X-ray Fluorescence Determination of Element Contents in Milk and Dairy Products
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X-ray Fluorescence Determination of Element Contents in Milk and Dairy Products Galina V. Pashkova
Received: 7 November 2008 / Accepted: 22 March 2009 / Published online: 23 April 2009 # Springer Science + Business Media, LLC 2009
Abstract The concentrations of minerals (Na, Mg, P, S, Cl, K, and Ca) and trace elements (Mn, Fe, Ni, Cu, Zn, Rb, Sr, and Br) in different types of milk, dairy products, and infant formulas have been determined using wavelengthdispersive X-ray fluorescence analysis (WDXRF). Freezedried samples pressed as tablets of 4 g have been analyzed. Calibrations have been established using both plant and milk standard reference materials. The matrix correction method based on the power function of Compton scattered intensity was applied. The paper provides calibration data, detection limits for each element, and testing the accuracy of the proposed technique. The elemental compositions of the samples obtained by WDXRF were compared with the previously reported data from different countries. Keywords X-ray Fluorescence Analysis (XRF) . Minerals . Trace Elements . Milk . Dairy Products . Infant Formulas
Introduction Milk and dairy products are balanced complex systems containing essential nutrients for human beings such as proteins, lipids, carbohydrates, vitamins, and minerals. Milk contains 0.7–0.8% inorganic elements, mainly associated with casein micelles (Ca, Mg, P, Zn), citrate and phosphate complexes (Ca, Mg, Na, K), chlorides (Na, K), milk fat
G. V. Pashkova (*) Institute of Geochemistry SB RAS, Favorsky Street 1a, Irkutsk 664033, Russia e-mail: [email protected]
membrane (Fe, Cu), enzymes (Fe, Mn, Zn), and vitamins (Co) (Gorbatova 2004). Broadly used methods for elemental analysis of milk, e.g. flame and graphite furnace atomic absorption spectrometry, inductively coupled plasma optical emission and mass spectrometry, include either preliminary dry or wet ashing (Saracoglu et al. 2007; Nabrzyski and Gajewska 2002; Kira and Maihara 2007) or microwave-assisted digestion of organic matrix (De la Fuente and Juarez 1995; Saracoglu et al. 2007). Such techniques of sample preparation are time-consuming and require large amounts of expensive reagents, which can produce hazardous waste and might contaminate samples with analytes (Korn et al. 2008). The X-ray fluorescence analysis (XRF) of milk and dairy products has not yet become widespread in dairy industry, although the method has a great potential, as the dried samples can be analyzed directly without any chemical treatment and XRF equipment is rather accessible. XRF spectrometry is a comparative technique and it requires a set of calibration standards in order to perform its quantitative measurements. The calibration samples must be representative of the matrix and elemental concentration ranges of the sample to be analyzed. Taking into account the wide diversity and difference in chemical composition of milk-based products, it is not easy to collect a relevant calibration set. Table 1 shows examples of XRF method application for determinatio
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