To protect your equipment investment and to help ensure compliance with FDA, CFR and other standards the procedures for using an analytical balance should be published in the company’s operations manual.

Before Anything

Analytical balance manufacturers such as Kern provide detailed operating instructions for each model offered, and these should be included in your company documentation. This discussion covers general procedures for operating analytical balances.

New balances must be calibrated before they are put into operation, and should be periodically recalibrated based on how they are used.  Recalibration procedures can be established in discussions with equipment suppliers such as Tovatech.  They are performed either by qualified internal personnel or by outside calibration services.

To help ensure accuracy balances must be level, on a solid weighing table and in a draft-free location away from sources of electromagnetic radiation.  If the balance is moved, it may require recalibration so select a “permanent” location if possible. Higher-end analytical balances such as the Kern ABJ, AEJ and ABT models are automatically internally calibrated but this should not be used as an excuse to unnecessarily move them about.

Prepare the Balance for Weighing

When an analytical balance is connected to a power source it will go through a series of internal checks.  Remember that the unit must warm up when first connected to a power source or after an extended power outage.  This allows it to reach the proper operating temperature.  The warm-up period can be at least 4 hours, or as indicated in the instruction manual.

Once warm up is completed the display panel indicates that the unit is in the standby mode. When you are ready to start the weighing operation turn the balance on and allow it to go through a short function test.  When the display indicates zero weight the balance is ready for use.

From this point on do not lean on, place objects on or bump the weighing table.

Weighing Operations

Open the door of the analytical balance.  Using Kimwipes, gloves, tongs or tweezers (not your bare fingers because fingerprints add mass) place the weighing container or weighing paper on the balance, shut the door and wait a few seconds until the unit stabilizes.  It is a good practice to record the weight of the container or paper, but to get an accurate readout of the substance being weighed you must cancel out the weight of the container or paper.  Do this by pressing the tare button until the display reads 0.0000 g.

Tip: The tare function should be performed no matter how much of a substance is to be weighed.

Open the door and carefully add the substance being weighed until the display shows the desired weight, then close the door and again wait until the scale stabilizes.  Record the weight either manually or by an optional statistics printer or standard printer depending on the model of analytical balance being used.

Tip: Center materials being weighed on the weighing pan.

Tip: Because hygroscopic materials absorb moisture they should be weighed rapidly.

Tip: If substances to be weighed are hot, first allow them to cool in a dry environment to avoid moisture absorption.  For example, warm hygroscopic samples should be allowed to cool in a desiccator prior to weighing.  This is particularly important when weighing samples that have just been removed from drying ovens.

When weighing is completed, return the analytical balance to the standby mode.  Use a soft brush to clean the weighing pan and cabinet.  Remove spilled materials from the weighing area.  For more extensive cleaning it is advisable to unplug the unit and use a damp cloth moistened with a mild soapy solution, taking care that no moisture enters the weighing apparatus.  Dry the unit thoroughly with a soft towel and be certain that the balance door is shut.  If the unit is unplugged it will have to be warmed up again before weighing can begin.

Follow the manufacturer’s instructions for all weighing functions such as percentage determination, tolerance weighing, recipe weighing and piece counting.  Ask the weighing professionals at Tovatech for help in setting up your weighing procedures.

What procedures are in place at your organization for weighing using an analytical balance?