Improvement of an efficient separation method for chemicals in diesel exhaust particles: analysis for nitrophenols.
OBJECTIVE
Diesel exhaust is believed to consist of thousands of organic constituents and is a major cause of urban pollution. We recently reported that a systematic separation procedure involving successive solvent extractions, followed by repeated column chromatography, resulted in the isolation of vasodilatory active nitrophenols. These findings indicated that the estimation of the amount of nitrophenols in the environment is important to evaluate their effect on human health. The isolation procedure, however, involved successive solvent extractions followed by tedious, repeated chromatography, resulting in poor fractionation and in a significant loss of accuracy and reliability. Therefore, it was crucial to develop an alternative, efficient, and reliable analytical method. Here, we describe a facile and efficient acid-base extraction procedure for the analysis of nitrophenols.


METHODS
Diesel exhaust particles (DEP) were collected from the exhaust of a 4JB1-type engine (ISUZU Automobile Co., Tokyo, Japan). Gas chromatography-mass spectrometry (GC-MS) analysis was performed with a GCMS-QP2010 instrument (Shimadzu, Kyoto, Japan).


RESULTS
A solution of DEP in 1-butanol was extracted with aqueous NaOH to afford a nitrophenol-rich oily extract. The resulting oil was methylated with trimethylsilyldiazomethane and subsequently subjected to GC-MS analysis, revealing that 4-nitrophenol, 3-methyl-4-nitrophenol, 2-methyl-4-nitrophenol, and 4-nitro-3-phenylphenol were present in significantly higher concentrations than those reported previously.


CONCLUSIONS
Simple acid-base extraction followed by the direct analysis of the resulting extract by GC-MS gave only broad peaks of nitrophenols with a poor detection limit, while the GC-MS analysis of the sample pretreated with (trimethylsilyl)diazomethane gave satisfactorily clear chromatograms with sharp peaks and with a significantly lowered detection limit (0.5 ng/ml, approximately 100 times).


CONCLUSIONS
The present method involving an acid-base extraction, in situ derivatization, and GC-MS analysis has shown to be a simple, efficient, and reliable method for the isolation and identification of the chemical substances in DEP.
Noya
Yoichi
Y
Central Institute of Isotope Science, Graduate School of Medicine, Hokkaido University, Sapporo 060-0815, Japan.
Mikami
Yusuke
Y
Taneda
Shinji
S
Mori
Yoki
Y
Suzuki
Akira K
AK
Ohkura
Kazue
K
Yamaki
Kouya
K
Yoshino
Shin
S
Seki
Koh-ichi
K
D000393:Air Pollutants / Q000032:analysis*; D001713:Biphenyl Compounds / Q000032:analysis; D002947:Cities; D003408:Cresols / Q000032:analysis; D003978:Diazomethane / Q000031:analogs & derivatives / Q000737:chemistry; D008401:Gas Chromatography-Mass Spectrometry; D006801:Humans; D007564:Japan; D008745:Methylation; D053758:Nanoparticles / Q000032:analysis* / Q000737:chemistry; D009596:Nitrophenols / Q000032:analysis*; D052638:Particulate Matter / Q000032:analysis* / Q000737:chemistry; D014297:Trimethylsilyl Compounds / Q000737:chemistry; D001335:Vehicle Emissions / Q000032:analysis*
C494060:4-nitro-3-phenylphenol; D000393:Air Pollutants; D001713:Biphenyl Compounds; D003408:Cresols; D009596:Nitrophenols; D052638:Particulate Matter; D014297:Trimethylsilyl Compounds; D001335:Vehicle Emissions; C008636:4-nitro-3-cresol; D003978:Diazomethane; C060070:trimethylsilyldiazomethane; C024836:4-nitrophenol