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How to Choose the Perfect Flux for Sample Preparation: Here’s the Secret

8 February 2018 No Comment

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Pre-weighed-300x270When performed correctly, fusion is the sample preparation technique that leads to the obtention of the most precise and accurate XRF and ICP analytical results. Among all factors that need to be considered to get great glass disks or solutions and therefore excellent analysis, the choice of flux is one of the most important.

Let’s discover why.

An Indispensable Chemical

The flux forms the matrix of the disk analyzed by the spectrometer. It must melt before the sample dissolves into it. An adequate flux allows to:

  • Optimize the solubility of the sample and glass disk stability
  • Reach the appropriate melting point
  • Improve fluidity, which in turn accelerates dissolution, prevents sticking to the platinum ware, retains fewer bubbles and improves pouring.

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The Answer to the Big Question

Having this in mind and considering that so many types of fluxes are available on the market, you might now ask yourself: “How can I select the right flux to fuse my sample?

The answer is simple. You must use the basic chemistry model called The acidity and alkalinity equilibrium.

Knowing that all samples tend to be either more acid (such as Fe2O3), or more alkaline (such as CaO), you need to select a flux that will neutralize their acidity or alkalinity level. Some fluxes are more acid (such as LiT), and others are more basic (such as LiM). The key here is to choose a basic flux to dissolve an acid sample or to take an acid flux to dissolve an alkaline sample, keeping in mind that samples are most often mixtures of different oxides with different acidities. It’s important to keep an acidity index of around 1.13 (neutral) as much as possible.

Here are the fluxes typically used with common samples when it comes to XRF analysis.

 

Cement LiT/LiM 67/33
Ceramics LiT/LiM 50/50 to 35/65
Catalysts LiT/LiM 67/33 to 35/65
Limestone LiT/LiM 67/33
Iron ores LiT/LiM 50/50 to 35/65
Alumina LiT/LiM 35/65

 

LiM flux is often the right choice when it comes to preparing samples for ICP analysis, since it has a lower melting point and that it easily crystallizes in contact with the acid solution. Crystals dissolve quicker than glass beads.

Get Expert Advice

We are always available to give you a hand. Contact Malvern Panalytical for guidance as well as useful tools designed to help you quickly select the right flux for your specific samples.

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