Vernier Spectrometer
The
Vernier Spectrometer is a visible light
spectrophotometer, which can be used to do the
following:
- Perform
a
continuous spectrum analysis of a liquid sample.
- Analyze
a
set of samples of varying
concentration at a selected wavelength, as in conducting a
Beer’s law
lab.
-
Measure the
absorbance of a reaction at a
selected wavelength over time, to conduct studies of reaction kinetics.
- Measure
emissions from a gas discharge tube, LED, or other source of light.
Setup and Calibration
- Connect the Vernier/Ocean Optics Spectrometer
to
computer
via USB cable.
- Start
Logger Pro.
- To
calibrate the device, open the Experiment menu and select Calibrate
→
Spectrometer. Prepare a blank cuvette
with the
solvent for your experiment.
- The
calibration dialog box will display the message: “Waiting
…seconds for
the lamp
to warm up.” The
minimum warm up time is one minute. You
may
wait longer than one minute, which will add a slight measure of
precision to
the calibration.

When
the warm up time is reached, insert a blank cuvette in the cuvette
holder. Click
the button “Finish Calibration,” wait for a few
seconds for the
calibration to
be completed, and then click OK.
Measuring the absorbance
spectrum of a
sample
(Absorbance
vs. Wavelength)
- Place
the cuvette containing your sample in the cuvette holder of the Spectrometer.
- Click
.
The absorbance spectrum
will be
displayed and updated continuously.
- If
you wish to adjust the display so that the peak absorbance is slightly
less
than 1.00, open the Experiment menu and select Set Up Sensors
→ Show
All
Interfaces. Increase or decrease the value in the Sample Time box
as needed, and close the dialog box.
- Click
to
halt the data collection.
- (optional)
Autoscale or manually rescale the graph.
- (optional)
To save the graph, select Store Latest Run from the Experiment menu. If
you proceed directly to another type of data collection, a prompt will
appear
at some point asking if you want to save the previous run.
Conducting a
Beer’s law experiment
(Absorbance vs.
Concentration)
- Place
a
cuvette of a standard in the
Spectrometer. Click on the Configure Spectrometer Data
Collection icon,
,
located on the
right hand side of
the toolbar.
- The configuration dialog box will appear.

- Click the circle next to “Abs vs.
Concentration” to select it, and the peak
wavelength
(maximum absorbance) has been selected automatically. You may select as
many
additional wavelengths as you wish. Note that there is an option,
beneath the
graph, to select a band of wavelengths and plot the absorbance readings
as a
single value. To select another wavelength:
- Check
the box next to the wavelength.
- Or,
click on the graph in the dialog box in the desired location on the
plot. A
small box will be placed on the graph as a marker.
- Click OK. Two graphs are now
displayed on the
main screen.
- Place
your first standard solution, for the Beer’s law lab, in the
cuvette
holder of
the Spectrometer.
Click
.
- When
the absorbance readings stabilize, click
. Type
in the
concentration of your
first standard, and click OK (or press ENTER).
- Repeat
Step 6 to collect absorbance readings for the remainder of your
standards.
Click
when
you are done.
- Click
the linear fit icon
to
calculate the
transfer function for the
standards.
- To
determine the molar concentration of an unknown, place a sample of the
unknown
in the cuvette holder of the Spectrometer.
Open
the Analyze menu and select Interpolation Calculator. A helper box will
appear,
displaying the absorbance and concentration of the unknown. Click OK.
- (optional)
To save the graph, select Store Latest Run from the Experiment menu.
NOTE: If
you proceed directly to another type of data collection, a prompt will
appear
at some point asking if you want to save the previous run.
Conducting a kinetics experiment
(Absorbance vs. time)
- Click
on the
Configure Spectrometer Data Collection
icon,
.
- Click
the circle next to “Abs vs. Time.”

- Again,
the peak wavelength (maximum absorbance) has been selected
automatically. You
may select as many additional wavelengths as you wish.
- Click OK. Depending on your saved
data, you
may have up to three separate graphs on the main screen.
- Choose Data Collection… from the Experiment
menu. Note that the
default
values
are 1 sample per second for 200 seconds. Adjust these values, if
necessary.
Click the Done button.
- Prepare
your reaction for analysis. Use a plastic Beral pipette or an
eyedropper
to
remove a small amount of the reaction mixture and transfer it to a
clean, dry
cuvette. Place the cuvette in the cuvette holder. Click
.
- Allow
the data collection to run its course, or click
to
halt the data collection early.
- Analyze
the graph of absorbance vs. time.
To fit a function
for the graphed data, click Curve Fit
and select a
suitable
function for
your data.
Dialog Boxes for the
Spectrometer
Spectrometer Dialog Box
There
are two ways to call up this box. One, open the Experiment menu and
select Set
Up Sensors → Show All Interfaces. Two,
click on the
Spectrometer
icon,
,
above
the table in
the left hand corner of
the main screen.

There
are four parameters listed:
- Sample
Time: think shutter speed of a
camera. You may change the sample time to modify the absorbance
peaks; the
greater the sample time the lesser the absorbance values.
- Wavelength
Smoothing: the number of
adjacent readings on either side of a given value that are used to
calculate an
average value.
- Samples to
Average: the number of samples
taken to calculate an average. Increasing this value can improve the
signal-to-noise ratio.
- Wavelength Range: the default range is determined
by the type
of
spectrometer. The range can be tightened, if desired, but widening the
range
will not affect the sensitivity or output of the spectrometer.
Configure
Spectrometer Data Collection Dialog
Box
To
see this box, click on its icon,
, located on
the right hand side
of the
toolbar

There are
three regions within this box and four buttons at the bottom.
- Graph: The
graph displays a full spectrum
analysis of the sample in the cuvette holder. By default, the
wavelength of
greatest absorbance (peak) will be marked with a box. You may select
other
wavelengths by clicking on the graph at the desired wavelength. A
checkbox
beneath the graph allows you to select a portion of the graph and
analyze it as
if it were a single wavelength.
- Set
Collection Mode: Three options for
data collection are offered. A full spectrum analysis (Abs. vs.
Wavelength) is
the default.
- Full
Spectrum: This column lists all of
the available wavelengths. This region becomes active for the
collection modes
Abs. vs. Concentration and Abs. vs. Time. Check the box for each
wavelength you
wish to use in an experiment.
Click
the Clear button
to remove all of the wavelengths selected on the
graph.
Determining
the Wavelength(s) to Use in an Experiment
When you conduct a Beer’s
law lab or a
kinetics lab,
it is common to select one wavelength at which to follow the
experiment.
However, in Logger Pro you may select as many wavelengths as you wish.
There
are three ways to select the wavelength or wavelengths.
- Perform
a Full Spectrum Analysis of the Solution to Be Tested
This method is best when you wish to keep a
copy of a full spectrum graph. Conduct the full spectrum of a sample of
solution and examine the graph. Go to the Configure Spectrum Data
Collection
dialog box and select Abs. vs. Time. The wavelength of maximum
absorbance will
be automatically selected.
- Use a Sample of
Solution to Determine the Peak Absorbance
This
is a variation of the previous method, in cases where
you don’t
wish to keep a copy of the full spectrum analysis. After calibrating
the
Spectrometer, place a sample of solution in the Spectrometer and go to
the
Configure Spectrum Data Collection dialog box. Select Abs. vs. Time for
a
kinetics experiment, or select Abs. vs. Concentration for a
Beer’s law
experiment. The wavelength of maximum absorbance will be automatically
selected.
- Select the
Wavelength
of Maximum Absorbance Manually This
method takes less time and can be used when you already know the
precise
wavelength to be used in an experiment. After calibrating the
Spectrometer, go
to the Configure Spectrum Data Collection dialog box. Select a
wavelength on
the graph or in the list of wavelengths.
Using
the Interpolation Calculator
- In a typical
Beer’s law experiment
you will measure
the absorbance of a set of standard solutions, after which you will
calculate a
best-fit line equation. Later, you will measure the absorbance of an
unknown
solution and use the best-fit line equation to determine the
concentration of
the unknown. Logger Pro 3.4.5 contains an option called the
Interpolation
Calculator that helps you test unknowns more efficiently. Follow the
steps
below.
- Measure
the absorbance of the standard solutions.
- Click linear
fit,
, to calculate the best-fit line equation for
the standard solutions.
- Place an
unknown sample
in the cuvette holder. Select Interpolation Calculator from the Analyze
menu. A helper box will appear, displaying the absorbance and
concentration of
the unknown.
- Click
.
This process can be
repeated with
multiple
unknowns.
The Interpolation Calculator can be
used with
imported or canned data as part of a pre-lab activity, or as a method
of
predicting the concentration of selected samples before measuring their
actual
absorbances.