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Modern chemical analysis has routinely used spectrophotometry in agricultural, clinical, environmental, pharmaceutical, and quality control laboratories for over fifty years. Spectrophotometry is the study of absorption or emission of light by a chemical species | Spectrophotometry for Quantitative Analysis Spectrophotometry for Quantitative Analysis Modern chemical analysis has routinely used spectrophotometry in agricultural clinical environmental pharmaceutical and quality control laboratories for over fifty years. Spectrophotometry is the study of absorption or emission of light by a chemical species. The versatility and ease of spectrophotometry makes it a cost-effective way to analyze large numbers of samples and even provide in-line quality assurance for the manufacturing of food beverage agrochemicals and pharmaceuticals. For example this technique is routinely used in the beverage industry to monitor phosphates sugars and coloring agents in soft drinks. The Tools in the Laboratory section Spectrophotometry in Chemical Analysis found in chapter 7 of Silberberg s Chemistry The Molecular Nature of Matter and Change effectively introduces the ideas of spectrophotometry. This supplement will expand on the ideas of utilizing spectrophotometry as a tool for quantitative analysis. The basis for using spectrophotometric measurements to quantitatively analyze a lightabsorbing chemical species generically called an analyte in solution is the Beer-Lambert law A 8b where A is absorbance at a given wavelength 8 is the molar absorptivity at that wavelength formerly known as molar extinction coefficient b is the distance the light travels through the solution called the pathlength and c is the concentration of the analyte in solution. The BeerLambert law simply states that absorbance is directly proportional to the concentration of analyte in the sample. One must know A e and b to determine an unknown concentration since A c Ạ Therefore if the solution pathlength is defined by the sample compartment often called a cuvette and 8 is known measuring A for a solution allows the concentration of the absorbing species in solution to be calculated. Absorbance is measured by a spectrophotometer as illustrated in figure B7.3 in the .