Preconcentration System For Cadmium Determination Research Articles

Application of modified simplex on the development of a preconcentration system for cadmium determination in sediments, food and cigarettes.

A modified simplex algorithm was used to optimize a system of preconcentration for cadmium determination in samples of sediments, cigarettes and food using flame atomic absorption spectrometry. The preconcentration system is based on the sorption of cadmium in a minicolumn packed with Amberlite XAD-2 resin functionalized with 3,4-dihydroxybenzoic acid (DHB). The optimized variables were pH and sampling flow rate and the optimum conditions found for these variables were, respectively 8.7 and 8.8 mL min-1. The developed system showed a preconcentration factor of 15.3, detection limit of 0.49 µg L-1, quantification limit of 1.65 µg L-1 and precision expressed as relative standard deviation (% RSD, n=10) of 5.9. The accuracy of the method was checked by analysis of estuary sediment certified reference material (NIST 1646-1). The cadmium concentrations found in sediment samples ranged from 1.73 and 1.90 µg g-1. In cigarette samples the results were 0.085 and 0.193 µg g-1, and in food samples (coriander and lettuce) the concentrations found of this metal were, respectively, 0.33 and 0.12 µg g-1.

Development and optimization of analytical method for the determination of cadmium from mineral water samples by off-line solid phase extraction system using sisal fiber loaded TAR by FAAS

In the present work, a minicolumn of sisal fiber loaded with tiazolylazo-Resorsinol (TAR) is proposed a preconcentration system for cadmium determination in drinking water samples by flame atomic absorption spectrometry. In the optimization was first of all a full factorial design of two levels (24) was used for preliminary evaluation of four factors, involving the variables: sampling flow rate, elution flow rate, buffer concentration and pH. This design has showed that, for the studied levels, buffer concentration and pH are significant factors. Using the established experimental conditions in the optimization step of: pH 7.0, buffer concentration of 0.009mol L−1 for elution utilized HCl at 2.0mol L−1, this system allows the determination of cadmium with a detection limit (LD) (3σ/S) of 0.05μg L−1 and a quantification limit (LQ) (10σ/S) of 0.17μg L−1, precision expressed as a relative standard deviation (R.S.D.) of 2.9 and 3.4% for a cadmium concentration of 10.0 and 20.0μg L−1, respectively, and a preconcentration factor of 30 for a sample volume of 50.0mL. The accuracy was confirmed by cadmium with spike tests with recuperations varying from 92% to 103%, procedure was applied for cadmium determination in drinking water samples collected from Salvador City, Bahia, Brazil. From the five samples analyzed, the achieved concentrations varied from 0.10 to 0.54μgL−1.

Unmodified Multi-Walled Carbon Nanotubes as Sorbent Material in Flow Injection on-Line Sorbent Extraction Preconcentration System for Cadmium Determination by Flame Atomic Absorption Spectrometry

Unmodified multi-walled carbon nanotubes (MWCNTs) were demonstrated as hydrophobic sorbent material for flow injection on-line microcolumn preconcentration coupled with flame atomic absorption spectrometry for cadmium determination in natural water samples. The method was based on on-line chelate complex formation between the analyte with sodium diethyldithiocarbamate and retention onto the surface of MWCNTs. Quantitative elution of the analyte was achieved with methanol which was whereupon delivered to the FAAS nebulizer for atomization and measurement. The microcolumn was packed with a mixture of MWCNTs and silica beads in order to minimize the generated back-pressure in the flow system which arises from the nano dimensions of MWCNTs. All factors affecting the performance of the proposed method were studied thoroughly. For a 180 s preconcentration time the enhancement factor was 54, the detection limit (3s) was 0.24 µg L−1, and the precision as relative standard deviation at a 5.0 µg L−1 Cd(II) concentration level was 3.2%. The method was applied to the analysis of environmental water samples and the accuracy evaluated via certified reference material and recovery experiments.

An on-line pre-concentration system for determination of cadmium in drinking water using FAAS

In the present paper, a minicolumn of polyurethane foam loaded with 4-(2-pyridylazo)-resorcinol (PAR) is proposed as pre-concentration system for cadmium determination in drinking water samples by flame atomic absorption spectrometry. The optimization step was performed using two-level full factorial design and Doehlert matrix, involving the variables: sampling flow rate, elution concentration, buffer concentration and pH. Using the established experimental conditions in the optimization step of: pH 8.2, sampling flow rate 8.5 mL min −1, buffer concentration 0.05 mol L −1 and elution concentration of 1.0 mol L −1, this system allows the determination of cadmium with detection limit (LD) (3σ/S) of 20.0 ng L −1 and quantification limit (LQ) (10σ/S) of 64 ng L −1, precision expressed as relative standard deviation (R.S.D.) of 5.0 and 4.7% for cadmium concentration of 5.0 and 40.0 μg L −1, respectively, and a pre-concentration factor of 158 for a sample volume of 20.0 mL. The accuracy was confirmed by cadmium determination in the standard reference material, NIST SRM 1643d trace elements in natural water. This procedure was applied for cadmium determination in drinking water samples collected from Salvador City, Bahia, Brazil. For five samples analyzed, the achieved concentrations varied from 0.31 to 0.86 μg L −1.

Application of Box–Behnken design in the optimisation of an on-line pre-concentration system using knotted reactor for cadmium determination by flame atomic absorption spectrometry

The present paper proposes an on-line pre-concentration system for cadmium determination in drinking water using flame atomic absorption spectrometry (FAAS). Cadmium(II) ions are retained as 1-(2-pyridylazo)-2-naphthol (PAN) complex at the walls of a knotted reactor, followed of elution using hydrochloric acid solution. The optimization was performed in two steps using factorial design for preliminary evaluation and a Box–Behnken design for determination of the critical experimental conditions. The variables involved were: sampling flow-rate, reagent concentration, pH and buffer concentration, and as response the analytical signal (absorbance). The validation process was performed considering the parameters: linearity and other characteristics of the calibration curve, analytical features of on-line pre-concentration system, precision, effect of other ions in the pre-concentration system and accuracy. Using the optimized experimental conditions, the procedure allows cadmium determination with a detection limit (3 σ / S) of 0.10 μg L − 1 , a quantification limit (10 σ / S) of 0.33 μg L −1, and a precision, calculated as relative standard deviation (RSD) of 2.7% ( n = 7) and 2.4% ( n = 7) for cadmium concentrations of 5 and 25 μg L − 1 , respectively. A pre-concentration factor of 18 and a sampling frequency of 48 h −1 were obtained. The recovery for cadmium in the presence of several ions demonstrated that this procedure could be applied for the analysis of water samples. The method was applied for cadmium determination in drinking water samples collected in Salvador City, Brazil. The cadmium concentrations found in five samples were lower than the maximum permissible levels established by the World Health Organization.

Design of a field flow preconcentration system for cadmium determination in seawater by flow-injection-atomic absorption spectrometry

A field flow preconcentration system (FFPS) for cadmium determination in seawater is described. Seawater samples are collected and preconcentrated in situ by passing them with a peristaltic pump through a minicolumn packed with Amberlite XAD-4 impregnated with the complexing agent 1-(2-pyridylazo)-2-naphthol. Thus, cadmium is complexed, retained, and preconcentrated without the interference of the saline matrix. Minicolumns loaded with cadmium are then returned to the laboratory where they are incorporated into a flow injection system and eluted with a small volume of an ethanolic solution of hydrochloric acid into the nebuliser–burner system of a flame atomic absorption spectrometer. The optimization of FFPS design is presented, and the stability and characteristics of the Cd-loaded minicolumns are studied in detail. The detection limit for Cd in seawater based on an enrichment factor of 1059 was 3.8 ng l −1. The precision (R.S.D.) obtained for different amounts of cadmium was in the range 4.1–6.5% at the 25–100 ng l −1 level. Analysis of certified reference materials (SLEW-3 and NASS-5) showed good agreement with the certified value. This procedure was applied to the determination of cadmium in seawater samples from Galicia (Spain).