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At least 235 records · Page 13Linked to original sources
PubMed2006

Determination of aflatoxins in high-pigment content samples by matrix solid-phase dispersion and high-performance liquid chromatography.

A fast, efficient, and cost-effective method was developed for the analysis of aflatoxins in farm commodities with high-pigment content, such as chili powder, green bean, and black sesame. The proposed method involved matrix solid-phase dispersion (MSPD) and high-performance liquid chromatography (HPLC)-fluorescence detection (FLD) with postcolumn electrochemical derivatization in a Kobra cell. The MSPD procedure combined the extraction with neutral alumina and pigment cleanup with graphitic carbon black (GCB) in a single step. The recoveries of aflatoxins ranged from 88% to 95% with the relative standard deviations (RSD) less than 6% (n = 6). The limits of detection (LODs) were 0.25 ng/g aflatoxin B1, G1, and 0.10 ng/g aflatoxin B2, G2, respectively. The analytical results obtained by MSPD were compared to those of the immunoaffinity column (IAC) cleanup method. No significant differences were found between the two methods by t-test at the 95% confidence level.

Aflatoxins↗
PubMed1977

Variation in the action spectrum of erythrolabe among deuteranopes.

1. Eight deuteranopes matched a mixture of a monochromatic light on the long wave side of the neutral point and a violet (450 nm) primary to a fixed white as well as a monochromatic light on the short wave side of the neutral point mixed with a red (650 nm) primary, to the same white. For lambda greater than 530 nm, the former set of matches defined the action spectrum of the long wave sensitive foveal cones, and for lambda less than 480 nm, the latter that of the short wave sensitive cones. 2. Individual differences in the former matches were approximately correlated with the respective ratio of the sensitivities of the wave-length of the anomaloscope primaries, in a way that individual differences of the latter were not. 3. Assuming that eye media differences alone account for the differences in long wave sensitive foveal action spectra, the spectral reflectivity of the foveal fundus was predicted for these deuteranopes. The prediction is inconsistent with measurement. 4. Thirteen deuteranopes matched monochromatic spectral lights with a green (535 nm) and a blue (460 nm) primary. The result were analysed by von Kries' method in which differences in matching due to differences in eye media absorption are obviated. The matches of five differed significantly from one another when so analysed. It was concluded that at least one of two action spectra of the foveal cones of every one of these five differed from that of all of the others. 5. The canon that deuteranopes accept normal colour matches was evaluated by confronting a single normal with five deuternopes in the analytical anomaloscope of Baker & Rushton, set in the mode of each of the five in turn. Obvious differences existed between this normal's matches and those of four of five deuteranopes. 6. Explanations for differences in the spectrum of erythrolabe in different deuteranopes are evaluated. The possibilities that all have the identical visual pigment but (a) in cones with different optical funnelling properties or (b) in different optical densities are considered. Preliminary results are not in agreement with the expectations of either of these ideas. 7. It is suggested that the visual pigment in the foveal long wave sensitive cones of different deuternopes (and of different normals) may have different extinction spectra. The idea is consistent with micro-spectrophotometric measurements of rhodopsin in individual rods from different frogs (Bowmaker, Loew & Leibman, 1975).

Color Vision Defects↗
PubMed1994

Nonperturbative methods in HZE propagation.

An analytical solution to the perturbative multiple collision series of a fragmenting HZE ion beam has limited usefulness since the first collision term has several hundred contributions, the second collision term has tens of thousands of contributions, and each successive collision term progresses to unwieldy computational proportions. Our previous work has revealed the multiple collision terms in the straight-ahead approximation to be simple products of a spatially dependent factor times a linear energy-dependent factor of limited domain and unit normalization. The properties of these forms allow the development of the nonperturbative summation of the series to all orders assuming energy-independent nuclear cross sections as matrix products of a scaled Green's function described herein. This nonperturbative Green's function with multiple scattering correction factors compares well with experiments using 670 MeV/u neon-20 ion beams in thick water targets.

Cosmic Radiation↗
PubMedDate not supplied

Efficacy of prolonged (48 h) selective enrichment for the detection of foodborne Salmonella.

The effect of prolonged (48 h) incubation on the productivity of five enrichment-temperature conditions (tetrathionate brilliant green, 35 and 43 degrees C; Muller-Kauffman tetrathionate brilliant green, 43 degrees C; Rappaport-Vassiliadis, 43 degrees C; selenite cystine, 35 degrees C) was compared to homologous results obtained under standard (24 h) conditions of selective enrichment. Of 797 high moisture and 166 low moisture foods tested, 171 (21.5%) and 80 (48.2%), respectively, were found to contain salmonellae by one or more analytical condition. Combined results of the five enrichment conditions after 24 and 48 h of incubation identified 247 (98.4%) and 250 (99.6%) of the 251 contaminated samples identified in this study. Our results are at variance with earlier reports on the greater method sensitivity with extended (greater than or equal to 48 h) periods of selective enrichment. The productivities of individual enrichment conditions after each period of incubation varied markedly where recovery rates with TBG43 and MKTBG43 exceeded that obtained with SC35 and TBG35. Our findings also underline the determinant role of enrichment at an elevated temperature (43 degrees C), and use of multiple enrichment and plating media for the optimal recovery of foodborne Salmonella.

Culture Media↗
PubMedDate not supplied

Capillary gas chromatographic determination of prometryn and its degradation products in parsley.

Residue analysis of the herbicide prometryn (2,4-bis(isopropylamino)-6-methylthio-1,3,5-triazine) is widely known, but an analytical method for determining its metabolities or degradation products in addition to the parent chemical has not yet been reported in the literature. The procedure reported here is for the extraction and determination of prometryn and 2 metabolites, 2-amino-4-isopropylamino-6-methyl-thio-1,3,5-triazine and 2,4-diamino-6-methylthio-1,3,5-triazine, in parsley. Crops were extracted with 2-propanol followed by concentration of the extract and partitioning with a minimum amount of hexane in the presence of a large excess of water to remove most of the green pigment. The aqueous phase was divided into 2 equal halves: (A) One-half portion was partitioned with dichloromethane in the presence of saturated sodium chloride solution, the dichloromethane phase was separated, and the aqueous phase was discarded. The organic solvent was evaporated, and the contents were reconstituted in petroleum ether before prometryn analysis. (B) The other half was made slightly alkaline with ammonium hydroxide solution and was partitioned with ethyl acetate in the presence of saturated sodium chloride solution. The ethyl acetate phase was concentrated, centrifuged to remove any turbidity, and analyzed for the 2 metabolities above. Fused silica capillary gas chromatography (GC) with nitrogen-phosphorus (N-P) detection was used for quantitation. The limit of detection was 0.05 mg/kg for all the compounds examined. Recoveries from fortified parsley samples ranged from 59 to 73% at fortification levels of 0.05 to 1.0 mg/kg.

Biodegradation, Environmental↗
PubMed1999

Determination of a novel bile acid sequestrant in rodent diet by near-infrared spectroscopy.

DMP 504 is a high molecular weight polymer currently under development by The DuPont Merck Pharmaceutical Company as a novel bile acid sequestrant to lower serum cholesterol. To assess its safety, DMP 504 is incorporated into rodent diet for oral administration to rats and mice. An analytical method was developed to determine the accuracy and homogeneity of the blends. Since a physical separation or extraction of DMP 504 from the diet was not feasible, near-infrared spectroscopy (near-IR) was employed. The near-IR method provides accurate and precise results for blends containing 1.5-8.0% of DMP 504. Comparison of results at the 1.5% level with a cholate binding referee method is also presented. Both methods provided equivalent results for the 1.5% level.

Animals↗
PubMed1983

Salivary urea nitrogen as an index to renal function: a test-strip method.

To investigate the feasibility of using salivary urea nitrogen as an index of renal glomerular filtration rate, we developed and applied a new analytical system consisting of a urease-containing test strip and an automatic reflectance spectrometer. The concentrations of urea nitrogen so determined correlate well (r = 0.93) with concentrations in serum. These preliminary data suggest that our method can be used routinely as a simple and reliable means of detecting abnormalities of renal function.

Adolescent↗
PubMed2003

Flame photometric detection inside of a capillary gas chromatography column.

A novel micro-flame photometric detector (FPD) employing a miniature counter-current flame is described. The micro-FPD flame, encompassing a volume of about 30 nL, is operated inside the end of a capillary gas chromatography column (i.e. on-column) or inside of a quartz capillary after the column (i.e. post-column). Either air or oxygen can support a hydrogen flame in the device, although oxygen is far preferable. The detector can be operated for several hours without any observed degradation in performance or flame stability. The optimal gas flows established for the detection of sulfur and phosphorus are in the range of 4 mL min(-1) of oxygen and 9 to 13 mL min(-1) of hydrogen. The fuel-rich micro-FPD flame generates chemiluminescent blue S2* emission for sulfur and green HPO* emission for phosphorus, similar to a conventional FPD. Sulfur response in the micro-FPD is quadratic over nearly 3 orders of magnitude while that of phosphorus is linear over nearly 5 orders of magnitude. The micro-FPD detection limit for sulfur is 1 x 10(-9) g S s(-1), and that of phosphorus is 2 x 10(-10) g P s(-1). The properties established for the initial prototype of the micro-FPD make this counter-current flame method potentially suitable for integration with on-chip gas chromatography or other micro-analytical devices where flame-based detection methods are desirable.

Journal Article↗
PubMed2006

Propagation of mechanical waves in a one-dimensional nonlinear disordered lattice.

The propagation of transverse waves along a string loaded by masses, each of them being fixed to a spring with a quadratic nonlinearity, is studied. After presenting the nonlinear model and stating the equation of propagation into a lattice with discrete nonlinearities and disorder, we propose a perturbation approach to wave propagation in a nonlinear lattice using the Green's function formalism. We show how the nonlinearity acts on the propagation into a disordered lattice. In the low-frequency approximation, an analytical expression of the boundary between the propagative regime and the evanescent one is found. Numerical results are compared to the analytical results and phase diagrams are proposed in the ordered and disordered cases. A behavior of the transmission coefficient is found, on an empirical basis, as a function of the length of the lattice and the localization length in the nonlinear case. Finally, a dynamic approach is developed and the ordered and disordered cases are addressed. This method is based on a finite difference equation and allows the construction of the Poincaré section describing the propagation of the wave into the lattice. This approach distinguishes between the properties of propagation in the lattice in a propagative regime and in an evanescent one.

Journal Article↗
PubMed2000

The central phobic position: a new formulation of the free association method.

The author discusses a particular quality of associative behaviour observed in some borderline patients, and its role in maintaining a central defensive position, clearly discernible in a complex use of the analyst, and a particular functioning of the mind that the author terms phobic. Illustrating his argument with a detailed clinical account of the gradual joining of associative themes in one particular patient, the author both demonstrates the theory underlying his practice and exemplifies the deeper theoretical underpinning of his approach to psychoanalysis. This implies a new formulation of the free association method. By constructing an analytic space in which free association and psychoanalytic listening are possible, the analyst can voice and link previously catastrophic ideas, quite unknown to the patient's consciousness, to help the patient to create meaning and obtain relief from previously dominant but unknown terrors. Concluding his paper, the author links his clinical account both to his ideas on temporality and negativity and to the relationship between oedipal and pre-oedipal elements.

Adult↗
PubMed1997

Rapid detection of 21-hydroxylase deficiency mutations by allele-specific in vitro amplification and capillary zone electrophoresis.

A quick diagnosis of the classic form of 21-hydroxylase deficiency (simple virilizing and salt wasting) is of great importance, especially for prenatal diagnosis and treatment in pregnancies at risk. A method for simultaneous detection of common point mutations in the P450c21 B gene is here proposed by combining a nested PCR amplification refractory mutation system (ARMS) with capillary zone electrophoresis (CZE) in sieving liquid polymers. In the first PCR, B genes are selectively amplified. In the nested reaction, ARMS-detected wild-type and mutated alleles are separately pooled and resolved by CZE. CZE is performed in coated capillaries in the presence of 30 g/L hydroxyethyl cellulose in the background electrolyte for size separation of the DNA analytes. For high-sensitivity detection the electrophoresis buffer contains the fluorescent dye SYBR Green I. Laser-induced fluorescence detection is obtained by excitation at 488 nm and signal collection at 520 nm. Specificity and reproducibility of the protocols were established by using samples from 75 Italian families with 21-hydroxylase deficiency already genotyped by allele-specific oligonucleotide hybridization or direct sequencing. Whereas dot-blot is time consuming because of the high number of hybridizations with radioactive probes, this present protocol is more rapid, giving sufficient separation on CZE after PCR reactions without preconcentration or desalting of samples.

Adrenal Hyperplasia, Congenital↗
PubMed2002

Simultaneous analysis of retinol, beta-carotene and tocopherol levels in serum of Vietnamese populations with different incomes.

In this study, we clarified the status of the fat-soluble vitamins retinol and tocopherol, as well as beta-carotene, as antioxidants in the prevention of cardiovascular disease in middle-aged Vietnamese populations with different incomes. In order to measure simultaneously the serum concentrations of retinol, beta-carotene and tocopherol, we carried out high-performance liquid chromatography analysis with three separate detectors. The analytical method was modified, omitting the saponification process, and used a multi-evaporating system with dry ice. This allowed the analysis to proceed more rapidly, use a small amount of serum (40 microL) and be free of hexane contamination to the environment. The analyses reflected an adequate status of vitamin A (serum retinol = 20 microg/dL), but inadequate status of beta-carotene and vitamin E (serum beta-carotene <40 microg/dL; serum tocopherol < 600 microg/dL) in all three Vietnamese populations. As large numbers of Vietnamese subjects were observed with very low serum concentrations of beta-carotene and tocopherol, higher consumptions of green and yellow vegetables, fruits, vegetable oils and other foods rich in vitamin E are recommended for these Vietnamese populations.

Adult↗
PubMedDate not supplied

The potential of electrospray ionization mass spectrometry for the diagnosis of hemoglobin variants found in newborn screening.

Analytical procedures have been developed for the detection and diagnosis of sickle cell disease in newborn babies by analyzing the hemoglobin extracted from dried blood spots on Guthrie cards using electrospray ionization mass spectrometry (ESI-MS). An essential requirement is the ability to reliably differentiate two globin chains whose molecular weights differ by only 1 Da such as adult hemoglobin (Hb A) and Hb C. This has been achieved by improving the accuracy and precision of the molecular weight determination to a fraction of a dalton. We report the potential of mass spectrometry for screening neonates for these debilitating diseases by presenting results from 147 blood spots that had been characterized by phenotypic methods and which include samples from 20 sickle cell disease, 1 beta-thalassemia major, 57 sickle cell trait, and 39 normal babies. In all cases, the mass spectrometric results agreed with the results obtained using conventional analytical practice with high-performance liquid chromatography (HPLC) and isoelectric focusing (IEF). We show that mass spectrometry is a viable technique for the diagnosis of newborns with sickle cell disease or homozygous beta0-thalassemia.

Anemia, Sickle Cell↗
PubMed1993

Reproduction of correct electrostatic field by charges and dipoles on a closed surface.

A general algorithm based on the Green function theorem has been developed to correctly reproduce electrostatic fields inside a closed space by point charges and point dipoles on the surface surrounding the space. For actual computations, limited numbers of point charges, including charge pairs replacing point dipoles, are enough to approximate the inner fields. As examples, reaction fields were reproduced by the current surface charges and dipoles for the dielectric models, where a monopole, dipole, or quadrupole was individually set at the center in a vacuum sphere surrounded by high dielectric continuum. The potentials due to those reaction fields agree well with the analytical ones. As an application of this method to the analysis of the electronic structure of the active site of a protein, a combination of the continuum dielectric model and ab initio molecular orbital calculation was carried out. Other applications to molecular dynamics and quantum mechanical calculations are also discussed.

Algorithms↗
PubMed2005

On-line coupled extraction and separation using superheated water for the analysis of triazine herbicides in spiked compost samples.

An on-line method, with a purely aqueous mobile phase, has employed linked superheated water extraction and superheated water separation for the analysis of triazine herbicides in spiked compost samples. After the superheated water extraction, a X-Terra solid-phase trap was used to collect and focus the extracted analytes. The trapped analytes were then released by thermal desorption and passed directly to a superheated water chromatographic separation using a PGC column. Two clean-up steps (prior to extraction and separation) were included to remove most of the interfering matrix components. The effects of the sample matrix and the extraction temperatures on the recovery of the triazines were investigated. Despite some thermal degradation of the chloro-triazines during the SWE, the on-line SWE-SWC method was sensitive and rapid. The coupled method could potentially reduce costs and labour and by using only water in every stage is compatible with the concepts of green chemistry.

Chemical Fractionation↗
PubMed1998

Volatile flavour of wine: correlation between instrumental analysis and sensory perception.

The aroma of wine consists of 600 to 800 aroma compounds from which especially those, typical for the variety, are already present in the grapes. There are significant varietal differences between the aromagrams ('fingerprint patterns'). Thus the amount of some flavour compounds ('key substances') shows typical dependence on the variety. Especially monoterpene compounds play an important role in the differentiation of wine varieties. The German white wines can be differentiated into three groups only by quantitative determination of 12 monoterpenes ('terpene profile'). These groups are: 'Riesling type', 'Muscat type' and 'Silvaner-Weissburgunder type'. Such 'terpene profiles' are also useful for the separation of real Riesling wines from others called Riesling (e.g. Welschriesling, Kap Riesling, Emerald Riesling) but not produced from grapes of the variety Riesling. Including further components and by means of statistical methods (discriminant analysis) even the different varieties within the mentioned groups for instance the 'Riesling'-group (e.g. Riesling, Kerner, Ehrenfelser, Bacchus, Müller-Thurgau) can be separated from each other. An analytical characterization of the neutral ('Silvaner-type') grape varieties Silvaner, Ruländer (Pinot gris), Weissburgunder (Pinot blanc) is also possible with about 20 compounds (e.g. monoterpenes, alcohols). Computing at the same time free and glycosidically bound aroma components (monoterpenes, alcohols, norisoprenes) in discriminant analysis the characterization of the neutral grape varieties can be considerably improved. To identify compounds causing 'off-flavours' sniffing technique is the method of choice. The off-flavour is pinpointed during gas chromatographic separation of the complex aroma mixture by effluent sniffing. Once allocated, the chemical nature of the off-flavours is elucidated by spectroscopic methods. Substances contributing to the green pepper taint, the strawberry note, moussiness, corkiness, etc. in wine could be found in this way.

Humans↗
PubMed2001

Production and specificity of mono and polyclonal antibodies against microcystins conjugated through N-methyldehydroalanine.

Microcystins (MCs) are a group of closely related toxic cyclic heptapeptides produced by common cyanobacteria (blue-green algae). Their toxicity is associated with specific inhibition of intracellular protein phosphatases type-1 and type-2A (PP1 and PP2A, respectively). We have developed a battery of antibodies to microcystins using chemical modification (aminoethylation) of one of its core amino acids, N-methyl-dehydroalanine. The developed antibodies displayed different reactivities to closely related MCs. Selected monoclonal antibodies were used for quantitative competitive ELISA assays. The analytical sensitivity of these assays was up to 1 ng/ml. Comparison of the developed ELISA tests with HPLC-based measurements of MCs in laboratory and field samples showed a good correspondence between the results yielded by these two methods. The antibodies developed by this technique provide the means for developing extremely sensitive and specific analytical assays for direct measurement of toxins in cyanobacterial or water samples.

Alanine↗
PubMed1999

Chiral discrimination using an immunosensor.

Based on the stereoselectivity of immunoglobulins, we have developed a new chiral sensor for the detection of low-molecular-weight analytes. Using surface plasmon resonance detection, enantiomers of free, underivatized alpha-amino acids can be monitored in a competitive assay by their interaction with antibodies specific for the chiral center of this class of substances. The sensitivity to the minor enantiomer in nonracemic mixtures exceeds currently available methods; therefore, such immunosensors can readily detect traces of enantiomeric impurities and are attractive for a range of applications in science and industry.

Amino Acids↗