2.1 Materials
CB
(99%) was obtained from Shanghai Aladdin Bio-Chem Technology Co., Ltd.
(Shanghai, China). Sulfuric acid (18.4 kmol/m3) was
procured from Beijing Lanyi Chemical Products Co., Ltd. (Beijing,
China). Lower-concentration sulfuric acid solutions were prepared by
diluting the concentrated acid in water. Fuming nitric acid (98 wt%)
was purchased from Sinopharm Chemical Reagent Co., Ltd. (Beijing,
China). High-performance liquid chromatography (HPLC)-grade methanol
(99.9%) was procured from Shanghai Titan Scientific Co., Ltd.
(Shanghai, China). Nitrobenzene (>99.8%) as an internal
standard was obtained from Shanghai Macklin Biochemical Co., Ltd.
(Shanghai, China). Standard samples of o -NCB
(>99%), p -NCB (>99.5%), m -NCB
(>99.5%) and DNCB (99%) were procured from Shanghai
Aladdin Bio-Chem Technology Co., Ltd. (Shanghai, China).