Weighing is essential to many industries, especially those that prioritize accuracy and consistency, such as pharmaceuticals. Precise weighing of ingredients for manufacturing can make the difference between a successful medication and one that fails.
Automated weighing systems can increase efficiency and ensure that batches are correct, but they don’t eliminate the need for human oversight. Using best practices for the entire weighing process is key to getting accurate measurements.
Preparation of Samples
Sample preparation is a vital step in the weighing process that has a direct impact on analytical results. It is important to develop a sample preparation method that meets quality and accuracy requirements, while balancing productivity and product safety.
The sample preparation methods used in a lab can vary from one facility to the next, but there are some common steps that must be taken to ensure accurate results. Depending on the type of analysis, these steps may include:
The sample must be free of any foreign particles or substances that can affect its weight. It is also important to make sure the sample is evenly distributed on the weighing pan. This is especially important for accurate moisture analyses. The weighing pan needs to be clean and free of residues from previous measurements. For this reason, it is best to use a separate container for the sample that can be tared and easily cleaned. A small sample can be placed directly on the weighing pan, but this method increases the risk of errors.
Placement of Samples on the Balance Pan
When it comes to weighing, consistency among operators is the key to accurate and repeatable results. This is because different handling techniques can introduce error. For instance, loss of material during transfer from one container to another can affect the measurement.
Also, vibrations and air currents can affect the readings of an analytical balance. This is why the weighing process should be carried out in a place that is free of such factors and controlled for temperature and humidity.
In addition, it is important to tare the balance pan before placing the sample. This is done by placing an empty container on the weighing pan and pressing the tare button. Once the tare is set, the weight displayed on the screen is the sum of the weight of the empty container and the sample. In addition, bare hands should be avoided when touching the weights as hand grease can cause errors. Instead, clean forceps should be used for this purpose.
Recording of Readings
One of the most common sources of measurement error is in reading and recording a measurement. Whether the measurements are made on a scale or measuring tape, if they are incorrectly read or recorded they can be inaccurate.
For this reason it is important to follow the proper procedure for recording your results. It is also recommended to use a data logging system for your analytical balance, as this will help eliminate transcription errors and prevent erroneous data entries.
Some weighing systems also incorporate advanced technology to reduce weighing errors and speed up the process. For example, in-motion weighing systems allow vehicles to be weighed while traveling over the weighbridge, resulting in higher accuracy and more efficient traffic flow. Similarly, automated weighing systems with user-friendly interfaces can reduce the traditional learning curve for new staff, enabling rapid onboarding. This can increase productivity and improve overall quality. This is especially true in pharmaceutical manufacturing processes such as ‘weigh and dispense’ procedures.
Cleaning the Balance Pan
Keeping the balance clean is essential for obtaining accurate results and avoiding contamination. Even small amounts of residual material from the previous user can affect weighing accuracy and potentially pose health hazards for other users.
After each weighing operation the balance should be thoroughly cleaned, especially when weighing toxic substances. Ideally, this is done after each use and before the next operator starts work. Laboratory SOPs should specify how often the equipment is required to be cleaned, taking into account the risks involved in the process and the sensitivity of the weighed samples.
To clean the balance, first switch off the display and unplug the power – but be sure not to tilt or disconnect any connected peripherals. Then wipe the entire surface area of the balance using a lint-free cloth or paper towel dampened with a mild cleaning agent. Remove the weighing pan and wipe carefully, paying special attention to any residues on the metal parts (weight lock, breeze break ring and dust plate). Removable parts that are stainless steel can be sterilized in a dishwasher.