LIQUID AIR PARTITION-COEFFICIENTS OF METHYL AND ETHYL T-BUTYL ETHERS,T-AMYL METHYL-ETHER, AND T-BUTYL ALCOHOL/

Partition coefficients are essential to a description of the uptake an d distribution of volatile substances in humans and in the development of physiologically based pharmacokinetic models. Liquid/air partition coefficients (lambda) of three ethers, methyl t-butyl ether (MTBE), e thyl t-butyl ether (ETBE), and t-amyl methyl ether (TAME) were determi ned in vitro by head space-gas chromatography. These ethers, and espec ially MTBE, are used in unleaded gasoline to enhance the oxygen and oc tane content, and to reduce the output of carbon monoxide during combu stion. Partition coefficients of t-butyl alcohol (TEA), a metabolite o f MTBE, were determined also. The liquids tested were fresh human bloo d, water (physiological saline), and olive oil. The lambda(blood/air) values were: 17.7 (95% confidence interval 17.0-18.4) for MTBE; 11.7 ( 11.3-12.1) for ETBE; and 17.9 (17.3-18.6) for TAME. Corresponding lamb da(water/air) values were 15.2 (14.9-15.5), 8.39 (8.19-8.59), and 11.9 (11.7-12.1). The ethers have a higher affinity for oil, the values fo r lambda(oil/air) being 120 (114-125), 190 (183-197), and 337 (320-354 ), respectively. As expected, the lambda(blood/air) and lambda(water/a ir) for TBA were much higher than for the ethers, 462 (440-484) and 60 3 (590-617), respectively. The lambda(oil/air) was 168 (161-174) for T BA. The interindividual variability of the lambda(blood/air) (10 subje cts) was calculated as the coefficient of variation, and estimated as: 14% for MTBE, 20% for ETBE, 20% for TAME, and 30% for TBA. No signifi cant difference was seen in the lambda(blood/air) between the sexes.