Total Chromium

Using a diisopropyl-ketone-xylene mixture, chromium is extracted as an anionic thiocyanate complex with thioethyl methyl ammonium chloride and measured in the extract in an air-acetylene flame or in a graphite tube cuvette. 

Dissolve 0.1 g bromophenol blue in 2 ml 0.1 m sodium hydroxide solution and dilute to 100 ml with water. 

Dissolve 20.2 g Adogen 6 (trioctyl methyl ammonium chloride) in 150 ml xylene and dilute to 500 ml with diisopropyl ketone. 

Dissolve 685 g ammonium thiocyanate and 77 g ammonium acetate in max. 330 ml water, heating gently, add 5 ml bromophenol blue solution and set to pH 5.5 with concentrated acetic acid. 

Extract the entire solution 5 times, each time with 40 ml Adogen 464 extraction solution for purification, discard organic phase in each case and make up extracted solution to 1 litre. 

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Nonferrous alloys account for only about 2 wt % of the total chromium used ia the United States. Nonetheless, some of these appHcations are unique and constitute a vital role for chromium. Eor example, ia high temperature materials, chromium ia amounts of 15—30 wt % confers corrosion and oxidation resistance on the nickel-base and cobalt-base superaHoys used ia jet engines the familiar electrical resistance heating elements are made of Ni-Cr alloy and a variety of Ee-Ni and Ni-based alloys used ia a diverse array of appHcations, especially for nuclear reactors, depend on chromium for oxidation and corrosion resistance. Evaporated, amorphous, thin-film resistors based on Ni-Cr with A1 additions have the advantageous property of a near-2ero temperature coefficient of resistance (58). 

To determine moderate amounts of Cr(III) and Cr(VI) in samples that have both oxidation states present, Cr(VI) is analyzed by direct titration in one sample, and the total chromium is found in a second sample after oxidation of the Cr(III). The Cr(III) concentration is determined as the difference. Trace quantities of Cr(VI) in Cr(III) compounds can be detected and analyzed by (3)-diphenylcarbazide. Trace quantities of Cr(III) in Cr(VI) may be detected and analyzed either photometrically (102) or by ion chromatography using various modes of detection (103). 

This use amounts to about 4% of the total chromium compound consumption (209,210). 

This method is used for the determination of total chromium (Cr), cadmium (Cd), arsenic (As), nickel (Ni), manganese (Mn), beiylhum (Be), copper (Cu), zinc (Zn), lead (Pb), selenium (Se), phosphorus (P), thalhum (Tl), silver (Ag), antimony (Sb), barium (Ba), and mer-cuiy (Hg) stack emissions from stationaiy sources. This method may also be used for the determination of particulate emissions fohowing the procedures and precautions described. However, modifications to the sample recoveiy and analysis procedures described in the method for the purpose of determining particulate emissions may potentially impacl the front-half mercury determination. 

Total chromium in urine End of shift at end of workweek 30 pg/g creatinine B... 

For metal compound categories (e.g.,chromiumcompounds), report releases of only the parent metal. Forexample, a user of various inorganic chromium salts would report the total chromium released in each waste type regardless of the chemical form (e.g., as the original salts, chromium ion, oxide) and exclude any contribution to mass made by other species in the molecule. 

Chromium lignosulfonates are the biggest contributions to heavy metals in drilling fluids. Although studies have shown minimal environmental impact, substitutes exist that can result in lower chromium levels in muds. The less used chromium lignites (trivalent chromium complexes) are similar in character and performance with less chromium. Nonchromium substitutes are effective in many situations. Typical total chromium levels in muds are 100-1000 mg/1. 

The calculation of C according to (6) shows (95) that if the catalyst splitting results in the formation of catalyst pellets about 1000 A in size, then even under the most unfavorable conditions (the concentration of the active centers is equal to the total chromium content in the catalyst, 2r2 = ) the diffusional restriction on the primary particle level is negligible. 

MDHS67 Total chromium in chromium plating mists. 

Veecoutere K, Cornelis R, Mees L, and Qubvauviller Ph (1998) Certification of the contents of the chromium(IIl) and chromium(VI) species and total chromium in a lyophOised solution (CRM 544). Analyst 123 965-969. 

Soares M, Bastos M and Ferreria M (1994) Determination of Total Chromium and Chromium (IV) in Animal Feeds by Electrothermal AAS. J Anal Atom Spectrom 9 1269-1272. 

Al-Shawi, A. W. and Dahl, R., Determination of total chromium in phosphate... 

Besides providing an environment for aquatic organisms, surface water is often used as a source of drinking water. The National Primary Drinking Water Standards are based on total chromium, the limit being 0.1 mg/L.19... 

Alternatively, hexavalent chromium can be reduced, precipitated, and floated by ferrous sulfide. By applying ferrous sulfide as a flotation aid to a plating waste with an initial hexavalent chromium concentration of 130 mg/L and total chromium concentration of 155 mg/L, an effluent quality of less than 0.05 mg/L of either chromium species can be achieved if a flotation-filtration wastewater treatment system is used.15... 

Cranston and Murray [35,36] took samples in polyethylene bottles that had been pre-cleaned at 20 °C for four days with 1% distilled hydrochloric acid. Total chromium Cr(VI) + Cr(III) + Crp (Crp particulate chromium) was coprecipitated with iron (II) hydroxide, and reduced chromium Cr(III) + Crp was co-precipitated with iron (III) hydroxide. These co-precipitation steps were completed within minutes of the sample collection to minimise storage problems. The iron hydroxide precipitates were filtered through 0.4 pm Nu-cleopore filters and stored in polyethylene vials for later analysis in the laboratory. Particulate chromium was also obtained by filtering unaltered samples through 0.4 pm filters. In the laboratory the iron hydroxide co-precipitates were dissolved in 6 N distilled hydrochloric acid and analysed by flameless atomic absorption. The limit of detection of this method is about 0.1 to 0.2 nM. Precision is about 5%. 

Mullins [37] has described a procedure for determining the concentrations of dissolved chromium species in seawater. Chromium (III) and chromium (VI) separated by co-precipitation with hydrated iron (III) oxide and total chromium are determined separately by conversion to chromium (VI), extraction with ammonium pyrrolidine diethyl dithiocarbamate into methyl isobutyl ketone, and determination by AAS. The detection limit is 40 ng/1 chromium. The dissolved chromium not amenable to separation and direct extraction is calculated by difference. In waters investigated, total concentrations were relatively high (1-5 xg/l), with chromium (VI) the predominant species in all areas sampled with one exception, where organically bound chromium was the major species. 

Whereas it is desirous to utilise analytical schemes that permit elucidation of the various chromium species particularly since CrVI is acknowledged to be a toxic form of this element, it is also useful to have the capability of rapid, total chromium measurement. 

The sequestered chromium was then eluted from the column with 10.0 ml 0.2 M nitric acid. More than 93% of chromium was recovered in the first 5 ml of eluate by this method. Extraction of 80 ng spikes of Crm from 200 ml aliquots of seawater was quantitative. Neither Crm nor CrVI could be quantitatively extracted. Between 0.15 and 0.19 xg/l total chromium was found in seawater by this method compared to the accepted value of 0.184 0.016 p,g/l. 

Dubovenko et al. [180] used chemiluminescence to determine total chromium in brines. The method is based on the enhancement of the chemiluminescence by chromium in the reaction of 4-(diethylamino) phthalhydrazide with hydrogen peroxide. The detection limit is 0.025 pg/1 of chromium, and the chemiluminescence is directly proportional to chromium concentrations in the range 5 x 10 10 to 10 6 M. 

Isotope dilution gas chromatography-mass spectrometry has also been used for the determination of ppb of total chromium in seawater [181-183]. The samples were reduced to ensure Cr111 and then extracted and concentrated as tris (l,l,l-trifluoro-2,4-pentanediono) chromium (III) [(Cr(tfa)3>] into hexane. The Cr(tfa)2 mass fragments were monitored into a selected ion monitoring (SIM) mode. 

The chemiluminescence technique has been used to determine trivalent chromium in seawater. Chang et al. [187] showed Luminol techniques for determination of chromium (III) were hampered by a salt interference, mainly due to magnesium ions. Elimination of this interference is achieved by seawater dilution and utilising bromide ion chemiluminescence signal enhancement (Fig. 5.7). The chemiluminescence results were comparable with those obtained by a graphite furnace flameless atomic absorption analysis for the total chromium present in samples. The detection limit is 3.3 x 10 9 mol/1 (0.2 ppb) for seawater with a salinity of 35%, with 0.5 M bromide enhancement. 

Diphenylcarbazone and diphenylcarbazide have been widely used for the spectrophotometric determination of chromium [ 190]. Crm reacts with diphenylcarbazone whereas CrVI reacts (probably via a redox reaction combined with complexation) with diphenylcarbazide [ 191 ]. Although speciation would seem a likely prospect with such reactions, commercial diphenylcarbazone is a complex mixture of several components, including diphenylcarbazide, diphenylcarbazone, phenylsemicarbazide, and diphenylcarbadiazone, with no stoichiometric relationship between the diphenylcarbazone and diphenylcarbazide [192]. As a consequence, use of diphenylcarbazone to chelate Crm selectively also results in the sequestration of some CrVI. Total chromium can be determined with diphenylcarbazone following reduction of all chromium to Crm. 

Mugo and Orlans [197] have discussed shipboard methods for the determination of chromium (III) and total chromium in seawater by derivatisation with trifluoroacetylacetone followed by gas chromatography using an electron capture detector. 

Concentrations of total chromium and CL6 in air, water, soil, and sludge near industrial sites and sewage outfalls in the United States... 

Table 2.2 Concentrations of Total Chromium and Cr 6 in Air, Water, Soil, and Sludge near Industrial Sites and Sewage Outfalls in the United States... 

Trivalent chromium was less effective than Cr+6 in reducing fecundity of Daphnia magna 44 pg Cr+VL vs. 10 pg Cr+6/L (USEPA 1980). Annelid worms (Tubifex sp.) accumulated about 1 mg total chromium/kg whole body during exposure for 2 weeks in sediments containing 175 mg ( T+3/kg, suggesting that benthic invertebrates have only a limited ability to accumulate chromium from sediments or clays (Neff et al. 1978). 

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