Volume 34(1) - Winter 2018

Thermal analysis instruments are used in a variety of fields of specialization, such as in new materials development, product evaluation, or quality control where the reaction temperature or reaction energy derived from the melting of a material can be measured easily. Differential Scanning Calorimeter (DSC) is an analytical tool that detects the change in thermal energy generated in a sample during the heating or cooling process.

Thermo plus EVO2 DSCvesta is equipped with an advanced furnace and is the leading DSC instrument with regard to measurement temperature range. Compared to the conventional model, the sensitivity and measurement range have significantly improved. The furnace adopts the innovative Δ (Delta) block structure, while low power consumption contributes to cooling and heating efficiency.

Moreover, expandability is improved through the availability of cooling attachments and attachments for complex measurements. The instrument can obtain a broad range of data in phenomena difficult to determine using the conventional model, and is extensively used for the analysis of materials in various fields.

The MiniFlex series has a 40-year legacy, and the MiniFlex benchtop X-ray diffractometer presented here is the latest model of this series. It is now possible to use MiniFlex with the HyPix 2D detector, an option previously available only for high-end models. This is a benchtop X-ray diffractometer, yet it still enables easy 2D measurement.

In straightforward terms, the XtaLAB Synergy-DW diffractometer combines the increased flux of a rotating anode source with the flexibility of two different wavelengths, making it ideal for laboratories exploring a wide range of crystallographic research interests. The system is based on Rigaku’s proven, low-maintenance MicroMax-007HF microfocus rotating anode. The target is constructed with two different source materials (Cu and Mo, for example) and is coupled with an autoswitching dual-wavelength optic, meaning that you can select between copper and molybdenum X-ray radiation at the click of a button.

Sample preparation by liquid and droplet methods have been discussed in the previous installment of “Sample preparation for XRF analysis”. In this issue, a novel preparation method by which liquid samples are solidified is described. Solidifying samples such as lubricating oils allows measurement to be performed in vacuum instead of helium and without the need of sample films. This is especially advantageous for the measurement of light elements which have poor X-ray transmission rates through helium atmosphere and films. Another benefit of the solidification method is prevention of particle settlement such as wear metals in used oils during measurement.

Sample preparation is performed by mixing the liquid sample with a solidifier, a material that is solid at room temperature but liquefies when heated. The well mixed heated liquid is then cooled down to form a solidified specimen. Due to the heating process, volatile liquids are not suitable for measurement by solidification. Once the sample is solidified, the original pure liquid cannot be isolated and therefore the method is technically a “destructive technique”.

This article describes the sample preparation procedure, suitable sample types, application examples and other considerations for analysis by solidification method with a wavelength dispersive X-ray fluorescent (WDXRF) spectrometer.

The fusion method and the pressed powder method are well-known and typical sample preparation techniques in X-ray fluorescence analysis of powder samples. In the fusion method, a sample is fused with some alkali borate flux at high temperature to make a glass bead. The method allows more accurate analysis because it provides a substantially homogeneous sample specimen for analysis. It is, however, a costly and time-consuming technique. For highly precise analysis, a fusion machine is essential for making fused beads under identical conditions.

In the pressed powder method, a briquette is formed by pressing a ground powder sample with a ring or cup using a pressing machine. The pressed powder method is a very simple technique that requires no skills or experience. Therefore, this method is suited for rapid analysis or analysis of large quantities of sample. The pressed powder method, however, can create some errors due to grain size and mineralogical heterogeneity effects during sample measurement. It is nearly impossible to eliminate these heterogeneity effects in all powder samples, especially with materials such as soils, rocks, ores, etc., which are composed of different types of grains. Therefore, large differences can occur between analysis results and the actual chemical content.

Both the fusion method and the pressed powder method have advantages and disadvantages as described above. Generally, the optimal sample preparation method for each material is determined by considering requirements such as precision, cost, preparation time, etc. This report provides a comparison between analysis results using the fusion method and the pressed powder method applied to three materials: iron ores, silicate rocks and cements. In the industrial and research fields, the X-ray fluorescence technique is commonly used to control manufacturing processes, to monitor product quality and to determine geochemical characterization. In these three material fields, either the fusion method or the pressed powder method is selected in accordance with the purpose of analysis.

In this report, calibration curves for major components are prepared by both sample preparation methods, and analyses of identical samples with chemical values are performed by each method. The standard error of the estimate as accuracy obtained by the differences between chemical values and analyzed values of calibration standards is calculated and compared between the two methods

The principle of single crystal X-ray structure analysis is the same for organic/inorganic materials and proteins. However, although the steps of structural analysis are the same, there are major differences in the method of executing each step between structural analysis of small molecules and proteins. One of the steps where there is a major difference is the phase determination method for solving the phase problem, regarded as the central problem of single crystal X-ray structure analysis.

The main method of phase determination in small molecule structure analysis is the direct method of inferring phase via statistical processing of diffraction intensity. In protein structure analysis, on the other hand, phase determination using the direct method is impractical, and thus phase is determined experimentally. In the direct method, a roughly assigned initial phase is improved by using a phase relation which takes the magnitude of diffraction intensity as a clue. Therefore, in protein crystals, which have a comparatively large lattice, and limited atomic species and deviation of the electron distribution in the crystal, the magnitude of diffraction intensity is small compared with a small molecule crystal, and thus it is difficult in principle to apply the direct method.

As an experimental phase determination method for protein structure analysis, the MIR (Multiple Isomorphous Replacement) method serves as the classical approach. The MIR method derives the phase of the target (native) protein by using the slight shifts in phase which occur when heavy atoms are incorporated. This paper explains the MIR method, and the MAD (Multiple Anomalous Dispersion) method which uses the wavelength dependence of anomalous dispersion.

In powder X-ray diffraction (XRD) measurements, the measurement mode (0D, 1D, 2D) and optical system are selected to suit the state of the sample and the purpose of the experiment. Until about 10 years ago, the typical approach was a 0D measurement using a scintillation counter (SC) combined with the Bragg-Brentano focusing method (BB optical system) or the parallel beam method. However, due to the development of semiconductor detectors, it became possible to also select 1D and 2D measurement, and the number of optical systems that can be used in combination is increasing every year. This paper presents examples where it is effective to change the measurement mode (0D, 1D, 2D) or optical system when the sample contains trace components, or when particle size or orientation have an effect on the sample. Table 1 summarizes the sample conditions and system configurations explained in this paper. The latest SmartLab SE powder X-ray diffractometer was used for most measurements.

In characterizing multi-component materials, constituent crystalline phases are first identified, and their relative abundances are quantified, in general, as a second step. Techniques of quantitative phase analysis (QPA) using the X-ray powder diffraction method have been used widely for materials characterization in research and development as well as in quality control of industrial products. Various techniques for QPA have been proposed since about 80 years ago. At present, certain techniques are specialized for QPA of specific materials, such as monoclinic-tetragonal Y-doped ZrO₂, α–β type Si₃N₄ etc., while other techniques have been used widely for QPA of general materials. In the latter category, the internal standard method using calibration curves, the Reference Intensity Ratio (RIR) method and the Rietveld method may be listed as major QPA techniques. As is well known, the internal standard method requires experimental procedures to draw the calibration curve, while the accuracy of the method in QPA is considered to be relatively high. Since single peak intensities and database-stored RIRs are used in the RIR method, it is less of a burden to conduct the experiment and data analysis, while the accuracy in QPA depends simply on the accuracy of the measured single peak intensity. The Rietveld method(8) uses crystal structure parameters in calculating powder diffraction patterns for the least-squares fitting, and this structure-constrained model exhibits its advantage in QPA using the intensity data of complicated powder diffraction patterns like those of cements. Moreover, intensity data of total diffraction patterns are used, and the accuracy in QPA is also considered to be relatively high. The Rietveld QPA technique, however, cannot be applied when crystal structure parameters are not available, and some techniques like the PONKCS (Partially Or Not Known Crystal Structure) method(12), which compensate for the disadvantages of Rietveld QPA, have been proposed. The PONKCS method can be applied to mixtures consisting of known structure and unknown structure components.
 

The 2017 Nobel Prize in Chemistry was awarded to Dr. Joachim Frank of Columbia University, Dr. Jacques Dubochet of Lausanne University and Dr. Richard Henderson of MRC Molecular Biology Institute for “developing cryo-electron microscopy for the high-resolution structure determination of biomolecules in solution”.

High-resolution atomic level structural analysis of proteins is essential for understanding life and for identifying and treating the causes of associated diseases. Particularly in the development of pharmaceutical drugs, the high-resolution structure is the most powerful information at the stage of optimization of a candidate compound. This is because it provides guidelines for improvement of the compound once interactions between it and the target protein have been identified, and the environment and space around the compound can be closely examined.