International
Tables for
Crystallography
Volume H
Powder diffraction
Edited by C. J. Gilmore, J. A. Kaduk and H. Schenk

International Tables for Crystallography (2018). Vol. H, ch. 3.10, pp. 383-384

Section 3.10.10. Conclusions

L. León-Reina,a A. Cuesta,b M. García-Maté,c,d G. Álvarez-Pinazo,c,d I. Santacruz,c O. Vallcorba,b A. G. De la Torrec and M. A. G. Arandab,c*

aServicios Centrales de Apoyo a la Investigación, Universidad de Málaga, 29071 Málaga, Spain,bALBA Synchrotron, Carrer de la Llum 2–26, Cerdanyola, 08290 Barcelona, Spain,cDepartamento de Química Inorgánica, Cristalografía y Mineralogía, Universidad de Málaga, 29071 Málaga, Spain, and dX-Ray Data Services S.L., Edificio de institutos universitarios, c/ Severo Ochoa 4, Parque tecnológico de Andalucía, 29590 Málaga, Spain
Correspondence e-mail:  g_aranda@uma.es

3.10.10. Conclusions

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  • (i) We have thoroughly studied the limit of detection for a well crystallized inorganic phase in an inorganic compound matrix. We have determined the following LoDs for insoluble anhydrite: ∼0.2 wt%, ∼0.3 wt% and lower than 0.1 wt% for Cu Kα1, Mo Kα1 and synchrotron radiations, respectively. We conclude that the LoD is slightly better for Cu Kα1 than for Mo Kα1 because the λ3 dependence of the diffraction intensity, with similar acquisition times, yielded slightly better signal-to-noise ratios in the Cu patterns. Of course, detector efficiencies also play a role in the measured signal-to-noise ratios.

  • (ii) We have also studied the limit of quantification for a well crystallized inorganic phase using laboratory X-ray powder diffraction. This phase could be quantified at the level of 0.12 wt% in stable fits with repeatable outputs and good precision. However, the accuracy of these analyses was quite poor, with relative errors close to 100%. Only contents higher than 1.0 wt% yielded analyses with relative errors lower than 20%.

  • (iii) The Rietveld quantitative phase analysis results from high-resolution Mo Kα1 powder diffraction (transmission geometry) and high-resolution Cu Kα1 powder diffraction (reflection geometry) were quite similar for a series of crystalline inorganic phase samples. We inferred the validation of the Mo-based analyses procedure from this initial study, as it yielded results very close to well established high-resolution Cu radiation analyses (see Fig. 3.10.7[link]a). From the comparison of the AKLD values for the two types of analyses, it was demonstrated that the Mo Kα1 analyses were slightly better than those using Cu Kα1.

  • (iv) Comparison of the results obtained from Mo-based and Cu-based patterns for a series of crystalline organic phase mixtures showed that the Mo Kα1 analyses gave slightly more accurate values. This conclusion was drawn because the calibration curve obtained from Mo patterns with increasing content of xylose gave an R2 value closer to 1.0, a slope closer to 1.0 and an intercept value close to 0.0 (see Fig. 3.10.7[link]b). The slightly poorer results from Cu Kα1 analyses are very likely to be due to the transparency effects in reflection geometry.

  • (v) Comparison of the results obtained from Mo Kα1 and Cu Kα1 patterns for a series containing increasing amounts of amorphous glass also indicated that the Mo-based analyses were slightly more accurate than the corresponding Cu Kα1 analyses. This conclusion was drawn because the obtained calibration curve from the Mo data has (1) a slope closer to 1.0, (2) a smaller amorphous value for the glass-free sample and (3) a closer agreement between the intercept from the least-squares fit and the determined amorphous value for the glass-free sample (see Fig. 3.10.7[link]c). The AKLD analysis confirmed this outcome. Furthermore, the results from synchrotron data have the best accuracy, as shown by the calibration plot and the AKLD analysis.

Finally, we conclude that for the challenging quantification analyses studied here, the results derived from high-energy Mo Kα1 patterns were slightly more accurate than those obtained from Cu Kα1 patterns. We justify this conclusion based on the larger tested volume for Mo Kα1 analyses, which led to better statistics/accuracy in the recorded powder-pattern intensities. The minimization of microabsorption in the Mo Kα1 transmission data is very likely to be an additional factor in the improved accuracy.

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