Analytical Balance- Definition, Principle, Parts, Types, Examples

An analytical balance is a laboratory instrument that can measure very small masses with high accuracy and precision. It is commonly used in quantitative chemical analysis, where the mass of a sample or a substance is an important parameter. An analytical balance can have a readability as low as 0.01 mg, which means it can detect changes in mass as small as 0.01 milligram.

An analytical balance has a transparent enclosure, also called a draft shield or a weighing chamber, that protects the samples from dust and air currents that could affect the measurement . The weighing chamber has doors that allow access to the weighing pan, where the sample or the container is placed. The weighing pan is connected to an electromagnet that generates a force to balance the mass of the sample. The force required is measured by an electronic sensor and displayed on a digital screen.

There are different types of analytical balances, such as electronic, mechanical, and electro-optical balances. They differ in their design, mechanism, and features, but they all share the same principle of measuring mass by balancing forces. Analytical balances require careful calibration, leveling, and cleaning to ensure accurate and reliable results. They also need to be used in a suitable environment that is free from vibrations, temperature changes, magnetic fields, and chemical reactions.

Analytical balances are essential tools for many scientific disciplines and applications. They can be used to determine the density, purity, composition, molecular weight, and stoichiometry of substances. They can also be used for sample preparation, pipette calibration, differential weighing, piece counting, interval weighing, formulation, percent weighing, filling, gross-net tare weighing, checkweighing, and animal weighing. Analytical balances are widely available in various models and specifications from different manufacturers.

An analytical balance is based on the principle of magnetic force restoration . It utilizes an electromagnet to measure the mass of an object, rather than directly measuring the mass itself. When an object is placed on the balance pan, the weight of the object creates a downward force. This force is counteracted by an upward force generated by an electromagnet that is controlled by a feedback loop. The feedback loop adjusts the current in the electromagnet until the balance pan is restored to its original position. The current required to achieve this equilibrium is proportional to the mass of the object and is displayed on a digital screen .

The principle of magnetic force restoration allows analytical balances to achieve high accuracy and precision in mass measurement. They can detect very small changes in mass, up to 0.00001 grams (0.01 mg), and have a maximum capacity of about 100-200 grams . Analytical balances are sensitive to environmental factors such as temperature, humidity, air currents, vibrations, and magnetic fields, which can affect the performance of the electromagnet and the feedback loop. Therefore, they are usually enclosed in a transparent chamber with doors to minimize external influences and ensure stable conditions .

An analytical balance consists of various parts that work together to provide accurate and precise measurements of the mass of an object. The following are some of the main parts of an analytical balance and their functions :

• Balance plate (Pan): This is a container that holds the sample material for mass measurement. It is usually made of stainless steel and placed inside a draft shield to protect it from external influences.
• Weights: These are objects whose exact mass is known and fixed. They are used to calibrate the balance and to check its accuracy and precision. They are usually stored in a separate case to prevent contamination or damage.
• Power button (on/off button): This is used to activate or deactivate the balance. It should be pressed gently and held for a few seconds until the display panel shows the ready status.
• Re-zero or Tare button: This is used to reset the balance to zero in the no-load condition or to exclude the mass of a container from the measurement. It should be pressed before placing or removing any object on the balance plate.
• Mode button: This is used to configure the measurement unit and conversion system of the balance. It allows the user to switch between different modes such as grams, milligrams, ounces, carats, etc.
• Draft shield: This is a transparent enclosure that surrounds the balance plate and prevents air currents, dust, or other environmental factors from affecting the measurement. It has doors that can be opened or closed to access the balance plate. Some models have automatic or touch-free doors that can be operated by sensors or buttons.
• Level indicator: This is a device that shows whether the balance is leveled horizontally or not. It usually consists of a bubble inside a circular tube that should be aligned with the center mark. The level indicator helps to ensure accurate and repeatable measurements.
• Level adjustment feet: These are movable legs that can be adjusted to bring the balance to the reference position indicated by the level indicator. They are located at the bottom of the balance and can be turned clockwise or counterclockwise to raise or lower the balance.
• Display panel: This is a screen that shows various information such as results, errors, settings, and functions. It can be either LCD or LED depending on the model. It should be clear, bright, and easy to read.

Weighing is a frequent step in analytical procedures, and the balance is an essential piece of laboratory equipment in most analyses. In spite of this, weighing is a common source of error that can be difficult to detect in the final analytical results. Therefore, it is important to follow some guidelines and best practices when using an analytical balance to ensure accuracy and reliability. The following steps summarize the general weighing procedure of an analytical balance :

1. Select a proper location. Several external environmental factors influence the measurement, such as temperature, humidity, air currents, vibrations, dust, and magnetic fields. Hence, it’s necessary to carry out the weighing procedures in a suitable location. Choose a stable and horizontal surface free from external disturbances. Avoid direct sunlight and make sure there are no extreme temperature changes. Refrain from touching magnetic or magnetic field-generating objects or equipment near the balance. The environment should be as dust-free as possible. Steer clear of air currents produced by ventilators, air conditioners, open doors, and windows.
2. Leveling the analytical balance. Repeatable measurements and precise findings require precise horizontal positioning. The analytical balance must be leveled to account for any slight deviations or tilts at this site. Until the air bubble in the indicator is in the center, the analytical balance’s leveling feet should be adjusted. The leveling mechanism is usually installed in front of the weighing chamber on standard analytical balances.
3. Calibrating the analytical balance. The analytical balance must be calibrated for the sample to be precisely weighed. The following circumstances call for calibrating the operations: Modifications to the usage location (including moving within the same room), alteration in the environment, and before each use. In-built internal calibration or external calibration can be performed. Internal calibration requires manual input from the users to reset the analytical balance, and external calibration is performed using certified calibration masses and external effort from the user to determine calibration settings based on the specific lab environment.
4. Weighing. It is preferable to preheat it for an hour before using it. Set the analytical balance to zero in the no-load condition by pressing the “tare” button. Place the weigh boat, weigh paper, or other vessel or container in the center of the weighing pan and then shut the glass door of the weighing chamber. Check the value that was displayed after it was stabilized. The appearance of the stability mark indicates a stable state. To exclude container mass from the measurement, press the ‘TARE’ button again to reset the mass to zero. Add the substance to be weighed after removing the container from the balance. Avoid putting things in direct contact with the balance pan because doing so can contaminate or damage the balance. Reset the container’s balance, then wait 5-10 seconds (up to a minute) for the mass reading to stabilize.
5. Cleaning. The analytical balance’s measurement accuracy and lifespan are improved by routine cleaning. Use only a piece of lint-free, soap-wet, mild detergent-coated cloth to clean the analytical balance. Avoid using any abrasive or harsh cleaning chemicals as well as organic solvents. Cut off the electricity and unplug the power cord while cleaning. Ensure no liquid or dust gets inside the housing of the analytical balance.

There are several types of analytical balance, but the major types are:

• Top Loading Analytical Balance: This type of balance has a single weighing pan on top of the balance and can measure mass up to several kilograms with a readability of 0.1 mg or 0.01 mg. It is suitable for routine weighing tasks that do not require very high precision. It is also faster and easier to use than other types of analytical balance.

• Microbalance: This type of balance can measure very small mass in the microgram range with a readability of 0.1 µg or 0.01 µg. It is used for weighing samples that are scarce, expensive, or toxic. It has a special design that minimizes the effects of air currents, temperature changes, and electrostatic forces on the measurement.

• Precision Balance: This type of balance can measure mass up to several hundred grams with a readability of 0.001 mg or 0.0001 mg. It is used for applications that require high accuracy and repeatability, such as pharmaceutical, chemical, or forensic analysis. It has a draft shield that protects the weighing pan from external influences.

• Single Pan or Unequal Arm Mechanical Balance: This type of balance has two knife edges with unequal balance arms. The shorter arm supports the balance pan and a full complement of weights, and the longer arm contains a constant counterweight built into the balance beam. The object to be weighed is placed on the pan and weights are removed from the shorter arm to compensate for its mass. This type of balance is also known as weighing by substitution.

• Electronic Single Pan Balance: This type of balance has an electromagnetic force restoration sensor that generates a force to counter the mass of the object on the pan and outputs the result by measuring the current required. It has a high resolution and sensitivity and can measure mass up to several grams with a readability of 0.00001 mg or 0.000001 mg. It is also known as an electromagnetic force balance.

• Two Pan or Equal Arm Analytical Balance: This type of balance has a beam with two pans attached at equal distances from the center. The object to be weighed is placed on one pan and a known weight is placed on the other pan until they are balanced. This type of balance is based on the principle of a first-class lever and was introduced by Joseph Black, a Scottish chemist and physicist.

An analytical balance is a versatile instrument that can be used for various purposes in different fields such as pharmaceuticals, food, plastic, chemical manufacturing, quality assurance lab, calibration laboratories, etc. Some of the common uses and applications of analytical balance are:

• Preparation of standards: An analytical balance can be used to prepare accurate and precise solutions of known concentrations by weighing the required amount of solute and solvent. These solutions can be used as standards for calibration or comparison in analytical methods such as titration, spectrophotometry, chromatography, etc.
• Formulation: An analytical balance can be used to formulate products such as drugs, cosmetics, paints, etc. by weighing the exact proportions of ingredients according to a recipe or formula. This ensures the quality and consistency of the final product.
• Determination of density: An analytical balance can be used to determine the density of solids or liquids by weighing them in air and in a known liquid medium. The density can be calculated by using the formula: $$\text{Density} = \frac{\text{Mass in air}}{\text{Mass in air} - \text{Mass in liquid}} \times \text{Density of liquid}$$
• Interval weighing: An analytical balance can be used to measure the weight change of a sample over time by weighing it at regular intervals. This can be useful for studying the kinetics of chemical reactions, the rate of evaporation or dissolution, the moisture content or water activity of foods, etc.
• Routine testing of micropipettes: An analytical balance can be used to check the accuracy and precision of micropipettes by weighing the volume of liquid dispensed by them. This can help to ensure the reliability and reproducibility of pipetting operations in laboratories.
• Preparation of sample: An analytical balance can be used to prepare samples for analysis by weighing the required amount of sample or diluting it to a desired concentration. This can help to optimize the analytical method and reduce errors or interferences.

These are some examples of how an analytical balance can be used in different applications. However, there may be other uses depending on the specific needs and objectives of each field or laboratory.

An analytical balance is a sensitive instrument that can measure very small masses with high accuracy and precision. However, its performance can be influenced by various environmental and operational factors that need to be considered and controlled. Some of these factors are:

• Temperature: Temperature changes can cause thermal expansion or contraction of the balance components, as well as evaporation or condensation of moisture from the sample or the air. These effects can alter the mass or the buoyancy of the sample, leading to errors in the measurement. Therefore, it is advisable to keep the balance in a stable and moderate temperature environment, away from direct sunlight, heat sources, or drafts .
• Vibrations: Vibrations can disturb the equilibrium of the balance and affect the stability of the reading. Vibrations can be caused by external sources such as nearby equipment, vehicles, or people, or by internal sources such as fans, motors, or relays. To minimize vibrations, the balance should be placed on a solid and level surface, preferably on a vibration-isolating table or pad .
• Air currents: Air currents can exert a force on the sample or the balance pan, causing fluctuations in the reading. Air currents can be generated by ventilation systems, air conditioners, doors, windows, or even breathing. To prevent air currents, the balance should be enclosed in a draft shield or a weighing chamber with transparent doors that allow easy access to the sample .
• Calibration: Calibration is the process of adjusting the balance to ensure that it displays the correct mass for a known standard weight. Calibration is necessary to compensate for any drifts or deviations that may occur over time due to aging, wear and tear, or environmental changes. Calibration should be performed regularly, preferably before each use, using certified calibration weights that match the range and accuracy of the balance .
• Magnetism: Magnetism can interfere with the electromagnetic force that balances the load on the pan. Magnetism can be caused by magnetic materials in the sample or in the vicinity of the balance, or by electric currents or fields. To avoid magnetism, the balance should be kept away from magnets, magnetic fields, or devices that generate electric currents or fields .
• Fingerprints: Fingerprints can transfer oils, dirt, or moisture to the sample or the balance pan, affecting their mass or adhesion. Fingerprints can also affect the reflectivity of the pan, which can influence the optical sensors that detect its position. To prevent fingerprints, gloves should be worn when handling samples or calibration weights, and the pan should be cleaned with a lint-free cloth after each use.

An analytical balance is a valuable instrument for measuring the mass of samples with high precision and accuracy. However, it also has some limitations that need to be considered when using it. Here are some of the advantages and limitations of analytical balance:

Advantages

• Accuracy: An analytical balance can measure small masses to the nearest 0.01 mg, which is essential for many laboratory applications. It can also detect tiny fluctuations in weight due to its high sensitivity and resolution.
• Display: An analytical balance has a digital display that shows the weighing results clearly and reduces reading errors. Some models also have a stability indicator that shows when the measurement is stable and reliable.
• Reliability: An analytical balance can provide consistent and reproducible measurements when calibrated regularly and maintained properly. It also has a self-calibration system that adjusts the balance automatically and ensures optimal performance.
• Features: An analytical balance has various features that simplify and streamline the weighing tasks, such as counting, piece counting, percent weighing, formulation, checkweighing, animal weighing, etc. It also has a draft shield that protects the sample from external influences such as air currents and dust .
• Affordability: An analytical balance is relatively affordable compared to other high-precision instruments, especially considering its technical capabilities and functions. It also helps to save costly and rare materials by dispensing small sample quantities.

Limitations

• Environmental Conditions: An analytical balance is sensitive to environmental factors such as temperature, humidity, air pressure, vibrations, etc. that can affect the weighing measurements. Therefore, it is important to place the balance in a suitable location that is stable, horizontal, dust-free, well-ventilated, and free from extreme temperature changes and air drafts .
• Chemical Reaction: An analytical balance can be affected by the chemical nature of the samples being weighed. If the samples are highly reactive or magnetic, they may interact with other elements or create a magnetic field that influences the sensor coil of the balance. Therefore, it is advisable to use inert and non-magnetic samples for accurate measurements.
• Fingerprints: An analytical balance can be influenced by fingerprints on the sample or the container if the sample size is very small (around 0.1 mg). Fingerprints may alter the weight of the sample due to their oils and moisture content. Therefore, it is recommended to use gloves or tweezers when handling small samples or containers.

• Cleaning: An analytical balance requires regular cleaning to ensure its accuracy and longevity. However, cleaning should be done carefully with a lint-free cloth and mild detergent, avoiding any abrasive or harsh chemicals or organic solvents. Also, care should be taken to prevent any liquid or dust from entering the housing of the balance.

  Precautions when using an analytical balance

An analytical balance is a highly sensitive and precise instrument that can measure mass to the nearest 0.1 mg or less. To ensure accurate and reliable results, it is important to follow some precautions when using an analytical balance. Here are some of them:

• Place the balance in a suitable location. The balance should be placed in a neutral zone, away from sources of air currents, vibrations, electromagnetic radiation, dust, direct sunlight, and temperature or humidity fluctuations. A stable and horizontal surface and an anti-vibration table are recommended. The balance should also be leveled using the leveling feet and indicator .
• Calibrate the balance regularly. The balance should be calibrated before each use or whenever there is a change in the location or environment. Calibration ensures that the balance is correctly set and produces consistent results. Calibration can be done using internal or external weights, depending on the model of the balance .
• Handle the objects to be weighed with care. The objects should be clean, dry, and at room temperature. They should not be touched with bare hands, as moisture, grease, and dirt can affect their weight. They should also be non-reactive and non-magnetic, as chemical reactions and magnetic fields can interfere with the measurement . Only glass, ceramic, metal, or plastic objects and containers should be placed in direct contact with the balance pan.
• Use the tare function to exclude the container mass. The tare function allows resetting the balance to zero after placing a container on the pan. This way, only the mass of the sample is measured, not the container. The tare function should be used before adding or removing any substance from the container .
• Close the balance door while weighing. The balance door protects the weighing chamber from external influences that can disturb the reading, such as air drafts, dust, or vibrations. The door should be closed while weighing an object and when finished .
• Wait for the reading to stabilize. The balance may take some time to reach a stable reading after placing or removing an object from the pan. A stability mark or indicator will show when the reading is stable. Do not record the reading until it is stable .
• Clean the balance after use. The balance should be cleaned regularly to prevent dust and dirt from accumulating and affecting its performance and accuracy. A soft cloth moistened with mild detergent can be used to wipe the balance gently. Avoid using abrasive or harsh chemicals or organic solvents. Make sure no liquid or dust gets inside the housing of the balance .

Following these precautions will help you use and maintain an analytical balance properly and obtain precise and accurate mass measurements for your lab applications.

Examples and products of analytical balance

Analytical balances are widely used in various fields and industries that require high precision and accuracy in measuring mass. Some examples of applications that use analytical balances are:

• Pharmaceutical and biotechnology: Analytical balances are essential for preparing samples, standards, and solutions for drug development, quality control, and research. They are also used for pipette calibration, density determination, and differential weighing.
• Chemical and petrochemical: Analytical balances are used for measuring the mass of pure substances, catalysts, additives, and intermediates in chemical synthesis, analysis, and testing. They are also used for determining the moisture content, ash content, and purity of samples.
• Food and beverage: Analytical balances are used for measuring the mass of ingredients, additives, and contaminants in food production, processing, and quality control. They are also used for determining the moisture content, fat content, and nutritional value of food products.
• Education and research: Analytical balances are used for teaching and learning the principles of mass measurement, gravimetric analysis, stoichiometry, and other scientific concepts. They are also used for conducting experiments and investigations in various fields of science.

There are many types and models of analytical balances available in the market, each with different features and specifications to suit different needs and preferences. Some examples of products of analytical balances are:

• Analytical laboratory balance XPR (Manufacturer: Mettler Toledo): This balance features an automatic balance door that eliminates the need for manual intervention and reduces errors. It also has a built-in sensor that dispenses small amounts of sample directly into the weighing pan, saving time and material. It has a maximum capacity of 220 g and a readability of 0.01 mg.
• BA-B Series Electronic Analytical Balance (Manufacturer: Biobase): This balance has a five-sided transparent windscreen that provides a clear view of the weighing pan. It also has an ultra-large LCD display that shows various information such as results, errors, and settings. It has a maximum capacity of 220 g and a readability of 0.1 mg.
• Analytical laboratory balance AS 62/220.R2 (Manufacturer: Radwag Balances and Sales): This balance has a dual-range system that allows switching between two weighing capacities with different readabilities. It also has a leveling mechanism that ensures the balance is in a horizontal position. It has a maximum capacity of 60 g / 220 g and a readability of 0.01 mg / 0.1 mg.
• Analytical laboratory balance 390 (Manufacturer: Precisa Gravimetric AG): This balance has a high-resolution touch screen that allows easy operation and configuration. It also has a self-linearization and calibration system that ensures accuracy and reliability. It has a maximum capacity of 320 g and a readability of 0.1 mg.

Analytical balances are widely used in various fields and industries that require high precision and accuracy in measuring mass. Some examples of applications that use analytical balances are:

• Pharmaceutical and biotechnology: Analytical balances are essential for preparing samples, standards, and solutions for drug development, quality control, and research. They are also used for pipette calibration, density determination, and differential weighing.
• Chemical and petrochemical: Analytical balances are used for measuring the mass of pure substances, catalysts, additives, and intermediates in chemical synthesis, analysis, and testing. They are also used for determining the moisture content, ash content, and purity of samples.
• Food and beverage: Analytical balances are used for measuring the mass of ingredients, additives, and contaminants in food production, processing, and quality control. They are also used for determining the moisture content, fat content, and nutritional value of food products.
• Education and research: Analytical balances are used for teaching and learning the principles of mass measurement, gravimetric analysis, stoichiometry, and other scientific concepts. They are also used for conducting experiments and investigations in various fields of science.

There are many types and models of analytical balances available in the market, each with different features and specifications to suit different needs and preferences. Some examples of products of analytical balances are:

• Analytical laboratory balance XPR (Manufacturer: Mettler Toledo): This balance features an automatic balance door that eliminates the need for manual intervention and reduces errors. It also has a built-in sensor that dispenses small amounts of sample directly into the weighing pan, saving time and material. It has a maximum capacity of 220 g and a readability of 0.01 mg.
• BA-B Series Electronic Analytical Balance (Manufacturer: Biobase): This balance has a five-sided transparent windscreen that provides a clear view of the weighing pan. It also has an ultra-large LCD display that shows various information such as results, errors, and settings. It has a maximum capacity of 220 g and a readability of 0.1 mg.
• Analytical laboratory balance AS 62/220.R2 (Manufacturer: Radwag Balances and Sales): This balance has a dual-range system that allows switching between two weighing capacities with different readabilities. It also has a leveling mechanism that ensures the balance is in a horizontal position. It has a maximum capacity of 60 g / 220 g and a readability of 0.01 mg / 0.1 mg.
• Analytical laboratory balance 390 (Manufacturer: Precisa Gravimetric AG): This balance has a high-resolution touch screen that allows easy operation and configuration. It also has a self-linearization and calibration system that ensures accuracy and reliability. It has a maximum capacity of 320 g and a readability of 0.1 mg.

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