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pH ORP Conductivity/TDS/Resistivity Dissolved Oxygen Turbidimeters Photometers

How often should I calibrate my pH meter ?

This question brings out another question; how accurate do you want to be? As no application is the same, here is a good way to know when calibration is due:


Perform a calibration on day 1. On the following day, simply soak your electrode in the original buffers you performed calibration with and note the readings.

If the readings are still within your expectations, keep doing this procedure everyday until you are not happy with the accuracy. Then proceed to calibrate and take note of the number of days that went by since day 1 of calibration. If 5 days went by, proceed to calibrate every 4-5 days.

As the pH electrode gets older, proceed to do this test monthly to confirm number of days required between calibrations. This is also a good way to forecast probe cleaning or replacement.

*All manufacturers specifications on accuracy are based on calibration prior to each measurement. Some specific samples do require calibration prior to each measurement, such as food products, very dirty sample or in presence of strong chemical concentration. Do not hesitate to contact us for tips about your specific application or consult this list of electrode applications.

What is the expected life of a pH electrode ?

Care and maintenance is the answer to this question. Generally speaking, a pH electrode that is well maintained can last up to 2 years.

High temperature applications & abrasive chemicals will greatly shorten the life of a pH electrode. Pressure is also a factor for in-line process. Make sure you have the proper electrode for your application.

What should I store my pH electrode in and why ?

pH electrodes need to be kept wet in order to keep the glass sensitive part in good condition. If the glass sensitive part dries out for more than 6 months, the pH electrode will die. If it dries out for a few months, it can be regenerated by soaking into storage solution overnight.

The storage solution brings and keeps a constant ion activity in the sensing part that will assure fast response and accurate readings. Always store your pH electrode after your series of tests are done. Electrodes that are not stored into storage solution will show slow response and fluctuations in readings.


Many people think that pure water is good for pH electrodes. This is wrong. Pure water actually kills pH electrodes by sucking its electrolyte out of the reference chamber. Pure water is excellent for rinsing between samples, but armful for storage purposes. If you are out of storage solution, a pH 4 buffer can be used for a few weeks. Long term storage into pH buffers is not recommended as they contain phosphate.

Why pH electrodes have different tip shapes ?

pH is a critical parameter for an incredible number of applications going from general water to food, soil, fruits & vegetables, blood, synthetic products and many others. For that, manufacturers have developed different pH sensors for all major applications. This ensures ease of use and longer life of the electrode in a specific application. Different types of junctions, electrolytes and materials used in electrode construction are also part of the design. Below are typical tips and their intend :

Sphere tip: it is the most common tip found in the market as it is mainly used in laboratories on general liquids.
Cone tip: its shape allows easy penetration into semi solids, emulsion solutions, cheese and meat. Mainly used in the food industry.

Flat tip: its construction in intended for surface measurement such as fruits & vegetables skin, drops of samples, human skin, etc.

Knife tip: the knife probe allows for penetration into semi-frozen food, meat, hard to penetrate food products or others.

Many other types of tips are available. The above are the most common.

What is this new ¨Replenishable junction¨ you guys have invented ?

Over time, the junction which is the most sensitive part of the pH electrode can become clogged. This results in the electrode response becoming increasingly sluggish and eventually impossible to calibrate. With the new Hanna replenishable junctions, by using an ordinary pair of tweezers, simply pull out 1-2mm (1/8’’) of the fiber junction and you will literally have a reconditioned pH electrode. This procedure can be repeated up to 15 times, before the whole fiber gets out.

What is the difference between single and double junction ?
Conventional electrodes are normally single junction. As depicted by the figure below, these electrodes have only a single junction which serves to put the reference electrode system in contact with the sample. Under adverse conditions e.g., high pressure, high temperature, highly acidic or alkaline solutions etc., the positive flow of the electrolyte through the junction is often reversed resulting in the ingress of sample solution into the reference compartment. If this is left unchecked, the reference electrode ultimately is contaminated, leading to complete electrode failure.
Hanna’s double junction system, as the name implies, has two junctions, only one of which is in contact with the sample. Under adverse conditions, the same tendency of sample ingress is evident. However, as the reference electrode system is separated physically from the intermediate electrolyte area, the contamination of the electrode is minimized. This leads to long electrode life. The chances of recovery are also higher if proper maintenance procedures are taken.

How do I measure pH & EC in soil with extraction method?

Extraction method to measure pH & EC is as follow.

1- Mix 3 oz. of soil with 6 oz. of water

2- Let mixture stand 15-20 minutes

3- Filter liquid into clean cup

4- Measure

Simplify these pH & EC measurement by measuring directly into soil with HI 99121 pH meter & HI 993310 EC meter.


Do I need to calibrate an ORP electrode?

No. ORP electrodes do not need calibration with the meter such as pH. Still, ORP electrodes need to be conditioned prior to use.

When the electrode is new, soak the tip in warm tap water. This will enhance the flow of the reference junction. To check function of the electrode, immerse the tip in ORP solution HI 7021L or HI 7022L. The reading should be +/- 50mV from the value indicated on the bottle.

If the reading is not within the +/-50mV, oxidizing or reduction treatment with HI 7092 or HI 7091 is required. It will also prepare the electrode’s surface and speed initial response time. Since in-line process electrodes are already in a solution, a simple test with either HI 7021L or HI 7022L will show you the electrode’s condition.

Should your probe not be accurate enough after conditioning & testing, follow the cleaning procedure.

ORP sensor, platinum or gold ?

Platinum sensor: use in oxidizing reaction (above 500mV) such as pools & spas, municipal drinking water.

Gold sensor: use in reducing environment (below 500mV) such as galvanic applications, mining industry (Cyanide).


What is the relation between conductivity & dissolved solids (TDS)?


By taking several water samples and making an analysis of each element in the water and then comparing the results with the EC measurement, a ratio was established:

Analysis EC Meter
Potassium 50 ppm
Magnesium 45 ppm
Calcium 96 ppm
Chloride 80 ppm
Sulphate 99 ppm
Sodium 120 ppm
Aluminum 3 ppm
Zinc 0 ppm
Manganese 1 ppm
Copper 4 ppm
Iron 2 ppm
Boron 0 ppm
Molybdenum 1 ppm
Phosphorus 0 ppm
Nitrate 11 ppm
TOTAL: 512 ppm 1000µS
Most samples had a ratio of approximately 0.5 for TDS (ppm) compared to EC (µS/cm). The following conversion factor was then established:

2 µS/cm = 1 ppm

(2 µS x 0.5 = 1 ppm)

From there, TDS meters were built to measure conductivity as usual and then multiply that reading internally by 0.5 to display a ppm reading.



The process of making an analysis of each dissolved element in water is long, expensive and usually requires experienced people such as chemists. Commercialization of TDS meters allows any user to have a good approximation of dissolved solids at an affordable price.


It is important to know that the conversion factor used for TDS meters is an approximation of what a complete analysis would give in TDS.

More important is the fact that this conversion factor of 0.5 was set from a general water analysis, containing normal values of each dissolved element.

For agricultural application, another type of TDS exist : TDS442. For detailed explanations of TDS442, click here.

Dissolved Oxygen

My electrode is dry. What should I do?

Remove the red and black plastic cap or the membrane assembly. Soak the bottom 1 inch in electrolyte solution for 5 minutes. Rinse the membrane with electrolyte and refill with clean electrolyte. Gently tap the sides of the membrane cap to ensure that no air bubbles remain trapped. Adjust O-Ring inside membrane cap. With the sensor facing down screw the membrane assembly.

My readings are not stable. What should I do?

The probe is under polarization with a fixed voltage of approximately 800mV. Probe polarization is essential for stable measurements with the same recurring degree of accuracy. With the probe properly polarized, oxygen is continually ''consumed'' by passing through the sensitive diaphragm and dissolving in the electrolyte solution contained inside the probe.


Why do I get "Err 1" reading on my turbidity meter?

"Err 1" is an error code that signifies that the light flow is reduced. The cuvet should be cleaned with the solution and the tissue designed for this use. If this procedure has not removed your error code, the light source will need cleaning. This should be performed yearly, more frequently if required. The light source inside the cavity should be cleaned with the aid of a cotton swab dipped in alcohol.


Why should I do if my readings are unstable?

The zeroing and the measurements should be done using the same cuvet. Interferences are possibly due to condensation or particles on the cuvet wall. Clean the outside of the cuvet with solution and tissue designed for this use.