# colorimetry

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Related to Colourimetry: spectrophotometry, colorimetry

## colorimetry

[‚kəl·ə′rim·ə·trē]
(optics)
Any technique by which an unknown color is evaluated in terms of standard colors; the technique may be visual, photoelectric, or indirect by means of spectrophotometry; used in chemistry and physics.

## Colorimetry

(1) In analytical chemistry, colorimetry is a group of photometric methods of quantitative analysis based on the determination of the concentration of substances in a colored solution by measuring the amount of light absorbed by the solution. The amount of light absorbed, the thickness of the layer of solution, and the concentration of the solution are related by a formula that obeys the Bouguer-Lambert-Beer law:

(1) I = Io · e-kcl

where I is the intensity of light after passing through the absorbing medium, Io is the intensity of the incident light, l is the thickness of the layer of solution (in cm), c is the concentration of the absorbing substance (in moles per liter), and K is a constant for light of a particular wavelength. After the logarithm is taken, equation (1) takes the form

(2) In (Io/I) = Kcl = D

where D is the optical density of the solution. It follows from equation (2) that D is directly proportional to the concentration of the substance in the solution.

A distinction is made between subjective (visual) and objective (photocolorimetric) methods of colorimetry. In visual methods, the optical density is determined by comparing the color of the solution being studied with the colors of a series of standard solutions, as well as by using visual colorimeters. In objective methods, photoelectric colorimeters are used.

(2) In physics, colorimetry is the methodology of measuring and expressing color in quantitative terms, and also the set of such methods.

## colorimetry

The science of measuring color. The International Commission on Illumination (Commission Internationale de l'Eclairage) governs this subject along with all aspects of lighting and illumination. See CIE Lab and colorimeter.
References in periodicals archive ?
Soil organic matter (OM; determined by oil bath-K2Cr207 titration), available nitrogen (AvN; measured by alkali-diffusion), available phosphorus (AvP; extracted by NaHCO-extraction, ammonium molybdate-tartaric emetic-ascorbic acid colourimetry) and available potassium (AvK; measured by atomic absorption spectrophotometer) were analysed in the study.
Samples were filtered through Whatman 41 papers and subsamples taken for analysis of inorganic P, organic P, and total P by molybdate colourimetry (Tiessen and Moir 1993).
Contents of [Ca.sup.2+] and [Mg.sup.2+] were determined by titration with 0.0125 m EDTA solution, Na and K by flame photometry, P by colourimetry, and [Al.sup.3+] and H + Al by titration with 0.025 M NaOH.
Ammonium nitrogen (N[H.sub.4]-N) was determined by indophenol blue colourimetry via flow injection analysis on a Lachat Instruments autoanalyser (NWASCO 1982).
Ammonium and nitrate concentrations in extract were measured by the indophenol-blue and phenol disulfonic acid colourimetry (Wang et al.
Inorganic P in each fraction was determined following neutralisation and automated molybdate colourimetry (Turner and Romero 2009).
Total P in the solution was determined using ascorbic acid-N[H.sub.4]-molybdate blue colourimetry at 700nm (Wang et al.
In summary, the orthophosphate in samples was extracted, after shaking for 16 h, in a 1 : 100 soil : solution of 0.5 M sodium bicarbonate buffered at pH 8.5, and the filtered extract was quantified for orthophosphate by automated colourimetry.
Mineral N was periodically extracted from soil by shaking for 4 h with 100mL of 0.5M KCI and centrifuging; it was analysed by continuous flow colourimetry (AutoAnalyzer 3, Bran Luebbe, France).
Phosphorus concentration was measured by sodium bicarbonate extraction and molybdate blue colourimetry (Colwell 1963).
Total phosphorus (P) content was determined by phosphor molybdenum-blue colourimetry after digesting soil with perchloric acid.
Soil OM was determined by colourimetry, using a solution of 0.2 mol/L of NaOH + 0.01 mol/L of ethylene diamine-tetra acetic acid (EDTA)+ 2% carbinol to extract.

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