Tech Note 1166 Detail

Measure absorbance/transmittance with SPARK SLS.

Affected Products:

PS-2008a SPARK Science Learning System

Problem/Symptom:
How to measure absorbance/transmittance with SPARK SLS and an Ocean Optics Spectrometer

PASCO Solution:

Equipment

Procedure for Measuring Absorbance Versus Wavelength

  1. Start the SPARK SLS.
  2. Connect the spectrometer to the larger USB port on the SPARK SLS.
  3. Connect the end port of the light source and optical port of spectrometer via the included fiber optic cable.
  4. Optional: The default integration is set to 50 ms, which is close to optimal; however, optimize the integration time manually will slightly improve the signal to noise ratio:
    1. Create a graph of Intensity(Wavelength).
      1. Click the Build button.
      2. Select Intensity versus Wavelength.
      3. Select the Graph button.
      4. Click OK. (You will see a graph of Absorbance versus Wavelength.)
    2. Turn on the light source.
    3. Press the Record button.
    4. When a spectrum becomes visible, press the Record button again to stop recording.
    5. If saturation of the CCD elements is visible as evidenced by a flat section of the spectrum, decrease the integration time by 10 ms; otherwise, increase the integration time.
    6. Click the Experiment Tools button in the lower right.
    7. Click Configure Sensor.
    8. Select Edit Spectrometer Properties...
    9. Set the Integration Time to the default value +/- 10 ms depending on whether saturation was visible in the spectrum.
    10. Click OK, Done, and OK to return to the graph.
    11. Repeat steps 3-10 until the CCD just barely does not saturate.
  5. Click the Build button.
  6. Select Absorbance and Wavelength.
  7. Select the Graph button.
  8. Click OK. (You will see a graph of Absorbance versus Wavelength.)
  9. Completely fill a clean cuvette with reference solution. (A reference is a sample of solution with none of the light-absorbing chemical of interest in it, that is otherwise identical to the solutions under test. The reference is typically pure water.)
  10. Click the Experiment Tools button in the lower right.
  11. Click Configure Sensor.
  12. Select Edit Spectrometer Properties....
  13. Insert the opaque black cuvette.
  14. Go to the Reference Lines category.
  15. Press Save Dark.
  16. Place the cuvette with the reference solution in the cuvette holder so that the smooth clean sides of the cuvette are in the path of the light.
  17. Place the the mirror inside the sample chamber and around the reference so that the hole is aligned with the detector side.
  18. Press Save Ref.
  19. Click OK, Done and OK to return to the Graph.
  20. Place your sample in the cuvette holder.
  21. Click the Record button.
  22. When a spectrum becomes visible, press the Record button again to stop recording.
  23. If you will be recording absorbance at a particular wavelength versus time, choose a wavelength at which there is significant absorbance.
  24. Go to …/Edit Spectrometer Properties/Time Acquisition and enter a wavelength value that you would like to track.
  25. Set the bandwidth to a value between 2-10 pixels.
  26. Click Ok, Done, OK to return to the graph.
  27. Click the graph button in the lower left.
  28. Select the graph properties button (three dots and three lines).
  29. Select time for the x-axis measurement.
  30. Click Start.

Note:

  • Some noise is normal below 400 nm because of the low sensitivity of the CCD sensor pixels at those wavelengths. If the signal below 400 nm is of interest, the noise can be reduced by increasing the integration time further; however, the absorbance spectrum in the saturated region of the spectrum will become meaningless.
  • Signal averaging does not work with spectra as a function of wavelength in SPARK SLS 1.30 firmware; this may be a feature in later firmware.

Creation Date: 03/6/2012
Last Modified:
Mod Summary: