Determination Of Ultratrace Cadmium Research Articles

Ultra-trace determination of cadmium in water and food samples by a thin-film microextraction using a supported liquid membrane combined with smartphone-based colorimetric detection.

A mixture of n-octanol and dithizone was introduced as an effective and novel extraction agent in a thin-film microextraction technique for the pre-concentration of cadmium ions. The extraction agent was immobilized on small pieces of porous polypropylene flat membrane as a supported liquid membrane. The analyte extraction was performed by immersing the modified film in the sample solution, and via a complex formation between the immobilized dithizone on the film and cadmium ions. After the thin-film microextraction process, the colored cadmium-dithizone complex was directly measured by a smartphone colorimetric analysis. Under optimized conditions, the linear dynamic range, the limit of detection, and the limit of quantification were 0.5-300.0, 0.1, and 0.4μg L-1, respectively. The developed technique was successfully employed to quantify cadmium ions in water and food samples. The high relative recovery values (95.0-103.0%) along with relative standard deviations of less than 2.5% were obtained for the spiked samples.

Multianalyte voltammetric determination of traffic-linked metals in marine organisms employed as pollution bio-monitors

ABSTRACT A new procedure is proposed for the voltammetric determination of ultra-trace cadmium(II), copper(II), lead(II), platinum(II), palladium(II), rhodium(III) and zinc(II) by a single run of square wave adsorptive catalytic stripping voltammetry. The voltammetric cell was based on a typical three-electrodes set-up: working electrode (stationary hanging mercury drop), reference electrode (Ag|AgCl|KClsat) and auxiliary electrode (platinum). The supporting electrolyte contained the formazone complex together with dimethylglyoxime and the disodium salt of ethylenediaminetetraacetic acid. Validation of the analytical procedure was obtained by the analysis of standard reference materials (Mussel Tissue BCR-CRM 278, Oyster Tissue NIST-SRM 1566a). Comparison with spectroscopic measurements was performed. Good accuracy was achieved. The analytical procedure was finally applied to mussels and clams sampled on the mouth of Po river, employed as bio-monitors.

Ion Imprinted Polymer for Preconcentration and Determination of Ultra-Trace Cadmium, Employing Flow Injection Analysis with Thermo Spray Flame Furnace Atomic Absorption Spectrometry.

This work proposes a preconcentration method using an ion imprinted polymer (IIP) for determination of cadmium, in several samples, employing a mini-column filled with the polymer coupled into a flow injection analysis system with detection by thermospray flame furnace atomic absorption spectrometry (FIA-TS-FF-AAS). The polymer was synthesized via bulk using methacrylic acid and vinylimidazole as a functional monomer. For the FIA system initial assessment, the variables: pH, eluent concentration and buffer concentration were studied, employing a 23 full factorial design. To obtain the optimum values for each significant variable, a Doehlert matrix was employed. After the optimization conditions as: pH 5.8, eluent (HNO3) concentration of 0.48 mol L-1 and buffer concentration of 0.01 mol L-1, were adopted. The proposed method showed a linear response in the range of 0.081-10.0 μg L-1, limits detection and quantification of 0.024 and 0.081 μg L-1, respectively; preconcentration factor of 165, consumptive index of 0.06 mL, concentration efficiency 132 min-1, and frequency of readings equal to 26 readings h-1 The accuracy was checked by analysis of certified reference materials for trace metals and recovery tests. The obtained results were in agreement with 95% confidence level (t-test). The method was adequate to apply in samples of: jewelry (earrings) (2.38 ± 0.28 μg kg-1), black tea (1.09 ± 0.15 μg kg-1), green tea (3.85 ± 0.13 μg kg-1), cigarette tobacco (38.27 ± 0.22 μg kg-1), and hair (0.35 ± 0.02 μg kg-1).

Combination of knotted reactor with portable tungsten coil electrothermal atomic absorption spectrometer for on-line determination of trace cadmium

In this work, flow injection (FI) on-line precipitation–dissolution in a knotted reactor (KR) was established and combined with a portable tungsten coil electrothermal atomic absorption spectrometer (W-coil ET-AAS) firstly for preconcentration and determination of ultra-trace cadmium. As a new instrument, the application of the portable W-coil spectrometer was expanded to carry out on-line preconcentration and detection through the coupling with a KR system. A self-assembled FI system was employed to hyphenate the KR system with W-coil ET-AAS. The instrumental conditions and influencing factors relevant to KR efficiency, such as concentration of ammonia, pH, conditions of sampling and elution were studied systematically. The coupling improved the analytical performance of the portable spectrometer considerably. Under the optimal conditions, the limit of detection (LOD) for cadmium was 0.006μg/L, with sensitivity enhancement factor (EF) of 41. The established method could be expanded and used for on-line preconcentration and detection of some other trace metal ions.

Direct Determination of Ultratrace Cadmium in Spinach by Electrothermal Vaporization Atomic Fluorescence Spectrometry Using On-line Atom Trap of Tungsten Coil

A novel solid sampling method of detecting cadmium in spinach by electrothermal vaporization atomic fluorescence spectrometer(SS-ETV-AFS) was established,which made use of a tungsten-coil as a Cd trap at room temperature to remove matrix interferences and foam graphite as a electrothermal vaporizer and a sample boat.In our wok,it was proven that the foam graphite vaporizer had a stable performance and different sample boats had no difference for testing;there was good homogeneity and representativeness for fresh spinach sample grinded with liquid nitrogen,16.3mg was calculated by the Pauwels equation as the minimum sample mass which satisfied microsampling of SS-ETV-AFS.After optimization,the ashing(50 W for 50 s then 70 W for 80 s) and evaporating(70 W for 30 s) procedures were separated,and 600 mL/min Ar/H2(9∶1,V/V) was chosen as the carrier gas.Under the optimized conditions,the limit of detection was 0.2 μg/kg;the recovery was 90.1%-106.1%,the relative standard deviation was less than 10%,and the analysis time was within 5 min.There was no interference from the other elements and organic matrix,and there was no significant difference(p0.05) between the methods of SS-ETV-AFS and microwave digestion graphite furnace atomic absorption spectrometer.

Determination of ultratrace cadmium in food and environmental samples by ETAAS after vapor generation and in situ preconcentration

A method is described for the determination of ultratrace cadmium by coupling a continuous flow vapor generation system with in situ preconcentration technique and electrothermal atomic absorption spectrometry (ETAAS). A graphite tube coated with Ir as permanent chemical modifier was used for trapping cadmium vapor species. The effects of the flow rates of carrier gas and sample injection in vapor generation systems on the trapping measurement for cadmium were respectively investigated. Graphite tubes with different characteristic surfaces were comparatively studied for trapping cadmium vapor. The experimental results showed that the permanent chemical modifier of Ir is an alternative to the thermolabile modifier of Pd for simplifying the trapping measurement. The trapping efficiency of cadmium on the graphite tube coated with Ir was estimated. The trapping temperature and time were also investigated. A detection limit (3σ) of 0.005 μg·L−1 was obtained for this proposed method. The relative standard deviation (RSD) was 1.4% for 0.5 μ·L−1 of Cd (n = 11). This method can be applied to the determination of ultratrace cadmium in food and environmental samples with good agreement between the certified and found values.

Liquid phase microextraction and ultratrace determination of cadmium by modified graphite furnace atomic absorption spectrometry

A powerful microextraction technique was used for determination of cadmium in water samples using liquid phase microextraction (LPME) followed by graphite furnace atomic absorption spectrometry (GF-AAS). In a preconcentration step, cadmium was extracted from a 2 ml of its aqueous sample in the pH 7 as 5,7-dibromoquinoline-8-ol (DBQ) complex into a 4 μl drop of benzyl alcohol. After extraction, the micro drop was retracted and directly transferred into a graphite tube modified by [W.Rh.Pd](c). Some effective parameters on extraction and complex formation, such as type and volume of organic solvent, pH, concentration of chelating agent, extraction time and stirring rate were optimized. Under the optimum conditions, the enrichment factor and recovery were 450% and 90%, respectively. The calibration graph was linear in the range of 0.008–1 μg L −1 with correlation coefficient of 0.9961 under the optimum conditions of the recommended procedure. The detection limit based on the 3Sb criterion was 0.0035 μg L −1 and relative standard deviation (RSD) for eight replicate measurement of 0.1 μg L −1 and 0.4 μg L −1 cadmium was 5.2% and 4.5%, respectively. The characteristic concentration was 0.0032 μg L −1 equivalent to a characteristic mass of 12.8 fg. In order to evaluate the accuracy and recovery of the presented method the procedure was applied to the analysis of reference materials and seawater.

Dispersive liquid–liquid microextraction combined with graphite furnace atomic absorption spectrometry: Ultra trace determination of cadmium in water samples

Dispersive liquid–liquid microextraction (DLLME) technique was successfully used as a sample preparation method for graphite furnace atomic absorption spectrometry (GF AAS). In this extraction method, 500 μL methanol (disperser solvent) containing 34 μL carbon tetrachloride (extraction solvent) and 0.00010 g ammonium pyrrolidine dithiocarbamate (chelating agent) was rapidly injected by syringe into the water sample containing cadmium ions (interest analyte). Thereby, a cloudy solution formed. The cloudy state resulted from the formation of fine droplets of carbon tetrachloride, which have been dispersed, in bulk aqueous sample. At this stage, cadmium reacts with ammonium pyrrolidine dithiocarbamate, and therefore, hydrophobic complex forms which is extracted into the fine droplets of carbon tetrachloride. After centrifugation (2 min at 5000 rpm), these droplets were sedimented at the bottom of the conical test tube (25 ± 1 μL). Then a 20 μL of sedimented phase containing enriched analyte was determined by GF AAS. Some effective parameters on extraction and complex formation, such as extraction and disperser solvent type and their volume, extraction time, salt effect, pH and concentration of the chelating agent have been optimized. Under the optimum conditions, the enrichment factor 125 was obtained from only 5.00 mL of water sample. The calibration graph was linear in the rage of 2–20 ng L −1 with detection limit of 0.6 ng L −1. The relative standard deviation (R.S.D.s) for ten replicate measurements of 20 ng L −1 of cadmium was 3.5%. The relative recoveries of cadmium in tap, sea and rivers water samples at spiking level of 5 and 10 ng L −1 are 108, 95, 87 and 98%, respectively. The characteristics of the proposed method have been compared with cloud point extraction (CPE), on-line liquid–liquid extraction, single drop microextraction (SDME), on-line solid phase extraction (SPE) and co-precipitation based on bibliographic data. Therefore, DLLME combined with GF AAS is a very simple, rapid and sensitive method, which requires low volume of sample (5.00 mL).

Ultratrace determination of cadmium by atomic absorption spectrometry using hydride generation with in situ preconcentration in a palladium-coated graphite atomizer

A very sensitive ETAAS method, with in situ trapping of the metal, is described for ultratrace determinations of Cd in liquid solutions. It is based on volatile Cd HG from a vesicular solution with subsequent trapping of the metal in a graphite platform coated with Pd. This Pd coating, on a pyrolytic graphite L'vov platform, acts as the atomizer. Sodium tetrahydroborate (III) in a vesicular medium of didodecyldimethylammonium bromide is used to generate Cd hydride from the sample solution. This volatile species is trapped by the Pd coating, pre-heated at 150 °C, the preconcentrated Cd then atomized at 1600 °C and the transient AAS signal measured. Detection limits (DL) observed are in the ng l–1 range (e.g., using a 1.4 ml Cd sample volume for preconcentration the DL was 60 ng l–1). Higher preconcentrations up to a maximum of 1.4 ng of total Cd deposited are possible with the proposed methodology. The RSD for ten replicate analyses of 1.4 ml of 500 ng l–1 Cd solution (0.7 ng of total Cd) was 1.7%. The combination of vesicles-mediated HG with the ease of decomposition of Cd hydride on the Pd coating at 150 °C, provides a convenient Cd preconcentration method for enhancing the sensitivity of direct determinations of Cd by conventional ETAAS or by HGAAS.

Direct ultratrace determination of cadmium in antarctic and Greenland snow and ice by laser atomic fluorescence spectrometry

Direct ultratrace determination of cadmium in antarctic and Greenland snow and ice by laser atomic fluorescence spectrometry

Fluorimetric use of morin in the ultra-trace determination of cadmium and its application to sewage sludge analyses.

A sensitive and fairly selective direct spectrofluorimetric method for the ultra-trace determination of cadmium with morin has been developed. The fluorescent chelate [λex.(max.)= 467 nm; λem.(max.)= 537 nm] shows a constant fluorescence intensity over a wide pH range (8.0–9.4). The reaction is instantaneous and the fluorescence intensity remains stable for 45 min. Beer's law is obeyed from 0.5 p.p.b. to 0.8 p.p.m. of cadmium; the stoicheiometric composition of the chelate is 1 : 2 (cadmium : morin). The method has been applied successfully to a number of synthetic mixtures of various composition and to some sewage sludge samples after a short, single clean-up step using an ion exchanger.

Determination of ultratrace cadmium by laser-induced photoacoustic absorption spectrometry

Determination of ultratrace cadmium by laser-induced photoacoustic absorption spectrometry