pH Meter Definition
- A pH meter is a precise instrument that weighs the hydrogen-ion movement in water-based suspensions, showing its acidity or alkalinity expressed as pH.
- It is also called a “potentiometric pH meter” because it measures the variation in electrical potential between a pH electrode and a reference electrode.
- The variation in electrical potential links to the acidity or pH of the suspension.
- This meter is used for experimentation, quality control, etc.
- The word pH is acquired from “p,” the scientific figure for negative logarithm, and “H,” the chemical symbol for Hydrogen.
- pH is a unit of measure that expresses the level of acidity or alkalinity of a suspension. It is graded on a range of 0 to 14. pH = -log[H+]
- In 1909 Nobel-Prize winning German chemist Fritz Haber (1868–1934) and his student Zygmunt Klemensiewicz (1886–1963) explained the glass electrode idea. The modern, electronic pH meter was introduced in 1934, by an American chemist Arnold Beckman (1900–2004).
The pH rate of a material is directly linked to the degree of the hydrogen ion [H+] and the hydroxyl ion [OH-] concentrations.
The quantitative data rendered via the pH meter shows the ratio of the movement of an acid or base in terms of hydrogen ion activity.
- If the H+ density is higher than OH-, the substance is acidic; i.e., the pH amount is less than 7.
- If the OH- intensity is higher than H+, the substance is basic, including a pH value higher than 7.
- If identical quantities of H+ and OH- ions are present, the substance is neutral, with a pH of 7.
free hydrogen and hydroxyl ions possess both Acids and bases. The connection between hydrogen ions and hydroxyl ions in a supplied suspension is fixed for a provided set of circumstances, either one can be resolved by recognizing the other.
pH Meter Working Principle
- A pH meter is made of a few vital components such as Measuring Electrode, Reference Electrode, Temperature Sensor.
- The pH Meter estimates the voltage of an electrochemical cell and based upon the Temperature Sensor defines the pH of a suspension.
- Most of the pH meters contain Combination Electrodes, in which the electrodes and the Temperature Sensor are fabricated within a single frame.
- The algebraic total of the potentials of the Measuring Electrode, Reference Electrode, and the Liquid Junction is known as the overall potential or the voltage.
- The Reference Electrode contains a neutral solution such as Potassium Chloride solution with a fixed concentration. It gives a stable voltage.
- On the opposite, the potential of the Measuring Electrode depends totally upon the pH of the suspension.
- The potential variation (voltage) between a glass membrane of Measuring Electrode and a Reference Electrode which is immersed in the Sample Liquid to be examined is estimated.
- When the two Electrodes are immersed into the Sample Suspension, the ion-exchange process transpires wherein some of the Hydrogen ions flow towards the outside surface of the Measuring Electrode and displace some of the metal ions within it.
- Likewise, some of the metal ions migrate from the Glass Electrode toward the Sample Suspension. The responsiveness of the Reference Electrode potential to variation in pH is negligible or it is unaffected by variations in pH and therefore produces a stable voltage.
- on-exchange processes additionally takes place on the interior surface of the Glass Electrode from the sample suspension.
- This generates a potential variation (Hydrogen- ion activity) among them. The Liquid Junction potential is normally minute and almost constant which essentially depends on the intensity of the ions in the sample suspension.
- Every three potentials are summed up and ranked by High Impedance Voltmeter.
- The potential voltage generated beyond the Glass Electrode membrane is temperature-dependent, by a temperature coefficient of around 0.3% per °C.
- The pH Meters hold provisions to improve the pH Measures as the temperature changes and it is termed as Automatic Temperature Compensation (ATC).
- The output of the Impedance Voltmeter is Voltage studies and it possesses to be calibrated to prepare precise pH Measurement.
- Calibration is performed by immersing the Measuring Electrode into Buffer Liquid of known pH which assists in understanding millivolt reading as pH measurement of the Sample Suspension at the delivered temperature.
Key Parts of a pH meter
- The Solution being examined.
- The Glass electrode, consisting of,
- a slim layer of silica glass including metal salts, inside which there is a potassium chloride solution.
- and an internal electrode
- Constructed from silver/silver chloride.
- Hydrogen ions produced in the experiment solution communicate with the outer surface of the glass.
- Hydrogen ions produced in the potassium chloride solution communicate with the inside surface of the glass.
- The meter regulates the variation in voltage between the two surfaces of the glass and turns this “potential difference” into a pH reading.
- Reference electrode serves as a baseline or reference for the analysis-or you can think of it as simply completing the circuit.
Operating Procedure of pH Meter
- Turn on the pH meter by pressing the ON switch on the meter. After turning on the pH meter the MEAS annunciator and ATC indicator will appear on the LCD.
- Then wash the electrodes with distilled water.
- Maintain the sample’s temperature at 25 degrees centigrade.
- After that, immersed the electrodes within the sample and stir it to create a homogenous sample. Make sure the tip of the electrode is completed dipped into the sample.
- Wait until the reading becomes stable.
- When the reading is stabilized the READY indicator will be activated. After that freeze the reading by pressing on the HOLD key and then press ENTER key to save it.
- Now record the pH and Temperature value.
- Finally, wash the electrodes with distilled water and store it with the buffer solution.
Calibration of pH Meter
To achieve highly accurate measures the pH meter must be calibrated before each measurement. Also, calibration is executed once per day of work. Calibration is required because the glass electrode does not provide reproducible electrostatic potentials across longer periods of time.
- First, make sure the correct measurement mode is selected in pH meter.
- Then wash the electrode with distilled water and don’t wipe the electrodes, otherwise it will generate an electrostatic charge on the electrodes.
- All standards and samples are brought to 25-degree centigrade before use.
- Now immerse the electrodes within the standard buffer solution or calibration solution (pH 7/pH 10). Make sure the endpoint of the electrodes are fully immersed within the buffer solution. To create the homogenous sample stire the electrodes within the buffer.
- Now enter in pH calibration mode by pressing the CAL/MEAS key. The CAL sign will be displayed.
- The measured reading will be shown by the primary display whereas the pH standard buffer solution reading is displayed by the smaller secondary screen.
- Wait until the pH values get stabilized.
- After stabilization confirm the calibration by pressing the HOLD/ENTER key.
- Now the pH meter is calibrated to the current buffer solution.
- Finally, wash the electrodes with distilled water and placed it into the buffer solution.
Types of pH Meter
Based on the types of requirement pH meter is divided into several classes such as;
- Based on portability, pH meter classified into:
- Portable pH meter: covering an extensive range of regularly employed instruments, the exception is the use of compact DC power equipment can be produced to the scene.
- Desktop pH meter: Same as Portable pH meter.
- Pen pH meter: normally composed of a single scale, conventional measurement range, for the easy and handy equipment.
- Based on purpose, pH meter classified into:
- Laboratory pH meter: measurement range, multi-function, high accuracy.
- Industrial online pH meter: It is identified by the demands of excellent stability, steady work, a specific level of measurement efficiency, environmental flexibility, anti-interference capability, by the analog output, digital intelligence, the upper and lower boundaries alarm and control functions.
- Based on advanced level, pH meter classified into:
- Economic pH meter
- Intelligent pH meter
- Precision pH meter or divided into pointer pH meter, digital pH meter.
- pH electrodes are composed of a specific construction glass which senses the hydrogen ion intensity.
- The glass is made of alkali metal ions. An ion-exchange reaction occurs between the alkali metal ions of the glass and the hydrogen ions in the solution. As a result of this ion-exchange, it generates a potential difference.
- The pH probe is the combination of two distinct electrodes such as the measuring pH electrode, and the other the reference electrode.
- The solution contains free hydrogen ions which help in the generation of potential at the junction site of the measuring portion.
- When the internal part comes in touch with the reference fill solution a potential is generated on the reference portion. In brief, the measuring pH electrode produces a different voltage and the reference electrode produces a consistent voltage to the meter.
- The voltage signal generated via the pH probe is a pretty small, large impedance signal. The data impedance demands that it be interfaced alone with devices with high impedance circuits.
- Electrodes are invented to measure essentially aqueous media. They are not created to be applied in solvents, like CCI4, which does not possess any free hydrogen ions.
- Kept the electrodes moist at all times. In order to function accurately, glass requires to be hydrated.
- To perform the exchange process, Hydration is mandatory.
- Junctions are present in pH electrodes which leak out the internal fill solution of the measuring electrode into the solution being measured. This junction can become closed by particulates in the suspension and can also promote poisoning via metal ions located within the solution.
- To dissolve or clear the material at the junction, dip the sensor in some warm tap water, in case a clogged junction is suspected. Always store the pH testers in a moistened state. If not in use it is most suitable to put the electrode in either buffer 4.0 or buffer 7.0.
- Electrode disease can normally be distinguished via a sluggish response, erratic readings or a reading which will not turn. pH electrodes are weak and possess a limited lifespan.
- How long an electrode will serve is decided by how properly the probe is kept and the pH application.
- Calibration is additionally a vital part of electrode subsistence. This ensures not only that the electrode is functioning accurately but that the system is working correctly.
Construction of pH Electrodes
- Glass electrodes are Widely used pH electrodes these are composed of glass tubes ended with a small glass bubble.
- A buffered solution of chlorides is loaded within the electrodes. A silver wire coated with silver chloride is steeped inside this solution.
- The pH value of the intimate solution is ranges- for example, it can be 1.0 (0.1M HCl) or 7.0 (various buffers employed by various producers).
- The glass bubble is the active part of the electrode.
- The tube portion of the electrode contains a strong and thick wall, whereas the bubble contains a thin wall.
- Both the internal and external solution protonate the glass surface until equilibrium is achieved. The adsorbed protons charged both sides of the glass which is responsible for potential difference.
- This potential in aid is defined by the Nernst equation and is directly equivalent to the pH variation between solutions on both surfaces of the glass.
- Most of the pH electrodes obtainable commercially are compound electrodes that contain both glass H+ ion-sensitive electrodes and further reference electrode conveniently installed in single housing.
- Separate pH electrodes and reference electrodes are still accepted for specific applications. They provide immense accuracy required sometimes for research purposes. The compound electrodes are very accurate and much more comfortable to practice.
- The development of compound electrode is in huge part determined by the processes that must take place when estimating pH. We require to estimate the variation of potentials within surfaces of glass in the glass electrode. To do so we require a closed circuit.
- The circuit is locked within the solutions – internal and external – and the pH meter. Though, for accurate and constant returns of estimations reference electrodes must be separated from the liquid so that they will not crosscontaminate – and it is not an easy job to attach and detach two solutions at the identical moment.
- The electrode body contains a small hole which makes this connection possible. This hole is prevented by a permeable membrane or ceramic (asbestous in older models) wick.
- The Internal liquid moves very gently through the junction, therefore such electrodes are designated as flowing electrodes. To reduce the leaking, in gel electrodes internal solution is gelled.
Types of Electrodes
There are present three types of pH electrodes such as
- Glass electrode
- Reference electrode
- Combination gel electrode.
Application of pH Meter
- In agriculture industries, it is used to measure the pH of soil.
- It is also used to measure water quality for municipal water supplies, swimming pools.
- In many chemical and pharmaceutical industries, it is used to measure the pH value of solutions.
- pH Meter is additionally employed in the Food industry particularly for dairy products like cheese, curds, yogurts, etc.
- It becomes a vital circumstance in the making of detergents.
Advantages of pH Meter
- pH Calibration is low-priced and robust.
- Pocket size pH Meters are user friendly.
- Accounts are reliable and specific.
Disadvantages of pH Meter
- Heat affects the output readings.
- pH Calibration utilizing glass electrodes need to be clean as deposition on the electrodes influences the readings.
- Touch the electrode with responsibility- it is breakable!
- Store the electrode always in immersed condition within the solution approved by the company or neutral solution of KCl (3M-4M).
- Always maintain the inner level of filling liquid beyond the level of measured solution.
- Load electrode (the flowing type) by exact filling solution (as suggested by manufacturer – normally KCl solution, 3M to saturated) to not let it dry inside.
- You may store the electrodes as dry if they are not used for a long period of time to prevent aging. The Aging only happens when the electrode is moist. Don’t do it with gel electrodes – certain must be put in a strong solution of KCl only.
- If the electrodes are dried soak them at least 24 hours before using.
- Clean the electrodes immediately when you are using a solution that contains substances that able to plug the junction or stick to the glass bubble.
- Avoid immersing electrodes in solvents that can dissolve glass such as hydrofluroic acid (or acidified fluroide solution), concentrated alkalies.
- Avoid immersing electrodes within a dehydrating solution such as ethanol, sulfuric acid, etc.
- Avoid rub or wipe electrode bulb.
- Don’t clean the electrodes with organic solvents.