Method For Determination Of Chromium Research Articles

Colorimetric detection of chromium (VI) via its instigation of oxidase-mimic activity of CuO.

Extensive use of chromium makes it one of the major pollutants of water resources. Chromium (VI) in particular is toxic and has detrimental health effects. Because of its high toxicity a tolerable concentration limit of chromium (VI) in drinking water has been recommended. Here we report a colorimetric method for determination of chromium (VI) in water based on the oxidase-like activity of solvothermal synthesized copper oxide. The particles have been characterized by X- ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and transmission electron microscopy (TEM). Using 3, 3', 5, 5'- tetramethylbenzidine (TMB) as a chromogenic substrate, CuO exhibited a pronounced oxidase-like activity in the presence of chromium (VI). This method enables successful colorimetric detection of chromium (VI). It demonstrated excellent selectivity for detection of chromium (VI) ions against potentially interfering ions. The method's feasibility to real sample analysis has been proven by testing tap water. Hence, we anticipate that the method can be successfully applied for analysis of chromium (VI) in environmental samples.

Method for the determination of chromium in feed matrix by HPLC

An improved method for the chromatographic separation and determination of chromium (III) and (VI) [Cr(III) and Cr(VI)] in mineral mixtures and feed samples has been developed. The method uses precolumn derivatization using ammonium pyrrolidinedithiocarbamate (APD) followed by reversed-phase liquid chromatography to separate the chromium ions. Both Cr(III) and Cr(VI) species are chelated with ammonium pyrrolidinedithiocarbamate prior to separation by mixing with acetonitrile and 0.5 mmol acetate buffer (pH 4.5). Optimum chromatographic separations were obtained with a polymer-based reversed-phase column (Kinetex, 5 μ, 250 × 4.5 mm, Phenomenex, Torrance, CA) and a mobile phase containing acetonitrile and water (7:3). Both Cr(III) and Cr(VI) ion concentrations were directly determined from the corresponding areas in the chromatogram. The effect of analytical parameters, including pH, concentration of ligand, incubation temperature, and mobile phase, was optimized for both chromium complexes. The range of the procedure was found to be linear for Cr(III) and Cr(VI) concentrations between 0.125 and 4 μg/mL (r2 = 0.9926) and 0.1 and 3.0 μg/mL (r2 = 0.9983), respectively. Precision was evaluated by replicate analysis in which the percentage relative standard deviation values for chromium complex were found to be below 4.0. The recoveries obtained (85–115%) for both Cr(III) and Cr(VI) complexes indicated the accuracy of the developed method. The degradation products, as well as the excipients, were well resolved from the chromium complex peak in the chromatogram. Finally, the new method proved to be suitable for routine analysis of Cr(III) and Cr(VI) species in raw materials, mineral mixtures, and feed samples.

Robust Ionic Liquid–Based Dispersive Liquid–Liquid Microextraction Method for Determination of Chromium(VI) in Saline Solutions

Robust ionic liquid–based dispersive liquid–liquid microextraction (IL-DLLME) is a fast and simple method for extraction and preconcentration of metal ions from samples with high salt content. This method can solve the problems associated with the limited application of the conventional IL-DLLME in these samples. In this procedure, the hydrophobic chelate of chromium with ammonium pyrrolidinedithiocarbamate (APDC) was extracted into the fine droplets of 1-hexyl-3-methylimidazolium hexafluorophosphate ([Hmim][PF6]), which was dispersed into the aqueous sample solution. Several factors that influence the microextraction efficiency were investigated. In optimum conditions a linear calibration graph in the range of 0.5–70 μg L−1 of Cr in the initial solution with r = 0.9998 was obtained. Detection limit was 0.16 μg L−1 and relative standard deviation (RSD) for 20 μg L−1 of Cr was 2.68% (n = 10), respectively. The proposed method was successfully applied for the determination of Cr(VI) in water samples and food additives.

Determination of Chromium(VI) in Waste Water by Reversed Flow Injection Spectrophotometry

A method for determination of Chromium(VI) by reversed flow injection spectrophotometry based on the catalytic effects of chromium on the oxidation reaction of methylene blue by sodium periodate in sulfuric acid medium is established. Effects of concentration of reagents and other conditions have been optimized. Calibration graphs are linear for ranges of 0 to 1.0mgl−1. A detection limit of 0.007mgl−1 chromium is achieved. The proposed method is successfully applied to the analyses of industrial waste water and electroplating waste liquor, with relative standard deviation of less than 1.5% and the recoveries are 92.9％ to 97.5％for the determination of chromium.

An organic-reagent-free method for determination of chromium(VI) in steel alloys, sewage sludge and wastewater

One of the active areas of green chemistry research and development is in the development of new analytical methods and techniques that reduce and eliminate the use and generation of hazardous substances. In this work, a rapid and organic-regent-free method was developed for the determination of chromium(VI) by sequential injection analysis (SIA). The method was based on the detection of a blue unstable intermediate compound resulting from the reaction of Cr(VI) with hydrogen peroxide (H 2O 2) in acidic medium. H 2O 2 and its reaction products were environmentally friendly, and chromogenic reagents and organic solvents were not used in the proposed method. Different SIA parameters have been optimized and used to obtain the analytical figures of merit. Under the optimum experimental conditions, the linear range for Cr(VI) was 0.5–100.0 μg mL −1, and the detection limit was 0.16 μg mL −1. The sample throughput was 80 h −1, and the total volume of only 145 μL was consumed in each determination of Cr(VI). The method was applied for the determination of Cr(VI) in seven real samples, including alloy steel, sewage sludge and wastewater samples, and the results were compared with those obtained by atomic absorption spectrometry as well as with the certified value of Cr(VI) in standard reference material. Statistical analysis revealed that there was no significant difference at 95% confidence level.

Spectrophotometric determination of Chromium(VI) using cyclam as a reagent

A simple, rapid, sensitive, and inexpensive method for spectrophotometric determination of chromium(VI), based on the absorbance of its complex with 1,4,8,11-tetraazacyclotetradecane (cyclam) is presented. The complex showed a molar absorbtivity of 1.5 × 104 L mol−1 cm−1 at 379 nm. Under optimum experimental conditions, a pH of 4.5 and 1.960 × 103 mg L−1 cyclam were selected, and all measurements were performed 10 min after mixing. Major cations and anions did not show any interference; Beer's law was applicable in the concentration range 0.2–20 mg L−1 with a detection limit of 0.001 mg L−1. The standard deviation in the determination is ±0.5 mg L−1 for a 15.0 mg L−1 solution (n = 7). The described method provides a simple and reliable means for determination of Cr(VI) in real samples.

Flow-injection microcolumn on-line preconcentration for the determination of chromium (VI)

A rapid and sensitive on-line preconcentration method for spectrophotometric determination of chromium (VI) in nature water is described. Preconcentration and determination are based on (i) the quantitative and fast adsorption of chromium (VI) on the high surface area nanometer-size TiO2 (anatase) powders, which prepared by a sol-gel method from hydrolysis of TiCl4 and (ii) the quantitative and reproducible elution of Cr (VI) by 2.0 mol·L−1 HCl. A mini-column system for preconcentration is developed, Cr(VI) on the mini-column is eluted and merged with a stream water and DPCB (1,5-diphenylcarbazide) as the chromogenic reagent. The proposed system permits throughputs of 6 sample h−1 (0.001 μg·mL−1 Cr(VI)) or 20 sample h−1 (0.1 μg·mL−1 Cr(VI)). The preconcentration factor is 55. The detection limit is 0.8 ng · mL−1 Cr(VI). The reproducibility is satisfactory with a relative standard deviation of less than 3.35% (0.01 μg·mL−1 Cr(VI),n=5).

Highly sensitive semi-quantitative field test for the determination of chromium (VI) in aqueous samples

A method for the semi-quantitative colorimetric determination of chromium(VI) at sub μg/L levels after sorptive preconcentration is presented. The method is based on the retention of the reaction product (preformed in liquid phase) between Cr(VI) and diphenylcarbazide on membrane embedded cation exchange material. The color intensity of the membrane can be correlated to Cr(VI) concentrations in the range 0.05–50 μg/L (i.e. almost three orders of magnitude lower than the conventional spectrophotometric procedure) with a detection limit of about 10 ng/L (using 50 mL of sample volume). Due to the visual inspection mode and comparative color detection the precision is only 30–80% rsd which, however, is regarded as sufficient for screening purposes. Analysis of real samples including different kinds of waters and extracts of soil and filter collected airborne particulate matter demonstrated the applicability of the method for fast and species selective screening. Recovery experiments generally gave reasonably good results, yet also revealed the risk of the conversion of chromium species during sample pretreatment procedures due to redox reactions.

Analysis and storage of samples for chromium determination in seawater

An improved method for determination of chromium in seawater has been developed. The procedure is based on the ion-pair extraction of Cr(VI) with tricaprylmethyl ammonium chloride (Aliquat-336) into methyl isobutyl ketone (MIBK). The extract is analyzed by Graphite Furnace Atomic Absorption Spectrophotometry (GFAAS). The possibility to determine total chromium by oxidation of Cr(III) is also shown. Different ways for storage of natural seawater samples in order to avoid speciation changes were also investigated. Coastal seawater could be stored at least one month at natural pH and at room temperature. Cr(VI) in frozen oceanic water is stable for at least eight months. The method allows rapid determination of Cr(VI). Measurements on CASS-2 reference material gave a Cr(VI) concentration of 2.76 ± 0.09 nM ( n = 6), compared to the certificated value 2.32 ± 0.40 nM. The detection limit based on 3σ of the blank is 0.1 nM. The determination of total chromium is more time-consuming and has a slightly lower precision.

Review of Spectrophotometric Methods for Determination of Chromium

Review of Spectrophotometric Methods for Determination of Chromium

Spectrophotometric determination of chromium with Iodonitrotetrazolium chloride and Tetrazolium Violet

The interaction of Iodonitrotetrazolium chloride and Tetrazolium Violet with chromium(VI) has been studied and the formation of ion-associates with a 1:1 composition in hydrochloric acid medium established. Extraction photometric methods for determination of chromium in steels and soils have been developed.

Spectrophotometric determination of chromium in waste water and soil

The reaction of Cr(VI) with o-nitrophenylfluorone (NPF) in presence of cetyltrimethyl-ammonium bromide (CTMAB) to form a purplish red complex at pH 4.7–6.6 by heating at 50° for 10 min has been investigated. The composition of the complex is 1:2:2 [Cr(VI):NPF:CTMAB], the wavelength of maximum absorbance is 582 nm. The molar absorptivity is 1.11 × 10 51.mole −1.cm −1. Beer's law is obeyed up to 0.2 μg ml Cr(VI) concentration. The interference of several ions, including Cu 2+, Fe 3+ and Al 3+, is eliminated by addition of a masking mixture containing KF, DCTA and tartrate. A new sensitive method for determination of chromium in waste water and soil is presented.

Effect of on-line complex formation kinetics on the flow injection analysis signal: the spectrophotometric determination of chromium(VI)

The sensitivity of the flow injection analysis (FIA) method for determination of chromium(VI) using 1,5-diphenylcarbazide (DPC) depends on the concentration of the acid used in confluence with the DPC solution. At low acid concentrations slower on-line reaction kinetics are observed for Cr - DPC complex formation. Hence the chemical contribution to the over-all dispersion value cannot be ignored. This indicates that the best experimental conditions for the static procedure may not always translate directly to the dynamic conditions of FIA. In the present instance the maximum signal is obtained with acid concentrations at or above 0.80 M. Although sulphuric acid may be used, as in the conventional procedure, the best working conditions are achieved using nitric acid.

Improved spectrophotometric determination of chromium in animal tissue digests with diphenylcarbazide

The usual spectrophotometric method for determination of chromium involves permanganate oxidation of chromium(III) to chromium(VI), followed by complex formation with diphenylcarbazide. When chromium-spiked liver tissue samples were mineralised by acid digestion, permanganate oxidation was not complete even on a boiling water-bath, but cerium(IV) oxidised chromium(III) completely at room temperature, the rate of oxidation being dependent on pH and matrix composition. Phosphate and iron(III) ions interfered. Precipitation of cerium(IV) by phosphate was avoided by addition of sulphuric acid. The coloured complex formed by iron(III) with diphenylcarbazide could be extracted with dichloromethane. High concentrations of some other metals and complexing agents interfered with the determination of chromium standards, but these substances did not occur in interfering concentrations in mouse liver digests. With the modified assay, standard chromium(III) and chromium(VI) solutions and mineralised liver samples containing standard additions of chronium(III) or chromium(VI) could be measured in the range 2.00 × 10 -5–4.00 × 10 -3 g dm -3. The four analytical curves were linear, and the superposition of standard and sample curves indicated that chromium was completely recovered from the tissue digestion step.

Direct Spectrochemical Determination of Chromium in Ruby Crystals

The aim of the present work was to develop a spectroscopic method for the routine determination of chromium in ruby crystals. Quantitative dissolution of the hard crystals is very difficult and can be accomplished only with an alkali fusion. Also, with this technique, there is a possibility of contamination from the fusion chemicals and the corrosion products from the reaction vessels. It was therefore decided to develop a method which does not require preliminary chemical preparation of the sample, thereby preventing contamination.

Twelve-fold amplification method for the volumetric determination of chromium(III) using potassium periodate as oxidant

Twelve-fold amplification method for the volumetric determination of chromium(III) using potassium periodate as oxidant

A sensitive method for determination of chromium in biological materials

Biological samples containing Cr(III) were wet-ashed and oxidized to Cr(VI) with a mixture of nitric, sulfuric, and perchloric acids. The oxidized chromium was extracted into 10% tributyl phosphate in methyl isobutyl ketone at 4°C. The ketone extract was aspirated into a fuel-rich air-acetylene flame and the absorption at 357.9 nm obtained. The sensitivity was 0.016 μg/ml of chromium.

Rapid Iodometric Method for Determination of Chromium in Chromite.

Rapid Iodometric Method for Determination of Chromium in Chromite.