Using Custom Sensors and Electrodes for Water Quality Monitoring

What is the Environment Act 2021 and what is Section 82?

The 2021 Environment Act is aimed at improving how water quality is measured, monitored, and managed in real-time, particularly in rivers, lakes, estuaries, and coastal waters. The Environment Act 2021 introduced several measures to improve environmental protections, and continuous water quality monitoring is a critical part of these efforts, especially for the management of wastewater and storm overflows. Section 82 of the Environment Act 2021 focuses on improving monitoring regarding water quality, specifically targeting how sewerage undertakers (i.e., water companies responsible for managing public sewer systems) handle wastewater discharges, including storm overflows, into rivers, streams, and coastal waters.

Sewerage undertakers are required to install and maintain monitoring equipment on storm overflows and combined sewer overflows to track how often they discharge untreated sewage into water bodies. Sewerage undertakers must ensure that any discharge from their sewer systems does not breach water quality standards, particularly in sensitive areas such as bathing waters and protected ecosystems.

The government guidance details the types of technologies and methodologies that sewerage undertakers should use to monitor water quality effectively. This includes specifications for:

• Flow meters and sensors for measuring discharge volumes.
• Water quality sensors for detecting pollutants (e.g., ammonia, pH, DO2, etc.).
• Data collection and management systems for storing and reporting monitoring data.

The legislation in place dictates that sewage undertakers must monitor their waste output upstream and downstream, of their asset being monitored, once per hour or every 15 minutes during a high-risk event. These changes are required to be rolled out as soon as practicably feasible and have started by 2025 with complete monitoring completed by 2035.

How can Sentek Help?

Electrochemical sensors play a significant role in supporting the Continuous Water Quality Monitoring Programme and compliance with the Environment Act 2021, particularly for sewerage undertakers in implementing Section 82. These sensors are designed to measure various chemical properties of water in real-time, offering precise and reliable data essential for maintaining water quality and detecting pollution. Sentek can provide a range of electrochemical sensors suitable for measuring common sewage works contaminants and key indicators of a water courses health:

• pH Levels
• Temperature
• Dissolved Oxygen
• Turbidity/Conductivity
• Ammonia – An increase in Ammonia is a common indicator of sewage contamination.
• Chlorine – Chlorine sensors can detect the presence of disinfectants that may be released from wastewater treatment plants.

Nitrate sensors help track nutrient levels, which can cause issues like eutrophication (excessive nutrient enrichment in water bodies leading to algal blooms and oxygen depletion).
As one of the leading UK sensor manufacturers, Sentek can support clients with design of custom electrochemical sensors, probes and sondes to meet their specific water quality monitoring requirements. These can be installed at combined sewer overflows and other wastewater discharge points to monitor when and how often untreated wastewater is being released into rivers or coastal waters. Sensors provide early detection of changes in water quality. For example, if a sensor detects a sudden rise in ammonia or a drop in dissolved oxygen, this could indicate a pollution event such as a sewage spill. Early detection allows companies to respond quickly and mitigate the environmental impact before it escalates.

Sentek electrochemical sensors have been used for long-term deployment across the globe, providing continuous monitoring that ensures companies remain compliant with the environmental regulations over time. By tracking trends and long-term changes in water quality, sewerage undertakers can identify problem areas, manage wastewater systems more effectively, and make informed decisions on infrastructure improvements.

Sensors from Sentek can be integrated with remote monitoring systems and data platforms, enabling seamless collection and transmission of water quality data. This integration is particularly useful for large-scale, continuous monitoring across multiple locations, such as river systems or coastal areas.

The sensors can also be incorporated into smart monitoring networks, where data is aggregated and analysed to provide insights into overall water quality trends and potential sources of pollution.

Sentek electrochemical sensors could significantly enhance water quality monitoring efforts by providing reliable, real-time data that helps sewerage undertakers meet their obligations under the Environment Act 2021 Section 82. These sensors enable proactive management of water resources, ensuring timely detection of pollution and helping to maintain high environmental standards.

Ammonia vs Ammonium

Ammonia is just one component in sewage that can be particularly harmful to aquatic life, it can be very challenging to monitor, particularly in the field. Ammonia ISE are available but presently are only practically useable in a lab-based setting.

Ammonia is only present as the deprotonated form NH3 in a basic pH greater than 7, below this it is mostly in the less harmful ammonium ion (NH4+). Ammonium is unable to cross cellular membranes so is therefore much less toxic than ammonia. As pH and temperature increases the proportion of ammonium being deprotonated to the smaller and more harmful ammonia increases so by monitoring NH4+, pH and temperature we can relatively accurately infer the ammonia concentration in the water. The table below shows the percentage of ammonia vs ammonium at varying pH and temperature.

This can be plotted onto a curve also shown here.

Schematic model of ammonium ion (NH4 + ) and neutral ammonia (NH3) proportions in function of the pH. At acidic and neutral pHs, NH4 + is the most abundant species. However, NH3 is dominant in highly alkaline solutions. Scientific Figure on ResearchGate. Available from: https://www.researchgate.net/figure/Schematic-model-of-ammonium-ion-NH4-and-neutral-ammonia-NH3-proportions-in_fig2_358973331

Calibration and Maintenance

Sensors or sondes can be pre calibrated prior to installing but will need periodic recalibration to maintain a high degree of accuracy. Over time the sensor will begin to drift away from the calibration point. Each sensor type will drift at a different rate as they age – the longer the sensors go without calibration the greater degree of uncertainty the measurement will have.

Regular maintenance will also be required to ensure that the sensors or sondes are working at their best, giving that monitoring a water way will naturally lead to an amount of biological fouling to the sensors. Contamination of the sensor junctions or plates will lead to increased resistance which in turn will skew measurements, so it is important that these are periodically cleaned off and recalibrated.

For more information on the Environment Act 2021 Section 82 and sensors used to measure chemical properties of water, contact a member of the team.

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Electrodes For Electrochemical Analysis and pH Control in Wastewater Treatment

Any wastewater produced in industry must be analysed, treated and decontaminated before it can be reused or released. It is important to set limits on the water quality to ensure that legislation is adhered to. Electrochemical analysis and pH control of wastewater pre and post treatment is needed to ensure that the treatment has had the desired effect, and the waste is safe to discharge.

How you treat wastewater really depends on the contaminants and their concentrations. A range of tools are available for quick in-lab or inline electrochemical analysis of water such as conductivity, pH and various different target ions can be measured using ISE. By using a selection or maybe just one of these electrodes you can take a more targeted approach to wastewater treatment allowing you to use the correct chemicals in the correct volumes to treat the contamination, ultimately reducing costs.

Batch or continuous pH monitoring and control?

Most water treatment systems are integrated into existing industrial facilities and need to be constantly adjusted based on environmental, operational and legal factors. As such, continuous monitoring control measures must be implemented at all times. This can be either done manually by qualified technicians or by automated instrumentation. Manual control measures involve testing the pH levels in water at least once a day and making any manual adjustments accordingly. Some facilities where the pH levels must be kept at a certain level at all times, precise automatic monitoring systems need to be used. Sentek produce a range of sensors suitable for inline monitoring these are specifically designed to withstand high pressures and temperatures so that they are suitable for CIP procedures. By using continuous monitoring, a system can automatically dose the wastewater to allow effluent to be safely withing the desired range at all times and can automatically alert operators when outside of defined limits to ensure that legal limits aren’t breached, and the facility is safe at all times. By using a feedback loop a facility can dose a precise amount to constantly stay within range minimising waste chemicals. Long term data monitoring can also give the operators the opportunity to analyse wastewater trends and optimize water treatment.

pH control in wastewater

Measuring pH levels in wastewater is one of the simplest and most common ways to determine the quality of the water and the best way to treat it. pH is measuring specific ions; either H+ or OH- in water. In the UK, drinking water must be between pH 6.5 and 9.0, this can be quickly measured either inline or by an operator using a pH electrode. Using pH measurement can take the guess work out of how to treat waste streams. You can deliver an exact amount of chemicals to balance the pH that is safe to dispose of. Water can be treated by manipulating the pH to remove certain impurities, for example a range of heavy metals can be removed by adjusting the pH of solution into a basic range to form metal hydroxides; these are insoluble compounds which can be easily filtered out before then adjusting the waste stream back into an acceptable range.

Chemical treatment efficiency – Many chemical processes used in wastewater treatment, such as coagulation and flocculation, depend on specific pH levels to work effectively. For instance, certain coagulants will work best at specific pH levels to aggregate and settle out contaminants.

Achieving optimal biological activity – Wastewater treatment often relies on beneficial microorganisms to break down contaminants. These microorganisms have an optimal pH range where they are most active. If the pH deviates significantly from this range, the microbial activity can decrease, leading to reduced treatment efficiency. By adjusting the pH to acid levels, you can quickly kill bacteria and inhibit further growth of organic matter until you are ready to adjust back to safe levels for disposal.

Infrastructure Protection – Maintaining the right pH level can help protect wastewater infrastructure. Highly acidic or basic wastewater can corrode pipes, tanks, and other system components, leading to premature equipment failure and increased maintenance costs.

Dissolved Oxygen Electrodes

The biological oxygen demand (BOD) and chemical oxygen demand (COD) is used to estimate the impact discharging the waste stream will have in the short term to the receiving body of water. These can be rough indicators on the quality of the water and whether or not it is safe to discharge. BOD is a measure of the oxygen used for all of the metabolic activity of the microorganisms in the water and this is often used as a measure of how polluted a river system is. A higher polluted waste stream may have more organic material for biological life to grow on which in turn will consume more oxygen. A pristine river is considered to have a BOD at 1mg/L or less whilst untreated sewage is 600mg/L or higher. So, by measuring the BOD the effectiveness of water treatment can be analysed. This is monitored by measuring the dissolved oxygen in a sample and incubating in a sealed container for 5 days before remeasuring the dissolved oxygen content.

COD similar to BOD as both measure the relative oxygen demand of the waste stream however, the COD is a measure of the amount of oxygen that is consumed by reactions occurring in the water. This can be tested by measuring the dissolved oxygen content before oxidising all of the organic matter into carbon dioxide using strong oxidisers in highly acidic conditions then remeasuring the dissolved oxygen content.

ISE (ion selective electrodes)

Ion selective electrodes work similarly to pH electrodes and will allow the user to measure specific ion concentration in their effluent stream. By continuous measurement of target pollutants or treatment reagents the effluent treatment efficiency can be monitored. There are a range of ions that are considered pollutants by environmental agencies which can be detected and measured directly using our electrochemical sensors.

Conductivity electrodes

Conductivity is an extremely simple low maintenance method to determine contamination levels of your water. Conductivity cannot give you the concentration of specific ions except in some very well controlled experiments but will give an indication of the overall ion concentration. By measuring the conductivity of a solution this will give us a good overall picture of what is dissolved in the water. An increase in conductivity indicates an increase in ions or charge conducting solids in the waste stream.

ORP/ redox electrodes

Oxidation reduction potential (ORP) is the measure of a solutions ability to accept or donate electrons. An oxidiser will readily donate electrons whilst a reducer will readily accept electrons. An ORP electrode is a low maintenance electrode that can be used to measure the overall oxidation/reduction potential of an effluent stream. Chlorine for example is a very common cleaning agent it is also a very strong oxidising agent by measuring the oxidation potential you can see how much of the chlorine has reacted in the solution and if further dosing is required. Another example could be Ferric (III) sulphate, this is a common coagulant used in water treatment; this is also a reducing agent so the dosage can be monitored and controlled using an ORP electrode.

Choosing an electrode

To get the most accurate measurement of the quality of water there are several electrodes you could choose:

• pH electrodes – This is the most common way to measure water quality. The electrode tests how acidic or alkaline the waste stream is. Often a waste stream can be treated entirely by adjusting this parameter.
• Redox electrodes – These measure the relative oxidising or reduction potential of a sample. This can be useful in measuring disinfection techniques and how effective they are.
• Conductivity electrodes – This electrode measures the ability of the water to conduct an electrical current. Higher quality water, the lower its ability to conduct a charge, a high conductance is an indication of ions or conducting solids.
• Ion selective electrodes – Used to measure the concentration of specific ions in water. By using a range of these ISE, you could potentially detect particular ions present in your manufacturing stream that are making it through into your wastewater.

Contact our technical team today and find out if we have any electrodes for you.

Choosing the right electrode for analysis of wastewater and treatment is a combination of understanding the specific challenges of your industry and matching them to the features and specifications of available electrodes. Once a suitable set of electrodes or chosen, these will allow you to monitor your specific wastewater to ensure environmental compliance. Regular maintenance, calibration, and periodic evaluations ensure that the chosen electrode provides accurate and consistent results over time.

These electrodes and other bespoke options are available to purchase from Sentek. Download our water and wastewater treatment brochure, or view electrodes online that are suitable for electrocheimcal analysis and pH conrol in wastewater treatment.

Not sure what you need, or want to know more about pH analysis in wastewater treatment? Get in touch with us today to speak to a specialist.

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New Look For Sentek Electrodes

Available to pre-order today, next generation sensors offer updated features that draw on the years of hands-on experience that have shaped the electrode cap and refill seal, all whilst maintaining the same affordable price.

When we introduced the Sentek blue and orange cap in 1998, it’s striking colour and original shape was a fresh approach to lab and testing equipment that could, at times, be somewhat samey. Through innovative geometry and material experiences, the team at Sentek created something that was reassuringly reliable and enjoyable to use.

Whether used for testing biological samples in a laboratory, monitoring pH in a brewery, or the measurement of soil conductivity, the electrodes, and their striking cap design, brought the dependable experience that we expect from Sentek at an incredible price point. This has always been the purpose of Sentek’s electrodes, and now the product is only getting better.

Meet the next generation sensors by Sentek Ltd

We’re delighted to announce a new look for Sentek’s electrodes. This product has been meticulously crafted to deliver our Sentek signature premium feel and features in a sleek new design. Refillable electrodes are ready to use straightaway without the need to refill or remove dried Kcl solution through zero-leakage technology on a fully remodelled refill seal.

Materials have been a defining characteristic of our product design. From the robust ABS barrel to the flexible, durable properties of TPE, we’ve focused on creating a reliable solution that is easy to maintain.

Whilst fashioning a beautiful product we are also committed to practicality. In addition to being a perfect fit for standard electrode holders, the key range of electrodes will now feature sensor information and specification conveniently displayed on the electrode stem for easy identification.

These enhancements continue to demonstrate the team’s commitment to detail and to you, blending form and function so that you can carry out vital research, routine measurements or lessons in a chemistry classroom. We are delighted to offer next generation electrodes at the same great price.

“We’re thrilled to be launching this exciting new product upgrade which provides our customers with a stylish and reliable sensor” said Kenny Petrie, Sentek’s founder and Technical Director. “At our core, we constantly strive to provide our customers with exceptional quality at a reasonable price, and the features of this new design achieves just that.”

Contact the Sentek team at www.sentek.co.uk/contact to pre-order today. Orders will begin shipping in 2024 and the new look cap and refill seal will be applied to the Sentek branded range of electrode.

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The Anatomy of pH Electrodes

In this article, we delve into the anatomy of pH electrodes. We will explore key elements; including the reference system, electrolytes, membrane, and the electrode body. Understanding the inner workings of a pH electrode is beneficial to achieve precise and accurate pH measurements for your specific application.

Firstly, what is pH and why do we measure it?

A pH probe is one example of many ion selective electrodes (ISE) that are produced at Sentek. ISE and pH measurement are used from lab applications to work in the field. Sentek manufactures probes for a variety of customers with applications including engineering projects, process control, agricultural, environmental, medical, pharmaceuticals and food and the brewing industry.

pH is a quantitative measurement of the acidity or basicity of an aqueous solution; this is directly related to the concentration of hydrogen ions (H⁺) or hydroxide ions (OH^–) in the solution. When the concentration of OH^– is equal to that of H⁺ the solution is considered neutral which occurs at pH 7. As the amount of H⁺ in the solution increases the pH of the solution decreases and as the OH^– increases the pH increases.

Figure 1 Showing an example pH scale and the logarithmic relationship between the pH scale and the H+ concentration. Source Microsoft Bing images

pH is a logarithmic scale defined by pH =-_Log10 (aH⁺). This means that at pH 6 the activity of the hydrogen ion is ten times greater than that at pH 7, and pH 5 is 100 times greater than pH 7. A pH electrode uses potentiometric techniques to determine the activity of hydrogen ions in a given solution using a potentiostat. The measured potential describes hydrogen activity by the Nernst equation:

In order to measure the potential difference a pH probe requires not only an H⁺ sensitive membrane but also a non sensitive stable reference to compare against.

Reference

When looking at the anatomy of a pH electrode, the most common type of pH electrode in use today uses the silver/silver chloride (Ag/AgCl) reference electrode.  In these cells a reversible redox reaction is occurring between solid AgCl and solid Ag and dissolved Cl^–. A redox reaction describes how a reaction progresses via either the loss or gain of an electron.

Half-cell equation of Ag/AgCl:

The Ag/AgCl electrode will offer a stable and reproducible potential regardless of pH which makes it perfect for a reference electrode. The most common type of reference electrode used today is the silver/silver chloride due to its stable reading and non-toxic materials. Mercury/mercurous chloride (Hg/Hg₂Cl₂) is another type of reference electrode used; Calomel electrodes are less prone to blockages and are considered to be extremely stable, however due to the toxicity of mercury, it is generally avoided for the much safer silver/silver chloride (Ag/AgCl) reference.

Half-cell equation of Hg/Hg₂Cl₂:

The half-cell electrochemical potentials(E⁰) above for AgCl and the Calomel only show half the picture. In order to measure the potential difference another electrode is required to measure against. The half cells in this scenario would have been measured against the standard hydrogen electrode (SHE):

The SHE is an arbitrary zero point to measure all other potentials against. Due to the impracticality of using hydrogen gas the SHE is only very rarely used. In a normal pH electrode, the other half cell is normally a silver/silver chloride electrode behind a H⁺ sensitive membrane.

Once the pH membrane and the reference electrode are in the test solution the circuit is complete, with the only varying potential being the working electrode inside the membrane glass. The change in H⁺ on the outside of the membrane glass will change the potential of the working electrode which can then be compared to the reference electrode. This is why reference electrodes have to be completely insensitive to a change in pH and have a stable potential.

The anatomy of pH electrodes can change for many reasons, one being that electrodes can come as a mono or part of a combination for convenience depending on the application. The reference is in contact with the sample solution via some type of porous material such as cotton, teflon and ceramic. Each of the junction types have variable characteristics depending on the requirements of the electrode.

Ceramics are a robust junction material that have low flow rates but high junction resistance. Ceramics have very stable readings this makes them a great general purpose junction material. Due to the small holes and low flow rate ceramic junctions are prone to blockages and need to be kept clean, this can be combatted by using multiple ceramic junctions.

Teflon junctions have a higher flow rate and are therefore less prone to blocking than a ceramic junction. Due to the lower maintenance of teflon junctions these are easier to handle.

The simplest type of junction would simply be a small hole called a ground joint, this would offer the lowest junction potential and the highest flow rate. These are simple to clean but will require a lot of re-filling, great for viscous samples or samples with lots of suspended solids.

A double junction or even a triple junction could extend the life of an electrode in harsh environments. An additional cavity filled with electrolyte and another junction is used to further separate the reference from the sample. Double junctions are often used when a sample is particularly hostile to the reference in use, however, the junction potential of all of the internal junctions used will have to be considered as well the external junction and the types of electrolyte(s) used.  Using an electrolyte similar to the sample medium in the outer chambers can decrease the amount of overall junction potential.

Sentek has also developed an iodine/iodide pH and reference system which offers a fast response time and a low temperature sensitivity.

Figure 2 shows a diagram of Sentek electrode with labels pointing to all of the key components of a pH electrode

Electrolytes

Potassium chloride (KCl) solution is the most common type of electrolyte used in pH probes, it allows for a connection i.e. a salt bridge between the reference electrode and the membrane glass. When reviewing the anatomy of pH electrodes for your experiments, consider that different types of electrolytes are available for different applications, which can be key for decreasing the junction potential for more precise measurements. An advantage of KCl is that the diffusion rates of the anion and cation are very similar which helps to establish a stable junction potential. The electrolyte can be made into varying types of solutions and gels to fit any requirements. The combination of junction material and electrolyte will determine the flow of the electrode. Standard KCl solution is a free-flowing liquid that will pass quickly through a junction, this will keep the junction wetted through and allow for good connection from the electrode to the sample, this type of electrolyte is well suited to the controlled lab environment where high precision is key. Gelled electrolytes are used more in the field, these restrict the flow of the electrolyte whilst still allowing for a good connection from the electrode to the sample solution, having a thicker gel will not only last longer between re-fills but will also help protect the reference from contamination, these are well suited to work in the field and industrial applications. Sentek has developed pH electrodes and reference electrodes that enable pH measurement in a variety of difficult samples e.g. non-aqueous samples, soil samples, high pH, high salt concentrations as well as slurries and viscous samples.

Membrane Glass

For a pH probe to make a potentiometric measurement two electrodes are required, one stable pH insensitive electrode and another behind an ion selective membrane. In this case our target ion is H⁺ and the membrane glass provides us with our selectivity. All membrane glass is specially made to be a good ionic conductor to allow the transfer of charge from the outside of the pH bulb to the inside. As a pH bulb is immersed in an aqueous solution the outer layers of Si-O groups become protonated by H⁺, this is the formation of what is known as the leached layer. The ionic equilibrium shown below is the key element in the selectivity of the membrane:

There are two glass membrane/solution interfaces, one outside of the membrane and one on the inside of opposing polarity. The internal solution is stable as it is completely sealed so the difference in potential arises from the internal glass membrane/solution interface. The difference of the inner glass leached layer and the outer glass leached layer.

Figure 3 A diagram showing a not to scale illustration of how the charge is transferred via alkali metals to the inner solution from outside of the electrode. pH Electrodes – Chemistry LibreTexts

Sentek can produce a variety of different types of pH sensitive glass to suit the needs of the application, with a selection of relatively low resistance glass for quick response times or high resistance glass for extremely hostile environments. The temperature of a sample can not only greatly change the resistance of the glass membrane but can also change the activity of the ions in the solution, this is why adding temperature compensation into probes is becoming increasingly popular. We have a selection of temperature compensation selections for all available pH meters.

External Shell

It’s impossible to explore the anatomy of pH electrodes without considering the external shell. Most electrodes have a glass external body. Glass has very good chemical resistance even for most acids and bases. Glass also allows the user to have a clear view of the inside of their electrode, very useful when the electrode is refillable or to see any contamination. The obvious draw back being is that glass is brittle, so whilst useful in some applications, such as the lab, it may not be well suited to more rugged work in the field. Electrode bodies can be made from durable types of plastic and have even been made into specially machined metal bodies for maximum protection.

pH Electrodes from Sentek Ltd

Sentek offers a vast range of standard pH electrodes, from the P11 Protected Bulb, to the P11/DJ/NaF for Non-Aqueous Samples. Here at Sentek we can also offer the option to design and build electrodes to your exact specifications. Your unique applications may require specialised solutions, and we have the expertise to tailor our products to your precise requirements.

We understand that selecting the right sensor for your application can be complex, so our dedicated team are ready to assist with any questions you may have.

Get in touch today to discuss your requirements.

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Introduction to Voltammetry

Voltammetry is an electrochemical technique based on the measurement of the current produced by an analyte as a function of the potential applied to a working electrode. In many cases the applied potential is varied or the current is monitored over a period of time. The applied potential forces a change in the concentration of an electroactive species at the electrode surface by electrochemically reducing or oxidising it. Analytical chemists routinely use voltammetric techniques for the quantitative determination of a variety of dissolved inorganic and organic substances. The analytical advantages of the various voltammetric methods include excellent sensitivity with a very large useful linear concentration range for both inorganic and organic species. There are also many other uses including fundamental studies of oxidation and reduction processes in various media, adsorption processes on surfaces, and electron transfer and reaction mechanisms. Voltammetric methods are also applied to the determination of compounds of pharmaceutical interest and, when coupled with HPLC, they are effective tools for the analysis of complex mixtures.

The electrochemical cell, where the voltammetric process is carried out, consists of a working electrode, a reference electrode, and usually a counter electrode. In general, the working electrode provides the interface across which a charge can be transferred or its effects felt. In practice, it can be important to have a working electrode with known dimensions and surface characteristics. The auxiliary electrode can be almost anything as long as it doesn’t react with the bulk of the analyte solution and conducts well.

The reference electrode should provide a reversible half-reaction with Nernstian behaviour, be constant over time, and be easy to assemble and maintain. The most commonly used reference electrodes for aqueous solutions are the calomel electrode, and the silver/silver chloride electrode.

Voltammetry has developed very rapidly, and several types have been introduced with high efficiency, sensitivity, and selectivity. Of the numerous types of voltammetric techniques the more common ones are:

Linear sweep voltammetry – in which the current at the working electrode is measured while the potential between the working electrode and the reference electrode is swept linearly with time. The potential at which oxidation or reduction of the analyte occurs at the working electrode is shown as a peak or trough in the current.

Cyclic voltammetry – in which the current at the working electrode is measured while the potential between the working electrode and the reference electrode is swept linearly with time. Unlike with linear sweep voltammetry when a set potential is reached the potential at the working electrode is swept in the opposite direction to return to the initial potential. A cyclic voltammogram is obtained by plotting the current at the working electrode against the applied voltage. The sweeps maybe repeated many times.

Stripping voltammetry – in which there is pre-concentration of an analyte on an electrode, followed by a potential sweep to selectively oxidize or reduce the analyte, with the current generated proportional to the amount of analyte present on the electrode.

The original dropping mercury electrode was originally the working electrode of choice, however, the use of mercury electrodes has fallen out of favour because of the toxicity of mercury. Other electrodes that have gained favour for use in voltammetric methods include carbon paste, glassy carbon, platinum and gold. In addition, with a glassy carbon electrode it is possible to create a thin film of mercury on the electrode by reducing Hg2+. This provides the advantages of mercury electrodes described earlier without the necessity for using large quantities of mercury.

Sentek produces a range of working electrodes as well as calomel and silver/silver chloride reference electrodes. Sentek can also supply customised electrodes to meet many requirements.

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Most Read Articles

Before we dive into 2023, we wanted to look back and revisit some of our most popular news articles from last year. We covered many topics on our blog in 2022, from the launch of our all-new website to tips on how to choose the correct conductivity electrode.

Read on for a summary of our 5 most popular blogs from last year.

#1 Coming Soon! Stay tuned for our all-new website. In January, we celebrated the launch of our all-new website. A full overhaul of the site is designed with an intuitive layout, increased range of products, and enhanced functionality to make it easier for users to find what they need, quickly. Read more >

#2 The Use of Disposable and Non-Disposable pH Sensors in Medicine Production. Monitoring and controlling pH is critical to biopharmaceutical manufacturing to ensure the quality and yield of the final product. In this article we look at the use of single-use or disposable bioprocessing equipment. Learn more >

#3 Introducing a new look for Sentek electrodes. Exciting news! We’re launching a sleek new cap design and an innovative zero-leakage refill seal – no more dried KCl solution! The next generation design will be rolled out across the range of sensors, including pH, reference, conductivity and ISE electrodes. Read more >

#4 Choosing a Conductivity Electrode. Choosing the right conductivity electrode is important to ensure that the right product is being used to give the most accurate readings. In this informative article, we cover the factors to consider when choosing a sensor, as well as application advice when using the probe. Learn more >

#5 The Importance of Lab Testing for Food Products. Here we answer the question ‘Why is laboratory testing for beverages and food products essential?’, exploring how pH affects food and outline some food testing processes. Learn more >

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Disposable and Non-Disposable pH Sensors in Biopharmaceutical Production

The term “biopharmaceuticals” was coined in the 1980s and refers to pharmaceuticals produced using molecular biology techniques as opposed to synthetic drugs that are the products of chemical processes.

Biopharmaceutical processing systems have traditionally employed stainless steel piping and bioreactors. However, for some years the industry has moved towards single-use production methods which rely on disposable elements such as the bioreactor vessels themselves.

Single-use or disposable bioprocessing equipment is now increasingly being adopted for small scale commercial manufacturing replacing classic fixed stainless steel equipment based bioprocessing facilities. Generally, single-use equipment is composed primarily of plastic components that have been sealed and pre-sterilised with gamma radiation. They frequently have a long shelf life of up to 2 years.

While single-use technology offers several advantages including flexibility, it also introduces new measurement and monitoring challenges that need to be met by sensors designed for these applications.

Monitoring and controlling pH is critical to biopharmaceutical manufacturing to ensure the quality and yield of the final product. Requirements for the pH electrodes used in these single‐use bioreactors are different from those used in conventional stainless steel bioreactors where cleaning and sterilisation of the bioreactors means that the pH electrode must be resistant to these procedures or removed or protected. There are cost implications with these requirements which mean that the pH sensor should have a long lifetime. With single use bioreactors, however, long in use lifetime or resistance to steam and cleaning procedures are less crucial factors but a low sensor cost on a per‐use basis is important as well as a long shelf life.

Potentiometric glass electrodes are the most common pH sensors for bioprocess monitoring and control. They are well established, reliable and robust but are generally too expensive to be disposed of after a single run. Therefore, single‐use glass pH electrodes have been developed that can be pre-sterilised with gamma radiation. There are 2 types that are available – wet or dry stored pH electrodes. The wet storage electrode is kept in its calibration buffer thus providing a one-point calibration capability.

The dry stored electrodes have been developed to be integrated directly into the bioreactor during manufacturing including a gamma irradiation process and can be stored dry. The challenge for these is that they may not be possible to calibrate them until the bioreactor has been set up and where failure is now an expensive result. Some dry stored electrodes are claimed to be pre-calibrated before committing to storage.

Meeting The Needs of The Market

At Sentek, we have been producing electrodes, OEM sensors, and other accessories for over 30 years. As the leading manufacturer of bespoke electrochemical sensors in the UK, we follow all the current trends. We have a wide range of custom sensors including pH electrodes that can be dry stored and biotechnology solutions to suit your needs. Whether you need a pharma pH probe, accessories, or a custom solution to a problem, we will work closely with you to fulfil your needs. Check our website today to view our products online, or contact us about a solution to suit you.

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Importance of Lab Testing for Food Products

Why is laboratory testing for beverages and food products essential? Food quality testing laboratories help ensure suitability for consumption by checking them for any contaminants and perform quality analysis on parameters such as pH, consistency, nutritional levels, consistency of chemical composition, degradation (expiry dates), also test for storage conditions and microbiological activity. Metals, cleaning agents, pesticides and other additives can affect the overall safety, taste and quality of many foods. In addition, bacteria, such as e-coli and salmonella can make food unsafe to consume. Below are some of the testing processes that food laboratories carry out to ensure food products meet quality standards.

WHY pH LEVELS MATTER IN FOOD

While most people don’t consider how much pH affects their food, the fact is it can alter the properties of food in a number of ways. pH values can alter the nutritional value of food, can lead to decomposition or alteration of the chemical composition, can increase the bacterial activity over the accepted levels, and can also affect how long you can conserve it for. A wrong pH level can lead to unwanted chemical interaction between the existing ingredients, leading to unwanted negative reactions during consumption in worst cases.
pH values in foods are affected by the amount of free hydrogen ions present. The more acidic the food, the more free hydrogen ions are released. This can affect everything from the taste to the appearance of food, as well as their shelf life. Therefore, testing pH levels in a food quality testing lab is not only important in determining the quality of food, but also how safe it is. For example, some low acidic foods can generate dangerous bacterial spores if the pH level rises above 4.6. This is why pH testing needs to be so precise.

HOW pH LEVELS CAN AFFECT FOOD

• Production Methods: The acidity levels found in ingredients can affect how we prepare different foods, such as bread and alcoholic beverages. The balance between the acid and the alkaline can alter the speed of the process as well as the duration of chemical reactions, e.g. in breadmaking the pH of the dough can affect the viscosity build up as well as preservation and microbial safety.
• Flavour: The pH level of a food product can drastically alter how it tastes. The more acidic the food, the sourer the taste, which works well in foods that require that extra bite.
• Texture: pH levels can also alter the feel of a food product, which can be just as important as the taste. This can mean the difference between a hard and crumbly cheese and a smooth and creamy soft cheese.
• Appearance: pH levels can determine the colour and feel of a food product, such as the greenness of a cabbage or how orange a carrot is. Some manufacturers can play with a food product’s look by altering the pH levels.

WHY IS MEASURING pH IMPORTANT

• It allows manufacturers to create food products with consistent qualities.
• pH measurements allow manufacturers to find more efficient and cheaper ways of producing food.
• Ensures any health risks, such as bacteria growth or food alteration, are not passed on to the consumer.

TESTING pH IN FOOD PRODUCTS

When conducting lab testing of food products, it is essential to determine the pH level for each product. pH affects all aspects of food including the texture, flavour, and aroma. pH also plays a role in the growth of microorganisms that can lead to illness if consumed.

When testing the pH in food, there are two primary methods used:

1. Direct Testing – A pH reading is taken directly from the food product, usually using an electrode designed for the particular application. There is a shape, size and type of pH sensor for any application, perfectly designed to ensure application and sample compatibility. A measurement is taken by inserting the electrode directly into the food product. This type of testing can only be carried out on samples which do not have both solid and liquid parts, and have a uniform consistency. If pH measurement is required during the production process a sensor can be fitted to monitor the entire process (in-line).
2. Sample Testing – A portion of the food is taken, tested, and then discarded.

SAMPLE TESTING USING THE SLURRY METHOD

The Slurry Method is a form of sample testing, which involves diluting a food sample with deionised water. As there is not a considerable number of ions present in distilled or deionised water, this does not significantly affect the pH readings of the sample. Slurries are particularly useful when testing semi-solid or solid food products with a spherical-tip electrode, as the sample can fully surround the electrode and provide a more accurate reading.

HOW TO CREATE A SLURRY

1. Prepare 50g of your solid or semi-solid sample.
2. Take 100g of deionised water.
3. Combine the food sample with the deionised water to create a uniform paste. Further dilution may be required to the right consistency for pH measurement but it is recommended that as little water as necessary is used.
4. Test using the relevant method below.

TESTING SOLID FOODS

Solid foods, such as raw meats and cheese, can be tested using the following method:

1. Ensure that your electrode is calibrated. Conical-tip or knife probes would be the most suitable choice.
2. Decide whether you are testing a sample or directly into the product.
3. Rinse the electrode with deionised water.
4. Insert the electrode into your sample. Leave until a stable reading can be taken, and record the pH.
5. Rinse the electrode.
6. Take a second reading, ensuring this is equal to your first reading.
7. Rinse and clean the electrode before storing.
8. Store in suitable cleaning solution to ensure hydration of the pH membrane. Ensure that the junction has been cleaned which is particularly important for dairy and meat products where proteins may block the reference junction. Cleaning solutions will often contain enzymes that digest/break down the proteins.

TESTING SEMI-SOLID FOODS

Semi-solid foods, such as soft cheeses, yoghurts, and bread dough, can be tested using the following method:

1. Ensure that your electrode is calibrated. Either a spherical or conical-tip electrode can be used.
2. Take a sample of your product and, if necessary, create a slurry following the method detailed above.
3. Rinse the electrode with distilled water.
4. Insert the electrode into your sample. Leave until a stable reading can be taken, and record the pH.
5. Rinse the electrode.
6. Take a second reading, ensuring this is equal to your first reading. This ensures that the mixture is homogeneous.
7. Rinse and clean the electrode before storing.
8. Cleaning overnight and in between measurements as above.

TYPES OF PROBES USED IN LAB TESTING FOR FOOD PRODUCTS

When it comes to probes used in food quality testing labs, Sentek supply the following:

• Drinking Water Probe – A double junction Ag/AgCl probe used to measure the pH level of drinking water. Especially good in low temperature, low ionic strength samples.
• Jam Probe – A single junction AgCl liquid filled probe with replaceable ceramic junctions. Used for pH measurement in jams, fruit juices and preserves.
• Dairy Products Probe – A partial gel filled single junction AgCl probe with porous Teflon junction type. Used for measuring the pH level of dairy products such as milk and yogurt, as well as surface measurements for paper, skin and more. Also comes in an S7 variant.
• Penetration Food Probe – An Ag/AgCl gel probe with porous Teflon junction type. Features a spear point probe for penetrating and testing meats, cheeses and fruits. Also comes in a Micro Food Penetration probe format.
• pH Knife Probe – An Ag/AgCl gel probe with ceramic junction type. The stainless steel knife end protects the probe as it penetrates and measures frozen and defrosted meat products.

SENTEK

Here at Sentek we manufacturer and supply pH probes for a range of sectors. To find out more about our wide range of food probes, please get in touch with us today.

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Tips for Accurate Electrode Measurements

The pH of a particular substance or solution is a figure that conveys its acidity or alkalinity. Accuracy in the matter of pH measurements is of the utmost importance when monitoring all types of processes in a range of industries. High accuracy measurements give the insight of a certain chemical’s condition or effect, for example, in the food industry, it informs of nutrient status, behaviour, and microbial activity. In the Pharmaceutical and chemical R&D, a highly accurate measurement can verify if a reaction has reached completion, or if the correct compound has been achieved. It can also affect yields and the quality of the end product.

Tips from Sentek to ensure Measurement Reliability

Measurement accuracy is not solely dependent on the use of a high-quality sensor, and the experimental set-up and methodology should also be considered. The tips below will ensure measurement reliability, repeatability and high accuracy.

• Ensure full temperature equilibration of the sensor and sample. If the sensors are not left long enough to stabilise, the readings will drift.
• It is best practise to perform both calibration and measurement at the same temperature. If the calibrating buffer temperature differs from the sample temperature with more than 15°C, an error as great as 0.1pH can occur.
• Temperature should not fluctuate during observations. Take measures to keep the temperature as stable as practically possible.
• Use temperature compensation (internal/external) for both calibration and sample measurements if not performed at room temperature.
• Ensure the temperature sensor is completely submerged in the sample and allow it to fully reach equilibrium.
• If the sensor is fitted with a fill hole, ensure the cover is opened during measurement. If the cover is tightly screwed, the electrolyte cannot flow/diffuse into the sample, giving drifty and unstable readings.
• Ensure sensors are periodically maintained (clean after each use, change fill solution regularly, ensure correct and continuous hydration of the pH membrane and junction).
• Remove air bubbles by shaking in a downward motion. Bubbles can form inside the sensor, or get trapped on the pH membrane and junction, giving erratic readings.
• Do not touch the pH membrane as this could contaminate with grease/sweat. If this happens, wipe with non-abrasive tissue and propanol, then rehydrate the membrane.
• Do not rub the sensor when drying, as it could create an electrical charge (polarisation), which can take up to a few hours to dissipate.
• Stir sample slowly during measurement.
• Condition the sensor in the sample for approximately 1 hour prior to measurement.
• Store the sensor in electrode storage solution to keep the pH glass membrane hydrated. Never store in tap water or deionised water, as this will dehydrate the pH membrane.
• Calibrate in buffers that bracket the expected pH of the sample.
• For the most accurate results, it is recommended to perform the tests in enclosed vessels to avoid contamination (for example, the sample or buffers can absorb CO2, thus, lowering the pH, or water can evaporate).

Steps to Ensure Accurate Measurement

To take high accuracy pH measurements, we must take the following steps to prepare the instruments for the measuring process:

1. Use a water bath. Set at 25°C and place both the sample and calibration buffer(s) into the bath and allow them to reach temperature. Cover the containers to avoid contamination.
2. Remove the soaker boot and rinse the sensor in deionised water, then blot the membrane dry (do not rub). Open the fill hole and leave for 30-60 mins in the first buffer (buffer 7 for example) to completely equilibrate.
3. Calibrate in the first buffer and rinse the sensor in deionised water, then place the sensor in the next buffer. Allow a few minutes to stabilise and calibrate.
4. Place the sensor into the sample, then start to slowly stir. Leave the sensor in the sample for 15-30 mins to equilibrate.
5. While the sample is stirring, take the measurement of the sample.

Follow These Steps Every Time

It may be troublesome to observe these steps every time, however, this exercise helps to ensure accuracy of measurement every time.

Here at Sentek, we specialise in a wide range of products, including dissolved oxygen electrodes, ion-selective electrodes, and electrodes designed for education purposes and for use within food and industrial sectors. Please contact us today for more information on our product range.

For more technical resource and insight, visit the Support area and Download Centre, or contact a member of the team.

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How to Choose a Conductivity Electrode

Conductivity is the ability of any material to pass an electric current. It is typically measured in aqueous solutions, and in this context, it can be defined as the ability of a solution to conduct an electric current between two electrodes. It is used as a measure of the number of ions dissolved in a solution.

Factors to consider

Conductivity can be measured in lab processes or in the field. Choosing the right conductivity electrode is important to ensure that the right product is being used to give the most accurate readings.

The following features require consideration:

• Measuring range/cell constant
• 2-pole or 4-pole
• Temperature compensation
• Meter or instrument being used (this will determine the connector)
• Material compatibility (plate material and shaft material)
• Physical requirements

All Sentek conductivity sensors have an analogue signal and can be used with most meters on the market.

Measuring Range

Conductivity electrodes are given cell constants, which is a ratio between the surface area of the plates of the sensor and the distance between them. The range is dependent upon the cell constant, and can be found on the specification for each sensor. As a general rule, if the measuring range is low (e.g. 0-500µS), then a low cell constant is desirable (e.g. K=0.1). Some sensors come with a predefined cell constant printed on the label, while others rely on customer calibration.

2-pole or 4-pole

• 2-pole sensors tend to be more economical and compatible with a vast range of instruments.
• The limitations are that 2 pole sensors have a maximum measuring range and can be subject to the effects of polarisation.
• 4-pole cells are less prone to error from polarisation, therefore have increased accuracy over a wider range (0.1 microSiemens to 1,000 millisiemens).

Temperature Compensation

Since conductivity is affected by temperature, the majority of conductivity electrodes have built-in temperature sensors; PT100, PT1000, 10KΩ and 30KΩ for example. The type of temperature sensor will depend upon the instrument or meter that is being used. If you are unsure, please get in touch with our team by telling us the make and model of your meter and we will be able to assist you.

Meter or Instrument

Sentek conductivity probes can be used with most meters that are on the market. The instrument that is used will determine the type of connector required – 7-pin-din, 8-pin-din, BNC, bananas, are examples of connectors that may be required to ensure compatibility with your instrument. Sensors can also be provided with clean finished ends, which allows customers to attach their own plug or hardwire into instruments. If this is the case, we are able to provide wiring diagrams on request.

Plate Material

Plate materials vary depending on the application. Carbon is used for samples that will cause the electrode to become dirty easily, as carbon can be easily cleaned with a small brush. Carbon is also a more robust option, and is often used for industrial applications. Platinum plates provide good levels of accuracy and reproducibility; however, the plates are more difficult to clean. Scratches on platinum plates can cause errors in measurement, however they can be replated if necessary. We offer a range of plate materials to suit a variety of applications, including Platinum, Graphite/Carbon and Stainless Steel.

Shaft Material

Glass is generally used for benchtop or laboratory measurements, or samples that may damage an epoxy body. Glass electrodes in general are able to withstand higher temperatures and are compatible with solvents. Epoxy is a more robust sensor, and is advisable for field measurements. Our industrial sensors are Ryton which are able to withstand high temperatures for prolonged periods of time, and have good chemical resistance.

Physical Requirements

Sensors are available in a wide range of shapes and sizes, from flat surface, to industrial , we are able to customise shape, diameter, length to suit any application. If you have a low volume of sample, we have micro designs that allow a small immersion depth, or flow cell conductivity electrodes. We can also customise cable length.

Temperature and Pressure Considerations

Some applications have demands for electrodes that are rated to certain temperatures or pressures. Higher temperature and pressure rated sensors are often fitted with threads to ensure they are fixed in place, and are built to ensure that the sealants and materials can withstand the conditions outlined in the product specification. We can offer a range of thread types to suit your needs, including PG13.5 or ¾” NPT. Please enquire for further information or custom requests.

Application Advice

Measuring conductivity is a vital part of monitoring and quality processes – it can provide useful information about the chemical concentration of a sample. It is often necessary to know if a certain threshold of ions has been reached, or if a water source has been contaminated, particularly in industrial and environmental applications.

The applications commonly used include;

High purity water: Purified water is used in many applications, such as laboratories, cosmetics, pharmaceuticals and the food industry and is monitored by conductivity measurement.

Environmental: Significant changes (usually increases) in conductivity may indicate that a discharge or some other source of disturbance has decreased the relative condition or health of the water body and its associated plant and animal life.

Agricultural: The measurement of soil conductivity is widely used in agriculture. It correlates with various soil properties, such as soil texture and water holding capacity. It can also be used for ‘precision fertilisation management’.

Industrial: Conductivity measurement is used to determine the effectiveness of water treatment processes in preventing corrosion in plant equipment and in leak detection. When cleaning in place is used in process equipment it is important to know that the appropriate amounts of cleaning solutions are used and that those solutions have been removed completely before the next processing run. Conductivity measurement can help confirm these processes. Conductivity measurement is used in chemical processing and food and beverage manufacturing. Conductivity is used to determine the effectiveness of desalination.

Pharmaceutical: The quality of highly-purified water is crucial to the pharmaceutical industry and conductivity measurement is the most widely accepted quality control method.

Conductivity Electrodes from Sentek

Here at Sentek we make a range of conductivity probes for use in the laboratory or in the field.

To find out more about our range of electrodes and for more technical insight, visit us online or contact us by phone to speak to a member of the team.

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