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MS Analytical provides a large scope of techniques for precious metal analysis. Selection of the best methodology for accurate determination of precious metal content is dependent on the sample matrix, distribution, grain size and the intent of the analysis. Our experienced chemists are available to help you select the most appropriate technique.
For a typical Fire Assay procedure, a measured amount of powdered sample is mixed with a combination of reagents including Sodium carbonate, Sodium borate, Litharge, Flour, Silica and Potassium nitrate. The mixture is heated to temperatures between 1000 Celcius and 1100 Celcius and any precious metals within the sample bind with the Lead added in the form of Litharge.
The lead button is separated from the slag and cupelled at 950 Celcius, which oxidizes the lead leaving a small button of pure precious metals. This bead is digested with acid and then the concentration is read using Atomic Absorption or ICP-AES.
When a sample has or is suspected of having metallic grains present, it is preferable to remove these prior to analysis in order to maintain the integrity of the sample. 500g or 1000g of sample will be screened to 150mesh (106micron). The entire plus (+) fraction is assayed, and the minus (-) fraction is assayed in duplicate using Fire Assay techniques and finished with gravimetric and instrumental techniques.
Both the (+) and (-) fractions are used in the determination of gold in the entire sample.