160ºC, 6.5ml, 20min for temperature, acid mixture volume and radiation period, respectively. The procedure was validated using standard reference materials (SRM3280) and applied to determine of calcium, cobalt, chromium, copper, iron, potassium, magnesium, manganese, sodium, nickle, selenium, vanadium and zinc in six commercial multivitamin/multimineral samples obtained from the local pharmacies. Recoveries were found to be in the range 88 – 107%. Moreover, ninety-three samples of widely used multivitamin/multimineral for pregnant and diabetic formulations available in the Sudan were analyzed by inductively coupled plasma mass spectrophotometry (ICP-MS), to estimate values of thirteen macro and micro elements (Calcium, Cobalt, Chromium, Copper, Iron, Potassium, Magnesium, Manganese, Sodium, Nickle, Selenium, Vanadium and Zinc) and the concentration levels were compared with those labelled. Concentration levels were acceptable for Ca, Co, Cu, Fe, K, Mg, Na, Ni, and V, but six products contained mineral levels much higher than those labelled, for Mn, Zn, Cr and Se. Although many elements were not labelled in the leaflet of the multivitamin/multimineral products, some were experimentally determined. Those elements could be introduced in the composition of the product, during formulation processing from excipients and water, such as K (from 0.657 mg/caps. to 0.024 mg/caps.), and Ca (from 2.083 mg/caps. to 6.686 mg/caps.) in addition to their salts as iodide, selenite and molybdate.