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Factors Affecting Analytical Balances

Updated 2020 January

Analytical balances are the basic tools of quantitative analysis. They are used to accurately weigh samples and precipitates. The balances are able to provide accurate measurements to four decimal places, for example, 0.0001 grams. Due to the extremely sensitive nature of these instruments, there are several factors that can cause them to give erroneous readings.

For an analytical balance to give an accurate reading, the instrument must be calibrated. Calibration is important because it defines the accuracy and quality of the measurements that are recorded by the balance. To ensure the integrity of the measurement results, there has to be an ongoing process of servicing and maintaining the calibration of the equipment throughout its lifetime. As a result, reliable, accurate, and repeatable measurements will always be achieved.

Here are some factors that can affect the accuracy of analytical balances:

  • Temperature
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The slightest change in room temperature can cause noticeable changes in the weight of the sample. Strict temperature controls are therefore needed to give accurate readings on the analytical balance. Here is an example of how temperature affects the sample: If the room temperature is too high, the sample can expand or lose some of its “water weight” due to evaporation. If the temperature is too low, the sample could contract or allow for the condensation of water in the sample’s container. Both factors can affect the accuracy of the measurement of the analytical balance.

  • Vibrations

Vibrations from refrigerators, ventilation systems, and other equipment that produce vibrations can affect the precision of an analytical balance. Since the sample size is really small, the slightest vibration can rearrange, displace, or spill the sample, thereby affecting the amount of material available for measuring as well as its distribution in the balance. Small vibrations can also disrupt the delicate machinery of the analytical balance. These disruptions may require recalibration of the analytical balance, which can mean lost time and money from pertinent research efforts.

  • Chemical Reactions
Chemical Reaction in Analytical Balance
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Samples can also be very sensitive to slight atmospheric changes in temperature and wind pressure. For instance, if you expose a piece of white phosphorous to open air, it will burst into flames. Exposure of such volatile samples to those conditions can lead to chemical reactions that are not only dangerous but can also alter the state of the sample. That is why users should take precautions to ensure that the sample remains chemically inert during the weighing process.

  • Air Currents

Air currents can affect the intricate mechanisms of the analytical balance the same as temperature and vibrations can alter the measurement of a small sample size. Changes in air pressure from ceiling fans, air conditioners, and open doors can also cause sensitive equipment to show wrong measurements.

  • Calibration
calibrating analytical balance
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Calibrating an analytical balance will ensure that it gives an accurate reading. Even though some balances have an internal calibration feature, many labs conduct their own calibration tests on new equipment with certified calibration weights that help users to determine the calibration settings for their specific lab environment. It is recommended that users test their balances every few months to ensure that the calibration settings are still accurate.

  • User Error

In most cases, faulty measurements are as a result of user error. A lab worker may accidentally leave a sample on the table, exposing it to reactions with atmospheric elements; or a lab worker may improperly calibrate the machine which can affect the accuracy of the balance. That is why most labs have strict procedures for maintaining atmospheric standards to ensure accurate readings and lower instances of user error.

  • Cluttered Work Space

The accuracy of analytical balances depends on how clean the work space is. A cluttered work space will impact the accuracy of results. Ensure that nothing comes in contact with the analytical balance. If anything touches or rubs against the balance, it will cause discrepancies in the readings.

  • Magnets

Some balances use magnets as a part of the weighing system. Therefore, placing the balance near magnetic equipment or weighing magnetic sample can result in erroneous readings.

  • Slope

The scale or balance must be placed on a level surface. Precision balance scales weigh the materials assuming that the load is applied parallel to the force of gravity and perpendicular to the weighing platform.

  • Improper Grounding

Make sure that the AC source is properly grounded to prevent the build-up of static energy. Secondly, ensure that the chassis is grounded to avoid electrostatic discharge.

  • Plastic or Glass Weigh Containers

Unlike metal containers, plastic and glass weigh containers can hold an electric current. Static charges can result in non-repeatable measurements or drifting measurement readings. Even an accurate weight scale can provide incorrect readings in such cases.

  • Not handling the sample appropriately

Lab workers need to handle the samples with care. For instance, hot or warm samples should be cooled first. Hygroscopic samples need to be weighed quickly with the balance doors closed to avoid absorption of moisture. Not following these steps will affect the measurements. Place the sample in the center of the balance for the most accurate results.

Contact Quality Scales Unlimited for more details on Analytical Balances and its calibration.

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