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Four Major Reasons for Inaccurate Weighing of Laboratory Analysis Samples:
Sometimes, no matter how meticulous the work is, the test results still fail to satisfy. Eventually, we realize that the data was incorrect from the very beginning of weighing. So, what are the reasons for inaccurate weighing of laboratory analysis samples?

In summary, the reasons can generally be categorized into uncalibrated analytical balances, incorrect installation, environmental and sample physical factors, and improper operation. Therefore, if weighing is inaccurate, look for the cause from these aspects.

1. The analytical balance was not calibrated before use

Before using an analytical balance, it is essential to confirm whether its accuracy is qualified; otherwise, the correctness of the measurements cannot be guaranteed. From the first use, an analytical balance should be calibrated regularly. For balances in continuous use, calibration should be performed approximately once a week. Calibration must be carried out according to the prescribed procedures using standard weights; otherwise, it will not serve the purpose of calibration.

2. Incorrect installation of the analytical balance

When installing an analytical balance, first choose a dust-proof, moisture-proof, shock-proof, wind-proof, sun-proof, and constant-temperature room as the balance room.

Secondly, the balance should be placed on a stable and reliable workbench, and an appropriate location should be selected. Before installation, check the packing list to ensure all components are complete and in good condition, and carefully clean all parts of the balance.

During installation, refer to the balance's instruction manual for correct assembly.

After installation, check again whether all parts are installed correctly, then verify if the power voltage meets the balance's requirements, and turn on the balance to check if it functions normally.

3. Influence of environmental and sample physical factors

During the weighing process using an analytical balance, environmental and physical factors can interfere with the weighing results, such as temperature, sample volatility, moisture absorption, magnetism, static electricity, etc.

1. Impact of temperature changes on the analytical balance

If a unidirectional drift in the displayed value is observed during weighing, it may be due to the influence of temperature changes. If there is a temperature difference between the sample and the surrounding environment, this difference will cause airflow along the weighing container.

Air flowing along the outer side of the container generates an upward force, which leads to errors in the weighing results: under dynamic buoyancy, the sample weighs lighter than its actual weight. This effect ceases only after temperature equilibrium is reached. When taking samples out of a drying oven or refrigerator, wait until the sample temperature matches the laboratory or weighing room temperature before weighing.

Samples should be placed in containers with as small a surface area as possible, and tweezers should be used to handle the weighing containers instead of placing hands inside the weighing chamber.

2. Impact of sample moisture absorption or volatility on weighing results

If the displayed value shows a continuous unidirectional drift during weighing, it may be due to measuring volatile or hygroscopic samples. If the sample is highly hygroscopic, its weight will increase; if the sample is volatile, its weight will decrease. For hygroscopic or volatile samples, use narrow-neck containers, cover or stopper the containers, use clean and dry weighing containers, and ensure the weighing pan is free of dust, contaminants, and water droplets.

3. Impact of static electricity on weighing results from samples or containers

If each weighing shows different results or the displayed value is unstable, or the repeatability of the results is poor, it may be due to static electricity on the weighing container or sample. The influence of static electricity will cause the weighing container to display different weights each time, resulting in poor repeatability. Materials with high insulation, such as glass or plastic weighing containers, are prone to static electricity. This charging phenomenon is mainly caused by stirring or friction during handling, and once charged, the discharge of electricity is very slow. The likelihood of static electricity on samples or containers increases in dry air with relative humidity below 40%. Measures such as using a humidifier or adjusting the air conditioning system to increase air humidity, placing the weighing container inside a metal container for weighing, and grounding the analytical balance can help remove static electricity from weighing samples.

4. Inaccurate weighing due to improper operation by the user

Failure to check before weighing, leading to盲目稱量 (blind weighing). Before weighing, check whether the balance is functioning normally, whether it is level, whether the weighing pan is clean, and whether the display is zeroed, etc. To address this issue, strictly follow the balance's operating requirements.

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