Our labs are equipped with GeneSys 20 spectrophotometers. Programming is very simple and is accomplished with a few buttons, as shown in the figure below. In our labs, we will be using the instruments in absorbance (A) mode, rather than the transmittance (T) or concentration (C) modes.
1. Calibrate the spectrophotometer. The spectrophotometer has a diagnostic program that needs to run before you start your measurements. Before turning on the spectrophotometer, check that the cuvette holder is empty and close the lid. Turn on the power to the spectrophotometer and wait until the diagnostics are complete. Keep the door closed. The progress of the diagnostics can be monitored on the instrument panel.
2. The spectrophotometer should be in absorbance mode, its default setting. Adjust the wave- length to the proper value (590 nm) using the arrow keys.
3. Prepare a cuvette containing deionized water to serve as a blank. Insert the cuvette into the cuvette holder. Be sure the cuvette is oriented correctly in the light path. The light path in the GeneSys 20 is from front to the back of the instrument. Close the lid.
Press the 0 Abs/100% T key. This will zero the instrument. Remove this cuvette. Save this blank for others to use.
Place a cuvette containing your sample into the cuvette holder. Read the absorbance values and record them in your notebook.
Repeat step 5 with all of your samples, recording the absorbance readings in your notebook.