4
8. Click Linear Fit,
, to see the best fit line equation for the standard
solutions.
9. If doing Beer’s law to determine the concentration of an unknown, place the
unknown sample in the cuvette holder. Choose Interpolation Calculator from
the Analyze menu. A helper box will appear, displaying the absorbance and
concentration of the unknown. Click
.
Measurement
vs.
Time (Kinetics)
1. Generate a spectrum as described above.
2. Click the Configure Spectrophotometer Data Collection button,
.
3. Select Absorbance
vs.
Time as the data-collection mode. The wavelength of
maximum absorbance will be selected. Click
to continue or click
and select a wavelength on the graph or in the list of
wavelengths. See the previous section for more details.
4. The default settings are 1 sample per second for 200 seconds. To change the
data-collection parameters for your experiment, choose Data Collection from
the Experiment menu and make the necessary changes. Click
.
5. Mix the reactants. Transfer ~2 mL of the reaction mixture to a cuvette and
place the cuvette in the Spectrophotometer. Click
. Click
if
you wish to end data collection early.
6. Click Curve Fit,
, to calculate a function for your data.
Measure Emission Spectra with a Computer
You may use your Spectrophotometer to measure the emission spectrum of a
light source such as an LED or a gas discharge tube. To do so, you will need to
purchase the Vernier Optical Fiber (order code: VSP-FIBER).
Note:
For best
results observing emission spectra, consider the Vernier Emission Spectrometer
(order code: VSP-EM).
Measure Intensity of Light Emissions
1. Insert the Vernier Optical Fiber into Go Direct SpectroVis Plus.
2. Choose Change Units ► Spectrophotometer ► Intensity from the
Experiment menu. Intensity is a relative measure with a range of 0–1.
Note:
The Spectrophotometer is not calibrated for measuring intensity.
3. Aim the tip of the optical fiber cable at a light source. Click
. Click
to end data collection.
If the spectrum maxes out (flat and wide peaks at a value of 1), increase the
distance between the light source and the tip of the optical fiber cable or reduce
the sample time (see Change the Settings in Logger
Pro
).
To adjust the sample time, choose Set Up Sensors ► Spectrophotometer: 1 from
the Experiment menu. Set the Sample Time to a suitable value. This value can
be adjusted during data collection.
Use the Stored Emissions Files in Logger
Pro
Logger
Pro
contains a folder of emissions graphs from selected discharge tubes,
including: argon, helium, hydrogen, mercury, oxygen, sodium, and xenon. You
Configure Spectrometer data-collection dialog box
3. Select Absorbance (or %T)
vs.
Concentration as the data-collection mode.
The wavelength with the maximum value from the spectrum (λ max) will be
automatically selected. There are three options when choosing a wavelength
(or wavelengths) for subsequent measurements.
l
Option 1
The default option is to use a single 10 nm band. This
measures the average absorbance from ~5 nm on either side of the chosen
wavelength. You can change the center wavelength value by clicking on
the graph or by choosing a wavelength from the list.
l
Option 2
If you wish to use the λ max chosen by Logger
Pro
, but you
want the absorbance to be measured only at that one wavelength, change
Single 10 nm Band to Individual Wavelengths. You may then select up
to ten wavelengths to measure at the same time.
l
Option 3
If you wish to measure an average over a range of contiguous
wavelengths of your choice, change Single 10 nm Band to Individual
Wavelengths. Click
. Select boxes in the list or drag your
cursor on the graph to select up to ten contiguous wavelengths. Check
Combine Contiguous Wavelengths.
4. Click
to continue.
5. Click
. Place your first sample in the cuvette slot of the
Spectrophotometer. After the readings stabilize, click
. Enter the
concentration of the sample and click
.
6. Place your second sample in the cuvette slot. After the readings stabilize,
click
. Enter the concentration of the second sample and click
.
7. Repeat Step 6 for the remaining samples. When finished, click
to
end data collection.
