in this lab you will review how to use the spectrophotometer with a spectrophotometer one can measure how much light of a particular wavelength(color) is absorbed by a solution the light is absorbed by a particular molecule of in terest in the solution freqently that molecule is produced or used up in a chemical reaction proceeds when we measuree these changes we measure the rate of a reaction as it occurscerectrophtain dyes interact with virtually all proteins to yield a protein-dye conjugate that absorbs light differently than the dys alone(there is a significant increase in the light absorption)this chhange in absorption can be quantified with a spectrotometer and is the basis of an indirect measure of the amount of protein in a sample in this procedure protein containing solutions will be exposed to a dye molecule called coomassie blue g-250 the interaction of coomassie blue g-250 with protein molecules produces an intensely blue complex
we use special cuvettes to hold samples of interest in the spectrophotometer cuvettes are made of thin uniform glass or plastic that is highly transparent to light at wavelengths used (some wavelengths such as those in the ultraviolet region (200 to 300 nm) require cuvettes made of other materials such as quartz) since cuvettes can be very expensive all cuvettes should be handled very carefully so they are not scratched or broken do not put anything sharp or hard into a cuvette when you use them always position them such that the light passes through the optical windows and not the sides of the cuvette intended for your fingers rinse your cuvettes with distilled water immediately after use to prevent materials from drying onto the inner surfaces
to use the spectrophotometer follow the detailed instructions found at: http://bio.winona.edu/berg/307s06/Labs/documents/Genesys6.doc. Solutions that are visibly blue (such as the Solutions containing coomassie blue g-250 and dissolved proteins ) absord red light so you should set the spectrophotometer to provide a measuring beam of red light red light has wavelengths ranging from about 600 to about 700 nm for the maximum sensitivity a wavelength at the absorption maximum is normally chosen red solutions absorb blue light blue light has shorter wavelengths(around 400 to 450 nm) than red light so to measure a red solution it is necessary to set the spectrophotometer to produce a blue measuring beam