Indirect spectrophotometric determination of chromium(VI)

A new simple and sensitive spectrophotometric method for the determination of chromium(VI) is established. It relies upon the oxidation of iron(II) with the titled ion, in acidic medium, to form iron(III) which is complexed with tiron to form a stable blue color with maximum absorption at 650 nm. Adherence to Beer's law is observed in the range 10–100 μg of chromium(VI) per 25 ml, with a molar absorptivity of 5.6 × 10³ liters mol^?1 cm^?1, sensitivity index of 0.0093 μg cm^?1, relative error of ?5.0 to +0.3%, and relative standard deviation of 0.3–4.0%, depending on the concentration level. Furthermore, the reaction needs neither temperature control nor an extraction step.     

Differential determination of antimony(III) and antimony(V) by indirect spectrophotometry with chromium(VI) and diphenylcarbazide,after reduction of antimony(V)

Antimony(III) is determined indirectly through its reaction with excess of chromium(VI), the excess being quantified with diphenylcarbazide and measurement at 540 nm. Antimony(V) is reduced to antimony(III) with sodium sulfite in hydrochloric acid solution; excess of sulfite is eliminated by boiling. The subsequent determination of antimony(III) gives the concentration of total antimony, and antimony(V) is found from the difference between the results before and after reduction. Antimony in its different oxidation states can be determined in the range 0.04–0.7 mg l^?1 within an error of about 10%.     

Kinetic spectrophotometric determination of antimony(III) based on induced oxidation of tris(1,10-phenanthroline)iron(II) by chromium(VI)

The method involves the measurement of the extent of the induced reaction, which ceases a few seconds after initiation. Antimony(III) can be determined in the range 0.4–10 μg ml^-1. The standard deviation is ±0.25 μg. The method is applied to marine sediments.     

Enhanced spectrophotometric determination of chromium (VI) with diphenylcarbazide using internal standard and derivative spectrophotometry

In the present work, erioglaucine A was applied as internal standard to enhanced spectrophotometric determination of chromium (VI) with diphenylcarbazide. The following procedure was used: (1) addition of internal standard and formation of ion pairs of Cr (VI) with benzyltributylammonium bromide (BTAB) (sample volume 100 ml), (2) extraction to 10 ml of methylene chloride, (3) evaporation in nitrogen stream, and (4) redissolution in a micro-volume with addition of diphenylcarbazide for color development (final volume 200 mul). The preconcentration factor achieved was about 400 and it was shown that, using internal standard, the analytical errors due to sample treatment were reduced. The analytical signals for chromium and internal standard were obtained at 591.30 and 653.50 nm from first derivative spectra, normalized against (1)D(653.50nm). The analytical characteristics evaluated were: detection limit = 0.06 mug l(-1), quantification limit = 0.19 mug l(-1), precision for 1 mug l(-1) 14.2%, and for 10 mug l(-1) 3.2%, correlation coefficient of linear regression was 0.9985. The proposed procedure was applied to determination of chromium (VI) in tap water. Total chromium was determined by electrothermal atomic absorption spectrometry, the recovery of hexavalent chromium added was then evaluated and compared with the results of the proposed procedure. In this experiment, good agreement was obtained between results obtained by the two methods.     

Ion flotation—spectrophotometric determination of traces of chromium(VI)

Ion flotation is used to concentrate chromium(VI) in the range 3–70μg l^-1 from 14 samples. The chromium(III)—diphenylcarbazone complex formed by reaction with diphenylcarbazide is floated efficiently with sodium lauryl sulfate, and the subsided foam is measured spectrophotometrically after simple dilution. Continuous flotation methods at solution flow rates of 2, 3 and 4 l h^-1 are discussed.     

Determination of antimony(III) by titration with chromium(VI)

Summary There is no need for a catalyst in the potentiometric or spectrophotometric titration of antimony(III) with chromium(VI). The failure of titrations using indicators is due to slowness of the oxidized indicator-Sb(III) reaction; the indicator reaction can be catalysed by iodine. The spectrophotometric titration yields accurate results, and shows that the Sb(III)-Cr(VI) reaction is rapid. Slowness in the potentiometric titration is due to unfavourable electrode kinetics.

---

Titration von Antimon(III) mit Chrom(VI)

Zusammenfassung Bei der potentiometrischen oder spektrophotometrischen Titration von Sb(III) mit Cr(VI) bedarf es keines Katalysators. Der Fehler bei Titrationen unter Verwendung eines Indikators hat seine Ursache in der langsam verlaufenden Reaktion zwischen dem oxydierten Indikator und Sb(III); die Indikator-Reaktion kann mit Jod katalysiert werden. Die spektrophotometrische Titration gibt genaue Resultate und zeigt, daß die Sb(III)-Cr(VI)-Reaktion rasch abläuft. Die Langsamkeit der potentiometrischen Titration ist durch die ungünstige Kinetik der Elektrode verursacht.

     

Extractions with long-chain amines-VIII Colorimetric determination of chromium(VI) with diphenylcarbazide

Traces of chromium(VI) are extracted from sulphuric acid solution into a chloroform solution of trioctylmethylammonium chloride. After the addition of solid diphenylcarbazide to the separated organic phase, a red colour is developed and is measured spectrophotometrically at 550 nm. A great number of common metals, including iron and copper, do not interfere when present in ratios up to at least 1:40,000 (chromium: metal).     

Radiochemical determination of traces of arsenic(III) and antimony(III)

Very simple and rapid radiochemical procedures for the determination of traces of arsenic(III) (up to 0.1 μg) and antimony(III) (up to 0.01 μg) have been developed. The method is based on the isotope exchange between labelled metal diethyldithiocarbamate in carbon tetrachloride and an aqueous sample containing the metal to be determined. The selectivity of the method is rather high; in the presence of thiourea most common metals do not interfere with the determination.     

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.     

Rapid spectrophotometric determination of chromium(III)

A spectrophotometric procedure is suggested for the determination of Cr(III). The reaction between Cr(III) and 2-(5-bromo-2-pyridylazo)-5-dimethylaminophenol is accelerated by sodium dodecyl sulphate(SDS), sodium benzoate causes a further increase in the absorbance of the chelate. The optimum pH range for the reaction is 5-5.8(benzoate buffer). The chelate exhibits maximum absorbance at 590 nm, obeys Beer's law over the concentration range 0.02-0.56 microg/ml of Cr(III), has molar absorptivity of 7.8 x 10(4) 1. mol(-1) cm(-1) and a Sandell sensitivity of 0.66 ng/cm. The metal to ligand ratio is 1:2 in the absence of SDS and 1:1 in its presence. A procedure for the determination of Cr(III) and Cr(VI), when present together, is described. The method has been applied to the analysis of Cr(III) in tap water.     

Indirect kinetic spectrophotometric determination of hydroxylamine based on its reaction with iodate.

A simple, precise and accurate method is proposed for rapid determination of trace amounts of hydroxylamine based on the reaction of hydroxylamine with iodate in acidic media. The reaction of neutral red by the produced nitrite ion was used to monitor the reaction spectrophotometrically at 525 nm by a fixed time method. Hydroxylamine in the range of 0.0400-1.200 microg mL(-1) could be determined. The relative standard deviation for 10 determinations of 0.500 microg mL(-1) hydroxylamine was 1.81% and the limit of detection was 0.010 microg mL(-1). The proposed method was applied to the determination of hydroxylamine in water samples with satisfactory results.     

Kinetic spectrophotometric determination of traces of molybdenum(VI) by its inhibitory effect on the oxidation of 4-hydroxycoumarine by potassium permanganate.

The present paper describes a simple, selective and sensitive kinetic method for the determination of trace amounts of molybdenum(VI) based on its inhibitory effect on the reaction oxidation of 4-hydroxycoumarine by KMnO(4) in the presence of hydrochloric acid, at pH 1.75 at 25 degrees C. The rate of the indicator reaction was followed spectrophotometrically by measuring the decrease in the absorbance of KMnO(4) at 525 nm. The development method includes optimization of the reagent concentration and temperature. The calibration graph was linear in the range of concentrations from 20 to 200 ng/cm(3) of molybdenum(VI). The probable relative error was in the interval 3.10 - 10.52% for the concentration range of 200 - 20 ng/cm(3) molybdenum(VI), respectively. The interference effects of the foreign ions were determined to assess the selectivity of the method. The developed method was found to have relatively good selectivity, sensitivity, simplicity and rapidity. The proposed method was applied to the determination of molybdenum(VI) in a particular type of steel and alloy (hastelloy).     

Sequential injection wetting film extraction applied to the spectrophotometric determination of chromium(VI) and chromium(III) in water

The spectrophotometric determination of Cr(VI) and Cr(III) via sequential injection was used to demonstrate the sensitivity enhancement provided by a newly developed wetting film extraction system. The reaction product of Cr(VI) with 1,5-diphenylcarbazide was ion-paired with perchlorate and extracted into an organic wetting film consisting of octanol and 4-methyl-2-pentanone on the inner wall of a Teflon tube. The wetting film, with the extracted analyte, was then eluted with 100 mul acetonitrile and the analyte determined spectrophotometrically at 546 nm. Important optimized parameters were the selection of wetting film and elution solvents, the flow rate, the length and diameter of the extraction coil and the conditions for the formation of the ion paired chelate. Cr(III) was previously oxidized to Cr(VI) and calculated as the difference between total Cr and Cr(VI). An enrichment factor of 25 and a detection limit of 2.0 mug l(-1) Cr(VI) were achieved with a sampling frequency of 17 h(-1). The calibration curve was linear up to 100 mug l(-1) Cr(VI) (r = 0.999). The relative standard deviations were 2.8 and 2.0% at the 25 and 100 mug l(-1) levels.     

偶氮胭脂红B动力学光度法测定Fe(III)

动力学光度法测定铁[1,2]多用2,4 二氯苯酚+4 氨基安替比林[3]、苄橙[4]、次甲基蓝[5]、酸性铬蓝Ｋ[6]和二溴对甲基偶氮羧[7]等为监测组分,以Ｈ2Ｏ2为氧化剂,α,α 联吡啶为活化剂。本文用催化光度法确定铁(ＩＩＩ)催化高碘酸钾氧化偶氮胭脂红Ｂ褪色反应的动力学条件及有关参数,仅以高碘酸钾为氧化剂,不使用活化剂,操作简单、快速,用于水样及生物样中铁的测定,结果满意。1　实验部分移取0 20ｍｌＦｅ(ＩＩＩ)标准工作溶液(1 0μｇ/ｍｌ)于25ｍｌ比色管中,依次加入2 0ｍｌ0 02ｍｏｌ/Ｌ硫酸溶液,1 5ｍｌ0 010ｍｏｌ/Ｌ高碘酸钾溶液,1 5ｍ…     

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.     

Simultaneous determination of chromium (III) and chromium (VI) by reversed-phase ion-pair HPLC with chromium-specific detection

A method for the simultaneous determination of Cr(III) and Cr(VI) with reversed-phase ion-pair HPLC employing chromium-specific detection by flame atomic absorption spectrometry (FAAS) and inductively-coupled plasma mass spectrometry (ICP-MS) is presented. Experimental parameters of the chromatographic separation, such as concentration of the ion-pairing reagent, pH and polarity of the mobile phase have been optimized for two different ion-pairing reagents, tetrabutylammonium phosphate (TBA) and tetraethylammonium nitrate (TEA). Best chromatographic conditions have been obtained with a polymer-based reversed-phase column (Hamilton PRP1) and mobile phases containing either TBA (1 mmol/l) in methanol-water (60:40, v/v) or TEA (2 mmol/l) in water at a pH between 3 and 4. With FAAS the detection limits (3) have been found to be 24 g/l for Cr(III) and 40 g/l for Cr(VI). A detection limit of 0.3 g/l Cr(3) for both chromium species has been obtained when ICP-MS has been used for detection. The method has been applied to analyze tap- and groundwater and to investigate the behaviour of Cr(III) and Cr(VI) in spiked tap-water, as well as to analyze aqueous extracts of coal fly ash (NIST SRM 1633a) and of an ash from a wood treatment company.     

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.