How Do I Choose a Sampler?
How Do I Choose a Sampler?
This is one of the most common questions we are asked. Eventhough there is no direct answer as every situation is different there are numerous factors that need to be considered when deciding on the best sampler. Usually poor sampling results are a direct result of not choosing the correct tool. For example a common mistake is a free flowing powder sampler is used when the powder being sampled is poor flowing (more on this later).
- Why am I Sampling
The reasons for sampling can be anything from goods in checking, sample retention to final quality testing. Clarity is needed at this point.
For example if you are carrying out particle size analysis sampling using a scroll type of sampler will give you poor results. In effect the powder will be milled leading to poor results and the possibility of a batch being needlessly rejected.
Other reasons for sampling could be microbiological testing. Therefore the use of a presterilised sampler or a sampler that can be easily sterilised will be critical.
The reason for sampling is critical on the choice of sampler.
- What am I Sampling?
Eventhough this sounds obvious it is the most common mistake. The choice of the correct sampler is critical otherwise you will end up with poor results.
Powder Sampling – Powder characteristic range hugely. Some powders are very flowing others flow very poorly. Poor flowing powders are generally harder to sample but you need the right equipment to make it a success
Many samplers rely pn the powder to flow into the sampler. If you are powder I snon free flowing it will not work properly. Therfeore a quick test to see what type of powder you have is the "co test". Simply push a clean cylinder or gloved finger into the powder. If the powder falls in on itself it is free flowing. If it is cohesive there will be the shape of the finger or cylinder left in the powder
Granule Sampling – How large are the granules. Some samplers can have small sampling holes. Will the granules fit in the sampler.
Liquid and Viscous Sampling – What is the viscosity of the medium. Again choosing the correct device is critical. Many viscous samplers are no good for liquids and vice versa.
- Where am I Sampling
A proper understanding is critical.
Headroom – Is there enough headroom above the machine, container etc for sampling. If you are sampling a in glove box is the sampler small enough
Cleaning Facilities – Is there the ability to clean down the sampler after use or should a single use disposable sampler be used
Location – Is the sampler to be fitted to a machine or is it manual sampling. Can the area be easily accessed
- Sampler Material
What does the sampler have to be made from needs to be considered.
- Is the material being sampled corrosive.
- Will the material being sampled react with the sampler
- What is the contact time of the material in the sampler
Chemical resistance charts are very useful. They give a good indication on which material is suitable.
However care needs to be taken when choosing disposable samplers. Chemical resistance charts are based on prolonged contact over weeks or months. Single use samplers may appear not suitable but because the contact time is only seconds they will be. Further investigations and testing may need to be carried out.
- Reusable versus Disposable
Traditionally reusable samplers have been the sampler of choice primarily due to the lack of disposable samplers available. However big in roads in disposable samplers mean that they are now preferred by many.
Advantages of Reusable Samplers
- 1 off cost and the sampler can be resued.
- They are often stronger than disposables so if the medium is dense/hard they are more likely to go to the required depth
Advantages of Single Use Samplers
- No cleaning costs
- No cleaning validation costs
- Speed – simply unwrap and use
- No risk of cross contamination
The design of the sampler needs to be suitable for the application. It is pointless buying a plastic sampler if you are sampling a hard material. It will simply bend.
- Ease of Cleaning
Other considerations include the ease of cleaning. If you need a sampler that needs to be properly cleaned it needs to be easily stripped to its components and designed for cleaning. Features to look out for include fully welded construction as opposed to spot welding. For critical applications is weld polishing required, electropolishing required.
- Removal of Sample
How easy is it to remove the sample after sampling. For some people this is critical usually when "unit dose sampling", sampling very small amounts or sampling very expensive material.
When taking small samples it is important that the sampler is reproducible time and time again but also that the full sample is removed.
- Surface Finish of the Sampler
Metal and stainless steel samplers can have different surafce finishes. Generally if you are looking for something that is easy to clean, surface that powder does not stick to so easily then a sampler with a very smooth surface finish will be required. Traditionally this has been called a mirror polish. However this is now classed as an Ra finish.
Satin Finish = Less than < 1 Ra
Mirror Finish = Less than < 0.2Ra
We suggest check the surface finish on the specification sheet before ordering. If required the finish can generally be improved to the desired level.
Electropolishing is a common option. This has 2 main advantages. Firstly it cleans the sampler and polishes the sampler in often difficult places eg. The internal bore of tube. Secondly it generally improves the surface finish (reduces the Ra) and gives a sample a more "polished" look.
What documentation is required with the sampler. Is it simply a generic certificate of conformity or are other certs required. For example:
- General certificate of conformity
- Certificate of conformity that relates directly to your order
- Material certification. XRF certification
- Surface finish certificate – Ra certification
- Welder certification
- Sterilisation certification (on disposable samplers)
- Batch specific documentation
- BSE/TSE documentation
- EC/EU certification
8) Electro Static
If you powder or liquid is flammable or id liable to create sparks it is imperative that the correct device be chosen. Earthing the sample must be carried out or buying a sampler that has been proven for use in ATEX, Ex areas should be carried out. A risk assessment should be carried out.
Some customers have also found that earthing the sampler (even if not required) because of electrostatics helps improve the results.
8) Good Sampling Practice
There are general practices which should be considered before, during and after:
- Minimise Sample Handling
When taking a sample the number if times it is transferred to a container, bag etc.. Should be minimised. Each time the sample is transferred small amounts of sample are left behind. This could lead to poor results.
- What am I Storing the Sample In
Again an assessment should be carried out on what the sample is being put in. The correct container or bag will make sampling easier but also keep the sample safe. Some samples can be retained for many years so it is important to check that the container is suitable for this period of time.
Other common considerations include does the container have to be sterile, what standard of sterility or cleanliness is required, size of container,
Advantages of Containers
Widely available in different sizes and shapes
Advantages of Bags
Use less space
- Risk Assessment
A risk assessment of the sampling area and process should be carried out. Very hazardous materials are frequently sampled and it Is important that not only the correct tools are used but the whole process of sampling be assessed
- Adequate ventilation
- Correct PPE is worn
- Adequate lighting
- Enough space
- Proper training of procedures
We hope that the above guide to how do I take a sample is helpful. The guide is meant to give brief overview of common questions and concerns we have found over the last 25 years.
If you have questions, comments please do not hesitate to ask Jonathan Fenner at firstname.lastname@example.org