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ISOTOPIC ages by potassium – argon and rubidium – strontium methods have been measured on some Spitsbergen rocks, in the hope of contributing to the Mid-Palaegeozoic time-scale and to the understanding of local geological history1. Rubidium, strontium and argon measurements were made by stable isotope dilution analysis, except for York's figure, which was by total volume (argon) measurement. The potassium measurements were made by flame photometer.

Mass spectrometric stable isotope dilution method for barium determination in G-1 and W-1 rock standards

Rare earth trace element variations in anorthosite and quartz mangerite determined, using stable isotope dilution technique of analysis

Rapid, sensitive and accurate stable isotope dilution assays were developed for the measurement of orotic acid and uracil in amniotic fluid. The method utilizes [15N2]orotic acid and [15N2]uracil as internal standards, isolation by liquid partition chromatography and quantitation by chemical ionization selected ion monitoring gas chromatography-mass spectrometry. Orotic acid at a concentration of 0.26 ± 0.05 μmol/1 and uracil at a concentration of 0.55 ± 0.13 μmol/l were detectable in normal amniotic fluid. As affected fetuses with argininosuccinate synthetase or ornithine carbamoyl transferase deficiency showed no significant elevation of orotic acid and/or uracil in their surrounding amniotic fluids, this method unfortunately seemed not to be useful for prenatal diagnosis of these inherited disorders. Nevertheless, it provides significant advantage over available methods for the quantitation of orotic acid and uracil in which the analysis of these compounds must be very accurate, highly specific and sensitive (e.g. detection of heterozygosity for omithine carbamoyl transferase deficiency).

Top of pageAbstract Glucose metabolism was studied in low birth weight (LBW) infants before any oral feeding was given. We have measured glucose utilization using a stable isotope dilution technique and calculated glucose oxidation from oxygen consumption and carbondioxide production measured with open circuit indirect calorimetry. Birth weight of the infants ranged from 1.29-2.26 kg, gestational age from 32-39 weeks. Results are shown in the table. The discrepancies between glucose utilization and glucose oxidation suggest that in some LBW infants substrates other than glucose are oxidized, and in some infants not all utilized glucose is oxidized.

Ages have been found by the rubidium-strontium method for the pair of meteorites (Forest City, a chondrite, and Johnstown, an achondrite) and for four lepidolites. The rubidium determinations made by stable isotope dilution are supported by neutron activation analysis. A brief mention is also made of the determination of lead in small samples of monazites by direct polarographic analysis.

Standard zircon samples studied earlier by Hurley, Larsen, and Gottfried (1955) have been analyzed for helium by an isotopic dilution technique using He3 as a spike yielding an accuracy of about ± 3 pct. The quantity of helium obtained is about 15 pct higher than that obtained by earlier volumetric techniques. Alpha activity determinations agree closely with earlier work. Measurements on non-metamict zircons from Ontario, Ceylon, and Oklahoma suggest that helium retentivity in excess of 80 pct is not unusual. Metamict zircons on the other hand may have retained only one per cent of radiogenic helium. Total irradiation is not the only factor in determining the quantity of helium retained. A helium age method is still possible under proper conditions.