The initial Oasis SPE procedure was based on the C18 SPE
procedures previously attempted.17,19 However, because 1-
hydroxynaphthalene and 1-hydroxypyrene metabolites were
inefficiently retained, with recoveries of 34 and 32%,
respectively, parameters, such as washing and elution steps,
were optimized using a mixed standard working solution at
1000, 50, and 150 ng/mL 1-hydroxynaphthalene, 2-hydroxyfluorene,
and 1-hydroxypyrene, respectively