A Hydrofluoric acid Microwave Digestion method to prepare samples for ICP-OES


Exeter Analytical’s Hydrofluoric acid Microwave Digestion method is highly effective for the preparation of difficult samples such as Titanium Oxides, Silicates and Zeolites for ICP-OES.

Why is acid digestion used?

The use of acid digestion is the primary step to enable the conversion of solid samples into solutions that can be analysed on ICP-OES. The application of high temperature and high pressure supplied by the microwave means digestion time is reduced significantly. Some common acids used in the digestion process are Nitric acid, Hydrochloric acid and Hydrofluoric acid.

What sample types are suitable for HF Digestion?

Unlike some laboratories, Exeter Analytical can perform Hydrofluoric Acid (HF) digestions with UKAS accreditation. Although Nitric and Hydrochloric acid can digest a large majority of materials, they are ineffective with certain materials such as silicon and titanium oxide compounds, for this a much more corrosive acid is required. HF is regarded as a weak acid, but it is extremely corrosive and unlike the other common acids used, it is readily able to digest a whole host of difficult samples such as Silicates, Zeolites and other samples containing Tungsten and Titanium Oxide.

HF in Action!

Exeter Analytical has been working closely with companies involved in the pigments and coatings industries. Many of the samples submitted for analysis contained TiO2 (Titanium Dioxide) often found in pigments and coatings. Exeter Analytical were able to use their HF Microwave Digestion method to provide the customer with high quality results, fully accredited by UKAS.

Neutralisation before or after?

Many HF digestion methods used in other laboratories neutralise HF with boric acid during the ICP-OES process. However, Exeter Analytical discovered that this was affecting results significantly by producing an extremely untidy background signal and therefore affected the precision of results. With a new and improved method, the HF is neutralised after the ICP-OES process enabling a smoother background and ultimately more precise and reliable results. This includes the use of a specially designed HF kit for the ICP-OES.

ICP with HF chamber
ICP with HF chamber

What are the safety precautions when using HF?

Hydrofluoric acid is extremely dangerous. When coming into contact with skin it dissociates into fluoride ions and in turn causes destruction of the deep tissue layers and bone, this can result in limb loss or death.

Due to this, it is important to be extremely careful when handling HF acid. In Exeter Analytical’s laboratory they implement strict health and safety procedures for the use of HF to protect their staff;

  • Neoprene gloves that cover the entire arm are worn, as HF can penetrate through standard Nitrile gloves.
  • HF is always used inside the fume cupboard as vapours are an inhalation hazard and can cause ocular irritation.
  • In date Calcium Gluconate antidote is always on hand whilst using HF.
  • Full PPE is worn throughout.
  • To ensure safety, a second analyst is on hand to observe the primary analyst completing the preparation process for the HF digestion.
Exeter Analytical PPE
Correct PPE when handling Hydrofluoric Acid

About Exeter Analytical

Exeter Analytical specialise in the manufacturing and sale of elemental analysers that offer accuracy and precision plus a vast range of sample applications. They provide elemental analysis to a range of industries from pharmaceutical to environmental.

With UKAS ISO17025 and BSI ISO9001 accreditation, Exeter Analytical consider themselves to be leaders in quality control testing with extensive knowledge across a wide range of elemental analysis. They have an ongoing program to bring more techniques under this demanding accreditation.

To find out more about the products and services Exeter Analytical have to offer, head to their directory listing here. 


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