Liwei Liu

Publications (3)7.59 Total impact

• Article: Microwave-enhanced cold vapor generation for speciation analysis of mercury by atomic fluorescence spectrometry.

  Li Wu, Zhou Long, Liwei Liu, Qin Zhou, Yong-Ill Lee, Chengbin Zheng
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  ABSTRACT: A new and simple cold vapor generation technique utilizing microwave irradiation coupled with atomic fluorescence spectrometry is developed for the speciation analysis of mercury in biological and geological samples. In the presence of formic acid, inorganic mercury (Hg(2+)) and total mercury (both Hg(2+) and methylmercury (MeHg)) can be converted to mercury cold vapor (Hg(0)) by microwave irradiation without and with H(2)O(2), respectively. The cold vapor was subsequently released from the liquid phase and rapidly transported to an atomic fluorescence spectrometer for the mercury detection. Optimum conditions for vapor generation as well as interferences from concomitant ions were carefully investigated. The conventionally required evaporation of the remnants of acid or oxidants was avoided because no significant interferences from these substances were observed, and thus analyte loss and potential contamination were minimized. A limit of detection of 0.005 ng mL(-1) for total mercury or inorganic mercury was obtained. A precision of less than 3% (RSD) at 2 μg L(-1) of mercury species was typical. The accuracy of the method was validated by determination of mercury in geological and biological certified reference materials. The speciation analysis of Hg(2+) and MeHg was achieved by controlling the conditions of microwave-enhanced cold vapor generation and validated via determination of Certified Reference Materials DORM-2, DORM-3 and a real river water sample.
  Talanta 05/2012; 94:146-51. · 3.79 Impact Factor
• Article: UV-induced carbonyl generation with formic acid for sensitive determination of nickel by atomic fluorescence spectrometry.

  Liwei Liu, Hao Deng, Li Wu, Chengbin Zheng, Xiandeng Hou
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  ABSTRACT: UV-induced carbonyl generation with formic acid is used for gaseous sample introduction into an atomic fluorescence spectrometer for the determination of ultra-trace nickel. Compared with conventional carbonyl generation, no toxic gas CO is involved in this work, and volatile Ni(CO)(4) is generated with a single reagent formic acid under the irradiation of UV light (253.7nm, 15W). The reaction conditions, including reaction medium, UV irradiation time and reaction temperature, are optimized for the best signal. Under the optimized conditions, a limit of detection of 10ngL(-1) for nickel is obtained without any analyte-pre-concentration, which is comparable to that using in situ trapping technique. Interferences from common transition metal ions, noble metal ions and mineral acids are also investigated. The proposed method is applied to the analysis of three certified reference materials and two organic acid samples for trace nickel, with analytical results in good agreement with certified values or those obtained by electrothermal atomic absorption spectrometry. This is a simple, fairly green and highly sensitive method for ultra-trace nickel determination.
  Talanta 01/2010; 80(3):1239-44. · 3.79 Impact Factor
• Article: Photochemical vapor generation of carbonyl for ultrasensitive atomic fluorescence spectrometric determination of cobalt

  Hao Deng, Chengbin Zheng, Liwei Liu, Li Wu, Xiandeng Hou, Yi Lv
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  ABSTRACT: UV photochemical vapor generation (photo-CVG) as sample introduction was first adapted for determination of ultratrace cobalt by atomic fluorescence spectrometry (AFS). Cobalt volatile species can be generated when the buffer system of formic acid and formate containing Co (II) is exposed to UV radiation. The generated gaseous products were separated from liquid phase within a gas–liquid separator and then transported to AFS for determination of cobalt. Factors affecting the efficiency of photo-CVG were investigated in detail, including type and concentration of low molecular weight (LMW) organic acid, buffer system, UV irradiation time, reaction temperature, carrier gas flow rate and hydrogen flow rate. With 4% (v/v) HCOOH and 0.4 mol L− 1 HCOONa buffer solution, 150 s irradiation time and 15 W low pressure mercury lamp, a generation efficiency of 23–25% was achieved. A limit of detection (LOD) of 0.08 ng mL− 1 without any pre-concentration procedure and a precision of 2.2% (RSD, n = 11) at 20 ng mL− 1 were obtained under the optimized conditions. The proposed method was successfully applied in the analysis of several simple matrix real water samples.
  Microchemical Journal.