Showing papers on "Detection limit published in 1991"

Electrochemiluminescence detection for development of immunoassays and DNA probe assays for clinical diagnostics.

Abstract: Electrochemiluminescence (ECL) has been developed as a highly sensitive process in which reactive species are generated from stable precursors (i.e., the ECL-active label) at the surface of an electrode. This new technology has many distinct advantages over other detection systems: no radioisotopes are used; detection limits for label are extremely low (200 fmol/L); the dynamic range for label quantification extends over six orders of magnitude; the labels are extremely stable compared with those of most other chemiluminescent systems; the labels, small molecules (approximately 1000 Da), can be used to label haptens or large molecules, and multiple labels can be coupled to proteins or oligonucleotides without affecting immunoreactivity, solubility, or ability to hybridize; because the chemiluminescence is initiated electrochemically, selectivity of bound and unbound fractions can be based on the ability of labeled species to access the electrode surface, so that both separation and nonseparation assays can be set up; and measurement is simple and rapid, requiring only a few seconds. We illustrate ECL in nonseparation immunoassays for digoxin and thyrotropin and in separation immunoassays for carcinoembryonic antigen and alpha-fetoprotein. The application of ECL for detection of polymerase chain reaction products is described and exemplified by quantifying the HIV1 gag gene.

Integrated fluid handling system for biomolecular interaction analysis.

Abstract: An integrated fluid handling system used for multichannel biomolecular interaction analysis is described. Reactions between biological molecules are monitored in real time by measuring changes in the angular position where surface plasmon resonance occurs at a biospecific active surface. The adsorption efficiency of the analyte onto the biospecific active surface is up to approximately 3%, due to the low channel height, 50 microns, in the flow cell. When a large part of the total biospecific active surface for surface plasmon resonance probing (approximately 0.15 mm2) is used, the sensitivity is high. Sample sizes in the order of 1-50 microL can be injected. The sample zone dispersion is minimized by the low dead volume in the system (approximately 0.4 microL) accomplished by using integrated sample loops and thin conduits. An asset of this integration is the low reagent consumption. The sensor chip with the biospecific active surface is reusable and easily exchanged. Experimental results obtained with a theophylline monoclonal antibody as the analyte are compared with a theoretical model. The standard deviation for the repeatability is approximately 5% typically with 50 microL of 250 pM analyte, and the assay time is 10 min. The detection limit is approximately 10 pg of the analyte on the probed spot of the surface. Possible improvements of the sensitivity and detection limit are discussed.

Determination of subnanomolar levels of iron(II) and total dissolved iron in seawater by flow injection and analysis with chemiluminescence detection

Abstract: The light is emitted by the reaction of brillant sulfoflavin with hydrogen peroxide and Fe(II) in a neutral medium. A cation-exchange column is used to preconcentrate the iron from seawater. The detection limit was 0.45 nmol/L when 4.4 mL of sample was passed through the column

Multiwavelength fluorescence detection for DNA sequencing using capillary electrophoresis

Abstract: Multiwavelength detection of laser induced fluorescence for dideoxynucleotide DNA sequencing with four different fluorophores and separation by capillary gel electrophoresis is described. A cryogenically cooled, low readout noise, 2-dimensional charge-coupled device is used as a detector for the on-line, on-column recording of emission spectra. The detection system has no moving parts and provides wavelength selectivity on a single detector device. The detection limit of fluorescently labeled oligonucleotides meets the high sensitivity requirements for capillary DNA sequencing largely due to the efficient operation of the CCD detector with a 94% duty cycle. Using the condition number as a selectivity criterion, multiwavelength detection provides better analytical selectivity than detection with four bandpass filters. Monte Carlo studies and analytical estimates show that base assignment errors are reduced with peak identification based on entire emission spectra. High-speed separation of sequencing samples and the treatment of the 2-dimensional electropherogram data is presented. Comparing the DNA sequence of a sample separated by slab gel electrophoresis with sequence from capillary gel electrophoresis and multiwavelength detection we find no significant difference in the amount of error attributable to the instrumentation.

Wood Sugar Analysis by Anion Chromatography

Abstract: Two wood and two wood-pulp samples were hydrolyzed in triplicate in sulfuric acid. The sugar monomers were separated by anion-exchange chromatography and quantitatively measured with a pulsed amperometric detector. A portion of each sugar solution was neutralized with sodium hydroxide and analyzed for the sugar content in the same manner as the unneutralized hydrolysates. The results from analyses of acid and neutral solutions were consistent. Detection limits for the individual sugars ranged from 25 ng for arabinose to 13 ng for glucose using a signal to noise ratio of three for the detection limit.

Peroxyoxalate Chemiluminescence Assay of Hydrogen Peroxide and Glucose Using 2,4,6,8-Tetrathiomorpholinopyrimido(5,4-d)pyrimidine as a Fluorescent Component.

Abstract: Peroxyoxalate chemiluminescence (CL) assay of hydrogen peroxide (H2O2) or glucose was developed by using 2, 4, 6, 8-tetrathiomorpholinopyrimido[5, 4-d]pyrimidine as a fluorescent component and bis(2, 4, 6-trichlorophenyl)oxalate (TCPO) as an oxalate. Linear relationships between CL intensity and final concentration of H2O2 from 10-8 to 10-4M were obtained. The detection limit at the ratio of CL intensities for sample and blank (S/B) of 3 was 10nM. The precision for five replicate measurements at 10-5 and 10-6M of H2O2 were 17.6 and 15.7% of relative standard deviations, respectively. α-D-Glucose was transformed to β-D-glucose with mutarotase and converted to H2O2 and D-gluconic acid with glucose oxidase, which was detected by using peroxyoxalate CL reaction. A linear calibration graph was obtained up to 1.5×10-4M of glucose solution. The method was applied to the assay of glucose in human serum. The recovery was 98.2% (n=4). The method correlated well with the conventional colorimetric method (r=0.968).

Assay for the major dog allergen, Can f I: investigation of house dust samples and commercial dog extracts.

Abstract: Monospecific rabbit antibodies were used to develop a sensitive two-site enzyme immunoassay to measure a major dog hair and dander allergen, Can f I. This Can f I assay demonstrated no reaction with 17 heterologous allergen sources, including dog albumin, cat, guinea pig, and horse. Analysis of serial dilutions of purified Can f I and the international standard for dog was parallel. The assay was considered specific for Can f I with a lower limit of detection at 0.03 μg/ml. Total imprecision was from 2% to 6%. Commercial dog extracts for specific immunotherapy contained from 0.7 to 290 μg of Can f I per milliliter. The assay was used to measure Can f I in 136 house dust samples collected from 103 homes across the United States. Concentration of the dog allergen was expressed as micrograms of Can f I per gram of dust. Prevalence of Can f I in the dust samples ranged from Can f I were parallel to the standard. The median Can f I value for homes with a dog in residence was 120 μg/gm, and for homes with no dog, 3 μ/gm. With few exceptions, homes with no dog in residence had Can f I assay will provide useful information for assessing commercial extracts as well as monitoring dog-allergen exposure and allergen-control methods.

Simultaneous determination of inorganic arsenic and antimony species in natural waters using selective hydride generation with gas chromatography/photoionization detection

Abstract: A method for the simultaneous determination of As(III)+Sb(III) and As(III+V)+Sb(III+V) has been developed that uses selective hydride generation, liquid nitrogen cooled trapping, and gas chromatography/photoionization detection. The detection limit for arsenic is 10 pmol/L, while that for antimony is 3.3 pmol/L; precision (as relative standard deviation) for both elements is better than 3%

Flame atomic absorption spectrometric determination of lead in biological samples using a flow injection system with on-line preconcentration by coprecipitation without filtration

Abstract: A procedure for the coprecipitation of lead in the presence of high concentrations of iron, originally described as a batch process, was modified and adapted to on-line preconcentration using a flow injection system for flame atomic absorption spectrometry. Lead was coprecipitated quantitatively with the iron(II)–hexahydroazepinium hexahydroazepin-1-ylformate (hexamethyleneammonium hexamethylenedithiocarbamate) complex and collected in a knotted reactor made of Microline tubing (150 cm × 0.5 mm i.d.) without using a filter. The precipitate was dissolved in isobutyl methyl ketone and introduced directly into the nebulizer–burner system of an atomic absorption spectrometer. An enrichment factor of 20 and an enhancement factor of 66 were obtained for a coprecipitation time of 30 s, resulting in a sampling frequency of 90 h–1. A detection limit (3σ) of 2 µg l–1 in the sample solution was obtained and the precision at the 200 µg l–1 level was 2.7% relative standard deviation (n= 12). Up to 250 mg l–1 of iron in the sample solution could be tolerated without causing any significant decrease in the lead signal. The results obtained for the determination of lead in reference materials (blood and bovine liver) demonstrate the applicability of the procedure to the analysis of biological materials.

Liquid-chromatographic determination of nicotine and cotinine in urine from passive smokers: comparison with gas chromatography with a nitrogen-specific detector.

Abstract: We describe a simple, sensitive, and specific high-performance liquid-chromatographic method with ultraviolet detection (256 nm) for the simultaneous analysis of nicotine and cotinine in urine of passive smokers. The analytes are extracted and purified from the complex and impure matrix in two stages; first, by liquid-liquid extraction and followed by solid-phase extraction (C2 column). We used a "DB" C8 5-microns-particle column (25 x 0.46 cm) and a mobile phase of phosphate-citrate buffer and acetonitrile (91:9 by vol) containing 5 mL of triethylamine and 600 mg of heptanesulfonate per liter, adjusted to pH 4.4, to separate the compounds. Two internal standards (2-phenylimidazole and N-ethylnorcotinine) were used. The detection limit of the HPLC assay was less than 1 microgram/L for both analytes. The average interassay CV for nicotine was 7.6%, for cotinine 6.5%, in the concentration range 0-60 micrograms/L. The mean analytical recovery of nicotine with respect to the internal standard N-ethylnorcotinine was 102% and that for cotinine was 99%; the mean absolute recoveries of the compounds were as follows: nicotine 85%, cotinine 87%, and N-ethylnorcotinine 87%. To compare the HPLC assay results of 20 samples with the more-sensitive in-laboratory gas-chromatographic method with a nitrogen-phosphorus detector, we used both N-ethylnornicotine and N-ethylnorcotinine as internal standards. The mean correlation coefficient for nicotine values between the two methods was 0.934; for cotinine, 0.987.

Nondetects, Detection Limits, and the Probability of Detection

Abstract: When chemists cannot quantify the concentration in a field sample, they report nondetect instead of a numerical measurement. A data analyst faced with environmental data containing nondetects might assume that all nondetects are zeros, all nondetects are smaller than the smallest detect (numerical measurement), or, if a detection limit is reported, that all nondetects are below the detection limit. This article shows that these assumptions can be incorrect and suggests better alternatives. The measurements that are likely to be reported as nondetect can be described by a new concept, the probability of acceptance, where acceptance means that a measurement passes the requirements for being reported as a detect. The 90th percentile of the probability of acceptance curve is a reasonable upper bound or censoring limit for a measurement reported as nondetect. The probability of acceptance also suggests the complexity of the data analysis task. For example, assuming that all nondetects are smaller than...

Lead speciation by HPLC-ICP-AES and HPLC-ICP-MS.

Abstract: Speciation of inorganic lead (Pb2+) and several trialkyllead species (trimethyllead chloride [TML], triethyllead chloride [TEL], and triphenyllead chloride [TPhL]) is investigated using high-performance liquid chromatography (HPLC) with detection by both inductively coupled plasma emission spectroscopy (ICP-AES), and inductively coupled plasma mass spectrometry (ICP-MS). Reversed-phase, ion-pairing, and ion-exchange HPLC modes are studied. Optimal chromatographic conditions for ICP-AES detection include a reversed-phase separation utilizing a step gradient from 10 to 70% methanol. However, the gradient has been found to destabilize the plasma when using ICP-MS detection. An isocratic separation with a 30% methanol mobile phase has been found to be the best compromise between plasma stability and chromatographic resolution. Detection limits using ICP-MS detection are 3 orders of magnitude improved over ICP-AES detection.