Vernier Spectrometer

The Vernier Spectrometer is a visible light spectrophotometer, which can be used to do the following:


Setup and Calibration
  1. Connect the Vernier/Ocean Optics Spectrometer to computer via USB cable.
  2. Start Logger Pro.
  3. To calibrate the device, open the Experiment menu and select Calibrate → Spectrometer. Prepare a blank cuvette with the solvent for your experiment.
  4. 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)
  1. Place the cuvette containing your sample in the cuvette holder of the Spectrometer.
  2. Click . The absorbance spectrum will be displayed and updated continuously.
  3. 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.
  4. Click to halt the data collection.
  5. (optional) Autoscale or manually rescale the graph.
  6. (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)
  1. 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.
  2. The configuration dialog box will appear.


  1. 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:
  1. Check the box next to the wavelength.
  2. 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.
  1. Click OK. Two graphs are now displayed on the main screen.
  2.  Place your first standard solution, for the Beer’s law lab, in the cuvette holder of the Spectrometer. Click .
  3. When the absorbance readings stabilize, click . Type in the concentration of your first standard, and click OK (or press ENTER).
  4. Repeat Step 6 to collect absorbance readings for the remainder of your standards. Click when you are done.
  5. Click the linear fit icon to calculate the transfer function for the standards.
  6. 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.
  7. (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)

  1. Click on the Configure Spectrometer Data Collection icon, .
  2. Click the circle next to “Abs vs. Time.”


  1. Again, the peak wavelength (maximum absorbance) has been selected automatically. You may select as many additional wavelengths as you wish.
  2. Click OK. Depending on your saved data, you may have up to three separate graphs on the main screen.
  3. 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.
  4. 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 .
  5. Allow the data collection to run its course, or click to halt the data collection early.
  6. 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:


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.

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.

  1. 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.
  2. 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.
  3. 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

  1. 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.
  2. Measure the absorbance of the standard solutions.
  3. Click linear fit, , to calculate the best-fit line equation for the standard solutions.
  4. 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.
  5. 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.