Thursday, 12 September 2019

How Should Analytical Balances Be Calibrated?


Weighing balances are an important part of the equipment used in analytical laboratories, even if the lab isn’t equipped with a wide range of analytical instruments. Weighing is involved in the preparation of sample solutions, reagents, precipitates, and more. At every stage of analysis, precise weight measurements are critical to getting accurate results.

A guest post by Kevin Hill.

Analytical balances are a highly sensitive type of weighing equipment, which can measure the mass of a substance to within 0.00001 grams. Such high precision may not be needed in every sector, but it’s often a basic requirement for pharmaceutical laboratory analysts when they’re weighing a sample.

The weighing accuracy of analytical balances is determined by measuring how close the actual weight of a sample is to the result displayed by the instrument. The process used to determine this accuracy is known as calibration.

Calibration Procedure for Analytical Balances

Here’s a step-by-step guide on how to calibrate an analytical balance:

1. Check whether there is a specific calibration procedure for the balance you’re testing. For certain laboratories, especially in the pharma industry, regulatory requirements include the calibration procedure that needs to be followed for each instrument.

2. If the analytical balance has a calibration sticker, check its expiry date. Out-of-date calibrations may require a more thorough testing than you can conduct, so call an expert to be sure that the balance will give accurate results during use.

3. Check the manufacturer’s documentation or the instrument’s calibration sticker to understand the recommended calibration frequency. Certain models of analytical balances require regular external calibration, while others only need it from time to time because they feature internal automatic calibration.

4. Make sure that no one has moved the instrument, or switched it off during the last hour. The accuracy of analytical balances is affected by these factors. Wait an hour after switching the instrument back on, and perform a thorough recalibration or call a professional if the balance has been moved.

5. Use the adjustable feet of the balance to raise one side higher or lower till the bubble on the spirit level is centered. If the instrument isn’t even, it will not deliver accurate results during calibration or use.

6. If the analytical balance has a door, open it and use a soft brush or dry cloth to clean the weighing surface. Make sure the balance is totally clean, since dust or particles on it may cause inaccuracies in measurement results.

7. After closing the door of the balance, press the “Tare” button and wait a few seconds for the reading to settle. Proceed to the next step after the reading from the balance shows zero.

8. Depending on the item types you weigh, choose standardized weights against which to calibrate the instrument. You can use one weight if it meets the requirements of your lab, or multiple weights across the capacity of the balance if you usually weigh a larger range. These weights should be traceable to international standards such as NIST.

9. Open the instrument’s door and gently place the first test weight on the center of the balance. Then, close the door and wait a few seconds for the balance to settle before recording and removing the test weight. Make sure you use tweezers or wear gloves while handling weights, since moisture and oil from your skin can affect the results.

10. Repeat the previous step for each of the test weights you’ve chosen. Check the device’s calibration guidelines or manual to confirm if any drift in measurements is within acceptable tolerance levels, before using the balance.

Author Bio: Kevin Hill heads the marketing efforts at Quality Scales Unlimited in Byron, CA. Besides his day job, he loves to write about the different types of scales and their importance in various industries. He also writes about how to care for and get optimized performance from different scales in different situations. He enjoys spending time with family and going on camping trips

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