Spectrophotometer(2)

Prof.Dr. Moustafa M. Mohamed

Spectrophotometer

•The spectrophotometer measures light absorption by a liquid substance at various

wavelengths.

•The components of an unknown material can be determined or the concentration of a

number of known substances can be measured.

•A monochrometer uses a diffraction grating or prism to disperse the light from the lamp (slit S1).

•The light is broken into its spectral components as it arises from slit S2 and falls on the sample in the

cuvette,•The angle of the diffraction grating determines light

wavelength.•The mirror reduces equipment size.•

•light output, photodetector sensitivity, and sample substance absorbance changes with

wavelength, and this necessitates zero calibration for each wavelength measurement.

•The double-beam spectrophotometer accomplishes this automatically by beam path

switching (sample to reference) via a mechanical shutter or rotating mirror.

Maintenance

• Maintenance includes:• Calibration adjustment and

replacement of light source bulbs and photo detectors.

• Mechanically rotating assembles (mirrors, diffraction grating) will occasionally malfunction.

• The electronics is very reliable.

General Operating Instructions

Turn on Spectrophotometer

•Turn the Power Switch Clockwise

• Allow the spectrophotometer to warm up for at least fifteen minutes to stabilize the source and detector before proceeding.

Set the Display Mode to TRANSMITTANCE

•Press the MODE CONTROL

•Until the LED beside TRANSMITTANCE is lit

Adjust the display to 0% TRANSMITTANCE

•With the Zero Control Knob.

Set the desired WAVELENGTH•By Adjusting the Wavelength

Control

Prepare Blank

•Fill clean cell with solvent and wipe the cell with a tissue to remove liquid droplets, dust, and finger prints.

•Place the cell firmly into the sample compartment, aligning the guide mark on the cell with the guide mark at the front of the

sample compartment.

Adjust Transmittance to 100%

•Close the sample compartment Lid

•Adjust the Transmittance knob until the display reads 100.

Check Absorbance•Press Mode Control Switch

until LED besides ABSORBANCE is lit.•The display should read 0.000.

The machine response changes EVERYTIME you change the

WAVELENGTH

You must reset the 100% Transmittance EVERYTIME you

change the WAVELENGTH

Making Sample Measurements

•Rinse the sample cell twice with a small amount of solution.

•Wipe cell with tissue and place in the sample compartment.

Read the Absorbance

•Align the guide marks and close the lid.

•Read the absorbance on the display.•Remove the cell from sample compartment.

If you must change the WAVELENGTH, you must

reset the BLANK ABSORBANCE at the new

wavelength

Can You Identify the Parts?

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