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This article was co-written by Bess Ruff, MA. Bess Ruff is a graduate student in geography at Florida. She received her Master’s degree in Environmental Science and Management from the Bren School of Environmental Science & Management, UC Santa Barbara in 2016. She has conducted survey work for marine spatial planning projects in the coastal area. Caribbean and support research as a contributor to the Sustainable Fisheries Group.
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Absorbance mp, also known as molecular extinction factor, is a measure of how well a chemical absorbs optically at a given wavelength of light. It allows you to compare compounds with each other without taking into account differences in concentration or solution thickness during measurement. [1] X Research Source The absorbance mp is commonly used in chemistry, and should not be confused with the more commonly used extinction factor in physics. The standard unit of absorbance mp is liters per mp centimeter (L mp -1 cm -1 ). [2] X Research Source
Steps
Calculate the absorption coefficient mp using the formula
- Absorbance can be calculated as the ratio between the incident light intensity and the emergent light intensity. We have the formula A = log 10 (I o /I) . [4] X Research Sources
- The intensity of the light is measured by a spectrophotometer.
- The absorbance of the solution will change with the wavelength of light passing through the solution. Some wavelengths will be absorbed more than others, depending on the composition of the solution. Remember to write down the wavelength you are using for the calculation. [5] X Research Sources
- The absorbance between measurements may vary due to the concentration of the solution and the shape of the vessel used to measure the intensity. The absorbance mp will compensate for these errors. [6] X Research Source
- Prepare a solution of known concentration c for analysis. The unit of concentration is mp/liter. [7] X Research Sources
- To find l , we measure the thickness of the cuvette. The unit of transmitted thickness is centimeters.
- Using a spectrophotometer measure the absorbance A at a given wavelength. The unit of wavelength is the meter, but most wavelengths are so small that nanometers (nm) are used. [8] X Research Source Absorbance is a dimensionless quantity.
- Example: Using a cuvette thickness of 1 cm, measure the absorbance of a solution with a concentration of 0.05 mp/L. The absorbance at 280 nm is 1.5. Calculate the absorbance mp of the solution?
- 280 = A/lc = 1.5/(1 x 0.05) = 30 L mp -1 cm -1
Calculate the absorbance mp using the standard curve method
- Draw a straight line through each point. If the measured values are correct, the points will form a straight line showing that the absorbance and concentration are directly proportional to Beer’s law. [10] X Research Source
- The slope equation of the line is (Y 2 – Y 1 )/(X 2 – X 1 ). The higher point on the line is denoted by a small 2 below, and the lower point is denoted by 1.
- Example: The absorbance of a solution with concentrations of 0.2 mp and 0.3 mp is 0.27 and 0.41, respectively. The absorbance is the Y value while the concentration is the X value. Use the straight-line equation (Y 2 – Y 1 )/(X 2 – X 1 ) = (0.41-0.27)/(0) ,3-0.2) = 0.14/0.1 = 1.4 is the slope of the line.
- Continuing with the above example: If the slope of the line is 1.4 and the transmission thickness is 0.5 cm, the absorbance mp is 1.4/0.5 = 2.8 L mp -1 cm -1 .
This article was co-written by Bess Ruff, MA. Bess Ruff is a graduate student in geography at Florida. She received her Master’s degree in Environmental Science and Management from the Bren School of Environmental Science & Management, UC Santa Barbara in 2016. She has conducted survey work for marine spatial planning projects in the coastal area. Caribbean and support research as a contributor to the Sustainable Fisheries Group.
This article has been viewed 46,248 times.
Absorbance mp, also known as molecular extinction factor, is a measure of how well a chemical absorbs optically at a given wavelength of light. It allows you to compare compounds with each other without taking into account differences in concentration or solution thickness during measurement. [1] X Research Source The absorbance mp is commonly used in chemistry, and should not be confused with the more commonly used extinction factor in physics. The standard unit of absorbance mp is liters per mp centimeter (L mp -1 cm -1 ). [2] X Research Source
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