Direct analysis of phthalate ester biomarkers in urine without preconcentration: Method validation and monitoring

• Phthalate ester metabolites are analyzed in urine without preconcentration.
• Direct analysis is a good, low-cost alternative for the reference method with SPE.
• The applicability of the direct analysis was successfully demonstrated.

Phthalates, which are ubiquitous in the environment, are readily metabolized in human bodies to their respective monoesters. These phthalate monoesters are non-persistent with short half-lives, which make them the ideal biomarkers of human exposure to phthalates. In this study a direct analysis method without preconcentration was developed and validated for the following phthalate ester metabolites in urine: mono-(2-ethylhexyl) phthalate, mono-(2-ethyl-5-hydroxyhexyl) phthalate, mono-(2-ethyl-5-oxohexyl)phthalate, monobenzyl phthalate, mono-isobutylphthalate, mono-n-butyl phthalate and monoethyl phthalate. The recovery of the phthalate ester metabolites varied between 97% and 104%. The intraday precision for the replicate analysis (n = 10) of a urine sample did not exceed 5% for most of the compounds. The coefficient of variance amounted to 2–3%. The limit of quantification was set equal to 0.5 μg/L for the majority of the compounds. A comparison between the direct analysis method and a foregoing solid phase extraction (SPE) of the urine sample was made. Finally, the applicability of the direct analysis method was tested in three interlaboratory comparisons.