Prince Ngobeni

Determination of lead and cadmium in organic solutions by electrothermal atomic absorption spectrometry with a transverse heated filter atomizer

The performance of a transverse heated filter atomizer (THFA) is investigated for the atomic absorption determination of Pb and Cd in organic solutions and compared with that of a conventional transverse heated graphite atomizer (THGA). Organometallic species of Pb and Cd are stabilized in the THFA at 1100 and 900 °C, respectively, without matrix modification. Pd and Ir modifiers can be used to increase the stabilization temperature by 100 and 200 °C, respectively. Ir provides permanent stabilization during, at least, 75 heating cycles with a cleaning temperature of 2450 °C. Sensitivity improvement (3–4 times), better repeatability, large sample volumes (up to 100 µl) and a short thermal program provide the advantages of the THFA over the THGA in the analysis of organic liquids. The precision and accuracy of the method is verified by the analysis of certified reference materials.

Speciation of Cr(VI) in environmental samples in the vicinity of the ferrochrome smelter

The impact of ferrochrome smelter on the contamination of its environment with toxic hexavalent chromium, Cr(VI), was assessed by analyzing smelter dusts, soil, grass and tree barks. For the separation of Cr(VI) from Cr(III), solid samples were treated with 0.1M Na(2)CO(3) and filtered through hydrophilic PDVF 0.45 microm filter prior to the determination of Cr(VI) by electrothermal atomic absorption spectrometry (ET-AAS). Ferrochrome smelter dust was found to contain significant levels of Cr(VI), viz. 43.5 microg g(-1) (cyclone dust), 2710 microg g(-1) (fine dust), and 7800 microg g(-1) (slimes dust) which exceeded the maximum acceptable risk concentration (20 microg g(-1)). The concentration of Cr(VI) in environmental samples of grass (3.4+/-0.2), soil (7.7+/-0.2), and tree bark (11.8+/-1.2) collected in the vicinity of the chrome smelter were higher as compared with the same kind of samples collected from uncontaminated area. The results of the investigation show that ferrochrome smelter is a source of environmental pollution with contamination factors of Cr(VI) ranging between 10 and 50.

Transverse heated filter atomizer: atomic absorption determination of Pb and Cd in urine

A transverse heated filter atomizer (THFA) was applied to the direct determination of Cd and Pb in urine, and its analytical performances were investigated using a PerkinElmer SIMAA 6000 atomic absorption spectrometer. Seronorm certified human urine reference materials and six realistic samples collected locally were used for the method validation. The urines were diluted ten- or five-fold with 0.2% HNO3. Cd and Pb nitrate solutions were employed as standards. Recoveries of the elements from the urine samples were investigated with the analyte addition method. Compared to the transverse heated graphite atomizer (THGA) with a platform, the THFA provided a significant reduction of spectral background and chemical interferences from the urine matrix, without the use of chemical matrix modifiers, a 1.5–2 times increase of the determination sensitivity and, therefore, a reduction of limits of detection up to 0.018 and 0.2 µg L−1 for Cd and Pb, respectively. The use of a THFA collector made from carbon fiber and a tungsten wire improved recoveries of lead and cadmium in urine (≥92%). A sampling temperature 150 °C enabled us to skip the drying period, thus a significantly reduced temperature program was obtained. The accuracies of the measurements of Cd and Pb in the Seronorm urine materials were in good agreement with the recommended values: 4.1 ± 0.1 µg L−1 of Cd (recommended 5) and 92 ± 1 µg L−1 of Pb (recommended 85). The lifetime of the THFA for Pb determination was longer than 700 firings, with the sensitivity loss not more than 25% after 500 firings.

Transverse heated filter atomizer: atomic absorption spectrometric determination of Pb and Cd in whole blood

A transverse heated filter atomizer (THFA) was applied to the direct determination of Cd and Pb in blood, and its analytical performances were investigated using a Perkin Elmer SIMAA 6000 atomic absorption spectrometer. Seronorm human blood reference materials (RM) and samples of bovine whole blood spiked with Pb were used for the method validation. The blood samples diluted 5 or 10 times with water to reduce their viscosity were injected in the THFA at temperature about 110–120 °C together with blank or analyte solution in 0.2% HNO3. Compared to the transverse heated graphite atomizer with a platform (THGA), the THFA provided significant reduction of non-specific background absorption and more than 90% recovery of Cd and Pb, without the use of chemical modifiers. The ‘hot’ sampling and injection of ethanol together with the blood solution improved repeatability of analytical signals. Periodical cleaning at elevated temperature after each 15–20 measurements prevented building up of solid residues in the THFA cavity. Limits of detection achieved for Cd and Pb were 0.05 and 1 µg L−1, respectively.

MINIATURIZED METHOD BASED ON MATRIX SOLID-PHASE DISPERSION FOR THE RAPID SCREENING OF 36 PESTICIDES IN AGRICULTURAL FOOD COMMODITIES

Matrix solid-phase dispersion and gas chromatography-mass spectrometry were used for the rapid screening of 36 pesticides in agricultural products. Homogenized sample (0.5 g), C8-modified silica (0.5 g) and Na2SO4 (1 g) were mixed and transferred to a cartridge containing activated silica (0.5 g). Best recoveries (>60%) were found using dichloromethane-ethyl acetate (4:1) for elution. Analytical characteristics at spiking levels (10–100 μg/kg) were calculated for each pesticide. Matrix effects were studied by comparing the slopes of the matrix-matched calibration curves. Fruit and vegetable samples from South Africa complied with EU and South African current regulation, except for cypermethrin in green beans.

The influence of filter tube dimensions on the determination of arsenic with a transversely heated filter atomizer and atomic absorption spectrometry

The performance of a transversely heated filter atomizer (THFA) for the determination of inorganic arsenic (As) compounds was studied. The gain in sensitivity with the THFA was influenced by the length and internal diameter of the inserted filter in correspondence with theory. The accuracy of determination was evaluated by analysis of several Certified Reference Materials (CRMs), with good agreement between determined and certified values.