Frequently Asked Questions - Stabilizing Si with HF and acid digestions

I recently ordered a 1000 ppm standard of SiO2 for testing on my MP-AES. The label on the standard says there is trace amounts of hydrofluoric acid; does this help the Si stay in solution? If so, are you aware of how accurate an acid digestion for Si would be without the use of HF?
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admin Total posts: 510

A liquid-liquid extraction generally relies upon combining the aqueous sample with an organic mixture composed of an extractant diluted in a solvent. The compounds listed (benzene, chloroform, etc.) would frequently represent the solvent, and would typically require an extractant specific for the metals of interest. A well designed liquid-liquid extraction would therefore use an extractant/solvent combination optimized for those specific metals to be measured. We would recommend a literature search, as there numerous general reviews of liquid-liquid extractions that could provide specific details for your exact analytical goals.

Posted: 09/06/18 22:19:12
admin Total posts: 510

Yes, the HF is present in this standard to stabilize the Si. At concentrations of approximately 10 ppm or lower, Si does not require HF for stability, and dilutions of this product at or below ~10 ppm can be made in water. The appropriateness of an acid digestion for Si analysis depends upon the form of Si present in the sample. If the Si is bound as silicate phases, then HF would be required for an acid digestion. If however, the sample is organic, then other digestion techniques may be more appropriate, and additional information may be found using the Interactive Periodic Table on our website (

Posted: 08/28/18 11:06:14

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