Determination Of Lead In Samples Research Articles

A Method Using Liquid-Liquid Microextraction in a Dynamic System for Preconcentration and Determination of Lead in Food Samples

In this paper, a method using liquid-liquid microextraction in a dynamic system combined with spectrophotometry was developed for preconcentration and determination of lead in samples of shrimp and oyster. In the procedure, a system is proposed in which the organic drop is maintained at the bottom of a glass tube, with the passage of a stream of aqueous solution, avoiding the use of a microsyringe. The method is based on the transfer of metal species present in the aqueous phase in the form of complexes with the ligand 2-(5-bromo-2-pyridylazo)-5-dimethylaminophenol (5-Br-PADAP) to the organic phase trichloroethylene. Experimental conditions, such as sample flow rate, concentration of the complexing reagent, extraction solvent, time of extraction, and pH, were optimized. Under optimized conditions, the limit of detection and quantification obtained were 0.48 and 1.60 μg L−1, respectively. The accuracy was evaluated by the determination of lead in the certified reference material BCR-414, Plankton. The procedure was applied to the determination of lead in samples of shellfish, with recoveries ranging from 92 to 103 %. The method enabled a fast, accurate, and simple alternative for the determination of lead in seafood samples.

The quality control of preanalytical variations for the determination of lead in samples of human origin

The aims of this article was to provide the quality control requirements of preanalytical variation for the determination of lead in samples of human origin, reduce the influence of preanalytical variation on the test results. According to the Clinical and Laboratory Standards Institute documents, control of preanalytical variation in trace element determinations, analytical procedures for the determination of lead in blood and urine and other references and guidelines, the methods of quality control of lead determination had been made, including: the factors needed to be considered before collection, preservation, transportation and other preanalytical factors, the abilities and considerations of laboratory staff, etc.

Determination of lead in samples of zooplankton, water, and sediments in a Mexican reservoir: Evidence for lead biomagnification in lower/intermediate trophic levels?

We have determined lead concentration of water, sediment, and zooplankton samples of El Niágara, a reservoir in Aguascalientes, Mexico. Our results include the first report of bioconcentration factor (BCF) obtained in an actual ecosystem (as opposed to the experimental setups in the laboratory) for a rotifer species; Asplanchna brigthwellii (BCF ca. 49 300). The BCF of this predatory zooplanktonic species (A. brigthwellii) are up to four times greater than those of two grazing zooplanktonic species (Daphnia similis and Moina micrura). In this contaminated reservoir that lacks fishes, Asplanchna, and Culex sp. together with ducks and other bigger invertebrates might represent the top predators. Our data suggest that biomagnification of lead through at least one trophic level can occur in freshwater systems. Biomagnification in A. brigthwellii might be explained in part by predation of this voracious predator on young of the herbivorous cladoceran, M. micrura. Our findings stand opposite to the current theoretical framework where lead biomagnification occurs only in lower trophic levels.

Determination of Lead and Cadmium at Silver Electrode by Subtractive Anodic Stripping Voltammetry in Plant Materials Containing Tl

Lead and cadmium have been determined by the subtractive anodic stripping voltammetry using the square-wave mode at a silver electrode without removal of oxygen. The samples containing large amount of thallium were collected from a highly contaminated region. The presence of thallium strongly affects the peak shape of Cd. The plant material digestion was performed with HNO3/HClO4 mixture using pressurised microwave decomposition. The proposed method used for the lead determination was validated by the inter-method comparison (ICP-MS). The cadmium determination was validated using certified reference material. The results obtained, supported by statistical tests, demonstrated the usefulness of the method for the lead determination in samples containing large amounts of Cd and Tl. It is important to note that Cd can only be quantified when the thallium concentration is much lower than that of cadmium.

Literature survey of on-line spectroscopic methods for lead determination in environmental solid samples.

A review is presented where are shown the advantages involved in the use of flow injection (FI) analysis for the determination of lead in environmental solid samples by spectroscopic detectors. The FI methods proposed for the determination of lead in these samples are described and compared according to the detection technique used. Analytical data of interest and interferences are discussed for each technique.

Electrochemical and quartz crystal microbalance studies of lead(II) deposition and stripping in the presence of copper on a gold electrode modified with 2,2′-bipyridyl in polyaniline

Electrochemical and quartz crystal microbalance (QCM) measurements were used to determine the mechanisms of anodic stripping voltammetry (ASV) processes during lead determination in samples containing copper on a solid electrode modified by 2,2′-bipyridyl (Bpy) in polyaniline (PANI). Deposition of lead and copper results in the formation of solid solutions, which may change the results. An improvement of lead determination was achieved by the formation of stable copper complexes with Bpy. The molecules of Bpy were immobilized on a solid electrode in a PANI film. Deposition and stripping of lead and lead with copper were compared on three different electrodes: gold, gold coated with PANI and gold coated with PANI modified by Bpy. The results were used to propose mechanisms of deposition and stripping processes as well as a practical procedure of using this kind of electrode.

On-line preconcentration system for lead determination in seafood samples by flame atomic absorption spectrometry using polyurethane foam loaded with 2-(2-benzothiazolylazo)-2- p-cresol

In the present paper, an on-line system for enrichment and determination of lead is proposed. It is based on the chemical sorption of lead(II) ions on a minicolumn packed with polyurethane foam loaded with 2-(2-benzothiazolylazo)-2- p-cresol (BTAC) reagent. After preconcentration, lead(II) ions are eluted by 0.10 mol l −1 hydrochloric acid solution and determined directly by flame atomic absorption spectrometry (FAAS). Chemical and flow variables as well as effect of other ions were studied. The results demonstrated that lead could be determinate with an enrichment factor of 26 for a sample volume of 7.0 ml and preconcentration time of 1 min. The detection limit (3 s) was 1.0 μg l −1 and the precision (assessed as the relative standard deviation) reached values of 6.0–0.7% in lead solutions of 10–500 μg l −1 concentration, respectively. The enrichment factor and the detection limit can be further improved by increasing preconcentration time without degradation in the efficiency due to the favorable kinetics and low hydrodynamic impedance of the present system. Achieved sampling frequency was 48 samples per hour. The effect of another ions in concentrations agreeing with biological samples was studied. It was found that the proposed procedure has necessary selectivity for lead determination in seafood and other biological samples. The accuracy was confirmed by analysis of the followings certified reference materials: fish tissue IAEA, lobster hepatopancreas NRCC TORT-1 and citrus leaves NIST 1572. Recoveries of spike additions (0.2 or 1.0 μg g −1) to several seafood samples were quantitative (90–107%). These results proved also that the procedure is not affected by matrix interferences and can be applied satisfactorily for lead determination in samples of shrimp, oyster, crab, fish and mussel contaminated by it.

Rapid determination of lead by analysis of solid samples using graphite furnace atomic absorption spectrometry

Lead was determined in the range of 0.1–1% m/m in poly(vinyl chloride)(PVC) samples by a simple and rapid method of direct analysis of the solid using electrothermal atomic absorption spectrometry. The selected analytical conditions permitted the determination of lead in samples of PVC by interpolation of the corresponding calibration graphs obtained in aqueous solution. No special sample introduction system, platform, background-noise correction or modification of the matrix was necessary. The determination of lead in several PVC samples is described for concentrations of between 0.2 and 1% with relative standard deviations of between 5 and 10%.

Determination of cadmium, lead and copper in milk and milk powder by means of flow potentiometric stripping analysis

A flow potentiometric stripping analysis procedure for the determination of cadmium, lead and copper in milk and milk powder samples is described. The instrumental arrangement consists of a glassy-carbon thin-layer cell through which six different solutions may be drawn by means of a peristaltic pump and magnetically operated valves. The glassy-carbon electrode is pre-coated with a film of mercury which can be employed for several analytical runs. The sample, diluted five-fold with Suprapur hydrochloric acid, is electrolysed for 0.5–4 min prior to stripping in Suprapur hydrochloric acid. Pump-rate, electrolysis time and potential, opening and closing of inlet valves and digital evaluation of stripping times are controlled automatically by the computer. The analytical results agree satisfactorily with the certified values for three milk powder reference samples. The detection limit for cadmium, lead and copper in milk samples after 4, 1 and 0.5 min of pre-electrolysis is 0.8, 4 and 8 μg l. , respectively. An analytical procedure for the determination of lead in samples containing high concentrations of tin is described.