Fluorescence spectroscopy is a very sensitive and delicate technique. It often requires a few attempts before getting great data. In our chemistry department, we have come across a few common problems and would like to share some solutions that fix or avoid them.
Collect an absorbance spectrum of your sample first. This will help you decide which excitation wavelength will work the best for your application. It will also help you narrow down the concentration of your sample for fluorescence measurements.
If the absorbance reading where you plan to excite it is greater than 0.1 absorbance units, dilute your sample until it is around 0.1. Fluorescence is a very sensitive technique and requires samples to be more dilute than absorbance measurements. If samples are too concentrated, you may see low fluorescence emission peaks and/or distorted band shapes. This is due to the inner filter effect which is the reabsorption of emitted radiation.
Try different sample time/integration times. The sample time is the time that the individual diodes (pixels) in the array are allowed to respond to light before they are “read out” and reset to zero. They respond linearly to light until they approach saturation. When students increase and decrease this value, the signal will get larger and smaller proportionally. In Logger Pro, you can adjust this value during live data collection to see the result.
Change the LED Intensity. This is similar to adjusting the slit width in a typical fluorescence spectrometer. Increasing the intensity should increase the signal.
Change the Samples to Average. This command sets the number of discrete spectral acquisitions that are accumulated before a spectrum is displayed. The higher the value, the better the signal to noise ratio. The drawback here is that the more samples your students are averaging, the longer they are going to have to wait for a stable spectrum.
Make sure you are using Logger Pro 3.15 or newer, or LabQuest 2.4.2 or newer. In older versions, you are forced to calibrate in fluorescence mode. There is a bug during fluorescence calibration that does not honor the sample time you typed in before the calibration. This will cause spectra to look much smaller than you may anticipate. If you chose to calibrate even in later versions, you will see this bug; the short-term fix is to change the sample time after calibration.
By participating in many regional and national trade shows each year, Vernier Software and Technology provides current and future customers with many opportunities to personally experience our products and services. It’s a great way to review the features of the latest Vernier products, or to bring any technical matters or applications questions to our attention. See our upcoming chemistry conference schedule below.
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In the review, Martin says:
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The Go Direct® O2 Gas Sensor measures gaseous oxygen concentration levels and air temperature. It is part of the complete Go Direct family of sensors that offers teachers and students maximum versatility to collect scientific data either wirelessly or via a USB connection. These low-cost sensors can be used in more than 300 teacher-tested experiments developed by Vernier and are supported by free graphing and analysis software, the Graphical Analysis™ 4 app.
After an initial round of online voting by educators, finalists and winners were ultimately selected by a panel comprised of two edtech thought leaders, two pre-K through 12th grade teachers, one college professor, two K through 12 administrators, one college administrator, and two pre-K through 12th grade parents. The winning products were chosen based on the extent to which they are transforming education.
The complete Go Direct family of sensors offers teachers and students maximum versatility to collect scientific data either wirelessly or via a USB connection. These low-cost sensors can be used in more than 300 teacher-tested experiments developed by Vernier and are supported by free graphing and analysis software, the Graphical Analysis 4 app.