Simultaneous Determination of N-(1,3-Dimethylbutyl)-N'-Phenyl-p-Phenylenediamine (6-PPD) and 6-PPD-Quinone (6-PPDQ) in Mouse Tissues After Intratracheal Administration Using a Validated LC-MS/MS Method.

N-(1,3-Dimethylbutyl)-N'-phenyl-p-phenylenediamine (6-PPD), a tire rubber antioxidant, and its oxidation product 6-PPD-quinone (6-PPDQ) have raised environmental and health concerns due to their widespread occurrence and toxicity. This study aimed to develop and validate a sensitive liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the simultaneous quantification of 6-PPD and 6-PPDQ in murine tissues. The method showed excellent linearity (r ≥ 0.9977), low detection limits (0.056-0.967 ng/mL), and high accuracy and precision across multiple tissue matrices, enabling reliable quantification at trace levels. Following repeated intratracheal administration in mice, both analytes were detected in the liver, lungs, and kidneys, but not in the spleen. Notably, 6-PPDQ exhibited marked dose-dependent accumulation in the lungs, whereas 6-PPD remained at low levels, suggesting strong pulmonary retention. In contrast, trace levels of 6-PPD and a dose-dependent increase in 6-PPDQ were found in the kidneys, indicating renal elimination as a clearance route. These results reveal selective organ distribution, with the lung as the primary deposition site, and highlight 6-PPDQ as a potential multi-organ toxicant. The validated LC-MS/MS method provides a valuable analytical platform for future toxicokinetic, biomonitoring, and mechanistic studies of tire-derived contaminants.