Measurement of phthalate metabolites
Phthalate metabolite concentrations were determined by gas
chromatography/tandem mass spectroscopy.14 Reported
phthalate concentrations were expressed relative to urinary creatinine
(µg/g UCr) to control for urine dilution. A total of 455 urine samples
were analyzed for the following 7 phthalate metabolites:
mono-(iso-butyl) phthalate (MiBP), mono-isononyl phthalate (MNP),
mono-benzyl phthalate (MBzP), mono-(3-carboxypropyl) phthalate (MCPP),
mono-(2-ethyl-5-hydroxyhexyl) phthalate (MEHHP),
mono-(2-ethyl-5-oxohexyl) phthalate (MEOHP), and
mono-(2-ethyl-5-carboxypentyl) phthalate (MECPP). (Appendix S1: Fig.
E1). Phthalate metabolites were grouped based on molecular weight and
reported as the sum of 4 major high-molecular weight phthalate
(Σ4HMWP) metabolites (MEHP, MEOHP, MECPP, and MCPP), or
the sum of the 3 major low-molecular weight phthalate
(Σ3LMWP) metabolites (MiBP, MNP, and MBzP). They were
further divided into quartiles according to concentration (lowest to
highest,Q1 to Q4). Previous research indicated these two groups of
metabolites have different physicochemical
properties.14,15