Analytical techniques colorimetry

Methods for iodine deterrnination in foods using colorimetry (95,96), ion-selective electrodes (94,97), micro acid digestion methods (98), and gas chromatography (99) suffer some limitations such as potential interferences, possibHity of contamination, and loss during analysis. More recendy neutron activation analysis, which is probably the most sensitive analytical technique for determining iodine, has also been used (100—102). 

Colorimetry, See Analytical techniques Combustion chemistry, 40 products, 41, 42, 502 spontaueous, 18, 41, 43, 214, 216 Communicatious, 427, 428 Compound specific analyzers, 311 Compressed gases colour coding, 271 construction materials, 266 first aid measures, 280 hazards, 265 precautions, 272, 403... 

Of course, not all dissolved ions produce colored solutions, and therefore not all ions in solution can be quantified by colorimetry. Noncolored solutions can sometimes, however, be converted to colored solutions by introducing chromophore species which complex with (i.e., attach themselves to) the target ion to produce a colored solution, which may then be measured by UV/visible colorimetry. An important archaeological example of this is the determination of phosphorus in solution (which is colorless) by com-plexation with a molybdenum compound, which gives a blue solution (see below). The term colorimetry applies strictly only to analytical techniques which use the visible region of the spectrum, whereas spectrophotometry may be applied over a wider range of the electromagnetic spectrum. 

The yield for a low-mass sample, e.g., 1 mg or less for alpha-particle measurement, can be determined with nonisotopic carrier in an aliquot taken before preparing the counting source. The analytical technique can be instrumental, such as colorimetry or atomic absorption spectrometry. Subsequent source preparation, by precipitation, evaporation, or electrodeposition, must be quantitative or highly reproducible so that a reliable yield value for this final step can be included in the total yield. 

The chemical characterization of soils and soil components include a number of methods, ranging from simple measurements such as pH or electrical conductivity to elemental analysis after total dissolution by digestion with HNO3/HCI/HF (Sparks 1996). Table 7.8 summarizes the most important analysis methods for elements of interest in soils. Many of these methods have been covered in previous sections. Some of them (e.g., chromatography, colorimetry) are common, well-known analytical techniques (Skoog et al. 2004 Harris 2010). 

There are many analytical techniques which may be used for lead analysis. These include X-ray fluorescence (XRF) spectroscopy, radioactivation methods, emission spectrography, ring oven methods, polarographic techniques [including anodic stripping voltammetry (ASV)], spark source mass spectrometry, colorimetry and atomic absorption spectrometry (AAS). Background information upon all of these methods may be found in the Handbook of Air Pollution Analysis [1]. 

Various analytical techniques such as spectrophotometry/colorimetry, FL and infrared spectrometry, voltammetry, thin-layer chromatography (TLC), gas chromatography (GC), and HPLC based on ultraviolet, diode array, or fluorometric detectors have been reported in the literature for analysis of vitamin E. Various critical and comprehensive reviews are available on vitamin E quantification in food and clinical samples (Ball, 1988, 1998 Lumley, 1993). The AOAC International Official Methods of Analysis (1995) provides several methods based on older, chemical approaches. The applications of these analytical techniques are briefly summarized below. 

The analytic principles that have been applied to accumulate air quality data are colorimetry, amperometry, chemiluminescence, and ultraviolet absorption. Calorimetric and amperometric continuous analyzers that use wet chemical techniques (reagent solutions) have been in use as ambient-air monitors for many years. Chemiluminescent analyzers, which measure the amount of chemiluminescence produced when ozone reacts with a gas or solid, were developed to provide a specific and sensitive analysis for ozone and have also been field-tested. Ultraviolet-absorption analyzers are based on a physical detection principle, the absorption of ultraviolet radiation by a substance. They do not use chemical reagents, gases, or solids in their operation and have only recently been field-tested. Ultraviolet-absorption analyzers are ideal as transfer standards, but, as discussed earlier, they have limitations as air monitors, because aerosols, mercury vapor, and some hydrocarbons could, interfere with the accuracy of ozone measurements made in polluted air. 

Spectrophotometry is any technique that uses light to measure chemical concentrations. A procedure based on absorption of visible light is called colorimetry. The most-cited article in the journal Analytical Chemistry from 1945 to 1999 describes a colorimetric method by which biochemists measure sugars.4... 

Wet chemical methods involve sophisticated sample preparation and standardization with National Bureau of Standards reference materials but are not difficult for the analytical chemist nor necessarily time consuming (Figure 1). The time from sample preparation to final results for various analytical methods, such as GFAA (graphite furnace atomic absorption), ICP (inductively coupled plasma spectroscopy), ICP-MS (ICP-mass spectrometry), and colorimetry, ranges from 0.5 to 5.0 h, depending on the technique used. Colorimetry is the method of choice because of its extreme accuracy. Typical results of the colorimetric analysis of doped oxides are shown in Tables I and II, which show the accuracy and precision of the measurements. 

Introduction. Metal indicators are organic molecules which form specifically colored soluble complexes with metal ions in aqueous media. Here, the color of the complexes and of the free indicator must be different. These reactions can be used in two analytical procedures volumetry (complexometry) and colorimetry/ photometry. In both methods, the concentration of metal ions is determined, but with different techniques. 

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