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Drift in Measurements with Analytical Balances

Posted in: Equipment Mastery and Hacks

Pharmaceutical laboratories and bioscience research institutes make extensive use of analytical balances that are highly sensitive. These analytical balances are greatly affected by their environment and also by the way they are installed and handled. This is why it is important to assess the lab environment to make the required on-site adjustments.

The weighing equipment you use in a lab should always deliver accurate results and all the elements that can cause any discrepancies should be eliminated. The opening and closing of a freezer door can cause the temperature to fluctuate and this should not occur for optimal conduction of weight measurements.

Analytical balances are designed to deliver extremely precise results — as low as 1 millionth of a gram and hence they are in use for quality checks in the production processes of many pharmaceutical manufacturing companies.

What Causes Drift in Analytical Balances & How to Avoid It

The phenomenon of drift can occur adversely affecting analytical balances when weighing compounds. It refers to unstable weight readings, which typically occur due to static charge and inconsistent temperatures. Drift can cause changes in the measurements and leads to imbalances in displays. If enough static electricity is present in the environment, readings also become unstable. Even if not applying any weight.

Pharmaceutical production lines areas are generally kept clean under highly controlled conditions. The humidity levels are generally below 20% with 24-hour air conditioning. This creates a dry environment and hence any movement of objects can cause friction. The friction can create static electricity which can lead to considerable errors and discrepancies in weighing measurements ranging up to dozens of milligrams.

Ways to Avoid Analytical Balance Drift

In order to keep static electricity from building up and causing the drift effect, it is essential to ensure that humidity levels for weighing equipment are raised to 40% at the time of installation. Despite that, if the static energy keeps accumulating and the rate of electrical discharge is slow, weighing operations should not be made until the electrical charges are eliminated from the weighing sample. After weighing samples should not be stored in plastic containers as they are porous and operators should always conduct weighing operations while standing on anti-static flooring.

Another external factor that has a dramatic impact on the accuracy and stability of analytical balances is temperature. Temperature control is crucial in avoiding the drift phenomenon. This includes maintaining constant temperatures in the environment as well as for your weighing equipment. The best way to ensure temperature stability is to maintain a variation of not more than two degrees round the clock. Also the weighing instrument should remain on at all times so that the temperature remains consistent.

Evaluating the Performance of Analytical Balances

You  need to evaluate analytical balances regularly to determine whether they need any on-site modifications, repairs, or calibration. Problems can occur due to defective components or because of how users operate them. You should test them for repeatability to ensure that they are delivering accurate results consistently for a given object.

  • The best test of repeatability is to use a solid, non-magnetic and non-porous container. Or use a test weight and weigh it repeatedly after returning to zero at the end of every weighing cycle. Also you can try weighing two objects separately that are exactly half of the total weighing capacity. Then the difference between the two readings should be less than the actual tolerance for accuracy.
  • If numerical readings turn blank or become frozen, it is safe to assume that your equipment has a contaminate, is damaged, or mishandled and thus is not producing the desired results.
  • Cornerload is term that indicates the ability of an instrument to generate the same readings for an object, regardless of where it is placed on the weighing pan. At all the positions on the weighing pan, the readings should be the same. And if there are errors, they can be fixed during a field service.
  • Linearity testing is done to ensure that the weighing instrument is delivering the same sensitivity throughout its functional range.

For bioscience labs and pharmaceutical companies, nothing is more critical than accuracy and quality. Even a minute error means manpower and money wasted. Not to mention serious reputation damage and the risk of losing consumers. Periodic calibration and maintenance are the best ways to ensure accuracy and reliability of analytical balances even with repeated use.

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1 Comment

  1. Albert Brew-Hagan on February 2, 2019 at 4:03 pm

    How do negative and positive charges manifest themselves during drifting?

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