pH Electrodes - At the Forefront of Electrode Technology

Hanna is the largest family-owned manufacturer of scientific analytical instrumentation, and a major European producer of electrodes. Hanna has helped propel the field of sensor technology with its innovative methodology. The Hanna line of pH electrodes is produced in state-of-the-art manufacturing facilities, and is available with glass or thermal plastic bodies.

In 1981, Hanna developed its own formulation for sensing glass with the help of the Experimental Institute for Glass in Murano Italy. From that point forward, the company has continued to offer these premium pH sensing glass electrodes that cannot be imitated. While other companies have reduced their offerings, Hanna has continued to expand their electrode line to support a multitude of specific applications. An extensive variety of cleaning and maintenance solutions are also available to keep electrodes at peak performance.

 

pH Electrode Manufacturing

Other electrode producers use the continuous fusion technique in crucibles with induction furnaces. In this practice, the glass is exposed to the fusion temperature for hours, making it difficult to retain the quality of the product due to the evaporation of some of its components. Hanna uses glass blowing technology typical of the Murano masters, with sensitive glass sticks fused in controlled batches. Only this technique, which exposes the sensitive glass to the high-fusion temperature for a matter of seconds, can guarantee the consistency and quality of the pH half-cell.

 

Connector Types

Connection and communication is the final consideration when selecting an electrode. It’s important to understand that not all electrodes connect to all meters. Some sensor connections are specific to a meter, brand, or manufacturer. Be sure to identify your connection requirements when replacing or purchasing a meter and electrode.

The BNC connector is the most versatile ,since it can be used with any meter that ues BNC, regardless of brand.

DIN, 3.5 mm, and screw type connections are generally proprietary to the meters they are supplied with.

 

BNC Connectors

BNC connector

A BNC connector is a universal connector for sensors. Any pH meter with a BNC connector is compatible with any pH electrode with a BNC connector, regardless of the device manufacturer.

 

 

 

DIN Connectors

DIN Connector

DIN Connectors are proprietary to the meter that uses the connector. The DIN connector allows for multiple wires to be in a single connector. Additional wires are used for temperature measurement and as a power source for amplifiers built into the probe. An amplifier in the probe prevents interference that a temperature signal can have on the pH signal. This threaded series of DIN connectors have a ferrule to attach the probe to the meter.

 

Quick Connect DIN Connectors

quick connect DIN connector

Like the DIN connectors above the quick connect DIN connector is proprietary to specific meters. The quick connect DIN connector simply pushes onto the meter. A rubber O-ring is used to fix the connector to the meter and provides a waterproof connection. Waterproof connectors are preferred since high humidity can create noise in the measuring circuit leading to inaccurate readings.

 

Digital Electrodes – 3.5 mm Connector

This digital connector contains a four-pole design used with digital electrodes. This connection allows digital data transfer from the sensor to the meter and is also meter-specific. he probe has an integrated microchip that stores calibration data, electrode type, and serial number, which allows for changing of sensors without having to recalibrate each time.

 

Digital Electrodes with Matching Pin – 3.5 mm Connector

3.5 mm digital probe connector

Like the Digital Electrodes with a 3.5 mm connector these electrodes take advantage of a matching pin to enable the Sensor Check technology. The Sensor Check technology measures the impedance across the glass sensing surface to evaluate if there are any micro fractures present and through the reference junction to indicate issues with the junction including if it becomes clogged.

 

 

 

Membrane Geometry (Tip Shape)

Our sensing membranes are fabricated in four different shapes; each serves a unique purpose, maximizing sensor accuracy, response, and longevity.

Spheric Profile

Spheric tips are recommended for general use in aqueous solutions. The round bulb geometry is the most common shape for a glass pH membrane and provides a wide surface area for a variety of liquid samples to contact.

 

 

 

 

 

 

Junction Design

The type of junction used in a pH electrode is one of the most important design considerations when selecting the right sensor for your application. The junction is the electrical pathway between the sample and the internal reference half-cell. This reference chamber contains an electrolyte solution, which diffuses through the junction into the sample. Any clogging of this junction may result in erratic and unstable readings.

Porous ceramic

A porous ceramic frit is one of the most common junctions available for standard laboratory applications. The ceramic material is easily fused with the electrode glass and has a similar coefficient of expansion. A single electrode may contain a single, double, or triple ceramic frit, allowing for enhanced electrolyte flow. Samples with low conductivity benfit from a higher flow rate since more electrolyte flows into the sample and increases the conductance for the measurement circuit to work.

Single Ceramic – 15 to 20 μl/hour flow rate

Double Ceramic- 30 to 40 μl/hour flow rate

Triple Ceramic- 40 to 50 μl/hour flow rate

 

Porous PTFE

Polytetrafluoroethylene (PTFE) contains hydrophobic properties, providing one of the most chemically resistant junctions available It is commonly used in pH sensors for industrial applications because of its chemical advantages and durability.

 

 

 

The Electrode Body

Whether you are using a half-cell pair or combination electrode, the body material is an important consideration. The body of a pH electrode can be made of many different materials that may help to make pH measurements easier. The right body material will vary depending on the testing environment, the sample type, and the frequency of use.

Glass Body

Glass bodies are a staple of pH electrode design. Glass is resistant to a variety of chemicals, is easy to clean, and transfers heat readily for fast thermal equilibrium between the sample and the sensor. Glass body electrodes are ideal for any type of laboratory application.

 

 

 

 

 

 

Refill Type

pH electrodes fall into two main types of categories. Either they are refillable, when solution is replaced on a regular basis or do not require refilling.

The type of solution a refillable probe uses is based on whether it is a single junction or double junction. The single junction probes will use 3.5M KCl with AgCl as a fill solution while the double junction probes use 3.5M KCl. Applications with heavy metals and Tris buffer should use the double junction probes, since the fill solution is silver free, to prevent any precipitation of silver that could clog the junction.

 

 

 

Gel Filled

The following probes are considered maintenance free since the probes are filled with a gel. All pH electrodes require maintenance including calibrating, cleaning, and storage, but these probes do not require the replacement of fill solution. Gel filled probes are common with probes used in the field and for food applications that need an open junction design to prevent clogging.

 

 

Polymer Filled

Like the gel filled probe these probes do not require a refill solution. These probes use a polymer based gel that allows measurement at higher temperatures and pressures.

 

 

 

Junction Type

Conventional electrodes are normally single junction. As depicted by the figure above, these electrodes have one junction, which puts the reference electrode system in direct contact with the sample. Under adverse conditions, such as high pressure, high temperature, highly acidic or alkaline solutions, 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 cell can become contaminated, leading to electrode failure. Another potential problem with single junction electrodes is the clogging of the junction due to AgCl precipitation. AgCl is less soluble in the sample than in the reference electrolyte solution. Especially when the sample contains heavy metals or Tris buffer. Therefore, when the electrolyte solution makes contact with the sample, some AgCl will precipitate on the external face of the junction, resulting in readings that drift or are erratic.

Hanna’s double junction system, as the name implies, has two junctions, only one of which is in contact with the sample as shown in the figure above. Under adverse conditions, the same tendency of sample ingress is possible, however, electrode contamination is minimized since the reference electrode system is separated physically from the intermediate electrolyte area. The likelihood of junction clogging is also reduced with a double junction electrode since the outer reference cell uses a fill solution that is “silver-free”. Since there is no silver present, no precipitate can form to clog the junction.

 

 

Half Cell Electrodes

Every pH electrode is combined of two cells. These two cells are known as half-cells. Most pH electrodes that are used are combination pH electrodes in which both half cells are combined into a single probe design.

Half-cell electrodes are available in either the pH indicating half-cell or the reference half-cell.

 

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