Showing papers on "Detection limit published in 1990"

Premium Calculation: Why Standard Deviation Should be Replaced by Absolute Deviation

Abstract: Average absolute (instead of quadratic) deviation from median (instead of expectation) is better suited to determine the safety loading for insurance premiums than standard deviation: The corresponding premium functionals behave additive under the practically relevant risk sharing schemes between first insurer and reinsurer.

Determination of picomolar concentrations of carbonyl compounds in natural waters, including seawater, by liquid chromatography

Abstract: Low molecular weight carbonyl compounds in natural waters were determined at picomolar to nanomolar levels by derivatization with 2,4-dinitrophenylhydrazine followed by liquid chromatography. The uniqueness of the method is attributed to the extremely low blanks obtained and the minimal sample preparation involved. The detection limit for direct injection of derivatized natural water samples is 0.5 nM for aldehydes and 5 nM for ketones with a precision of {approximately}7% RSD at the 30 nM level for aldehydes. The detection limit can be further lowered by using off-line cartridge enrichment in which derivatized natural water is passed through a C18 extraction cartridge. Recoveries for the enrichment method were 95-105% for a sample volume of 20 mL and for concentrations of carbonyl compounds in the 1-30 nM range. A field procedure for storage of derivatized sample extracts for extended periods is also presented. Applications of enrichment and sample storage techniques to marine and estuarine waters are presented.

Catalytic oxidation and flow detection of carbohydrates at ruthenium dioxide modified electrodes.

Abstract: Ruthenium dioxide (RuO2) containing carbon paste electrodes exhibiting electrocatalytic response toward carbohydrates are described. The electrocatalytic behavior is exploited for developing a highly stable and sensitive flow detection scheme for carbohydrates at a low and fixed potential (+0.4 V vs Ag/AgCl). The effects of pH, flow rate, operating potential, surface "loading", concentration, and other variables are explored. The electrode response was stable for more than 48 h, with a signal loss of less than 10% over this period. The detection limits at the picomole level and a relative standard deviation of 1.2% (n = 72) are reported. Electrocatalytic oxidation is described also for related polyhydroxyl compounds (aldonic and aldaric acids and alditols).

Determination of linear alkylbenzenesulfonates and dialkyltetralinsulfonates in water and sediment by gas chromatography/mass spectrometry

Abstract: Les limites de detection pour les alkylbenzenesulfonates lineaires (LAS) et les dialkyltetralinesulfonate (DATS) dans l'eau sont d'environ 0,001 mg/L; dans les sediments elles sont de 0,5 mg/kg pour LAS et de 0,2 mg/kg pour DTAS respectivement

Analysis of biological reference materials, prepared by microwave dissolution, using inductively coupled plasma mass spectrometry

Abstract: A procedure has been developed for the analysis of biological materials by inductively coupled plasma mass spectrometry (ICP-MS). Fast, efficient and complete sample digestion is achieved by a combined microwave-nitric acid/open beaker-nitric acid-hydrogen peroxide procedure. The ICP-MS analysis is performed with an on-line five-element internal standard to correct for matrix and instrumental drift effects. Results are presented for 24 elements in three biological reference materials (National Institute of Standards and Technology Standard Reference Materials 5277a Liver and 1566 Oyster and International Atomic Energy Agency Certified Reference Material H4 Animal Muscle). For all elements significantly above the detection limit and reagent blank concentrations, good agreement exists between ICP-MS and certified values.

Determination of carbon-centered radicals in aqueous solution by liquid chromatography with fluorescence detection

Abstract: A simple method to detect subnanomolar to micromolar levels of photochemically generated carbon-centered radicals in aqueous solutions has been developed and optimized. This method is based on the efficient trapping of radicals by a water-soluble amino nitroxide, followed by derivatization of the trapped products with fluorescamine to produce highly fluorescent adducts. These adducts can be separated by reversed-phase high-performance liquid chromatography and detected fluorometrically. The fluorescent derivatives are stable over a period of days. The detection limit, primarily determined by reagent interferences, ranged from 0.3 to 1 nM per analyte for a 500-{mu}L injection at a signal-to-noise ratio of two. The precision of the method for the determination of adduct concentrations in the 1-10 nM range varied from 2.4 to 8.4% relative standard deviation (n = 6). A direct comparison with electron paramagnetic resonance spectroscopy/spin trapping illustrates the advantages of our technique. One important feature of the method is that it permits the simultaneous detection of an array of radicals, as demonstrated through the study of the photochemical production of radicals in a variety of natural water samples and in Suwanee River fulvic acid.

Determination of platinum in blood by adsorptive voltammetry

Abstract: This work describes a sensitive method for the determination of platinum in blood, which can be used for determining the natural levels of platinum in human blood, for monitoring patients treated with platinum cytotoxic drugs, and for monitoring occupational exposure to these drugs and other platinum compounds. The method involves dry ashing of blood samples in a muffle furnace and determination of platinum by adsorptive voltammetric (AV) measurement of the catalytic reduction of protons by the platinum-formazone complex. The detection limit for a 100-microL sample of blood is 0.017 micrograms/L, with a recovery of 94% and a relative standard deviation of 7% at a platinum level of 1 microgram/L. By using this method, the natural levels of platinum in human blood were found to be in the range 0.1-2.8 micrograms/L (median = 0.6 micrograms/L). These results were verified by inductively coupled plasma mass spectrometry (ICP-MS) with blood prepared by wet ashing and using gold as an internal standard.

Flow injection on-line sorbent extraction pre-concentration for graphite furnace atomic absorption spectrometry

Abstract: Flow injection (FI) techniques were used to develop an efficient on-line sorbent extraction pre-concentration system for graphite furnace atomic absorption spectrometry with lead as a model trace element. Bonded silica with octadecyl functional groups (C18) was used as sorbent in a 15-µl conically shaped micro-column. The lead diethyldithiocarbamate chelate was formed on-line, loaded on to the column for 60 s, washed with de-ionised water and eluted with ethanol into a collector with a volume of 75 µl, made from 0.35 mm i.d. polytetrafluoroethylene tubing. The collected eluate was introduced into the graphite tube by an air flow on initiation of the FI system for pre-concentration of the next sample. The reproducibility of FI peak gradients was exploited through precise timing of the collection of the eluate fraction so that end sections of the eluate bolus containing lower analyte concentrations were discarded. A 26-fold enhancement in peak area compared with 50 µl direct introduction was obtained with 60-s pre-concentration while achieving a precision of 1.9% relative standard deviation for 0.1 µg l–1 of Pb (n= 11), and a detection limit of 0.003 µg l–1(3σ). The complete cycle of operation was 150 s which conveniently fitted into the time interval between successive graphite furnace firings. Determination of Pb in sea water samples showed that the interfering matrix had been almost completely removed during the pre-concentration, and determinations were made without using chemical modifiers. Results obtained for National Research Council of Canada Standard Reference Materials CASS 1, CASS 2 [Seawater (Coastal)] and NASS 1 [Seawater (Open Ocean)] using matrix-matched standards and for the SLRS 1 Riverine Water using simple aqueous standards agreed well with certified values.

Minimization of interferences in inductively coupled plasma mass spectrometry using on-line preconcentration

Abstract: A semiautomated system is used to preconcentrate Ti, V, Mn, Fe, Co, Ni, Cu, Cd, and Pb, in order to remove high salt matrices. The preconcentration system accepts digests with acid concentrations equivalent to 0.8-1.4% HNO{sub 3}, neutralizes them, and loads them onto a macroporous iminodiacetate resin. The alkali and alkaline-earth metals, along with deleterious anions such as chloride, are washed off the resin before and analyte metals are eluted with nitric acid. A total of 13 isotopes of the analytes are measured. An examination of the apparent concentration efficiencies, as well as the behavior of two internal standard elements added to the eluate stream, indicates that the elution front matrix enhances the inductively coupled plasma mass spectrometry response of the analytes. Investigation of the nature of the blank signal suggests that the detection limits of several of the isotopes could benefit by much larger preconcentration factors, while those of vanadium, copper, cadmium, and lead are currently limited by reagent purity and laboratory contamination. The preconcentration system is evaluated on several simple synthetic matrices, as well as on synthetic seawater and three wastewaters. Digestion of samples containing natural organic chelators is required.

Continuous flow vapor generation for inductively coupled argon plasma spectrometric analysis. Part 2. Arsenic.

Abstract: Total arsenic is determined by inductively coupled plasma atomic emission using hydride vapor generation. A 1 g sample is wet washed in a 16 x 150 mm 10 mL volumetric test tube on a programmed heating block with nitric, sulfuric, and perchloric acids at up to 310 degrees C. After treatment with hydrochloric acid and potassium iodide, arsenic is reduced by sodium borohydride to arsine in a simplified continuous flow manifold. A standard pneumatic nebulizer affects the gas-liquid separation of AsH3, which is quantified by ICP atomic emission at 193.756 nm. The instrument detection limit for the method has been determined to be 0.4 microgram/L. For a 10:1 dilution of a nominal 1 g sample, the detection limit is 4 micrograms/kg and the linear range is up to 4 mg/kg. Recoveries from 3 matrixes were 99-104%, with a typical RSD of 2%. The method has demonstrated statistical control for samples of biological interest and is especially well suited to analysis of small samples.

Determination of L-ascorbic acid in fruit and vegetable juices by flow injection with immobilised ascorbate oxidase.

Abstract: Ascorbate oxidase was immobilised on cyanogen bromide activated-Sepharose 4B and incorporated in a flow-injection system with amperometric detection at a glassy carbon electrode at +0.6 V. On passage through the immobilised ascorbate oxidase a fraction of the L-ascorbic acid was converted into dehydroascorbic acid and the decrease in signal was measured. This could be directly related to the amount of L-ascorbic acid present. The calibration graph was linear over the range 0-400 ng ml(-1) with a correlation coefficient of 0.9994. The detection limit (2 sigma) in phosphate buffer (0.08 M, pH 5.5) was 4.0 ng ml(-1). The relative standard deviation for a 200 ng ml(-1) standard was 1.0% (n = 10) and the sampling throughput was 30 samples h(-1). The method was used for the simple and rapid determination of L-ascorbic acid in fruit and vegetable juice.

Nonenzymatic method for the determination of hydrogen peroxide in atmospheric samples

Abstract: A nonenzymatic method is developed and compared with the well-known enzymatic (p-hydroxyphenyl)acetic acid (pOHPAA) method for the determination of hydrogen peroxide in aqueous atmospheric samples. The new method is based on the Fe(II)-catalyzed oxidation of benzoic acid by H{sub 2}O{sub 2} to form hydroxylated products (OHBA), which are analyzed by fluorescence detection. The limit of detection and linear response range of the new method are comparable to those of the pOHPAA technique. In addition, the new Fenton-OHBA method has the advantage of using inexpensive, stable, easily available chemical reagents that do not require refrigeration. The new method is insensitive to moderate transition-metal concentrations often found in atmospheric samples.

Analysis of the monosaccharide composition of purified polysaccharides in Ganoderma atrum by capillary gas chromatography

Abstract: Introduction – Ganoderma, one of the best-known traditional Chinese medicines, has attracted considerable attention owing to the fact that dozens of polysaccharides isolated from it have shown diverse and potentially significant pharmacological activities. However, no work has been reported on the analysis of monosaccharide composition of polysaccharide isolated from the aqueous extract of Ganoderma atrum yet. Objective – To develop a simple and sensitive GC-based method for the analysis of monosaccharide composition of purified polysaccharides in Ganoderma atrum. Methodology – The polysaccharide was first hydrolysed to give the constituent monosaccharides, which were subsequently derived into acetylated aldononitriles and analysed by gas chromatography using a capillary column packed with a (5%phenyl) methylpolysiloxane stationary phase with the addition of acetyl inositol as the inner standard. High-performance liquid chromatography was also used for comparison. Results – The stable derivatives of the most common monosaccharides could be separated and reproducibly determined with high sensitivity. The limits of detection and quantification were 0.013 and 0.043 mg/mL, respectively. The intermediary precision values (expressed as the RSD) were less than 10%. The mean recovery of the method was 100 ± 3%, with RSD values of less than 5%. The results obtained from GC and HPLC methods were found to be close to each other within acceptable error ranges. Conclusion – This study demonstrated that the developed method could be applied as an accurate method for the compositional analysis of monosaccharides in the field of biological and biochemical study. Copyright © 2009 John Wiley & Sons, Ltd.

A polishable amperometric biosensor for bilirubin

Abstract: An amperometric enzyme electrode for bilirubin based on the incorporation of bilirubin oxidase and horseradish peroxidase within a graphite-epoxy matrix is reported. The resulting bienzyme electrodes are renewable (by polishing) and offer low-potential detection of bilirubin. The limit of detection is 4 × 10−6 M and the response is linear up to 1 × 10−4 M. The influence of various experimental variables is described. The surface-to-surface reproducibility is 14% (in terms of relative standard deviation). The fabrication scheme is simple and the response times are short. The prospects of using amperometric bilirubin electrodes for diagnostic work are discussed.

Elimination of the argon chloride interference on arsenic speciation in inductively coupled plasma mass spectrometry using ion chromatography

Abstract: Ion chromatography has been combined with inductively coupled plasma mass spectrometry for the speciation of arsenic compounds commonly found in urine. Ion chromatography was used to eliminate or reduce the mass spectral interference formed from chloride, namely argon chloride, by resolving chloride chromatographically from the arsenic compounds. A 20-fold dilution of the urine samples was necessary in order to avoid column overloading from chloride and subsequent argon chloride interference. Detection limits in urine of 3.4 p.p.b. AsIII, 4.2 p.p.b. AsV and 7 p.p.b. dimethylarsinic acid were obtained. Three commercially available freeze-dried urine standards were analysed using the standard additions method. Good agreement was obtained for total arsenic content, which was calculated from the sum of the species with accepted arsenic concentration. The relative standard deviation of peak height for each of the species was approximately 5% in urine.

Competitive heterogeneous enzyme immunoassay for theophylline by flow-injection analysis with electrochemical detection of p-aminophenol

Abstract: A competitive enzyme-linked immunoabsorbent assay based on the flow-injection amperometric detection of p-aminophenol has been investigated with use of the materials and general procedure of a commercial kit for the determination of theophylline in human serum. The antibody is immobilized on glass beads, and the enzyme label is alkaline phosphatase (EC 3.1.3.1). The high currents generated during the electrochemical detection allowed a rapid (35 min) and simple determination of theophylline throughout its therapeutic range (10-20 mg/L) and also in the subtherapeutic range (detection limit of about 80 micrograms/L).

Detection of fentanyl and its analogs by enzyme-linked immunosorbent assay.

Abstract: A prototype enzyme-linked immunosorbent assay (ELISA) for fentenyl, a potent synthetic narcotic analgesic, was used to detect the presence of fentenyl and its analogs in human urine. Human drug-free urine was spiked with 0.02 to 100 ng/mL of fentanyl or with 0.1 to 500 ng/mL of.each analog and used as a sample in the ELISA. Sensitivity and precision of the assay were analyzed specifically for detection of fentenyl. Cross-reactivities of fentanyl and nine analogs, acetylfentanyl, p-methylfentanyl, p-fluorofentanyl, butyrylfentanyl, ( + )trans.3-methylfentanyl, ( + )cis-3methylfentanyl, ,~-methylfentanyl, benzylfentanyl, and alfentanil for this assay were also determined. The results indicate that the ELISA was capable of detecting urinary fentanyl with a limit of detection of 0.25 ng/mL and a reasonable "working cutoff" of 0.5 ng/mL. The assay was moderately precise with within-run precision, determined at fentanyl concentrations of 10.0 and 2.5 ng/mL, showing coefficients of varlatlon from 7.7 to 10.4% and between-run precision, determined at concentrations of I0.0 and 2.5 ng/mL, showing coefficients of variation from 14.2 to 23.7%. Acetylfentanyl, p-fluorofentanyl, p-methylfentanyl, and butyrylfentanyl show good cross-reactivity in the assay relative to fentanyl. The cross-reactlvltles equivalent to 2 ng/mL of fentanyl for acetylfentanyl, p-fluorofentanyl, p-methylfentanyl, butyrylfentanyl were 111, 93, 87, and 77%, respectively. The (+)trena-3-methylfentanyl, o-methylfentanyl, and ( :I: )cis-3-methylfentanyl show less cross-reactivlty; their percent cross-reactivities equlvalent to 2 ng/mL of fentanyl were 50, 19, and 3%, respectively. Benzylfentanyl and alfentanil, however, do not show any cross-reactivlty. The data suggest that the ELISA may be useful in screening urine for fentanyl and certain of its analogs.