In the laboratory, weighing plays an essential role in experimental outcomes. Accurate measurements bolster the integrity of research results and enhance scientific advancements.
Regular calibration and documented weighing processes help minimize measurement errors. In addition, taring removes extraneous weight from calculations and increases accuracy. This article covers different types of balances, their operation, best practices and common pitfalls to avoid when measuring solids and liquids.
Analytical balances
Analytical balances are used for weighing small masses and substances to high degrees of precision. They often incorporate draft shields or enclosures to protect the weighing chamber from external factors, such as air currents and vibration. These features enhance precision for weighing tasks in a variety of laboratories, manufacturing facilities and educational institutions.
These instruments must be calibrated frequently to maintain accuracy and reliability. The exact calibration frequency should be based on several factors, including the required measurement uncertainty and risk of exceeding tolerance limits, usage extent and history, manufacturer recommendations, environmental conditions, and other relevant criteria.
Before a weighing, it is important to ensure that the analytical balance is tared, or recalibrated, to read 0.0000 g. The Tare button should be pressed and released to achieve this. Additionally, it is important to make sure that the instrument is located in a room with minimal disturbances to the atmosphere and foot traffic. Also, anti-vibration tables and mats can help to improve stability for better results.
Microbalances
Weighing with a microbalance is especially important when small changes in mass can impact a measurement. These instruments are used often in product testing and QA labs, where precise results are essential.
Micro-analytical balances are ideal for pipette calibration, weighing chemically sensitive samples, stent weighing, and checking coatings. They feature microgram readability and high capacity, making them able to accommodate larger labware. Their second inner draft shield also helps protect the weighing chamber from environmental factors that can cause fluctuations in the weight measurement.
Because of their extreme sensitivity, microbalances need to be placed in a temperature-controlled environment. They are also susceptible to vibration, so they need to be placed on a stable weighing table in a quiet place where foot traffic is minimal. When a balance is disturbed, it may need to settle completely before accurate measurements can be taken. That’s why the settling time of a vibration isolation system is an important criterion to consider when choosing a micro balance.
Force balances
Unlike spring-based balances, force balances are not susceptible to metal fatigue or other degradation of spring characteristics. However, it is important to follow maintenance procedures as specified by the manufacturer and to regularly calibrate the instrument.
Using clean, lint-free gloves helps prevent sweat and oil from transferring to objects placed on the balance, thereby eliminating potential errors caused by added weight or corrosion of calibration materials. It is also recommended to use a tweezer or forceps rather than your fingers when handling objects on the balance in order to reduce impact and prevent fingerprints from being transferred to the weighing pan.
It is advisable to install the balance in an area that is free from air currents, especially those originating from heating/cooling vents, which may disrupt the temperature control system of the instrument and lead to reading variations. This is particularly true when weighing large weights, such as standard reference masses, called poises. These weights must be moved into place on the comparators with specialized hoists or cranes to minimize impact and damage.
Weights
As the saying goes, “garbage in, garbage out.” Poorly weighed samples can skew data and muddy experimental outcomes. A systematic approach to weighing enhances accuracy and fosters a foundation of robust methodology in laboratory practices.
Avoid Contamination: Ensure that the weighing area is free of moisture, corrosive gases, dust, and other contaminants. Using a clean forceps and avoiding touching the weights with bare hands helps to minimize contamination and resulting reading errors. Store the weights in a container to reduce their exposure to air and other environmental factors.
Minimize Exposure to Hazardous Materials: When weighing volatile, flammable, or corrosive chemicals, perform the measurements in a fume hood to limit exposure. In addition, weighing samples in a controlled environment can help to ensure consistent temperature and humidity throughout the weighing process.
Observe Routine Maintenance: Develop a regular schedule for cleaning, inspection, and calibration of your balances to minimize potential errors. This also helps to extend the lifespan of your weighing equipment and minimize costly repairs.