Showing papers on "Detection limit published in 2000"
TL;DR: A new approach to ultrasensitive detection of DNA hybridization based on nanoparticle-amplified surface plasmon resonance (SPR) is described, with a greater than 10-fold increase in angle shift and a more than 1000-fold improvement in sensitivity for the target oligonucleotide as compared to the unamplify binding event.
Abstract: A new approach to ultrasensitive detection of DNA hybridization based on nanoparticle-amplified surface plasmon resonance (SPR) is described. Use of the Au nanoparticle tags leads to a greater than 10-fold increase in angle shift, corresponding to a more than 1000-fold improvement in sensitivity for the target oligonucleotide as compared to the unamplified binding event. This enhanced shift in SPR reflectivity is a combined result of greatly increased surface mass, high dielectric constant of Au particles, and electromagnetic coupling between Au nanoparticles and the Au film. DNA melting and digestion experiments further supported the feasibility of this approach in DNA hybridization studies. The extremely large angle shifts observed in particle-amplified SPR make it possible to conduct SPR imaging experiments on DNA arrays. In the present work, macroscopic 4 × 4 arrays were employed, and a ∼10 pM limit of quantitation was achieved for 24-mer oligonucleotides (surface density ≤8 × 108 molecules/cm2). Even...
909 citations
TL;DR: Stripping voltammetric measurements of microgram per liter levels of cadmium, lead, thallium, and zinc in nondeaerated solutions yielded well-defined peaks, along with a low background, following short deposition periods, indicating great promise to centralized and decentralized testing of trace metals.
Abstract: Bismuth-coated carbon electrodes display an attractive stripping voltammetric performance which compares favorably with that of common mercury-film electrodes. These bismuth-film electrodes are prepared by adding 400 μg/L (ppb) bismuth(III) directly to the sample solution and simultanously depositing the bismuth and target metals on the glassy-carbon or carbon-fiber substrate. Stripping voltammetric measurements of microgram per liter levels of cadmium, lead, thallium, and zinc in nondeaerated solutions yielded well-defined peaks, along with a low background, following short deposition periods. Detection limit of 1.1 and 0.3 ppb lead are obtained following 2- and 10-min deposition, respectively. Changes in the peak potentials (compared to those observed at mercury electrodes) offer new selectivity dimensions. Scanning electron microscopy sheds useful insights into the different morphologies of the bismuth deposits on the carbon substrates. The in situ bismuth-plated electrodes exhibit a wide accessible po...
896 citations
TL;DR: A high-throughput, robust, sensitive, accurate, and precise assay for simultaneous measurement of trace levels of eight phthalate metabolites in human urine by HPLC-MS/MS to help elucidate potential associations (if any) between human exposure to phthalates and adverse health effects.
Abstract: Because of the ubiquity of phthalates and their potential role in increasing risk for cancer and reproductive dysfunction, the need for human exposure assessment studies is urgent. In response to this need, we developed a high-throughput, robust, sensitive, accurate, and precise assay for simultaneous measurement of trace levels of eight phthalate metabolites in human urine by HPLC−MS/MS. Human urine samples were processed using enzymatic deconjugation of the glucuronides followed by solid-phase extraction. The eluate was concentrated, and the phthalate metabolites were chromatographically resolved by reversed-phase HPLC, detected by APCI-tandem mass spectrometry, and quantified by isotope dilution. This selective analytical method permits rapid detection (7.7 min total run time) of eight urinary metabolites of the most commonly used phthalates with detection limits in the low nanagram per milliliter range. Assay precision was improved by incorporating 13C4-labeled internal standards for each of the eight...
339 citations
TL;DR: A novel method that combines two on-line concentration techniques in capillary electrophoresis (CE), namely, sample stacking with electrokinetic injection (field-enhanced sample injection, FESI) and sweeping, afforded the detection of positively chargeable analytes in parts per trillion (ppt) levels.
Abstract: A novel method that combines two on-line concentration techniques in capillary electrophoresis (CE), namely, sample stacking with electrokinetic injection (field-enhanced sample injection, FESI) and sweeping, afforded the detection of positively chargeable analytes in parts per trillion (ppt) levels. The main idea is to selectively introduce by FESI as many molecules of cationic analytes as possible from a very dilute sample solution and focus the resulting zone by sweeping. Limit of detection values (signal-to-noise ratio 3) of 4.1 and 8.0 ppt-the lowest concentration reported by direct UV detection in CE-with average plate numbers of 3.6 x 10(5) and 4.4 x 10(5) are obtained for laudanosine and naphthylamine (standard solutions), respectively. This translates to improvements in peak heights compared with usual injection approaching a million-fold. Optimization schemes and application to quantitative and qualitative analyses are also investigated.
289 citations
TL;DR: In this article, a new competitive ligand exchange-adsorptive cathodic stripping voltammetric (CLE-ACSV) method for the determination of iron speciation in seawater has been developed using the iron binding ligand TAC 2-(2-thiazolylazo)-p-cresol.
Abstract: A new sensitive competitive ligand exchange-adsorptive cathodic stripping voltammetric (CLE-ACSV) method for the determination of iron speciation in seawater has been developed using the iron binding ligand TAC 2-(2-thiazolylazo)-p-cresol. An earlier method for determining iron using TAC [1] was reexamined and optimized for measurements in seawater at pH 8.0. The sensitivity was improved by employing a fast (10.12 V/s) linear sweep scan waveform. The detection limit (3σ of blank) is 0.10 nM after an adsorption time of 300 s; the detection limit can be lowered, however, by using a longer deposition time or for the determination of total iron, by increasing the pH to 8.5. This method was applied to samples from Swedish coastal waters and the results indicate the possible efflux of iron binding ligands from sediments in coastal waters.
266 citations
TL;DR: The method has been used for analysis of various fruits and vegetables, such as apple, banana, cabbage, carrot, cucumber, lettuce, orange, pear, pepper, and pineapple, and limits of detection range between 0.02 and 1.0 mg/kg for most compounds.
Abstract: A method is described for the determination of 251 pesticide and degradation product residues in fruit and vegetable samples. Extraction of the sample with acetonitrile is followed by a salting-out step. Co-extractives are removed by passing a portion of the acetonitrile extract through an octadecyl (C18) solid-phase extraction cleanup cartridge and then, in a second cleanup, through a carbon cartridge coupled to an amino propyl cartridge. Determination is by gas chromatography with mass-selective detection in the selected-ion monitoring mode, and by liquid chromatography with post-column reaction and fluorescence detection for N-methyl carbamates. The method has been used for analysis of various fruits and vegetables, such as apple, banana, cabbage, carrot, cucumber, lettuce, orange, pear, pepper, and pineapple. Limits of detection range between 0.02 and 1.0 mg/kg for most compounds. Over 80% of the compounds have a limit of detection of < or = 0.04 mg/kg.
236 citations
TL;DR: Solid-phase microextraction with an 85 microm polyacrylate fiber, coupled to gas chromatography-mass spectrometry was used to determine six phthalate esters and bis(2-ethylhexyl) adipate in water samples to analyze both tap and commercial mineral water samples.
227 citations
TL;DR: A new luminescent rhenium(I) polypyridyl-based receptor for a variety of inorganic anions has been designed and synthesized in this article.
211 citations
TL;DR: On-site analysis of groundwater containing arsenic was performed with a small battery-powered potentiostat and quantification was done through standard additions, and these results were compared to the standard EPA methodology.
Abstract: Rapid on-site analysis of arsenic in groundwater was achieved with a small battery-powered unit in conjunction with a microfabricated gold ultramicroelectrode array (Au-UMEA). The sensor, consisting of 564 UME disks with a unique gold surface created by electron beam evaporation, was demonstrated to be highly sensitive to low-ppb As3+ using square wave anodic stripping voltammetry. The influence of the square wave frequency, pulse amplitude, and deposition potential on the arsenic peak stripping current was investigated. Varying those theoretical parameters yielded results surprisingly similar to those for the thin Hg film case. The performance of the Au-UMEA was evaluated for reproducibility and reliability. Three stability tests showed an average relative standard deviation of 2.5% for 15 consecutive runs. Limits of detection were investigated, and 0.05 ppb As3+ could be measured while maintaining a S/N of 3:1. Interference studies were performed in the presence of 50-500 ppb of Cu2+, Hg2+, and Pb2+. On-site analysis of groundwater containing arsenic was performed with a small battery-powered potentiostat. Quantification was done through standard additions, and these results were compared to the standard EPA methodology.
211 citations
TL;DR: In this article, a simple and highly reliable method for the determination of mercury on a rotating gold disk electrode is reported, which is linear with concentration over a wide concentration range (0.2 −400 nM).
204 citations
TL;DR: SPME revealed to be a rapid and sensitive method for the extraction and quantitation of trace volatile compounds from plant oils even at ambient temperature.
Abstract: Headspace solid-phase microextraction (HS-SPME) was used to isolate the volatile compounds, which are formed during peroxidation of fatty acids in vegetable oils. Isolated compounds were characterized by GC−MS and quantified using GC with FID detection. Four fibers for HS-SPME method development were tested, and the divinylbenzene/carboxene/PDMS fiber was selected as providing the best detection of analyzed compounds. Extraction curves, limits of detection, repeatability, and linearity were investigated for 14 aldehydes, ketones, hydrocarbons, and alcohols being products of fatty acids autoxidation. Limits of detection for 11 of these were below 1 μg/L. For quantitative purposes, to minimize the influence of temperature on hydroperoxide formation and the changes in the volatiles profile of the extracts, sampling was performed at 20 °C. For compound characterization by GC−MS, sampling temperature of 50 °C was applied. The developed method was applied to the analysis of refined and cold-pressed rapeseed oil...
TL;DR: A method is reported for the determination of cyromazine and melamine residues in soil and it is reported that this method passed an Independent Laboratory Validation (ILV) as per U.S. EPA FIFRA Good Laboratory Practice Guidelines 40 CFR 160.
Abstract: A method is reported for the determination of cyromazine and melamine residues in soil. Soil samples are extracted twice via mechanical shaking, each time with 70% acetonitrile/30% 0.050 M ammomium carbonate for 30 min. An aliquot portion of the pooled extracts is subjected to strong cation exchange (SCX) purification on AG 50W-X4 resin. Final analysis is accomplished using liquid chromatography-ultraviolet (LC-UV) detection at a wavelength of 214 nm. Confirmatory analyses can be performed using gas chromatography-mass selective detection (GC-MSD) in the selected ion monitoring (SIM) mode. The limit of detection (LOD) is 2.5 ng injected and the limit of quantification (LOQ) is 10 ppb when using LC-UV for the analysis of N-cyclopropyl-1,3,5-triazine-2,4, 6-triamine (cyromazine) and 1,3,5-triazine-2,4,6-triamine (melamine). The LOD is 0.050 ng injected and the LOQ is 10 ppb when using GC-MSD for confirmatory analyses. The mean procedural recoveries were 97 and 95% and the standard deviations were 16 and 11% for cyromazine and melamine, respectively (n = 24), when using LC-UV. The mean procedural recoveries were 107 and 92% and the standard deviations were 9.9 and 16% for cyromazine and melamine, respectively (n = 29), when using GC-MSD. The method validation study was conducted under U.S. EPA FIFRA Good Laboratory Practice Guidelines 40 CFR 160. The method also passed an Independent Laboratory Validation (ILV) as per U.S. EPA FIFRA Subdivision N.
TL;DR: A high-performance liquid chromatography method with on-line coupled ultraviolet (UV), mass spectrometry (MS) and biochemical detection for acetylcholinesterase (AChE) inhibitory activity has been developed and AChE inhibitors can be rapidly identified.
TL;DR: From these results, the HPLC-ED method should be the most useful in the determination of bisphenol A at low concentration levels in water and biological samples.
TL;DR: In this article, a method based on capillary electrophoresis with electrochemical detection (CE-ED) was developed for the determination of daidzein, rutin and quercetin.
TL;DR: The utility of these assays was demonstrated in the standardization of nitric oxide-saturated cell culture media, and the release ofNitric oxide by the NONOate compound DEA/NO.
TL;DR: The practical analytical utility of the differential pulse voltammetry and chronoamperometry method is demonstrated by the measurement of UA in human urine and serum without any preliminary treatment.
Abstract: Electrochemically anodized diamond film electrodes were used for selective detection of uric acid (UA) in the presence of high concentrations of ascorbic acid (AA) by differential pulse voltammetry and chronoamperometry. Because the oxidation peak potential for AA is ∼450 mV more positive than that for UA at anodized diamond electrodes, UA can be determined with very good selectivity. By use of chronoamperometry, linear calibration curves were obtained for UA over the concentration range up to 1 × 10-6 M in 0.1 M HClO4 solution, with the lowest experimental value measured being 5 × 10-8 M. This is consistent with the fact that a statistical analysis of the calibration curve yielded a detection limit of 1.5 × 10-8 M (S/N = 3). AA in less than 20-fold excess does not interfere. The practical analytical utility of the method is demonstrated by the measurement of UA in human urine and serum without any preliminary treatment.
TL;DR: A simple reversed-phase high-performance liquid chromatographic method was developed and validated for simultaneous analysis of nine quinolones in chicken tissue, suitable for porcine, bovine, ovine and fish muscle tissue.
TL;DR: A one-dimensional TLC method to determine aflatoxins in various food matrices was elaborated which abstains fully on the use of chlorinated solvents and is likely to give satisfactory performance if tested in a future collaborative trial.
TL;DR: Because NAT is well separated from DAN and other fluorescent components present in biological samples, the HPLC method offers the advantages of high sensitivity and specificity as well as easy automation for quantifying picomole levels of nitrite and nitrate in cell culture medium and biological samples.
TL;DR: A reversed-phase LC method, optimised for the separation of trans- and cis-resveratrol, catechin, epicatechin, quercetin and rutin, is reported, although the use of a fluorimetric detector considerably lowered the detection limits.
TL;DR: An integrated collection and vaporization cell has been developed to provide automated, 10-min resolution monitoring of fine particle nitrate in the atmosphere as mentioned in this paper, where particles are collected by a humidified impaction process and analyzed in place by flash vaporization and chemiluminescent detection of the evolved nitrogen oxides.
Abstract: An integrated collection and vaporization cell has been developed to provide automated, 10-min resolution monitoring of fine particle nitrate in the atmosphere. Particles are collected by a humidified impaction process and analyzed in place by flash vaporization and chemiluminescent detection of the evolved nitrogen oxides. Particle collection efficiency was measured between 95% and 100% for particles above 0.1 μm. Evaporative losses for ammonium nitrate were 2 ± 4%. Average nitrate values from the automated system were compared to traditional denuder filter measurements in three cities, with correlation coefficients of greater than 0.97 and regression slopes ranging from 0.96 to 1.06. The detection limit is governed by the field blank, which for the Los Angeles area was 0.4 μg/m3. The system operated unattended for days at a time, with data recovery of 97%.
TL;DR: In this paper, a spectrophotometric sequential injection (SI) determination of phosphate and silicate in environmental samples and cell cultivation medium using the molybdenum blue reaction was presented.
TL;DR: The new in-tube SPME technique has been demonstrated as a very efficient extraction method for the analysis of polar and thermally labile analytes and was evaluated according to the reproducibility, linear range and limit of detection.
TL;DR: The CE-chip is able to determine a protein biological threat agent simulant, ovalbumin (Ov), by performing an immunoassay separation of Cy-5 labeled anti-ovalbumin from its complex with Ov, in under 30 s.
TL;DR: A novel method for determination of Hg, Se, Bi, As and Sb based on microwave digestion followed by continuous flow vapour generation atomic fluorescence spectrometry was developed and excellent agreement with the certified value was obtained for all elements.
TL;DR: Inductively coupled plasma dynamic reaction cell mass spectrometry (ICP-DRC-MS) was characterised for the detection of the six naturally occurring selenium isotopes as mentioned in this paper.
Abstract: Inductively coupled plasma dynamic reaction cell mass spectrometry (ICP-DRC-MS) was characterised for the detection of the six naturally occurring selenium isotopes. The potentially interfering argon dimers at the selenium masses m/z 74, 76, 78 and 80 were reduced in intensity by approximately five orders of magnitude by using methane as reactive cell gas in the DRC. By using 3% v/v methanol in water for carbon-enhanced ionisation of selenium, the sensitivity of 80Se was 104 counts s−1 per ng ml−1 of selenium, and the estimated limit of detection was 6 pg ml−1. The precision of the isotope ratios was close to the theoretical values for selenium concentrations at 1 and 10 ng ml−1. The accuracy of the isotope ratios, however, was improved by correcting the count rate of all selenium isotopes equivalent to the formation of SeH at 9.6 ± 0.5% one mass unit above the selenium isotopes. A linear relationship (r < 0.98) was found between the error of the corrected isotope ratios and the difference in mass from the 80Se reference isotope. This indicated that the error was caused by mass bias. The slope of the curve at −3.0% error per mass unit can be used for correction of the measured ratios. Deuterated methane used as the DRC gas showed that hydrogen transfer from methane was not involved in the formation of SeH as SeD was absent in the mass spectrum. The almost interference-free detection of selenium by ICP-DRC-MS made the detection of the 80Se isotope possible for detection of selenoamino acids separated by cation exchange HPLC. The limit of detection of the HPLC-ICP-DRC-MS method was in the range 3–5 pg as selenium.
TL;DR: Results obtained by calibration with aqueous solutions of Hg and with standard addition were found to be in good agreement with those of cold-vapor atomic absorption spectrometry.
Abstract: A new low-power, small-scale 2.45 GHz microwave plasma source at atmospheric pressure for atomic emission spectrometry based on microstrip technology is described. The MicroStrip Plasma (MSP) source was produced in microstrip technology on a fused-silica wafer and designed as an element-selective detector for miniaturized analytical applications. The electrodeless microwave-induced plasma (MIP) operates at microwave input power of 10-40 W and gas flows of 50-1000 mL.min-1 of Ar. Rotational (OH) and excitation (Fe) temperatures were found to be 650 and 8000 K, respectively. Spatially resolved measurements of the Hg I 253.7-nm atomic emission line with an electronic slitless spectrograph (ESS) showed that a cylindrically symmetric plasma with a diameter of about 1 mm is obtained. With the MSP, Hg could be determined by applying the flow injection cold vapor (FI-CV) technique with a detection limit of 50 pg.ml-1. In terms of the relative standard deviation, a time stability of < 1.4% for 45 replicates within 80 min can be realized at a concentration level of 10 ng.ml-1 of Hg. Hg could be determined in the leachate of a certified standard reference soil (STSD-4) obtained by treatment with aqua regia at the 930 +/- 76 ng.g-1 level. Results obtained by calibration with aqueous solutions of Hg and with standard addition were found to be in good agreement with those of cold-vapor atomic absorption spectrometry.
TL;DR: The possibility of determination of twelve flavonoids using adsorptive stripping voltammetry in a flow injection system is examined and in some cases the differences are so high that determination of certain flavonoid in the presence of excess of others is allowed.
TL;DR: Headspace solid-phase microextraction (SPME), as a simple, solvent-free method, has been applied to the analysis of 10 chlorinated benzenes (CBs) present at trace levels in water samples.