Instructions for using the Spectronic 20

1.Connect the Spectronic 20 to an electrical outlet.

Most spectrophotometers need to warm up for about 20 minutes before use.

Turn on the instrument by rotating the power-zero control knob clockwise - (see the figure).

Turn the wavelength control knob to the appropriate wavelength:

• For the spectroscopy/pipetting experiment use 510 nm
• if you are measuring bacterial growth use 600 nm). Wait about 20 minutes.

2. With the sample holder empty and closed rotate the power-zero control knob until the needle on the galvanometer reads: 0% Transmittance.

(To read the dial accurately move your head until the needle is at eye level and directly in front of its mirrored reflection).

You have now "zeroed" the spectrophotometer.

3. Align the index lines of the sample holder and a cuvette containing your "blank" solution:

• plain water in the spectroscopy/pipetting experiment
• uninoculated medium if you are going to measure bacterial growth

4. Insert the cuvette and close the lid of the sample holder.

5. Rotate the light control knob until the needle on the galvanometer reads: 100% Transmittance. You have now "standardized" the spectrophotometer.

6. Repeat steps 2 through 4 until the readngs remain consistent, then start reading the absorbance and the % Transmittance of your samples.

• Don't adjust any knobs when you read your samples!

After measuring a few samples, repeat steps 2 through 4 again. The Spectronic 20 is more accurate when it is frequently zeroed and standardized.