Frank L. Chan

4,5-Diamino-6-thiopyrimidine as an analytical reagent—I: Spectrophotometric determination of selenium

Abstract A number of organic compounds have been screened as reagents for the spectrophotometric determination of small amounts of selenium. 4,5-Diamino-6-thiopyrimidine shows promise for this determination. In ammoniacal solution, even on long standing, this reagent is colourless in the presence of quadrivalent selenium. However, at pH 1.5–2.5 or lower, 4,5-diamino-6-thiopyrimidine forms a yellow colour with quadrivalent selenium, and this has a strong absorption peak at 380 mμ when compared with a reagent blank of the same concentration. Beers Law holds when the selenium concentration is between 0.1–2.5 μg per ml. The conditions for the quantitative determination of selenium have been investigated. When selenium in solution is in the quadrivalent state, measurement of absorption should be carried out within 30 min of the addition of the reagent. On longer standing, the reagent gives a slight yellow colour with the formation of elemental selenium. The formation of elemental selenium is slow in dilute solutions of selenium.

X-RAY DIFFRACTION STUDY OF NEW HAFNIUM COMPOUNDS

The important use of x-ray powder diffraction as a tool in the identification of unknown crystalline materials is dependent on the proper standards being in the reference file. Such new standards are added yearly to the Powder Diffraction File. The main purpose of this paper is to present new data on several well characterized salts based primarily on hafnium both in the hydrated and anhydrated form.

SOME OBSERVATIONS ON THE USE OF CERTAIN ANALYZING CRYSTALS FOR THE DETERMINATION OF SILICON AND ALUMINUM

During the past several years, a number of analyzing crystals have been prepared in the U.S. Air Force Aerospace Research Laboratories. Crystals such as alkaline acid malonates, sucrose, pentaerythritol (PET), and several others have been grown with the sole purpose of application in X-ray fluorescence analysis of silicon, aluminum, and other elements of low atomic number. Crystals from natural sources, such as quartz, mica, and gypsum, have also been procured from different parts of the world for this purpose.

Determination of Zirconium, Hafnium, Niobium, Tantalum, Molybdenum and Tungsten in Aqueous Solutions by Radioisotopic Excited X-Ray Fluorescence

Previous investigations on the quantitative determination of sulfur, chlorine, potassium, calcium, scandium and titanium in aqueous solutions by a radioisotopic excited fluorescent spectrometer has been extended to include other elements which are very difficult to separate and determine quantitatively by chemical methods. Six elements taken for the investigation and some of the results to be presented in this paper are: (1) zirconium, (2) hafnium, (3) niobium, (4) tantalum, (5) molybdenum and (6) tungsten. As in previous investigations, aqueous solutions have been used because of the ease in obtaining exact concentrations and homogeneous mixtures of the elements under investigation.

An Apparatus for the Analysis of Liquid Samples by the X-Ray Fluorescence Method with a Vacuum Spectrograph

It is well known that analysis of elements by the X-ray fluorescence method is rapid, reliable, and nondestructive in nature, especially for those samples that are solid in the form. However, because of the attenuation of the secondary X-rays of longer wavelengths by the air path, analysis of elements with atomic number smaller than 22 necessitates the use of a helium atmosphere or a vacuum spectrometer. Where a helium atmosphere is used, a layer of thin Mylar or similar film is used on liquid samples. This film can be placed over the surface or on the bottom of liquid container when inverted optics are used. In recent days, sophisticated X-ray fluorescence vacuum spectrographs have been investigated and placed on the market by a number of manufacturers. These spectrographs have many outstanding and desirable features. However, the present vacuum spectrograph has a number of limitations. The purpose of this paper is to present an apparatus for the analysis of liquid samples using the X-ray fluorescence method with the vacuum spectrograph. The experimental results and their interpretations are presented and discussed.

Some X-Ray Diffraction Spectra and Characteristic Properties of Deuterium Oxide Inorganic Compounds

Preparation of deuterium oxide and hydrated compounds were carried out simultaneously and side by side from starting materials which had been heated to produce their anhydrous form.

Separation and identification of 3,3′,4′,5,7-pentahydroxyflavanone and related compounds by thin-layer chromatography

Abstract Attempts have been made to find a simple, rapid and inexpensive method based on TLC for the separation of 3,3′,4′,5,7-pentahydroxyflavanone from the closely related compound 3,3′,4′,5,7-pentahydroxyflavone. On commercially available TLC sheets no less than eighteen solvents were tried. Using an UV light source (3660 A, 2540 A) for detecting the extent of separation of these two compounds, it has been found that a majority of these solvents do not completely or only partially separate these compounds. Among the solvents tried, water at a pH of 4.8–5.0 appears to give a sharp and rapid separation. The average RF values calculated from many thin-layer chromatograms were found to be 0.05 for 3,3′,4′,5,7-pentahydroxyflavoneand 0.66 for 3,3′,4′,5,7-pentahydroxyflavanone. The penta-acetate of the flavanone has been prepared from the 3,3′,4′,5,7-pentahydroxyflavanone using acetic anhydride and catalyzed by pyridine. The separation procedure described can also be used for the separation of the penta-acetate from its parent substance. This procedure could be used not only for ascertaining the presence of the 3,3′,4′,5,7-pentahydroxyflavanone and 3,3′,4′,5,7-pentahydroxyflavone but could also be used for reaction kinetic studies involving numerous substances or conditions that may catalyze this reaction. For confirmation of these compounds, the TLC spots were eluted and collected on a capillary after the separation and X-ray diffraction experiments were performed. X-ray diffraction patterns of the compounds are presented.

Dispersive and Nondispersive X-Ray Fluorescence Methods for the Measurement of the Thicknesses of Films of Cadmium Sulfide and Other II-VI Compounds

Cadmium sulfide and other II-VI compounds have been deposited on various substrates by the vacuum technique using a setup consisting of a mechanical pump and a diffusion pump. Attempts are being made to employ a high-speed turbo-molecular pump to produce the necessary vacuum. Such pumps have been claimed to produce higher vacuum than those of earlier types. The use of x-ray fluorescence seems to be the best method for the determination of thicknesses of films of these compounds. By using this method the determination can be carried out both rapidly and nondestructively, so that the samples can be used for further experimentation or preserved for future reference. Both the vacuum and air-path spectrometers were employed with the dispersive (conventional) x-ray fluorescence method, depending on the x-ray spectra used and the film thickness to be determined. The vacuum spectrometer described earlier has been modified to improve the intensity of the secondary x-ray. The modified setup with low-Z kit has been changed to accommodate four analyzing crystals in the vacuum chamber. The radioisotopes dysprosium-159, iodine-125, and others were used with the nondispersive x-ray fluorescence method. Recent instruments based on the dispersive and nondispersive systems are described here. Some of these instruments have been used to measure the thicknesses of films of II-VI compounds.