How to Maintain your Sonde and Get the Most from your Multiparameter Meter!
Using a Multiparameter Water Quality Meter can a very valuable analytical tool! Having quick access to a range of critical water quality parameters such as pH, electroconductivity (EC), dissolved oxygen, turbidity, temperature, and others – all in a single convenient meter – makes analyzing trends and changes in surface, ground, waste, and storm waters much easier!
We are often asked questions about these meters – things such as how best to store them when not in use, or how often to calibrate. Let’s explore some of the most commonly asked questions we receive so that you can be fully informed about how to get the most from your instrument!
Top 8 Questions You Should Be Asking (And Their Answers)
Q.1 What Exactly Is A Multiparameter Water Quality Meter?
Multiparameter water quality meters incorporate multiple sensors into a single large “probe,” commonly referred to as a sonde. In doing so, the user can wield a single instrument capable of providing multiple pieces of information in a single system. Common sensors you might find meters of this variety include things like pH, ORP, Dissolved Oxygen, Electroconductivity/TDS, Turbidity, Temperature, Pressure, and even GPS coordinates.
Q.2 What Items Do I Need To Have To Ensure Accurate Results and Proper Care Of My Meter?
Caring for these meters can be very simple! When dealing with a meter that uses a sonde, you will need to be mindful of what each sensor needs to remain in optimal condition. In general, that will come down to – does my sensor need to be Cleaned? Calibrated? Conditioned?
Depending on your specific meter, and which sensors you need to maintain, you may need different things on hand. Here are some guidelines:
- pH/ORP sensors – storage/conditioning solution, calibration solution(s), and cleaning solution
- Conductivity – calibration solution
- Dissolved Oxygen sensors – replacement membranes, electrolyte, and an optional zero-oxygen solution for a two-point calibration
- General Purpose – polishing brush, abrasive pad, o-ring grease, and optionally spare o-rings
Q.3 How Do I Clean My Meter?
Okay, you won't be scrubbing your meter clean, but there are certain things you can do to cleanse the sensors.
When we discuss cleaning a sensor, there is general rinsing, and there is also the use of a pH cleaning solution.
- General Rinsing: When cleaning off your sonde and sensors between samples, after recent use and before storage, after calibration, or after being exposed to a pH electrode cleaning solution, you will generally be simply rinsing off your sensors with some sort of fresh water. Ideally deionized, pure water will be best to avoid contaminating any future readings or calibrations. This applies to sonde as a whole and all your sensors.
- pH Cleaning Solution: A wide range of pH electrode-specific cleaning solutions are available, and these are optimized to break down common build-ups from pH sensors. Generally, pH sensors are more sensitive to buildup impacting their performance, so therefore solutions are available to help with things like algae, fungi, bacteria, oils, minerals, etc.
pH cleaning solutions are designed for the pH/ORP sensor but can be used on certain other sensors without issue, such as your EC sensor.
Q.4 How Can I safely Disinfect My Sonde If Required For My Testing Needs?
Sometimes you may need to disinfect your entire sonde beyond just rinsing it off, especially when dealing with multiple sampling sites to prevent cross-contamination. Some safe options include:
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Dilute detergent solution.
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Dilute a bleach/chlorinated solution.
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Most quaternary disinfectants without extreme pH’s or any aggressive additives or solvents.
Q.5 How Often Should I Calibrate And What Solutions Should I Use?
You will need to be sure to calibrate your pH, Conductivity, Turbidity, and ISE sensors regularly. The frequency required will vary. Typically, there is a separate solution used for each sensor, but we also offer a QuickCal solution to help make things more convenient when speed and convenience are important. Remember that a good calibration translates into a more accurate result.
pH
- pH – The pH sensor (commonly pH and ORP in one) will likely need calibration the most frequently of your sensors because it is the most sensitive and has a finite life as the glass slowly breaks down over time (with or without use). You should calibrate this daily (if the pH electrode is used daily and/or in aggressive conditions), or just before using it (in case the electrode is used periodically). Unless using QuickCal solution, it is recommended to calibrate to at least 2 pH points such as 7.01 and 4.01, with the best accuracy over the widest range achieved by calibrating to 3 points such as 7.01, 4.01, and 10.01. Ideally you should bracket your testing range when choosing your buffers.
EC/Electrical Conductivity
- EC – The EC/TDS sensor is more resistant to drift between calibrations, but should still be calibrated daily when used daily, or before use otherwise. The response across the measurement range is more linear than pH, so it is recommended to calibrate to a single EC value close to the expected range.
DO/Dissolved Oxygen
- DO – The DO sensor, like the pH sensor, should be calibrated daily or just before using it. DO can be calibrated to one or two points. You can choose to calibrate to just a single point with DO, which will be 100% DO and doesn’t require any specific solutions. To further ensure accuracy especially for lower level DO measurements, a second calibration point at 0% DO is recommended by using a zero-oxygen solution, such as HI7040L. (You can also verify your membrane condition by ensuring the meter reads “0.0” in the HI7040 solution.)
Turbidity
- Turbidity – This sensor needs calibration the least, but calibration is required every time the sensor is removed/replaced and is recommended to be part of yearly validation of your system. For best results, the recommendation is to perform a three-point calibration at 0.0, 20.0 and 200.0 FNU
A note on QuickCal solution – This single calibration solution is capable of calibrating your pH sensor to a single point with a standard value of 6.86, and your conductivity sensor to 5.00 mS/cm. Since this necessitates performing the calibration in a calibration beaker, it is also very easy to empty the beaker and use it as a humidified environment to calibration your Dissolved Oxygen sensor to 100% saturation. This is very convenient, but if precision is paramount, especially for pH measurements outside of the neutral range, a traditional 3-point calibration of 4.01, 7.01, and 10.01 may be superior.
Q.6 How Should I Store My Meter When Not In Use?
Each of your sensors will have different storage requirements, and it will vary depending on how long the meter will go without use.
| Type of Storage | pH/ORP | EC/TDS | DO | Turbidity | ISEs | Temperature |
| Regular Storage (Less Than 3 Days) | Store in cap with storage solution. |
Rinse, and then store dry. |
Rinse, and store dry (you can keep the membrane cap on). | Rinse, and then store dry. | Store dry in the protective cap when not in use. | Rinse, and then store dry. |
| Long-Term Storage (Over 3 Days) | Store in cap with storage solution. | Rinse, and then store dry. | Remove the membrane, dry the tip, polish the metal, and install the protective cap. | Rinse, and then store dry. | Store dry in the protective cap when not in use. | Rinse, and then store dry. |
Q.7 Does It Cost A Lot To Maintain A Multiparameter Meters Such As The HI9829, HI98194, HI98195, and HI98196?
Nope! The only annual costs items when using a multiparameter meter would include:
- pH and Conductivity calibration solutions – Cost varies based on use Optional DO 2nd point 0% Oxygen Calibration Solution
- pH cleaning solution
- DO Membranes and Electrolyte
- pH/ORP Sensor (Lasts 12-18 months; we recommend budgeting for annual replacements)
- DO Sensor (Lasts 1-2 years; we recommend budgeting for annual replacements)
Q.8 What Maintenance Should I Be Performing Besides Cleaning, Calibrating, And Properly Storing My Sensors?
There are only a few other things to keep in mind for the best results with your meter.
DO – Change your membrane and electrolyte, and polish the sensor!
- Change the membrane whenever: a) it has been 2 months, b) they do not read “0.0” in a zero-oxygen solution, or c) when measurements are unstable
- Replace your electrolyte monthly, ensuring that you tap the cap to ensure that no air bubbles remain trapped. Avoid touching the membrane.
- Polish the sensor every time you change your membrane! With the sensor facing down, completely unscrew the cap counterclockwise. If any deposit scales are found on the sensor, gently brush the sensor surface with the supplied brush, while paying attention to not damage the plastic body. Do not use the brush on the membrane. If the deposits cannot be removed by brushing use the supplied abrasive pad and try to achieve as much luster as possible for best performance.
Turbidity – At least annually, clean, inspect, and calibrate!
- Gently remove any material that is attached to the face of the turbidity sensor taking care to not scratch the optical windows. Use a soft cloth and non-abrasive detergent. If there are cracks or scratches on the optical windows, the EC/turbidity sensor must be replaced.
ISEEs – Ion Selective Electrodes for Multiparameter meters are best when used for short-term deployments and can yield trend information for specific ion activity levels. WARNING: FOR ALL ISES, TO AVOID DAMAGE, ONLY TO BE USED IN FRESHWATER
- For chloride ISE sensors (HI7609829-11), if the sensor pellet appears tarnished, use a polishing strip to remove the oxidized surface. Cut off approximately a 1-inch piece of the strip. Wet the frosted side with water and place against damaged surface. Place your thumb against the shiny backing and slowly rotate back and forth while applying gentle pressure. If dark deposits appear on the frosted surface, move the paper slightly. Continue polishing until you are satisfied with the surface. Rinse sensor with water. After every series of measurements, rinse the probe with tap water. If a more thorough cleaning is required, clean the sensor with the supplied brush or a non-abrasive detergent. Ensure that the two cylindrical holes in the sensor are free of foreign material.
General Meter Considerations
- When the probe and sensors are disassembled for routine cleaning, it is important to inspect o-ring for nicks, cracks and damage that may cause leakage. We offer a complete kit that includes: DO electrolyte, DO membranes, small polishing brush, and replacement o-rings and grease for the sensors.
We hope that all if this information can help you get the most out of your meter! As always, if you have any doubts, please don’t hesitate to contact our Technical Service team or your Hanna Representative!
Got Questions?
For more information regarding how Hanna Instruments can help you with your testing needs, contact us, as sales@hannainst.com or 1-800-426-6287.
