BS ISO 20649:2015 pdf free.Infant formula and adult nutritionals – Determination of chromium, selenium and molybdenum – Inductively coupled plasma mass spectrometry (ICP-MS).
BS ISO 20649 specifies a method for the quantitative determination of chromium, selenium and molybdenum in infant formula and adult nutritional formula.[Il The method has been validated in an interlaboratory study on seven different matrices.
2 Principle
A test portion is heated with nitric acid in a closed vessel microwave digestion system at 200 °C. The digested test solution, or an appropriate dilution, is presented to the inductively coupled plasma-mass spectrometer (ICP-MS) instrument standardized with acid matched standard calibrant solutions. An ionization buffer (potassium) is LiSed to minimize easily ionizable element (EIE) effects, methanol is added to normalize the carbon content, and germanium and tellurium are used as internal standards. It is permissible to combine the analysis of Cr/Mo/Se with simultaneous determination of any or all of these elements: Na, K, P, Mg, Ca, Fe, Zn, Cu, Mn. An ionization buffer would not be added if the calibration standards already contained Na, K, Mg, and/or Ca.
3 Reagents and materials
During the analysis, unless otherwise stated, use only reagents of recognized analytical grade and distilled or demineralized water or water of equivalent purity. Equivalent chemicals and reagents may be used.
3.1 Purified water, 18 Mfl/cm.
3.2 Concentrated nitric acid (H NO3), 65 % to 70 %, trace metal grade.
3.3 Hydrogen peroxide (H202), 30 % ACS reagent grade.
3.4 Methanol, purity  99,99 %, analytical reagent grade for matrix matching.
3.5 Potassium solution, mass concentration p = 10 000 mg/I in nitric acid for matrix matching.
The potassium solution may be replaced by multi-element standards that contain K, if major minerals are determined simultaneously.
3.6 Standards
3.6.1 Cr/Mo/Se multi-element stock standard solution in nitric acid, PCr = 2 mg/I, PMo = 2 mg/I and p = 1 mg/i. High-Purity” Standardsfl, or equivalent.
3.6.2 Ge/Te multi-element stock standard solution in nitric acid, PGe = 5 mg/I and PTe = 5 mg/i.High- Purity”’ Standards1), or equivalent.
3.6.3 Standard reference material SRM 1849a, from the National Institute of Standards and
Technology (N 1ST) or other suitable standard reference material to serve as a control for this analysis.
3.7 Preparation of standard solutions
Prepare intermediate standards from commercial stock standards at 40 ng/ml for Cr and Mo and at 20 ng/ml for Se. Custom blended multi-element stock standard in HNO3 is acceptable. Prepare three multi-element working standards containing 0.8 ng/ml. 4,0 ng/ml and 20 ng/ml Cr and Mo and 0,4 ng/ml, 2,0 ng/ml and 10 ng/ml Se, plus a blank, with both 50 ng/ml Ge and Te internal standards, in H NO3. Ge is used as the internal standard for both Cr and Mo, and Te shall be used for Se.
4 Apparatus
Usual laboratory glassware and equipment and, in particular, the following.
4.1 Microwave oven. Use a commercial microwave designed for laboratory use at 0 °C to 300 °C, with a closed vessel system and a controlled temperature ramping capability Select the vessel design that will withstand the maximum possible pressure, since organic material, and also carbonates if not given sufficient time to predigest, will generate significant pressure during digestion, Vent according to the manufacturer’s recommendation. CAUTION — Microwave operation Involves hot pressurized acid solution. Use appropriate face protection and laboratory clothing.
4.2 ICP-MS. ICP mass spectrometer with collision reaction cells and hydrogen and helium source. In the collaborative study, five different mode ICP-MS instruments from three major vendors delivered equivalent performance.
4.3 Various plasticware and pipets. Disposable plastic tubes/autosampler tubes to hold sample solutions, Class A volumetric pipets for standard preparation, adjustable 1 000 pL micropipette or fixed 500 .il pipet to add internal standards, calibrated at point of use.
4.4 Analytical balance. The balance shall read to 0.0001 g.BS ISO 20649 pdf free download.