LIQUID-CHROMATOGRAPHIC METHOD FOR DETERMINATION OF IODINE IN MILK - COLLABORATIVE STUDY

Nine laboratories participated in an AOAC International/International Dairy Federation collaborative study on a liquid chromatographic (LC) method for determination of iodine in milk. Liquid milk is passed thro ugh a 25 000 MW membrane filter to remove protein and insoluble materi al. Iodine (in the form of iodide) in the clear filtrate is separated by reversed-phase ion-pair LC and is detected electrochemically. Parti cipants analyzed 2 commercial pasteurized whole milks and 5 nonfat dry milk powders in blind duplicate. Each sample was tested in duplicate on 2 days. Repeatability and reproducibility standard deviations (S(r) and S(R), respectively) and repeatability and reproducibility relativ e standard deviations (RSD(r) and RSD(R), respectively) for determinat ions of iodine in whole milk (mean recovery, 86.7%) were as follows: S r, 22 mug/L; SR, 22 mug/L; RSD(r), 8.2%; and RSD(R), 8.3%. For powdere d milk (mean recovery, 91 %), the values were as follows: Sr, 0.14 mug /g; SR, 0.22 mug/g; RSD(r), 9.0%; and RSDR, 12.7%. The method was adop ted first action by AOAC International.