Chromium colorimetric

Chromium (hexavalent) in chromium plating mists Colorimetric field method using 1,5-diphenylcarbazide 52/3... 

Discussion. Small amounts of chromium (up to 0.5 per cent) may be determined colorimetrically in alkaline solution as chromate uranium and cerium interfere, but vanadium has little influence. The transmittance of the solution is measured at 365-370 nm or with the aid of a filter having maximum transmission in the... 

Aliphatic amines have been determined by a number of methods. Batley et al. [290] extracted the amines into chloroform as ion-association complexes with chromate, then determined the chromium in the complex colorimetri-cally with diphenylcarbazide. The chromium might also be determined, with fewer steps, by atomic absorption. With the colorimetric method, the limit of detection of a commercial tertiary amine mixture was 15ppb. The sensitivity was extended to 0.2 ppb by extracting into organic solvent the complex formed by the amine and Eosin Yellow. The concentration of the complex was measured fluorometrically. Gas chromatography, with the separations taking place on a modified carbon black column, was used by Di Corcia and Samperi [291] to measure aliphatic amines. 

Chromium metal may be detected in high nanogram to low microgram ranges by these techniques. While AA, ICP, and colorimetric methods require chromium to be brought into aqueous phase, the metal may be analyzed non-destructively in the solid phase by x-ray techniques. ICP-MS technique may... 

Colorimetric Methods are used only for the estimation of very small percentages of vanadium, e.g. in vanadium steels and alloys. The most important depend on the intensity of the reddish-brown colour produced by the action of hydrogen peroxide on an acid vanadate solution.3 If chromium is present, an equal amount must be introduced into the standard vanadium solution under the same conditions of temperature, acid concentration, etc. Phosphoric acid is added to destroy any yellow colour due to ferric iron, and either hydrofluoric acid or ammonium fluoride to destroy any colour produced by titanium.4 A colorimetric method for the simultaneous estimation of small quantities of titanium and vanadium has also been worked out.5 Other colorimetric processes are based on (a) the formation of a yellow to black coloration, due to aniline black, in the presence of aniline hydrochloride and potassium chlorate or other oxidising agent,6 and (b) the orange coloration finally produced when an acid solution of a vanadate is brought into contact with strychnine sulphate.7... 

Nouri AME, Mansouri M, Hussain RF, et al. 1995. Super-sensitive epithelial cell line and colorimetric assay to replace the conventional K562 target and chromium release assay for assessment of non-MHC-restricted cytotoxicity. J Immunol Methods 180 63-68. 

Colorimetric Methods.—The intensity of the yellow colour of a solution of an alkali chromate is proportional to the amount of chromate in the solution. If, therefore, a given quantity of the solution to be tested has the same tint as an equal depth of a standard solution, it is assumed that there is the same concentration of alkali chromate in both solutions. The sensitiveness is found to be greatest at concentrations between 0-004N and 0-008N with respect to the gram-atom of chromium. ... 

Colorimetric comparisons have also been made with green chromium-chloride solutions, and it is found that, in general, the sensitiveness is similar to that of potassium chromate solutions. 

When an alcoholic solution of diphenylcarbazide, containing a little acetic acid, is added to a very dilute solution of chromic acid, a violet coloration is produced. This has been made the basis of a colorimetric estimation. With more concentrated solutions the reaction gives a reddish-brown colour, and finally a brown precipitate containing about 18 per cent, of chromium. 

The formation of chromium(iii) complexes of ethanolamine-NN-diacetic acid in aqueous solution has been investigated by potentiometric and colorimetric methods. A1 1 complex is found to be formed in the pH range 3—6. At pH > 6 hydrolysis takes place. Isolation of mono-, di-, and hetero-nuclear Cr chelates of ttha (ttha = triethylaminetetra-aminehexa-acetic acid) has been accomplished. No evidence for exchange coupling was found for either the dinuclear complex or for the heteronuclear Cr, Cu complex, CrCu(Httha)2,7H20. ... 

Figure 5.16 A colorimetric method, based on diphenylcarbazide, used for the analysis of hexavalent chromium[24].

United States Environmental Protection Agency, Chromium, hexavalent (colorimetric) , EPA Method 7196A, National Technical Information Service, Springfield, VA, 1992. 

There exist several analytical methods for chromium VI determination, often very complex [37]. One of the most simple and widespread is the diphenylcarbazide colorimetric method. Its detection limit is about 1 p.g/L, but the procedure is time consuming. 

A number of methods exist for the determination of parts-per-billion (ng/g) levels of chromium in aqueous media (Table 8.1). These are repeatedly reviewed as new techniques are introduced (4,5,6). Potentially all these techniques could be applied to petroleum samples after matrix destruction, but in practice, only a few have been utilized. After wet oxidation of a large sample (> 100 g), 10 to 50 fig of chromium may be determined by a colorimetric procedure with 1,5-diphenylcarbohydrazide after iron, copper, molybdenum, and vanadium are extracted as the cup-ferrates (3). In survey analyses, Cr levels as low as 5 ng/g have been measured by optical emission spectroscopy after ashing (2,3) or directly by neutron activation with extended irradiation and counting times (1). Concentrations of chromium above 100 ng/g in used lubricating oils have been measured directly by flame atomic absorption (8) for lower concentrations, heated vaporization atomic absorption (HVAA) has been utilized (9). In the Trace Metals Project, two procedures using this latter technique were evaluated for the determination of 10 ng Cr/g in a variety of petroleum matrices. 

Chromium(VI) can be quantitated without coprecipitation by forming a metal chelate. Method 7196A provides a procedure to prepare the diphe-nylcarbazone complex with Cr(VI) in an aqueous matrix. The method is not sensitive in that it is useful for a range of concentrations between 0.5 and 50 mg/L Cr. A more sensitive colorimetric method converts Cr(VI) to Cr(VI) chelate with ammonium pyrrolidine dithiocarbamate (APDC), followed by LLE into methyl isobutyl ketone (MIBK). The molecular structure for APDC is as follows ... 

Chromium exists in three oxidation states of which Cr(III) and Cr(VI) are the most stable. Hexavalent Cr is classified as a known human carcinogen via inhalation and Cr(III) is an essential dietary element for humans and other animals. Certain soils which exhibit a strong chemically reducing potential have been shown to convert Cr(VI) to Cr(III). It is possible for the analysis of soils from a hazardous waste site to reveal little to no Cr(VI) via the colorimetric method because this method is selective for Cr(VI) only (1, 2). Because atomic absorption spectrophotometric methods yield total Cr, the difference between analytical results from both methods should be indicative of the Cr(III) content of a given soil type. Both methods will be implemented in this lab exercise and applied to one or more soil types. 

Chromium oxide (Cr203). Up to 0.1% colorimetrically with diphenylcarbizide at 540 nm. Above 0.1% but as a minor constituent, colorimetrically with EDTA at 550 nm. As a major constituent by oxidation to dichromate by peroxodisulfuric acid using a silver nitrate catalyst, destruction of permanganate with HCl and titration against ferrous ammonium sulfate using diphenylamine-4-sulfonate indicator. 

A further check on the occurrence of systematic errors in a method is to compare the results with those obtained from a different method, if two unrelated methods are used to perform one analysis, and if they consistently yield results showing only random differences, it is a reasonable presumption that no significant systematic errors are present. For this approach to be valid, each step of the two experiments has to be independent. Thus in the case of serum chromium determinations, it would not be sufficient to replace the atomic-absorption spectrometry step by a colorimetric method or by plasma spectrometry. The systematic errors would only be revealed by altering the sampling methods also, e.g. by minimizing or eliminating the use of stainless-steel equipment. A further important point is that comparisons must be made over the whole of the concentration range for which an analytical procedure is... 

The precision of the colorimetric method is slightly poorer than that for the chromium titration-based procedure. Nevertheless, in other investigations it has been indicated that this method affords precision values up to seven times better than the opened reflux method [37]. 

The experiments reported here make use of the Thin Film Colorimetric Interferometry technique for film thickness measurement. In this technique, 3 X 8 bit SXGA still pictures are after transformation from RGB to CIELAB colour space converted to the film thickness map using appropriate colour/film thickness calibration curves. They are obtained from Newton rings for static contact formed between the steel ball and the glass disc coated with the chromium layer only. During several last years the accuracy and resolution of TFCI has been improved and it is now able to measure film thickness to within 1 nm [13]. 

Mo, Z. Fan, Y. Wen, Z. Xiang, X. Colorimetric determination method for simultaneously determining hexavalent chromium and lead ion. Faming Zhuanli Shenqing CN 102288600, 2011. 

The technique is not viable for elements low in the periodic table (from fluorine downward) although there is research into the use of X-ray fluorescence for fluorine and boric oxide. To this end, a method has been developed for the determination of B2O3, which allows either a wet chemical or inductively coupled plasma (ICP) finish, the latter being based on methods for the pottery industry. Another wet (colorimetric) method for the determination of Hexavalent chromium has also been produced. Finally, in the area of black and nitride ceramics, a series of standards is appearing that allow their characterization using a mixture of X-ray fluorescence. X-ray diffraction, and special chemical speciation methods. 

Dissolved chromium was determined by colorimetric comparison of the red-violet chromous diphenylcaibazone complex formed by the simultaneous oxidation of diphenylcaibazide and reduction of the chromic ions. The maximum error is 0.005 mg/1. 

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