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, choose Calibrate > Spectrometer from the Experiment menu. 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.
  5. When the warm up time is complete, insert a blank cuvette in the cuvette holder.
  6. Click Finish Calibration, wait for a few seconds for the calibration to be completed, and then click OK.

Experiments with a Spectrometer

Below are examples of experiments you can perform with a Spectrometer. .

Measuring the Absorbance Spectrum of a Sample (absorbance vs. vavelength)

  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, 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.
  4. Click to halt the data collection.
  5. (optional) Autoscale or manually rescale the graph.
  6. (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)

  1. Place a cuvette of a standard in the Spectrometer. Click the Configure Spectrometer Data Collection icon . The configuration dialog box will be displayed.
  2. 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.
  3. Click OK. Two graphs are now displayed on the screen.
  4. Place your first standard solution for the Beer's law lab in the cuvette holder of the Spectrometer. Click .
  5. When the absorbance readings stabilize, click . Enter the concentration of your first standard, and click OK (or press ENTER).
  6. Repeat this process to collect absorbance readings for the remainder of your standards. Click when you are done.
  7. Click to calculate the transfer function for the standards.
  8. 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.
  9. (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)

  1. Click the Configure Spectrometer Data Collection icon, .
  2. Select Abs vs. Time.
  3. Again, the peak wavelength (maximum absorbance) has been selected automatically. You may select as many additional wavelengths as you wish.
  4. Click OK. Depending on your saved data, you may have up to three separate graphs on the screen.
  5. 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.
  6. 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 .
  7. Allow the data collection to run its course, or click to halt the data collection early.
  8. 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: 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.

Configure Spectrometer Data Collection Dialog Box

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.


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

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.

  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 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. Choose Interpolation Calculator from the Analyze menu. A helper box will appear, displaying the absorbance and concentration of the unknown.
  5. Click OK. This process can be repeated with multiple unknowns.