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A new formula is presented for transforming fluorescence measurements in accordance with Kubelka-Munk theory. The fluorescence signals, the absorption signals, and data from a selected reference are combined in one expression. Only diode-array techniques can measure all the required data simultaneously to linearize fluorescence data correctly. To prove the new theory HPTLC quantification of the analgesic flupirtine was performed over the mass range 300 to 5000 ng per spot. The fluorescence calibration curve was linear over the whole range. The transformation of fluorescence measurements into linear mass-dependent data extends the technique of in-situ fluorescence analysis to the high concentration range. It also extends Kubelka-Munk theory from absorption to fluorescence analysis. The results presented also emphasize the importance of Kubelka-Munk theory for in-situ measurements in scattering media, especially in planar chromatography.

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In this study, we present a significant improvement in the minimum detection limit (MDL) for strontium measurement in bone with X-ray fluorescence using 125I as the excitation source. The improvement was achieved thanks to a new collimator in the 90 degree geometry and a different source positioning in the 180 degree geometry. The achieved MDL in the 90 degree geometry is 0.0426±0.0006 mg Sr/g Ca, which is 5.5 times better than the one previously reported. In the 180 degree geometry, the new source positioning improved the MDL from 0.118±0.004 to 0.0446±0.0009 mg Sr/g Ca.

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We investigated the potential application of the genetic algorithm in the analysis of X-ray fluorescence spectra from measurement of lead in bone. Candidate solutions are first designed based on the field knowledge and the whole operation, evaluation, selection, crossover and mutation, is then repeated until a given convergence criterion is met. An average-parameters based genetic algorithm is suggested to improve the fitting precision and accuracy. Relative standard deviation (RSD%) of fitting amplitude, peak position and width is 1.3-7.1, 0.009-0.14 and 1.4-3.3, separately. The genetic algorithm was shown to make a good resolution and fitting of K lines of Pb and g elastic peaks.

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Abstract  

The quantitative interpretation of X-ray fluorescence /XRF/ data is often difficult because of matrix effects. The intensity of fluorescence measurement for a given element is not only dependent on the concentration of the element, but also on the mass absorption coefficients of the sample for both excitation and fluorescent radiation. In this paper, a new approach for the determination of absorption and transmission correction factors is described.

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In-situ densitometry for qualitative or quantitative purposes is a key step in thin-layer chromatography. It offers a simple way of quantifying by measuring the optical density of the separated spots directly on the plate. A new TLC scanner has been developed which is able to measure TLC plates or HPTLC plates, at different wavelengths simultaneously, without destroying the plate surface. The system enables absorbance and fluorescence measurements in one run. Fluorescence measurements are possible without filters or other adjustments.The measurement of fluorescence from a TLC plate is a versatile means of making TLC analysis more sensitive. Fluorescence measurements with the new scanner are possible without filters or special lamps. Improvement of the signal-to-noise ratio is achieved by wavelength bundling. During plate scanning the scattered light and the fluorescence are both emitted from the surface of the TLC plate and this emitted light provides the desired spectral information from substances on the TLC plate. The measurement of fluorescence spectra and absorbance spectra directly from a TLC plate is based on differential measurement of light emerging from sample-free and sample-containing zones.The literature recommends dipping TLC plates in viscous liquids to enhance fluorescence. Measurement of the fluorescence and absorbance spectra of pyrene spots reveals the mechanism of enhancement of plate dipping in viscous liquids — blocked contact of the fluorescent molecules with the stationary phase or other sample molecules is responsible for the enhanced fluorescence at lower concentrations.In conclusion, dipping in TLC analysis is no miracle. It is based on similar mechanisms observable in liquids. The measured TLC spectra are also very similar to liquid spectra and this makes TLC spectroscopy an important tool in separation analysis.

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Journal of Thermal Analysis and Calorimetry
Authors: T. P. Shakhtshneider, M. A. Vasilchenko, A. A. Politov, and V. V. Boldyrev

The method of mechanical activation was used to obtain solid-state dispersions of some drugs in polyvinylpyrrolidone, polyethylene glycol and talc as carriers. Solid dispersions obtained by mechanical activation were found to have higher apparent solubilities and dissolution rates than mechanically activated drugs or their physical or eutectic mixtures with carriers used. It was shown by IR-spectroscopy and fluorescence measurements that mechanical treatment gave rise to an interaction between components which was apparently responsible for the solubilization effects observed.

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Journal of Thermal Analysis and Calorimetry
Authors: E. Kowalska, J. Radomska, P. Konarski, R. Diduszko, J. Oszczudłowski, T. Opalińska, M. Więch, and Z. Duszyc

Abstract  

Two components of electronic wastes (sample A – a mixture of three types of printed circuit boards, sample B – a mixture of electronic junctions with metal wires) were investigated using thermogravimetric analysis (TG). Thermogravimetric and derivative thermogravimetric data (TG and DTG) give information on the thermal stability of A and B samples and allows finding the correct conditions for their degradation using pyrolysis in an experimental system, built on the laboratory scale for utilization of hazardous wastes. X-ray fluorescence measurements prove that brominated flame retardant is present in sample A, whilst chlorinated flame retardant is a probable component of sample B. Preliminary liquid chromatography of oil products obtained as a result of thermal waste degradation shows that the hydrocarbons released during pyrolysis could be used as a fuel.

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A new HPTLC method has been established for separation and quantification of six given apolar, fluorescent pyrolytic heterocyclic aromatic amines (HA) of the carboline group. The mobile phase was selected by using a practical and systematic four-level optimization scheme based on the solvent classification system according to Snyder and the PRISMA model of Nyiredy et al. The amines were separated on silica gel 60 F 254 HPTLC plates by a multiple development with diethyl ether. Quantification by fluorescence measurement at λ = 366/>400 nm was performed immediately after development. Limits of detection were in the lownanogram range. The results show that modern planar chromatography is a rapid and cost-efficient alternative method for determination of HA. The method is suitable for both screening and quantification.

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Banana is a really chilling injury sensitive product. Its sensitivity to cold temperatures generates serious practical, economical and commercial problems. Chilling injury related physiological responses of Cavendish type green banana samples stored at 2.5, 5, 10 °C and near optimal (15 °C) cold storage temperature were investigated by nondestructive optical methods (surface color and chlorophyll fluorescence measurement, DA-index® evaluation) and by the determination of the physiological reactions (respiration, ethylene production, symptom manifestation) during cold storage and the 8-day long subsequent shelf-life. The positive effects of low temperature storage were proven on mass loss, respiration and ethylene production. In case of bananas stored at 2.5–10 °C, the chilling injury related changes in chlorophyll content related DA-index®, IR-values; Fm and Fv chlorophyll fluorescence values, the L*, a*, b*, C* and hue angle color characteristics suggested clearly from day 3 the onset of chilling injury several days before the visible signs of chilling injury appeared.

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Abstract  

Bovine serum albumin (BSA) is a soft globular protein that undergoes conformational changes through several identified transition steps in the pH range 2–13.5. The ability to change conformation makes BSA capable of complexing different ligands from fatty acids to cations or drugs and carries them in the bloodstream. Microcalorimetric titration of BSA with NaOH solution was performed to measure the enthalpy of conformational changes. Two exothermic enthalpy changes were found in the course of the titration between pH 3 and 9.5, which can be identified with the E–F, and the F–N transitions. The enthalpy change at pH 3.5 (transition from the E to the F form of BSA, folding of intra-domain helices in domain I) is independent of the protein concentration. The second transition (F–N, folding of domain III) was observed at pH 4.8 for the 0.1% BSA solution, but it shifted to higher pH values as the protein concentration increased to 0.2% and 0.3%. The tightening of the protein structure with increasing pH was verified measuring intrinsic fluorescence of tryptophan residues. At even higher pH value, pH 10.5, fluorescence measurements revealed protein expansion. The BSA conformational changes were also measured by dynamic light scattering. The hydrodynamic diameter was smaller at the i.e.p. of BSA (5–7 nm at pH ~5) and larger at the two ends of the pH range (17.5 nm at pH 2 and 8.3 nm at pH 10).

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