Determination of cadmium in water by ICP-AES with on-line adsorption preconcentration using DPTH-gel and TS-gel microcolumns

Two flow injection inductively coupled plasma atomic emission spectrometric methods for the preconcentration and determination of trace amounts of cadmium in sea-water and waste-water samples are described based on the adsorption of the metal ion on a micro-column placed in the injection valve of the FI manifold and packed with silica gel funtionalised with 1,5-bis(di-2-pyridyl) methylene thiocarbohydrazide (DPTH-gel) and silica gel functionalised with methylthiosalicylate (TS-gel), respectively. Various parameters and chemical variables affecting the preconcentration and determination of this metal by ICP-AES are evaluated. The DPTH-gel preconcentration method has a linear calibration range from 5 to at least 100 ng ml(-1) of cadmium, with a R.S.D. of 1.1% for ten independent analyses of 100 ng ml(-1), a detection limit of 1.1 ng ml(-1) and a throughput of 40 samples per hour using a 60 s preconcentration time. The TS-gel preconcentration method shows a linear range between 10 and 100 ng ml(-1), with a R.S.D. of 2.5% for ten independent analyses of 100 ng ml(-1), a detection limit of 4.3 ng ml(-1) and a sample throughput of 24 samples per hour for a preconcentration time of 120 s. Validation was carried out against a certified reference water sample and by determining the analyte content in spiked synthetic sea-water, sea-water and waste-water.     

Cloud point extraction of vanadium in parenteral solutions using a nonionic surfactant (PONPE 5.0) and determination by flow injection-inductively coupled plasma optical emission spectrometry

A preconcentration and determination methodology for vanadium at trace levels in parenteral solutions was developed. Cloud point extraction was successfully employed for the preconcentration of vanadium prior to inductively coupled plasma atomic optical emission spectrometry (ICP-OES) coupled to a flow injection (FI) system. The vanadium was extracted as vanadium-2-(5-bromo-2-pyridylazo)-5-diethylaminophenol [V-(5-Br-PADAP)] complex, at pH 3.7 mediated by micelles of the nonionic surfactant polyoxyethylene (5.0) nonylphenol (PONPE 5.0). The extracted surfactant-rich phase (100 mul) was mixed with 100 mul of ethanol and this final volume injected into ICP-OES for the vanadium determination. Under these conditions, the 50 ml sample solution preconcentration allowed raising an enrichment factor of 250-fold; however, it was possible to obtain a theoretical enrichment factor of 500-fold. The lower limit of detection (LOD) obtained under the optimal conditions was 16 ng l(-1). The precision for 10 replicate determinations at the 2.0 mug l(-1) V level was 2.3% relative standard deviation (RSD), calculated with the peak heights. The calibration graph using the preconcentration system for vanadium was linear with a correlation coefficient of 0.9996 at levels near the detection limits up to at least 50 mug l(-1). The method was successfully applied to the determination of vanadium in parenteral solution samples.     

Continuous flow system for the determination of trace vanadium in natural waters utilizing in-line preconcentration/separation coupled with catalytic photometric detection

A sensitive and rapid method is presented for the determination of vanadium at ng to sub-ng ml(-1) levels in natural waters, in which in-line preconcentration/separation is directly coupled with catalytic detection of vanadium in a flow-injection system. Vanadium was adsorbed on a small column packed with Sephadex G-25 gel and desorbed with a small volume of 0.010 M HCl. The catalytic action of vanadium on the oxidation of chromotropic acid (1,8-dihydroxy-3,6-naphthalenedisulphonic acid) by bromate in pH 3.8 buffered media was used in the sensitive determination of vanadium. Effective preconcentration/separation of trace vanadium can be achieved from Fe(III), Cu(II) and a large excess of sodium chloride in seawater sample. A linear calibration using a 5 m sample loop was obtained for vanadium in the range 0-2.5 ng ml(-1). The limit of detection was 0.02 ng ml(-1) and the relative standard deviation was 1.2% for 1.0 ng ml(-1) vanadium (n=5). The present FIA system is rapid and sensitive and can be readily applied to river water and coastal seawater samples.     

Flow Injection On‐line Preconcentration Coupled with Hydride Generation Atomic Fluorescence Spectrometry for Ultra‐Trace Amounts of Bismuth Determination in Biological and Environmental Water Samples

Abstract

A simple and sensitive flow injection on line separation and preconcentration system coupled to hydride generation atomic fluorescence spectrometry (HG‐AFS) was developed for ultra‐trace bismuth determination in water and urine samples. The preconcentration of bismuth on a nylon fiber‐packed microcolumn was carried out based on the retention of bismuth complex with Bismuthiol I. A 15% (v/v) HCl was introduced to elute the retained analyte complex and merge with KBH₄ solution for HG‐AFS detection. Under the optimal experimental conditions, an enhancement factor of 20 was obtained at a sample frequency of 24/h with a sample consumption of 13.0 ml. The limit of detection was 2.8 ng/l and the precision (RSD) for 11 replicate measurements of 0.1 µg/l Bi was 4.4%.     

Flow Injection On-Line Two-Stage Solvent Extraction Preconcentration Coupled with Et-Aas for Determination of Bismuth in Biological and Environmental Samples

ABSTRACT

A robust flow injection/sequential injection(FIA/SIA) on-line two-stage solvent extraction separation/preconcentration procedure coupled to electrothermal atomic absorption spectrometry (ETAAS) is described and demonstrated for the determination of trace-levels of bismuth. In 1-4% (v/v) nitric acid medium, diethyldithiophosphate (DDPA) chelates bismuth and the chelating complex formed is extracted into isobutyl methyl ketone (IBMK), which is separated from the aqueous phase by means of cavity gravitational phase separation. Both single and two-stage separations are used. In each case, 40 μl of the concentrate is entrapped and metered in a loop, and subsequently delivered via air-segmentation into a pyrolytically coated graphite tube. The ETAAS determination is performed in parallel with the preconcentration process of the ensuing sample. Enrichment factors of 17.8 and 31.5, detection limits of 12 ng 1^?1 and 10.5 ng 1^?1 for single and two-stage extractions, respectively, along with a sampling frequency of 13 h^?1 were obtained with 100 s of sample loading time at a sample flow rate of 5.4 ml min^?1. The relative standard deviations were 2.8% and 1.9% for single and two-stage extractions, respectively. The procedure was validated by determining the bismuth content in a certified reference material and i8543220 human urine samples.     

On-line preconcentration of mercury by sorption on an anion-exchange resin loaded with 1,5-bis[(2-pyridyl)-3-sulphophenyl methylene] thiocarbonohydrazide and determination by cold-vapour inductively coupled plasma atomic emission

1,5-Bis[(2-pyridyl)-3-sulphophenyl methylene] thiocarbonohydrazide (PSTH) immobilized on an anion-exchange resin (Dowex) has been used for the on-line preconcentration of mercury from biological samples and waters prior to its determination by inductively coupled plasma atomic emission spectroscopy. The metal was eluted from the column using a solution of 2 M HNO(3) and mixed on-line with SnCl(2). The optimum experimental conditions were evaluated for the continuous preconcentration of Hg, the direct generation of mercury vapour and the final determination of this element by ICP-AES. The enrichment, together with low blank levels of the optimized procedure, allow the simple determination of this toxic element at concentrations down to a few nanograms per milliliter. The proposed method has a linear calibration range 5-1000 ng ml(-1) of mercury, with a detection limit of 4 ng ml(-1) (S/N=3) and a sampling rate of 40 h(-1), investigated with a 9 ml sample volume. The precision of the method (evaluated as the relative standard deviation obtained after analyzing ten series of ten replicates) was +/-3.6% at the 10 ng ml(-1) level of Hg(II) and +/-1.3% at the 100 ng ml(-1) level. The accuracy of the method was examined by the analysis of certified reference materials.     

Synthesis of cross-linked chitosan modified with the glycine moiety for the collection/concentration of bismuth in aquatic samples for ICP-MS determination.

A chelating resin, cross-linked chitosan modified with the glycine moiety (glycine-type chitosan resin), was developed for the collection and concentration of bismuth in aquatic samples for ICP-MS measurements. The adsorption behavior of bismuth and 55 elements on glycine-type chitosan resin was systematically examined by passing a sample solution containing 56 elements through a mini-column packed with the resin (wet volume; 1 ml). After eluting the elements adsorbed on the resin with nitric acid, the eluates were measured by ICP-MS. The glycine-type chitosan resin could adsorb several cations by a chelating mechanism and several oxoanions by an anion-exchange mechanism. Especially, the resin could adsorb almost 100% Bi(III) over a wide pH region from pH 2 to 6. Bismuth could be strongly adsorbed at pH 3, and eluted quantitatively with 10 ml of 3 M nitric acid. A column pretreatment method with the glycine-type chitosan resin was used prior to removal of high concentrations of matrices in a seawater sample and the preconcentration of trace bismuth in river water samples for ICP-MS measurements. The column pretreatment method was also applied to the determination of bismuth in real samples by ICP-MS. The LOD of bismuth was 0.1 pg ml(-1) by 10-fold column preconcentration for ICP-MS measurements. The analytical results for bismuth in sea and river water samples by ICP-MS were 22.9 +/- 0.5 pg ml(-1) (RSD, 2.2%) and 2.08 +/- 0.05 pg ml(-1) (RSD, 2.4%), respectively.     

Natural analcime zeolite modified with 5-Br-PADAP for the preconcentration and anodic stripping voltammetric determination of trace amount of cadmium.

A procedure for separation and preconcentration of trace amounts of cadmium has been proposed. A column of analcime zeolite modified with benzyldimethyltetradecylammonium chloride and loaded with 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP) was used for retention of cadmium. The cadmium was quantitatively retained on the column at pH approximately 9 and was recovered from column with 5 ml of 2 M nitric acid with a preconcentration factor of 140. Anodic stripping differential pulse voltammetry was used for determination of cadmium. A 0.05 ng/ml detection limit for the preconcentration of aqueous solution of cadmium was obtained. The relative standard deviation (RSD) for eight replicate determinations at the 1 microg/ml cadmium levels was 0.31% (calculated with the peak height obtained). The calibration graph using the preconcentration system was linear from 0.01 to 150 microg/ml in final solution with a correlation coefficient of 0.9997. For optimization of conditions, various parameters such as the effect of pH, flow rate, instrumental conditions and interference of number of ions, were studied in detail. This method was successfully applied for determination of cadmium in various complex samples.     

Hydride generation atomic absorption spectrometric determination of bismuth after separation and preconcentration with modified alumina

A simple and sensitive method has been developed for the trace determination of bismuth in aqueous samples by a combination of solid‐phase extraction and hydride generation atomic absorption spectrometry. The method is based on the use of a column packed with 2‐mercaptobenzothiazole immobilized on sodium dodecyl sulfate coated alumina. Different parameters influencing the separation and preconcentration of bismuth such as pH, sample volume, type, and concentration of eluent, and the flow rate of sample and eluent were studied. A sample volume of 500.0 mL resulted in a preconcentration factor of 100. The precision (relative standard deviation, N = 10) at the 300 ng/L level and the limit of detection (3s) were found to be 2.3% and 12 ng/L, respectively. The developed method was successfully applied to the determination of bismuth in natural water samples and two certified reference materials.     

Lead ultra-trace on-line preconcentration and determination using selective solid phase extraction and electrothermal atomic absorption spectrometry: applications in seawaters and biological samples

In this work, a new chelating resin [1,5-bis (2-pyridyl)-3-sulphophenyl methylene] thiocarbonohydrazide immobilised on aminopropyl-controlled pore glass (550 A; PSTH-cpg) was synthesised and packed in a microcolumn which replaced the sample tip of the autosampler arm. The system was applied to the preconcentration of lead. When microliters of 10% HNO3, which acts as elution agent, pass through the microcolumn, the preconcentrated Pb(II) is eluted and directly deposited in a tungsten-rhodium coated graphite tube. With the use of the separation and preconcentration step and the permanent modifiers, the analytical characteristics of the technique were improved. The proposed method has a linear calibration range from 0.012 to 10 ng ml(-1) of lead. At a sample frequency of 36 h(-1) with a 90 s preconcentration time, the enrichment factor was 20.5, the detection and determination limits were 0.012 and 0.14 ng ml(-1), respectively and the precision, expressed as relative standard deviation, was 3.2% (at 1 ng ml(-1)). Results from the determination of Pb in biological certified reference materials were in agreement with the certified values. Seawaters and other biological samples were analysed too.     

On-line preconcentration and determination of nickel in natural water samples by flow injection-inductively coupled plasma optical emission spectrometry (FI-ICP-OES)

An on-line nickel preconcentration and determination system implemented with inductively coupled plasma optical emission spectrometry (ICP-OES) associated to flow injection (FI) was studied. Trace amounts of nickel were preconcentrated by sorption on a conical minicolumn packed with activated carbon (AC) at pH 5.0. The nickel was removed from the minicolumn with 20% nitric acid. An enrichment factor of 80-fold for a sample volume of 50 ml was obtained. The detection limit (DL) value for the preconcentration method proposed was 82 ng l⁻¹. The precision for ten replicate determinations at the 0.5 μg l⁻¹ Ni level was 3.0% relative standard deviation (R.S.D.), calculated from the peak heights obtained. The calibration graph preconcentration method for nickel was linear with a correlation coefficient of 0.9997 at levels near the detection limits (DL) up to at least 100 μg l⁻¹. The method was successfully applied to the determination of nickel in natural water samples.     

Cloud point extraction and graphite furnace atomic absorption spectrometry determination of manganese(II) and iron(III) in water samples

Cloud point extraction (CPE) was applied as a preconcentration step prior to graphite furnace atomic absorption spectrometry (GFAAS) determination of manganese(II) and iron(III) in water samples. After complexation with 1-phenyl-3-methyl-4-benzoyl-5-pyrazolone (PMBP), the analytes could be quantitatively extracted to the phase rich in the surfactant p-octylpolyethyleneglycolphenylether (Triton X-100) and be concentrated, then determined by GFAAS. The parameters affecting the extraction efficiency, such as solution pH, concentration of PMBP and Triton X-100, equilibration temperature and time, were investigated in detail. Under the optimum conditions, preconcentration of 10 ml of sample solution permitted the detection of 0.02 ng ml(-1) of Mn(II) and 0.08 ng ml(-1) of Fe(III) with enrichment factors of 31 and 25 for Mn(II) and Fe(III), respectively. The proposed method was applied to determination of trace manganese(II) and iron(III) in water samples with satisfactory results.     

Ion chromatographic preconcentration of Cu and Cd from ultra-high-purity water and determination by electrothermal atomic absorption spectrometry

A method based on preconcentration of Cu and Cd from ultra-high-purity water by ion chromatography (IC) and determination by electrothermal atomic absorption spectrometry is described. A small low-capacity ion-exchange concentrator Dionex HPIC-CG5 and mobile phase of 3 mM pyridine-2,6-dicarboxylic acid (PDCA) are used. Water samples are loaded onto the preconcentration column at a flow-rate ranging from 1 to 3.5 ml min(-1). Large sample volumes (up to 200 ml) can be loaded onto the concentrator without losing metal ions. Elution is carried out in the reverse direction of sample loading and the volumes of effluent are as small as 0.150 and 0.200 ml for copper and cadmium, respectively. Under these conditions the preconcentrated ions coelute. The detection limits, based on the Hubaux-Vos method, for Cu using a 1300-fold preconcentration in the IC step was found to be 1 pg ml(-1), and was limited due to impurity in PDCA, while the detection limit found for Cd using a 1000-fold preconcentration was 0.02 pg ml(-1). Ultra-high-purity water produced by a Millipore system is successfully analysed by the proposed method and the content of Cu and Cd are found to lie in the range 1-10 pg ml(-1).     

Determination of trace impurities in some nickel compounds by flame atomic absorption spectrometry after solid phase extraction using Amberlite XAD-16 resin

A simple flame atomic absorption spectrometric (FAAS) procedure for the determination of lead, bismuth, gold, palladium and cadmium as impurities in Raney nickel and nickel oxide was developed using a preconcentration step on an Amberlite XAD-16 resin packed column. Lead, bismuth, gold, palladium and cadmium were quantitatively recovered and separated from a solution containing 1 M HCl and 0.3 M NaI by the column system. Effects of the various parameters such as reagent concentrations, sample volume, matrix effects, etc. have been investigated. Under optimized conditions, the relative standard deviation of the combined method of sample treatment, preconcentration and determination with FAAS (n = 7) is generally lower than 12%. The limit of detection (3s, n = 20) was between 10–270 ng/g. The results were used for separation and preconcentration of five trace elements from nickel matrices.     

Hydrodynamic voltammetry at tubular electrodes-III Determination of traces of bismuth by differential-pulse anodic-stripping voltammetry at a glassy-carbon tubular electrode with in situ mercury plating

An equation for the current in differential-pulse anodic-stripping voltammetry at tubular electrodes is derived. Application of a glassy-carbon tubular electrode to determination of traces of bismuth in environmental water samples by differential-pulse anodic-stripping voltammetry is described. In hydrochloric acid medium, the stripping peak current is proportional to the concentration of bismuth in the range 2-100 ng/ml, with a deposition time of 3-10 min. The detection limit is 0.5 ng/ml.     

Sensitive determination of paraquat and diquat at the sub-ng ml-1 level by continuous amperometric flow methods.

Two methodologies are described for the determination of paraquat and diquat. The first is based on the pre-treatment of an electrode with a surfactant solution, which improves the electrochemical determination of the herbicides. Linear calibration graphs were obtained in the ranges 10-80 and 10-100 ng ml-1 for paraquat and diquat, respectively. The limits of detection were 6.32 for paraquat and 4.80 ng ml-1 for diquat. The method was applied to the determination of the herbicides in synthetic water samples. The second methodology is based on the preconcentration of paraquat and diquat in a minicolumn packed with a cation-exchange material. The determination ranges and detection limits depend on the sample volume used (5-50 ml). Thus, 50 ml of sample provides limits of detection of 0.016 and 0.020 ng ml-1 for paraquat and diquat, respectively. The applicability of the method was demonstrated with the determination of the herbicides in both synthetic and real water samples.     

On-line preconcentration and determination of cadmium in honey using knotted reactor coupled to flow injection-flame atomic absorption spectrometry

An on-line cadmium preconcentration and determination system implemented with flame atomic absorption spectrometry (FAAS) associated with flow injection was studied. Cadmium was retained as Cd-2-(5-bromo-2-pyridylazo)-5-diethylaminophenol Cd-(5-Br-PADAP) complex, pH 9.3. The Cd complex was removed from the knotted reactor (KR) with ethanol. A total enhancement factor of 140 was obtained with respect to FAAS (40 for KR and 3.5 due to the use of ethanol) with preconcentration time of 120 s. The detection limit value for preconcentration of 1 g sample was 0.5 ng/g. The repeatability for 10 replicate determinations at 5.0 ng/g Cd level was 3.5% relative standard deviation, calculated from peak heights obtained. The calibration graph using the preconcentration system for Cd was linear with a correlation coefficient of 0.9990 at levels near the detection limits to at least 2000 ng/g. The method was successfully applied to determination of total Cd in honey samples.     

Determination of cadmium and bismuth in high-purity zinc metal by inductively coupled plasma mass spectrometry with on-line matrix separation

Traces of cadmium and bismuth in high-purity zinc metal were determined by inductively coupled plasma mass spectrometry (ICP-MS) in combination with flow injection (FI) on-line matrix separation (FI-ICP-MS). The anion-exchange separation method of the potassium iodide (KI) system was applied to the separation of the analytes from the matrix zinc. The analytes, cadmium and bismuth, were adsorbed on the anion-exchange (BIO. RAD AG1-X8) mini-column (1.0 mm i.d.x 100 mm bed length), while the matrix zinc can be completely removed from the anion-exchange resin. The analytes were eluted by 2 mol/l HNO(3) and directly introduced into the ICP-MS. The detection limits (D.L.) obtained by using a single injection (350 microl) were 0.81 and 0.075 ng g(-1) for cadmium and bismuth, respectively. In the case of multi-injection concentration onto the anion-exchange mini-column (five injections 350 microl each), the detection limits could be improved to 0.16 and 0.014 ng g(-1) for cadmium and bismuth, respectively. The reproducibilities of the single injection and the multi-injection method were satisfactory with a relative standard deviation of less than 5% (at the 10 and 1 ng ml(-1) level for the single injection and the multi-injection method, respectively). The method was successfully applied to the determination of trace impurities in four samples of high-purity zinc metal (7 nines grade) and three standard reference materials of high-purity unalloyed zinc samples (from NIST).     

Trace humic and fulvic acid determination in natural water by cloud point extraction/preconcentration using non-ionic and cationic surfactants with FI-UV detection

A preconcentration and determination method for humic and fulvic acids at trace levels in natural water samples was developed. Cloud point extraction was successfully employed for the preconcentration of humic acid (HA) and fulvic acid (FA) prior to the determination by using a flow injection (FI) system coupled to a spectrophotometric UV-Vis detector. The quantitative extraction of HA and FA within the pH range 1-12 was obtained by neutralization of the anionic charge on the humic substances with a cationic surfactant, hexadecyltrimethylammonium bromide (CTAB). This generated a hydrophobic species that was subsequently incorporated (solubilized) into the micelles of a non-ionic surfactant polyethylene glycol, tert-octylphenyl ether (Triton X-114). The FI method for HA and FA determination was developed by injection of 100 microl of the extracted surfactant-rich phase using an HPLC pump with spectrophotometric detection at 350 nm. A 50 ml sample solution preconcentration allowed an enrichment factor of 167. The limit of detection (LOD) obtained under the optimal conditions was 5 microg l(-1). The precision for ten replicate determinations at 0.2 mg l(-1) HA was 3.1% relative standard deviation (RSD), calculated from the peak heights. The calibration using the preconcentration system for HA and FA was linear with a correlation coefficient (r2) of 0.9997 at levels near the detection limits up to at least 1 mg l(-1). The method was successfully applied to the determination of HA and FA in natural water samples (river water).     

A simple flow injection spectrophotometric determination of nitrite based on its reaction with thiourea.

A simple flow injection spectrophotometric method for the determination of nitrite is described. Nitrite injected into the flow system reacts with thiourea in acidic medium and the generated thiocyanate ion reacts with Fe(III) in the reagent solution to produce a highly colored product. The influences of chemical and physical parameters including reagent concentrations, sample volume injected, flow rates of the carrier and reagent solutions, reaction coil length and reaction temperature, were studied and optimum values of these parameters were established. Under the optimum conditions, the calibration curve for nitrite was linear over the concentration range 0.36 - 90 microg ml(-1) without preconcentration and over the range 3.8 - 500 ng ml(-1) with a simple online preconcentration step using an anion exchange column. The corresponding detection limits were 0.36 micro ml(-1) and 3.8 ng ml(-1), respectively. Up to 25 samples can be analyzed per hour, with an average relative standard deviation of < or = 1.2%. Interferences by various foreign ions were studied and the method was applied to the determination of nitrite in water and spiked water samples.