Follow These 5 Tips to Get the Best Data from Your Ammonium Sensor
by ANNMARIE DELFINO05 March 20259 min read
The UK 2021 Environment Act (EA) lists ammonia among the parameters water companies are required to monitor upstream and downstream of sewer overflow points to assess their impact on water quality. Even low levels of ammonia are toxic to fish and other aquatic life, so monitoring ammonia is crucial to understanding the health of rivers and other waterways.
Ammonia levels can be derived from measurements taken by ammonium sensors, a type of ion-selective electrode (ISE). These sensors measure the concentration of ammonium through an electrode comprised of two half-cells: one with a membrane selectively porous to the ammonium ion, and a reference half-cell to provide a stable reference value. When deployed with conductivity/temperature and pH sensors, the instrument will use the ammonium concentration to calculate a value for ammonia using the Nernst equation.
ISEs are known for being finicky; certain design elements essential for their operation also mean the sensors require regular maintenance. But don’t let that stop you! If you know their basic requirements, ISEs are a valuable addition to your monitoring program, both for spot checking and long-term trend analysis.
If you’ve never used an ISE or just want to brush up on best practices, here are five tips that lay out the most important considerations when working with ammonium sensors, so you can have confidence in your deployment and get the most out of your ammonia data.
Tip #1: Condition your sensor before use
Ammonium ISE sensors need to be properly prepared and conditioned before every deployment.
Start by refreshing the reference solution to ensure the reference electrode presents a stable value. Maintaining this stability is essential to getting quality data from your ammonium sensor.
In-Situ’s Aqua TROLL ammonium sensor has a refillable reference solution so you don’t have to purchase a new sensor every time reference solution runs out. Before use, empty the old reference solution and refill the sensor with new solution. Slightly overfill the chamber before replacing the junction to ensure there are no air bubbles.
The ISE membrane then needs to be conditioned for deployment. We recommend soaking the sensor in at least 140 mg/L as N standard for at least two hours, and preferably overnight. Rinse thoroughly with deionized (DI) water before calibration.
ISE membranes need to be hydrated to provide reliable data; repeat the conditioning process before every new deployment to ensure high-quality data collection.
Tip #2: Calibrate, calibrate, calibrate!
ISEs need more frequent calibration and maintenance than other types of sensors. An ISE’s reference junction must be porous for the sensor to read accurately. However, this requirement means the reference solution slowly leaks into the water. When the reference solution runs low, the data will start to drift. This is the main reason why calibration and maintenance are key to ammonium data collection.
How frequently one should calibrate depends on environmental conditions. In most freshwater scenarios, a four-week schedule is typically sufficient for In-Situ ammonium ISEs. But because reference solution is consumed in the process of measuring, sensors in high-ammonium environments may require more frequent calibration. In other scenarios, sensors may be able to last longer than four weeks. ISEs should also be calibrated every time you refill or replace the reference solution or reference junction.
As with pH sensors, you should perform at least a two-point calibration on your ammonium sensor, but three is even better. The VuSitu app makes calibration incredibly easy with detailed instructions and visual guides, including range warnings during calibration if it appears the sensor is reading outside the appropriate range.
In-Situ recommends a three-point calibration with our 14, 140 and 1400 mg/L standards, specifically formulated to optimize performance of our probes. Clean the sensor according to manual instructions before calibration, then start with the lowest concentration of standard and work your way up—this leaves less chance of contaminating the first two calibration solutions with a higher-concentration standard.
At each concentration, pay attention to the raw mV readings. The user’s manual has guidance on the slopes you should expect.
After each calibration, rinse your ammonium sensor thoroughly with DI water to prevent any lingering standard from creating false readings. You should only clean your sensor with DI water; detergents can damage the membrane.
If you’re not seeing the desired slope after calibrating your ammonium sensor, or if you receive range warnings from VuSitu during calibration, your ammonium sensor may need its reference solution refilled or the reference junction replaced. Always calibrate your ammonium sensor after refilling or replacing either of these elements.
In-Situ instruments are designed to accommodate batch calibration of up to five ISE sensors in a single Aqua TROLL 700 or 800, or up to three ISE sensors in an Aqua TROLL 500 or 600 sonde (with a temperature sensor filling the remaining port) to cut down on time and calibration solution required.
The VuSitu app also streamlines the calibration process by automatically uploading calibration reports to your HydroVu account for instant, secure storage of calibration data for every sensor in a central, easily searchable location. Automatic cloud uploads make it easier to keep track of calibration schedules, so you don’t have to remember when ISEs are due for maintenance—or find out they’re overdue when data starts to drift.
Between deployments, always store your ISEs in the appropriate storage solution, to maintain that all-important hydration of the ammonium-selective membrane. Never store your ISE sensor in DI water.
Tip #3: Know what can interfere with your ammonium ISE
ISEs are not equally suited to all environmental conditions. Many application roadblocks are easily averted if you know what to avoid, but those new to ammonia monitoring may inadvertently deploy sensors in conditions that hinder accurate data collection.
ISEs are susceptible to interferences from high concentrations of ions around the sensor. Each ISE is vulnerable to a different set of ions—ammonium ISEs are particularly sensitive to concentrations of sodium, potassium and magnesium. This can complicate ammonium monitoring in saltwater environments. Sampling for these ions prior to deployment allows for consideration of these factors in sensor accuracy and longevity.
Secondly, in order to derive ammonia or total ammonia values from your ammonium sensor, instruments require data from other water quality parameters alongside ammonium. In-Situ’s multiparameter sondes, for example, should include a conductivity/temperature sensor and a pH sensor alongside ammonium to calculate ammonia measurements.
As with any sensor, it’s a good idea to study the manual before deployment, to fully understand any special requirements for accurate data collection. Knowing limitations like these not only sets you up to get high-quality data from your sensors but also help explain unexpected data should it occur.
Tip #4: Design installations around critical environmental factors
Location is always a consideration when setting up a new deployment, but it’s an even more important factor when deploying ISEs.
Take extra care not to deploy the sensor at the base of a river—either in sediment or in a location where sediment can build up. Long-term functionality of the sensor relies on the ammonium-selective membrane remaining in good condition. Any materials that can block or tarnish the membrane interfere with its ability to let in the ammonium ions, therefore interfering with data collection. You may also want to adjust wiper settings to rotate at less frequent intervals to avoid eventual wear and tear on the membrane. This is a balancing act, however, as it’s important to keep the sensor faces clean. Avoiding locations with sediment buildup will also help with this, as less sediment reduces the need for more frequent antifouling measures.
Another important consideration is selecting a site where water level remains high enough to completely cover the sensor at all times. ISEs need to stay hydrated; if the coating across the ion-selective membrane is allowed to dry out, their performance will be compromised even if reconditioned. Keep variable water level top of mind when designing a monitoring installation for your ammonium sensor, as your data will drift if the sensor dries out in the field.
Tip #5: Know when to replace your sensor
Ammonium and other ISEs have a shorter deployment life than other sensors, but they also have a limited shelf life generally—one that varies depending on deployment conditions and other factors.
Use your calibration data (paying particular attention to mV values) to make a call on when your ammonium sensor has reached end of life. You’ll notice data drift between calibrations happens more quickly as sensors age. If your sensor is stabilizing more slowly—either during spot check readings or during calibration—that’s another likely sign that your sensor is approaching end of life.
Regularly refilling and replacing the reference solution and junction will significantly extend the sensor’s life, but eventually the membrane becomes ineffective. At that point the sensor will need to be replaced. While cost or the hassle of setting up a new sensor may give you pause, the data is most important—and you won’t get any readings, let alone good ones, from a dead sensor.
If you have a large deployment of ISEs, it’s a good idea to track the ages of each individual sensor. VuSitu HydroVu Cloud Connection ensures instant data upload from VuSitu to HydroVu, which means that all your calibration reports and logs—from first to last deployment for every sensor—are automatically stored in a central location." You can review a sensor’s entire calibration history at a glance and quickly determine if it requires attention.
Don’t be afraid of the ISE
While ISEs may require a bit more attention than other types of sensors, you can have confidence in your ISE data when you follow these tips. Regular conditioning, calibration and maintenance, attention to deployment conditions, and awareness of the requirements specific to ISEs are all that’s needed for high-quality data collection.
In-Situ designs ISEs with features to make calibration and maintenance easier.
The stable reference design of the electrode extends the time between maintenance cycles.
A refillable reference junction allows for each reference solution and junction replacement, so you don’t need a new sensor every time solution runs low.
And all water quality sensors are designed to reach stability within seconds, to support spot-checking applications and quickly record changing conditions.
With design on your side and these tips in your toolbox, you can trust your ammonium ISEs to deliver quality data.
ISEs are known for being finicky; certain design elements essential for their operation also mean the sensors require regular maintenance. But don’t let that stop you! If you know their basic requirements, ISEs are a valuable addition to your monitoring program, both for spot checking and long-term trend analysis.
If you’ve never used an ISE or just want to brush up on best practices, here are five tips that lay out the most important considerations when working with ammonium sensors, so you can have confidence in your deployment and get the most out of your ammonia data.
Tip #1: Condition your sensor before use
Ammonium ISE sensors need to be properly prepared and conditioned before every deployment.
Start by refreshing the reference solution to ensure the reference electrode presents a stable value. Maintaining this stability is essential to getting quality data from your ammonium sensor.
In-Situ’s Aqua TROLL ammonium sensor has a refillable reference solution so you don’t have to purchase a new sensor every time reference solution runs out. Before use, empty the old reference solution and refill the sensor with new solution. Slightly overfill the chamber before replacing the junction to ensure there are no air bubbles.
The ISE membrane then needs to be conditioned for deployment. We recommend soaking the sensor in at least 140 mg/L as N standard for at least two hours, and preferably overnight. Rinse thoroughly with deionized (DI) water before calibration.
ISE membranes need to be hydrated to provide reliable data; repeat the conditioning process before every new deployment to ensure high-quality data collection.
Tip #2: Calibrate, calibrate, calibrate!
ISEs need more frequent calibration and maintenance than other types of sensors. An ISE’s reference junction must be porous for the sensor to read accurately. However, this requirement means the reference solution slowly leaks into the water. When the reference solution runs low, the data will start to drift. This is the main reason why calibration and maintenance are key to ammonium data collection.
How frequently one should calibrate depends on environmental conditions. In most freshwater scenarios, a four-week schedule is typically sufficient for In-Situ ammonium ISEs. But because reference solution is consumed in the process of measuring, sensors in high-ammonium environments may require more frequent calibration. In other scenarios, sensors may be able to last longer than four weeks. ISEs should also be calibrated every time you refill or replace the reference solution or reference junction.
As with pH sensors, you should perform at least a two-point calibration on your ammonium sensor, but three is even better. The VuSitu app makes calibration incredibly easy with detailed instructions and visual guides, including range warnings during calibration if it appears the sensor is reading outside the appropriate range.
In-Situ recommends a three-point calibration with our 14, 140 and 1400 mg/L standards, specifically formulated to optimize performance of our probes. Clean the sensor according to manual instructions before calibration, then start with the lowest concentration of standard and work your way up—this leaves less chance of contaminating the first two calibration solutions with a higher-concentration standard.
At each concentration, pay attention to the raw mV readings. The user’s manual has guidance on the slopes you should expect.
After each calibration, rinse your ammonium sensor thoroughly with DI water to prevent any lingering standard from creating false readings. You should only clean your sensor with DI water; detergents can damage the membrane.
If you’re not seeing the desired slope after calibrating your ammonium sensor, or if you receive range warnings from VuSitu during calibration, your ammonium sensor may need its reference solution refilled or the reference junction replaced. Always calibrate your ammonium sensor after refilling or replacing either of these elements.
In-Situ instruments are designed to accommodate batch calibration of up to five ISE sensors in a single Aqua TROLL 700 or 800, or up to three ISE sensors in an Aqua TROLL 500 or 600 sonde (with a temperature sensor filling the remaining port) to cut down on time and calibration solution required.
The VuSitu app also streamlines the calibration process by automatically uploading calibration reports to your HydroVu account for instant, secure storage of calibration data for every sensor in a central, easily searchable location. Automatic cloud uploads make it easier to keep track of calibration schedules, so you don’t have to remember when ISEs are due for maintenance—or find out they’re overdue when data starts to drift.
Between deployments, always store your ISEs in the appropriate storage solution, to maintain that all-important hydration of the ammonium-selective membrane. Never store your ISE sensor in DI water.
Tip #3: Know what can interfere with your ammonium ISE
ISEs are not equally suited to all environmental conditions. Many application roadblocks are easily averted if you know what to avoid, but those new to ammonia monitoring may inadvertently deploy sensors in conditions that hinder accurate data collection.
ISEs are susceptible to interferences from high concentrations of ions around the sensor. Each ISE is vulnerable to a different set of ions—ammonium ISEs are particularly sensitive to concentrations of sodium, potassium and magnesium. This can complicate ammonium monitoring in saltwater environments. Sampling for these ions prior to deployment allows for consideration of these factors in sensor accuracy and longevity.
Secondly, in order to derive ammonia or total ammonia values from your ammonium sensor, instruments require data from other water quality parameters alongside ammonium. In-Situ’s multiparameter sondes, for example, should include a conductivity/temperature sensor and a pH sensor alongside ammonium to calculate ammonia measurements.
As with any sensor, it’s a good idea to study the manual before deployment, to fully understand any special requirements for accurate data collection. Knowing limitations like these not only sets you up to get high-quality data from your sensors but also help explain unexpected data should it occur.
Tip #4: Design installations around critical environmental factors
Location is always a consideration when setting up a new deployment, but it’s an even more important factor when deploying ISEs.
Take extra care not to deploy the sensor at the base of a river—either in sediment or in a location where sediment can build up. Long-term functionality of the sensor relies on the ammonium-selective membrane remaining in good condition. Any materials that can block or tarnish the membrane interfere with its ability to let in the ammonium ions, therefore interfering with data collection. You may also want to adjust wiper settings to rotate at less frequent intervals to avoid eventual wear and tear on the membrane. This is a balancing act, however, as it’s important to keep the sensor faces clean. Avoiding locations with sediment buildup will also help with this, as less sediment reduces the need for more frequent antifouling measures.
Another important consideration is selecting a site where water level remains high enough to completely cover the sensor at all times. ISEs need to stay hydrated; if the coating across the ion-selective membrane is allowed to dry out, their performance will be compromised even if reconditioned. Keep variable water level top of mind when designing a monitoring installation for your ammonium sensor, as your data will drift if the sensor dries out in the field.
Tip #5: Know when to replace your sensor
Ammonium and other ISEs have a shorter deployment life than other sensors, but they also have a limited shelf life generally—one that varies depending on deployment conditions and other factors.
Use your calibration data (paying particular attention to mV values) to make a call on when your ammonium sensor has reached end of life. You’ll notice data drift between calibrations happens more quickly as sensors age. If your sensor is stabilizing more slowly—either during spot check readings or during calibration—that’s another likely sign that your sensor is approaching end of life.
Regularly refilling and replacing the reference solution and junction will significantly extend the sensor’s life, but eventually the membrane becomes ineffective. At that point the sensor will need to be replaced. While cost or the hassle of setting up a new sensor may give you pause, the data is most important—and you won’t get any readings, let alone good ones, from a dead sensor.
If you have a large deployment of ISEs, it’s a good idea to track the ages of each individual sensor. VuSitu HydroVu Cloud Connection ensures instant data upload from VuSitu to HydroVu, which means that all your calibration reports and logs—from first to last deployment for every sensor—are automatically stored in a central location." You can review a sensor’s entire calibration history at a glance and quickly determine if it requires attention.
Don’t be afraid of the ISE
While ISEs may require a bit more attention than other types of sensors, you can have confidence in your ISE data when you follow these tips. Regular conditioning, calibration and maintenance, attention to deployment conditions, and awareness of the requirements specific to ISEs are all that’s needed for high-quality data collection.
In-Situ designs ISEs with features to make calibration and maintenance easier.
The stable reference design of the electrode extends the time between maintenance cycles.
A refillable reference junction allows for each reference solution and junction replacement, so you don’t need a new sensor every time solution runs low.
And all water quality sensors are designed to reach stability within seconds, to support spot-checking applications and quickly record changing conditions.
With design on your side and these tips in your toolbox, you can trust your ammonium ISEs to deliver quality data.