Optimization of an improved analytical method for the determination of 1-nitropyrene in milligram diesel soot samples by high-performance liquid chromatography–mass spectrometry

A method for determination of nitrated polycyclic aromatic hydrocarbons (NPAHs) in diesel soot by high-performance liquid chromatography–mass spectrometry with atmospheric pressure chemical ionization (APCI) and detection by ion-trap following ultrasonic extraction is described. The determination of 1-nitropyrene that it is the predominant NPAH in diesel soot was emphasized. Vaporization and drying temperatures of the APCI interface, electronic parameters of the MS detector and the analytical conditions in reversed-phase HPLC were optimized. The patterns of fragmentation of representative NPAHs were evaluated by single and multiple fragmentation steps and negative ionization led to the largest signals. The transition (247 → 217) was employed for quantitative analysis of 1-nitropyrene. Calibration curves were linear between 1 and 15 μg L−1 with correlation coefficients better than 0.999. Typical detection limit (DL) of 0.2 μg L−1 was obtained. Samples of diesel soot and of the reference material (SRM-2975, NIST, USA) were extracted with methylene chloride. Recoveries were estimated by analysis of SRM 2975 and were between 82 and 105%. DL for 1-nitropyrene was better than 1.5 mg kg−1, but the inclusion of an evaporation step in the sample processing procedure lowered the DL. The application of the method to diesel soot samples from bench motors showed levels ≤1 μg of 1-nitropyrene per gram of diesel soot.