Principle

Analytical balance works on the principle of “magnetic force restoration.” It is an electromagnetic balance that measures the mass of an object using an electromagnet. These balances do not directly measure the mass; rather, they measure the force that acts in the downwards direction on the balancing pan. An electromagnetic motor measures this force and ultimately determines the mass of the object. The motor requires an electric current for this purpose, and this current is directly proportional to the weight of the object and thus can be used to measure the object’s mass. This mass is displayed on the balance screen. Many balances possess a “null detector” that uses a light source to indicate when the object’s weight is equal to the electromagnetic forces. 

Apparatus and Equipment

The electronic analytical balance consists of a stainless-steel balancing pan enclosed within a glass chamber, which shields against the interference of air currents or vibrations while weighing. The mass to be measured is placed in the balance pan within the weighing chamber. The instrument’s front is provided with a digital display system that displays the measured mass. A power button along the LCD screen turns on the balance. Furthermore, a “TARE” button is used to eliminate container mass and reset the balance at zero. In addition, there are buttons to set the measuring mode (the apparatus can measure the mass in different units) and a print button. 

Conduct Science’s electronic analytical balance comes with easy external calibration and can measure mass in different units like grams, pounds, ounces, and carats. It has a pan size of 9cm which is well suited for measuring the mass of acute substances. This analytical balance can measure accurately up to 1×10-4 grams and has a measuring range of 210grams. It also has a built-in port to transfer data to the computer or print it.

Protocol

1. Place the analytical balance on a smooth surface or a benchtop. Ensure that it is lying on a leveled surface and is turned on.
2. Press the “TARE” button to set the balance at zero. 
3. Now place the container/vial with the help of clean tongs in the center of the weighing pan. 
4. Close the glass chamber and wait for 5 to 10 seconds to stabilize the LCD readout. 
5. Now press the “TARE” button again to reset the balance to zero. This step is required if you do not want to include the mass of the container in your measurement. 
6. Remove the container/vial and add the substance to be weighed. 
7. Replace the container with the weighing pan and wait for the reading on the digital display to stabilize. 
8. Take a minimum of three readings and calculate the average to avoid errors. 
9. Record the data on the datasheet.
10. Thoroughly clean the weighing pan after use.

Applications

Analytical balance has a wide range of weighing applications in the pharmaceutical industry, food and plastic industries, quality assurance cells, and chemical laboratories. For example, Abu Bakar et al. (2019) studied how milk-drug tablet formulations can increase the solubilization of poorly water-soluble drugs. They used an analytical balance to measure the mass of compounds before adding them into scintillation vials during tablet formulation. 

Monitoring a Transesterification Reaction

Tubino et al. (2018) established a monitoring system using an analytical balance to observe the changes during a transesterification reaction. In this system, they connected a round bottom flask in which the reaction was occurring to a peristaltic pump and phase separators. The pump was connected to an electronic analytical balance that was ultimately connected to a laptop in which the entire research data was recorded. For the transesterification reaction, they took 700g of soyabean oil and 120g of methanol and catalyzed it with 30% m/v sodium, methoxide solution in methanol in the round bottom flask. The reaction was stirred using a magnetic stirrer at increasingly faster speeds. The liquid product of the transesterification reaction is pumped and passed through the phase separators that remove glycerol (transesterification byproduct) and air bubbles. Finally, the liquid reaches the beaker placed in the weighing pan of the analytical balance, which contained a small piece of cotton to dampen the oscillations produced by the peristaltic pump. They constantly monitored the mass until the reaction reached equilibrium with the help of the balance and recorded mass data on a datasheet in the computer system. Then they plotted the mass curve. They concluded that the addition of catalyst at different rates decreases the mass over time, and the slope of the mass-time graph shifts to negative as the temperature increases. They also deduced that the mass decreases when methanol is added to the oil.

Precautions

• Clean the weighing pan before and after use to ensure that the weighing sample does not get contaminated. 
• Ensure that the apparatus is lying on a plain surface to avoid measurement error. 
• Check and guard the analytical balance at regular intervals to maintain accuracy and precision. 
• Air currents in the lab environment can alter the measurements. As a precaution, use the glass draft shield and close it from all sides while measuring. However, after closing the draft shield, the pan will still take some time to stabilize because of the air movement within the glass chamber. To resolve this problem, reduce the airflow incident on balance and maintain the ambient temperature. Use tweezers to place the objects in balance. Do not use your hands. 
• Various factors such as temperature, static electricity, air currents, and gravitational acceleration affect the analytical balance’s working.
  • Gravitational acceleration is different in different parts of the world, due to which calibration needs a local adjustment across the globe. 
  • Temperature differences may also affect the measurement. Lab temperature, hot and cold objects may cause variations; therefore, one must equilibrate the object and balance temperatures. 
  • Moisture: Some substances may absorb moisture, due to which their mass increases. For instance, the objects are just removed from a desiccator. Others might evaporate and lose some mass. 
  • The experimenter should control air currents across the lab. 
  • Static electricity might be the greatest concern while using the balance. The static electric field of the mass to be measured might interrupt the balance’s electromagnetic field. Use an anti-static device to neutralize the positive or negative static charge from the mass and keep away from frustration. 

Strengths and Limitations

An analytical balance is a simple and easy-to-use instrument that can measure precisely and accurately up to four places to the right of the decimal point, i.e., very small values can be measured with it. However, random environmental factors like air currents, temperature, static charge, etc., can cause drift in analytical balances. Drift means ‘unstable mass readings,’ and there are several ways to avoid it. For example, the humidity levels of the lab should be around 40% at the time of weighing equipment installation to get rid of static charge. Moreover, the experimenter should not store the mass in a plastic container after weighing it. Similarly, the constant temperature must be maintained throughout the weighing experiment.

Summary

• Analytical balance is an instrument that measures the mass of chemicals and objects accurately and precisely up to 0.0001 grams.
• It works on the principle of “magnetic force restoration.” 
• It has numerous applications in the pharmaceutical industry, food and plastic industries, quality assurance cells, and chemical laboratories.
• Various factors such as temperature, static electricity, air currents, and gravitational acceleration affect the analytical balance’s working. Therefore, one must avoid these factors for precision and accuracy in measurement.

References

Tubino, M., Oliveira, A. G., & Salomão, A. A. (2018). Continuous monitoring of a transesterification reaction using an analytical balance. Journal of the Brazilian Chemical Society, 29, 200-204.

Bernard Y., C., & Angelo, G., G. (2019). Introduction to the Analytical Balance.

Bakar, S. Y. B. A., Salim, M., Clulow, A. J., Hawley, A., & Boyd, B. J. (2019). Revisiting dispersible milk-drug tablets as a solid lipid formulation in the context of digestion. International journal of pharmaceutics, 554, 179-189.