Weighing the Right Way

Factors affecting weighing accuracy can negatively influence the results of a whole analysis, such that 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, yet critical and time consuming, tasks undertaken in the laboratory; therefore, weighing the right way is crucial.

Balances have developed to the point that, in general, they provide accurate results in most lab environments, with the possible exception of 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 analysis results caused by multiple factors affecting weighing accuracy. External influences are defined as physical effects that are measurable for all laboratory balances. Examples of external influences include:

• Electrostatic forces
• Airflow
• Environmental vibrations
• Effects of magnetism
• Evaporation
• Moisture uptake

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

The purpose of this guide is to identify the most common factors affecting weighing accuracy and to explain the basic rules of weighing the right way with laboratory balances. The guide begins with suggestions for finding an optimal location for the 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).