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Results for “Green analytical method”

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At least 19 recordsLinked to original sources
PubMed2026

Vortex-assisted liquid-liquid microextraction based on natural deep eutectic solvents for the determination of pyrethroid pesticides in urine.

A novel, facile, and environmentally friendly analytical method was developed based on vortex-assisted liquid-liquid microextraction and high-performance liquid chromatography with diode-array detection for detecting pyrethroid pesticides (PPs) in urine. Natural deep eutectic solvents (NADESs) were prepared using plant essential oil-derived monoterpenoids (thymol, carvacrol, and menthol) combined with aromatic primary alcohols (benzyl alcohol, phenethyl alcohol, and phenylpropyl alcohol) as hydrogen bond donors and acceptors. These solvents served as environmentally benign extraction media, thereby avoiding the use of conventional volatile, toxic organic solvents. NADESs are naturally derived, easy to prepare, biodegradable, and environmentally friendly solvents. Hydrophobic and π-π interactions between the NADESs and PPs may contribute to enhancing the affinity of PPs toward the NADESs phase. Vortex technology, accelerating mass transfer between the sample and extractant phases, enables fast extraction of PPs. Under optimized conditions, the method achieved a low detection limit (0.002 mg L-1), satisfactory precision with relative standard deviations (0.3%-2.4%), and acceptable recovery (80.7%-86.2%). The method demonstrated excellent performance in urine analysis and was feasible as a facile and green strategy for monitoring the content of PPs in biological matrices and assessing exposure risk.

Liquid Phase Microextraction↗
PubMed2001

Determination of UV-filters in sunscreens by HPLC.

Simultaneous determination of six internationally authorised organic UV-filters in sunscreen formulations was performed by HPLC with UV spectrophotometric detection. The filters determined were: sulisobenzone, oxybenzone, octyl dimethyl PABA, octyl methoxycinnamate, octyl salicylate and homosalate. A C18 stationary phase and a mobile phase of ethanol water acetic acid (70:29.5:0.5) were used with a flow rate of 0.5 mL/min. UV measurements were carried out at 313 nm. The time required for the analysis was 25 min and the limits of detection were between 0.2 and 2 mg/L, except for sulisobenzone, which gave a limit of detection of 20 mg/L. The procedure proposed provides an accurate, fast and green analytical method, that does not involve toxic organic solvents.

Chromatography, High Pressure Liquid↗
PubMed2001

Determination of the UV filters worldwide authorised in sunscreens by high-performance liquid chromatography. Use of cyclodextrins as mobile phase modifier.

Simultaneous determination of organic UV filters worldwide authorised in sunscreen formulations was performed by HPLC with UV spectrophotometric detection. The filters determined were: benzophenone-4, benzophenone-3, butyl methoxydibenzoylmethane, octyl dimethyl PABA, octyl methoxycinnamate, homosalate and octyl salicylate. A C18 stationary phase and an isocratic mobile phase of ethanol-water-acetic acid (70:29.5:0.5) containing 65.4 mM of hydroxypropyl-beta-cyclodextrin, were used with a flow-rate of 0.6 ml/min. UV measurements were carried out at 313 nm. The time required for the analysis was 20 min and the limits of detection were between 1.5 and 2.3 mg/l. The procedure proposed provides a green analytical method with a basic instrumental configuration, it is fast and accurate and does not involve highly toxic organic solvents.

Chromatography, High Pressure Liquid↗
PubMed2001

[Study on the analytical methods of catechins in tea and green tea polyphenol samples by high performance liquid chromatography].

Hypersil BDS C18 and Zorbax SB C18, suitable to separate simultaneously seven kinds of catechins and caffeine, were screened out from seven brands of reversed-phase columns. Mobile phase was a solution of methanol-water-acetic acid (or trifluoro acetic acid). Seven kinds of catechins in tea samples from six places in China and three green tea polyphenol(GTP) samples from different producers were separated and determined in 30 min by isocratic and gradient elutions. The effects of mobile phase components and temperature of column on retention parameters of catechins and caffeine are reviewed. Chromatographic conditions and pretreatment methods of samples were optimized. Gallocatechin gallate(GCG) and (-)-catechin gallate(CG) were identified by electrospray ionization mass spectrometry(ESI-MS) and prepared by high performance liquid chromatography for quantitative analysis. The other catechins, (-)-epigallocatechin (EGC), (+)-catechin (D-C), (-)-epicatechin(EC), (-)-epigallocatechin gallate(EGCG), (-)-epicatechin gallate(ECG) were identified with standards.

Caffeine↗
PubMed2001

Green's function analysis of electromagnetic waves in two-layered periodic structures with fluctuations in thickness.

A general method for the construction of the Green's function for finite one-dimensional inhomogeneous layers is developed. Using the results of this method the exact analytical Green's function for periodic dielectric structures is found. As an example of its application, the influence of fluctuations of the widths of the basic layers on the reflection and transmission of electromagnetic waves propagating through the structure is investigated. The results are applied to the design of optical switching systems with periodic dielectric structures as the operating medium. The same Green's function can be used to solve a wide variety of other problems.

Journal Article↗
PubMed2005

Two-dimensional thin-layer chromatographic method for the analysis of ochratoxin A in green coffee.

A low-cost thin-layer chromatographic method has been developed for the presumptive measurement of ochratoxin A (OTA) at 5 microg/kg in green coffee beans. The analytical method consisted of extracting OTA by shaking the beans with a mixture of methanol and aqueous sodium bicarbonate solution, which was then purified by liquid-liquid partition into toluene. OTA was separated by normal-phase two-dimensional thin-layer chromatography and detected by visual estimation of fluorescence intensity under a UV lamp at 365 nm. The chromatography solvents were toluene-methanol-formic acid (8:2:0.03) for the first development and petroleum ether-ethyl acetate-formic acid (8:10:1) for the second dimension development. This method was tested with uncontaminated green coffee bean samples spiked with an OTA standard at four different concentrations (5, 10, 20, and 30 microg/kg). The method is rapid, simple, and very easy to implement in coffee-producing countries. It is highly selective and does not involve the use of chlorinated solvents in the sample extraction step. This inexpensive method has been applied to different types of green coffee samples from various countries (Zimbabwe, Brazil, India, Uganda, Colombia, and Indonesia) and different manufacturers, and no OTA below the detection limit of 5 microg/kg was detected in any samples analyzed.

Chromatography, Thin Layer↗
PubMed2005

Determination of tannin in green tea infusion by flow-injection analysis based on quenching the fluorescence of 3-aminophthalate.

A flow-injection analytical system was developed to determine tannin content in green tea infusions. The flow-injection system is based on measuring the quenching effect of tannin on the fluorescence of 3-aminophthalate. Fluorophore was obtained by auto-oxidation of luminol during solution preparation. System performance was satisfactory for routine analysis (sample throughput >20 h(-1); linear dynamic range for tannic acid, 0.005-0.3 mg/mL; linear dynamic range for green tea tannin, 0.02-1.0 mg/mL; CV < 3%). The flow-injection method is immune from interference by coexisting ascorbate in green tea infusion. Analytical results were verified by the ferrous tartrate method, the Japanese official analytical method.

Ascorbic Acid↗
PubMedDate not supplied

Nonlinear summation of junction potentials in a three-dimensional syncytium.

A three-dimensional "cable" equation with reversal potentials is derived for an infinite syncytium. Its solution is found analytically by using Green's function methods for the special case of two impulsive conductance changes activated at different "points" in space. It is shown that junction potentials generated at different sites in the syncytium do not in theory sum linearly.

Action Potentials↗
PubMed2002

Neuronal integrative analysis of the "Dumbbell" model for passive neurons.

We analyze the so called "Dumbbell" model of Jackson (J. Neurophysiol. 69 (1993) pp. 464) for a single neuron consisting of a patch-clamped cell body attached to dendritic cable of finite length terminating in an oblique derivative ("natural termination") boundary condition representing a dendritic swelling or a natural ending sealed by a continuous surface of the cell membrane. The model is solved analytically via the Green's function method. Large and small time asymptotic behavior of the membrane potential is developed when there is a somatic voltage-clamp imposed. We discuss the difference in the voltage distribution if a sealed-end (Neumann) termination is used instead of the natural termination boundary condition. If the access resistance is large the differences between the potentials corresponding to the two boundary conditions are small at the soma, but can vary significantly near the dendritic termination. This discrepancy is amplified at the soma if there is a synaptic stimulus introduced between the soma and dendritic tip.

Animals↗
PubMed1984

Analyte and matrix problems in the calibration and quality assessment of the bromocresol green method for albumin in serum.

Different batches of bromocresol green were used in a study of several modifications of the bromocresol green method for serum albumin. No major batch variation was observed. Lyophilized animal sera and a certain batch of lyophilized human sera, however, responded differently from a pool of fresh human sera when the method was modified. These phenomena should be taken into account in calibration procedures and in quality assessment.

Animals↗
PubMed1997

Plasma volume estimation using indocyanine green with biexponential regression analysis of the decay curves.

We studied seven analytical methods of estimating the plasma volume from the decay curves of indocyanine green. Fifteen volunteers received 1.0 mg.kg-1 of the dye by intravenous injection and the plasma concentration was measured continuously using spectrophotometry. Plasma volumes were calculated using three single-regression methods (1-a, 1-b, 1-c) and four biexponential regression methods (2-a, 2-b, 2-c, 2-d). The means (SD) of 1-a, 1-b and 1-c were 39 (5.0), 44 (5.7) and 54 (11.5) ml.kg-1, respectively, and these were significantly different from each other (p < 0.05). The values for methods 2-b, 2-c and 2-d were similar to each other: 39 (4.6), 40 (4.1) and 40 (4.0) ml.kg-1, respectively. These required more than 3 min circulation or mixing time. When the time allowed for mixing was less than 3 min (method 2-a) the plasma volume was underestimated. We conclude that plasma volume estimation using indocyanine green and spectrophotometry is most accurate when the mixing time is adequate (3-5 min) and the decay curves are analysed using biexponential regression.

Adult↗
PubMed1995

A rudimentary system for automatic discrimination among basic skin lesions on the basis of color analysis of video images.

BACKGROUND: Detection of differences in color is necessary for an automatic diagnostic system for skin lesions. OBJECTIVE: The purpose of this study was to examine whether color analysis of an image obtained with a videomicroscope can be used as a key to distinguish basic skin lesions. METHODS: We carried out quantitative color analyses of nine kinds of natural or artificial skin lesions. After images of the lesion and adjacent normal skin were obtained, the difference in the mean quasiabsorbance (logarithm of the inverse reflectance) values between the two were examined in each color band of red, green, and blue by an image analytic method. RESULTS: We could determine a set of thresholds of quasiabsorbance values to distinguish between basic lesion colors. On the basis of these results we developed a rudimentary system that automatically offers possible diagnoses of a test site. CONCLUSION: The algorithm that we developed may be of value in an initial screening of skin lesions in an automatic diagnosis system.

Absorption↗
PubMed2002

Free and total amino acid composition in blue-green algae.

A simple, accurate and reproducible analytical method is described for the extraction and the simultaneous determination of 18 amino acids in different for geographical origin Spirulina alga samples using phenylisothiocianate as derivatizating agent in natural feed. The best experimental hydrolysis conditions have been studied varying the temperature, the time and the hydrolyzing reagent. The separation and the quantitative analysis of the by-products have been carried out by HPLC analysis and UV detection. An amino acid pattern is compared with that proposed by the Food Agriculture Organization (FAO) for an ideal protein and with those of some traditional feed.

Amino Acids↗
PubMed2004

Anomalous hydrodynamical dispersion and the transport with multiple families of paths in porous media.

We investigate a family of probability distributions that shows anomalous hydrodynamic dispersion, by solving a particular class of coupled generalized master equations. The Fourier-Laplace solution is obtained analytically in terms of the matrix Green function method; then the Coats-Smith concentration profile is revisited in a particular case. Two models of disorder are worked out explicitly, and the mean current is asymptotically calculated. We present an approximation method to calculate the first passage time distribution for this stochastic transport process, and as an example an exact Markovian result is worked out; scaling results are also shown. We discuss the comparison with other different methods to work out complex diffusion phenomena in the presence of disordered multiple transport paths. Extensions when the models are nondiffusive can also be solved in the Fourier-Laplace representation.

Journal Article↗
PubMed2001

Determination of phosphate in urine by sequential injection analysis.

Two simple turbidimetric methods for the determination of phosphate in urine are presented and compared. One method is based on the calcium phosphate crystallisation, and the other one on the inhibitory action of phosphate on the calcium carbonate crystallisation. The analytical features of both methods were: linear range = 0.2-1.5 g L-1, LOD = 14 mg L-1 and RSD 1.1-2.0% for the calcium phosphate method, linear range = 0.1-1.8 mg L-1, LOD = 0.01 mg L-1 and RSD 0.97-1.90% for the inhibitory method. Urines with high calcium content (> or = 400 mg L-1) can interfere the method based on the crystallisation of calcium phosphate. This interference was solved using a cation exchange resin as a part of the manifold. Considering the low toxicity of used reagents, these methods can be considered as a contribution to Green Analytical Chemistry.

Calcium Carbonate↗
PubMed1984

Wave propagation and dispersion in the cochlea.

Insight into cochlear mechanics can be obtained from semi-analytical and asymptotic solution methods of which the Liouville -Green (LG) method - in another context known as the WKB method - is the most important one. This paper describes the dispersion properties of fluid waves in general terms and develops the LG formulation on that basis. The eikonal equation of the LG method is shown to be identical to the dispersion relation in dispersive-wave theory. Consideration of the group velocity then leads to the derivation of the central LG formula as it has been used in an earlier paper on the LG method ( Boer , E. and Viergever , M.A. (1982): Hearing Res. 8, 131-155). The formulation appears to apply as well to dissipative and active (i.e., energy-producing) systems. Of the many possible collateral subjects two are selected for a deeper discussion: amplification, concentration and expansion of energy, and the problem of reflection of cochlear waves. In the latter context, it is shown why - and under which conditions - cochlear waves are not reflected, despite the large degree of dispersion that they show. The analysis brings to light a fundamental asymmetry of the model regarding the direction of wave travel: waves travelling in the direction opposite to the normal one are likely to undergo reflection, while waves in the normal direction are not reflected.

Basilar Membrane↗
PubMed2002

Poly(methyloctadecylsiloxane) immobilized on silica by gamma radiation for use in solid-phase extraction.

This work presents a fast, easy and effective procedure to obtain silica-based C18 type sorbents for use in solid-phase extraction (SPE). The solid-phase was made by depositing a polymer, poly(methyloctadecylsiloxane) (PMODS), on the silica support followed by immobilization using gamma irradiation. The method presents an application of green chemistry in the analytical laboratory, since there are no toxic residues after the synthesis. Water samples spiked with a mixture of pesticides (benomyl, tebuthiuron, diuron, simazine, atrazine and ametryn) were extracted in the off-line mode in order to evaluate the performance of this sorbent.

Absorption↗
PubMed1988

Membrane voltage changes in passive dendritic trees: a tapering equivalent cylinder model.

An exponentially tapering equivalent cylinder model is employed in order to approximate the loss of the dendritic trunk parameter observed from anatomical data on apical and basilar dendrites of CA1 and CA3 hippocampal pyramidal neurons. This model allows dendritic trees with a relative paucity of branching to be treated. In particular, terminal branches are not required to end at the same electrotonic distance. The Laplace transform method is used to obtain analytic expressions for the Green's function corresponding to an instantaneous pulse of current injected at a single point along a tapering equivalent cylinder with sealed ends. The time course of the voltage in response to an arbitrary input is computed using the Green's function in a convolution integral. Examples of current input considered are (1) an infinitesimally brief (Dirac delta function) pulse and (2) a step pulse. It is demonstrated that inputs located on a tapering equivalent cylinder are more effective at the soma than identically placed inputs on a nontapering equivalent cylinder. Asymptotic solutions are derived to enable the voltage response behaviour over both relatively short and long time periods to be analysed. Semilogarithmic plots of these solutions provide a basis for estimating the membrane time constant tau m from experimental transients. Transient voltage decrement from a clamped soma reveals that tapering tends to reduce the error associated with inadequate voltage clamping of the dendritic membrane. A formula is derived which shows that tapering tends to increase the estimate of the electrotonic length parameter L.

Animals↗