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. 381-382

Section 3.10.8. Increasing crystalline organic phase content series

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

3.10.8. Increasing crystalline organic phase content series

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Table 3.10.3[link] shows RQPA results for six mixtures prepared with G, F, L and an increasing amount of X measured with Mo Kα1 (transmission) and Cu Kα1 (reflection). In general, the values obtained using both radiations are quite similar to the weighed values. The AKLD values and the KLD values for the xylose phase are also reported in Table 3.10.3[link]. The AKLD values from Mo Kα1 and Cu Kα1 radiations are relatively similar. The main problem for RQPA of organic mixtures measured in reflection geometry is related to the low X-ray absorption of the samples and the transparency effects that lead to poor peak shapes and even some split peaks in the powder patterns, as discussed previously (León-Reina et al., 2016[link]).

Table 3.10.3| top | pdf |
RQPA for the crystalline organic mixtures measured with Cu Kα1 and Mo Kα1 radiations

Weighed amounts (wt%) are also shown for the sake of comparison. Absolute values of the Kullback–Liebler distance (AKLD) for each mixture and the KLD value for xylose are also included. Trm, transmission; rfl, reflection.

 GFL_0.0XGFL_0.25XGFL_0.50X
Phaseswt%Mo trmCu rflwt%Mo trmCu rflwt%Mo trmCu rfl
G 33.4 33.8 (1) 33.5 (3) 33.3 33.6 (1) 33.1 (2) 33.2 32.3 (2) 33.5 (2)
F 33.5 31.7 (1) 32.7 (3) 33.4 32.3 (1) 34.3 (2) 33.3 32.1 (2) 33.4 (2)
L 33.1 34.5 (1) 33.7 (3) 33.0 33.7 (1) 32.0 (2) 33.0 35.0 (3) 32.5 (2)
X   0.27 0.33 (4) 0.57 (9) 0.55 0.53 (8) 0.61 (9)
                   
AKLD sum   0.0362 0.0150   0.0216 0.0231   0.0410 0.0096
(X) KLD     −0.001 −0.002   0.000 −0.001

 GFL_1.0XGFL_2.0XGFL_4.0X
Phaseswt%Mo trmCu rflwt%Mo trmCu rflwt%Mo trmCu rfl
G 33.0 34.7 (1) 33.6 (2) 32.7 32.2 (1) 31.5 (2) 32.0 32.8 (1) 33.6 (2)
F 33.1 32.6 (1) 33.7 (2) 32.8 31.7 (1) 34.4 (2) 32.2 30.7 (1) 32.5 (2)
L 32.8 31.6 (2) 31.4 (2) 32.5 34.3 (1) 32.0 (2) 31.8 32.9 (1) 30.5 (2)
X 1.1 1.10 (5) 1.3 (1) 2.0 1.76 (5) 2.1 (1) 3.9 3.70 (5) 3.4 (2)
                   
AKLD sum   0.0338 0.0280   0.0363 0.0339   0.0361 0.0372
(X) KLD   0.000 −0.002   0.003 −0.001   0.002 0.005

Fig. 3.10.7[link](b) shows the quantified xylose contents (wt%) as determined by the Rietveld methodology as a function of the weighed amount of xylose added to the mixtures. The results were plotted to obtain the calibration lines with increasing content of the analyte. Both plots gave R2 values close to 1.0. However, the slope values were 0.92 and 0.82 for Mo Kα1 and Cu Kα1 radiations, respectively. Slope values close to 1.0 mirror accurate analyses. Furthermore, the y-intercept values were 0.04 and 0.30 for Mo Kα1 and Cu Kα1 radiations, respectively. A y-intercept value close to 0.0 mirrors accurate analyses. Hence, it can be concluded that slightly more accurate analyses are obtained for Mo Kα1 powder diffraction in transmission when compared with Cu Kα1 powder diffraction in reflection for organic crystalline samples.

References

León-Reina, L., García-Maté, M., Álvarez-Pinazo, G., Santacruz, I., Vallcorba, O., De la Torre, A. G. & Aranda, M. A. G. (2016). Accuracy in Rietveld quantitative phase analysis: a comparative study of strictly monochromatic Mo and Cu radiations. J. Appl. Cryst. 49, 722–735.Google Scholar








































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