Direct determination of major and trace elements in milk by inductively coupled plasma atomic emission and mass spectrometry

The direct determination of major elements (Ca, K, Mg, Na and P) and Zn by inductively coupled plasma atomic emission spectrometry (ICP-AES) and trace elements (Al, Ba, Cu, I, Mn, Mo, Pb, Rb, Se, Sr and Zn) by inductively coupled plasma mass spectrometry (ICP-MS) in powdered, skimmed and whole milk was developed. Samples were diluted with a 5 or 10% v/v water-soluble, mixed tertiary amine reagent at pH 8. This reagent mixture dissociated casein micelles and stabilized liquid phase cations. Analyte emission or mass intensities losses were not observed. Reference solutions were prepared in 10% v/v mixed amine solution, and no internal reference element was needed for ICP-AES. The quantitative ICP-MS, procedure applied the standard additions method with a yttrium internal reference. Except for Se in whole milk powder, all determined values in NIST Standard Reference Material (SRM) Non-Fat Milk (SRM 1549) and Whole Milk (SRM 8435) Powders agreed with certified values at the 95% confidence level. This direct technique is as fast as slurry approaches without particle size effects and sensitivity losses.