A comparative study of diffusion samplers for the determination of hexavalent chromium by sequential injection spectrophotometry

A method is described for determining hexavalent chromium in high particulate-containing surface waters by sequential injection (SI). The relative performance of two membrane-based methods for sampling is compared. The first membrane approach is based on a commercial design known as the ‘supported capillary membrane sampler (SCMS)’ (Wolcott, D.K., US Pat. 5 317 932 (1995)) that uses tubular membranes; the second approach is based on a conventional parallel-plate dialyzer (PPD) design that uses planar membranes. The membranes are evaluated using the well-known colorimetric method for the determination of hexavalent chromium by complexation with 1,5-diphenylcarbazide (DPC). Thin-walled (∼200 μm) microporous (pore size ∼0.2 μm) polypropylene membranes are equilibrated with DPC during each sampling period. Formation of the DPC-Cr(VI) complex allows for efficient membrane transport; without the membrane, Cr(VI) transport decreases ∼90%. Factors optimized included reagent concentrations, sampling time, flow rate, and spectrophotometric conditions. Optimal conditions were 2.00 mM DPC and 0.100 M nitric acid for the reagent, and 600 and 900 s sampling times for the planar and tubular designs, respectively. The planar (PPD) design increased the sensitivity relative to the tubular (SCMS) design by ∼225%. The PPD-SI method was applied to the determination of dissolved Cr(VI) in high particulate-containing surface water samples. Figures of merit included a detection limit of <20 μg/l, precision of 1.1% R.S.D. at 100 μg/l (n=4), and selectivity for dissolved Cr(VI) in several surface water samples with high levels of particulate matter.     

Determination of trace concentrations of hexavalent chromium

A simple and sensitive solvent extraction-atomic spectrometric technique has been developed for the determination of hexavalent chromium in fresh and saline waters. The technique is based on the reaction of chromium with diphenylcarbazide. The method has been tested on a variety of water samples over an analytical range of 0-2 microg l(-1). A limit of detection of 0.024 microg l(-1) was achieved. Spiking recoveries in the range 87-115% were achieved in river water, drinking water and marine waters.     

快速溶剂萃取-离子色谱法同时测定塑料中的三价铬和六价铬

建立了采用快速溶剂萃取-离子色谱同时测定塑料中三价铬和六价铬的方法。三价铬和六价铬分别以吡啶-2,6-二羧酸(PDCA)和1,5-二苯卡巴肼(DPC)作为络合剂在柱前和柱后进行衍生化,分别在紫外和可见波长下采用紫外检测器进行检测,灵敏度高,基体干扰小。本方法对三价铬和六价铬的检出限分别为5.0 μg/L和0.5 μg/L;分别在50～1000 μg/L和5.0～100 μg/L范围内呈现良好的线性关系,线性相关系数分别为0.9994和0.9998;三价铬和六价铬的回收率范围为90.7%～101.1%,相对标准偏差(RSD)为1.7%～4.4%。该方法分析速度快、灵敏度高、重现性好,可用于塑料中三价铬和六价铬的同时测定。     

Detection of Natural Cr(VI) with Computer Screen Photo-assisted Technology

The combined use of a computer screen and a webcam has been demonstrated in several cases to provide a platform for measuring optical properties of liquid and solid samples. Here the method is utilized to measure the absorbance change in an analytical procedure aimed at determining the amount of hexavalent chromium (Cr(VI)) in water. The method calibrated on standard solutions was tested on-field on naturally contaminated spring waters. Results show a sufficient resolution to measure Cr(VI) concentration down to 5 ppb. World Health Organization recommends a maximum concentration of 0.05 mg/l (50 ppb) for chromium (as hexavalent) in drinking waters.     

Simultaneous determination of hexavalent and total chromium in water and plating baths by spectrophotometry

A new spectrophotometric determination method of hexavalent chromium in waste water and plating baths is described based on the oxidation of beryllon III by chromium(VI) in 0.02M sulphuric acid medium. The decrease in the absorbance of beryllon III was measured at 482 nm with an apparent molar absorptivity of 5.15 x 10(4)1.mole(-1).cm(-1). Beer's law was obeyed for chromium(VI) over the range 0-25 mug/25 ml. After the oxidation of Cr(III) to Cr(VI) by ammonium persulphate, total chromium can be determined. Therefore, chromium(III) can be calculated by subtracting chromium(VI) from total chromium. The detection limit is 0.015 and 0.020 mug/25 ml for chromium(VI) and total chromium, respectively. A sensitive spectrophotometric method for trace Cr(III) and Cr(VI) in waste water and plating baths was developed with good precision and accuracy. The reaction is also discussed.     

The simple and rapid spectrophotometric determination of trace chromium(VI) after preconcentration as its colored complex on chitin

Preconcentration method with collection of metal complexes on a chitin has been applied to the spectrophotometric determination of chromium(VI) in water. The chromium(VI) is collected as its 1,5-diphenylcarbazide(DPC) complex on a column of chitin in the presence of dodecyl sulfate as counter-ion. The Cr-DPC complex retained on the chitin is eluted with a methanol-1 M acetic acid mixture (7:3, v/v), and the absorbance of the eluent is measured at 541 nm. Beer's law is obeyed over the concentration range of 0.05-0.6 mug of chromium(VI) in 1 ml of the eluent. The apparent molar absorptivity is 3.5x10(4) dm(3) mol(-1) cm(-1). The tolerance limits for Fe(III) is low, i.e. ten times that of chromium(VI), but some metal ions and common inorganic anions do not interfere in concentration range of 100-10 000 times that of chromium(VI). The present method can be applied to the determination of chromium(VI) in natural water samples.     

Highly integrated flow assembly for automated dynamic extraction and determination of readily bioaccessible chromium(VI) in soils exploiting carbon nanoparticle-based solid-phase extraction

An automated dynamic leaching test integrated in a portable flow-based setup is herein proposed for reliable determination of readily bioaccessible Cr(VI) under worst-case scenarios in soils containing varying levels of contamination. The manifold is devised to accommodate bi-directional flow extraction followed by processing of extracts via either in-line clean-up/preconcentration using multi-walled carbon nanotubes or automatic dilution at will, along with Cr(VI) derivatization and flow-through spectrophotometric detection. The magnitude of readily mobilizable Cr(VI) pools was ascertained by resorting to water extraction as promulgated by current standard leaching tests. The role of carbon nanomaterials for the uptake of Cr(VI) in soil leachates and the configuration of the packed column integrated in the flow manifold were investigated in detail. The analytical performance of the proposed system for in vitro bioaccessibility tests was evaluated in chromium-enriched soils at environmentally relevant levels and in a standard reference soil material (SRM 2701) with a certified value of total hexavalent chromium. The automated method was proven to afford unbiased assessment of water-soluble Cr(VI) in soils as a result of the minimization of the chromium species transformation. By combination of the kinetic leaching profile and a first-order leaching model, the water-soluble Cr(VI) fraction in soils was determined in merely 6 h against >24 h taken in batchwise steady-state standard methods.     

Selective separation and determination of dissolved chromium species in natural waters by atomic absorption spectrometry

A procedure for determining the concentrations of dissolved chromium species in natural waters is described. Chromium(III) and chromium(VI), separated by co-precipitation with hydrated iron(III) oxide, and total dissolved chromium are determined separately by conversion to chromium(VI), extraction with APDC into MIBK and determination by a.a.s. The detection limit is 40 ng l^?1 Cr. The dissolved chromium not amenable to separation and direct extraction is calculated by difference. In the waters investigated, total concentrations were relatively high (1–5 μg l^?1) with Cr(VI) the predominant species in all areas sampled with one exception, where organically bound chromium was the major species.     

Simultaneous speciation of arsenic,selenium, and chromium: species stability,sample preservation,and analysis of ash and soil leachates

An analytical method using high-performance liquid chromatography separation with inductively coupled plasma mass spectrometry (ICP-MS) detection previously developed for the determination of Cr(III) and Cr(VI) has been adapted to allow the determination of As(III), As(V), Se(IV), Se(VI), Cr(III), and Cr(VI) under the same chromatographic conditions. Using this method, all six inorganic species can be determined in less than 3 min. A dynamic reaction cell (DRC)–ICP-MS system was used to detect the species eluted from the chromatographic column in order to reduce interferences. A variety of reaction cell gases and conditions may be utilized with the DRC–ICP-MS, and final selection of conditions is determined by data quality objectives. Results indicated all starting standards, reagents, and sample vials should be thoroughly tested for contamination. Tests on species stability indicated that refrigeration at 10 °C was preferential to freezing for most species, particularly when all species were present, and that sample solutions and extracts should be analyzed as soon as possible to eliminate species instability and interconversion effects. A variety of environmental and geological samples, including waters and deionized water [leachates] and simulated biological leachates from soils and wildfire ashes have been analyzed using this method. Analytical spikes performed on each sample were used to evaluate data quality. Speciation analyses were conducted on deionized water leachates and simulated lung fluid leachates of ash and soils impacted by wildfires. These results show that, for leachates containing high levels of total Cr, the majority of the chromium was present in the hexavalent Cr(VI) form. In general, total and hexavalent chromium levels for samples taken from burned residential areas were higher than those obtained from non-residential forested areas. Arsenic, when found, was generally in the more oxidized As(V) form. Selenium (IV) and (VI) were present, but typically at low levels.     

Speciated isotope dilution analysis of Cr(III) and Cr(VI) in water by ICP-DRC-MS

An isotope dilution method has been developed for the speciation analysis of chromium in natural waters which accounts for species interconversions without the requirement of a separation instrument connected to the mass spectrometer. The method involves (i) in-situ spiking of the sample with isotopically enriched chromium species; (ii) separation of chromium species by precipitation with iron hydroxide; (iii) careful measurement of isotope ratios using an inductively coupled plasma mass spectrometer (ICP-MS) with a dynamic reaction cell (DRC) to remove isobaric polyatomic interferences. The method detection limits are 0.4 μg L⁻¹ for Cr(III) and 0.04 μg L⁻¹ for Cr(VI). The method is demonstrated for the speciation of Cr(III) and Cr(VI) in local nullah and synthetically spiked water samples. The percentage of conversion from Cr(III) to Cr(VI) increased from 5.9% to 9.3% with increase of the concentration of Cr(VI) and Cr(III) from 1 to 100 μg L⁻¹, while the reverse conversion from Cr(VI) to Cr(III) was observed within a range between 0.9% and 1.9%. The equilibrium constant for the conversion was found to be independent of the initial concentrations of Cr(III) and Cr(VI) and in the range of 1.0 (at pH 3) to 1.8 (at pH 10). The precision of the method is better than that of the DPC method for Cr(VI) analysis, with the added bonuses of freedom from interferences and simultaneous Cr(III) determination.     

The catalytic adsorptive stripping voltammetric determination of chromium with TTHA and nitrate

A sensitive voltammetric method is presented for the determination of trace amounts of total chromium (Cr(III) and Cr(VI)) in natural waters, employing the square wave mode. The method is based on the preconcentration of the Cr(III)-TTHA complex by adsorption at the HMDE at the potential of –1.0 V vs. Ag/AgCl. The adsorbed complex is then reduced producing a response with a peak potential of –1.29 V and the peak height of the Cr(III) reduction is measured. The catalytic action of the nitrate ions on the Cr(III)-TTHA reduction has been elucidated using cyclic voltammetry. The adsorption of chromium complexes at the HMDE was investigated using out-of-phase a.c. voltammetry and the potential range of adsorption was determined.Based on these investigations optimal conditions for the determination of the total chromium concentration in the range 155–2000 ng 1^–1 have been established. The determination limit is 15 ng 1^–1 and the RSD is 3.5% for chromium concentrations 200 ng 1^–1.The usefulness and wide scope of this method for reliable and highly sensitive chromium analysis down to the ultra trace levels existing in various types of natural waters is demonstrated by determinations of the total chromium content in lake, sea and rain water.     

Preconcentration and speciation of chromium using a melamine based polymeric sequestering succinic acid resin: its application for Cr(VI) and Cr(III) determination in wastewater

A new melamine based polymeric sequestering resin was prepared for preconcentration and separation of hexavalent chromium from water, and its sequestering action was investigated. The water-insoluble, cross-linked sequestering resin was formed by reaction with bromosuccinic acid and cross-linking of melamine. The active sequestering group on the resin is NH-(Succinic acid) or salt thereof. The resulting chelating resin was characterized by infrared spectra. The newly prepared resin quantitatively retained Cr(VI) at pH 2.0-4.0 when the flow rate was maintained between 1 and 5 ml min⁻¹. The retained Cr(VI) was instantaneously eluted with 25 ml of 0.1 M NaOH. The chromium species were determined by a flame atomic absorption spectrometer. The limits of detection for Cr(VI) and Cr(III) were found to be 5.3 and 4.2 μg l⁻¹, respectively. The precision and accuracy of the proposed procedure was checked by the use synthetic and reference steel samples. The established preconcentration method was successfully applied to the determination and selective separation of Cr(VI) in electroplating industry wastewater. Total concentrations determined by the spectrophotometric method (110.3±0.6 g l⁻¹ Cr(VI) and 1.2±0.3 g l⁻¹ Cr(III)) are compared with those found by FAAS and the obtained results (110.4±1.8 g l⁻¹ Cr(VI) and 1.4±0.5 g l⁻¹ Cr(III)) show good agreement.     

Iodnitrotetrazolium chloride-A new analytical reagent for determination of chromium

The extraction of chromium (VI) with iodnitrotetrazolium chloride (INT) was studied spectrophotometrically. The basic spectrophotometric characteristics of the ion associated formed were determined. Using different methods it was found that the ratio between chromium and INT was 1:1. The molar absorptivity of the associate is (250) = (3.70 +/- 0.08) x 10(4) 1.mole(-1).cm(-1). Performing the reaction in acid medium (0.1-1.1M hydrochloric acid) allowed the determination of chromium in the presence of large amounts of W(VI), Mo(VI), Fe(III) and V(V). Hence INT is suggested as a sensitive and selective reagent for extractive-spectrophotometric determination of microquantities of chromium(VI).     

Spectrophotometric study of the complexation and extraction of chromium(VI) with cyanine dyes

Solvent extraction of chromium(VI) ion associates with symmetric cyanine dyes including the heterocyclic radicals of 1,3,3-trimethyl-3N-indoline, benzooxazol, benzothiazol and quinoline has been studied by means of spectrophotometric method. In the acidic medium in the presence of chloride ions, extractable by aromatic hydrocarbons and esters of acetic acids, chromium(VI) ion associates are formed. The molar absorptivities of ion associates are 2.5-3.6x10(5) l mol(-1) cm(-1) in dependence on extractant and dye. The absorbance of the coloured extracts obeys the Beer's law in the range 0.01-2.1 mg l(-1). The extraction of chromium is the highest during extraction from the sulphuric acid medium in the range 0.05-03 M H(2)SO(4). It was found that the Cr(VI):Cl:R molar ratio is 1:1:1. A novel procedure of chromium(VI) extraction and spectrophotometric determination in various types of soils and sewage doped with chromium(VI) was examined.     

印制电路板中六价铬测定方法的研究进展

阐述了近年来国内外印制电路板中六价铬Cr(Ⅵ)的测定方法,主要包括分光光度法、柱后衍生法、离子色谱-电感耦合等离子体质谱联用(IC-ICP-MS)等方法,未来印制电路板中六价铬的测定方法一定向着新技术联用方向发展。     

Analysis of interferents by means a D-optimal screening design and calibration using partial least squares regression in the spectrophotometric determination of Cr(VI)

Using a central composite design, the signal of the process for the spectrophotometric determination of hexavalent chromium (λ = 543 nm) is maximised and its variability minimised using as complexing agent 1,5-diphenylcarbazide in sufficiently acid medium. To analyse the interference of various analytes (Mo(VI), V(V), Fe(III) and Mn(VII)) on the Cr(VI) as a function of concentration of interferent, a factorial design was prepared at three levels of each (zero, medium and high concentration), which implies performing 81 determinations. However, a D-optimal design with just nine experiments is sufficiently good to estimate the model proposed.The interference of these metals makes it impossible to determine Cr(VI) when they are present in the sample. To avoid prior separation steps, a multivariate regression by partial least squares, PLS, is proposed to calibrate the Cr(VI) in the presence of these analytes varying the concentration of the Cr(VI) between 0.1 and 0.9 μg ml⁻¹ and that of the interferents between 3 and 5 μg ml⁻¹. The average errors obtained were 4.5% and 3.29% fitted and in prediction, respectively, with a standard error in prediction (RMSEP) of 0.016% presenting absence of both constant and proportional bias.The detection limit with the PLS regression in the presence of interferents is 0.1 μg ml⁻¹ with a probability of false positive equal to 5% and less than 5% for false negative. The capability of detection is similar to that obtained with the univariate calibration (absorbance at 543 nm) in absence of interferents.With the PLS regression it is possible to discriminate 0.085 μg ml⁻¹ of Cr(VI) in a sample with 0.5 μg ml⁻¹ of Cr(VI) with probabilities of false compliance and false non-compliance equal to 0.05. For the univariate calibration without interferents, it was established at 0.0971 μg ml⁻¹ of Cr(VI) for the same nominal concentration.In relation to interference of V(V), Fe(III) and Mn(VII), the PLS calibration could be an efficient alternative to the separation step for Cr(VI) spectrophotometric determination using 1,5-diphenylcarbazide.     

Reduction of hexavalent chromium at solid electrodes in acidic media: reaction mechanism and analytical applications

The electrochemical detection of hexavalent chromium species was investigated. It was found that Cr(VI) can undergo chemically irreversible reduction in acidic solutions at gold, glassy carbon and boron-doped diamond electrodes. The process was found to be diffusionally controlled at all three electrodes studied. The response obtained at a gold electrode towards the reduction of chromium(VI) produced an electrochemically reversible wave in contrast to those recorded at glassy carbon and boron-doped diamond electrodes. The analytical response of the hexavalent species was studied at gold electrodes in the presence of common environmental interferences: Ni²⁺, Cu²⁺, Fe³⁺, Cr³⁺ and Triton X-100 (surfactant), with an LoD of 4.3 μM obtained in the presence of 5 mM Cr(III).     

Application of 2,2′-Diquinoxalyl to the spectrophotometric determination of gold(III) and chromium(VI)

The reaction of 2,2′-diquinoxalyl with tin(II) and titanium(III) was used for spectrophotometric determination of chromium(VI) and gold(III). The conditions of the reactions were determined. The curves for determination of chromium(VI) and gold(III) were found. The influence of foreign ions was examined.     

Automation of liquid-liquid extraction-spectrophotometry using prolonged pseudo-liquid drops and handheld CCD for speciation of Cr(VI) and Cr(III) in water samples.

A simple spectrophotometric system, based on a prolonged pseudo-liquid drop device as an optical cell and a handheld charge coupled device (CCD) as a detector, was constructed for automatic liquid-liquid extraction and spectrophotometric speciation of trace Cr(VI) and Cr(III) in water samples. A tungsten halogen lamp was used as the light source, and a laboratory-constructed T-tube with two open ends was used to form the prolonged pseudo-liquid drop inside the tube. In the medium of perchloric acid solution, Cr(VI) reacted with 1,5-diphenylcarbazide (DPC); the formed complex was automatically extracted into n-pentanol, with a preconcentration ratio of about 5. The organic phase with extracted chromium complex was then pumped through the optical cell for absorbance measurement at 548 nm. Under optimal conditions, the calibration curve was linear in the range of 7.5 - 350 microg L(-1), with a correlation coefficient of 0.9993. The limit of detection (3sigma) was 7.5 microg L(-1). That Cr(III) species cannot react with DPC, but can be oxidized to Cr(VI) prior to determination, is the basis of the speciation analysis. The proposed speciation analysis was sensitive, yet simple, labor-effective, and cost-effective. It has been preliminarily applied for the speciation of Cr(VI) and Cr(III) in spiked river and tap water samples. It can also be used for other automatic liquid-liquid extraction-spectrophotometric determinations.     

Simultaneous determination of uranium(IV) and iron(II) with a stopped-flow inductive kinetic spectrophotometric method

A kinetic method for simultaneous determination of multielements is proposed, and a procedure for simultaneous determination of uranium(VI) and iron(II) is established based on their inductive effect on the chromium(VI)-iodide redox reaction in weak acidic medium. The reaction was monitored with the stopped-flow spectrophotometric technique by using I ₃ ^– -starch complex as indicator. The calibration graphs are linear for 0–3.6 g.cm^–3 U(IV), and 0–2.5 g.cm^–3 Fe(II), respectively. Most foreign ions, except for V(IV), Sb(III), do not interfere with the determination.