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A new method using solid phase extraction (SPE) combined with liquid chromatography-tandem mass spectrometry (LC-MS/MS) has been developed for the determination of six polyether antibiotics, including lasalocid, salinomycin, monensin, narasin, madubamycin and nigericin residues, in foods of animal origin. The samples were extracted with acetonitrile and purified by ENVI-Carb SPE columns after comparing the impurity effect and maneuverability of several SPE cartridges. Subsequently, the analytes were separated on a Hypersil Gold column (2.1×150mm, 5μm) and analyzed by MS/MS detection. The limit of quantization (LOQ) for milk and chicken was 0.4μg/kg, and for chicken livers and eggs, it was 1μg/kg. The linearity was satisfactory with a correlation coefficient of >0.9995 at concentrations ranging from 2 to 100μg/L. The average recoveries of the analytes fortified at three levels ranged from 68.2 to 114.3%, and the relative standard deviations ranged from 4.5 to 12.1%. The method was suitable for quantitative analysis and confirmation of polyether antibiotic residues in foods of animal origin.

A method has been developed for the generation of a “cold vapor” of cadmium by means of continuous flow chemical vapor generation from aqueous samples and for use in derivative atomic absorption spectrometry. Variables such as acidity, reducing agent concentration, atomization temperature, argon flow rate, reaction coil length, and other parameters were optimized. Detection limits and repeatability were measured, and cadmium was also determined in certified reference material and in tap water. The results showed that the proposed automated method is simple and accurate with a detection limit of 0.021 ng mL−1 when the derivative system’s sensitivity was 2 mV min−1

The species of Cr(III) and Cr(VI) in water samples were determined by flow injection on-line preconcentration and separation on two-microcolumn system-derivative flame atomic absorption spectrometry during a collaborative analysis for certification. The Cr(III) and Cr(VI) in water samples were retained on two microcolumns with ion exchange resin and were eluted directly to nebulizer by 15% HNO3 and 8% NH4NO3, respectively. The characteristic concentration (at the sensitivity grade of 2 mV min−1 for 1 min of preconcentration time) for Cr(III) and Cr(VI) were 0.130 and 0.0985 μg l−1, in the order which were 332- and 431-fold better than those of FAAS, and 45- and 47-fold better than those of FI-FAAS, respectively. The relative standard deviations were 3.27% and 3.66% with corresponding detection limits (3σ) of 0.244 and 0.235 μg l−1, respectively. The linear ranges of determinations for Cr(III) and Cr(VI) were 0∼100 μgm l−1 with correlation coefficients of 0.9984 to 0.9996. The satisfactory recovery of 94.4%∼106% for Cr(III) and Cr(VI) could be obtained from water samples.

A rapid and sensitive method has been proposed for the sequential determination of chromium(III) and total chromium in water samples by flame atomic absorption spectrometry combined with a flow injection on-line preconcentration on a double-microcolumn. The chromium(III) and total chromium in samples were retained on a double-microcolumn with a cation exchange resin, respectively, and eluted directly into a nebulizer by 3 mol L(-1) HNO3. The characteristic concentration (gives a derivative absorbance of 0.0044) and the detection limit (3sigma) for chromium were 0.512 microg L(-1) and 0.647 microg L(-1) for a preconcentration time of 1 min, respectively. This is an improvement of 20 and 14-times than those of conventional FI-FAAS. The proposed method allows the determination of chromium in the range of 0-90 microg L(-1) with a relative standard deviation of 3.63% at the 10 microg L(-1) level. The method has been applied for the analysis of chromium in reference water of National Research Center for Certified Reference Materials (GBW08607) and other water samples with satisfactory results.

A new method is developed for the direct determination of trace and ultra-trace level of arsenic and antimony in waters by hydride generation derivative atomic absorption spectrometry (DHGAAS). The signal model and fundamentals of DHGAAS are described. The effects of atomization temperature, argon flow rate, acidity and concentration of KBH(4)and KI were investigated and analytical conditions were optimized. The sensitivities for arsenic and antimony were increased 36.4 and 27.6 times better than those of conventional hydride generation atomic absorption spectrometry (HGAAS). For a 2 mV min(-1) sensitivity range setting, the characteristic concentration was 0.003 microg L(-1) for arsenic and 0.004 microg L(-1)for antimony, and the detection limits (3sigma) were 0.015 micro g L(-1) for arsenic and 0.020 microg L(-1) for antimony. The proposed method was applied to the determination of arsenic and antimony in several water samples with satisfactory results.

Fundamentals of derivative hydride-generation atomic absorption spectrometry (DHGAAS) are described. A linear relationship was obtained between the derivative absorbance and the concentration of analysis in a sample. The new DHGAAS method was applied to the determination of traces of lead in water. The conditions affecting the derivative absorbance of lead were evaluated and optimized. The detection limit and sensitivity of the proposed method were 26 times and 8.8 times better, respectively, than those of conventional hydride-genera-tion atomic absorption spectrometry. The characteristic concentration (for a derivative absorbance of 0.0044) and detection limit (3sigma) for lead were 0.017 and 0.096 ng mL(-1), respectively, for a 2 mV min(-1) sensitivity range setting. The recovery range was 92.5-103%.

Most works focused on the Trichel pulses at an atmosphere pressure in the past. In this paper, the characteristics of Trichel pulses at low pressure (several Torr) in air used by a needle-to-plane discharge structure are investigated. The current-voltage (I-V) characteristics, the images of discharge and the time evolution of the current and voltage of Trichel pulses are measured under different conditions. Results show that Trichel pulses exist in the negative differential resistance of I-V curves, and disappear when the discharge transits to the abnormal glow discharge mode with an abrupt contraction of discharge area around the needle tip. The pulses are consisted of a very short rising time (about 10 μs) and a short durations time (tens of μs) separated by longer inter-pulse periods (more than 100 μs). The frequency of pulses can be tuned continuously from a few kilohertz to more than ten kilohertz by adjusting the averaged current and the pressure. It increases with the increase of averaged current at the same pressure, and rises as the pressure increasing at the same averaged current. These results will be helpful to understand the mechanism of Trichel pulses.