Vitamin D
The city pair composites were analyzed for vitamin D3 at Lab A
by high performance liquid chromatography with ultraviolet
detection (HPLC-UV) as previously described in detail (Phillips
et al., 2008a; Byrdwell, 2009). Lab B determined vitamin D3 and 25-
OH-D3, in the single-city composites using ultra high performance
LC–MS–MS (UHPLC–MS–MS) (Huang et al., 2009; Huang and
Laluzerne, 2011).