Showing papers on "Detection limit published in 1971"

Copper in edible oils: trace amounts determined by atomic absorption spectroscopy.

Abstract: The application of atomic absorption spectroscopy to trace copper analysis in fats was investigated. Copper spectral resonance lines 3248 A and 3274 A possess the most useful sensitivities applicable to fats and vegetable oils. These sensitivities were determined to be 0.15 and 0.25 ppm in oil, respectively, with detection limits about tenfold lower. Data show that copper absorption depends strictly on the amount of oil aspirated into the flame. In soybean oil-solvent mixtures, aspiration rates decrease logarithmically and linearly with increasing fat content. The accuracy and precision of atomic absorption techniques were established by comparing results from atomic absorption with those from two independent techniques. Error estimates were determined by analysis of copper-hydrogenated soybean oil diluted to low copper levels. The standard deviation, relative standard deviation and analytical error were 0.0108 ppm, 5% and 2.5%, respectively, over a range of 0.05–0.40 ppm copper in soybean oil.

The gas-chromatographic determination of 2,3,7,8-tetrachlorodibenzo-p-dioxin in 2,4,5-trichlorophenoxyacetic acid (“2,4,5-T”), 2,4,5-T ethylhexyl ester, formulations of 2,4,5-T esters and 2,4,5-trichlorophenol

Abstract: A gas-chromatographic method for the determination of trace amounts of a toxic impurity, 2,3,7,8-tetrachlorodibenzo-p-dioxin, is described. A purified extract of the sample was subjected to gas chromatography on a column containing either 2 per cent. of OV-17 on Diatomite CQ or 1 per cent. of Hi-Eff 8 BP on Gas-Chrom Z with electron-capture detection. 2,4,5-Trichlorophenoxyacetic acid and 2,4,5-trichlorophenol were purified by chromatography of an ether extract of the sample on a column of alumina, followed by shaking with sulphuric acid. For 2,4,5-trichlorophenoxyacetic acid esters and formulations, saponification and chromatography on a Celite-sulphuric acid column, followed by chromatography on a column of alumina, were necessary.Recoveries of 2,3,7,8-tetrachlorodibenzo-p-dioxin ranged from 89 to 98 per cent., and the standard deviation of the method at a level of 0·3 p.p.m. was 0·03 p.p.m. The limit of detection was about 0·05 p.p.m.

Investigation of the Hollow Cathode Discharge as an Atomic Absorption Medium

Abstract: A hollow cathode discharge has been studied as a means for vaporizing and atomizing samples for atomic absorption. The design and operational characteristics of the cell are presented with detection limits and precision data for Ag, As, Ca, Cd, Hg, Pb, Se, and Zn. In general, detection limits between 1 and 10 ng were obtained. The present limitation of the method due to the sample holder blank is discussed.

The determination of fluorine in rock materials by γ-activation and radiochemical separation

Abstract: A technique is described for the determination of fluorine in rock materials involving irradiation in a source of high energy γ-photons to induce the 19F (γ,n)18F reaction. Fluorine-18 is then separated from the radioactive matrix by distillation and its activity measured either in the distillate or as precipitated calcium fluoride and compared with that of irradiated calcium fluoride standards. The technique has been applied to the analysis of standard rock materials G1 (638 p.p.m.), W1 (221 p.p.m.), T1 (476 p.p.m.) and to Apollo 11 lunar fines (76 p.p.m.). Precautions are taken to eliminate interferences. The results obtained for the standard rocks are in good agreement with those of conventional methods but disagree with other activation results. The limit of detection of the method is 0·002 µg.

Qualitative detection limits for specific compounds utilizing gas chromatographic fractions, activated charcoal and a mass spectrometer.

Abstract: Qualitative identification of gas chromatograph (G.C.) fractions has created problems for the organic chemist. One of these concerns the limit of detection for any given compound which can be achieved with a method designed to trap a G.C. peak for further analysis. This paper presents the limits of detection found attainable in the qualitative analysis of specific organic compounds. These limits were established by utilizing an activated charcoal capillary to trap the G.C. fraction prior to introduction into a Bendix Time-of-Flight mass spectrometer via the hot filament probe.

The determination of lithium, sodium and potassium in geological materials by atomic-emission spectrophotometry with the nitrous oxide-acetylene laminar-flow flame

Abstract: A straightforward method is described for the determination of lithium, sodium and potassium by atomic-emission spectrophotometry on an acidic solution of the sample without separation or concentration. In routine application detection limits of 0·002, 0·01 and 0·01 per cent., respectively, have been obtained with no spectral or chemical interferences. Results are presented for eight standard samples, and long-term relative standard deviations of 2·4 per cent. (lithium), 1·7 per cent. (sodium) and 2·5 per cent. (potassium) have been found on a B.C.S. firebrick.By using wavelength scanning the determination of trace amounts of lithium has been demonstrated, with a detection limit of about 0·1 p.p.m. in the sample. If blank problems can be controlled the direct determination of sodium and potassium at the parts per million level should be possible even for limestones.

Determination of iodine in urine by flame spectrometry

Abstract: Flame spectrometry allows the fast, specific and simple determination of drugs containing iodine as exemplified with Urografin®. 1 μl samples are needed. The detection limit is about 0.012 μg J. It can be decreased further by preconcentration of the samples. Precision and accuracy are sufficient.