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Abstract No.: ThP-096
Session: Environmental Analysis
Presentation date: Thu, Aug 31, 2006
Presentation time: 14:30 – 16:00

Determination of Nitropolycyclic Aromatic Hydrocarbons in Diesel Soot by HPLC-MS.

Annibal Duarte Pereira Netto1, Renata Pinheiro Barreto1, Flavio Cortinas Albuquerque2

1 Federal Fluminense University, Niteroi, Brazil
2 PETROBRAS/CENPES, Rio de Janeiro, Brazil

Correspondence address: Annibal Duarte Pereira Netto, Federal Fluminense University, Department of Analytical Chemistry, Outeiro de Sao Joao Batista, s/n, Niteroi, 24020-150 Brazil.

Keywords: Fuel; Mass Spectrometry, Ion Trap Quadrupole; Quantitative Analysis; Trace Analysis.

Novel aspect: The application of ion trap and MRM to low levels of nitropolycyclic aromatic hydrocarbons in diesel soot.

 

Polycyclic aromatic hydrocarbons (PAHs) and nitropolycyclic aromatic hydrocarbons (NPAHs) are environmental contaminants of concern due to mutagenic or pro-carcinogenic properties of many of them. Pyrosynthesis and/or incomplete combustion of organic compounds or they mixtures such as fossil fuels including diesel oil can form PAHs and NHPAs. Moreover NHPAs are formed in the atmosphere by reaction of parent PAHs and NOx. Possibly 1-nitropyrene (1-NPi) is the most well known NPAH and it is considered a marker of diesel combustion. Here we describe a method for determination of NPAHs in diesel soot by ultrasonic extraction followed by APCI-HPLC-MS analysis with emphasis in 1-NPi determination since it is the predominating NHPA in diesel soot. The HPLC consisted of a quaternary pump, an automated injector and a column oven (Agilent 1100, USA) interfaced to an Ion Trap detector (SL, Agilent 1100, USA) through an APCI interface. Chromatographic conditions were optimized in a Vydac 201TP54 (4.6mm; 25 cm; 5µm) column. Mobile phase composition (acetonitrile-methanol, acetonitrile-H2O and methanol-H2O) and flow-rates were optimized. Vaporization and drying temperatures of the APCI interface were also optimized. NPAH fragmentation of representative NPAHs (1,8-dinitronaphtahlene, 9-nitroanthracene, 2-nitrofluorene and 1-nitropyrene) were studied by single and multiple fragmentation (MSn) steps. Negative ionization lead to the largest signals. MRM of ions of M-30 that were the predominant fragments were employed in quantitative analysis. SRM-2975 (NIST, USA) and diesel soot samples were ultrasonically extracted with methylene chloride (DCM) followed by filtration through PTFE membrane (0.45 µm; 13mm) and dilution of the filtered extract in methanol. Best signal intensities were obtained when methanol was used as a mobile phase. The presence of water increased both NHPA resolution and analysis time with a strong signal reduction leading to worse detection limits. A proportion of 10 to 30% of DCM in methanol solutions lead to no signal reduction when compared to methanol solutions but larger concentrations of DCM lead to signal reduction and even to its complete suppression. For 1-NPi analytical calibration in MRM monitoring the fragmentation 247 to 217 were linear up to 15 ppb with very good correlation coefficients (r > 0.99). Typical detection limits (DL) of 1 ppb were found. Recoveries estimated with SRM 2975 were between 82 and 105%. DL for 1-NPi expressed in terms of sample mass were better than 10 µg of 1-NPi/g of sample but the inclusion of an evaporation step in the sample processing procedure lowered the DL to 1 µg of 1-NPi/g of sample. The application of the method to the determination of 1-NPi to diesel soot samples from bench motors led to levels lower than 1 µg of 1-NPi/g of diesel soot and other NPAHs were absent. Motor exhaust samples are being studied and preliminary results indicate that large levels of 1-NPi occur in those samples.