Dear Sir. Concerning your issue about the best approach for determination of chemical composition of silica powder compared with XRF and ICP-OES Both techniques, XRF and ICP-OES , are capable of giving excellent accuracy and precision. Both techniques have potential problems as does any analytical method. EDXRF and/or Wavelength XRF suffer from matrix and interelement interference issues, as does ICP (OES and MS). With XRF, the standard and sample must be matrix matched with respect to both the matrix and the particle size. In addition, I have seen that different chemical forms can cause problems such as alkyl Si versus Si oxides in an organic matrix, i.e. the elemental composition is similar, yet results for the methyl silicon are much lower than oxygenated silicon due to scattering. Furthermore, the analyte emission intensity is enhanced by matrix elements lower in atomic number and suppressed by analytes higher in atomic number.

With respect to inorganic samples such as catalysts by XRF, it is possible to fuse them into a glass using lithium borate/carbonate. This eliminates the physical interferences and leaves the analyst to make corrections on the interelement effects - calculations are involved and not perfect. The standardless XRF determinations were started 20+ years ago and I have tried it. The common term then was 'MARS' (Matrix Analysis Routine using Scatter). It is an approach that I found to give reasonable results provided that major components are of prime interest and agreements to around 10 to 15 % relative are acceptable. I have used MARS for screening and semi-quantitative analysis (I love math and physics and this technique attracted me for those reasons, plus it was new at the time) but the ICP-OES approach has the potential for giving very accurate and precise results. Using the lithium borate fusion-dissolution in dilute nitric acid (matrix matched at this point) and using lines that do not spectrally interfere, theICP-OES technique can do this while XRF cannot. With XRF, the analyst is stuck making corrections that contain a level of uncertainty.

In short, I would choose ICP-OES over ICP-MS and XRF because the systematic errors are much easier to eliminate and the random measurement error can be as low as 0.5 %. I think the following the below links may help you in your analysis:

https://www.inorganicventures.com/advice/compare-icp-oes-and-xrf-determination-metal-composition-catalyst-powder-samples

http://www.iach.cz/departments/env/www-docekal/pdf/bd_08.pdf

http://wiredspace.wits.ac.za/jspui/bitstream/10539/8620/1/M.Sc%20Chemistry%20Final%20Dissertation.pdf

Thanks

Dear Dr. Isam Eldin Hussein Elgailani,

Thank you for your valuable comments and files. I fully agree with you about better accuracy of ICP-OES compared with XRF.

We have applied lithium borate fusion then used ICP-OES. But I believe that chemical analysis's (C.A; i.e., gravimetric and titration methods, Spectrophotometers and flame photometer) can be more accurate compared with XRF and ICP-OES.

Please see the attached file.  In this case, XRF and ICP-OES methods were uncertain when measuring SiO2 and Al2O3 grades. It should be noted that gravimetric method was applied to measure SiO2 and Al2O3 while both gravimetric and titration were employed during CaO measurement. To record accurate Fe2O3 and TiO2 grades, Jenwey-6300 and Unico-2100 Spectrophotometers were used. Although for K2O measurement, Jenwey-PFP flame photometer was utilized. The entire procedures followed according to ISO/IEC 17025:2005 standard.

I believe CA was more accurate comparing ICP-OES therefore I am looking for some published work which it can confirms my idea. What is your comment in this respect? Have you ever faced with publication which it compares CA and ICP-OES for determination of chemical composition of silica powder?

Thanks and best regards,

H. Haghi

Dear Hamed Haghi

Thank you very much. Regarding your attached file it seems to be CA more accurate, but as you know that the component of silica depend mainly on the site from which it was taken. I think the following below attached files may help you in your analysis as the analysis was carried by CA.

Thanks