Optimization of the solid phase extraction method for determination of Cu(II) in natural waters by using response surface methodology

A solid-phase extraction method was proposed for the preconcentration of Cu(II) in different samples in a mini-column packed with functionalized multi-walled carbon nanotubes (MWCNTs-COOH) as an effective sorbent, without using any complexing reagent, prior to its determination by flame atomic absorption spectrometry using response surface methodology. The experimental optimization step was performed by both a two-level full factorial design, with a center point, and a Box-Behnken design combined with response surface methodology. Three variables (pH, amount of Cu(II), and sample volume) were regarded as factors in the optimization. It was found that pH is the most significant factor affecting the preconcentration of Cu(II). The preconcentration factor was obtained as 100. The linear range was 1-5 mg L(-1) (R(2) = 0.999). Under the optimized experimental conditions, the detection limit (3s) of the proposed method followed by FAAS was found to be 0.27 μg L(-1). The relative standard deviation for 10 replicate measurements of 50 and 100 μg L(-1) Cu(II) was 2.39% and 0.98%, respectively. The response surface methodology was successfully applied to the determination of Cu(II) in water samples and mussel samples, and in a certified standard reference material (BCR-320R, Channel sediment).     

Pre-concentration of trace metals from sea-water for determination by graphite-furnace atomic-absorption spectrometry

Determination of Cd, Zn, Pb, Cu, Fe, Mn, Co, Cr and Ni in coastal sea-water by graphite-furnace atomic-absorption spectrometry after preconcentration by solvent extraction and use of a chelating ion-exchange resin is described. Following the extraction of the pyrrolidine-N-carbodithioate and oxinate complexes into methyl isobutyl ketone, the trace metals are further preconcentrated by back-extraction into 1.5M nitric acid. Preconcentration on the chelating resin is effected by a combined column and batch technique, allowing greater preconcentration factors to be obtained. Provided samples are appropriately treated to release non-labile metal species prior to preconcentration, both methods yield comparable analytical results with respect to the mean concentrations determined as well as to mean relative standard deviations. Control and treatment of the analytical blank is also described.     

Development of a cloud point extraction and preconcentration method for determination of trace aluminum in mineral waters by FAAS

A cloud point extraction (CPE) method has been developed for the preconcentration of trace aluminum prior to its determination by flame atomic absorption spectrometry (FAAS). The CPE method is based on the complex of Al(III) with Xylidyl Blue (XB) and then entrapped in non-ionic surfactant Triton X-114. The main factors affecting CPE efficiency, such as pH of sample solution, concentration of XB and Triton X-114, equilibration temperature and time, were investigated in detail. An enrichment factor of 50 was obtained for the preconcentration of Al(III) with 50 mL solution. Under the optimal conditions, the detection limit of this method for Al(III) is 1.43 μg L^− 1, and the relative standard deviation is 2.7% at determination of 100 μg L^− 1 Al(III). The proposed method has been applied for determination of trace amount of aluminum in mineral water samples with satisfactory results. Also, the proposed method was applied to the certified reference materials. The results obtained were in good agreement with certified values.     

Particle discrimination effects in the determination of trace metals in natural fresh waters

Instrumental neutron activation analysis (i.n.a.), atomic absorption spectrometry (a.a.s.), and inductively-coupled plasma atomic emission spectrometry (i.c.p.a.e.s.) have been applied to the determination of Na, K, Mg, Ca, Al, Mn, Fe and Zn in fresh waters containing naturally occurring particles. Scattered results were obtained for the total concentrations of trace metals which were associated to some extent with particles retainable by 0.45-μm filter membranes. Particle discrimination effects are indicated and the fraction of elements included in the final result depends on the method used. For the simultaneous determination of the total concentrations of Al, Mn, Fe and Zn, i.n.a.a. is preferred, as all element fractions present are included in the result. When a.a.s. or i.c.p.a.e.s. is applied, lower results are obtained when particulate matter is present, the results referring only to the acid-soluble low-molecular-weight fraction (< 0.45 μm diameter). When particles are removed prior to the quantifying step, the results obtained on the filtrates by all methods are in good agreement. However, considering the low concentrations of several elements in the separated fractions, i.n.a.a. is most favourable for the determination of aluminium while graphite-furnace a.a.s. is most suitable for zinc. Both methods are applicable for manganese. For Ca, Fe, K, Mg and Na, i.c.p.a.e.s. is recommended.     

Solvent extraction with ammonium pyrrolidinedithiocarbamate and 2,6-dimethyl-4-heptanone for the determination of trace metals in effluents and natural waters

A method is described for the determination of ten trace metals (V, Cr, Fe, Co, Ni, Cu, Zn, Mo, Cd, Pb) in aqueous samples by simultaneous solvent extraction followed by flame atomic absorption spectrometry. 2,6-DimethyI-4-heptanone is preferred to 4-methyl-2-pentanone as the solvent, and ammonium pyrrolidinedithiocarbamate to sodium diethyl-dithiocarbamate as the extractant except when relatively large amounts of iron are present. Calibration graphs are linear, usually over the range 0–50 μg l^-1. The effects of interfering substances, in particular iron, are shown, and the need for calibration by standard additions is demonstrated. The general need for preoxidation of samples is discussed.     

Determination of organically-associated trace metals in estuarine sea-water by solvent extraction and atomic-absorption spectrometry

Chloroform extraction of trace metals (Ni, Cu, Mo, Mn, Cd and Pb) in estuarine sea-water was studied at pH 8 and pH 3, on the basis that the metals would be associated with dissolved organic matter (DOM), which has recently been characterized by reversed-phase liquid chromatography. Ni, Cu, Mo and Mn were extracted more at pH 8 than at pH 3. Cd and Pb were not associated with the DOM at either pH 8 or 3. The percentage of the total dissolved trace metals in sea-water associated with DOM varied from 0 to 14%. The metals extracted into chloroform at pH 8 were assumed to be associated with neutral or weakly basic DOM while at pH 3 they could be associated with either the neutral (or weakly basic) DOM or two types of acidic DOM.     

Comparison of preconcentration procedures for trace metals in natural waters

The relative merits of eight procedures for preconcentrations of trace metal ions from natural water samples and synthetic solutions are evaluated. Spikes (100 μg l^?1 ) of Mn, Co, Zn, Eu, Cs and Ba and the corresponding radioactive tracers were added to batches of drinking water, estuarine water, sea water, ground water, twice-distilled water and ahumic material solution. After equilibration for 2–5 months, the following techniques were applied: passage through columns of Dowex Al chelating resin and ofsilylated silica gel, filtration through laminate membrane filters and chelating diethylenetriamine cellulose filters, precipitation with sodium diethyldithiocarbamate and l-(2-pyridylazo)-2-naphthol, extraction with ammonium pyrrolidinedithiocarbamate, and chelation by 8-quinolinol (oxine) followed by adsorption on activated carbon. The quantitative characteristics of these techniques and the influence of the water matrix effects are discussed, as well as the applicability for x-ray fluorescence analysis.     

Preconcentration by dithiocarbamate extraction for determination of trace elements in natural waters by inductively-coupled plasma atomic emission spectrometry

Preconcentration by dithiocarbamate extraction into 2-ethylhexyl acetate for simultaneous determination of trace elements in natural water is described. After 250-fold concentration, the organic phase is used directly for inductively-coupled plasma atomic emission spectrometry. Thirteen elements (As, Se, Mo, Zn, Cd, Ni, Co, Sn, Fe, Cr(VI), Pb, V and Cu) are simultaneously concentrated at pH 4.3 with the combination of ammonium tetramethylenedithiocarbamate and dibenzylammonium dibenzyldithiocarbamate and are determined in the extract; Mn and Cr(III) are also determined after preconcentration at pH 6.9 with the same chelating agents. Lake waters are analyzed by this method.     

The miniaturised solid phase extraction of some trace metals using graphene nanoplatelets by GFAAS

In order to separate and enrich of cadmium, copper, lead and nickel before its determination with graphene nanoplatelets by atomic absorption spectrometry was described. For this aim, analyte elements were collected on sorbent in mini filter. The influences of experimental conditions (pH of sample, amount of sorbent, concentration of eluent, foreign ions), retention and elution parameters on the recovery of the analyte elements were examined. After the optimisation of experimental parameters, a successful separation and enrichment were obtained at pH = 7 and eluted with 0.1 M of HNO₃ applying a 20 mL/min of drawing and discharging rates for sorption and elution steps with high (>95%) quantitative recovery and high precision (<10% relative standard deviation). Using the proposed technique, the cadmium, copper, lead and nickel in various water samples (tap water and river water) could be practically and easily removed and enriched with 95% confidence level. The limit of detection for cadmium, copper, lead and nickel was 0.78, 0.41, 5.40 and 0.44 μg/L (3σ, N = 10), respectively. The proposed technique was fast, simple, environmental friendly and economic.     

Multielement preconcentration of trace metals from natural waters by solvent extraction with an alkylated oxine derivative

Kelex 100, a commercially available alkylated oxine derivative, is shown to be effective, in purified form, for the simultaneous extraction of trace levels of Cd(II), Co(II), Cu(II), Mn(II), Ni(II), Pb(II), and Zn(II) from natural waters into toluene. The high lipophilicity of the extractant and its chelates affords large preconcentration factors in a single batch-extraction. Back-extraction with a small volume of nitric acid provides additional enrichment for subsequent determination of total (soluble) metal by graphite-furnace atomic-absorption spectrometry (GFAAS). Calibration with standard solutions can be used, which has advantages over the method of standard additions.     

Development of a solid phase extraction method for simultaneous determination of corticoids and tranquilizers in serum samples

A simple and fast solid phase extraction (SPE) method allowing the preconcentration, clean-up, and subsequent separate elution of phenothiazines (chlorpromazine hydrochloride, acetopromazine, and propionylpromazine hydrochloride) and glucocorticoids (dexamethasone, betamethasone acetate, and phenylbutazone) from serum samples has been developed. Both fractions were separately collected and analyzed without any additional treatment by high performance liquid chromatography with UV-Vis. The performance of the complete procedure was satisfactory irrespective of the spiking level with recoveries in the range 64-85% for all analytes investigated but for phenylbutazone (20%). Repeatability, evaluated as the relative standard deviation, was globally better than 12%. LC-MS was used for final confirmation of the results.     

Voltammetric methods for speciation analysis of trace metals in natural waters

Trace metals play an important role in the regulation of primary productivity and phytoplankton community composition. Metal species directly affects the biogeochemical cycling processes, transport, fate, bioavailability and toxicity of trace metals. Therefore, developing powerful methods for metal speciation analysis is very useful for research in a range of fields, including chemical and environmental analysis. Voltammetric methods, such as anodic stripping voltammetry (ASV) and competing ligand exchange-adsorptive cathodic stripping voltammetry (CLE-AdCSV), have been widely adopted for speciation analysis of metals in different natural aquatic systems. This paper provides an overview of the theory of voltammetric methods and their application for metal speciation analysis in natural waters, with a particular focus on current voltammetric methods for the discrimination of labile/inert fractions, redox species and covalently bound species. Speciation analysis of typical trace metals in natural waters including Fe, Cu, Zn, Cd, and Pb are presented and discussed in detail, with future perspectives for metal speciation analysis using voltammetric methods also discussed. This review can elaborate the particular knowledge of theory, merits, application and future challenge of voltammetric methods for speciation analysis of trace metals in natural waters.     

Development of a method for speciation of inorganic arsenic in waters using solid phase extraction and electrothermal atomic absorption spectrometry

A solid phase extraction (SPE) procedure based on Amberlite IRA 900 resin was developed for speciation and separation of inorganic arsenic species (III, V) and total As in water samples. The As species and total As in eluent solutions were determined by electrothermal atomic absorption spectrometry (ETAAS) using Ni chemical modifier with 1200°C pyrolysis temperature. Experimental parameters such as pH value, sample volume, flow rate, volume and concentration of eluent solution for As(V) were optimised and 98.0 ± 1.9% recovery was found at pH 4.0. Experimental adsorption capacity of the resin for As(V) was investigated and 229.9 mg g^–1 was found. Under optimised experimental conditions, instrumental parameters such as limit of detection (LOD) and limit of quantification (LOQ) found were 0.126 and 0.420 µg L^–1, respectively. Interference effects of coexisting ions in the sample matrix on the recovery of As(V) were investigated. Concentration of As(III) was obtained by subtracting As(V) concentration found at pH 4.0 from total As(III + V) found at pH 8.0. The accuracy of the method proposed by using the resin was tested for analysing As species in a waste water standard reference material (SRM, CWW-TM-D) and spiked real water samples with recovery above 95%. The method proposed was also applied to the determinations of As species and total As in underground hot waters and tap water with relative error below 3%.     

Trace metals species in sea-water-I: removal of trace metals from sea-water by a chelating resin

A significant fraction of the copper, lead, cadmium and zinc in sea-water exists in a form which is not retained by a chelating resin (Chelex-100) or extracted by ammonium pyrrolidinedithiocarbamate. Anodic stripping voltammetric results suggest that the major part of the unavailable trace metal is adsorbed on, or occluded in, organic or inorganic colloidal particles. An ionic equilibria computer program was used to predict the effect of various complexing agents on trace metal species in sea-water. Citric acid and amino-acids, with the exception of l-cysteine, were shown to be unimportant as complexing agents, and the ability of an EDTA-like ligand to complex Cu, Pb, Cd and Zn is controlled entirely by the concentrations of the ligand and of "labile" Fe(III) and Cr(III) in sea-water, since these two ions together will react quantitatively with EDTA. l-Cysteine, if present in sea-water, would also complex the trace metals.     

The spectrophotometric determination of ammonia in natural waters with particular reference to sea-water

The conditions for the precise spectrophotometric determination of microgram amounts of ammonia by means of the sodium phenate-hypochlorite method of RUSSELL have been investigated. Several modifications of her procedure have been introduced, particularly in the time and temperature used for development of the blue colour. BEER'S Law is obeyed up to a concentration of 2 mg NH₄-N/1 and ammonia can be determined with a standard deviation of 0.7%. The method can be used for the determination of up to at least 6 mg NH₄-N/l if recourse is made to a calibration curve. The interference of a number of inorganic ions has been studied, none of those which occur in natural fresh waters causes any marked diminution of the colour. The method can, therefore, be employed directly for the determination of ammonia in fresh waters. The most serious interferences are produced by copper and hydroxylamine. Hydrazine, however, does not interfere with the determination of ammonia unless it is present to the extent of at least 500 times the weight of the ammonia.The phenate-hypochlorite method cannot be used for the direct estimation of ammonia in sea-water owing to the interference of magnesium and calcium ions. The ammonia is therefore separated from the sea-water by a preliminary distillation under reduced pressure in a slow current of air as suggested by KROGH. A metaborate buffer has been employed for the liberation of the ammonia, and the optimum conditions of alkalinity for its separation determined. If two distillation apparatus are used concurrently 40–50 samples of sea-water may be examined per day with a standard deviation of less than 1 mg NH₄-N/m³Amino acids and urea do not interfere in either the sodium phenate-hypochlorite procedure or the distillation.     

APDC-MIBK extraction system for the determination of trace elements in saline waters by atomic-absorption spectrophotometry

A technique has been developed for the determination of "soluble" cobalt, copper, iron, lead, nickel and zinc in saline waters by simultaneous extraction of their complexes with ammonium pyrollidine dithiocarbamate (APDC) into methyl isobutyl ketone (MIBK) and subsequent analysis by atomic-absorption spectrophotometry. Particulate matter is analysed separately by dissolving millipore filters in an acetone-hydrochloric acid mixture. Various analytical and instrumental parameters have been evaluated. The method is selfcompensating in that it makes allowance for any incomplete extraction of the complexes. The technique has been applied to the determination of these elements in sea-water and saline lakes.     

On-line preconcentration and GFAAS determination of trace metals in waters

An on-line separation preconcentration system coupled to electrothermal (graphite furnace) atomic absorption spectrometry was developed. A miniature column packed with iminodiacetic acid ethyl cellulose (IDAEC) was inserted into the loop. A peristaltic pump was used to deliver solutions. A flow of air was driven into the packed column, evacuating it between sample loading, washing and elution. The retained analyte was introduced on-line to graphite furnace using countercurrent elution with HNO₃. The system was applied for the determination of V, Co and Pb in medicinal mineral water samples, and nickel in sea water samples. The detection limits (3σ) were 0.058, 0.022, 0.067, 0.062 μg/l for Co, Pb, V, and Ni, respectively. The R.S.D. (n=5) was <5% at 0.4–1.0 μg/l concentration range.     

Flow-injection photometric determination of trace copper in natural waters

A procedure for the flow-injection photometric determination of trace copper(II) in fresh natural waters is developed using a sorption preconcentration on the Diasorb-IDK-130 adsorbent with iminodiacetate groups. The procedure provides the determination of copper in the concentration range from 0.5 to 20 μg/L     

Competing ligand exchange-solid phase extraction method for the determination of the complexation of dissolved inorganic mercury (II) in natural waters

A method employing dual competitive ligand exchange followed by solid phase extraction (CLE-SPE) for characterizing the complexation of inorganic Hg(II) in natural waters is described. This method employs parallel use of two competing ligands: diethyldithiolcarbamate (DEDC), which forms hydrophobic complexes with Hg(II), and thiosalicylic acid (TSA), which forms hydrophilic complexes with Hg(II). Inorganic mercury complexed by natural and competing ligands are separated based on hydrophobicity using C₁₈ solid phase extraction columns.Data modeling allows for the calculation of the concentration and conditional stability constants of natural ligands capable of complexing Hg(II) in both the operationally defined hydrophilic and hydrophobic fractions. The use of multiple ligand concentrations, and thus multiple analytical windows, to characterize different ligand classes within both of these two fractions is described. Studies of the kinetics of the ligand exchange involved, potential for changes in the stability of natural ligands during freezing and thawing, potential breakthrough during solid phase extraction, as well as the method's precision and estimation of error, are presented and discussed.Results from the application of the method to natural freshwaters demonstrated that in the limited samples collected over 99.99% of the ambient inorganic mercury is strongly complexed by ligands with conditional stability constants (, Hg²⁺) on the order of 10³⁰, values similar to that of reduced sulfur ligands. At ambient conditions 85-90% of the mercury exists in hydrophobic complexes in these freshwaters, but strong Hg-binding ligands exist in both the hydrophobic and hydrophilic fractions.