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 through a 25 000 MW membrane filter to remove protein and insoluble material. Iodine (in the form of iodide) in the clear filtrate is separated by reversed-phase ion-pair LC and is detected electrochemically. Participants 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 (sr and SR, respectively) and repeatability and reproducibility relative standard deviations (RSDr and RSDR, respectively) for determinations of iodine in whole milk (mean recovery, 86.7%) were as follows: sr, 22 μg/L; SR, 22 μg/L; RSDr, 8.2%; and RSDR, 8.3%. For powdered milk (mean recovery, 91 %), the values were as follows: sr, 0.14 μg/g; SR, 0.22 μg/g; RSDr, 9.0%; and RSDR, 12.7%. The method was adopted first action by AOAC International.

Analysis of Fat-Soluble Vitamins. XXVII. High Performance Liquid Chromatographic arid Gas-Liquid Chromatographic Determination of Vitamin D in Fortified Milk and Milkpowder: Collaborative Study

A collaborative study of the high performance liquid chromatographic (HPLC) method for vitamin D in fortified milkpowder (skimmed and whole milk) and a milkpowder preparation was carried out on 182 samples distributed to 26 laboratories. Thirteen laboratories submitted results. The level of vitamin D was 2-7IU vitamin D3/g milkpowder. All samples also contained vitamin A. Three laboratories were excluded from the statistical evaluation because of incomplete results or deviation from the analytical procedure. Other laboratories reported acceptable results. At the same time, 63 samples were distributed to 9 laboratories which used a gas-liquid chromatographic method for determining vitamin D in milkpowder. Only one laboratory reported results. The HPLC method has been adopted official first action.

Determination of added blood in ground beef

Blood added to ground beef is estimated from hemoglobin extracted with water. Since myoglobin is co-extracted with the hemoglobin, the 2 heme pigments are separated in one portion of the extract by precipitating the hemoglobin in an 85% (NH4)2SO4 solution. The myoglobin remaining in solution is used as the reference solution for determining the hemoglobin in another portion of the extract containing both pigments. The hemoglobin is converted to cyanomethemoglobin and quantitated by its absorbance at 422 nm.