The Vernier Spectrometer is a visible light spectrophotometer, which can be used to do the following:
Below are examples of experiments you can perform with a Spectrometer. .
Measuring the Absorbance Spectrum of a Sample (absorbance vs. vavelength)
- 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, choose Set Up Sensors > Show All Interfaces from the Experiment menu. Increase or decrease the Sample Time value 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, choose 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 the Configure Spectrometer Data Collection icon
. The configuration dialog box will be displayed.
- Select Abs vs. Concentration. The peak wavelength (maximum absorbance) will be 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 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
. Enter the concentration of your first standard, and click OK (or press ENTER).
- Repeat this process to collect absorbance readings for the remainder of your standards. Click
when you are done.
- Click
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. Choose Interpolation Calculator from the Analyze menu. A helper box will appear, displaying the absorbance and concentration of the unknown. Click OK.
- (optional) To save the graph, choose 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 the Configure Spectrometer Data Collection icon,
.
- Select 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 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 Done.
- 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.
There are two ways to call up this box: choose Set Up Sensors > Show All Interfaces from the Experiment menu or click the Spectrometer icon, , above the table in the left hand corner of the screen.
Sample Time
The Sample Time is like the 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
Enter the number of adjacent readings on either side of a given value that are used to calculate an average value.
Samples to Average
Enter the number of samples taken to calculate an average. Increasing this value can improve the signal-to-noise ratio
Wavelength Range
The default Wavelength 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.
Click to display the Spectrometer Data Collection dialog.
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.
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.
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.