1. Turn on the computer. Open the StellarNet software by double clicking on the desktop icon StellarPro 
to open the application.
2. When you first open the software, you should see a screen similar to the one below:
3. Remove the cuvette holder cap. Place your blank cuvette into the cuvette holder and replace the cuvette holder cap.
4. Select the Scope tab in the Graph window. This will show you the number of counts (photons) the detector receives. You should see a spectrum of counts versus wavelength.
5. Set the integration time so that your spectrum is not saturated but as close to 65,000 counts as possible. Enter the desired time in the integration time input box, then click on the “Int Time (ms)” button next to the input textbox to apply the entered time. This is also the point at which you should adjust the number of scans to average (more scans averaged will increase accuracy, but will take more time for each reading). You can also add smoothing controls at this time in the Device Settings block. A pixel box car set to 3 and averaging set to 5 often gives nice results.
|
6. Light Reference. Make sure that your blank cuvette is in the cuvette holder and the cap is on the cuvette holder. Take the blank/light reference by clicking on the Blank / Light Reference 
in the toolbar at the top right of the screen.
7. Dark Reference. First, hold the red shutter button for at least three seconds. You should see the spectrum fall flat everywhere on your graph. Second, while still holding the shutter button, left click on the Dark Reference button in the toolbar at the top right of the screen. The baseline will drop to zero. Finally, you can release the shutter button. You should see the spectrum return to its original profile.
8. Now that you have taken the dark and light reference, click on the Absorbance tab in the graph window to display a spectrum in absorbance units (AU). 
9. You should see a nearly flat absorbance spectrum once you switch to absorbance if you have blanked and zeroed the spectrometer correctly.
| Depending on the cuvettes you use, you may see fluctuations below 300 nm. This is simply due to the cuvette absorbing UV radiation at these wavelengths. |
Taking Absorbance Measurements
1. Remove your blank sample from the cuvette holder. Place the most concentrated standard cuvette in the holder and replace the cuvette cap. The instrument will now display absorbance in real time if you are running in Loop capture mode, or you can click on the Capture button to capture the spectrum if you are in single mode.
2. Look at the spectrum and select the wavelength of maximum absorbance.
3. To find a peak, use the mouse to left-click on the left or right arrow next to the Peak button. Note: The Peak button toggles between Peak and Pixel modes. In Peak mode, the software will find the peak of the spectrum, while in Pixel mode, it will provide the spectrum pixel value at a specific point. Make sure it is set to Peak when searching for the peak.
The left arrow will find a peak to the left of the vertical line in the spectra. The right arrow will find a peak to the right of the vertical line in the spectra.
4. You can also right click directly onto the spectrum to find the photon count of a specific wavelength. To find the specific wavelength your cursor is at, look to the yellow annotation box on the top right of the graph window. Wave gives the specific wavelength and Value gives the photon count for that particular point in the spectrum.
| Warning: If your system saturates at all integration times or you need to reduce your exposure time <15ms to get a signal, then you must use a CR2-Aperture (CR2-AP) or inline neutral density filter to reduce light intensity to your system’s detector. There are other possible solutions as well. Please contact a StellarNet technical sales associate to choose which solution is best for your application. For Radiometric applications it is recommended to use exposure times >15ms. |