Improvement on Simultaneous Determination of Cr(III) and Cr(VI) by Capillary Electrophoresis and Chemiluminescence Detection

Chromiumexistsindifferentoxidationstatesingroundwater,industrialwastewater,seawater,andsoilofourenvironment1,2.Chromium(III)isanessentialtraceelementforhumans,requiredforthemaintenanceofnormalglucose,cholesterol,andfattyacidmetabolism.Ontheotherhand,watersolublechromium(VI),intheformCr2O72-orCrO42-,ishighlyirritatingandtoxictohumansandanimals3.Itsacutetoxiceffectsincludeanimmediatecardiovascularshockandlatereffectsonkidney,liver,andblood-formingorgans.Therefore,itisnecessaryforriskassessme…     

Speciation of Cr(III) and Cr(VI) by reversed phase high-performance liquid chromatography using UV-detection

Summary A method for the simultaneous determination of Cr(III) and Cr(VI) in water samples is described. The different reaction products of Cr(III) and Cr(VI) species with ammonium pyrrolidinedithiocarbamate (APDC) are extracted with ethyl acetate and determined by reversed phase HPLC using UV-detection. The procedure is optimized and its detection limit accordingly improved as compared to literature data. The detection limits achieved are 2.4 g/l for Cr(III) and 2.1 g/l for Cr(VI) and the calibration curves are linear between 5 g/l and 5000 g/l. For the speciation of Cr, APDC was demonstrated to be more suitable as chelating agent than sodium diethyldithiocarbamate (NaDDC). The procedure was applied to the determination of both Cr species in galvanic waste waters and its accuracy was approved by comparing the results (at the 100 g/l level) with those of a photometric determination of Cr(VI) species.Dedicated to Professor Dr. Wilhelm Fresenius on the occasion of his 80th birthday     

The effect of Cr(III)-organic complexes on the determination of inorganic chromium species in groundwater by ammonium pyrrolidinedithiocarbamate–methylisobutylketone extraction procedure

Groundwater samples collected from a tannery contaminated area were analyzed for chromium species with the objective of investigating the interference of Cr(III)-organic complexes in the determination of Cr(VI) using APDC–MIBK extraction procedure. The contribution of Cr(III), Cr(VI) and Cr(III)-organic complexes towards total chromium ranged between 2 and 61%, 27 and 86%, and, 6 and 23%, respectively. The Cr(III)-organic complexes were not extractable by APDC–MIBK, however, HNO₃ digestion released the organic bound Cr(III). Interference of organic bound Cr(III) in Cr(VI) determination due to MIBK soluble Cr(III) was not observed. Significant difference between total dissolved chromium determined after appropriate digestion procedure, and the sum of dissolved Cr(III) and Cr(VI) determined indicates the presence of the Cr(III)-organic complexes. MIBK extraction of samples without APDC is an useful way to check the extractability of organic bound Cr(III). The presence of soluble Cr(III)-organic complexes thus add complexity to chromium speciation analysis by APDC–MIBK procedure.     

Speciation of Cr(III) and Cr(VI) in potable waters by using activated neutral alumina as collector and ET-AAS for determination

The speciation of Cr(III) and Cr(VI) has been performed by using activated neutral alumina as adsorbent. Both species were quantitatively adsorbed on a small column filled with neutral alumina. The adsorbed Cr(III) was eluted with 4 mol L(-1) HNO(3) and Cr(VI) with 1.0 mol L(-1) ammonia solution. Recoveries of Cr(III) and Cr(VI) were 99% and 100%, respectively. Using ET-AAS for Cr determination the limit of detection in the sample was 0.01 microg L(-1). The combined procedure is fast and sensitive. It can be applied for routine analysis of water samples at sub-microg L(-1) levels with a relative standard deviation (RSD) of 2-10% (three determinations).     

Determination of Cr(III) and Cr(VI) in industrial and environmental liquid samples by EDXRF method

A rapid, sensitive and selective procedure for determination of Cr(III) and Cr(VI) in environmental and industrial liquid samples via preconcentration with ammonium pyrrolidine dithiocarbamate (APDC) and determination by means of the EDXRF was described. The effect of pH in the range of 3-11 on the recovery of Cr(III) and Cr(VI) has been investigated separately and in combination of these two species. The influence of organic matter, carbonate species and elements V, Mn and Fe on the recovery of each chromium specie (separately/in combination) over whole pH range was also tested in order to simulate condition occurring in natural waters that usually contain certain amount of dissolved organic matter and carbonate ions. Cr(VI) and Cr(III) have shown different behaviors in reaction with APDC at different pH ranges and therefore it is possible to separate those two species. It was found that Cr(VI) creates complex with APDC only in the pH range from 3 to 5 with quantitative recovery (app. 98%) at pH 3, but there was no recovery of Cr(III) at that pH. On the contrary, in pH range from 6 to 11, reaction with Cr(III) and APDC reviled that the only reaction product is Cr(OH)₃ instead of the expected Cr(III)-APDC complex. All reaction products were characterized by IR spectroscopy.     

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。     

Cloud point extraction for high-performance liquid chromatographic speciation of Cr(III) and Cr(VI) in aqueous solutions

Cloud point extraction (CPE) was applied as a preconcentration step for HPLC speciation of chromium in aqueous solutions. Simultaneous preconcentration of Cr(III) and Cr(VI) in aqueous solutions was achieved by CPE with diethyldithiocarbamate (DDTC) as the chelating agent and Triton X-114 as the extractant. Baseline separation of the DDTC chelates of Cr(III) and Cr(VI) was realized on a RP-C18 column with the use of a mixture of methanol-water-acetonitrile (65:21:14, v/v) buffered with 0.05 M NaAc-HAc solution (pH 3.6) as the mobile phase at a flow rate of 1.0 ml min(-1). The precision (R.S.D.) for eight replicate injections of a mixture of 100 microg l(-1) of Cr(III) and Cr(VI) were 0.6 and 0.5% for the retention time, 4.1 and 4.6% for the peak area measurement, respectively. The concentration factor, which is defined as the concentration ratio of the analyte in the final diluted surfactant-rich extract ready for HPLC separation and in the initial solution, was 65 for Cr(III) and 19 for Cr(VI). The linear concentration range was from 50 to 1000 microg l(-1) for Cr(III) and 50-2000 microg l(-1) for Cr(VI). The detection limits of Cr(III) and Cr(VI) were 3.4 and 5.2 microg l(-1), respectively. The developed method was applied to the speciation of Cr(III) and Cr(VI) in snow water, river water, seawater and wastewater samples.     

Speciation studies by capillary electrophoresis- Simultaneous determination of chromium(III) and chromium(VI)

A method for the simultaneous determination of chromium(III) and chromium(VI) by capillary electrophoresis (CE) has been developed. The chromium(III) has been chelated with 1,2-cyclohexanediaminetetraacetic acid (CDTA) in order to impart a negative charge and similar mobility to both the chromium(III) and the chromium(VI) species. The effects of the amount of the reagent, pH and heating time required to complete the complexation have been studied. Factors affecting the CE behaviour such as the polarity of electrodes and the pH of electrophoretic buffer have been investigated. The separated species have been monitored by direct UV measurements at 214 nm. The detection limits achieved are 10 microg/l for Cr(VI) and 5 microg/l for Cr(III) and linear detector response is observed up to 100 mg/l. The procedure has been applied to the determination of both chromium species in industrial electroplating samples and its accuracy was checked by comparing the results (as total chromium) with those of atomic absorption spectrometry. No interference occurred from transition metal impurities under optimized separation conditions. The method is also shown to be feasible for determining Cr(III) as well as other metal ions capable to form complexes with CDTA (like iron(III), copper(II), zinc(II) and manganese(II)) in pharmaceutical preparations of essential trace elements.     

Sequential injection analysis for Cr(VI) and Cr(III) with renewable surface reflection spectrophotometry.

On the basis of the chromogenic reaction of chromium(VI) with 1,5-diphenylcarbohydrazide (DPC) on the surface of Polysorb C-18 beads and the sequential injection renewable surface technique (SI-RST), a highly sensitive reflect spectrophotometric method for the determination of chromium(III) and chromium(VI) was proposed. Considerations of system and flow cell design, and factors that influence the determination performance were discussed. With 300 microl of sample loaded and 0.6 mg of beads trapped, the linear response range was 0.02 - 0.5 mg l(-1) Cr(VI) with a detection limit (3 sigma) of 2.4 microg l(-1) Cr(VI). The method achieves a precision of 1.3% RSD (n = 11) and a throughput of 53 samples per hour. The determination of Cr(III) was based on the same reaction for the determination of Cr(VI) after being oxidized by (NH4)2S2O8. The precision of the oxidation method was evaluated using a 0.2 mg l(-1) Cr(III) standard, yielding an RSD of 2.5% (n = 11). The average recovery of Cr(III) oxidized was tested to be 99.1%. The proposed method was used in the simultaneous determination of Cr(VI) and Cr(III) in water samples, and the error was less than 3%.     

Simultaneous determination of Cr(III) and Cr(VI) with prechelation of Cr(III) using phthalate by ion interaction chromatography with a C-18 column

Ion interaction chromatography has been successfully used for the simultaneous determination of Cr(III) and Cr(VI) in waste water. A C-18 column which had been dynamically coated with octylamine was used for the separation of Cr(III) and Cr(VI) based on anionic interaction. Cr(III) was chelated with potassium hydrogen phthalate (KHP) before injecting into the column since the Cr(III) did not exist in an anionic form like the Cr(VI) (Cr₂O₇²⁻) presented at the optimum condition. The analytes were detected at 200 nm and linear relationship between absorption with the concentration of Cr(III) or Cr(VI) was 0.1-50 mg/L. Most of the interested interferences including alkali metals, heavy metals and organic materials have no significant effect on Cr(III)-KHP complexation and Cr(VI) stability, only NH₄⁺ and ascorbic acid yielded the serious effect on the Cr(VI) stability. The relative standard deviations calculated from both of peak area and retention time were 0.75-2.20%. The sensitivity of the method at the level concentration of sub mg/L enabled the simultaneous determination of Cr(III) and Cr(VI) contents in waste water samples without any special sample preparation step.     

Simultaneous determination of Cr(III) and Cr(VI) in water by reversed phase HPLC,after chelating with sodium diethyldithiocarbamate

Summary A method for simultaneous determination of Cr(III) and Cr(VI), using sodium diethyldithiocarbamate as chelating agent is given. At room temperature and pH 5.8 sodium diethyldithiocarbamate reacts with both Cr(III) and Cr(VI). Examination of this reaction by reversed phase high-performance liquid chromatography, makes it possible to correct for the interference between Cr(III) and Cr(VI) when determining the amount of Cr(III) present in the solution.     

Simultaneous determination of Cr(III)-EDTA and Cr(VI) by ion interaction chromatography using a C18 column

The simultaneous determination of Cr(III) and Cr(VI) by ion interaction chromatography has been investigated. The mobile phase consisted of a 5 mM octylammonium orthophosphate at pH 4.0 with 35% (v/v) MeOH. The Nucleosil-100, C18 (5 microm, 250 x 4.6 mm) was used as the separating column and the component was detected at 200 nm. The separation of Cr(III) and Cr(VI) was based on anionic interaction. Since the Cr(III) did not exist as an anionic form like the Cr(VI) (Cr2O7(2-)) presented at the optimum condition, Cr(II) was firstly reacted with EDTA (1:40 mole ratio) to form the anionic complex prior to injecting into the chromatographic system. The characteristics of the method for separation of Cr(III)-EDTA and Cr(VI) were satisfactory. The wide linear range (0.3-50.0 mg l(-1)) was achieved. The repeatabilities (%R.S.D.) calculated from peak areas were 0.49% and 0.14%, detection limit (signal to noise ratio of 3) of 0.02 mg l(-1) and 0.3 mg l(-1) were obtained and the average of percent recoveries were found to be 98.5% and 99.6% for Cr(III) and Cr(VI), respectively.     

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.     

Speciation of Fe(II) and Fe(III) by the modified ferrozine method,FIA-spectrophotometry,and flame AAS after cloud-point extraction

A method has been developed for the simultaneous determination of traces of Fe(III) and Fe(II) in water by on-line coupling of spectrophotometry with flame atomic absorption spectrometry (FAAS). The method involves cloud-point extraction (CPE) of both species with ammonium pyrrolidinecarbodithioate (APDC) under standard conditions, which facilitates the in situ complexation and extraction of both species. Differentiation of the oxidation states of iron is achieved by using mathematical equations to overcome the interference of Fe(III) in the spectrophotometric determination of Fe(II) when they are both present in the same solution. In this manner the time-consuming and labor-intensive steps of preoxidation of Fe(II) or reduction of Fe(III) are eliminated. By preconcentrating a 10-mL sample solution detection limits as low as 7 microg L(-1), were obtained after a single-step extraction procedure. The relative standard deviation (n=4, 30 microg L(-1)) was 2.6 % and 1.8 % for spectrophotometry and FAAS, respectively. Recoveries in the range of 96-105 % were obtained by analysis of spiked real samples. The method was further verified by analyzing a certified reference material (IMEP-9); for this the recovery was 98.5 %.     

Simultaneous determination of Co(II), Cr(VI), Ni(II) and Pb(II) in water by solvent extraction and high-field 1H NMR Spectrometry

A novel analytical approach is described that combines the preconcentration power of solvent extraction with the resolution and sensitivity of a 500 MHz ¹H NMR spectroscopic detection method for the quantitative determination of metals. Co(II), Cr(VI), Ni(II) and Pb(II) in water are extracted into chloroform as dithiocarbamate complexes. By decoupling the protons and employing a solvent-induced shift method, the ¹H NMR spectrum containing the dithiocarbamate complexes of Co(II), Cr(VI), Ni(II) and Pb(II) is fully resolved at CDCl₃/ C₆D₆ below 40%/60%. The detection limits for Co(II), Cr(VI), Ni(II) and Pb(II) are estimated to be 0.12, 0.073, 0.11 and 0.27 μg/mL, respectively, in the sample solution.     

Application of double-spike isotope dilution for the accurate determination of Cr(III), Cr(VI) and total Cr in yeast

A method is presented for the simultaneous determination of Cr(III) and Cr(VI) in yeast using species-specific double-spike isotope dilution (SSDSID) with anion-exchange liquid chromatography (LC) separation and sector field inductively coupled plasma mass spectrometric (SF-ICP-MS) detection. Total Cr is quantitated using ID SF-ICP-MS. Samples were digested on a hot plate at 95±2 °C for 6 h in an alkaline solution of 0.5 M NaOH and 0.28 M Na₂CO₃ for the determination of Cr(III) and Cr(VI), whereas microwave-assisted decomposition with HNO₃ and H₂O₂ was used for the determination of total Cr. Concentrations of 2,014±16, 1,952±103 and 76±48 mg kg⁻¹ (one standard deviation, n=4, 3, 3), respectively were obtained for total Cr, Cr(III) and Cr(VI) in the yeast sample. Significant oxidation of Cr(III) to Cr(VI) (24.2±7.6% Cr(III) oxidized, n=3) and reduction of Cr(VI) to Cr(III) (37.6±6.5% Cr(VI) reduced, n=3 ) occurred during alkaline extraction and subsequent chromatographic separation at pH 7. Despite this significant bidirectional redox transformation, quantitative recoveries for both Cr(III) and Cr(VI) were achieved using the SSDSID method. In addition, mass balance between total Cr and the sum of Cr(III) and Cr(VI) concentrations was achieved. Method detection limits of 0.3, 2 and 30 mg kg⁻¹ were obtained for total Cr, Cr(VI) and Cr(III), respectively, based on a 0.2-g sub-sample.     

Determination of manganese (VII), chromium (VI) and nickel (II) in medicinal herb samples by cloud-point extraction and high-performance liquid chromatography

A highly sensitive method for the determination of manganese (VII), chromium (VI) and nickel (II) in medicinal herb samples is proposed. The method is based on analytes reacted with ammonium pyrrolidinedithiocarbamate (APDC) to give hydrophobic chelates (M–APDC), which were separated and enriched by cloud-point extraction (CPE) with non-ionic surfactant Tergitol TMN-6 as extractant. The surfactant-rich phase containing the chelates is determined with a high-performance liquid chromatography system. To achieve the best CPE method, the Box–Behnken design was used to study the concentration of Tergitol TMN-6, equilibrium temperature, equilibrium time as well as their interaction. What followed was the individual research for the pH of the sample solutions and the concentration of APDC. What is more, in the given optimized experimental conditions, calibration plots were found to be linear in the range of 0.0200–0.500 mg/L for Mn (VII) and Cr (VI), meanwhile 0.0500–1.00 mg/L for Ni (II), the linear correlation coefficients were between 0.996 and 0.999, the recoveries ranged from 91.8 to 97.8 % and the relative standard deviations were between 1.09 and 2.30 % (n = 3). The limits of detection were 0.164 μg/L for Mn (VII), 0.562 μg/L for Cr (VI) and 5.12 μg/L for Ni (II), respectively. The proposed method was applied to determine manganese (VII), chromium (VI) and nickel (II) in medicinal herb samples with satisfactory results.     

Speciation of Cr(III) and Cr(VI) in Environmental Samples after Solid Phase Extraction on Amberlite XAD–2000

A method for speciation of Cr(III) and Cr(VI) in real samples has been developed. Cr(VI) has been separated from Cr(III) and preconcentrated as its pyrrolidinedithiocarbamate (APDC) complex by using a column containing Amberlite XAD–2000 resin and determined by FAAS. Total chromium has also been determined by FAAS after conversion of Cr(III) to Cr(VI) by oxidation with KMnO₄. Cr(III) has been calculated by subtracting Cr(VI) from the total. The effect of pH, flow‐rate, adsorption and batch capacity and effect of various metal cations and salt anions on the sorption onto the resin were investigated. The adsorption is quantitative in the pH range of 1.5–2.5, and Cr(VI) ion was desorbed by using H₂SO₄ in acetone. The recovery of Cr(VI) was 97 ± 4 at a 95% confidence level. The highest preconcentration factor was 80 for a 200 mL sample volume. The adsorption and batch capacity of sorbent were 7.4 and 8.0 mg g^?1 Cr(VI), respectively, and loading half time was 5.0 min. The detection limit of Cr(VI) is 0.6 μg/L. The procedure has been applied to the determination and speciation of chromium in stream water, tap water, mineral spring water and spring water. Also, the proposed method was applied to total chromium preconcentration in microwave digested moss and rock samples with satisfactory results. The developed method was validated with CRM‐TMDW‐500 (Certified Reference Material Trace Metals in Drinking Water) and BCR‐CRM 144R s (Certified Reference Material Sewage Sludge, Domestic Origin) and the results obtained were in good agreement with the certified values. The relative standard deviations were below 6%.     

Separation of chromium (III) and chromium (VI) by capillary electrophoresis using 2,6-pyridinedicarboxylic acid as a pre-column complexation agent

A simple method was developed for the simultaneous determination of Cr(III) and Cr(VI) by capillary zone electrophoresis (CZE), where Cr(III) was chelated with ligands to form anionic complexes. Nitrilotriacetic acid, N-2-hydroxyethylenediaminetriacetic acid, ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, and 2,6-pyridinedicarboxylic acid (PDCA) were investigated as Cr(III) complexing ligands. Of all the ligands studied, 2,6-PDCA with Cr(III) gave the largest UV response and high selectivity for Cr(III). In addition, the condition for pre-column derivatization, including pH, concentration ratio [Cr(III)/2,6-PDCA] and the stability of Cr(III) complexes were also examined. The separation of anionic forms of Cr(III) and Cr(VI) was achieved using co-CZE with UV detection at 185 nm. The electrolyte contained 30 mM phosphate, 0.5 mM tetradecyltrimethylammonium bromide, 0.1 mM 2,6-PDCA and 15% (v/v) acetonitrile at pH 6.4. The detection limits were 2 microM for Cr(III) and 3 microM for Cr(VI) and linear plots were obtained in a concentration range of 5-200 microM. The utility of the method was demonstrated for the determination of Cr(III) and Cr(VI) in contaminated soils.     

Preconcentration method on modified silica fiber for chromium speciation

A new method involving pre-concentration on modified silica fiber is described for the speciation of chromium(III) [Cr(III)] and chromium(VI) [Cr(VI)] in aqueous media. This method is based on the different chelating behavior of Cr(III) and Cr(VI) with morpholine-4-carbodithioate (MDTC). Both complexes are extracted on silica fiber modified by sol-gel technology by using 3-aminopropyltriethoxysilane (APS) as a precursor. All extracted samples are directly injected into an high-performance liquid chromatography injector for the simultaneous determination of Cr(III) and Cr(VI). Cr(VI) forms two different complexes, and Cr(III) forms a single complex with MDTC. Therefore, the concentration of Cr(VI) is determined directly from the peak area obtained at 5.4 min; whereas, the assay of Cr(III) is based on subtracting the peak area of Cr(VI) from the total peak area obtained at 4.3 min. Under the optimized conditions, the limits of detection for Cr(III) and Cr(VI) are found to be 0.7 ng/mL and 0.2 ng/mL, respectively.