Separation and spectrophotometric determination of very low levels of Cr(VI) in water samples by novel pyridine-functionalized mesoporous silica

A modified SBA-15 mesoporous silica was developed, as an adsorbent, for the removal of Cr(VI) ions from natural-water samples. The effects of experimental parameters, including pH of solution, sample and eluent flow rate, the eluent composition, the eluent volume, and the effect of coexisting ions on the separation and determination of Cr(VI), were investigated. It was shown that Cr(VI) was selectively adsorbed from aqueous solution at pH 3, but Cr(III) could be adsorbed from solution at alkaline pH range. The retained Cr(VI) was eluted with 0.5?mol?L^?1 KCl solution in 0.1?mol?L^?1 Na₂CO₃ subsequently. Under the optimum conditions, the modified mesoporous silica (py-SBA-15) with a high pore diameter exhibited an adsorption capacity of 136?mg?g^?1 and a lower limit of detection than 2.3?µg?L^?1 by using diphenylcarbazide as a chromophorous reagent for the determination of Cr(VI) ions. A preconcentration factor as high as 200 was calculated for Cr(VI). The loaded py-SBA-15 can be reactivated with recovery of more than 98.5% over at least eight cycles. The relative standard deviation (RSD) for Cr(VI) ion recovery was less than 1.8%. Validation of the outlined method was performed by analysing a certified reference material (BCR 544). The proposed method was applied to determine Cr(VI) value in natural and waste water samples successfully.     

Chromium(III, VI) speciation analysis with preconcentration on a maleic acid-functionalized XAD sorbent

Chromium may exist in environmental waters as Cr(III) and Cr(IV), the latter being the toxic and carcinogenic form. Since atomic absorption spectrometry (AAS) and inductively coupled plasma atomic emission spectrometry can only yield information on total Cr concentration, a polymer resin bearing O,O-donor chelating groups such as the maleic acid-functionalized XAD(CO)CHCHCOOH resin was synthesized to selectively retain Cr(III) at pH 4.0-5.5. The dynamic breakthrough capacity of the resin for Cr(III) at pH 5.0 was 7.52 mg g⁻¹, and the preconcentration factor extended to 250-300. Chromium(III) in the presence of 250-fold Cr(VI)—which was not retained—could be effectively preconcentrated on the NH₄⁺-form of the resin and determined by AAS or diphenylcarbazide (DPC) spectrophotometry. When Cr(VI) was reduced to Cr(III) with Na₂SO₃ solution brought to pH 1 by the addition of 1 M H₂SO₄, and preconcentrated on the resin, total Cr could be determined. The developed method was validated with a blended coal sample CRM-1632. Since the adsorption behavior as a function of pH of possible interferent metal ions, e.g. Ni(II), Co(II), Cu(II), Cd(II), Zn(II), Pb(II) and Fe(III), was similar to that of Cr(III), selective elution of Cr(III) from the resin was realized using a mixture of 1 wt.% H₂O₂+1 M NH₃. The eluate containing Cr as chromate could be directly analyzed by diphenyl carbazide spectrophotometry without any adverse effect from the common interferents of this method, i.e. Fe(III), Cu(II) Hg(II), VO₃⁻, MoO₄²⁻ and WO₄²⁻. Various synthetic waste solutions typical of electroplating bath effluents containing Cr, Cu, Ni, Zn, Na, Ca, cyanide (and chemical oxidation demand (COD), achieved by glucose addition) were subjected to pretreatment procedures such as hypochlorite oxidation (of cyanide) and catalytic oxidation (of COD) with peroxodisulfate. Chromium determination gave satisfactory results. The combined column preconcentration—selective elution—diphenylcarbazide spectrophotometric determination was also successfully applied to the determination of Cr in artificial and real seawater.     

Continuous flow analysis: Photometric determination of Cr(III) with chrome Azurol S using microwave treatment

The effect of microwave and ultraviolet radiation and ultrasonic treatment on the reaction of chromium(III) with Chrome Azurol S, Arsenazo I, Alizarin, and Thoron was studied in the batch and flow modes. It was found that the reaction of chromium with the above photometric reagents is most efficiently activated by microwave radiation of the power 500-200 Wt. The best analytical properties were found for Chrome Azurol S. A flow system was proposed for the photometric determination of chromium(III) with Chrome Azurol S using microwave treatment. The throughput of the system is 68 samples per hour, the analytical range for chromium(III) is 0.03-60 mg/L. Na, K, Mg, Ca, Zn, Cd, Pb, C1^-, SO ₄ ^2- , NO_3/-, CH₃COO^- in 1000-fold amounts; Cu(II) and F^- in 500-fold amounts; Fe(III) in a 10-fold amount; and Cr(VI) in a sevenfold amount do not interfere with the determination of Cr(III). Procedures for the photometric determination of chromium under batch conditions were developed. The accuracy of the developed procedures was verified in the analysis of tanning agents and dyes for leather. Deceased.     

The extraction-spectrophotometric determination of chromium(III) with 4-(2-pyridylazo)-resorcinol

The extraction-spectrophotometric determination of chromium(III) with 4-(2-pyridylazo)-resorcinol (PAR) is described. PAR(H₂R) forms a 1:3 complex with chromium(III) in a boiling acetate buffer solution at pH 5. The complex forms an ion-association compound with tetradecyldimethylbenzylammonium ion (TDBA⁺):Cr(R)(HR)₂^--TDBA⁺ which can be extracted into chloroform, the molar absorptivity being 4.7 ·10⁴ at 540 nm. If EDTA is added as a masking agent after the Cr(HR)₃ has been formed, only iron, cobalt and nickel interfere seriously, and the method can be made specific for chromium by a preliminary extraction of these metals with cupferron. The sensitivity of the method is seven times higher than that of the diphenylcarbazide method.     

Complexation of copper(II) with 3-(2-hydroxyphenylazo)pentadione-2,4

It is shown that 3-(2-hydroxyphenylazo)pentadione-2,4 (H₂L) can exist in three tautomeric forms (enol-azo, keto-azo, and hydrazo). The effective atomic charges in the tautomeric forms of H₂L are calculated by the Hückel MO LCAO method. The molar fractions and molar absorptivities of the tautomers at different pH are found. The complexation of copper(II) with H₂L is studied by spectrophotometry. Beer’s law is obeyed for 0.51–5.12 μg/mL of copper. The assumed complex structure is given. The effect of foreign ions and masking agents on the complexation is studied. A procedure for the photometric determination of copper(II) in zinc-based alloys is proposed. Original Russian Text ? S.R. Gadzhieva, T.M. Mursalov, K.T. Makhmudov, F.G. Pashaev, F.M. Chyragov, 2006, published in Zhurnal Analiticheskoi Khimii, 2006, Vol. 61, No. 6, pp. 598–603.     

Protocol for Extraction and Determination of Cr(VI) in Solid Materials with a High Cr(III)/Cr(VI) Ratio Using EDDS as a Leaching Agent for Cr(VI) and a Masking Agent for Cr(III)

A sensitive and selective protocol for the extraction of all forms of Cr(VI) from solid materials followed by determination by catalytic adsorptive stripping voltammetry has been elaborated. Cr(VI) was leached to a solution with 0.2 mol L^?1 (NH₄)₂SO₄/NH₄OH+0.1 mol L^?1 EDDS (pH 9.5) and simultaneously Cr(III) was transferred to a nonactive electrochemical complex with EDDS. The method allows for Cr(VI) determination in solid samples containing even a 1000–2000 fold excess of extractable Cr(III) without its noticeable influence. The effects of several experimental variables such as the composition and pH of the extractant, the time and temperature of the solid sample mixing with the extractant were studied. At the optimized conditions more than 95% of total Cr(VI) recoveries from solid samples were achieved. The validation of the proposed procedure was carried out by Cr(VI) determination in certified reference material CRM 019 Ash, spiked and unspiked with Cr(III), and by comparing the obtained results with those obtained using other common extraction procedures.     

Ionic liquid-modified silica-coated magnetic nanoparticles; promising anion-exchange sorbent for extraction of Cr(VI)

In the present study, ionic liquid-modified silica-coated magnetic nanoparticles (MNPs) were synthesised and applied as a new anion-exchange sorbent for extraction and determination of Cr(VI) followed by inductively coupled plasma atomic emission spectrometry. The characterisation of MNPs was carried out by scanning electron microscope, Fourier transform infrared and vibrating sample magnetometer. Experimental design and response surface methodology were used for optimisation of different parameters which affect extraction efficiency of Cr(VI). Under the optimised conditions, extraction recoveries within the range of 25–33% with relative standard deviations (RSD%, n = 4) within the range of 3.0–5.0% were obtained. The limit of detection was found to be 0.1 µg L^?1. The linearity was studied in the range of 0.5-200 µg L^?1 with the determination coefficient of 0.9958. Also, calculated Errors% for determination of Cr(VI) in the range of 5-15 depict that the method offers acceptable accuracy for analysis of Cr(VI). The method was successfully applied for extraction and determination of Cr(VI) selectively in some tannery waste water samples.     

Speciation analysis of chromium by separation on a 5-palmitoyl oxine-functionalized XAD-2 resin and spectrophotometric determination with diphenylcarbazide

The method developed in this work for the separation and preconcentration of Cr(III) is based on its retention by an Amberlite XAD-2 copolymer resin functionalized with 5-palmitoyl-8-hydroxyquinoline (oxine), abbreviated XAD-POx, with the ligand covalently bound to the copolymer. Cr(III) sorption was quantitative within the pH range 4.5–7.0 and Cr(VI) was not retained. The Cr(III) held by the resin column was eluted with a hot solution of H₂O₂ in pH9.0 aqueous NH₃–NH₄Cl buffer, and Cr oxidized to CrO₄^2– was rejected by the chelating cation-exchanger column. Any Cr(VI) originally present with Cr(III) could be reduced with an acidic solution of H₂O₂, and retained by the column yielding total Cr results, Cr(VI) being determined from the difference. The resin showed a maximal preconcentration factor of 60 for Cr(III), the LOD and LOQ being 9.3 and 30.1 nmol L^–1, respectively. The developed preconcentration-speciation analysis was finished with a diphenylcarbazide (DPC) spectrophotometric procedure suitable for conventional laboratories. The resin showed excellent salt tolerance, enabling Cr analysis in seawater, and was stable over extended use. All the interferents of this procedure that normally occur in an electroplating effluent, a blended coal CRM, and a standard steel sample could be removed by the recommended procedure, by use of partial and total selectivity at the adsorption and desorption stages, respectively, enabling preconcentration and colorimetric determination of chromium in various complex matrices.     

Preconcentration and separation of Cr(III) and Cr(VI) using sawdust as a sorbent

A simple, inexpensive method based on solid-phase extraction (SPE) on sawdust from Cedrus deodera has been developed for speciation of Cr(III) and Cr(VI) in environmental water samples. Because different exchange capacities were observed for the two forms of chromium at different pH—Cr(III) was selectively retained at pH 3 to 4 whereas Cr(VI) was retained at pH 1—complete separation of the two forms of chromium is possible. Retained species were eluted with 2.5 mL 0.1 mol L⁻¹ HCl and 0.1 mol L⁻¹ NaOH. Detection limits of 0.05 and 0.04 μg mL⁻¹ were achieved for Cr(III) and Cr(VI), respectively, with enrichment factors of 100 and 80. Recovery was quantitative using 250 mL sample volume for Cr(III) and 200 mL for Cr(VI). Different kinetic and thermodynamic properties that affect sorption of the chromium species on the sawdust were also determined. Metal ion concentration was measured as the Cr(VI)–diphenylcarbazide complex by UV–visible spectroscopy. The method was successfully applied for speciation of chromium in environmental and industrial water samples.     

Hydrogen peroxide interference in the determination of chromium(VI) by the diphenylcarbazide method

Hydrogen peroxide at concentrations ?10^?5 mol l^?1 interferes in the spectrophotometric determination of chromium(VI) with dephenylcarbazide, because Cr(VI) is reduced to Cr(III) in acidic conditions. The interference depends on the H₂O₂ concentration and on the standing time between the additions of acid and diphenylcarbazide, and can be avoided (for ?0.4 mmol l^?1 H₂O₂) by adding a larger amount of reagent before the acid. The latter observation suggests that storage of samples under acidic conditions could cause a decrease in Cr(VI) concentration.     

Photometric determination of calcium with antipyrylazo III

Antipyrylazo III or diantipyrylazo (3,6-bis(4-antipyrylazo)-4,5-dihydroxy-2, 7-napthalenedisulfonic acid) forms at PH 12.7 a complex Ca₂HL with calcium. The logarithmic overall stability constant, 10g β₂₁₁, is 23.99 ±0.03 (0.1 MNaClO₄,25°C).The effective molar absorptivity is 21,500 ±100 l mole^-1 cm^-1 at 605 nm. The complex can be used for a selective photometric determination of calcium(0.25–3.50μmole) if tri-and tetravalent ions are removed by extraction with cupferron (into chloroform) and transition divalent ions are masked with sodium cyanide. Only strontium (0.5 μmole) and EDTA (0.1 μmole) interfere seriously.     

Simultaneous flow-injection determination of aluminium and zinc using LED photometric detection

A flow photometer with a multi-LED detector was applied to the simultaneous determination of aluminium and zinc with microcomputer control of photometric measurements and data processing. Xylenol Orange is the photometric reagent and the reaction is carried out in acetate buffer. Calibration graphs are linear for both metals in the concentration ranges 0.2–25 μg ml^?1 (Al) and 0.2–30 μg ml^?1 (Zn). Both elements can be determined for Al to Zn ratios varying from 0.01 to 100 with r.s.d. 1.1 and 1.4%, respectively. The method developed was applied to the determination of Al and Zn in alloys.     

Cr(III)/Cr(VI) determination in waste water by ICP/AES with on-line HPLC (HHPN) sample introduction

Using hydraulic high-pressure nebulization (HHPN) for sample introduction, an on-line high-pressure flow system (HPLC system) becomes a functional component of the ICP spectrometer. By placing additionally an HPLC column between the sample valve and the high-pressure injection/nebulization nozzle, an improved species analysis is attained. An example is given by on-line separation and determination of Cr(III)/Cr(VI) in real waste water samples with ICP/AES. The detection limit of each Cr oxidation state is 4 μg L^–1 with an analysis cycle time of 5 min. In comparison to conventional coupling of HPLC and ICP spectrometry a considerably higher sensitivity is achieved. Using spiked samples the recovery of HHPN-ICP/AES was on an average better than 98% in contrast to only 79% for Cr(VI) determination with a UV photometric reference method. Due to chromatographic separation of Cr(VI) from matrix components and Cr (III), the technique no longer shows the typical spectral interferences caused by Ca (267.716 nm Cr line) and Fe (283.563 nm Cr line).     

Downscaling a multicommuted flow injection analysis system for the photometric determination of iodate in table salt

In this work a downscaled multicommuted flow injection analysis setup for photometric determination is described. The setup consists of a flow system module and a LED based photometer, with a total internal volume of about 170 μL. The system was tested by developing an analytical procedure for the photometric determination of iodate in table salt using N,N-diethyl-henylenediamine (DPD) as the chromogenic reagent. Accuracy was accessed by applying the paired t-test between results obtained using the proposed procedure and a reference method, and no significant difference at the 95% confidence level was observed. Other profitable features, such as a low reagent consumption of 7.3 μg DPD per determination; a linear response ranging from 0.1 up to 3.0 m IO₃⁻, a relative standard deviation of 0.9% (n = 11) for samples containing 0.5 m IO₃⁻, a detection limit of 17 μg L⁻¹ IO₃⁻, a sampling throughput of 117 determination per hour, and a waste generation 600 μL per determination, were also achieved.     

Application of Tri-n-octylamine for the substoichiometric separation of chromium(VI) in activation analysis

A method has been developed for the substoichiometric separation of Cr(VI) by extraction with tri-n-octylamine solution in benzene from 0.1M H₂SO₄ solution. The method has been applied to the determination of chromium in silicon and aluminium by the neutron activation method.     

Spectrophotometric Determination of Titanium in Super Alloys with Diantipyrylmethane and Tiron

Diantipyrylmethane and tiron spectrophotometric determinations of Ti in the super alloys, Inconel 718 and Inconel 600, have been studied thoroughly. Both reagents formed stable yellow complexes with Ti(IV) in acidic medium. The possible interference from Ni, Fe and Cr was examined. Interference from Fe(III) was eliminated by the reduction of Fe(III) to Fe(II). Cr was removed as chromyl chloride which led to a dramatic improvement in the analytical results for Ti by the tiron photometric method. However, the removal of Cr was not necessary when the diantipyrylmethane method was employed. Consequently, lengthy manipulation of super alloys was required for the tiron determination. These two spectrophotometric methods are compared in terms of simplicity, reproducibility and accuracy.     

Consecutive sorption of molybdenum(VI) and chromium(VI) from a single sample onto fiber materials filled with an anion exchanger and their solid-phase determination with phenylfluorone and diphenylcarbazide

We have considered the possibility of the sorption-spectrometric determination of molybdenum(VI) with phenylfluorone and chromium(VI) with diphenylcarbazide from a single sample by consecutive sorption from different media onto fiber materials filled with an AV-17 anion exchanger. The dependences of analytical signals of molybdenum and chromium on the sorption conditions (pH of the initial solution, NaCl concentration, sizes of the support disc, agitation time) have been studied in the batch mode. The conditions of analytical signal registration have been determined and the analytical ranges have been established (0.01–0.06 μg/mL for Cr and 0.02–0.2 μg/mL for Mo). It has been demonstrated that molybdenum and chromium can be determined at their ratios from 1: 1 to 5: 1 from a single sample after chromium sorption from 0.1 M HCl and molybdenum sorption at pH 4 by diffuse-reflection spectroscopy or visual test. The selectivity of molybdenum and chromium determination in the presence of interfering ions has been studied.     

Determination of impurities in high-purity niobium(V) oxide by high-resolution continuum source graphite furnace atomic absorption spectrometry after sorption preconcentration

Method of sorption–atomic-absorption determination of Co, Cr, Cu, Fe, Mn, and Ni in samples of high-purity Nb₂O₅ with heterochain S,N-containing sorbents was developed. The method is based on the sorption preconcentration of trace impurities followed by their determination by high-resolution continuum source graphite furnace atomic absorption spectrometry (HR CS GFAAS). Selectivity of three original inhouse synthesized S,N-containing heterochain sorbents was studied. The recoveries of Co, Cr, Cu, Fe, Mn, and Ni using heterochain sorbents OKS, MTH, and GLSH were 100, 80, and 76%, correspondingly. Sorbent “OKS”, which provided the quantitative recovery of trace impurities, was chosen for further research. The sorption conditions for chloride solutions of different acidities (0.1–3 M HCl) were studied and optimized. Using the conditions established for the sorption and HR CS GFAAS analysis, trace Co, Cr, Cu, Fe, Mn, and Ni were determined in high purity Nb₂O₅ with a relative error less than 5%. The trueness control of the obtained results is confirmed by the “added–found” method. The developed method allows us to determine concentrations of analytes: 0.02–0.20 ppm Co, 2.0–3.3 ppm Cr, 0.2–1.5 ppm Cu, 6.0–21.0 ppm Fe, 0.6–0.8 ppm Mn, and 2.8–3.5 ppm Ni. The proposed methodology can be successfully extended to the determination of various trace elements in other high-purity inorganic materials.     

Determination of trace organophosphorus pesticides in water samples with TiO2 nanotubes cartridge prior to GC‐flame photometric detection

This article described a new method for the sensitive determination of organophosphorus pesticides in water samples using SPE in combination with GC‐flame photometric detection. In the procedure of method development, TiO₂ nanotubes were used as SPE adsorbents for the enrichment of organophosphorus pesticides from water samples. Several factors, such as eluent and its volume, sample pH, sample volume, sample flow rate, and concentration of humic acid, were optimized. Under the optimal conditions, the proposed method had good linear ranges as 0.1–40 μg/L for each of them, LOD of 0.11, 0.014, and 0.0025 μg/L, and LOQs of 0.37, 0.047, and 0.0083 μg/L for chlorpyrifos, phorate, and methyl parathion, respectively. The proposed method was validated with real environmental water samples and the spiked recoveries were over the range of 86.5–115.1%. All these results indicated that TiO₂ nanotubes, as a new SPE adsorbent, would be used widespread for the preconcentraiton and determination of environmental pollutants in the future.     

Cr(III)/Cr(VI) determination in waste water by ICP/AES with on-line HPLC (HHPN) sample introduction

Using hydraulic high-pressure nebulization (HHPN) for sample introduction, an on-line high-pressure flow system (HPLC system) becomes a functional component of the ICP spectrometer. By placing additionally an HPLC column between the sample valve and the high-pressure injection/nebulization nozzle, an improved species analysis is attained. An example is given by on-line separation and determination of Cr(III)/Cr(VI) in real waste water samples with ICP/AES. The detection limit of each Cr oxidation state is 4 μg L^–1 with an analysis cycle time of 5 min. In comparison to conventional coupling of HPLC and ICP spectrometry a considerably higher sensitivity is achieved. Using spiked samples the recovery of HHPN-ICP/AES was on an average better than 98% in contrast to only 79% for Cr(VI) determination with a UV photometric reference method. Due to chromatographic separation of Cr(VI) from matrix components and Cr (III), the technique no longer shows the typical spectral interferences caused by Ca (267.716 nm Cr line) and Fe (283.563 nm Cr line). Received: 2 August 1997 / Revised: 11 October 1997 / Accepted: 21 October 1997