While teaching chemistry and physics for 34 years in public schools in Maryland, nearly every semester, students asked, “When will I use this in real life?” When I supplied a scenario for a lab activity, students could see how a topic studied in their chemistry lab could have real-world application.
For instance, it might be difficult for a student to see where absorbance spectroscopy and Beer’s law could be useful to a chemist. But, what if the technique is used to analyze poisoned wine from a crime scene? This definitely piqued the interest of my students.
The scenario: At a local dinner party, some of the guests became ill and had to be transported to the hospital. Most of the stricken guests recovered, although it took varying amounts of time for them to recover. Some guests even died. What could have stricken these people and why was the effect different?
Using a Go Direct® SpectroVis® Plus Spectrophotometer, students can compare samples of fresh wine to those collected at a crime scene. Samples of tainted wine will show absorbance spectra different from those of fresh wine. By comparing the spectra of suspected toxins with those from the crime scene, the nature of the poison can be determined.
Once the identity of the poison is determined, Beer’s law can be used to determine the concentration of poison in the tainted wine. From additional evidence from the crime scene, including estimates of the wine consumed and body mass of the victims, students then calculate the amount of poison consumed and compare this to the LD50 for that poison.
Due to the local restrictions on the presence of alcohol containing products in schools, the poisoned wine and suspected poisons are all created using food dyes. A similar activity called “Killer Cupa Joe” in the Vernier lab manual Forensics with Vernier uses coffee. My students and I did this lab and used food dye as the poison.
Vernier sensors can also be used for other forensic scenarios. Future blog postings will discuss more activities.
A Safety Data Sheet (SDS) serves the same purpose as a Material Safety Data Sheet (MSDS). They provide a formal and consistent format, in 16 sections, that are organized in a specific order to make them easy for people to understand. The SDS also follows the Globally Harmonized System of Classification and Labeling of Chemicals (GHS).
What is the difference between an MSDS and SDS?
While the MSDS came in multiple forms, the SDS is presented in one format. Many MSDS components can be found in an SDS. New sections and types of information have been added to make SDS more useful. To be categorized as a Safety Data Sheet, it must include all 16 of the required sections and conform to the Globally Harmonized System of Classification and Labeling of Chemicals (GHS). That format consists of a specific order and set of headlines. The OSHA® QuickCard™ lists the 16 sections.
Define health, physical, and environmental hazards of chemicals.
Create classification processes that use available data on chemicals for comparison with the defined hazard criteria.
Communicate hazard information, as well as protective measures, on labels and Safety Data Sheets (SDS).
Does Vernier provide an SDS?
Yes. An SDS is provided for each chemical that we ship. In 2015, Vernier adopted the Globally Harmonized System of Classification and Labeling of Chemicals (GHS). All of our MSDS have been updated to an SDS. The Safety Data Sheet for chemicals and solutions sold by Vernier can be found on each product’s web page and in our Product Manuals and Reference Guides.
Traditionally visual techniques are used to measure the concentration of ions in solution. Concentration is determined by comparing colors of solutions with charts and tables. Vernier ion-selective electrodes (ISEs), offer a much easier and more reliable method to measure ammonium, calcium, chloride, nitrate, and potassium ions in solution. By adhering to a few best practices, students can consistently get good data with our ion-selective electrodes.
Common customer questions about the use of ion-selective electrodes.
1. My ion-selective electrode is not reading correctly or will not calibrate.
The most common reason for this is the age of the module in the electrode. All of our ion-selective electrodes have replaceable modules, with the exception the chloride electrode.
To replace the module, carefully, unscrew the end of the electrode and extract the module from the body. The replaceable module will have a date stamped on the side. The modules are warranted for 1 year past the date of purchase. Under typical classroom use, you should expect to replace the module after a year. For this reason, we recommend purchasing modules as close to the time you will use them as possible.
The chloride specific electrode uses a solid state membrane that does not need to be replaced with time. However, the response of this electrode may slow with use. Cut a 1 in2 piece of the polishing strip that came with the electrode, Thoroughly wet the dull side of the polishing strip and electrode with distilled water. Gently polish the end of the electrode to remove accumulated material that is impeding the performance. Rinse the electrode with distilled water and calibrate it.
When collecting data with LabQuest ISEs (those with a white, plastic BTA connector), you can store the calibration to the sensor itself. After the calibration procedure, look for the Storage tab in the software. Click or tap the Storage tab, and select the option to “Save the Calibration to the Sensor” or “Set Sensor Calibration.” This will ensure that, after the sensor is disconnected, the most recent calibration will load automatically when the sensor is used again—even if connected to a different LabQuest or computer. For more information about calibrating and storing calibrations with various sensors and interfaces, visit How do I calibrate my sensor? Note: When collecting data with LabQuest ISEs and Graphical Analysis 4, the calibration cannot presently be stored; calibrate your ISEs each time you use them.
When using Go Direct ISEs and Graphical Analysis 4 app, the calibration information is automatically stored in the the memory of the sensor; there is no need to do additional steps to store the calibration.
3. My ISE is reading off from the calibration standards, even right after I calibrate it.
The response time of ISEs is much slower than most of our other sensors. This means that both the calibration and data collection must be done slowly and consistently:
Make sure to soak your ISE in the high standard solution for at least 30 minutes before calibrating.
When performing the calibration wait at least 90 seconds to 2 minutes in each standard solution before keeping the calibration point.
When using the sensor to read the concentration of an ion in solution, make sure to wait the same amount of time you did when you calibrated the probe.
Vernier Ion-Selective Electrodes can offer another way to enhance your chemistry and water quality studies. With a little foreknowledge you will be able to do some interesting experiments with these sensors.
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.
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.
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.
Instrumentation is used in the undergraduate chemistry curriculum to help demonstrate the fundamental aspects of chemical reactions and demonstrate how it can be used to determine certain properties of a chemical system. For example, absorbance spectroscopy teaches students about transmission and absorption of radiation by a compound and how these measurements can be used to determine concentration or chemical reaction order. Chromatography illustrates to students how the structure of compounds can help isolate them from others. When certain techniques are coupled together, the concepts are layered and even more can be learned about the system being studied.
Flash photolysis spectroscopy is a type of time-resolved absorbance spectroscopy that helps students investigate chemical reaction order as well as the basics of photochemistry. Flash photolysis is often referred to as a “pump-probe technique” because it involves an excitation source or a “pump” and a detection source or a “probe”. This technique was so groundbreaking that the 1969 Nobel Prize in Chemistry was awarded to the scientists who developed it.
The diagram below shows a typical flash photolysis setup. In this system, white light from an LED light source probes any spectral changes made in the system by the excitation light pulse. A xenon flash lamp provides the photo-excitation pulse. The white light from the LED source is focused on the sample. From the sample this beam goes through a wavelength filter as it is focused on a photodiode, which detects this light’s intensity. When the xenon lamp is flashed, an intense near-UV, white light pulse enters the sample. If it causes changes in the absorption of the sample at the filter’s wavelength, the detector measures these changes. The voltage from the detector is collected, digitized, and stored as a function of time.
With recent advances in photochemistry in a number of disciplines, understanding photo-induced chemical kinetics is quickly becoming an essential part of the undergraduate chemistry curriculum. Due to limitations in affordable instrumentation, photochemical kinetics is often left to the textbook alone. The Vernier Flash Photolysis Spectrometer is an affordable option available to instructors to help students get hands-on experience with this important technique. We provide a number of free experiments to get you started, including one that involves exploration of a simple light-induced, cis-trans isomerization of Congo Red. Congo Red is a diazo dye that is a derivative of azobenzene. When light excites the ground state trans- form at its visible broadband absorbance, some ground state molecules are converted to a higher energy cis- form instantaneously (on this time scale, at least). The cis- state is metastable with respect to the trans- ground state resulting in slow conversion back to this trans- ground state, as shown in the state diagram below. The loss of the absorbance at 600 nm observed by the Vernier Flash Photolysis Spectrometer gives students the opportunity to follow the progress of a thermal cis-trans isomerization and measure its rate on timescales that cannot be achieved by traditional mixing methods.
The data and analysis provides an opportunity for discussion with students about various topics, including perturbation kinetics, photochemistry, fast kinetics, and bimolecular rate constants. This experiment, and others like it, allow for easy incorporation of time-resolved spectroscopy into the undergraduate physical chemistry, biochemistry, organic chemistry, and inorganic chemistry curriculums.
Whether you are teaching general or upper-level college chemistry courses, our affordable sensors and instrumentation make it possible for every student to participate in hands-on learning. Our combination of sensors, software, college-level experiments, and instructional resources engage students and instructors in scientific discovery. We have assembled a collection of products and experiments for commonly taught college chemistry courses.
General Chemistry: Complete an acid-base titration with our pH probes that have 0.1 pH unit accuracy and a drop counter that accurately converts drops to volume.
Organic Chemistry: Measure and analyze the GC retention times of a Fischer esterification reaction mixture using the Mini GC Plus Gas Chromatograph with room air as the carrier gas.
Biochemistry: The Vernier UV-VIS Spectrophotometer can be used to measure the 260/280 nm ratio when purifying proteins and DNA. Its range, 220 nm to 850 nm and 3 nm optical resolution, makes it ideal for biological applications.
Do you teach environmental chemistry? Are you looking for lab experiment ideas and equipment?
Students taking environmental chemistry will learn basic techniques for chemical analysis of environmental samples, including air, water and soil. Many of these experiments may take place in the field requiring rugged and portable equipment. These Go Direct® Sensors connect directly to your mobile device, Chromebook™, or computer using our free Graphical Analysis™ 4 app or Spectral Analysis™ 4 app. The sensors can be used wired via USB or wirelessly via Bluetooth® wireless technology, allowing you to choose the best solution.
Here are five products from Vernier, selected by our experts, for environmental chemistry.
The flat glass shape of the Go Direct Tris-Compatible Flat pH Sensor is useful for measuring the pH of semisolids such as soil slurries. It features a sealed, gel-filled, double-junction electrode, making it compatible with Tris buffers and solutions containing proteins or sulfides.
The Go Direct Optical Dissolved Oxygen Probe combines the power of multiple sensors to measure dissolved oxygen, water temperature, and atmospheric pressure. The Go Direct Optical Dissolved Oxygen Probe uses luminescent technology to provide fast, easy, and accurate results. This waterproof probe is perfect for the field or for the laboratory.
Investigate the relationship between temperature and dissolved oxygen in water
Measure primary productivity or biological/biochemical oxygen demand
Our Go Direct family of Ion-Selective Electrodes are great for monitoring five environmentally-important ions: calcium (Ca2+), chloride (Cl–), ammonium (NH4+), nitrate (NO3–), and potassium (K+). These are combination-style, non-refillable, gel-filled electrodes with the option to report measurements in mV or mg/L.
Measure changes in nitrate concentration due to acidic rainfall or fertilizer runoff from fields
Study changes in levels of ammonium ions introduced from fertilizers
Quantify chloride in ocean water
Use the calcium concentration to evaluate water hardness
Go Direct Conductivity Probe determines the ionic content of an aqueous solution by measuring its electrical conductivity. It features a built-in temperature sensor to simultaneously read conductivity and temperature. Automatic temperature compensation allows students to calibrate the probe in the lab and then make measurements outdoors without temperature changes affecting data. The Go Direct Conductivity Probe has a range of 0 to 20,000 μS/cm (0 to 10,000 mg/L TDS) to provide optimal precision in any given range.
Use conductivity to study soil salinity
Measure total dissolved solids (TDS)
Investigate the difference between ionic and molecular compounds, strong and weak acids, or ionic compounds that yield different ratios of ions.
Check out Environmental Science and Water Quality for additional options. Everything we offer includes our unparalleled customer service, technical support, and resources, so you are always supported when integrating our technology.