Differential contribution of albumin and lipids to the hydrophobic extraction of bis-(2-ethylhexyl) phthalate from hemodialysis tubing by human serum: Analysis by gas chromatography - Stable isotope dilution mass spectrometry

A method is presented which allows quantitative assignment of hydrophobic h uman serum components to the extraction of bis-(2-ethylhexyl) phthalate (DE HP) from medical tubing. Under optimized conditions (sample pH 5.5; fluid-f luid extraction with ethyl acetate + tert-butyl methyl ether I + I v/v; DEM P-ring-D4 as internal standard with ratios of endogenous (m/z = 149) and ad ded deuterated DEHP (m/Z similar or equal to 153) adjusted to around 1.0; e quilibration of added internal standard with the hydrophobic sample for 24 hours), a high precision can be achieved with an intra-assay coefficient of variation of 1.5% (n = 7) for sample DEHP quantification. Phthalate migrat ion from hemodialysis tubing wa. quantified by use of a peristaltic pump an d recirculation (200 minutes) of serum with different degrees of hypertrigl yceridemia (range from 2.26 to 14.5 g/L) or solutions of human albumin (10 to 50 g/L). Only DEHP, but no other phthalates are detected in the extracts . There exist linear relations between DEHP extraction and triglyceride con tent (increase by 1.01 mug DEHP / g tubing material per g triglyceride / L serum) as well as between DEHP extraction and albumin content (0.59 mug DEH P / g tubing material per g albumin / L). Under physiological conditions, t he total amount of albumin extracts 17.7-fold more DEHP than the total trig lyceride amount in human serum. The suitability of the proposed method as a candidate reference method as well as consequences for dyslipidemic and hy palbuminemic patients on hemodialysis schemes are discussed.