MesuLab pH Meter

Main Features:  

A pH meter is an instrument that uses a pH indicator electrode to measure the pH of a solution through potentiometry. It is a precise electronic millivoltmeter specifically designed for use with ion-selective electrodes. Since the potential of the pH indicator electrode changes with the pH of the solution, when the pH indicator electrode (such as a pH glass electrode) and a reference electrode (such as a saturated calomel electrode) are immersed in the solution to form a measurement cell, the resulting electromotive force is related to the pH of the solution. The pH meter converts the electromotive force output into a pH reading, with each pH interval corresponding to 2.303RT/F volts. This value varies with the temperature of the solution in the measurement cell, so pH meters are equipped with a temperature compensation knob. Adjusting it ensures that the change in electromotive force per pH interval precisely corresponds to the required value at the measurement temperature. The pH meter also features a positioning regulator, which adds an appropriate voltage to the cell's electromotive force, aligning the pH meter reading with the standard pH value. As a result, the pH of the solution is directly displayed on the instrument. The typical measurement range of a pH meter is pH 0–14, and it includes a ±mV range to extend its usability.

Product Classification

pH meters can be classified as follows:

Classification of Meters

(1) By Application Scenario:

Pen-type pH meters: Primarily used as an alternative to pH test strips, featuring low accuracy and user-friendly operation.

Portable pH meters: Designed for on-site and field measurements, requiring relatively high accuracy and comprehensive functionality.

Laboratory pH meters: Intended for laboratory use, offering high precision and advanced features.

Industrial pH meters: Built for continuous monitoring in industrial processes, with robust designs to withstand harsh environments.

(2) By Instrument Precision:

Classified into 0.2, 0.1, 0.02, 0.01, and 0.001 grades. A smaller number indicates higher precision.

(3) By Readout Display:

Analog (pointer-style) pH meters: Rarely used today but still employed in titration analysis due to their ability to display continuous data changes.

Digital pH meters: Modern devices with digital displays for precise readings.

(4) By Component Type:

Transistor-based pH meters: Early models using transistor technology.

Integrated circuit (IC)-based pH meters: Improved designs with ICs.

Microcontroller-based pH meters: Contemporary devices utilizing microcomputer chips, significantly reducing instrument size and unit cost, though chip development costs remain high.

Laboratory pH Meters

Laboratory pH meters are benchtop instruments designed for high-precision analytical applications. They offer advanced features such as data printing, processing, and comprehensive functionality.

Industrial pH Meters

Industrial pH meters are used for continuous monitoring in industrial processes. They not only measure and display pH values but also include alarm and control functions. Additional considerations include ease of installation, cleaning, and resistance to interference.

Maintenance and Care

Maintenance of pH Meters

Storage of Glass Electrodes

Short-term: Store in a pH=4 buffer solution.

Long-term: Store in a pH=7 buffer solution.

Cleaning of Glass Electrodes

Contamination of the glass electrode bulb may prolong response time. Remove contaminants using CCl₄ or soap solution, then immerse the electrode in distilled water for 24 hours before reuse. For severe contamination, soak in a 5% HF solution for 10–20 minutes, rinse immediately with water, and immerse in 0.1N HCl solution for 24 hours before reuse.

Aging Treatment of Glass Electrodes

Electrode aging is related to gradual changes in the gel layer structure. Older electrodes may exhibit slow response, high membrane resistance, and reduced slope. Etching the outer gel layer with hydrofluoric acid (HF) often restores performance. Regular removal of inner and outer gel layers can extend the electrode’s lifespan indefinitely.

Storage of Reference Electrodes

The optimal storage solution for silver-silver chloride electrodes is saturated potassium chloride (KCl). High-concentration KCl prevents silver chloride precipitation at the junction and maintains the junction’s functionality. This method also applies to combination electrodes.

Regeneration of Reference Electrodes

Most issues with reference electrodes are caused by junction clogging. Solutions include:

Soaking the Junction: Use a mixture of 10% saturated KCl and 90% distilled water heated to 60–70°C. Immerse the electrode ~5 cm deep for 20 minutes to 1 hour to dissolve crystals.

Ammonia Soaking: For silver chloride clogs, soak the junction in concentrated ammonia for 10–20 minutes without allowing ammonia to enter the electrode interior. Rinse with distilled water, refill the internal solution, and reuse.

Vacuum Method: Attach a soft tube to the junction and use a suction pump to draw internal solution through the junction, removing mechanical blockages.

Boiling the Junction: Immerse the junction of a silver-silver chloride electrode in boiling water for 10–20 seconds. Cool the electrode to room temperature before repeating.

Sandpaper Polishing: If other methods fail, mechanically polish the junction with sandpaper. Note: This may embed sand particles, causing permanent clogging.

Care of pH Meters

Modern laboratory electrodes are typically combination electrodes, offering convenience, resistance to oxidizing/reducing substances, and fast equilibrium. During use, remove the rubber sleeves from the refill opening and bottom to maintain hydraulic pressure difference in the KCl solution. Below are simplified guidelines for use and care:

When not in use, fully immerse combination electrodes in 3M KCl solution. Avoid cleaning with detergents or hygroscopic reagents.

Before use, inspect the glass electrode bulb. It should be transparent and crack-free, filled with solution, and free of air bubbles.

For high-concentration solutions, minimize measurement time and clean thoroughly afterward to prevent contamination.

After cleaning, blot the glass membrane dry with filter paper instead of wiping to avoid damage and cross-contamination.

Ensure the silver-silver chloride reference electrode is immersed in the chloride buffer solution inside the bulb to prevent erratic readings. Gently shake the electrode before use.

Do not use electrodes in strong acids, strong alkalis, or other corrosive solutions.

Avoid use in dehydrating media such as anhydrous ethanol or potassium dichromate.