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.
Photosynthetic organisms such as plants and algae use electromagnetic radiation from the visible spectrum to drive the synthesis of sugar molecules. Special pigments in chloroplasts of plant cells absorb the energy of certain wavelengths of light, causing a molecular chain reaction known as the light-dependent reactions of photosynthesis. The best wavelengths of visible light for photosynthesis fall within the blue range (425–450 nm) and red range (600–700 nm). Therefore, the best light sources for photosynthesis should ideally emit light in the blue and red ranges. In this study, we used a Go Direct® SpectroVis® Plus Spectrophotometer with a Vernier Spectrophotometer Optical Fiber and LabQuest 2 to collect spectra from four different light sources. This allowed us to determine the wavelengths emitted by each source and to get an idea of their relative intensities.
Wavelengths of light outside of the red and blue ranges are not used by most plants, and can contribute to heat build-up in plant tissues. This heat can damage plants and even interfere with photosynthesis. In order to identify the ideal light source for photosynthesis studies we compared the output or emission spectra of four different E27 type bulbs in the same desk lamp: a) 60 W incandescent bulb, b) 35 W halogen bulb, c) 28 W-equivalent LED “plant bulb” (6–9 W), and d) 13 W compact fluorescent light (CFL) bulb. Each light was measured at a standard distance of 50 cm.
Based on our results, the best light bulb for promoting photosynthesis in plants was the LED plant bulb. This bulb produces a strong output in both the blue and red wavelengths, with very little additional light in other regions to cause heat build-up. All of the other light sources had very little output in the blue range. The halogen and incandescent bulbs had extremely broad output ranges from green to deep into the red portion of the spectrum, but with little to nothing in the blue range. The least suitable lamp for photosynthesis was the CFL bulb. While it emitted some light in both the blue and red ranges (with several peaks in between), the intensity of this bulb was the weakest when compared to all the other lamps. LED plant lights are available from a variety of online merchants and home and garden stores. They have become very affordable, and work well for experiments that investigate photosynthesis.
Marta L. Dark and Derrick J. Hylton; Journal of College Science Teaching, 2018, (47) 3.
If you take the Physics and the Arts course at Spelman College in Atlanta, Georgia, you will be exposed to many applications of a traditional physics class as they apply to various areas in the arts. Light, color, sound, gravity, equilibrium, and space time are some of the topics that are explored. Students explore the topics with a guided inquiry approach. At the end of the course, students create artwork that illustrates a physical concept. Students use a Go Direct® SpectroVis® Plus Spectrophotometer and Logger Pro 3 software while they study aspects of color and light.
Enhancing a Scientific Inquiry Lesson Through Computer-Supported Collaborative Learning
Kathleen Koenig, Janet Mannheimer Zydney, Doug Behr, and Lei Bao; Science Scope, September, 2017.
In this guided inquiry activity, students learn about energy transformations as they apply to renewable energy. Students use the KidWind Basic Wind Experiment Kit to design windmill turbines that result in the highest energy output. The students research about how windmill blades work, and brainstorm which designs are most likely to produce the highest output. Students are expected to be able to identify controls, independent variables, and dependent variables. They also demonstrate how they control those variables in their designs. They develop prototypes that they test with a box fan. After initial tests, they modify their design to improve energy output. This project is closely linked to NGSS and CAST standards.
Where Does The Energy Go?
Marta R. Stoeckel (Tartan High School, Oakdale, MN); The Science Teacher, Vol. 85, No. 1, January, 2018.
This article explains how to use evidence-based reasoning to study the bounce of a ball. It is linked to NGSS standards and the authors use Logger Pro 3 video analysis to plot a ball’s position.
Burst Mode Composite Photography for Dynamic Physics Demonstrations
James Lincoln; The Physics Teacher, May, 2018.
Many digital cameras, and even camera phones, have “burst mode.” This allows the cameras to take a series of photos in rapid succession. The author explains how to take and composite these photos, which results in one image showing the photos overlaid. If a moving object is in the scene, you can use our photo analysis to get distance, velocity, and acceleration data of that image.
Heat Evolution and Electrical Work of Batteries as a Function of Discharge Rate: Spontaneous and Reversible Processes and Maximum Work
Robert J. Noll and Jason M. Hughes; J. Chem. Educ., 2018, 95, pp 852−857.
This article describes an experiment in which students compare the enthalpy change of the useful electrical work to the heat lost from the electrochemical reaction in batteries. AA alkaline batteries are installed in a battery holder and connected to a heater resistor and sensors. The apparatus is suspended in a Dewar flask and the water is stirred gently at 200 rpm. The potential, current, and temperature are measured over a period of 30 minutes. The students use a Current Probe and a Voltage Probe connected to a computer running through a LabQuest Mini to measure the work output of the battery. The waste heat produced is measured calorimetrically using a Stainless Steel Temperature Probe. This activity combines concepts from electricity, electrochemistry, and thermodynamics in one experiment.
Measuring the Force between Magnets as an Analogy for Coulomb’s Law
Samuel P. Hendrix and Stephen G. Prilliman; J. Chem. Educ., 2018, 95, pp 833−836.
The authors describe a simple demonstration to illustrate the relationship between charged particles as described by Coulomb’s law. They use a Dual-Range Force Sensor mounted on a LEGO® platform. The sensor is connected to a computer with a Go!Link and monitored with our free Logger Lite software. A neodymium magnet is attached to the end of a screw. It is installed where the hook or bumper would normally go in the sensor. A second neodymium magnet is mounted to another LEGO® piece that is mounted on the same LEGO® platform. Attractive and repulsive forces can be demonstrated by switching the orientation of one of the magnets. The force between the magnets is plotted as a function of distance using the Events with Entry mode of data collection. This plot represents a Coulomb’s law force between charged particles and would be useful when teaching ionization, bonding, intermolecular forces, lattice energy, and PES (photoelectron spectroscopy).
Using Open-Source, 3D Printable Optical Hardware To Enhance Student Learning in the Instrumental Analysis Laboratory
Eric J. Davis, Michael Jones, D. Alex Thiel, and Steve Paul; J. Chem. Educ., 2018, 95, pp 672−677.
The authors describe the ability to use 3D printing technology to construct analytical instruments. They also discuss how to make the components of an absorbance spectrometer. Various mounts, posts, and slits are printed on a 3D printer are mounted on a platform with lenses and diffraction gratings with light sources and detectors. Even cuvette holders are fabricated. Common full-absorption spectra and Beer’s law plots are done with copper (II) sulfate solution. The results are compared to those from a Go Direct® SpectroVis® Plus Spectrophotometer. The plots of absorbance vs. wavelength and absorbance vs. concentration from the 3D-printed spectrometer compare favorably with those produced by the SpectroVis Plus.
Penny Snetsinger and Eid Alkhatib; J. Chem. Educ., 2018, 95, pp 636−640.
The goal of this activity is to provide students with the opportunity to design an experiment that studies the effect of activated carbon on dyes. Students select dyes to study as well as conditions to vary such as pH, salinity, water hardness, and time of contact between the dye and the carbon. The experiment lasts multiple weeks to provide ample time for the students to vary experiment conditions and to analyze their results. Additionally, students use various analytical statistics and techniques to evaluate the outcome of their experiments. They also employ a factorial experiment design that allows them to simultaneously vary more than one variable. They used a Beer-Lambert plot to spectrophotometrically determine the concentration of dye left in the solution after exposure to the activated carbon. Students use a Go Direct® SpectroVis® Plus Spectrophotometer in this experiment.
Physicians as the First Analytical Chemists: Gall Nut Extract Determination of Iron Ion (Fe2+) Concentration
Mary T. van Opstal, Philip Nahlik, Patrick L. Daubenmire, and Alanah Fitch; J. Chem. Educ., 2018, 95, pp 456−462.
This article describes a guided inquiry activity that measures the iron in drinking water, using oak gall nut extract. This activity is geared toward students who are interested in medical careers. The idea is to use a naturally occurring substance to react with the iron ion in a solution and to form a colored solution from which the iron concentration can be determined. The students create standard Beer-Lambert plots of absorbance vs. concentration, then measure the absorbance of the gall-iron solution to determine the concentration of the iron ion. In this experiment students use a Go Direct® SpectroVis® Plus Spectrophotometer.
Measuring Yeast Fermentation Kinetics with a Homemade Water Displacement Volumetric Gasometer
Richard B. Weinberg; J. Chem. Educ., 2018, 95, pp 828−832.
This article describes how to build a volumetric gasometer from simple equipment such as plastic bottles and tubing. The students then use the device to measure the volume of carbon dioxide produced while sugar is metabolized by yeast. As the CO2 is produced the water in one bottle is displaced into a second bottle. The rate of metabolism is measured by timing the amount of water displaced. The activity is appropriate for students from middle school well into college and describes how to use the experiment with different age groups. Some of the inspiration for this activity came from Experiment 12A, “Respiration of Sugars by Yeast” from our Biology with Vernier lab book and “Sugar Metabolism with Yeast” from our lab book Investigating Biology through Inquiry.
In July, more than 100 students from 35 countries used our Go Direct sensors to test the water in Ireland’s Killarney National Park as part of the 2018 GLOBE Learning Expedition (GLE). This event is part of the GLOBE Program and is held every few years in different locations around the world. The GLE brings together students, teachers, and scientists for a week of sharing and learning about science, the environment, and each other’s cultures. As part of this year’s student field experience, Go Direct sensors were used to measure temperature, pH, conductivity, and dissolved oxygen levels along the Deenagh River. This beautiful river runs along the edge of the park, near the town of Killarney. The students’ sensor data, along with a survey of macroinvertebrates, indicated that the Deenagh is in excellent health.
Using Go Direct sensors wirelessly in this type of environment was a game-changer for many students and their teachers. The new Go Direct® Optical Dissolved Oxygen Probe was especially useful as it reports not only dissolved oxygen concentration, but temperature and atmospheric pressure as well. By connecting Go Direct sensors via Bluetooth® wireless technology, one student can stay safely on the shore with a LabQuest 2, mobile phone, or other device, while another student holds the sensor in the water. Everyone agreed that the simplicity and accuracy of Go Direct sensors make them an excellent choice for students conducting field work.
We are proud to work with the GLOBE Program, an international science and education program whose mission is to promote the teaching and learning of science, enhance environmental literacy and stewardship, and promote scientific discovery. For more information, visit the GLOBE Program page»