The Importance of Pressed Pellets and Pellet Dies in XRF Analysis Sample Preparation

In this interview, AZoM speaks to Alejandro Tomassi, Business Development Manager at Specac, about the importance of pressed pellets and pellet dies within XRF analysis sample preparation.

Can you give a brief overview of Specac and the work you do?

Specac history can be traced back to the 50s, the company has been designing and manufacturing analytical chemistry products, such as instruments and accessories, ever since. Nowadays, Specac brings to the market FTIR spectroscopy accessories and sample preparation, XRF sample preparation and polarisers.

As a business development manager, I look after our XRF sample preparation portfolio, making sure that our offering is relevant to our customer base. I coordinate marketing and sales initiatives to increase the awareness of Specac brand within the different industries and academia sectors who use XRF as an analytical technique.

Can you please explain why sample preparation is important for XRF analysis?

It is very important, as in any analytical technique, sample preparation is critical to obtain consistent and reliable results. Particularly in XRF, sample preparation is key, not only because of the quality of results but also because of the throughput that can be achieved.

Choosing which sample prep to use also depends on the element that is analyzed. For heavier elements such as iron, sample prep can be as simple as just using powder, but for calcium or sodium, pressing in pellets or fusing in beads makes a significant difference in the results.

In XRF, there are two main effects affecting measurements than can be minimized with the appropriate sample prep.

• The mineralogical effect influences results because the analyzed element is in different crystal phases, this can only be minimized using fused beads in which the minerals in the sample are fused and the elements are brought to the same oxidation state.
• Particle size effect, influences results because the distance one particle is from the next, due to the grain size and voids, is not uniform and the X-ray beam follows different paths before hitting the detector. It can be minimised by pressing pellets because particles come together more uniformly pressing at high loads.

Additionally, it is important to bring the particle size down as much as possible, using crushers, grinders, and millers before pressing the pellet. It is commonly considered as acceptable a particle diameter of 40 µm or lower.

What are the most common ways to prepare samples for XRF analysis?

The most common ways are, in order of complexity and quality of results

• No prep, which is basically a powder sample
• Pressed pellets
• Fused beads

Before these three, other steps might be necessary, depending on the raw sample particle size and material, to bring down the particle size enough to be used as a powder or pressed in pellets, it also helps when preparing fused beads to have a smaller particle size.

What are the advantages of using pressed pellets for XRF analysis?

Pressing pellets delivers better results compared to no prep at all, also greater consistency. An analyst can produce samples very fast in automated system or slower using manual presses and obtain the same pellet quality. Overall, it is considered a convenient, cost-effective and reliable sample preparation technique that has become an industry standard.

Pressing pellets has greater flexibility at a relatively lower cost with excellent results, although fusing beads deliver the best results because it eliminates the two main effects I mentioned earlier, this, of course, incurs in higher running cost, including maintenance and gas or electricity consumption.

Why are pellet dies required when using pressed pellets for XRF analysis?

Pellet dies are needed to form the pellet; they function as the mold in which the pellet is pressed. They must withstand the load and have the right size for the sample holder the spectrometer uses. Also, dies can be designed to speed up the process and make it easier and safer for the user to prepare the pellets.

What are the benefits of using Specac’s Atlas range for pressing pellets?

Our range of presses and dies are manufactured to deliver optimal pellet quality. We offer three types of presses:

• Manual Press, which requires manipulating a lever to pump the load
• Power Press, a power-assisted press with no pumping required
• Autotouch Press, a user-programmable power assisted press

Atlas range of presses is small footprint benchtop systems, which can be easily set up on-site or laboratories without complex installation. They were designed with three different throughput regimes in mind, users who require pressing few samples, such as ad hoc or back up analysis, can purchase a Manual press, whereas customers who require continuous pellet production can opt for the Autotouch press, which in conjunction with the Apex die, delivers the fastest throughput.

Our combination of dies and presses have a low cost of maintenance, as they are robust enough to deliver consistent results over time with little or no further intervention.

What are the benefits of Specac’s pellet dies?

Our dies are made of stainless steel suitable to withstand the high loads necessary to press pellets. We offer two sizes, 32 mm and 40 mm diameter, which are widely used in industry and academia. There are two types of die produced by Specac, standard dies, which are the traditional plunger, body and pellet die that must be assembled and dissembled to load and unload the sample, and the Apex die, which is a compressible die that doesn’t need user intervention after loading the sample.

Apex die is the new addition to our portfolio, launched last year. It is a unique product that delivers a significant increase in throughput by eliminating user intervention in the middle of pressing cycles, as is the case with traditional dies. It opens up the semi-automatic sample prep market for customers who want to benefit from a benchtop system without compromising faster pellet production for more demanding applications.

What’s next for Specac?

Specac has been very successful in the XRF sample prep market, we are working on bringing innovative products, such as last years’ launch of the Apex die. I think the next step will focus in making pressing pellets even easier, faster and convenient for users from any background so they can focus on what is important which is consistent and reliable results.

About Alejandro Tomassi

A Polymer chemist with experience in a wide variety of analytical chemistry techniques. Began his career as a research scientist in Oil & Gas, developing materials for oil production applications. He then moved to the analytical chemistry industry, initially working on the manufacturing side, helping to bring new instrumentation to the market, and currently on the business side within the Specac’s sales team.