If you want accurate weight measurements of laboratory samples, you need to have the right kind of scales. For example, you can use an analytical balance to correctly weigh the lab samples. The accuracy and precision of the results are dependent on how reliable the weighing system is.
Five precautions you must take for accurate sample weighing
It is crucial that you take the right precautions and adhere to the standard operating procedures to ensure the reliability of your reports.
1. Keep the balance calibrated
First and foremost, keep the analytical balance calibrated at all times. Samples are always weighed against the standard reference weights. Therefore, the lab always has to have a set of certified standard weights.
The scales’ calibration must be validated as per the requirements of a recognized national calibration laboratory. Keep the balance calibrated using the standard calibration procedures against daily, weekly, and monthly schedules.
Never touch the standard weights with your hands.
2. Ensure appropriate environment
Use the built-in spirit level to check the horizontal positioning of the balance. Keep the balance in a vibration-free environment.
Ensure that you place the balances in an area with controlled humidity and temperature. They should not be exposed to direct sunlight since it can cause temperature variations inside the weighing chamber.
Don’t place the balances next to doors or windows since opening or closing them will result in air drafts. This could affect the weighing process.
Ensure that you weigh the samples only after closing the weighing chamber doors. Lastly, keep the weighing chamber clean to prevent cross-contamination of samples and erroneous readings.
3. Handle the weights properly
Never touch the weights with bare hands as hand grease can cause errors in the readings. Always use a pair of clean forceps while placing the samples.
Place the samples gently in the center of the pan. Once you are done using the weights, do not leave them outside the workbench. Keep them inside the slots present in the weight box and keep the box closed. This helps in avoiding minimum environmental exposure.
Use wooden tweezers or tweezers covered with rubber on the tips to prevent the weights from getting scratched. Use gloves when handling heavy weights.
Don’t allow the weights to slip on the balance pans as constant slipping may rub and wear down their base. This will cause their mass to decrease and affect the weighing readings. Ensure they don’t bump against hard objects.
4. Store the weights in the right manner
Always store the weights in a room free of moisture, corrosive gases, and dust. If the weights get rusted or dust sticks to them, the mass of the weights will increase. This will result in inaccurate readings.
After using the weights, place them inside a desiccator to keep them dry.
5. Take the right measures to weigh the samples
Use a clean spatula of appropriate size while placing the sample. Weigh the sample quantity in a volumetric flask rather than opting for butter paper weighing. The latter can introduce errors.
Before you record the readings, allow them to stabilize. If you want to weigh small amounts of sample, you need to take extra precautions. For instance, use disposable gloves and head caps to prevent hair fall and use a face mask to prevent breath from affecting the reading.
Record the reading directly into the lab notebook. Avoid writing the weight measurement on scrap paper or hands.
You can even add a printer to the balance. This will allow you to print the weight slips without any transcription errors.
Factors that affect readings on analytical balances
Several factors can affect the analytical balance and produce incorrect readings of the samples. Some include:
- Air drafts
- Chemical reactions
- Uncalibrated scales
- User error
- Improper grounding
- Inappropriate handling of the sample
Weighing of samples is an important part of analytical determinations. By adopting the above-mentioned weighing practices, you can successfully eliminate errors.
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.