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The Basics of Analytical Balances and Proper Weighing Techniques

Accurate use of an analytical balance depends on an SOP

by
Mike May, PhD

Mike May is a freelance writer and editor living in Texas.

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In many ways, an analytical balance is only as good as the person using it. Although scientists receive training early in their careers on how to use an analytical balance, it’s easy to get lax in the details over the years. Here’s a  refresher on the steps to always apply when using an analytical balance.

Before getting started with weighing any samples, Aleksandar Delic, category manager—laboratory at KERN & SOHN in Stuttgart, Germany, recommends five things to consider:

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  • What will be weighed and how large and heavy are the samples? This helps in selecting the right balance to use and to prevent overloading it.
  • What are the minimum tolerances for the project? 
  • How should the weighing result be documented, such as a paper printout, transcription by hand, or transfer to a computer?
  • Which metadata—such as the date, time, user, and serial number of the scale—are needed in addition to the  weighing value?
  • Does the scale have to be calibrated and/or verified?

With these steps complete, it’s time to start weighing samples, but the process should always follow a standard operating procedure (SOP). When asked how important it is to develop and adhere to an SOP, Delic says, “Essential!”

As Delic explains, “Only a defined SOP can ensure that personnel are trained, the scale is operated correctly, and the scale is checked regularly.” 

An analytical balance’s location also matters. Make sure to place it where it won’t be subjected to air currents or vibrations. Although it’s usually difficult to completely avoid these factors, it helps to minimize them. 

Here are a few other common factors that can lead to incorrect readings:

  • Temperature
  • Air drafts
  • Chemical reactions
  • Uncalibrated scales
  • Magnets
  • User error
  • Improper grounding
  • Slope

Following the SOP

The first step in the SOP should be ensuring that the balance is calibrated. A lab manager should “observe the defined time intervals for recalibration by an accredited laboratory,” Delic says, and “use calibrated test weights before starting work to ensure the correctness of results.” The calibrated weights should go down as far as the lowest readability of the balance. For example, use a 0.1 milligrams calibrated weight for a readability of 0.1 milligrams.

With an analytical balance calibrated, leveled, and ready to go, MRC—a developer, manufacturer, and supplier of laboratory equipment—recommends several crucial steps.

Before weighing:

  • Warm up the balance for at least 30 minutes.
  • With the door closed and a weighing paper or container to hold the sample in place, tare the balance to zero.
  • Let the balance stabilize.

To weigh a sample:

  • Open the door or doors to put the sample on the weighing paper or container.
  • Center the sample as much as possible.
  • Close the balance door and let the balance stabilize. During that time, don’t touch the balance. Don’t even breathe on it.
  • Document the weight.

For anyone who would like to see these steps in action, Shimadzu made a three-minute video about the general weighing procedures for analytical balances. 

Accurate and repeatable weighing depends on following an SOP and doing it every time. A consistent weighing process produces the most consistent results.