Metal analysis colorimetric methods

Nickel also is deterrnined by a volumetric method employing ethylenediaminetetraacetic acid as a titrant. Inductively coupled plasma (ICP) is preferred to determine very low nickel values (see Trace AND RESIDUE ANALYSIS). The classical gravimetric method employing dimethylglyoxime to precipitate nickel as a red complex is used as a precise analytical technique (122). A colorimetric method employing dimethylglyoxime also is available. The classical method of electro deposition is a commonly employed technique to separate nickel in the presence of other metals, notably copper (qv). It is also used to estabhsh caUbration criteria for the spectrophotometric methods. X-ray diffraction often is used to identify nickel in crystalline form. 

Fluorimetry is generally used if there is no colorimetric method sufficiently sensitive or selective for the substance to be determined. In inorganic analysis the most frequent applications are for the determination of metal ions as fluorescent organic complexes. Many of the complexes of oxine fluoresce strongly aluminium, zinc, magnesium, and gallium are sometimes determined at low concentrations by this method. Aluminium forms fluorescent complexes with the dyestuff eriochrome blue black RC (pontachrome blue black R), whilst beryllium forms a fluorescent complex with quinizarin. 

In the past, the reduction of metallic ions and certain diazotised organic compounds by hindered phenols has served as the basis for colorimetric methods of analysis [112-114],... 

The metal may he analyzed hy atomic absorption or emission spectrophotometry (at trace levels). Other techniques include X-ray diffraction, neutron activation analysis, and various colorimetric methods. Aluminum digested with nitric acid reacts with pyrocatechol violet or Eriochrome cyanide R dye to form a colored complex, the absorbance of which may be measured by a spectrophotometer at 535 nm. 

Measurement of trace metals, including nickel in seawater can be completed using an in-line system with stripping voltammetry or chronopotentiometry (van den Berg and Achterberg 1994). These methods provide rapid analysis (1-15 minutes) with little sample preparation. The detection limit of these methods for nickel was not stated. Recommended EPA methods for soil sediment, sludge, and solid waste are Methods 7520 (AAS) and 6010 (ICP-AES). Before the widespread use of AAS, colorimetric methods were employed, and a mrmber of colorimetric reagents have been used (Stoeppler 1980). 

Snell et al, "Colorimetric Methods of Analysis," vol IIA, Van Nostrand(1959), 156-87 Aluminum Alkyls were prepd in 1865 hy the action of aluminum on mercury alkyls(Refs 1 6)(see also Note below). Later they were made by the action of "electron metal (alloy of Al and Mg) on a sola of the alkyl halide in ether (Refs 2 6). The Al trialkyU are volatile liquids, violently attacked by air or water. Following are examples trimethylaluminum A1(CHS), d 0.752 at 20°/4°, mp 15.0°, bp 126. la, tri-ethyl-, Al(CaH5) d 0.837 at 20°/4°, mp -52.5°, bp 185.6a, tri-n-propyl-, Al(n-CjH,),. d 0.823 at 20°/4°, mp -107°, bp ca 250° (Refs 3,4,5 6). These three compds are inflammable in air and for this reason may be of interest as components of liquid propellants for rockets Note The prepn of a compd called "Aethyl-aluminium" was claimed by W.Hallwachs A.Schaffarik, Ann 109, 207(1859) hut it was not properly identified and its props (except that it is violently decomp by water) were not detd... 

Snell et al, "Colorimetric Methods of Analysis," vol II A, Van Nostrand(1959), 156-87 Aluminum Alkyls were prepd in 1865 by tbe action of aluminum on mercury alkyls(Refs 1 6)(see also Note below). Later they were made by the action of "electron metal (alloy of Al and Mg) on a soln of the alkyl halide in ether (Refs 2 6). The Al trialkyls are volatile liquids, violently attacked by air or water. 

Colorimetric methods are most common and widely employed in environmental wet analysis. Most anions, all metals, and many physical and aggregate properties can be determined by colorimetric technique, which is fast and cost-effective. The method may, however, be unreliable for dirty and colored samples. Often, the presence of certain substances in samples can interfere with the test. In addition, if the color formation involves a weak color such as yellow, additional confirmatory tests should be performed. Despite these drawbacks, colorimetry is often the method of choice for a number of wet analyses. 

Zinc. AAS analysis of zinc by P CAM 173 is a standard application of the method as seen in NIOSH PAT. Zinc in the divalent state has been analyzed by dithiozonate (13). This colorimetric method suffers interferences from many other dithi-zone complexing metals. Zinc is easily determined after nitric acid wet ashing with an oxidizing air-acetylene flame using the 213.9 nm analytical line and background correction. The AAS analysis for Zn is as sensitive as more complex activation or plasma techniques. 

With such a bright future in detection, it was worthy in this chapter to also remind researchers in the held of the early application of these complexes. The use of 1,2-enedithiolates to generate metal complexes for metal analysis predates the advent of modem spectroscopy. These colorimetric methods evolved to spectrometric methods as UV-vis spectrophotometers became commonplace in the 1960s. While the sensitivity of these classical methods is not that of modem analytical techniques, these methods are still important in metal analysis and are important to our understanding of this class of molecules. 

Limitations in colorimetric and atomic absorption spectrophotometric measures have prompted development of alternative methods of transition metal analysis. One example is the use of ion exchange chromatography to assess transition metals in serum and whole blood, a method developed by the company Dionex. While identification of transition metal complexes can also be made on the basis of symmetry (Laporte mle) or spin selection rule or analysis of charge transfer spectra, one of the most significant methods is on the basis of magnetism. The... 

Metal ion-imprinted polymers can be applied to the pre-concentration and the sample clean-up stages for metal ion determinations. Most elemental techniques such ICP-AES and ICP-MS suffer from the difficulties imposed by complex matrices that produce high dissolved salt concentrations. The use of imprinted resins for selective extraction of metal ions allows these methods to be used with greater flexibility and can significantly lower detection limits. The selectivity of some imprinted resins has been sufficient to allow selective and sensitive analyses of metal ions at ultra-trace levels using simpler and less expensive detection methods. By reducing the detection step to a simple colorimetric method, economy and simplicity are assured. The combination of imprinted polymer clean-up and colorimetric detection are attractive as the basis of an FIA system for the ultra-trace analysis of a specific metal or combination of metals. 

Photometry and colorimetry are used by crude oil chemists to determine the content of different metals and heteroatomic compounds in crude oil and petrochemical products. Many references on photometry and colorimetry are given at the end of this chapter. Many authors have described the successful analysis of different metals in motor fuels by photometric and colorimetric methods. The composition of additives used during fuel production can be characterized by photometric and colorimetric methods because very many additives contain metals. It is not only fuels that can be characterized by photometry and colorimetry. Lubricants, which contain metals as an important component, can be successfully determined by these methods. These methods can quickly give qualitative information on heavy metals and heteroatomic compounds such as oxygen and sulfur in crude oil. More on this topic can be found in references 76 and 77 at the end of this chapter. 

The major serum electrolytes—sodium, potassium, calcium, magnesium, chloride, and bicarbonate (CO2)—are fairly easy to determine. The metals are most readily determined by the use of fiame-spectrophotometiic or atomic absorption methods, although colorimetric methods exist for calcium and magnesium. Calcium and, less frequently, magnesium are also titrated with EDTA. Ion-selective electrodes are used for the routine analysis of sodium, potassium, and calcium. Bicarbonate is analyzed also by titration against standard acid (see Experiment 8) in addition to a manometric method. Chloride is widely determined by automatic coulometric titration with electrogenerated silver ion. 

Amin (2001) reported a colorimetric method for vitamin E in pure form and multivitamin capsules based on the reduction of tetrazolium blue to formazan derivative by vitamin E in alkaline medium. The reaction mixture was incubated at 90 2 C for 10 min and the absorbance of the reaction product was monitored at 526 nm with relative standard deviation of 0.7%-1.5%, a limit of detection 0.012 mg/E and sample throughput of approximately 6/h. The reduction of tetrazolium blue to formazan derivative requires 3 h at room temperature and the color developed was stable for 3 h. EDTA was added to sample solution for masking any metal ions during analysis. 

Analysis of zinc solutions at the purification stage before electrolysis is critical and several metals present in low concentrations are monitored carefully. Methods vary from plant to plant but are highly specific and usually capable of detecting 0.1 ppm or less. Colorimetric process-control methods are used for cobalt, antimony, and germanium, turbidimetric methods for cadmium and copper. Alternatively, cadmium, cobalt, and copper are determined polarographicaHy, arsenic and antimony by a modified Gutzeit test, and nickel with a dimethylglyoxime spot test. 

Acid-base (neutralization) reactions are only one type of many that are applicable to titrimetric analysis. There are reactions that involve the formation of a precipitate. There are reactions that involve the transfer of electrons. There are reactions, among still others, that involve the formation of a complex ion. This latter type typically involves transition metals and is often used for the qualitative and quantitative colorimetric analysis (Chapters 8 and 9) of transition metal ions, since the complex ion that forms can be analyzed according to the depth of a color that it imparts to a solution. In this section, however, we are concerned with a titrimetric analysis method in which a complex ion-forming reaction is used. 

Part—I has three chapters that exclusively deal with General Aspects of pharmaceutical analysis. Chapter 1 focuses on the pharmaceutical chemicals and their respective purity and management. Critical information with regard to description of the finished product, sampling procedures, bioavailability, identification tests, physical constants and miscellaneous characteristics, such as ash values, loss on drying, clarity and color of solution, specific tests, limit tests of metallic and non-metallic impurities, limits of moisture content, volatile and non-volatile matter and lastly residue on ignition have also been dealt with. Each section provides adequate procedural details supported by ample typical examples from the Official Compendia. Chapter 2 embraces the theory and technique of quantitative analysis with specific emphasis on volumetric analysis, volumetric apparatus, their specifications, standardization and utility. It also includes biomedical analytical chemistry, colorimetric assays, theory and assay of biochemicals, such as urea, bilirubin, cholesterol and enzymatic assays, such as alkaline phosphatase, lactate dehydrogenase, salient features of radioimmunoassay and automated methods of chemical analysis. Chapter 3 provides special emphasis on errors in pharmaceutical analysis and their statistical validation. The first aspect is related to errors in pharmaceutical analysis and embodies classification of errors, accuracy, precision and makes... 

The section Analysis starts with elemental composition of the compound. Thus the composition of any compound can be determined from its elemental analysis, particularly the metal content. For practically all metal salts, atomic absorption and emission spectrophotometric methods are favored in this text for measuring metal content. Also, some other instrumental techniques such as x-ray fluorescence, x-ray diffraction, and neutron activation analyses are suggested. Many refractory substances and also a number of salts can be characterized nondestructively by x-ray methods. Anions can be measured in aqueous solutions by ion chromatography, ion-selective electrodes, titration, and colorimetric reactions. Water of crystallization can be measured by simple gravimetry or thermogravimetric analysis. 

W.Keyser, "Colorimetric Analysis , Chapman Sc Hall, London (1957) 7)D.F.Boltz, "Colorimetric Determination of Nonmetals , Wiley (1958) 8)E.B.Sandell, "Colorimetric Determination of Traces of Metals , Wiley, NY (1959 ) 9)Tintometer Ltd "Colormetric Chemical Analytical Methods , The Author, Salisbury, England (1959) 10)Vogel, InorgAnalysis (1961) 738-837 (Colorimetric and spectrophotometric analysis description of various colorimeters) ll)Pamphlets and catalogs of A.H.Thomas,... 

A few of the elements in orange juice are present in large enough concentrations and/or have chemical characteristics which permit the use of classical analysis. Phosphate and some heavy metals like zinc and iron may be measured colorimetrically. Calcium has been measured as the oxalate, but such methods are time consuming and may require prior separation from the inevitable matrix before analysis. 

Me tals and metallic compounds are among the toxic substances most often found in workplace environments (1,2), Industrial hygienists and hygiene chemists must accurately determine the presence and amount of toxic metals and their compounds in the industrial environment. Accurate methods for the quantification of metals in biological and atmospheric samples are required for the industrial hygienist to properly evaluate the environment. Atomic absorption spectroscopy (AAS) has been the primary method of analysis for toxic metals because AAS is sensitive, specific, and rapid especially compared to colorimetric analysis. 

As described in the previous section, azophenol crown 4 (n = 1) shows a characteristic coloration only for Li+ ion among alkali metal ions. After extensive examinations in a number of solvent systems, lithium analytical conditions were determined as shown in Table 2 [18a]. The resulting reddish purple color is very stable and its absorbance is maintained for 10-90 min after developing color. The calibration curve for Li+, in other words, sensitivity is linear from 25-250 ppb. Na+ does not interfere, but K+, Rb+, Ca2+, Sr2+, Ba2+, and Mg2+ interfered in the determination with a similar coloration. This method was applied to the analysis of a commercial pharmaceutical preparation, a lithium carbonate tablet, since the Li2C03 tablet has been used for medical treatment of manic depressive illness [18 b]. On the other hand, the azophenol crown 4 (n = 1) is also useful as a reagent for colorimetric determination of Rb+ and Cs+ [19]. 

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