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At least 595 records · Page 33Linked to original sources

PubMed1985

Improvement of ion chromatography with ultraviolet photometric detection and comparison with conductivity detection for the determination of serum cations.

Studies were made of the analytical conditions required for indirect photometric ion chromatography using ultraviolet photometric detection (UV method) for the determination of serum cations following a previously developed serum pre-treatment. The sensitivities of the conductivity detection (CD) and UV methods and the amounts of serum cations determined by both methods were compared. Attempts to improve the sensitivity of the conventional UV method are reported. It was found that the mobile phase previously reported by Small and Miller showed no quantitative response when more than 4 mM copper(II) sulphate pentahydrate was used. As a result, there was no significant difference in the amounts of serum cations shown by the CD and UV methods. However, by adding 0.5-5 mM cobalt(II) sulphate heptahydrate, nickel(II) sulphate hexahydrate, zinc(II) sulphate heptahydrate or cobalt(II) diammonium sulphate hexahydrate to 0.5-1.5 mM copper(II) sulphate pentahydrate, higher sensitivity and a quantitative response were attained.

Calcium↗

PubMed2000

Determination of estramustine phosphate and its metabolites estromustine, estramustine, estrone and estradiol in human plasma by liquid chromatography with fluorescence detection and gas chromatography with nitrogen-phosphorus and mass spectrometric detection.

Bioanalytical methods for the determination of estramustine phosphate by liquid chromatography and its four main metabolites estromustine, estramustine, estrone and estradiol by gas chromatography are described. For the estramustine phosphate assay the plasma was purified by protein precipitation followed by a C18 solid-phase extraction. For the metabolite assay the plasma samples were purified by a C18 solid-phase and liquid-liquid extraction procedure and derivatised by silanization. Thereafter, estramustine and estromustine were quantified by gas chromatography with nitrogen-phosphorus detection and estradiol and estrone were quantified by gas chromatography with selected ion monitoring. The methods were validated with respect to linearity, selectivity, precision, accuracy, limit of quantitation, limit of detection, recovery and stability. The limit of quantitation was 2.3 micromol/l for estramustine phosphate, 30 nmol/l for estromustine and estramustine, 12 nmol/l for estrone and 8 nmol/l for estradiol. The results showed good precision and accuracy for estramustine phosphate and the four metabolites. The intermediate precision was 6.2-13.5% (C.V.) and the accuracy was 91.8-103.9%.

Antineoplastic Agents, Alkylating↗

PubMed2003

Rapid detection of pulmonary tuberculosis using the BDProbeTEC ET Mycobacterium tuberculosis Complex Direct Detection Assay (DTB).

The ability to rapidly detect tubercle bacilli in respiratory secretions was determined for the BDProbeTEC ET Mycobacterium tuberculosis Complex Direct Detection Assay in comparison with the acid-fast smear (AFS). A total of 267 respiratory specimens obtained from 89 patients were evaluated. The DTB assay was positive in 70 of 78 culture positive specimens (89.7%) and 12 of 177 culture negative specimens (6.8%). The AFS was positive in 33 of 78 culture positive specimens (42.3%) and 3 of 186 culture negative specimens (1.6%). The sensitivity, specificity, positive predictive value, and negative predictive value of DTB assay were 89.7%, 93.7%, 85.4%, and 95.7%, respectively. The sensitivity of a single DBT (74.4%) was 2.1-times greater than three AFS (35.9%). The greater cost of the DTB assay compared to the AFS was compensated by its valuable information for the diagnosis and control of tuberculosis. These results demonstrated the clinical usefulness of the DTB assay for the rapid diagnosis of tuberculosis in respiratory specimens.

Bacteriological Techniques↗

PubMedDate not supplied

Monoclonal antibody detection of 2-acetyl-aminofluorene-modified DNA probes for the specific detection of nucleic acids in hybridization procedures.

We describe the use of acetoxy-acetyl-aminofluorene-modified DNA probes in several hybridization techniques. Hybrids were detected with the help of a monoclonal antibody raised against AAF-guanosine and a second antibody coupled to an enzyme. The sensitivity achieved with AAF-DNA probes routinely detected 0.25 pg DNA bound to a filter. AAF-DNA probes were highly stable and were prepared by simple chemical modification of DNA. Their use as a possible diagnostic tool is discussed.

2-Acetylaminofluorene↗

PubMed1998

Development of a new immunosensor for pesticide detection: a disposable system with liposome-enhancement and amperometric detection.

The development of a disposable amperometric immunomigration sensor for the detection of triazine pesticides in real samples is presented. Thick film electrodes printed on PVC were used as strip-type transducers. Monoclonal antibodies against atrazine and terbutylazine served as biorecognition element. For the generation and amplification of the signal, hapten-tagged liposomes entrapping ascorbic acid as a marker molecule were chosen. A capillary gap and a wicking filter membrane strip served as migration zone. For signal detection on a graphite electrode, liposomes were lysed by Triton X-100 and the released ascorbic acid was quantified at a potential of + 300 mV vs printed Ag/AgCl. Signal response time was 1-3 min, and sensitivity of measurements in tap water was below 1 microgram l-1 of atrazine and terbutylazine. Atrazine determinations in soil extracts correlated well with standard procedures based on ELISA and HPLC.

Biosensing Techniques↗

PubMed2001

Searches for new interstellar molecules, including a tentative detection of aziridine and a possible detection of propenal.

Rotational spectroscopy at millimeter wavelengths is a powerful means of investigating the chemistry of dense interstellar clouds. These regions can exhibit an interesting complement of gas phase molecules, including relatively complex organics. Here we report the tentative first astronomical detection of aziridine (ethylenimine), the possible detection of propenal (acrolein), and upper limits on the abundances of cyclopropenone, furan, hydroxyethanal (glycolaldehyde), thiohydroxylamine (NH2SH), and ethenol (vinyl alcohol) in various interstellar clouds.

Acetaldehyde↗

PubMed1992

The ENZYMEBA test: detection of intestinal Entamoeba histolytica infection by immuno-enzymatic detection of histolysain.

We describe a new, improved test for the detection of intestinal infection by Entamoeba histolytica. The test depends upon immunoadsorption of the E. histolytica cysteine proteinase, histolysain, from faecal samples, and subsequent visual detection of the enzyme by a colour reaction. With samples from 200 volunteers, results agreed closely with those obtained by the conventional microscopic technique, and there were no false positive reactions with samples containing other parasites. The test is suitable for use either in the laboratory or in the field.

Amebicides↗

PubMed1999

Evaluation of antigen detection and antibody detection tests for Trypanosoma evansi infections of buffaloes in Indonesia.

Two Ag-ELISAs, an IgG-specific antibody detection ELISA (IgG ELISA) and a card agglutination test (CATT) for the detection of Trypanasoma evansi infections in buffaloes in Indonesia, were compared. Diagnostic sensitivity estimates were obtained by testing sera from 139 Indonesian buffaloes which had been found to be infected by parasitological tests. Diagnostic specificity was estimated by testing sera from 263 buffaloes living in Australia. Response-operating characteristic curves were constructed, and optimal ELISA cut-off values, which minimized the number of false-negative and false-positive results, were chosen. The IgG ELISA had the highest sensitivity (89%) and the CATT had the highest specificity (100%). There was a significant difference between the sensitivities (71 and 81%), but not between the specificities (75 and 78%), of the two Ag-ELISAs. The four tests were further compared by calculation of post-test probabilities of infection for positive and negative test results using a range of prevalence values, and likelihood ratios. The results suggested that the CATT was the best test to 'rule-in' infection (i.e. the highest probability of infection in test-positive animals) and the IgG ELISA was the best test to 'rule-out' infection (i.e. the lowest probability of infection in test-negative animals).

Agglutination Tests↗

PubMed2003

Improving the detection limit of anion-selective electrodes: an iodide-selective membrane with a nanomolar detection limit.

The lower detection limit and the selectivity behavior of anion-selective electrodes (ISEs) are improved by using optimized inner solutions and membrane compositions. With a membrane based on the recently described ionophore [9]mercuracarborand-3, a detection limit of 2 x 10(-9) M has been achieved for iodide. Nevertheless, the improvements are less pronounced than in the case of cation ISEs. This is mainly due to the fact that so far no anion ISE is known with the extremely high selectivities of cation ISEs. If the membrane does not contain an ionophore, leaching of the ion exchanger from the membrane into the sample is also a relevant limiting factor except for ion exchangers of very high lipophilicity.

Anions↗

PubMed1999

Ultrasensitive detection of closely related angiotensin I peptides using capillary electrophoresis with near-infrared laser-induced fluorescence detection.

A novel near-infrared (NIR) fluorescent dye (NN382, LICOR, Inc.) was evaluated as an ultrasensitive peptide-labeling reagent for use with capillary electrophoresis (CE). Six angiotensin I (Ang-I) variants were selected as model peptides for the derivatization and separation studies. The closely related decapeptides were labeled with the NIR dye, separated using CE, and detected by NIR laser-induced fluorescence. Derivatization of the peptides was achieved under aqueous conditions using 2.5-500 pmol of Ang-I in a 50-microL sample (5 x 10(-8)-1 x 10(-5)M), and between 1.3 and 254 amol of the labeled peptides were injected on column. The fluorescence response was linear over a 200-fold range (correlation r > or = 0.9986). The limit of detection (SNR = 3, signal/RMS noise) ranged from 100 to 300 zmol, for the six Ang-I variants. Four of six peptides were resolved from each other and excess dye using capillary zone electrophoresis with a simple 50 mM phosphate run buffer, pH 7.2. Two pairs of coeluting peptides were successfully resolved using micellar electrokinetic chromatography with a nonionic surfactant, Triton X-100. The NIR amine-labeling reagent NN382 is a viable alternative to using visible fluorophores for CE methods requiring high sensitivity.

Amino Acid Sequence↗

PubMed2001

Detection of disulfide bonds in bovine brain tubulin and their role in protein folding and microtubule assembly in vitro: a novel disulfide detection approach.

Cysteine residues in tubulin are actively involved in regulating ligand interactions and microtubule formation both in vivo and in vitro. These cysteine residues are sensitive reporters in determining the conformation of tubulin. Although some of the cysteines are critical in modulating drug binding and microtubule assembly, it is not clear how many of these normally exist as disulfides. The controversy regarding the disulfide bonds led us to develop a disulfide detection assay to reexamine the presence of the disulfide linkages in purified alphabeta tubulin and explore their possible biological functions in vitro. The accessible cysteine residues in alphabeta tubulin were alkylated with an excess of iodoacetamide to prevent artifactual generation of disulfide linkages in tubulin. After removal of excess iodoacetamide, tubulin was unfolded in 8 M urea. Half of the unfolded tubulin was treated with dithiothreitol to reduce any disulfide bonds present. The aliquots were then treated with iodo[(14)C]acetamide and the incorporation of radioactivity was measured. We also used the same approach to detect the disulfide linkages in the tubulin in a whole-cell extract. We found in both cases that the samples which were not treated with dithiothreitol had little or no incorporation of iodo[(14)C]acetamide, while the others that were treated with dithiothreitol had significant amounts of (14)C incorporation into tubulin. Moreover, the reduction of the disulfide linkages in tubulin resulted in inhibition of microtubule assembly (29-54%) and markedly affected refolding of the tubulin from both an intermediate and a completely unfolded state. All these data therefore suggest that tubulin has intrachain disulfide bonds in the alpha- and beta-subunits and that these disulfides assist in correct refolding of tubulin from the intermediate unfolded state or help to recover the hydrophobic domains from the completely unfolded state. These disulfides also regulate microtubule assembly and the stability of tubulin in vitro. Our results suggest that tubulin disulfides may play a role in tubulin folding and that thiol-disulfide exchange in tubulin could be a key regulator in microtubule assembly and dynamics of tubulin in vivo.

Ammonium Sulfate↗

PubMed2000

Data evaluation in high-performance liquid chromatography-diode-array detection-fluorescence detection by information theory

The concepts of information theory were applied to the high-performance liquid chromatography (HPLC) technique, with diode-array (DAD) and/or fluorescence (FLD) detections. The information amount for a complete analysis can be computed as a function of analytical parameters, such as the number of analytes, level of concentration, and standard deviation of determinations. By means of the proposed method, the information content of a qualitative and quantitative analysis accomplished by HPLC-DAD-FLD was estimated, and sensitivity was optimized taking into account a maximum information content, while the detection limit was estimated considering that at this level of concentration the information content approaches zero.

Journal Article↗

PubMed2002

Optimization of method for detecting and characterizing NOM by HPLC-size exclusion chromatography with UV and on-line DOC detection.

High-performance liquid chromatography (HPLC)-size exclusion chromatography (SEC) with ultraviolet absorbance (UVA) and on-line dissolved organic carbon (DOC) detectors has been adapted and optimized under various conditions. An enhanced HPSEC-UVA system employing a modified commercially available DOC detector provides a better understanding of the qualitative and quantitative natural organic matter (NOM) properties in water samples by detecting aromatic and nonaromatic fractions of NOM as a function of molecular weight (MW). The most critical merit of this system is that the DOC detector is readily available and widely used. With only a few modifications, a commercially available TOC analyzer served as a DOC detector, integrated with the HPSEC to measure DOC along with UVA, and provided a specific UVA (SUVA) chromatograph that is useful information for drinking water plant design and operation. Without preconcentration, samples can be analyzed with a small amount of sample, with a DOC detection limit as low as 0.1 mg/L (as DOC).

Calibration↗

PubMed2005

A microarray platform for parallel detection of five transgenic events in foods: a combined polymerase chain reaction-ligation detection reaction-universal array method.

We recently developed a multiplex polymerase chain reaction (PCR) system for the simultaneous detection of four transgenic maize (MON810, Bt176, Bt11, and GA21), one transgenic soybean (Roundup Ready), and two control genes (lectin and zein). Because PCR can lead to ambiguous interpretations due to low specificity, we have developed the ligation detection reaction (LDR) combined with a universal array as a molecular tool to confirm results of PCR analysis. Here, we describe the PCR-LDR-universal array procedure and demonstrate its specificity in revealing the presence of transgenic DNA in experimental samples, raw materials, and commercial foodstuffs.

Base Sequence↗

PubMed2006

Multiresidue method for determination of 35 pesticides in virgin olive oil by using liquid-liquid extraction techniques coupled with solid-phase extraction clean up and gas chromatography with nitrogen phosphorus detection and electron capture detection.

A method for the multiresidue determination of 35 pesticides (30 insecticides and five herbicides) in olive oil by gas chromatography (GC) is described. Three liquid-liquid extraction (LLE) procedures based on (i) partition of pesticides between acetonitrile (ACN) and oil solution in n-hexane, (ii) partition of pesticides between saturated ACN with n-hexane and oil solution in n-hexane saturated with ACN, and (iii) partition of pesticides between ACN and oil were tested for the optimization of the highest pesticide recoveries with the lowest oil residue in the final extracts. Experimental tests were preformed in order to study the efficiency of different clean up procedures with N-Alumina, Florisil, C18, and ENVI-Carb solid-phase extraction (SPE) cartridges for the compounds analyzed by GC-nitrogen phosphorus detection. A second step of clean up was also performed for the compounds analyzed by GC-electron capture detection (ECD), by using phenyl-bonded silica (Ph), diol-bonded silica (Diol), cyanopropyl-bonded silica (CN), and amino propyl-bonded silica (NH2) SPE cartridges. LLE of the oil solution in hexane with ACN followed by an ENVI-Carb SPE clean up of the extract gave the best results for all target compounds. The ACN extract was additionally cleaned through a Diol-SPE cartridge for the determination of pesticides analyzed mainly by GC-ECD. Pesticide recoveries form virgin olive oil spiked with 20, 100, and 500 microg/kg concentrations of pesticides ranged from 70.9 to 107.4%. The proposed method featured good sensitivity, pesticide quantification limits were low enough, and the precision, expressed as relative standard deviation, ranged from 2.4 to 12.0%. The proposed method was applied successfully for the residue determination of the selected pesticides in commercial olive oil samples.

Chromatography, Gas↗

PubMed2006

Equal performance of TaqMan, MGB, molecular beacon, and SYBR green-based detection assays in detection and quantification of roundup ready soybean.

We have tested and compared the performance of 12 different assays representing four different real-time polymerase chain reaction (PCR) chemistries in the context of genetically modified organism detection. Several different molecular beacon, SYBR Green, TaqMan, and MGB assays were designed for the event specific detection and quantification of the 3' integration junction of GTS 40-3-2 (Roundup Ready) soybean. Sensitivity as well as robustness in the presence of background DNA were tested. None of the PCR-based approaches appeared to be significantly better than any of the other, but the molecular beacon assays had the lowest efficiency and also seemed more sensitive to changes in experimental setup.

DNA, Plant↗

PubMed2006

Detection of noncovalent complexes in biological samples by intensity fading and high-mass detection MALDI-TOF mass spectrometry.

Matrix-assisted laser desorption/ionization (MALDI) mass spectrometry has not yet contributed widely to the study of intact noncovalent biomolecular complexes, because MALDI is known to cause dissociation of the interaction partners and induce formation of nonspecific aggregates. Here, we present a new strategy to circumvent this problem. It is based on intensity fading (in the low m/z range) and high-mass detection MALDI mass spectrometry (MS), using a cryodetector (in the high m/z range), with and without chemical cross-linking of the interaction partners. The study focuses on noncovalent interactions between the human enzyme carboxypeptidase A (hCPA) and three protease inhibitors (PCI, TCI, and LCI) present in heterogeneous mixtures of other nonbinding molecules derived from a biological source, an extract from leech (Hirudo medicinalis). Another example involves an extract of the sea anemone Stichodactyla helianthus, which is used without previous fractionation to detect the specific complex between the enzyme trypsin and the endogenous SphI-1 inhibitor. The results give insight into the mechanism of intensity fading MS and demonstrate that the specificity of binding is greatly favored when the overall concentrations of the analytes (nonbinding molecules, protease inhibitor and target enzyme) present in a biological sample of interest are kept at low concentrations, in the sub-micromolar range. Higher concentrations may lead to unspecific interactions and the formation of aggregates both during the MALDI process and during reaction with the cross-linking reagents. This strategy is expected to advance the field of high-throughput affinity-based approaches, by taking advantage of a new generation of high mass detectors for MALDI-TOF instruments.

Animals↗

PubMed1997

Detection and characterization of two major ethylated deoxyguanosine adducts by high performance liquid chromatography, electrospray mass spectrometry, and 32P-postlabeling. Development of an approach for detection of phosphotriesters.

Postlabeling can be one of the most sensitive methods for the measurement of DNA adducts. However, for the determination of alkylated adducts, essential requirements are standards which must be fully chemically characterized. In order to develop a postlabeling assay for monitoring exposure to genotoxic ethylating agents, the reaction of diethyl sulfate with 2'-deoxynucleoside 3'- and 5'-monophosphates was examined. The adducts generated were fully characterized using HPLC, electrospray tandem mass spectrometry, UV, and postlabeling. The major product was the phosphodiester derived from alkylation of the phosphate, and alkylation of the base occurred to a lesser extent. The phosphodiester standard, 2'-deoxyguanosine 3'-(mono-O-ethyl phosphate) (3'Et-pdG), was used to develop a postlabeling assay for the detection of this adduct in DNA samples. Since alkylated phosphodiesters in DNA are not susceptible to the actions of micrococcal nuclease and calf spleen phosphodiesterase, they can be obtained as alkylated phosphodiester dinucleosides from DNA. Nuclease P1 was used as enhancement step which allowed the separation of these adducted phosphotriesters from the unmodified nucleotides by HPLC. Subsequent hydrolysis of the phosphotriester dinucleosides in alkali yielded phosphodiesters, including 3'Et-pdG, which was efficiently postlabeled. This approach was shown to be capable of detecting this adduct in liver DNA from mice treated intraperitoneally with N-nitrosodiethylamine.

Adenosine Triphosphate↗