Chromium analysis

A. Bassimane, C. Porte and A. Delacroix, Optimisation of chromium analysis by atomic absorption without flame and interference study, Analusis, 25(5), 1997, 168-171. 

Turbid groundwater with poor clarity often produces elevated RLs for hexavalent chromium analysis by the colorimetry technique. 

Chromium analysis can be performed on the ash sample from leather or can be perfonned on the leather directly. ASTM D2807 is a method for testing chromium by leather digestion (ASTM D 2807-1998). In this method, weigh 1 g of leather to the nearest 0.0001 g and cut it into small pieces 0.5 cm in diameter. Transfer the specimen to a 250 ml flask and add sequentially 20 ml of concentrated nitric acid (HNOj), 15 ml of perchloric acid (HCIO ) and 10 ml of sulphuric acid (H. SOj. 

Separation of chromium(III) and chro-mium(VI) on a small activated neutral alumina column and elution of fractions with 4 mol HNO3 and 1.0 mol ammonia solution achieved a GFAAS detection limit of 0.01 pg L i (Sahayam 2002). A method based on selective absorption of chromiu-m(III) on a cellulose micro column at pH 11 with subsequent reduction of chro-mium(VI) for total chromium analysis produced detection limits of 1.8 ng and 5.1 ng for chromium(VI) and chromiu-m(III), respectively (Shemirani and Rajabi... 

In the past, chromium analysis of foods has not been routine, at least partially because of methodological problems such as the need to avoid stainless steel blenders and knives in sample preparation. Therefore, little is known about regional variations in chromium concentrations in foods. In one study, the mean chromium daily intake for males was 33 3 pg (range 22-48 pg), and intake for females was 25 1 pg (range 13-36 pg) (Anderson and Kozlovsky 1985). Chromium concentration of 22 well-balanced diets ranged from 8.4 to 23.7 pg per 1000 kcal, with a mean of 13.4 ... 

The equilibrium dialysis of IMC samples was made using pre-treated Spectra/pore2 membrane tubings. The samples were dialyzed at 25°C for two weeks before being analyzed for chromium to insure equilibrium. The chromium analysis was made by atomic absorption at a wavelength of 359 nm using a Perkin-Elmer Model 460 Atomic Absorption Spectrophotometer. 

This brief overview illustrates that few definitive investigations were made on exchange reactions between sample and container. Moreover, some of the reported data should be interpreted with caution. For example, in the study of Anand and Ducharme [65] on the long-term storage of serum for chromium analysis, levels in the pooled material were substantially higher than in real samples. So doubts remain as to whether the observations are representative for what happens in real practice. 

All compounds of chromium are colored the most important are the chromates of sodium and potassium and the dichromates and the potassium and ammonium chrome alums. The dichromates are used as oxidizing agents in quantitative analysis, also in tanning leather. 

Analysis of Trace or Minor Components. Minor or trace components may have a significant impact on quaHty of fats and oils (94). Metals, for example, can cataly2e the oxidative degradation of unsaturated oils which results in off-flavors, odors, and polymeri2ation. A large number of techniques such as wet chemical analysis, atomic absorption, atomic emission, and polarography are available for analysis of metals. Heavy metals, iron, copper, nickel, and chromium are elements that have received the most attention. Phosphoms may also be detectable and is a measure of phosphoHpids and phosphoms-containing acids or salts. 

The classical wet-chemical quaUtative identification of chromium is accompHshed by the intense red-violet color that develops when aqueous Cr(VI) reacts with (5)-diphenylcarba2ide under acidic conditions (95). This test is sensitive to 0.003 ppm Cr, and the reagent is also useful for quantitative analysis of trace quantities of Cr (96). Instmmental quaUtative identification is possible using inductively coupled argon plasma—atomic emission spectroscopy... 

Instrumental Quantitative Analysis. Methods such as x-ray spectroscopy, oaes, and naa do not necessarily require pretreatment of samples to soluble forms. Only reUable and verified standards are needed. Other instmmental methods that can be used to determine a wide range of chromium concentrations are atomic absorption spectroscopy (aas), flame photometry, icap-aes, and direct current plasma—atomic emission spectroscopy (dcp-aes). These methods caimot distinguish the oxidation states of chromium, and speciation at trace levels usually requires a previous wet-chemical separation. However, the instmmental methods are preferred over (3)-diphenylcarbazide for trace chromium concentrations, because of the difficulty of oxidizing very small quantities of Cr(III). 

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. 

Such significant increase of accuracy may be explained on the base of analysis of the numerical values of the theoretical correction coefficients and calculated for 1, , and for analytical pai ameter lQ.j,yipj.j,jj- Changing from lines intensities for the ratios of analytical element line intensity to the intensity of the line most effecting the result of analytical element (chromium in this case) measurement enables the decreases of the error 5 or even 10 times practically to the level of statistics of the count rate. In case of chromium the influencing elements will be titanium, tungsten or molybdenum. 

X-ray analysis of corrosion products and deposits removed from internal surfaces showed 68% iron, 12% phosphorus, 8% silicon, 3% sulfur, and 2% each of zinc, sodium, chromium, and calcium other materials made up the remainder of deposits and corrosion products. 

If a sample of polycrystalline material is rotated during the sputtering process, the individual grains will be sputtered from multiple directions and nonuniform removal of material can be prevented. This technique has been successfully used in AES analysis to characterize several materials, including metal films. Figure 9 indicates the improvement in depth resolution obtained in an AES profile of five cycles of nickel and chromium layers on silicon. Each layer is about 50 nm thick, except for a thinner nickel layer at the surface, and the total structure thickness is about 0.5 pm. There can be a problem if the surface is rough and the analysis area is small (less than 0.1-pm diameter), as is typical for AES. In this case the area of interest can rotate on and off of a specific feature and the profile will be jagged. 

In XPS, chemical information is comparatively slowly acquired in a stepwise fashion along with the depth, with alternate cycles of sputtering and analysis. Examples of profiles through oxide films on pure iron and on Fe-12Cr-lMo alloy are shown in Fig. 2.9, in which the respective contributions from the metallic and oxide components of the iron and chromium spectra have been quantified [2.10]. In these examples the oxide films were only -5 nm thick on iron and -3 nm thick on the alloy. 

Cadmium and inorganic compounds of cadmium in air (X-ray fluorescence spectroscopy) Chromium and inorganic compounds of chromium m air (atomic absorption spectrometry) Chromium and inorganic compounds of chromium m air (X-ray fluorescence spectroscopy) General methods for sampling and gravimetnc analysis of respirable and mhalable dust Carbon disulphide in air... 

Samples Analyzed by Inductively Coupled Plasma (ICP) Metals — Where two or more of the following analytes are requested on the same filter, an ICP analysis may be conducted. However, the Industrial Hygienist should specify the metals of interest in the event samples cannot be analyzed by the ICP method. A computer print-out of the following 13 analytes may be typically reported Antimony, Beryllium, Cadmium, Chromium, Cobalt, Copper, Iron, Lead, Manganese, Molybdenum, Nickel, Vanadium, Zinc. Arsenic — Lead, cadmium, copper, and iron can be analyzed on the same filter with arsenic. 

Fig.3.52 Microstructureof30< o chromium iron. Analysis total C 1-6,Si I-8, Cr 31. Etched in Murakami s reagent, total magnification x 150...

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