title: Optimization of a New Mass Spectrometry Method for Measurement of Breast Milk Iodine Concentrations and an Assessment of the Effect of Analytic Method and Timing of Within-Feed Sample Collection on Breast Milk Iodine Concentrations.
abstract: BACKGROUND
  Breast milk iodine concentration (BMIC) may be an indicator of iodine status during lactation, but there are few data comparing different analytical methods or timing of sampling. The aims of this study were: (i) to optimize a new inductively coupled plasma mass spectrometry (ICP-MS) method; and (ii) to evaluate the effect of analytical method and timing of within-feed sample collection on BMIC.
  
  
  METHODS
  The colorimetric Sandell-Kolthoff method was evaluated with (a) or without (b) alkaline ashing, and ICP-MS was evaluated using a new (129)I isotope ratio approach including Tellurium (Te) for mass bias correction (c) or external standard curve (d). From iodine-sufficient lactating women (n = 97), three samples were collected within one breast-feeding session (fore-, mid-, and hind-feed samples) and BMIC was analyzed using (c) and (d).
  
  
  RESULTS
  Iodine recovery from NIST SRM1549a whole milk powder for methods (a)-(d) was 67%, 24%, 105%, and 102%, respectively. Intra- and inter-assay coefficients of variation for ICP-MS comparing (c) and (d) were 1.3% versus 5.6% (p = 0.04) and 1.1% versus 2.4% (p = 0.33). The limit of detection (LOD) was lower for (c) (0.26 μg/kg) than it was for (d) (2.54 μg/kg; p = 0.02). Using (c), the median [95% confidence interval (CI) obtained by bootstrap] BMIC (μg/kg) in foremilk (179 [CI 161-206]) and in mid-feed milk (184 [CI 160-220]) were not significantly different (p = 0.017), but were higher than in hindmilk (175 [CI 153-216]; p < 0.001). In foremilk using (d), BMIC was 199 ([CI 182-257]; p < 0.001 vs. (c)). The variation in BMIC comparing (c) and (d) (13%) was greater than variation within feeding (5%; p < 0.001).
  
  
  CONCLUSIONS
  Because of poor recoveries, (a) and (b) should not be used to measure BMIC. Compared with (d), (c) has the advantages of higher precision and a lower LOD. In iodine-sufficient women, BMIC shows low variation within a breast-feeding session, so timing of sampling is not a major determinant of BMIC.
authors.affiliation: 1 Human Nutrition Laboratory, Institute of Food Nutrition and Health, ETH Zurich , Zurich, Switzerland .
authors.forename: Susanne
authors.initials: S
authors.lastname: Dold
authors.affiliation: 2 Centre of Excellence for Nutrition, North-West University , Potchefstroom Campus, South Africa .
authors.forename: Jeannine
authors.initials: J
authors.lastname: Baumgartner
authors.affiliation: 1 Human Nutrition Laboratory, Institute of Food Nutrition and Health, ETH Zurich , Zurich, Switzerland .
authors.forename: Christophe
authors.initials: C
authors.lastname: Zeder
authors.affiliation: 1 Human Nutrition Laboratory, Institute of Food Nutrition and Health, ETH Zurich , Zurich, Switzerland .
authors.forename: Adam
authors.initials: A
authors.lastname: Krzystek
authors.affiliation: 2 Centre of Excellence for Nutrition, North-West University , Potchefstroom Campus, South Africa .
authors.forename: Jennifer
authors.initials: J
authors.lastname: Osei
authors.affiliation: 3 Division of Risk Assessment, Federal Food Safety and Veterinary Office , Bern, Switzerland .
authors.forename: Max
authors.initials: M
authors.lastname: Haldimann
authors.affiliation: 1 Human Nutrition Laboratory, Institute of Food Nutrition and Health, ETH Zurich , Zurich, Switzerland .|4 Iodine Global Network , Zurich, Switzerland .
authors.forename: Michael B
authors.initials: MB
authors.lastname: Zimmermann
authors.affiliation: 1 Human Nutrition Laboratory, Institute of Food Nutrition and Health, ETH Zurich , Zurich, Switzerland .|4 Iodine Global Network , Zurich, Switzerland .
authors.forename: Maria
authors.initials: M
authors.lastname: Andersson
mesh_terms: D001942:Breast Feeding; D003124:Colorimetry; D005260:Female; D006801:Humans; D007455:Iodine / Q000032:analysis*; D007457:Iodine Radioisotopes / Q000032:analysis; D007774:Lactation; D013058:Mass Spectrometry / Q000379:methods*; D008895:Milk, Human / Q000737:chemistry*; D011208:Powders; D015203:Reproducibility of Results; D013691:Tellurium / Q000737:chemistry; D013997:Time Factors
chemical_list: D007457:Iodine Radioisotopes; D011208:Powders; D007455:Iodine; D013691:Tellurium