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Demystifying Ion-Selective Electrodes

Vernier Go Direct ISEs

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.

Go Direct Nitrate ISE module

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.

Replacement modules can be found on our Replacements and Accessories web page.

2. My ion-selective electrode loses its calibration right after I calibrate it.

Other than age, the most common reason for an ISE to lose its calibration right away is that the calibration data was not saved to the memory of the sensor.

LabQuest ISEs

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.

Go Direct ISEs

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:

  1. Make sure to soak your ISE in the high standard solution for at least 30 minutes before calibrating.
  2. When performing the calibration wait at least 90 seconds to 2 minutes in each standard solution before keeping the calibration point.
  3. 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.

For more tips on using Vernier ion-selective electrodes, see General tips for using Ion Selective Electrodes (ISE).

Happy Halloween

Tips for Better Fluorescence Data

Elaine using the Fluorescence spectrometer

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.

While these helpful tips are designed for improving your Vernier Fluorescence/UV-VIS Spectrophotometer data, the majority of them can be used with any combination fluorescence/absorbance spectrometer.

  1. 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.
  2. 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.
  3. 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.
  4. Change the LED Intensity. This is similar to adjusting the slit width in a typical fluorescence spectrometer. Increasing the intensity should increase the signal.
  5. 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.
  6. 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.

To get acquainted with the Vernier Fluorescence/UV-VIS Spectrophotometer software and instrument, we suggest following the free lab instructions for “A Guided Inquiry Approach to Understanding Fluorescence Spectroscopy“.

The experiment walks through a lot of common sticking points and really helps students understand what they are looking at when taking fluorescence data.

Want to see more? I will be showing off the Vernier Fluorescence/UV-VIS Spectrophotometer at the Fall Regional ACS shows (MWRM, SERMACS, and SWRM) as well as at WCCTA. See a full list of the college chemistry conferences we attend »


Upcoming Conference Schedule for Vernier

Vernier booth

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.

We also offer free Professional Development Workshops that include hands-on Vernier equipment training to help you integrate data-collection technology into your science curriculum.

NSTA Recommends Takes the Vernier Go Direct® O2 Gas Sensor on a Flight

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.

Photo of Go Direct O2 Gas sensor tucked in seat pocket for data collection.
A student, who was travelling with Martin Horejsi on a trip to a NASA facility, collected data with Go Direct O2 Gas while on an airplane. The Go Direct O2 Gas Sensor is tucked into an airplane seat pocket. (Image provided by Martin.)
Graph of oxygen gas levels in airplane cabin during approach for landing
The oxygen gas level in the cabin rose upon the plane’s approach for landing. (Image provided by Martin.)

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.

Read more about the Go Direct O2 Gas Sensor on NSTA Recommends »

Vernier Go Direct® Sensors Win a 2018 Tech Edvocate Award

The Tech Edvocate Awards 2018 Winner Logo

Our Go Direct family of sensors, along with Graphical Analysis 4, recently won a 2018 Tech Edvocate Award. The family of wireless sensors and its accompanying software were recognized in the Best STEM/STEAM Education App or Tool category.

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.

Learn more about Go Direct sensors and Graphical Analysis 4 »

Spectral Analysis® 4.6 Released

Spectral Analysis 4.6 is now available for iOS, Android, macOS®, Windows®, and ChromeOS.

New Features

  • Intensity mode data collection for Vernier SpectroVis Plus and Vernier Go Direct SpectroVis Plus
  • Y-Axis Plot Manager provides new controls over graphing

    • Individual Data Set display can be enabled or disabled
    • Data Sets can be renamed
    • Column Options and other column operations can be performed from the graph
  • More flexible graph scaling options, including Manual scaling
  • Graph traces are identified by color on the y axis label, assisting reading of graphs with two or more traces.
  • On touch screens, graph can now be zoomed (pinch) and panned (two-fingers)
  • Redesigned New Experiment dialog
  • iOS now saves only to local storage, but files can be copied to cloud locations using the Files app
  • Numeric entry keyboard on iOS small screens now allows negative values and scientific notation

Download the update for Spectral Analysis 4 »

Get Your 260/280 Ratio with Logger Pro

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.

In order to make the determination of a 260/280 ratio easier with a Vernier UV-VIS Spectrophotometer or a Vernier Fluorescence/UV-VIS Spectrophotometer, we have developed a Logger Pro 3 template that you can use to easily see the ratio without having to go through the entire process every time. A screenshot of the Logger Pro template is shown below.

A screenshot showing Logger Pro's 260/280 ratio template

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.

Download our Logger Pro template for completing a 260/280 ratio »

The Centripetal Force Apparatus Goes Wireless

Go Direct® Centripetal Force Apparatus

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.

Graph of force vs. angular velocity with a curve fit
Applying a curve fit to the raw data will provide students with clues to nature of this relationship.

The relationship can be further explored as students apply knowledge gained from the curve fit to linearize the data.

Graph of force vs. angular velocity linearized
Linearized data for a rotating mass. What are the units of the slope of the line? Can your students predict the mass given the position on the beam?

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.

Robotic Hand Project

We have had a lot of fun with the Robotic Hand project, which we discovered in the Hacking STEM Library from Microsoft®. Using our Low-g Accelerometer, an Arduino, and our Vernier Arduino Interface Shield, we modified the project to create an easier control system.

See instructions for building and controlling the hand »

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