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.
NSTA Recommends recently featured the Go Direct® O2 Gas Sensor. In his review, Martin Horejsi used the wireless sensor to collect data during various investigations, including an out-of-the-classroom experiment on an airplane. He highlighted the sensor’s features, plug-and-play functionality, and overall ease of use.
In the review, Martin says:
“With [the] new Go Direct® O2 Gas Sensor, the ability for students to measure relative oxygen concentration has never been easier or faster.”
“As a wireless probe the Vernier Go Direct® O2 Gas Sensor provides all the necessary capabilities of an O2 sensor with none of the pesky cables that limit use, knock over experiments, and require an additional interface.”
He concludes by saying:
“The Vernier Go Direct® O2 Gas Sensor pushes the boundary of experimental measurement forcing a teaching evolution beyond the analog. We can now fulfill the dream as science teachers to where our students leave us behind as they accelerate past us.”
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.
Molecular biologists and biochemists are always talking about their sample’s 260/280 ratio. It is so commonly used that entire instruments are dedicated to displaying this value when analyzing a sample. The A260/A280 ratio is a procedure that tells scientists the extinct of contamination of their nucleic acid solution by proteins, carbohydrates, and other organic molecules.
The basis of this test relies on the Beer-Lambert law: A = εbc; where A is absorbance, e is the molar extinction coefficient, b is the cell path length, and c is the sample concentration. The commonly accepted average extinction coefficients for a 1 mg/mL nucleic acid solution at 260 nm and 280 nm are 20 and 10, respectively. In proteins, the extinction coefficient values at 260 nm and 280 nm at a concentration of 1 mg/mL are 0.57 and 1.00, respectively. Therefore, nucleic acid samples would be expected to have a higher absorbance at 260 nm than at 280 nm; in a protein sample, the opposite is true. Using these extinction coefficients, pure nucleic acid samples would have an A260/A280 ratio of 2.0, while protein would be 0.57.
To use this template, first download the template file. Connect the spectrometer to your computer and open the file in Logger Pro. After you have properly calibrated your spectrometer and prepped your sample, insert your sample into the spectrometer. Press the Collect button and the A260/A280 ratio value will be displayed live in the meter. The table is also displayed in the Logger Pro template. If you double click on the 260/280 header in the table, you can see the calculations used to generate the value and make modifications, if desired.
Vernier has great options for biochemistry, be sure to visit our biochemistry solution page for more free resources and great tips.
The new Go Direct® Centripetal Force Apparatus makes it easier than ever to investigate rotational dynamics. Students can investigate the relationships among force, mass, and radius wirelessly—all you need is the Go Direct Centripetal Force Apparatus, a Go Direct Force and Acceleration Sensor, and a device running our free Graphical Analysis™ 4 app. No additional interface is needed.
With Go Direct Force and Acceleration mounted on the apparatus’ beam, you are ready to investigate centripetal acceleration. Attach the mass carriage, and you can explore Newton’s second law as it applies to rotational dynamics. No tangled wires to worry about. All you need to do is slide the sensor onto the beam, attach the mass carriage, and secure the sensor at the desired location. Select the appropriate data-collection channels in Graphical Analysis 4 for your investigation: Z-axis gyro to capture angular velocity, X-axis acceleration for centripetal acceleration, and/or Force for centripetal force. Then, you’re ready to collect data. As you turn the spindle to rotate the beam, the sensor will apply the force necessary to pull the carriage in a circular motion.
The relationship can be further explored as students apply knowledge gained from the curve fit to linearize the data.
Students can quickly devise their own experiments to develop a model for the effect of mass or radius of rotation on the force, and then test the model. Select a mass and position and see if it matches their prediction.
Have you ever done an experiment that you wish you could repeat with different chemicals or concentrations but lacked the time and materials? This is where Pivot Interactives new activities for chemistry can become a valuable teaching tool.
Pivot Interactives is a browser-based collection of videos and analysis tools that enable students to control real results—not simulations. The videos come with appropriate tools for measuring volume, mass, temperature, time, and even color intensity. There are additional tools to carefully control the progression of the video and experiment. Online tables and graphs are used for students to graph relationships between the variables being studied. Calculated columns can be built and graphed.
Topics include Beer-Lambert law, acid-base titration, kinetics, rate laws and activation energy, gas laws, density, specific heat, and more.
Wait until you see how the “black box” around a colorimeter or spectrometer is stripped away to show the essence of how the device measures transmittance and absorbance. The students use their own eyes as the detector with a clever combination of tools and filters to determine the appropriate wavelength to use for the experiment.
Many teachers are interested in using our EKG sensors to record an electromyogram (EMG), the electrical activity produced from muscle contractions. Recording an EMG is straightforward, but there are multiple ways that an EMG can be analyzed. The most robust technique is to measure the integral of the rectified EMG signal, which can easily be done using the Go Direct EKG Sensor.
A normal EMG has both positive and negative deflections. A rectified EMG uses a function that makes all of the EMG deflections positive—the larger the integral, the larger the muscle contraction. In the past, we have offered special Logger Pro and LabQuest files that provide the proper filtering and calculated column support to record and analyze rectified EMGs. But, the Go Direct EKG Sensor makes recording rectified EMGs much simpler. No special files or filter settings are required—just change the channel to EMG Rectified and start collecting data. Then simply measure the integral of the signal in Graphical Analysis.
The sample graph shows an example of an EMG and rectified EMG recorded from the forearm using Go Direct EKG. A digital high-pass filter that has been optimized for recording EMGs is automatically applied to the EMG channel. The EMG Rectified channel returns the absolute value of the EMG channel, making all of the EMG deflections positive.
To analyze the rectified EMGs, simply select the region of the rectified EMG you want to analyze and use the View Integral feature in Graphical Analysis 4. You can even compare the integrals of different rectified EMGs to see which condition produced less or more muscle activity. For example, in the sample graph, the area of the rectified EMG increases with each burst of activity. The first, second, and third rectified EMGs have areas of 0.181, 0.329, and 0.441 mV s.