Analytical Balances are highly sensitive and accurate laboratory instruments designed to measure the mass of smaller samples or objects. They typically have weighing capacities from 100g to 300g and have display resolutions between 0.1mg – 0.001mg. Analytical Balances are enclosed by a transparent draft shield that protects the weighing pan from dust and air currents. The weighing pan is usually smaller than in top-loading balances, and is designed to measure small samples.
Due to the sensitive nature of Analytical Balances, a wide variety of environmental conditions such a temperature, vibration, air currents, and gravity all can have a large effect on their operation and the accuracy of the measurements obtained.
Setting up an Analytical Balance
Analytical Balances should first be placed on a solid, vibration-free worktable. Special weighing tables can be purchased that absorb vibrations that could distort the weighing results. The table should be placed in a location free from passing foot traffic and away from any vents so that the balance will not be affected by temperature/humidity fluctuations and drafts.
Analytical Balances should not be moved so a permanent location should be selected. The balance must be calibrated at the location where it will be used and if it is moved, it must be re-calibrated at the new location.
The balance should be connected to power and allowed to reach room temperature for a minimum of 4 hours before being used in the laboratory environment.
Analytical Balances must be leveled prior to use. Most balances are equipped with leveling bubbles to assist with the leveling of the balance.
Cleaning an Analytical Balance
The inside of the balance needs to be clean and dry before use. Each balance manufacturer will have recommendations to follow for proper cleaning of their units in the user manual.
Remove any loose samples first by using a soft brush or small vacuum to clean the weighing pan and cabinet. Never use compressed air to blow into the chamber as this could transport dirt or spilled sample materials inside the balance.
Use an absorbent cloth to remove any standing liquids. Use a soft cloth dampened with water or isopropyl alcohol to clean any remaining substances. Never use solvents for cleaning the balance. Certain parts of the balance could be damaged with aggressive or abrasive cleaning materials. Wipe the balance with a soft, dry cloth after cleaning.
Weighing using an Analytical Balance
The balance door must be closed when weighing an object in order to prevent air currents from disturbing the reading and dust and dirt from entering the balance. Even the slightest flow of air can make a weighing operation unstable.
Raw chemical samples should never be placed directly on the balance pan. Containers such as beakers and weighing trays made of glass, plastic, or metal should always be used with chemicals. A number of chemicals can react with the balance pan and cause corrosion and interfere with weighing.
Some chemical samples or containers made of plastics, glass or metals may carry an electrostatic charge that can influence the weighing mechanism and could adversely affect the measuring result. Special ionizers can be purchased to neutralize any electrostatic charge in the area surrounding the balance.
Items should never be handled with bare hands. Even placing one’s hands in the weighing area can cause a disruption in the temperature. Gloves or tweezers should be used when handling any objects or samples to be weighed. Temperature variations, moisture, dirt and oils from hands can affect the measurement accuracy.
All objects must be allowed to sufficient time to acclimate in the room environment before being weighed. A warmer object induces thermal currents inside the balance enclosure which affects the buoyancy of the object and will make it weigh lighter than it actually is. This is important when weighing samples or objects that have just been removed from drying ovens or environmental chambers.
Taking the measurement should be conducted as quickly as possible and the enclosure door should not be opened longer than necessary. If the door is left open too long, the air within the weighing area will be replaced and the temperature fluctuations will cause a reduction of accuracy and repeatability.