Determination of vanadium in food and traditional Chinese medicine by graphite furnace atomic absorption spectroscopy

Various experimental conditions were described for the vanadium determinationby graphite furnace atomic absorption spectroscopy (GFAAS). The experiments showed that whenatomization took place under the conditions where the combination of a pyrolytic coating graphitetube and fast raising temperature were used and the temperature was stable, the signal peak shapescould be improved, the sensitivity was enhanced, and the memory effect was removed. The vanadium infood and traditional Chinese medicinal herbs can be accurately determined using the standard curvemethod.

Determination of Trace Amounts of Nickel (Ⅱ) by Graphite Furnace Atomic Absorption Spectrometry Coupled with Cloud Point Extraction

A new method based on the cloud point extraction（CPE） for separation and preconcentration of nickel（Ⅱ） and its subsequent determination by graphite furnace atomic absorption spectrometry（GFAAS） was proposed, 8-hydroxyquinoline and Triton X-100 were used as the ligand and surfactant respectively. Nickel（Ⅱ） can form a hy-drophobic complex with 8-hydroxyquinoline, the complex can be extracted into the small volume surfactant rich phase at the cloud point temperature（CPT） for GFAAS determination. The factors affecting the cloud point extraction, such as pH, ligand concentration, surfactant concentration, and the incubation time were optimized. Under the optimal conditions, a detection limit of 12 ng/L and a relative standard deviation（RSD） of 2.9% were obtained for Ni（Ⅱ） determination. The enrichment factor was found to be 25. The proposed method was successfully applied to the determination of nickel（Ⅱ） in certified reference material and different types of water samples and the recovery was in a range of 95%―103%.

Preconcentration of Vanadium(Ⅴ) on Crosslinked Chitosan and Determination by Graphite Furnace Atomic Absorption Spectrometry

A new method is proposed for the preconcentration of vanadium(Ⅴ) with crosslinked chitosan (CCTS) and determination by graphite furnace atomic absorption spectrometry (GFAAS). The adsorption rate of vanadium(Ⅴ) by CCTS was 97% at pH 4.0, and vanadium(Ⅴ) was eluted from crosslinked chitosan with 2 mL 2.0 mol·L -1 chlorhydric acid and determined by GFAAS. The detection limit (3σ,n=7) for vanadium(Ⅴ) was 4.8×1 0 -12g and the relative standard deviation (R.S.D) at concentration level of 2.6 μg·L -1 is less than 3.6%. The method shows a good selectivity and high sensitivity, and it was applied to determination of vanadium(Ⅴ) in oyster and water samples. The analytic recoveries are (97±5)%.

Determination of Trace Iron in High Purity Sodium Fluoride by Graphite Furnace Atomic Absorption Spectrometry

A method is described for the direct determination of iron in high purity sodium fluoride using graphite furnace atomic absorption spectrometry. Interferences caused by the matrix are investigated. It is shown that the ashing temperature can be increased to 1 400°C and matrix interferences eliminated, the sensitivity of iron increased in 1. 27 fold by the addition of nickel nitrate. The method is applied to the determination of iron in sodium fluoride and satisfactory results are obtained.

A Study of the Background Absorption of Slurry Algae in the Graphite Furnace Atomic Absorption Spectrometry

In general, biological organisms have the ability to absorb a specific element selectively. Holcombe and his co-workers reported that copper, nickel and cobalt could be separated from riverine and sea-water samples and cadmium from river water samples by unicellular green algae and were determined by slurry GFAAS. Dar-

Determination of Pb Content in Soil Samples by Graphite Furnace Atomic Absorption Spectrometry

[ Objective] A method was established to determine trace Pb in soil by graphite furnace atomic absorption spectrometry. [ Method] The pre-treatment of soil sample was conducted by nitric acid -perchloric acid -hydrochloric acid system. Palladium nitrate was added to eliminate ma- trix interference. Digestion acid, ashing and atomization temperature of the sample were selected. The operating parameters of instrument and tem- perature-rise program of graphite furnace were optimized. National standard matter was used to verify accuracy of the method. [Result] The detec- tion limit for Pb was 0.27 μg/g by graphite furnace atomic absorption spectrometry, and the recovery rate was 91.0% -96.1%. [ Conclusion The method had rapid analysis velocity, high sensitivity, less interference and easy operation. When applied to determination of trace Pb in the soil, the method obtained satisfactory results.

Application of Back-propagation Artificial Neural Network in Speciation of Cadmium

A method for predicting the five species contents of cadmium was developed by combining the back-propagation artificial neural network with graphite furnace atomic absorption spectrometry（BP-ANN-GF-AAS）.Based on the strong learning function and the features of the information distributed storage of artificial neural network（ANN）,a single ANN was constituted in which only one determination point of every sample was required.The exchangeable,carbonated,Fe-Mn oxidable,organic and residual species of cadmium for 20 kinds of soil samples from the two sections of Changchun（China） were determined by BP-ANN-GF-AAS.The detection limit of the method is 0.024 μg/L and the limit of quantification is 0.080 μg/L.t-Test indicates that there is not any systemic error of the results obtained by the Tessier sequential extraction graphite furnace atomic absorption spectrometry method（Tessier-GF-AAS） and BP-ANN-GF-AAS.Compared with those of the Tessier-GF-AAS,the prediction errors of BP-ANN-GF-AAS are less than 10%.The proposed method is fast,convenient,sensitive,and can eliminate the interference among various species.

Application of Nanometer-Size Titanium Dioxide in Extreme-Trace V(Ⅴ) Analysis

The adsorption properties of nanometer-size TiO2 for V（Ⅴ ） were studied. The adsorption rate could reach above 99~ when the pH values were at the range of 4 10. The adsorption balance time was 10 min , the saturation capacity of adsorption of nanometer-size TiO2 to V（Ⅴ） was 6.43 mg per gram. Using 2 mL 1.5 mol · L^-1 NaOH as elution, we found the elution rate could reach 95%. A novel method of extreme-trace V（Ⅴ ） preconeentration with nanometer-size titanium dioxide and determination by graphite furnace atomic absorption spectroscopy （GFAAS） was advanced. The detection limit（3σ）of the method was 0.61μg ·L^-1 , and the relative standard deviation was 8.1% （n=6） of 2.5μg ·L-^1 V（Ⅴ）. Environmental samples experiments were also conducted to test the feasibility of the method, and it came out that the recovery rates were between 91.2% and 102.0%.

Mechanism of boron atomization in graphite furnace atomic absorption spectroscopy

The mechanism of the atomization of boron and the enhancement of sensitivity by matrix modifier Sr(NO_3)_2 in graphite furnace AAS were discussed.X-ray diffraction and thermodynamic calculation were applied to study the mechanism of boron atomization with and without matrix mo- difier Sr(NO_3)_2.The formation of boron atom is due to the sublimation of solid boron which derived from the reduction of B_2O_3 by carbon.The enhancement of boron signal in the presence of Sr(NO_3)_2 is due to the formation of SrB_6 before atomization,which decreased the volatization losses of B_2O_3 and retarded the formation of B_4C.

Effect of environmental factors on the complexation of iron and humic acid

A method of size exclusion chromatography coupled with ultraviolet spectrophotometry and off-line graphite furnace atomic absorption spectrometry was developed to assess the complexation properties of iron（Fe） and humic acid（HA） in a water environment. The factors affecting the complexation of Fe and HA, such as ionic strength, pH, temperature and UV radiation, were investigated. The Fe–HA complex residence time was also studied. Experimental results showed that pH could influence the deprotonation of HA and hydrolysis of Fe, and thus affected the complexation of Fe and HA. The complexation was greatly disrupted by the presence of NaCl. Temperature had some influence on the complexation. The yield of Fe–HA complexes showed a small decrease at high levels of UV radiation, but the effect of UV radiation on Fe–HA complex formation at natural levels could be neglected. It took about 10 hr for the complexation to reach equilibrium, and the Fe–HA complex residence time was about 20 hr.Complexation of Fe and HA reached a maximum level under the conditions of pH 6, very low ionic strength, in the dark and at a water temperature of about 25°C, for 10 hr. It was suggested that the Fe–HA complex could form mainly in freshwater bodies and reach high levels in the warm season with mild sunlight radiation. With changing environmental parameters, such as at lower temperature in winter or higher pH and ionic strength in an estuary, the concentration of the Fe–HA complex would decrease.