Colorimetry (chemical method)

<h2 id="absorption-colorimeter">Absorption colorimeter</h2>
<p>A <a href="/facts/Colorimeter_(chemistry)/AfqldtCV">colorimeter</a> is a device used to test the concentration of a solution by measuring its absorbance of a specific wavelength of light. To use this device, different <a href="/facts/Solution_(chemistry)/MGchhMQV">solutions</a> must be made, and a control (usually a mixture of <a href="/facts/Distilled_water/AkXShA73">distilled water</a> and another solution) is first filled into a <a href="/facts/Cuvette/SpAJp2Nx">cuvette</a> and placed inside a colorimeter to calibrate the machine. Only after the device has been calibrated you can use it to find the densities and/or concentrations of the other solutions. You do this by repeating the calibration, except with cuvettes filled with the other solutions. 
The filter on a colorimeter must be set to red if the liquid is blue. The size of the filter initially chosen for the colorimeter is extremely important, as the wavelength of light that is transmitted by the colorimeter has to be same as that absorbed by the substance.
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<h2 id="colorimetric-assays">Colorimetric assays</h2>
<p class="note">Main article: <a href="/facts/Colorimetric_analysis/yQrX0oYc">Colorimetric analysis</a></p>
<p>Colorimetric assays use reagents that undergo a measurable color change in the presence of the <a href="/facts/Analyte/qWzKoY8L">analyte</a>. They are widely used in biochemistry to test for the presence of enzymes, specific compounds, antibodies, hormones and many more analytes. For example, 
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<ul><li><a href="/facts/Para-Nitrophenylphosphate/8JLt967z">para-Nitrophenylphosphate</a> is converted into a yellow product by <a href="/facts/Alkaline_phosphatase/awQHo7F1">alkaline phosphatase</a> enzyme.</li>
<li><a href="/facts/Coomassie_Blue/MG1azW3G">Coomassie Blue</a> is an aromatic dye that binds to aromatic proteins and positively charged amino acid residues within the protein structure.<a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a> The binding interaction results in a spectrum shift, enabling quantitative measurement of the protein concentration. A similar colorimetric assay, the <a href="/facts/Bicinchoninic_acid_assay/BF9K723d">Bicinchoninic acid assay</a>, uses a chemical reaction to determine protein concentration.</li>
<li>The Biuret assay utilizes a biuret reagent which turns purple in the presence of proteins due to the chelation of copper salts in an alkaline solution.<a class="footnote-ref" id="fnref:4" href="#fn:4"><sup>4</sup></a></li>
<li><a href="/facts/ELISA/8yvpYDtH">Enzyme linked immunoassays</a> use enzyme-complexed-antibodies to detect antigens. Binding of the antibody is often inferred from the color change of reagents such as <a href="/facts/3%2c3%2527%2c5%2c5%2527-Tetramethylbenzidine/c8dytBT0">TMB</a>.</li></ul>
<h2 id="see-also">See also</h2>
<ul><li><a href="/facts/Jules_Duboscq/4Hqg1BP6">Jules Duboscq</a></li>
<li><a href="/facts/Permanganometry/YrbKUT2Q">Permanganometry</a></li>
<li><a href="/facts/Lovibond_comparator/ldpk80aw">Lovibond colorimeter</a></li>
<li><a href="/facts/Turbidimetry/58Go49Ff">Turbidimetry</a></li></ul>

<h2 id="references">References</h2>

<ol>
<li id="fn:1"><p>Housecroft, Catherine; Constable, Edwin (2006). Chemistry: an introduction to organic, inorganic, and physical chemistry. Pearson Education. pp. 349–353. ISBN 978-0-13-127567-6. <a href="978-0-13-127567-6" target="_blank">978-0-13-127567-6</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li>
<li id="fn:2"><p>Louis Rosenfeld (1999). Four centuries of clinical chemistry. CRC Press. pp. 255–258. ISBN 978-90-5699-645-1. <a href="978-90-5699-645-1" target="_blank">978-90-5699-645-1</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li>
<li id="fn:3"><p>Astrof, Nathan S.; Horowitz, Gail (July 10, 2018). "Protein Colorimetry Experiments That Incorporate Intentional Discrepancies and Historical Narratives". Journal of Chemical Education. 95 (7): 1198–1204. doi:10.1021/acs.jchemed.7b00633. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li>
<li id="fn:4"><p>Bianchi-Bosisio, A. (2005). "PROTEINS | Physiological Samples". Encyclopedia of Analytical Science. pp. 357–375. doi:10.1016/B0-12-369397-7/00494-5. ISBN 978-0-12-369397-6. <a href="978-0-12-369397-6" target="_blank">978-0-12-369397-6</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li>
</ol>

Colorimetry (chemical method) open-in-new

Colorimetry (chemical method)