Showing papers on "Detection limit published in 1993"

Automated determination of iron in seawater by chelating resin concentration and chemiluminescence detection

Abstract: A new automated shipboard analytical method for determining iron(III) in seawater has been developed. The method is based on a combination of selective column extraction using chelating resin and improved chemiluminescence (CL) detection in a closed flowthrough system. In this method, Fe(III) in an acidified sample solution is selectively collected on 8-quinolinol immobilized chelating resin and then eluted with dilute hydrochloric acid. The resulting eluent is mixed with luminol solution, aqueous ammonia, and hydrogen peroxide solution successively, and then the mixture is introduced into the CL cell. The iron concentration is obtained from the CL intensity. The detection limit of iron(III) is 0.05 nmol L -1 when using an 18-mL seawater sample

Determination of volatile chlorinated hydrocarbons in air and water with solid-phase microextraction

Abstract: A method for sampling volatile chlorinated hydrocarbons in either gaseous or aqueous samples using solid-phase microextraction (SPME) is presented. In the liquid phase, method limits of detection of 1–130 ng l–1 can be achieved with an electron-capture detector. The method is linear over at least 2–4 orders of magnitude and has a relative standard deviation of 1–5%. In the gaseous phase, the method has limits of detection in the parts per trillion (v/v) range when used with an electron-capture detector. The linear range is at least two orders of magnitude and the relative standard deviation is 1–7%. Sample preparation times range from 10 min for gaseous samples to 20 min for liquid samples. The method is comparable to US Environmental Protection Agency (EPA) methods 502.2 and TO-14. The precision of the technique is relatively independent of the number of injections made per container. Samples can be stored for up to 20 min on the fibre if they are capped and refrigerated. The amount absorbed by the fibre decreases with increasing temperature and increasing humidity.

Determination of methylmercury in fish samples using GC/AA and sodium tetraethylborate derivatization

Abstract: A simple technique is described for the rapid determination of methylmercury in fish tissue. Following simple dissolution in methanolic KOH solution, aqueous phase ethylation by derivatization with NaB(C2H5)4, cryogenic trapping on a packed chromatographic column, and GC separation, volatile mercury species are detected by atomic absorption spectrometry. Absolute detection limits are 4 pg of Hg for CH3Hg+ and 75 pg of Hg for labile Hg2+. Concentration detection limits for this optimized procedure are 4 ng of Hg for CH3Hg+ and 75 ng of Hg for labile Hg2+ per gram of pulverized dried fish tissue. Analysis of standard reference materials demonstrates the accuracy, precision, and reproducibility of the analytical method.

Elemental speciation by anion exchange and size exclusion chromatography with detection by inductively coupled plasma mass spectrometry with direct injection nebulization

Abstract: A direct injection nebulizer (DIN) is used with packed microcolumns for anion chromatography (AC) and size exclusion chromatography (SEC). Two Se species (SeO[sub 3][sup 2[minus]] and SeO[sub 4][sup 2[minus]]) are separated by AC with detection limits of 15 pg of Se. The isotope ratio [sup 74]Se/[sup 78]Se can be measured with a relative standard deviation of 0.5% on 25 ng of each Se species during the actual chromatographic separation. Proteins in human serum are separated by SEC without sample pretreatment. The metals present in each molecular weight fraction are determined by ICP-MS with detection limits of 0.5-3 pg of metal. These absolute detection limits are 1-2 orders of magnitude better than those obtained with conventional nebulizers. 56 refs., 3 figs., 7 tabs.

L-Cysteine as a reducing and releasing agent for the determination of antimony and arsenic using flow injection hydride generation atomic absorption spectrometry—Part 1. Optimization of the analytical parameters

Abstract: L-Cysteine was investigated as the reducing and releasing agent for the determination of antimony and arsenic using flow injection hydride generation atomic absorption spectrometry with the aim of replacing the previously used potassium iodide. The prereduction of the pentavalent to the trivalent form at room temperature was completed within 5 and 30 min for antimony and arsenic, respectively, which was essentially identical with the performance of potassium iodide. However, much lower acid and reagent concentrations were required with L-cysteine than with potassium iodide. In addition, even dilute analyte solutions containing L-cysteine were stable for at least one week, whereas solutions containing potassium iodide had to be prepared fresh daily. Under optimized conditions, in the presence of 1% m/v L-cysteine and 1 mol l–1 HCI for antimony or 0.1 mol l–1 HCI for arsenic, detection limits (three times the standard deviation of a blank solution, n= 10) of 0.05 and 0.01 µg l–1 were obtained for antimony and arsenic. The calibration graphs were linear (r > 0.999) for up to 10 µg l–1 of antimony and 5 µg l–1 of arsenic, using integrated absorbance for evaluation. The precision was better than 2% relative standard deviation (n= 10) for both elements at the 5 µg l–1 concentration level.

Determination of total mercury by single-stage gold amalgamation with cold vapour atomic spectrometric detection

Abstract: The two-stage gold amalgamation technique with elemental mercury vapour detection was compared with a technique employing a single gold trap. When peak area was measured, and special attention paid to the gold trap orientation, the one-stage amalgamation procedure provided the same precision, accuracy and detection limits as the benchmark two-stage technique (Fitzgerald and Gill, 1979). The overall analysis time, however, was reduced from about 10 to 2 min per sample. An absolute detection limit (2σ of trap blanks) of less than 1 pg of Hg0 was attained using an atomic fluorescence detector, while relative standard deviations of 2.8, 1.5 and 2.2% were obtained for 500, 1000 and 2000 pg of Hg, respectively. Recoveries of close to 100% with RSDs of <3% were obtained in the determination of certified reference materials, intercalibration hair samples and lakewater using this more rapid procedure.

An HPLC Method for the Detection of Ergot in Ground and Pelleted Feeds

Abstract: A high performance liquid chromatography (HPLC) method is described for detecting ergot in ground or pelleted forages and grains. Samples were extracted with alkaline chloroform, filtered, and applied to silica gel/organic binder cleanup columns. Following elution of pigments with acetone: chloroform, ergopeptine alkaloids were eluted with methanol and analyzed by HPLC with fluorescence detection. Average recovery of ergotamine, the major ergopeptine alkaloid produced by Claviceps, was 93%, with a relative standard deviation of 4.9%. The detection limit of ergotamine was approximately 50 ppb in all feedstuffs. Confirmation of ergopeptine alkaloids was accomplished by treating the parent ergopeptine alkaloids with 0.2% acetic acid to produce their -inine isomers and reexamining by HPLC with fluorescence detection or silica gel/organic binder column cleanup in combination with tandem mass spectroscopy. The method described is a valid alternative to microscopic inspection for detecting ergot contamination in ground or pelleted feedstuffs.

Use of a sheath flow cuvette for chemiluminescence detection of isoluminol thiocarbamyl‐amino acids separated by capillary electrophoresis

Abstract: A post-column reactor was designed for chemiluminescence detection in the capillary electrophoresis separation of isoluminol thiocarbamyl derivatives of amino acids. This system was characterized with respect to hydrogen peroxide concentration and flow rate, surfactant concentration, microperoxidase concentration, and mixing distance. A linear calibration curve (R >0.999) was constructed for isoluminol ranging from at least 30 femtomoles to the detection limit of 40 attomoles injected; the dynamic range of the instrument is at least three orders of magnitude. Detection limit for the isoluminol thiocarbamyl derivative of valine was 500 attomoles. The theoretical plate counts for the raw data are typically 1 × 105 for labeled amino acids, and a factor of two better for isoluminol.

A sensitive and simple high-performance liquid chromatographic method for the determination of doxorubicin and its metabolites in plasma

Abstract: A sensitive high-performance liquid chromatographic (HPLC) method for the measurement of doxorubicin and its metabolites in plasma is described. After precipitation with zinc sulphate and methanol, samples are resolved by isocratic elution from a C18 reverse phase support within 20 min and quantified by endogenous fluorescence. Recoveries over a concentration range from 5 to 1,000 nM of doxorubicin, doxorubicinol, doxorubicinone, doxorubicinolone, and 7-deoxydoxorubicinolone were 80-110%, while recovery for 7-deoxydoxorubicinone was approximately 60%. At concentrations of 5 nM, within-run and between-day coefficients of variation for each compound were < 8 and < 16%, respectively. Limits of detection for the compounds were 1-2 nM and standard curves were linear up to at least 1,000 nM. The drug and its metabolites are stable in deproteinized plasma samples at room temperature and in the dark for at least 24 h. The method requires few manipulations and is readily adaptable to automated analysis of large series of samples.

Analytical study on the determination of boron in environmental water samples

Abstract: An analytical study on the determination of boron in environmental water samples was carried out. The curcumin and carmine standard methods were compared with the most recent Azomethine-H method in order to evaluate their analytical characteristics and feasibility for the analysis of boron in water samples. Analyses of synthetic water, ground water, sea water and waste water samples were carried out and a statistical evaluation of the results was made. The Azomethine-H method was found to be the most sensitive (detection limit 0.02 mg 1−1) and selective (no interference of commonly occurring ions in water was observed), showing also the best precision (relative standard deviation lower than 4%). Moreover, it gave good results for all types of samples analyzed. The accuracy of this method was tested by the addition of known amounts of standard solutions to different types of water samples. The slopes of standard additions and direct calibration graphs were similar and recoveries of added boron ranged from 99 to 107%.

Electrophoretically mediated microanalysis of leucine aminopeptidase in complex matrices using time-resolved laser-induced fluorescence detection.

Abstract: Leucine aminopeptidase, a clinically significant enzyme, was assayed in complex biological samples using a new technique termed electrophoretically mediated microanalysis. The assay was performed in capillary electrophoresis columns using time-resolved laser-induced fluorescence detection. Human serum, human urine, and Escherichia coli supernatant samples were assayed using this method. Results for serum and urine were within the ranges of expected values found in the literature. A low concentration of 6 x 10(-13) M enzyme in buffer was detected using this method. A detection limit (3 sigma) of 400 enzyme molecules in buffer was determined.