[LAB2]spec.10w - Biology 05LA Winter Quarter 2010 Lab 2...

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Biology 05LA – Winter Quarter 2010 Lab 2 – page 1 LAB 2 : SPECTROPHOTOMETRY AND QUANTITATIVE DATA ANALYSIS This exercise will introduce the use of a spectrophotometer (or colorimeter) to measure a particular chemical property of many biological (and non-biological) materials. We will also learn to quantify spectrophotometric data, learn several "wet lab" techniques, and learn how to properly prepare scientific graphs. Be advised that you will be using all of these newly acquired skills in the labs of the weeks to come, so come to lab prepared to master these skills – your potential success in these future labs will be greatly enhanced if you do so. Absorption Spectra All solutions that are colored to the human eye absorb electromagnetic radiation in the visible portion of the electromagnetic spectrum (Fig. 1). The color that we perceive represents those wavelengths of light that are not absorbed by the substance, or, conversely, represents those wavelengths that are transmitted . For example, if a solution is green, it absorbs in the blue and red portions of the spectrum. If it is red, we would expect it to absorb in the green and blue portions of the spectrum. Another way of saying this is that a solution transmits light of a color complementary to that which it absorbs (Fig. 1). The absorption of certain wavelengths of electromagnetic radiation is as characteristic of a compound as is its molecular weight, solubility properties, melting point or any other intrinsic property. Thus, the absorption spectrum of a compound may be used to identify it. The fact that a compound, solution or substance is not colored does not mean that it does not absorb electromagnetic radiation. It merely means that it does not absorb visible light. However, it may absorb strongly in other regions of the spectrum. Water, for example, is colorless, but it absorbs far infrared light, a band of wave- lengths to which the human eye is insensitive. The radiation that is absorbed by water is converted to heat, and the water becomes warm. Many other compounds of biological importance absorb in non-visible regions of the electro- magnetic spectrum. Absorbance and transmittance are measured with either a colorimeter or a spectrophotometer. The instruments used in Biology 05LA are technically called colorimeters. A colorimeter is an instrument that selectively projects narrow bands of visible light upon a solution (see Fig. 2). A spectrophotometer does the same thing but also can utilize wavelengths in non-visible regions of the near ultraviolet and infrared. Both colorimeters and spectrophotometers function in the same manner. Light from a source
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Biology 05LA – Winter Quarter 2010 Lab 2 – page 2 that emits light at the required wavelength is focused upon a monochromator by a lens-like collimator. The monochromator, either a prism or diffraction grating, separates the light into its component
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This note was uploaded on 04/06/2010 for the course BIOL 5LA taught by Professor Haimo during the Spring '08 term at UC Riverside.

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[LAB2]spec.10w - Biology 05LA Winter Quarter 2010 Lab 2...

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