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 Z n 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, ski mmed 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 reagen t mixture dissociated casein micelles and stabilized liquid phase cati ons. Analyte emission or mass intensities losses were not observed. Re ference solutions were prepared in 10% v/v mixed amine solution, and n o 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 determine d values in NIST Standard Reference Material (SRM) Non-Fat Milk (SRM 1 549) 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.