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At least 163 records · Page 9Linked to original sources
USGS2002

Determination of uranium in natural waters

The fluorophotometric determination of uranium was studied to develop a procedure applicable to the routine analysis of waters. Three grams of the high carbonate flux are used in a dilution procedure with spiking. Because of the comparatively high reflectivity of this large disk and the low uranium concentration, a correction for nonquenched light is required. A formula is developed to compensate for the effect, an electrical fusion device is described, and the problem of fixing uranium in waters is discussed.

Analytical Chemistry↗
USGS2002

Modified zirconium-Eriochrome Cyanine R determination of fluoride

The Eriochrome Cyanine R method for determining fluoride in natural water has been modified to provide a single, stable reagent solution, eliminate interference from oxidizing agents, extend the concentration range to 3 p.p.m., and extend the phosphate tolerance. Temperature effect was minimized; sulfate error was eliminated by precipitation. The procedure is sufficiently tolerant to interferences found in natural and polluted waters to permit the elimination of prior distillation for most samples. The method has been applied to 500 samples.

Analytical Chemistry↗
USGS1958

Apparatus and technique for multiple tests by the confined-spot method of colorimetric analysis: Application to field estimation of nickel and copper

The confined-spot method of colorimetric analysis is generally applicable to the semiquantitative estimation of traces of ions in solution that form colored precipitates or otherwise alter material on a confined area of reagent paper. For precise results, the rate of flow of test solutions through the reagent paper must be reproduced on successive runs, so that the same proportion of reaction products is collected each time on the confined spot. A simple apparatus gives a controlled rate of flow and makes possible the analysis of many samples at one time with good reproducibility. This apparatus utilizes the increasing pull, resulting from the gradual lowering of the water level in a tank, to draw a sample solution through a confined area of reagent paper at a reproducible rate. Application to the rapid determination of nickel with dimethylglyoxime and of copper with rubeanic acid provides a method for determination of as little as 0.06 γ of nickel and 0.03 γ of copper. The coefficients of variation are 14 and 22%, respectively. This method has wide applicability in more rapid and convenient determination of trace amounts of many metals.

Analytical Chemistry↗
USGS2002

Dithizone method for determination of lead in monazite

In the determination of lead in monazite-to be used as the basis for geologic age measurements-it was necessary to eliminate interferences due to the presence of phosphates of thorium and the rare earth metals. The method involves attacking the monazite samples with hot, concentrated sulfuric acid, then taking them up with dilute nitric acid. Lead is extracted as the dithizonate and determined spectrophotometrically at 520 mµ. Rapid determinations were made with good reproducibility on a series of monazite samples.

Analytical Chemistry↗
USGS2002

Spectrochemical method for the determination of selenium

Selenium can be determined in pyrite, chalcocite, and marcasite by a simple and rapid spectrochemical method that requires no complicated arrangement of spectrographic equipment or chemical pretreatment of samples. Advantage is taken of the new short wave length radiation plates (Eastman) and the addition of copper oxide to enhance the selenium lines 2039.85 and 2062.78 A. The possibility exists of determining many other elements on the same exposure of the sample. The method is applicable in the range of 0.0015 to 2% selenium. Tests indicate an average difference from the chemical results of 0.07% in the few per cent range, 0.03% in the 0.1 to 1.0% range, 0.005% in the 0.01 to 0.1% range, and 0.00075% in the 0.001 to 0.01% range. The relative accuracy over the entire range is to about 7% of the concentration.

Analytical Chemistry↗
USGS2002

Potassium bromide method of infrared sampling

In the preparation of potassium bromide pressed windows for use in the infrared analysis of solids, severe grinding of the potassium bromide powder may produce strong absorption bands that could interfere seriously with the spectra of the sample. These absorption bands appear to be due to some crystal alteration of the potassium bromide as a result of the grinding process. They were less apt to occur when the coarser powder, which had received a relatively gentle grinding, was used. Window blanks prepared from the coarser powders showed smaller adsorbed water peaks and generally higher over-all transmittance readings than windows pressed from the very fine powders.

Analytical Chemistry↗
USGS2002

Use of ion exchange resins in the analysis of rocks and minerals: Separation of sodium and potassium

This procedure was developed primarily for analyses in which limited amounts of sample are available. Sodium and potassium can be separated from the other constituents of silicate rocks by cation exchange resin (Amberlite IR-120). The sample is decomposed with hydrofluoric and sulfuric acids and passed through the resin bed after expulsion of the fluorine. The column is eluted with 0.12N hydrochloric acid at a fast flow rate of 4 ml. per sq. cm. per minute and the sodium and potassium are recovered together within a reasonable time. Other constituents of the sample, except silica, can be determined on the same portion of sample.

Analytical Chemistry↗
USGS2002

Semimicrodetermination of tantalum with selenous acid

Tantalum is separated and determined gravimetrically by precipitation with selenous acid from a highly acidic solution containing oxalic and tartaric acids. The method is selective for the determination of up to 30 mg. of tantalum pentoxide, and tolerates relatively large amounts of scandium, yttrium, cerium, titanium, zirconium, thorium, vanadium, niobium, molybdenum, tungsten, uranium, iron, aluminum, gallium, tin, lead, antimony, and bismuth. The separation of tantalum from niobium and titanium is not strictly quantitative, and correction is made colorimetrically for the small amounts of niobium and titanium co-precipitating with the tantalum. The method was applied to the determination of tantalum in tantaloniobate ores.

Analytical Chemistry↗
USGS2002

Semimicrodetermination of combined tantalum and niobium with selenous acid

Tantalum and niobium are separated and determined gravimetrically by precipitation with selenous acid from highly acidic solutions in the absence of complexing agents. Hydrogen peroxide is used in the preparation of the solution and later catalytically destroyed during digestion of the precipitate. From 0.2 to 30 mg., separately or in mixtures, of niobium or tantalum pentoxide can be separated from mixtures containing 100 mg. each of the oxides of scandium, yttrium, cerium, vanadium, molybdenum, iron, aluminum, tin, lead, and bismuth with a single precipitation; and from 30 mg. of titanium dioxide, and 50 mg. each of the oxides of antimony and thorium, when present separately, with three precipitations. At least 50 mg. of uranium(VI) oxide can be separated with a single precipitation when present alone; otherwise, three precipitations may be needed. Zirconium does not interfere when the tantalum and niobium contents of the sample are small, but in general, zirconium as well as tungsten interfere. The method is applied to the determination of the earth acids in tantaloniobate ores.

Analytical Chemistry↗
USGS2002

Determination of chlorine in silicate rocks

In a rapid accurate method for the determination of chlorine in silicate rocks, the rock powder is sintered with a sodium carbonate flux containing zinc oxide and magnesium carbonate. The sinter cake is leached with water, the resulting solution is filtered, and the filtrate is acidified with nitric acid. Chlorine is determined by titrating this solution with mercuric nitrate solution using sodium nitroprusside as the indicator. The titration is made in the dark with a beam of light shining through the solution. The end point of the titration is found by visually comparing the intensity of this beam of light with that of a similar beam of light in a reference solution.

Analytical Chemistry↗
USGS2002

Fluorometric study of the magnesium—Bissalicylidene-ethylenediamine aystem

Magnesium ions combine with bissalicylidene-ethylenediamine in slightly alkaline N,N′-dimethylformamide to form a highly fluorescent complex which serves for the determination of trace amounts of magnesium. The yellow complex fluoresces blue when irradiated with ultraviolet light. The chelate shows maximum fluorescence excitation at 355 mμ and has a fluorescence emission maximum at 439 mμ. A complex having a metal to ligand ratio of 1 to 1 is formed. The method is sensitive to 7 × 10 −6 μmole of magnesium per ml. The analysis of Bureau of Standards samples with the reagent showed excellent correlation between the fluorometric and spectrophotometric procedures

Analytical Chemistry↗
USGS2002

Spectrophotometric study of the magnesium-bissalicylidene-ethylenediamine system

Magnesium reacts with bissali-cylene-ethylenediamine in N,N′-dimethylformamide to yield a yellow complex. A spectrophotometric study was made on the reaction as used for the determination of trace amounts of magnesium. Maximum absorbance was obtained at 355 mμ when the solution contained 0.25 ml. of 0.5M isobutylamine per 25-ml. volume. A complex having a metal to ligand ratio of 1 to 1 is formed. The absorbance obeys Beer's law, and 3.8 × 10 -4 γ of magnesium per ml. can be detected if a 5-cm. light path is used. A value of 13,450 liter mole -1 cm. -1 was obtained for the molar absorptivity. The procedure of analysis is simple and results show a standard deviation of less than 1%

Analytical Chemistry↗
USGS2002

Determination of niobium in the parts per million range in rocks

A modified niobium thiocyanate spectrophotometric procedure relatively insensitive to titanium interference is presented. Elements such as tungsten, molybdenum, vanadium, and rhenium, which seriously interfere in the spectrophotometric determination of niobium, are separated by simple sodium hydroxide fusion and leach; iron and magnesium are used as carriers for the niobium. Tolerance limits are given for 28 elements in the spectrophotometric method. Specific application is made to the determination of niobium in the parts per million range in rocks. The granite G-1 contains 0.0022% niobium and the diabase W-1 0.00096% niobium.

Analytical Chemistry↗
USGS2002

Automatic measurements and computations for radiochemical analyses

In natural radioactive sources the most important radioactive daughter products useful for geochemical studies are protactinium-231, the alpha-emitting thorium isotopes, and the radium isotopes. To resolve the abundances of these thorium and radium isotopes by their characteristic decay and growth patterns, a large number of repeated alpha activity measurements on the two chemically separated elements were made over extended periods of time. Alpha scintillation counting with automatic measurements and sample changing is used to obtain the basic count data. Generation of the required theoretical decay and growth functions, varying with time, and the least squares solution of the overdetermined simultaneous count rate equations are done with a digital computer. Examples of the complex count rate equations which may be solved and results of a natural sample containing four alpha-emitting isotopes of thorium are illustrated. These methods facilitate the determination of the radioactive sources on the large scale required for many geochemical investigations.

Analytical Chemistry↗