Determination Of Cadmium In Seawater Research Articles

Determination of cadmium in seawater by chelate vapor generation atomic fluorescence spectrometry

A method for the determination of cadmium in seawater by chelate vapor generation (Che-VG) atomic fluorescence spectrometry is described. Several commercially available chelating agents, including ammonium pyrrolidine dithiocarbamate (APDC), sodium dimethyl dithiocarbamate (DMDTC), ammonium dibutyl dithiophosphate (DBDTP) and sodium O,O-diethyl dithiophosphate (DEDTP), are compared with sodium diethyldithiocarbamate (DDTC) for the Che-VG of cadmium, and results showed that DDTC and DEDTP had very good cadmium signal intensity. The effect of the conditions of Che-VG with DDTC on the intensity of cadmium signal was investigated. Under the optimal conditions, 85±3% Che-VG efficiency is obtained for cadmium. The detection limit (3σ) obtained in the optimal conditions was 0.19ngml−1. The relative standard deviation (RSD, %) for ten replicate determinations at 2ngml−1 Cd was 3.42%. The proposed method was successfully applied to the ultratrace determination of cadmium in seawater samples by the standard addition method.

Direct Determination of Cadmium in Seawater by Standard Addition ICP-QMS/QMS with an ORC.

A method for direct and precise determination of Cd in seawater by ICP-QMS/QMS was developed, where a high matrix introducing unit permitted the direct introduction of seawater without clogging the cones while the matrix effect of seawater was canceled by standard addition. NH3 gas was selected as the reaction gas for removing the MoO interferences with the measurement of Cd isotopes, effectively improving the signal to background ratio. The lower limit of detection obtained at 114Cd was 0.0002 ng mL-1, which is enough for the determination of Cd in natural seawater. The validity of the present method was confirmed by the analysis of two certified reference materials, i.e. NASS-5 and NASS-6, whose observed values of Cd concentration agreed with the certified values. The analytical figures of merit of the present method were comparable to or better than those reported for direct analysis of seawater.

Determination of Cadmium in Seawater by Vapor Generation Atomic Fluorescence Spectrometry After Online Preconcentration with a Novel Alkyl Phosphinic Acid Resin

Vapor generation atomic fluorescence spectrometry (VG‐AFS) coupled with online preconcentration on a short column (4.6 mm×50‐mm length) packed with a newly synthesized alkyl phosphinic acid resin (APAR) was developed for the determination of trace Cd in seawater. During the online preconcentration process, Cd in seawater was concentrated on the column while the matrix of seawater was separated flowing out of the column. Cd concentrated on the column was then eluted effectively from the column with 0.1 mol L−1 tartaric acid within 40 s. When the sample volume was 200 mL, an enrichment factor 189 was achieved. The detection limit of this proposed method for Cd is 2.67 ng L−1. The recovery of Cd is 96.6% obtained by spiking the correspondence standard, and the precision (RSD) is 4.34% (n=6). The established APAR/VG‐AFS was applied to the determination of soluble Cd in the seawater around Xiamen Island, China.

Ultrasensitive determination of cadmium in seawater by hollow fiber supported liquid membrane extraction coupled with graphite furnace atomic absorption spectrometry

A new procedure, based on hollow fiber supported liquid membrane preconcentration coupled with graphite furnace atomic absorption spectrometry (GFAAS) detection, was developed for the determination of trace Cd in seawater samples. With 1-octanol that contained a mixture of dithizone (carrier) and oleic acid immobilized in the pores of the polypropylene hollow fiber as a liquid membrane, Cd was selectively extracted from water samples into 0.05 M HNO 3 that filled the lumen of the hollow fiber as a stripping solution. The main extraction related parameters were optimized, and the effects of salinity and some coexisting interferants were also evaluated. Under the optimum extraction conditions, an enrichment factor of 387 was obtained for a 100-mL sample solution. In combination with graphite furnace atomic absorption spectrometry, a very low detection limit (0.8 ng L − 1 ) and a relative standard deviation (2.5% at 50 ng L − 1 level) were achieved. Five seawater samples were analyzed by the proposed method without dilution, with detected Cd concentration in the range of 56.4–264.8 ng L − 1 and the relative spiked recoveries over 89%. For comparison, these samples were also analyzed by the Inductively Coupled Plasma Mass Spectrometry (ICP-MS) method after a 10-fold dilution for matrix effect elimination. Statistical analysis with a one-way ANOVA shows no significant differences (at 0.05 level) between the results obtained by the proposed and ICP-MS methods. Additionally, analysis of certified reference materials (GBW (E) 080040) shows good agreement with the certified value. These results indicate that this present method is very sensitive and reliable, and can effectively eliminate complex matrix interferences in seawater samples.

Application of liquid membranes to sample preconcentration for the spectrometric determination of cadmium in seawater

A bulk liquid membrane system has been used as preconcentration tool for the spectrometric determination of cadmium in seawater. The membrane contained di-(2-ethylhexyl)-phosphoric acid (DEHPA) as mobile carrier dissolved in kerosene. The effects of the composition of both organic and aqueous solutions on the permeation of Cd across the membrane were studied, and optimum conditions were found by the modified simplex method. Maximum preconcentration rates were obtained at a sample pH of 4.7, maintained with a 0.1 mol l −1 acetate buffer solution, a 0.3 mol l −1 HNO 3 receiving solution, and a carrier concentration of 0.17 mol l −1. Under optimum conditions, a preconcentration yield of 100% was obtained for both synthetic and real seawater. The method was successfully applied to the determination of cadmium in real seawater.

Minicolumn field preconcentration and flow-injection flame atomic absorption spectrometric determination of cadmium in seawater

A simple method for the continuous field preconcentration of trace dissolved cadmium in seawater samples has been developed based on the minicolumn field sampling technique. For this purpose, minicolumns containing Chelite P (aminomethylphosphonic groups) were connected to a field flow preconcentration system (FFPS). Once in the laboratory, these minicolumns are sequentially inserted into a flow-injection system for on-line cadmium elution and detection by flame atomic absorption spectrometry. Factorial designs have been used to optimise the FFPS and the flow-injection elution process. Six experimental variables were optimised: sample pH, sample flow-rate, eluent concentration, eluent volume, eluent flow-rate and minicolumn diameter. The detection limit (3 F ) of the procedure was 2.7 ng l −1 for a sample volume of 300 ml. The precision (expressed as relative standard deviation) for 11 independent determinations was 0.5–9.4% for cadmium solutions of 10–300 ng l −1. Analysis of certified reference materials (SLEW-3 and NASS-5) showed good agreement with the certified values. This procedure has been successfully applied to the determination of cadmium in seawater samples from Galicia (Spain).

Experimental designs in the development of a new method for the sensitive determination of cadmium in seawater by adsorptive cathodic stripping voltammetry

A new differential pulse adsorptive cathodic stripping voltammetric (DPAdCSV) method for the direct determination of cadmium at subnanomolar levels in saline waters based on metal complexation with 2-acetylpyridine salicyloylhydrazone (APSH) and subsequent adsorptive deposition onto a hanging mercury drop electrode (HMDE) is presented. A study strategy based on experimental designs has been followed. Operating conditions were improved with exploratory (Plackett–Burman) and surface response (central composite) experimental designs, involving several chemical and instrumental parameters (pH, ligand concentration, pulse amplitude, time interval for voltage step, voltage step, deposition potential and deposition time). Analytical parameters as repeatability, linearity and accuracy were also investigated and a detection limit (DL) of 0.06 nM was achieved which could be lowered by extending the adsorption time. The interference of other metals and major salts present in seawater was also studied. The method was validated with reference water samples: NIST-SRM 1643d and BCR-CRM 505, showing good concordance with the certified values.

Field preconcentration of cadmium from seawater by using a minicolumn packed with Amberlite XAD-4/4-(2-pyridylazo) resorcinol and its flow-injection-flame atomic absorption spectrometric determination at the ng L(-1) Level.

A flow injection analysis-flame atomic absorption spectrometric method for the determination of cadmium in seawater was developed with the aim of yielding a sensitive assay with a low detection limit. The method employs a field flow preconcentration technique involving a minicolumn containing Amberlite XAD-4 impregnated with the complexing agent 4-(2-pyridylazo) resorcinol. A Plackett-Burman 2(7)x3/32 design for seven factors (sample pH, sample flow rate, eluent volume, eluent concentration, eluent flow rate, ethanol percentage in the eluent and minicolumn diameter) was carried out in order to find the significant variables affecting the field continuous preconcentration system (FCPS) and the flow injection elution manifold for cadmium determination in seawater samples by flame atomic absorption spectrometry. Cadmium can be preconcentrated with an enrichment factor of 1053 for a sample volume of 200 mL and a preconcentration time of 57 min. In these experimental conditions, the method provides a linear relationship between absorbance and cadmium concentration in the range from 22-1900 ng L(-1), with a detection limit (3SD) of 6 ng L(-1). The precision (expressed as relative standard deviation) for eleven independent determinations reached values of 8.9-0.8% in cadmium solutions of 50-700 ng L(-1). 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 from Galicia (Spain).

Automatic on-line column preconcentration system for determination of cadmium by electrothermal atomic absorption spectrometry

An automatic separation–preconcentration system coupled to an electrothermal atomic absorption spectrometer is described. The preconcentration step is performed on a chelating resin microcolumn [silica gel functionalized with 1,5-bis(di-2-pyridyl)methylene thiocarbonohydrazide] placed in the autosampler arm. The combination of a peristaltic pump for sample loading and the atomic absorption spectrometer pumps for elution through a selection valve simplifies the hardware. The peristaltic pump and the selection valve are easily controlled electronically with two switches placed in the autosampler, which are activated when the autosampler arm is down. Thus, the process is fully automated without any modification of the software of the atomic absorption spectrometer. The system is applied to the determination of cadmium in sea-water. Validation is carried out against the certified reference materials BCR CRM 403 Sea-Water and BCR CRM 505 Estuarine Water, and by determining the analyte content in sea-water and synthetic sea-water. The results showed good agreement with the certified values and the recoveries of Cd added to water samples were 94–104%.

Determination by fluorescence spectroscopy of cadmium at the subnanomolar level: application to seawater

This paper reports the development of a molecular fluorescence spectroscopy-based approach for the determination of cadmium in seawater. Anthrylazamacrocycle derivatives—the fluorescence of which is enhanced when chelated to zinc or cadmium—are used as chemosensors. A detection limit of 5 nM has been found at pH 10 for both metals, and spectral shifts allow simultaneous Cd(II)/Zn(II) determination using multiwavelength analysis. While cadmium emission behavior is similar at pH 13, zinc is not detected anymore. This enables the selective detection of cadmium even at a high Zn(II)/Cd(II) ratio. The detection limit is 1 nM. Interferent removal and preconcentration have been developed using a Dowex resin, with a view to determine cadmium in seawater. A global procedure including interferent elimination, cadmium preconcentration (30 fold), and fluorescence detection at pH 13 has been evaluated on certified reference material SLEW-2.

Determination of cadmium in seawater using automated on-line preconcentration and direct injection graphite furnace atomic absorption spectrometry

An on-line preconcentration method for the determination of cadmium in seawater was developed for graphite furnace atomic absorption spectrometry (GFAAS) using deuterium lamp background correction. The technique was adapted from a previously reported technique and was fully automated. Automated preconcentration of cadmium reduced the concentrations of matrix elements in samples to levels that did not interfere with the determination of cadmium at ultratrace levels. The soluble ligand, 1-pyrrolidinecarbodithioic acid (APDC), was mixed with the sample in a continuous flow system to form a non-polar metal complex which was absorbed onto a C 18 column. The metal complex was then eluted from the column directly into the graphite furnace. The addition of an in-line nitric acid rinse step between sample load cycles allowed for the determination of cadmium with one elute cycle. Other modifications included laboratory purification of the ammonium acetate rinse solution, a non-buffered APDC ligand solution, and a computer-activated load cycle to reduce sample consumption. The average column recovery was 73% with a sample loading flow rate of 2.2 ml/min and 55 s preconcentration time. Sample throughput was approximately 15 samples/h with 2 ml of sample preconcentrated and analyzed every 4 min. The small sample volume required made this method useful where sample volumes are limited. The 3 σ limit of detection for replicate blanks was 42 pM Cd ( n=5) for a 2 ml sample. The effectiveness of the method was demonstrated for the determination of Cd in certified open ocean reference materials NASS-3 and NASS-4. Analysis of Cd in equatorial Pacific seawater demonstrated that the system produces oceanographically consistent results.

Use of 4-(2-pyridylazo)resocinol or 2-(2-pyridylazo)-5-dimethylaminophenol as chelating agent for determination of cadmium in seawater by atomic absorption spectrometry with on-line flow-injection sorbent extraction

A home-made automatic on-line flow-injection sorbent extraction system for graphite furnace atomic absorption spectrometry (GFAAS) was used to determine Cd in seawater using octadecyl functional group (C 18) bonded silica gel as sorbent, 4-(2-pyridylazo)resocinol (PAR) or 2-(2-pyridylazo)-5-dimethylaminophenol (PADMAP) as chelating agent and methanol as eluent. The range of pH for the determination of Cd in seawater was 4.7–7.4 and 7.1–9.0 for using PAR and PADMAP as chelating agents, respectively. For the long-term stability studies, the complexes (PAR–Cd or PADMAP–Cd) are stable within the pH range 4.7–7.4 (for PAR) or 7.1–9.0 (for PADMAP) for 1 h at least. Sample volume of only 500–1000 μl was required to determine Cd in seawater. The simple calibration curve method was used and the detection limits of the determination of Cd in seawater were 4.0 and 1.7 ng l −1 for PAR and PADMAP as chelating agents, respectively. The sample throughput is 9–12 h −1. The accuracy and precision of the method were confirmed by the analysis of three kinds of certified reference saline water.

Determination of Cadmium in Seawater by Cathodic Stripping Voltammetry of Complexes with 5-Fluorouracil

A reduction current is obtained when an aqueous solution of cadmium and 5-fluorouracil (5-FU) is subjected to linear sweep cathodic stripping voltammetry. This current is attributed to the reduction of cadmium-5-FU complex ions which adsorbed onto the hanging mercury drop electrode. The resulting peak current is characterized with respect to supporting electrolytes, pH, accumulation potential, scan rate, possible interferences and other variables. A linear relationship between the peak current and cadmium concentration was obtained over the range 5 × 10−9–1 × 10−7 mol dm−3 with correlation coefficient of 0.9973. A detection limit of 9.0 × 10−11 mol dm−3 was obtained with standard deviation of 1.9 %. The method was successffuly applied for the determination of cadmium in seawater.

Use of flow injection cold vapour generation and preconcentration on coated graphite tubes for the determination of cadmium in sea-water by electrothermal atomic absorption spectrometry

Methods have been developed for the trace determination of total and inorganic mercury in natural waters by cold vapour generation–trapping and atomization in a graphite furnace by selective reduction with NaBH 4 and SnCl 2 . Iridium, tungstate and zirconium coated graphite tubes were investigated for the preconcentration of the mercury vapour. The carrier solution was 0.4 m of HCl, and 0.2% NaBH 4 and 1.0% SnCl 2 were used as reducing solutions for total and inorganic mercury, respectively. Using iridium coated graphite tubes characteristic masses of 300 and 240 pg for total and inorganic mercury, respectively, and detection limits of 90 and 60 ng l -1 for total and inorganic mercury were obtained for a 1500 µl sample volume. The precision was between 0.7 and 2.1%. Accuracy of method was confirmed by the analysis of IAEA/W-4 fresh water reference material.

Direct determination of cadmium in sea-water with a graphite furnace atomic absorption spectrometer

Cadmium in sea-water was determined directly using a graphite furnace atomic absorption spectrometer, with a stabilized temperature platform furnace technique, and Zeeman effect background correction. A matrix modifier containing (NH 4) 2HPO 4 and HNO 3 was used. The detection limit was 0.012 μg l with injection of a 20 μl aliquot of sea-water sample. As the matrix interference was removed completely, a calibration curve using deionized water was used. The detection limit was further diminished to 0.005 solμg l using multiple injection (injection of three 20 μl aliquots of sea-water). However, standard addition should be used in conjunction with the latter technique.

Direct determination of cadmium in sea-water by electrothermal atomic absorption spectrometry with sodium hydroxide as a chemical modifier

The use of sodium hydroxide as a chemical modifier for the direct determination of trace amounts of cadmium in sea-water by electrothermal atomic absorption spectrometry is described. It permits a selected ashing temperature up to 1400 °C and markedly reduces the background signal caused by high sea-salt contents, while the ashing time is prolonged up to 100 s. Colloidal magnesium hydroxide precipitates were produced by the addition of NaOH modifier to sea-water, and trace amounts of cadmium were considered to be coprecipitated with magnesium hydroxide. The proposed method was used for the direct determination of cadmium in open ocean sea-water. The validity of the procedure was checked with two certified reference sea-waters (CASS-1 and CASS-2) and the results were found to be in good agreement with the certified values. A detection limit of 0.015 ng ml–1 was obtained for 80 µl injections.

Direct determination of cadmium in sea-water using electrothermal atomization atomic absorption spectrometry with Zeeman-effect background correction and oxalic acid as a chemical modifier

A method for the determination of cadmium in sea-water using an electrothermal atomization atomic absorption spectrometry system with Zeeman-effect background correction is presented. The effect of various inorganic and organic acids, used as chemical modifiers, on the atomization of cadmium and the sea-water background absorption signals were examined. Of all the different modifiers studied, oxalic acid suppresses chloride interference, promotes a lower atomization temperature and does not introduce any simultaneous significant background absorption signal, and was therefore of particular interest. Optimization of the experimental conditions gave a characteristic mass of 0.23 pg. For an injection of 99 µl of sea-water into the furnace, the detection limit was 3 ng l–1.

Determination of Cadmium in Sea-Water

1-(2-ピリジルアゾ)-2-ナフトール,“PAN”を用いる微量カドミウムの吸光度定量法の各種条件を検討し,これを応用して海水申の微量カドミウムの定量法を確立した。海水申のカドミウムの濃縮法として硫化銅による共沈法を,またカドミウムの銅その他妨害元素からの分離には陽イオン交換樹脂Dowex50WX8を用い,0.5N塩酸を溶離液として交換分離する方法を採用した。溶離したカドミウムの定量にはPANを用いる吸光度法によった。本法においては90%以上の収率で微量のカドミウムが分離定量できる。本法により白浜沖,浜寺沖海水中のカドミウムを定量し,0.08～0.17μgCd/lなる値を得た。また海産生物試料(カキ,ハマグリ,コンブ,ワカメ)中のカドミウムを定量し,灰分に対して2.5～18.4×10-4%なる値を得た。