When manufacturing powders, especially pharmaceutical and biopharmaceutical products, several complex issues and challenges may arise. Sampling schemes must be created to ensure the process runs smoothly, and for most operations, knowledge of particle size distribution (PSD) is required. From grams to kilograms, powder batches can vary in size, so various devices and techniques may be necessary to process and segregate the appropriate samples.
Sampling Systems – What are They?
Sampling systems are employed in various industries. These systems draw samples from a process line and prepare them for analysis in an analyser. Many variations of the powder sampler system have been designed to streamline the process, and these can be manually or automatically operated. Most powder sampling systems work by sampling powders as they pass through or fall down a pipe. After sampling, the extracted sample is down a chute and sent directly into a bottle or other container. Most sampling systems are made from hygienic stainless steel for easy cleaning, and they come with several benefits, including:
- Automatic and manual operation
- Save time – processing time is reduced: usually, the operator only needs to cap the sample jars.
- Many can be fitted to existing equipment
- Guaranteed not to get stuck during operation
- They can connect to various machinery like pipework, mills, sieves, and packing and charging stations.
The Wrights Dowson Group has manufactured a Sample Collection System (SCS) known as the carousel, allowing separate samples to be collected either at or near the sampling point. The controller also includes an override feature that can switch to manual operation if the user requires it.
The sampler will deposit a preset number into the sample jars over a specific period. When this preset number has been reached, the sample collection system moves the jars filled with composite samples into a position to await collection. The system will then place a new, empty jar ready to take a new selection of samples.
When creating a sampling system to process powders, several factors must be considered. These are:
- The area where the sample is being drawn from
- The cost of sampling
- The level of precision required to sample successfully
These factors will determine which sampling method is best for the operation. In addition, to sample collection systems like those created by the Wrights Dowson Group, a few other sampling methods can be used to process powders. These are:
With this method, samples are extracted from a heap or store. The three basic methods for static sampling include scooping, thieving, and cone & quartering. Unfortunately, these methods are often prone to error as samples are taken only from the surface and may not represent the bulk of the material.
Typically, this is the preferred sampling method. These processes involve extracting samples from a moving powder bulk. This means the powders don’t get a chance to split, making the final extraction more accurate. There are three primary dynamic sampling processes. These are table sampling, chute splitting and spin riffling.
Powder Processing – Segregation
Segregation is one of the most common problems faced in powder processing. Even when particles are mixed appropriately, they tend to unmix during handling, transport or conveying. The de-mixing process is usually caused by the density, and different sizes and shapes, of particles.
When materials are stored, vibrational energy causes the fine particles to move. Over time, they’re forced to rise to the top of the container. This process is what makes static sampling so unreliable.
When powders are poured onto a surface, air enters the container and causes the surface particles to be released into the atmosphere. As the quantity of powder on the surface increases, the powder starts to unmix as the fine and coarse particles segregate themselves to different regions of the bulk.
To reduce segregation, sample processing operations should consider the following:
- Make sure the size distribution of constituents is as similar as possible
- Reduce particle size where possible
- Add small quantities of a liquid binding agent
Powder sampling isn’t strictly a pharmaceutical operation. It’s also used in the cosmetic and food industry, and the same sampling methods and procedures still apply, and segregation will always need to be minimised. Sample collection systems and automated processes offer the most reliable and efficient ways to do it.