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CHEMISTRY 1210
Spring, 2019Kate Mazloumi
How to use the Spectronic 20
UV/Visible Spectrophotometer
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NOTE!
We have several models of Spectronic 20, so the
instrument that you use may look a bit
different, however, all have the same
components and the following general
instructions will apply.
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Plug in the instrument, then rotate the front left knob clockwise to turn on. Allow 15 minutes’ warm-up time.
APPLY POWER:
Knob in OFF position
Light is on when knob in on position
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SELECT THE WAVELENGTH
Adjust the wavelength control dial to the required setting, indicated on the wavelength scale.
You must set the W.E.B.S to catch the
result.W: Wavelength,
E: Empty, B: Blank, and S: Sample
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THE CUVETTE
Two cuvettes in a test tube rack will be found
beside each instrument.
One cuvette will be used for the “blank” while
the other will be used for the sample being
measured.
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The Cuvet te
*Every cuvette has a white line and dot that is
used to align it the same way each time in the
sample chamber.
*Never use a brush to clean a cuvette, as it
could scratch the inside of the glass causing
measurement errors.
*Rinse the cuvettes well with distilled water at
the end of the lab.
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Before you insert the cuvette into the
instrument, wipe away any fingerprints
or liquid with a clean Kimwipe!
Align the vertical mark with the mark in
the sample chamber of the instrument.
USING THE CUVETTE
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Empty compartment
With the sample compartment empty and the lid closed, adjust the power reading to 0.0% transmit tance using the left- hand knob.
ZEROING THE INSTRUMENT
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Standardize the light control: Rinse the cuvette well with the blank solution. Half fill the cuvette with the blank. Wipe the outside of the cuvette with a Kimwipe.
The blank can be distilled water or another reference liquid or solution.
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“BLANKING THE INSTRUMENT” (Adjusting to give 100% transmittance)
• Slide the cuvette gently into the sample compartment, then push it down until the bottom of the cuvette touches the bottom of the sample compartment.
• Flip the cover closed.• Adjust to 100% T using the knob on the
right-hand side at the front of the instrument.
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THE BLANK
Store the blank sample in the provided test tube rack. It will be reused throughout the experiment!
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Rinse the second cuvette three times with a small amount of the sample solution to be measured.
Fill cuvette to at least halfway with the sample.
Wipe the outside of the cuvette with a Kimwipe, then place the sample into the sample compartment.
Read and record the transmittance, estimating to one decimal place.
THE SAMPLE
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SUMMARY1- Apply power; Plug in, turn on (15 min warm up)
2- Select the desired wavelength.
3- Zero the instrument.
4- Standardize the light control.
5- Make a sample measurement. Note: step 4 must be repeated each time wavelength is changed.
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To create a calibration curve, you will be asked to prepare a numberof solutions with different known concentrations.
The transmittance of each must be measured. Dump the previoussample into the waste beaker, rinse the sample cuvette with a little ofthe new sample, then fill at least halfway. After wiping the cuvette,place it in the sample compartment and read the transmittance.
Check that the blank sample reads 100% transmittance betweenevery second sample. Adjust the right front knob if needed.
CALIBRATION CURVES
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*Reset your full WEB (in % T mode) if you change the wavelength.*Turn off the power switch and unplug the instrument. *Rinse the cuvettes well with distilled water and return them to the rack beside the instrument.
Convert transmittance to absorbance by using [2-log(%T)].
Other important points…