Weighing the Right Way

Factors affecting weighing accuracy can negatively influence the results of the whole analysis, therefore it is important to be aware of the rules that need to be followed when working with laboratory balances.

Weighing is one of the most common, critical task and time consuming tasks in the laboratory, therefore, weighing the right way is crucial.

Balances have developed to the point that, in general, no special weighing room is necessary, except maybe for ultra-micro balances.

Technological advances in electronics have considerably simplified the operation of balances, reducing weighing times. Moreover, the touchscreen digital display makes operation of the balance intuitive.

However, this apparent ease of use can lead to insufficient care being taken to avoid the negative influence on analyses results caused be multiple factors affecting weighing accuracy. External influences are defined as physical effects which are measurable for all laboratory balances. Examples of external influences include:

• Electrostatic forces
• Airflow
• Environmental vibrations
• Magnetism effects
• Evaporation
• Moisture uptake

Certain sample characteristics could also be mistaken for external influences – such as evaporation of liquids, or hygroscopic/hydrophobic solid materials gaining or losing weight.

The purpose of this guide is to identify most common factors affecting weighing accuracy and to explain the basic rules of weighing the right way with laboratory balances. This guide begins with suggestions for the optimum location of a balance. It then describes proper operation of this sensitive instrument, before analyzing possible external influences and their effects. Most of these influences are recognizable by a slow change in the weight display (drift).