1. Turn on OD absorbance spectrometer. If using UV wavelength, turn on UV source and wait 5-10 minutes for the UV source to stabilize. UV bulbs have short life time, avoid leaving it on for a long time before or after the experiment.

2. Plastic cuvette may be used for measurements in the visible range, quartz cuvette must be used for UV reading, since plastic cuvettes are not UV transparent.

3. Rinse the measurement cuvettes with dH2O.

4. Dilute your sample and standards to the linear range of your measurements (e.g., the reading should be within 0.1-2).

5. Adjust the wavelength.

6. Place in a blank (cuvette filled with the buffer your sample is dissolved in). Don't use an empty cuvette.

7. When the reading has stabilized, zero the spectrometer, i.e., the OD reading for the blank should be 0.

8. Remove the blank and place in the sample.

9. Record the reading when it has stabilized.

10. Continue for multiple samples. It is not necessary to zero the spectrometer for every sample as long as the buffer for all the samples is the same.

11. Plastic disposable cuvettes may be disposed. Otherwise, rinse the cuvette with water and/or 70% ethanol. Quartz cuvette may be stored inverted or soaked in a NaOH solution.

12. Turn off the UV source and the spectrometer.

13. Calibration of spectrometer may be required periodically.