The borate fusion technique consists of mixing a ground sample with a borate flux (lithium or sodium) inside a 95% Pt - 5% Au crucible, heating to 1000 °C with agitation until the flux melts, and then dissolving the sample homogeneously in the flux. When the sample needs to be prepared for X-ray fluorescence (XRF analysis), the hot melt is then cast into a mold and cooled, resulting in a glass disk. The melt can otherwise be poured into diluted acid for subsequent inductively coupled plasma (ICP analysis) or atomic absorption (AA analysis).
Significant benefits that make the difference
Since XRF is a comparative technique, the standards used to prepare the calibration curve have to closely match the characteristics of the unknown sample to provide an accurate and precise analysis. Fusion is the only sample preparation technique that allows you to matrix-match the standards and unknown that cover a wide range of materials. The glass disks prepared by borate fusion lead to XRF analytical results that are far more precise and accurate than the ones obtained with pressed pellets. In addition of being simple, fast and effective, this preparation technique reduces the number of certified reference materials and calibration applications. Fusion is also well-suited to prepare samples for ICP analysis and AA analysis since unlike common acid digestion techniques, it allows the complete digestion/dissolution of highly refractory materials, ferroalloys and sulfides. It is also safer for the operator (no use of dangerous acids such as HF and HClO4), faster and automated.