Where thought meets action CHEMISTRY 1210 Spring, 2019 Kate Mazloumi How to use the Spectronic 20 UV/Visible Spectrophotometer
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Where thought meets action
CHEMISTRY 1210
Spring, 2019Kate Mazloumi
How to use the Spectronic 20
UV/Visible Spectrophotometer
Where thought meets action
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.
Where thought meets action
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…
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