XRF Applications Blog

Wednesday, December 12, 2007

XRF Applications: Gold Alloy Analysis

XRF Application: Gold Alloy Analysis

If you have seen the Reconditioned XRF page of the Eastern Applied website, then you know that we currently have a Seiko 2110 XRF available (a rarity).  While reviewing some older application briefs from Seiko XRF I found one regarding Gold (Au) Alloy Analysis using a 2110 and figured, what better time to have an XRF Applications Blog about this…below is an overview of the Seiko report, but the detailed one (includes charts, full results, etc) can be downloaded at our documents section.

OVERVIEW
There are many types of gold alloys.  These alloys cannot be distinguished by their physical appearance.  This leads to fears of misapplication and a need for a simple technique of identifying gold alloys.

The Seiko 2110 and 2210A can rapidly determine the composition ratio of a variety of gold alloys without pre-treatment.  Because the Fundamental Parameter Method (theoretical calculation method) is employed as the quantitative method, analysis is possible without standard samples.  Furthermore, it is simple enough that anybody can attain accurate analysis - below is an example:

ANALYSIS CONDITIONS (summary of Seiko Application Briefs chart)
The instrument used was the Seiko SEA-2120, with a 10mm collimator.  Tube Voltage was at 50kV and tube current at auto-setting.  The target was Rh (Rhodium), the atmosphere was air and the preset measuring time was 300 seconds.

ANALYSIS SAMPLE
Seven (7) types of gold alloys were selected at random; each sample was also analyzed by ICP-OES (very expensive, destructive method of testing) in order to check the accuracy of the SEA-2120 (both new and reconditioned currently available).

QUANTITATIVE METHOD
Fundamental Parameter (FP) Method (theoretical calculation method)
*** NOTE: Eastern Applied Research’s headquarter technician said that FP works best when set-up to look for a specific element and removing all other elements from the analysis chart (in this case, gold percentage of the alloy).  For the most accurate readings, he would utilize Bulk-FP method with standards.

ANALYSIS RESULTS
As noted in the preface, the full report with charted results can be reviewed in our documents page. However, a few were randomly selected for this blog. 

Sample ‘C’ contained parts of nine (9) elements.  Using the highly accurate, but destructive, ICP-OES method, the Au content was determined to be 60.60.  When testing the same sample with the Seiko 2120 XRF the Au contact read 54.16 without a standard sample and it read 60.40 with a standard sample.

In order to check the repeatability, this sample (sample ‘C’) was analyzed twenty times on the same point at different preset measuring times.  The standard deviation for the gold readings was at 0.08 for 300 seconds, 0.11 with 100 seconds and 0.15 with 50 second readings. 
Complete results can be reviewed as a .pdf here.

SUMMARY
The result of analysis of each alloy shows values to be roughly close to values from ICP-OES; important to note is that the accuracy is greatly improved by using standard samples.   Regarding the repeatability, 100 seconds measuring time would be acceptable for the analysis of the primary element.  Accordingly, analysis of gold alloy with the SEA2120 is precise, quick, does not require pre-treatment and is very useful in exterminating many types of gold alloy.

*** The analysis of gold alloys is primarily useful in the jewelry industry and the Seiko 2000-series (2010, 2110 and now the 2210A) is known as a reliable and accurate instrument for this application.  The newest model from the series (SEA-2210) is always available and we are currently offering a reconditioned 2110 for an excellent price; please contact Scott Kramer (716-625-8311) with any questions relating to that.

- JGH

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