Vernier Software and Technology
Vernier Software & Technology
Tech Info Library

Do you have instructions on how to use a spectrophotometer to conduct the Photosynthesis lab?

Yes, we have written instructions on how to conduct the AP Biology Photosynthesis lab using DPIP with a spectrophotometer as well as a Colorimeter. The instructions have been incorporated into our Advanced Biology with Vernier lab book, but you may need to adjust your concentration of DPIP. See below.

Our spectrophotometers, such as the SpectroVis Plus, are much more sensitive than the Colorimeter to DPIP. This is because the spectrophotometer can pick out the actual lambda max (the wavelength at which the peak absorbance occurs) of the solution. With a Colorimeter you will use 635 nm as your wavelength and this is off the lambda max. The problem with higher sensitivity is that most spectrophotometers will begin to lose their linearity above an absorbance of 1.0.

You can bring the absorbance down into the linear range quite easily by diluting the stock solution of DPIP (diluting by 50% should work), but you should test your own solution to be sure. A simple test procedure is given below.

Calibrate your spectrophotometer as instructed. Next, fill a cuvette with 1 mL phosphate buffer, 1 mL dH20, and 1 mL DPIP solution. Measure the absorbance of the solution. If the absorbance is above 1.0, then dilute the stock solution of DPIP by 25%. To do this, make a new cuvette containing 1 mL phosphate buffer, 1 mL dH20, and 1 mL of new DPIP stock solution. Repeat this step until your working solution has an absorbance value below 1.0.

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