N Bausch and Lomb Spectronic 20 Spectrophotometer

The zero absorbance adjustment, made with the cuvette or the indexed reference test tube in the sample holder, must be checked each time the wavelength is changed. In addition, during operation at a fixed wavelength for extended periods of time, both the infinite absorbance adjustment, made with nothing in the sample holder, and the zero absorbance adjustment, made with the cuvette or the indexed reference test tube in the sample holder, must be checked periodically. 

An absorbance measurement of a sample is obtained as follows. Rinse a clean cuvette or the indexed sample test tube with distilled water and then with several milliliters of sample solution. Half fill the cuvette or the test tube with sample solution, and make certain that the solution is free of bubbles and that the exterior surface of the cuvette or the test tube is wiped clean with a tissue. Then insert the cuvette or the test tube carefully into the sample holder, and close the door. Read the absorbance of that solution directly from the meter. Then remove the cuvette or the test tube from the sample holder, and rinse the cuvette or the test tube with distilled water so that it is ready to receive the next sample. Repeat the above procedure until all absorbance readings at a given wavelength have been obtained. 

If nobody else will use the instrument during your laboratory period, turn OFF the instrument by rotating the amplifier control counterclockwise past a click, and unplug the power cord. 

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