Showing papers on "Detection limit published in 2001"

Determination of endocrine-disrupting phenolic compounds and estrogens in surface and drinking water by HRGC-(NCI)-MS in the picogram per liter range.

Abstract: A method for the analysis of phenolic estrogenic active compounds in surface and drinking water in the picogram per liter range is described. Besides the widely used monomer bisphenol A, 4-tert-octylphenol [4-(1,1,3,3-tetramethylbutyl)phenol] and the technical isomer mixture of 4-nonylphenol; phenolic steroid hormones such as the endogenous estrogens estrone, 17α-estradiol, and 17β-estradiol; and the exogenous estrogen 17α-ethinylestradiol were determined in water at the 20−200 pg/L level. Water samples from 1 to 5 L were extracted by solid-phase extraction (SPE) on a cartridge system containing LiChrolut EN as sorbent. The phenols and steroids were converted into their pentafluorobenzoylate esters in an extractive derivatization reaction. The derivatives were then determined by high-resolution gas chromatography with negative chemical ionization mass spectrometric detection (HRGC−(NCI)−MS) in the selected ion mode (SIM). All results were also confirmed by HRGC with electron capture detection (ECD). This ...

Europium Nanoparticles and Time-resolved Fluorescence for Ultrasensitive Detection of Prostate-specific Antigen

Abstract: Background: Nanoparticle-based detection technologies have the potential to improve detection sensitivity in miniature as well as in conventional biochemical assays. We introduce a detection technology that relies on the use of europium(III) nanoparticles and time-resolved fluorometry to improve the detection limit of biochemical assays and to visualize individual molecules in a microtiter plate format. Methods: Streptavidin was covalently coated on 107-nm nanoparticles containing >30 000 europium molecules entrapped with β-diketones. In a model assay system, these nanoparticles were used to trace biotinylated prostate-specific antigen (PSA) in a microtiter plate format. Results: The detection limit (mean + 3 SD of the zero calibrator) of biotinylated PSA was 0.38 ng/L, corresponding to 10 fmol/L or 60 zeptomoles (60 × 10−21 moles) of PSA. Moreover, single nanoparticles, representing individual PSA molecules, were visualized in the same microtiter wells with a time-resolved fluorescence microscope using a ×10 objective. Single nanoparticles, possessing high specific activity, were also detected in solution by a standard time-resolved plate fluorometer. Conclusions: The universal streptavidin-coated europium(III) nanoparticle label is suitable for detection of any biotinylated molecule either in solution or on a solid phase. The europium(III) nanoparticle labeling technology is applicable to many areas of modern biochemical analysis, such as immunochemical and multianalyte DNA-chip assays as well as histo- and cytochemistry to improve detection sensitivities.

Rapid, sensitive, microscale determination of phosphate in water and soil.

Abstract: ample, is not widely used because it has a relatively high detection limit (0.1 mg L 1 ) and cannot be used for A rapid and sensitive analysis of inorganic and organic phosphorus samples with high concentrations of interfering anions (P) is needed to analyze water and soil extracts at submicromolar concentrations. The proposed method, based on the complexation of without sample pretreatment. The automated ascorbic malachite green with phosphomolybdate under acidic conditions, was acid colorimetric method is extensively used because it adapted to a 96-well microtiter plate format, and was tested for matrix overcomes most of these obstacles. Moreover, many interferences using 15 soils and some common extractants, including automated techniques can save time when they are conwater, KCl, CaCl2, NaOH, and HCl. The accuracy of P determination figured to simultaneously determine several compowas affected when CaCl2 and HCl concentrations were greater than nents in a sample mixture. However, many automated 0.1 M and when NaOH concentration exceeded 0.4 M. Potassium techniques require expensive and dedicated equipment chloride concentration up to 1 M did not interfere with P determina- and a high degree of technical expertise to operate, and tion. The molar absorptivity was 46 841 M 1 cm 1 and the reagent generate large volumes of waste. Considering the short blank absorbance was 0.071 0.003 (n 10). At the 99% confidence holding time for analysis of soluble inorganic P (48 h limit, the method detection limit was calculated to be 0.006 mg P L 1 . Recovery of added inorganic P in different types of soils and extracts for refrigerated samples) and the number of samples ranged between 95 and 112% with an average of 102%. The proposed involved, these constraints put a burden on many labomicroplate method allows P to be determined rapidly in a wide range ratories. of soil types and extracts and requires limited volume (20–200 L). The malachite green (MG) colorimetric procedure The procedure uses limited quantities (40 L) of two stable reagents has also been used to determine P at submicromolar (1 yr), and generates low amounts of hazardous waste. concentrations in water and soil–water extracts (van Veldhoven and Mannaerts, 1987; Ohno and Zibilske, 1991). Both the ascorbic acid (AA; Murphy and Riley,

Roundup Ready® soybean event-specific real-time quantitative PCR assay and estimation of the practical detection and quantification limits in GMO analyses

Abstract: An event-specific real-time PCR method for detection and quantification of genetically modified Roundup Ready soybean with TaqMan chemistry on the LightCycler, targeting the nopaline synthase terminator (3') junction between recombinant and host plant DNA is described. We distinguish between three types of detection and quantification limits: the absolute limits (referring to the initial number of template copies in the PCR), the relative limits (referring to the relative percentage of initial template copies of the recombinant sequence to copies of the haploid soybean genome that is detected), and the practical limits (referring to what is applicable in the PCR with the DNA that is being analysed). The absolute detection limit was determined to be a single initial template copy, while the absolute quantification limit was determined to be approximately 30 initial template copies. We discuss the relative and practical limits, and provide guidelines to estimating the practical limits.

Electrochemical Enzyme Immunoassays on Microchip Platforms

Abstract: A microfluidic device for conducting electrochemical enzyme immunoassays is described. The new "lab-on-a-chip" protocol integrates precolumn reactions of alkaline phosphatase-labeled antibody (anti-mouse IgG) with the antigen (mouse IgG), followed by electrophoretic separation of the free antibody and antibody-antigen complex. The separation is followed by a postcolumn reaction of the enzyme tracer with the 4-aminophenyl phosphate substrate and a downstream amperometric detection of the liberated 4-aminophenol product Factors influencing the reaction, separation, and detection processes were optimized, and the analytical performance was characterized. An applied field strength of 256 V/cm results in free antibody and antibody-antigen complex migration times of 125 and 340 s, respectively. A remarkably low detection limit of 2.5 x 10(-16) g/mL (1.7 x 10(-18) M) is obtained for the mouse IgG model analyte. Such combination of a complete integrated immunoassay, an attractive analytical performance, and the distinct miniaturization/portability advantages of electrochemical microsystems offers considerable promise for designing self-contained and disposable chips for decentralized clinical diagnostics or on-site environmental testing.

Chemiluminescence detection for hybridization assays on the flow-thru chip, a three-dimensional microchannel biochip.

Abstract: Chemiluminescence (CL) detection is seldom used in two-dimensional solid support microarray platforms because adequate sensitivity and spatial resolution is difficult to achieve. The three-dimensional ordered microchannels of the Flow-thru Chip increase both the sensitivity and spatial resolution required for quantitative CL measurements on microarrays. Enzyme-catalyzed CL reactions for the detection of hybridizations on microchannel glass were imaged using a CCD camera. Signal uniformity, sensitivity, and dynamic range of the detection method were determined. The relative standard deviation of signal intensities across an array of 64 spots was 8.1%. A detection limit of 250 amol of target with a linear dynamic range of 3 orders of magnitude was obtained for a 3-h assay. Similar to two-color fluorescence measurements, multiple enzyme labels were employed to demonstrate two-channel chemiluminescence. A unique method for measuring the relaxation time of a chemiluminescent species is also described.

Amplified detection of DNA and analysis of single-base mismatches by the catalyzed deposition of gold on Au-nanoparticles.

Abstract: A novel amplification route for DNA detection based on the deposition of gold on a 10 nm Au-colloid/avidin conjugate label acting as a ‘seeding’ catalyst, is described. Microgravimetric quartz-crystal-microbalance measurements are employed to transduce the catalyzed deposition of gold on the piezoelectric crystals. Three different DNA detection schemes are described: (i) analysis of a 27-base nucleic acid fragment; (ii) analysis of the entire M13ϕ DNA (7229 bases); and (iii) detection of a single-base mismatch in a DNA. Ultrasensitive detection of DNA is accomplished by the catalyzed deposition of gold, detection limit ∼1 × 10−15 M.

An oxygen insensitive microsensor for nitrous oxide

Abstract: A method to create an O 2 insensitive and fast responding microsensor for N 2 O is presented The elimination of O 2 interference was obtained by attaching a capillary with an alkaline solution of ascorbate in front of the tip of an electrochemical microsensor that was sensitive to both O 2 and N 2 O A 01 mm layer of 2 M ascorbate at pH 12 was able to remove all O 2 when measuring in air-saturated solutions (O 2 partial pressure 21 kPa), and no reduction of N 2 O by the ascorbate was observed The response of the sensor to N 2 O was linear from 0 to 12 mM, and the detection limit was less than 1 μM The tip diameters of the sensors described in detail were 50–80 μm, but much smaller sensors can be constructed The 90% response times were about 40–50 s Interference of carbon dioxide was shown to be negligible with respect to environmental monitoring, and the sensitivity to acetylene, which is commonly used to inhibit nitrous oxide reductase in denitrification studies, could be kept sufficiently low for experimental work

Determination of Heavy Metals in Soils, Sediments and Geological Materials by ICP-AES and ICP-MS

Abstract: Sixteen soil and sedimentary geological reference materials were analysed for As and the heavy metals Cd, Co, Cr, Cu, Ni, Pb and Zn by inductively coupled plasma-atomic emission spectrometry (ICP-AES) and inductively coupled plasma-mass spectrometry (ICP-MS) in combination with total and partial dissolution of the samples. It can be demonstrated that none of the modern ICP methods is completely free from analytical problems. This applies in particular when the concentrations are close to the detection limits (e.g. in ICP-AES) and is mainly due to the wide variation in the bulk composition of soils resulting in complex matrix effects (e.g. in ICP-MS). In order to determine the extent of soil pollution by heavy metals, both partial and total dissolution have to be performed prior to analysis.

Effect of lipophilic ion-exchanger leaching on the detection limit of carrier-based ion-selective electrodes.

Abstract: The equilibrium partitioning of lipophilic ion-exchanger salts from ion-selective polymeric membrane electrodes (ISEs) and its possible effect on the lower detection limit of these sensors is described. Predictions are made on the basis of various parameters, including the knowledge of tetraphenylborate potassium salt partitioning constants, the selectivity of ionophore-free ion-exchanger membranes, and ionophore stability constants in the membrane. Ion-exchanger lipophilicities are significantly increased if the membrane contains an ionophore that strongly binds the primary ion. Predicted detection limits are on the order of 10-5−10-8 M for ionophore-free membranes, and may reach levels as low as 10-18 M with adequate ionophores in the membrane. Experiments are performed for well-described lead-selective membranes containing different tetraphenylborate derivatives, and detection limits appear to be independent of the ion-exchanger used. However, they are much higher if a more hydrophilic carborane cation...

Optical Determination of Low-Level Water Concentrations in Organic Solvents Using Fluorescent Acridinyl Dyes and Dye-Immobilized Polymer Membranes

Abstract: The fluorescent acridinyl indicators 4-(9-acridinyl)-N-(5-hexenyl)-N-methylaniline (KD-F0011), 6-(9-acridinyl)-1,2,2,3-tetramethyl-2,3-dihydro-1H-perimidine (KD-F0021), and 6-(9-acridinyl)-2-(3-butenyl)-1,2,3-trimethyl-2,3-dihydro-1H-perimidine (KD-F0022) were designed, synthesized, and applied for highly sensitive optical determination of low-level water in organic solvents. All these dyes were found useful as fluorescence indicators for the detection of water below 1% (v/v) in different solvent media with a low detection limit of 0.002% (v/v) or 20 mg/L (22 ppm by weight) for KD-F0021 in THF solution. Sensing membranes made from poly(ethylene glycol) dimethacrylate by photocopolymerization with the indicator KD-F0011 were also prepared. Using the membrane sensor, the lowest detection limit of 0.001% (v/v) or 14 mg/L (20 ppm) water was achieved in diethyl ether samples. This system enables the continuous monitoring of the water content in a flow-through arrangement, where single-wavelength excitation (40...

Voltammetric detection of copper(II) at a carbon paste electrode containing an organically modified silica

Abstract: A carbon paste electrode modified with aminopropyl-grafted silica gel (APS) was evaluated as an electrochemical sensor for copper species in aqueous medium. The overall analysis involved a two-step procedure: an accumulation step at open circuit, followed by medium exchange to a pure electrolyte solution for the voltammetric quantification. During the preconcentration step, copper(II) was accumulated on the APS surface by complexation with the amine groups. In the detection step, copper(II) was desorbed in acidic medium, then cathodically electrolyzed at −0.5 V for 60 s, and detected by anodic stripping square wave voltammetry. The influence of various experimental parameters on the sensor response was investigated (i.e. pH of the detection and accumulation media, electrolysis time, carbon paste composition, silica gel porosity, accumulation time). Reproducible results were obtained, giving after optimization a linear calibration in the 5×10 −8 –2×10 −7 M concentration range, with a detection limit of 3×10 −9 M. This new sensor was applied to copper analysis in laboratory tap water.

Tailored Chemosensors for Chloroaromatic Acids Using Molecular Imprinted TiO2 Thin Films on Ion-Sensitive Field-Effect Transistors

Abstract: The SiO2 gate of an ion-sensitive field-effect transistor, (ISFET), is functionalized with a TiO2 film that includes imprinted molecular sites for 4-chlorophenoxy acetic acid, (1), or 2,4-dichlorophenoxy acetic acid, (2). The functionalized devices that include the imprinted interfaces reveal an impressive selectivity in the sensing of the imprinted substrates Na+-1 or Na+-2. The detection limit for Na+-1 is (5 ± 2) × 10-4 M, which corresponds to 38 mV·dec-1 in the concentration range of 0.5 to 6 mM. The detection limit for the analysis of Na+-2 is (1.0 ± 0.2) × 10-5 M, which corresponds to 28 mV·dec-1 in the concentration range 0.1−9.0 mM. The equilibration time of the devices is ca. 5 min.

Electrocatalytic oxidation and sensitive detection of cysteine on a lead ruthenate pyrochlore modified electrode

Abstract: Electrocatalytic oxidation of cysteine (CySH) at Nafion/lead ruthenate pyrochlore (Py) chemically modified electrodes was thoroughly studied. Electrochemical ac impedance spectroscopy analysis indicated the formation of Py microparticles in the interfacial galleries of Nafion. Experiments with benchmark systems of Fe(CN)63-/4- and Ru(bpy)2+/3+ reveal the suppression of Nafion's anionic character after the in situ precipitation of Py. Michaleis−Menten-type kinetics with the rate determination step of CyS−Py−RuVI → Py−RuIV + CyS−SCy was proposed for this catalytic oxidation. The electrocatalytic behavior is further developed as a sensitive detection scheme for CySH by square-wave voltammetry (SWV) and flow injection analysis (FIA). Under the optimized conditions, the calibration curve is linear up to 560 μM with a detection limit (signal/noise 3) of 1.91 μM in SWV. The detection limit can be improved to 1.70 nM (i.e., 24.22 ng in a 20-μL sample loop) in FIA. This is the lowest value ever reported for direct...

Elemental Analyses Using Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS) of Geological Samples Fused with Li2B4O7 and Calibrated Without Matrix-Matched Standards

Abstract: Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) was used as a complementary technique to X-ray fluorescence (XRF), for multi-element analysis of geological samples fused with lithium-tetraborate Li2B4O7). Different calibration strategies using external non-matrix matched reference materials were investigated. Various internal standards were tested, including the use of Li from the flux, and the use of the naturally occurring internal standards, Si or Ca. The use of a naturally occurring standard is not as efficient as this required a prior analysis of the samples using XRF. The obtained values for the analysis of geological reference materials were compared with consensus literature values, and satisfactory agreement was found. Laser pits, which were formed, had a diameter of 80 μm and 3–5 replicates on each fused disc were measured. The reproducibility of the method was better than 10% for concentrations above 1 μg/g and better than 15% for lower concentrations. The use of Li as the internal standard offers the possibility of multi-element determinations in geological samples, which have an unknown composition when the laser ablation analysis is carried out. However, using the calculated stoichiometric composition of the lithium-tetraborate for the calculation of the Li concentration leads to a constant deviation from the recommended values. Therefore, it was necessary to determine the Li concentration within each sample batch using at least one lithium tetraborate fused geological reference material. This resulting Li concentration in the beads was then used for all subsequent samples in a run. Limits of detection, reproducibility, deviation from reference values indicate the potential of LA-ICP-MS for such bulk analysis without matrix matched calibration standards.

Analysis of organic esters of plasticizer in indoor air by GC-MS and GC-FPD.

Abstract: The aim of this study was to assess the performance of a method of analyzing organic esters of plasticizer in indoor air by sampling air in a charcoal tube and extracting the esters in toluene using a gas chromatography−mass spectrometer (GC−MS) and flame photometric detector (FPD). An internal standardization method was used for the GC−MS measurement of phthalate esters, whereas an external calibration method was employed to determine the levels of phosphate esters by FPD. The instrumental detection limit, the instrumental lower limit of determination, and the blank and method detection limits were also determined. Mean recoveries of phthalate esters from the charcoal tube were 97.9−115%. Mean recoveries of phosphate esters were lower but reproducible. Recoveries of the esters from indoor air were generally greater than 80%. For all the compounds, no significant breakthrough was detected up to 100 μg. Thus, indoor organic esters could be accurately determined in the range of 0.6 × 10-3−23 μg/m3 by the pr...

Automated solid phase dynamic extraction--extraction of organics using a wall coated syringe needle.

Abstract: Extractions of liquid samples were carried out using wall coated needles prepared from stainless steel capillary columns instead of syringe needles. This micro extraction technique was applied to the analysis of pesticides in water. Important parameters influencing the extraction such as sample velocity, extraction time and also the desorption parameters were investigated and optimized. Automation of this technique was realized using a conventional automatic sampler. Limits of detection were improved using the multiple extraction / desorption technique. Chromatographic data and limits of detection were compared with those obtained by solid phase micro extraction (SPME). Using a needle with a 7 μm film yielded limits of detection varying from 0.001–0.1 μg/L and were in the same range as those resulting from the extraction using a 100 μm polydimethylsiloxane (PDMS) SPME fiber. The main advantages of the needle extraction technique were the significantly higher extraction speed and the practical aspects of a stable steel needle compared to those of a fragile fiber. The extraction speed using a needle with a ¶7 μm film was up to five times higher than the speed of SPME using a 100 μm PDMS fiber. The steel needle could be stressed mechanically in a higher extent than a SPME fiber. Sample volumes and aliquots of liquid media could be handled and moved from one bottle to another using the automatic sampler.