November 4, 2020 How to Prepare Samples for XRF Analysis?

Common methods in which samples are prepared for an XRF study.

There are several methods to prepare the XRF sample. They apply to various sample types. So which method should you try?

XRF refers to chemical analysis method done for many different materials. It has applications in many areas like controlling the metal alloy’s quality, analyzing the sulfur content in gasoline, presence of metals within electronics, plastics. The XRF methodology can examine any material, but the analysis is better if samples are prepared accurately.

Which sample preparation methodology to employ is influenced by result quality desired, how much effort is given (complexity, labor), money factor (labor, equipment used for preparing a sample, analysis time). The method selected sometimes differs, depending on the material and your requirement for analysis.

Here are common methods in which samples are prepared for an XRF study.

Solid Samples

These samples might be metal, metallic objects that have been cut & polished, electronics, plastics. The surface will be flat for good analysis samples because if the surface is irregular, then the X-ray’s distance will change and this can cause an error. The XRF systems work best when samples to be tested are at a fixed distance from the source. When the distance is changed, it can make the intensity from element go up or down.

You can polish, cut samples like metal alloys to get a better quantitative analysis. Remember, surface finish may also affect the analysis even when the sample is mostly flat, especially for elements that are light. Also, rough surfaces may re-absorb or scatter the long wavelength elements. ElvaTech makes some of the best handheld XRF analyzers for sample testing. Their devices are from lots of research and testing.

Loose Powders

For their material analysis, normally you will have to make sure that samples are kept within a film made of plastic or a cup made of the same material. This will make sure that the analyzer sees the surface as flat. The beam will then be able to work with these samples. Limit void spaces by grinding your sample fine. This will give you an improved analysis.

Make sure enough powder has been used so that the elements have infinite thickness. You can do this when you use 15 grams of samples in most materials. Remember to be careful always while analyzing high-powered metal powders. These things can become very hot and also melt otherwise.

Pressed Pellets

Making ready the samples through the powder press method into the pellets is always more difficult than merely placing loose powder within cups. You will get fine powder by grinding your sample. The grain size is best less than 75um. Binding or grinding aid mixes this. Then this mixture is pressed between 20-30 T. This makes sure your sample pellet will be homogeneous.

This method allows improved analytical results compared to loose powders. This is because there will be little dilatation and zero empty spaces because of grinding, compression. In most elements, you will get higher intensities.

Remember how essential it is that you make sure that the pellets have been ground fine. A mineralogical effect will be another limitation in this approach. It can impact analysis of important elements. They can also be prepared cheaply and very simply. You will just need a simple press, and also a pulverizing mill.

Liquids

You can prepare liquid samples by pouring into cups made of plastic. This process is thus much like how you treat the loose powdered samples. However, there are only a limited number of ways in which liquid sample types can be analyzed. It is essential to focus on selecting the right support film, which will give balanced transmission capacities, contamination, strength.

Best, choose a great support film for studying liquids. There are several good films out there like Mylar, Kapton, and Polypropylene, which offers better transmission. However, they all have their own advantages and disadvantages. So do some research before selecting.

Fused Beads

Many people believe that samples prepared in this manner are very good for solids. You must mix flux with finely powdered sample to create these beads. The flux to sample ratio needs to be 5:1 to 10:1. Heat then between 900 C and 1000 C. This sample will become dissolved in this flux and then it must be cast into mold.

In this way, the matrix goes down, which makes your examination more accurate. You can also mix different types of matrix into same curves of calibration.

Author: Sarah Hagi
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