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.

DNA analysis of unilateral twin ectopic gestation

Although the overall incidence of ectopic gestation has been rising over the past 30 years, unilateral twin tubal gestation is still a relatively rare event. In the 93 cases reported to date, zygosity determined solely by subjective observations of the fetuses indicated monozygosity in more than 95%. We report a case of unilateral twin tubal gestation in which zygosity of the twins was determined by using DNA probes that detect restriction fragment length polymorphisms. We used six human DNA probes and M13 phage DNA to compare the genotypes of the twins. Three of the six human probes and the M13 probe showed differences, proving that these twins were dizygotic. We speculate that many of the unilateral ectopic twins who were thought to be monozygotic may actually have been dizygotic.

Methods of Analysis for Infant Formula: Food and Drug Administration and Infant Formula Council Collaborative Study, Phase III

Phase III of the collaborative study of methods of assay for nutrients in infant formulas was conducted. The study included assay of chloride, phosphorus, proxiraates (ash, fat, protein, total solids, and carbohydrates), thiamine, total pantothenates, and vitamins A, Bu, and E. Most of the methods were those in Official Methods of Analysis, 13th edition, with slight modifications, or methods of the Infant Formula Council. On the basis of the results obtained by the collaborators, the methods for chloride, phosphorus, proximates, thiamine, and vitamin Bu have been adopted official first action. Methods for total pantothenates, vitamin A, and vitamin E were not recommended for adoption at this time because of anticipated improvements in methodology in the foreseeable future.