Friday, October 31, 2008
In an earlier Blog-Entry (9/4), we discussed the importance of utilizing accurate reference standards to obtain the optimum performance from any XRF analyzer. Below are ‘Golden Rules’ developed for organizations using XRF analyzers for gold and precious metal analysis (note that two focus on appropriate calibration standards).
1) The sample and standards must be homogeneous. For use as standards, we recommend the use of pin dip samples, quick quenched in water within three seconds of drawing then rolled flat. Surface should then be sanded and cleaned. The samples should then be scanned on the assay system to insure that the spot to spot variation of the sample does not vary more than 0.1wt%. Another option is to utilize reference standards from an accredited laboratory.
2) Appropriate calibration standards must be used to calibrate the instrument. Standards must be matrix matched to the sample to include all of the same elements that will be present in the samples to be measured. These elements should also be present in the same concentrations (within 1.0wt% or less).
3) Enough measurement time must be used to achieve adequate precision. If precision better than approximately 0.1wt% gold (Au) at one standard deviation is desired, then the average of multiple readings on the same spot must be used. For example, 3 repetitions at 90 seconds or 2 repetitions at 120 seconds must be taken in order to reduce the magnitude of the standard deviation.
4) All of the elements in the sample must be within the detection limits to achieve the gold accuracy specification. If some light elements such as Silicon (Si), Boron (B) or other trace elements are present, or elements below the detection limit of the instrument are present in the sample, then those elements must be accounted for and be negligible in order to achieve the accuracy specifications.
XRF Instruments provide accurate analysis for a wide range of applications and many factors play a part in obtaining the best performance from every XRF Instrument; feel free to contact Skyray XRF to discuss any aspect of XRF performance.