Lighting colorimetry

Colorimetry, in which a sample absorbs visible light, is one example of a spectroscopic method of analysis. At the end of the nineteenth century, spectroscopy was limited to the absorption, emission, and scattering of visible, ultraviolet, and infrared electromagnetic radiation. During the twentieth century, spectroscopy has been extended to include other forms of electromagnetic radiation (photon spectroscopy), such as X-rays, microwaves, and radio waves, as well as energetic particles (particle spectroscopy), such as electrons and ions. ... 

Absorbance. Analyte measurements in clinical analyzers using Hquid reagents are most commonly performed by transmission of light, ie, by absorbance photometry or colorimetry (Fig. 3a). The Hquid to be analyzed is either held in a cuvette or passed through a flowceU having transparent walls. 

The technique somewhat resembles colorimetry with white light. An... 

The widely used technique of light spectroscopy has also been applied to the qual and quant detn of bound N in energetic materials. There are five distinct systems used colorimetry, infrared spectroscopy, polarimetry, Raman spec troscopy and ultraviolet spectroscopy... 

The measurement of absorbance of light by a dyestuff-anionic surfactant complex, which has been extracted into an organic solvent is a key feature of many methods, and Sodergren has successfully used segmented flow colorimetry for an automated version of this procedure (2 ). An alternative is the two phase titration technique, pioneered by Herring (3) which uses dimidium... 

Before the concentration could be determined through colorimetry, the student needed to know the wavelength of light that was most absorbed by the complex ion in order to set the spectrophotometer properly. The student calibrated the spectrophotometer by setting the transmittance to 100% with the FeCl3-KCl-HCl solution as a reference. The optimal wavelength was found to be 525 nm (see Figure 1). 

Colorimetry can be used to determine the concentration of coloured substances in solution. A colorimeter essentially consists of a light source, a coloured filter, a light detector and a recorder. The filter chosen is the complementary colour to the solution as this will result in the maximum absorbance. The light passes through the filter and then through the coloured solution. The difference in absorbance between the coloured solution and water is detected and noted as an absorbance value. Colorimetry uses the relationship between the intensity of the colour of the solution and the concentration. 

Colorimetry. Colorimetric methods, that is, wet chemical methods in which reagents are added to generate a light-absorbing species whose absorbance can... 

The term colorimetry comes from the fact that initial measurements in this spectral domain, well before the invention of spectrophotometers, were carried out with white light without any optical instrument. Visual comparison of the sample colour with that of a reference solution of known concentration was then performed. 

Numerous tests using strips that change colour when dipped into a medium represent current applications of colorimetry. However, the result obtained by visual examination of the reflected light is related to reflectometry more than to transmission colorimetry (see Fig. 11.18). These selective tests, which are ready to use and do not require an instrument, are complementary to established methods. Because they yield immediate results, they are useful for all sorts of semiquantitative analyses. 

Figure 11.19— Visual colorimetry. To the left, a rotating filter comparison system. By using two cells, one of which contains the sample and the other the blank, it is possible to take into account the normal coloration of the two lubes. Observation is made by comparing the transparency for a specific filter against white light. To the right, a portable reflectomeler that allows comparisons to be made without the human eye. (Reproduced by permission of Merck.)...

Nephelometry, a technique that differs from colorimetry, also uses Beer Lambert s law. This method involves the formation of a precipitate and, based on the absorbed light at a given wavelength, allows the concentration of the precursor... 

Visual colorimetry, probably the oldest analytical method, was last used by the Greeks and Romans. This method found its scientific basis in 1729 when Pierre Bouguer theorised that if a given width of glass absorbs half of the light emitted by a source then double the width will reduce the fight by one quarter its initial value . 

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... 

COLORIMETRY. A method of chemical analysis thal deals with the measurement of the light absorption by colored solutions. Since light absorption depends upon the concentraiion of a specific constituent in solution, colorimetry is frequently used by geologists to determine qualitatively the trace quantities of many elements. 

The fundamental principle of colorimetry slates that the amount of light absorbed by a given substance in solution is proportional to the intensity or incident light and to the concentration of the absorbing species. This is expressed mathematically in the Lambert-Beer law. 

Colorimeter. An instrument for routine chemical analysis. Compounds or ions which absorb light in the visible part of the spectrum (400 to 800 nanometers) or which are convertible by specific reagents to such compounds can be analyzed with a colorimeter. The instrument typically incorporates an incandescent light bulb as light source, filters to separate the spectral region, a cuvette to contain the sample solution, and a photometer. See also Colorimetry,... 

SPECTROCHEMICAL ANALYSIS (Visible). Chemical systems that exhibit a selective light absorptive capacity are colored. Hence, the terms colorimetric analysis and colorimetry often are used to designate the measurement of such systems when the objective is to determine the concentration of die constituent responsible for the color. The use of the term colorimetry in this respect is not to be confused with the use of the same term in physics where the term refers strictly to the measurement of color. See also Colorimetry. 

A strict definition of color includes (1) the object appearance that depends on light, object, and observer, and (2) the visual perception described with color names. Color is a primary attribute of appearance and it can be quantified. The measurement of color is known as colorimetry. The colorimetric principles associated with the response of the normal eye are important when reviewing color analysis. The eye-brain combination is sensitive, flexible. 

The International Commission on Illumination (CIE) International Commission on Illumination (CIE) has defined a set of standard illuminants to be used for colorimetry (International Commission on Illumination 1996). Figure 3.21 shows the CIE illuminants A, C, Z>5o, Z>55, Z>65, and D15. Illuminant A represents the power spectrum of light from a black-body radiator at approximately 2856 K. If this type of light is required for experiments, a gas-filled tungsten filament lamp that operates at a temperature of 2856 K is to be used. Illuminant Z>65 represents a phase of daylight with a correlated color temperature of approximately 6500 K. The CIE recommends to use this illuminant wherever possible. 

Whitening can be assessed either visually or instrumentally (by colorimetry). The quantities evaluated are the degree of whiteness and the tint. Special attention must be paid to the spectral distribution of the incident light in the UV and visible ranges, since this controls the fluorescent contribution of the brightener to the whiteness [171],... 

---