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By simulating opaque metals systems with a transparent salt, NBS investigators were able to determine molten metal flow patterns and velocity. Here, a hori zontal boat containing a salt in the heating element is being positioned for an experiment.

CHARACTERIZATION

Composition

Nondestructive Analysis of Proteins.-In a practical solution to a major problem of biochemical analysis, a method has been devised for determining the total elemental content of proteins. With the use of neutron activation methods, 10-milligram samples of amino acids and

proteins have been analyzed with a precision of 5 percent. Futhermore, the analysis has been accomplished without destroying or damaging the specimen. Analytical results comparing well with those obtained by tedious, destructive chemical methods have been obtained for four elements: oxygen, nitrogen, sulfur, and phosphorus. The method is of considerable promise for biomedical research, particularly where a knowledge of the elemental composition is necessary prior to biological tests.

Rapid and Accurate Electron Probe Analyses.-The electron probe microanalyzer, a recent development, has proven to be a powerful tool for the nondestructive analysis of solid surfaces. Surfaces are scanned with a very narrow beam of electrons and the resulting x-ray emission produces a spectral pattern characteristic of the elements present and their amounts. These patterns are complex and their analysis is timeconsuming when quantitative data are required. Rapid and accurate analyses were accomplished by constructing an electronic device which clearly distinguishes the first-order x-ray lines from those of higher orders. Simplified wavelength tables were also prepared, and with their aid the elements present in the sample can quickly and easily be identified from the x-ray lines observed.

Determination of Oxygen in Steel.-The great sensitivity of the mechanical properties of structural steel to the amount of dissolved or interstitial oxygen has made the routine determination of oxygen of considerable importance in steel fabrication. A new biaxial rotating assembly for use with neutron activation techniques for oxygen analysis has brought about a tenfold increase in analytical precision. In the use of the new assembly, the unknown and standard samples are injected pneumatically into the neutron field where they rotate about two perpendicularly oriented axes in such a way that both experience an identical neutron environment.

Increased Precision of Lead Isotope Determinations.-A new technique for the mass spectrometric determination of lead isotope composition has been developed. This technique, which involves the use of a triple-filament solid-sample source, increases the precision of lead isotope measurements by a factor of 5 as compared to previous methods. The increased precision will be of great help to earth scientists involved in the study of fundamental chemical characteristics of the earth as well as in age determination studies of rocks, minerals, and meteorites. The technique is presently being used for the determination of the absolute lead isotope composition of a number of standard reference materials, and in a study of the possible use of lead isotopes as a marker for distinguishing sources of archaeological artifacts.

Trace Quantities of Carbon in Sodium Metal.-Development of breeder nuclear reactors requires analysis of liquid sodium (a coolant) for trace elements such as carbon. A variety of analytical techniques have been used for carbon analysis with little success. This has now been done with the use of photonuclear activation analysis. This technique permits carbon analysis in sodium metal to a level of 10 to 100 parts per million with a precision of 5 percent relative standard deviation of a single determination. Where other analytical methods have required several hours per sample, this technique requires approximately 30 minutes per sample for analysis.

Procedure Enhances Accuracy of Spectrophotometric Analysis.Spectral absorption in the visible or ultraviolet regions of the spectrum forms the basis for some of the most useful methods of chemical analysis. Unfortunately, the inherent sensitivity of the spectrophotometric technique is governed by cross sections of the light-absorbing molecules which never exceed their physical dimensions. "Amplification" procedures have recently been explored as a means of overcoming these sensitivity barriers. In the determination of arsenic in highpurity selenium, for example, the arsenic can be separated from the matrix and determined spectrophotometrically by the heteropoly molybdenum-blue method. The detection limit is about 5 ppm. However, an increase in sensitivity can be obtained by converting the arsenic into an arsenomolybdate complex which is subsequently decomposed and molybdenum determined spectrophotometrically as the yellow chelate with quercetin. Inasmuch as 12 atoms of molybdenum combine with each atom of arsenic, a twelvefold "amplification” is achieved. Accordingly, the sensitivity limit is found to have been lowered from 5 ppm to about 0.5 ppm by the new procedure.

High-Accuracy Titration for Small Samples.-Modern analytical chemistry is continually being urged to provide methods capable of yielding accurate results with ever smaller samples, and frequently it is essential that the analysis be made without contaminating the sample and destroying its subsequent usefulness. An improved method of null-point potentiometry has been refined to the point where it is now possible to determine one ten-millionth of a gram of silver in two drops of solution with a accuracy of about 5 perecent. To achieve this, the small sample is brought into electrical contact through a porous glass septum with a similar solution containing no silver. A carefully measured amount of electricity is then made to generate silver in this reference solution until indicating electrodes show that the concentrations are equal in the two solutions. The entire analysis can be carried out without contaminating or altering the sample in any way. Automation of the process is possible, and computer analysis of the results provides a considerable saving of time.

LIB.

New Method for Determining Trace Elements by Mass Spectrometry.-A new method has been developed for the determination of trace elements in the parts per million range. The method combines the principle of isotope dilution with electrolytic separation and determination by the spark source mass spectrometer. The new method yields high sensitivity and permits several elements to be determined simultaneously. Furthermore, the use of the isotope dilution technique makes it unnecessary to assure a quantitative yield or even to determine the yield percentage. This method was used in an analysis of zinc metal to be issued as a standard reference material. Lead up to the 10 ppm level was determined with a precision of about 4 percent, whereas cadmium and thorium at the 1 percent and 0.1 percent levels were determined with a precision of about 10 percent.

High Precision Flame Emission Spectrophotometry.-A new technique of differential flame emission spectrophotometry was developed whereby a precision of one part in a thousand was obtained over a concentration range from a few ppm to several percent. This is a tenfold increase in precision over the previous procedure. The new approach has made it possible to achieve the needed accuracy in the determination of the lithium content of glass beads for neutron flux measurement. Although only a small amount of valuable sample is required, the error of the analysis is below the set limits of 0.2 percent. To achieve this increase in precision a phase shifter and attenuator were built for the a-c synchronous detector. This modification in the electric circuit permitted the setting of any desired concentration at zero percent transmission and then a finite concentration above this value was expanded to give full-scale deflection.

Improved Sensitivity of Sulfur Analysis.-Emission spectrochemical procedures are commonly used to evaluate the relative purity of sulfur samples, yet the high volatility of sulfur in the arc results in poor sensitivity of detection for the impurity elements. A new way has been found to concentrate these elements twentyfold, thus enhancing significantly the sensitivity of detection. At the same time, the troublesome volatility of the sulfur is avoided by complete oxidation of the sample, whereupon the metallic oxides are then easily determined in the conventional way. By this method, 11 elements present in a sulfur sample at less than one part per million have been detected easily.

Glass Electrode in Heavy Water. The behavior of the glass electrode in heavy water has been determined. The electrode was found to be nearly as suitable for measurements of acidity in heavy water as in ordinary water. The way is paved, therefore, for establishment of a practical scale of acidity or pD in heavy water which is a major constituent of many nuclear reactors.

THE UNIVERSITY

OF

MICHIGAN LIBRARIES

The response of glass electrodes to deuterium ions in heavy water is determined by direct comparison with the deuterium gas electrode. A knowledge of the glass electrode errors in heavy water is essential to accurate pD measure. ments with the pH meter.

Structure

Kossel Microdiffraction Generator.-A Kossel x-ray generator has been developed to permit diffraction studies of local areas of crystalline materials typically 2 microns in size. The samples can be oriented in space with respect to the incident electron beam about any axis of tilt in order to obtain the desired diffraction conditions. A microtensile stage was developed to permit the application of stress to the specimen while under study. Local measurements of the lattice constant can be made with great precision by this technique.

Photographic Scanner for Quantitative Microscopy. An automatic optical scanner has been developed for digitalizing pictorial information present in photographic prints up to 10 x 10-in size. The continuous intensity data is represented as one of 16 different levels on a grey scale and a spatial resolution of 14 mm can be obtained. The scanner has been applied to studies of grain size and precipitate size in several metallurgical alloys of commercial interest. Greatly increased precision and lack of reader bias have been demonstrated over previous manual methods of analysis.