Scattering curve sample preparation

A good solution scattering curve is dependent on careful sample preparation, satisfactory biochemical and physical assays, accurate background subtractions, a suitable sample holder and instrumental calibration. Aspects of these five topics are briefly noted. 

Fig. 5. Structure factor S(k) for polyethylene melt (N — 6429) as a function of wavevector k at T = 430 K. The points are experimental results [32,33] of Narten and Habenschuss from X-ray scattering (the k a 0 data is inaccurate due to sample preparation related scattering). The soiid curve is the PRISM theory with the hard core diameter d = 3.90 A. Use of a value of d = 3.7 A results in roughly a 10% underestimate of the intensity rf the amorphous halo feature. Disagreement between experiment and theory at large k is eliminated if thermal broadening, due to vibrational and torsional oscillations, is taken into account [33,34]...

PrPtBi Measurements were initially made on powder samples prepared by arc melting (Suzuki et al., 1997). The electrical resistivity ( 1 mf2cm at 300 K) and Hall coefficient ( 0.7 cm /C at low temperatures) are consistent with semiconductivity. The magnetic susceptibility follows the Curie-Weiss law above 50 K but tends to become temperature-independent below 50 K. The specific heat curve shows a prominent anomaly at 1.35 K. A crystalline electric field (CEF) level scheme was derived from inelastic neutron scattering... 

The scattering curves of samples of the gel region, shown in Fig. 9, show a more or less pronounced shoulder between 0.07 and 0.22 nm . This feature can be interpreted as a smeared correlation peak caused by periodic lamellar structures. It occurs in a similar range of Q values as the peaks observed for the more concentrated SDS/CA-SA/water system investigated by X-ray scattering [1]. For sample J3 the lamellar correlation peak corresponds to a periodic distance of 39.3 nm, which is higher than the value observed for the more concentrated system with a mixture of the alcohols CA and SA. There is no obvious trend in position or shape of the correlation peak for samples with different y. This may be due to the fact that the applied protocol of sample preparation does not ensure a fully reproducible structure of the samples. 

In a classic study that illustrates the principles of the method, an XRPD procedure was described for the estimation of the degree of crystallinity in digoxin samples [35]. Crystalline product was obtained commercially, and the amorphous phase was obtained through ballmilling of this substance. Calibration mixtures were prepared as a variety of blends from the 100% crystalline and 0% crystalline materials, and acceptable linearity and precision was obtained in the calibration curve of XRPD intensity vs. actual crystallinity. Figure 7.13 shows the powder pattern of an approximately 40% crystalline material, illustrating how these workers separated out the scattering contributions from the amorphous and crystalline phases. 

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