Chromium analytical techniques

In the 1980s, an analytical technique was developed for the study of chromium speciation in natural waters based on the atomization of electrodeposited species on graphite tubes.79 Two independent automated platforms consisting of an ultraviolet (UV) on-line unit and a chelation/preconcentration/... 

Improved analytical techniques are needed to detect the important configurational and chemical diflFerences among adsorbed films formed spontaneously from complex solutions on various substrates. Internal refiection IR does not reveal significant diflFerences in the adsorbed protein films which accumulate on variously treated Stellite 21 devices (a cobalt-chromium alloy used to make synthetic heart valve struts and seats) in some instances these devices are thrombogenic, and in others they are apparently thromboresistant (39). Yet, scanning electron microscopy reveals that arriving blood platelets can discern diflFerences in the films immediately on contact with them. 

Chromium(vi). This inorganic pollutant can be determined by a whole range of analytical techniques, e.g. FAAS, ICP-AES/MS or XRF. However, in this situation the requirement is to determine a particular oxidation state of chromium. While not mentioned specifically in the list of analytical techniques above, a method does exist for the spectrophotometric determination of hexavalent chromium based on extraction with a chelating agent (see Chapter 5 for details). 

Because hexavalent chromium is the toxic form of the metal, a number of researchers have focused on methods for distinguishing between chromium(III) and chromium(VI). Analytical techniques for chromium speciation in liquid matrices were reviewed recently (Marques etal. 2000). There are concerns about chromium as a drinking water contaminant in some areas, and samples most frequently analyzed were standard waters, potable waters and wastewaters. 

Some of the difficulties in the unbiased determination of certain trace elements in biological materials may be due to problems of speciation. The range of complex organo-metallic species that can be found in nature is very wide (Frausto da Silva and Williams, 1991). In carrying out an analysis for a particular element in any type of biological fluid or tissues, major assumptions are made concerning the precise chemical composition of element species present. Different analytical techniques will have different sensitivities towards particular element species. Much of the early understanding of the special analytical problems posed by element speciation comes from studies of arsenic (Buchet et al., 1980 Buchet et al., 1981) and mercury (Clarkson, 1983). Problems with other metals remain to be resolved and may require considerable analytical sophistication such as in the analysis of chromium speciation (Urasa and Nam, 1989). 

The life scientist interested in the concentration, distribution and speciation of chromium in biological systems is in need of reliable and precise analytical data. These can only be obtained by applying first of all a representative sampling and handling procedure, followed by the correct use of an analytical technique with suitable sensitivity. Finally, the bias of the whole method can be tested by analyzing biological standard reference materials, certified for chromium at comparable levels as the unknowns. 

Zinc has been quantitatively coprecipitated with Fe(OH)3 from solution 23-28), from river water (26, 27), and from 200 liters of seawater (28). Suzuki and Ozaki (25) used Fe(II) and Fe(III) to produce a precipitate whose filtration was facilitated by a magnetic field. Many other metals have been coprecipitated with iron(III) hydroxide, including the following lead(II) (25, 27) mercury(II) (25, 26, 29) chromium (25, 30) cadmium (25, 26) manganese(II) and or-ganomanganese (28) thallium (57) silver (52) selenium as selenite (25, 55) arsenic(III) and (V) (25, 34-39) antimony(III) (37-39) zinc(II) and or-ganozinc (28). The combination of coprecipitation with sensitive analytical techniques allows the determination of the metal content of water at the ppb and... 

FI systems have been successfully used with spec-trophotometric detection, for example, for the determination of nitrogen and phosphorus species in rivers and streams. It has also been used to determine anionic surfactants (e.g., sodium lauryl sulfate, sodium dodecyl sulfonate), chloride, and organophos-phoric insecticides in freshwater bodies. FI also can be coupled with other analytical techniques for sample introduction purposes. Such methods include FI coupled with atomic absorption spectrometry for online preconcentration and separation of chromium species and with mass spectrometry for the determination of polar organic pollutants. 

While the same basic mechanisms for passivity of pure metals also applies to alloys, the processes involved in the passivation of alloys have an added complexity. In many cases only one component of the alloy has the property of being passive in a particular environment. Alloys such as steiinless steels, which contain highly passive components (chromium in this case), owe their corrosion resistance to the surface enrichment of the passivating component Thus stainless steels resist corrosion in many acidic systems (where iron or carbon steel would be poorly passive or not passive at all) by a passivating oxide film containing Cr predominantly as Cr(III). Surface analytical techniques such as Auger electron and X-ray photoelectron spectroscopies reveal substantial enrichment of chromium in the passivating oxide film on these alloys " . There are only two ways by which this enrichment can... 

The role of alloying elements in the passivation process has been briefly discussed. Alloying additions such as chromium and molybdenum can substantially influence the structure and composition of the passive oxide film and thereby the process of passivation. The alloys discussed have been of the fairly simple binary type, where it is easier to analyze the surface oxide films by surface analytical techniques and to understand the results. This treatise provides a basis for the following discussion of stainless steels, where the number of alloy additions is increased as is the complexity of the passivation process. 

This book is written by experts from disciplines as diverse as analytical chemistry, nuclear chemistry, environmental science, molecular biology, and medicinal chemistry in order to identify potential hot spots of metallomics and metalloproteomics. The scientific fundamentals of new approaches, like isotopic techniques combined with ICP-MS/ESI-MS/MS, the synchrotron radiation-based techniques. X-ray absorption spectroscopy, X-ray diffraction, and neutron scattering, as well as their various applications, with a focus on mercury, selenium, chromium, arsenic, iron and metal-based medicines are critically reviewed, which can help to understand their impacts on human health. The book will be of particular interest to researchers in the fields of environmental and industrial chemistry, biochemistry, nutrition, toxicology, and medicine. Basically, the book has two aims. The first deals with the educational point of view. Chapters 2 to 7 provide the basic concept of each of the selected nuclear analytical techniques and should be understandable by Master and PhD students in chemistry, physics, biology and nanotechnology. The... 

Petring L, Alonso MI, Audrey D et al (2001) An evaluation of analytical techniques for determination of lead, cadmium, chromium, and mercury in food-packaging materials. Fresenius J Anal Chcm 370(1) 76-81... 

Reported concentrations of chromium in open ocean waters range from 0.07 to 0.96 xg/l with a preponderance of values near the lower limit. Methods used for the determination of chromium at this concentration have generally used some form of matrix separation and analyte concentration prior to determination [170-173], electroreduction [174,175] and ion exchange techniques [176,177]. 

The application of the Chelex 100 resin separation and preconcentration, with the direct use of the resin itself as the final sample for analysis, is an extremely useful technique. The elements demonstrated to be analytically determinable from high salinity waters are cobalt, chromium, copper, iron, manganese, molybdenum, nickel, scandium, thorium, uranium, vanadium, and zinc. The determination of chromium and vanadium by this technique offers significant advantages over methods requiring aqueous final forms, in view of their poor elution reproducibility. The removal of sodium, chloride, and bromide allows the determination of elements with short and intermediate half-lives without radiochemistry, and greatly reduces the radiation dose received by personnel. This procedure was successfully applied in a study of... 

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