By HG-AFS, a new method was proposed for simultaneous determination of total arsenic and total selenium existed in the Chinese medicinal herbs in tartaric acid medium. The effects of analytical conditions and coexisting ions on the fluorescence signal intensity of analytes were investigated. The proposed method was provided with linear response ranges above 22µg l−1 for As and 44 µg l−1 for Se, and the detection limits of 0.13 and 0.12 µg l−1 were obtained for As and Se respectively. The recoveries of 93.8-96.1% for As and 95.3-99.1% for Se, and the precision of 1.2-3.8% and 2.4-5.3% (R.S.D., n=8) respectively, were obtained via simultaneous determined four samples of Chinese medicinal herbs and three certified botanic reference materials successfully. The proposed method has the advantages of simple operation, high sensitivity and high efficiency.

Flame atomic absorption spectrometry (FAAS) is an accepted and widely used method for the determination of trace elements in a great variety of samples. But its sensitivity doesn't meet the demands of trace and ultra-trace analysis for some samples. The derivative signal processing technique, with a very high capability for enhancing sensitivity, was developed for FAAS. The signal models of conventional FAAS are described. The equations of derivative signals are established for FAAS, flow injection atomic absorption spectrometry (FI-FAAS) and atom trapping flame atomic absorption spectrometry (AT-FAAS). The principle and performance of the derivative atomic absorption spectrometry are evaluated. The derivative technique based on determination of variation rate of signal intensity with time (dI/dt) is different from the derivative spectrophotometry (DS) based on determination of variation rate of signal intensity with wavelength (dI/dλ). Derivative flame atomic absorption spectrometry (DFAAS) has higher sensitivity, lower detection limits and better accuracy. It has been applied to the direct determination of trace elements without preconcentration. If the derivative technique was combined with several preconcentration techniques, the sensitivity would be enhanced further for ultra-trace analysis with good linearity. The applications of DFAAS are reviewed for trace element analysis in biological, pharmaceutical, environmental and food samples.

Simultaneous vapor generation of zinc (Zn) and cadmium (Cd) was evaluated by atomic fluorescence spectrometry coupled with an intermittent flow vapor generation system. Some complexing reagents, surfactant and transition metal ions were respectively tested as enhancement reagents. Experiments showed that an appropriate amount of 8-hydroxyquinoline or phenanthroline and nickel ion simultaneously, effectively improved the vapor generation efficiency of Zn and Cd. The volatile species generation was presumed to be a hydrogenation process interpreting how the enhancement reagents played an important role in vapor generation. Additionally, due to the instability of volatile species, reaction temperature, rapid and sufficient mixing of reagents and rapid separation of the volatile species from liquid phase were also crucial. The method of simultaneous determination of Zn and Cd by intermittent flow vapor generation led to the development of atomic fluorescence spectrometry. The detection limits (3σb) were 1.6μg l−1 for Zn and 0.01μg l−1 for Cd and the relative standard deviations were 3.6% for Zn (50μg l−1, n=11) and 1.7% for Cd (2μg l−1, n=11) respectively. Results for the determination of Zn and Cd have been confirmed by the analysis of CRMs with good agreement between the certified and found values.

A new method was developed for simultaneous determination of trace arsenic and antimony in Chinese herbal medicines by hydride generation-double channel atomic fluorescence spectrometry with a Soxhlet extraction system and an n-octanol-water extraction system, respectively. The effects of analytical conditions on the fluorescence intensity were investigated and optimized. A water-dissolving and methanol-water-dissolving capability were compared. The contents of different species in five Chinese herbal medicines and their decoctions were analyzed. The concentration ratios of n-octanol-soluble As or Sb to water-soluble As or Sb were related to the kinds of medicine and the acidity of the decoction. Soxhlet extraction was found to be an effective method for plants pretreatment for determination of arsenic and antimony species in Chinese herbs; the interferences of coexisting ions were evaluated. The proposed method has the advantages of simple operation, high sensitivity and high speed, with 3σ detection limits of 0.094µgg−1 for As(III), 0.056µgg−1 for total As, 0.063µgg−1 for Sb(III) and 0.019µgg−1 for total Sb in a 1.0g of the sample.

A reversed-phase ionpair chromatographic method with tetramethylene oxide as organic modifier has been developed for the simultaneous separation and detection of the sulfides NH2CSNH2, (NH4)2CS3, (NH4)2S, and NH4SCN. The optimized separation conditions were determined by means of a U7(76) uniform design experiment, and tetramethylene oxide played an important role in adjusting the retention behavior of(NH4)2S and NH4sSCN. The linearity of the calibration plots for the four components was investigated; correlation coefficients were from 0.9989-0.9999. The proposed method was successfully applied to the determination of NH2CSN H2, (NH4)2CS3, (NH4)2S, and NHSCN in synthesis and isomerization samples.