Search results for "Spectroscopy"

Picosecond absorption spectroscopy: Methods and applications in photophysical and photochemical systems

1985

Density Functional Theory Modelled Absorption and Raman Spectra Applicable to Ergocalciferol (Vitamin D2) and Cholecalciferol (D3)

2021

The study establishes optically relevant lines by modelling ergocalciferol (D2) and cholecalciferol (D3) and compare these to measured and earlier reported absorption and Raman spectra lines. This is a step to reach a further goal of finding if minute Vitamin D (D2 and D3) concentration changes could be determined so that a non-invasive sensor could be developed with a reference to non-invasive measurements reported in [1] describing a Raman spectroscopy method of blood glucose concentration of threshold of 5 mmol/l. However, our concentrations are lower by two orders, i.e., 50 nmol/l. At such concentrations random-type metabolites may have an important role, like those related with person’…

FIA-fluorimetric determination of thiamine.

1990

A flow injection-fluorimetric determination of thiamine is reported. The procedure is based on the oxidation of the analyte with potassium hexacyanoferrate(III) immobilized on an anionic exchange resin; the fluorescence is monitored in aqueous basic solution. Concentrations of the vitamin of 0.1-4 ppm have been determined; the relative standard deviation was 1.8%. The injection rate was 28 samples/h. The influence of other substances and the determination of the drug in a pharmaceutical formulation are also reported.

Spectrophotometric determination of vitamin C using the copper(II)-nioxime-ascorbic acid system following stabilization in a propylene glycol medium

1989

Abstract A spectrophotometric method for the determination of Vitamin C is proposed. The procedure is based on formation and stabilization of the ternary complex Cu(II)-nioxime-ascorbic acid in 80% ( v v ) propylene glycol-water medium. The method has a high degree of tolerance for the determination of ascorbic acid in the presence of other active substances or excipients likely to be present along with vitamin C in pharmaceutical formulations. The suggested method has proved to be rapid and precise and has been successfully applied to different commercial pharmaceutical preparations of vitamin C. Precision, measured on the relative standard deviation, did not exceed 0.73%.

Liquid chromatographic determination of Vitamin D3 in infant formulas and fortified milk

2005

Abstract An isocratic reverse-phase liquid chromatographic (LC) method with electrochemical (EC) detection has been developed and validated for determining Vitamin D 3 in fortified milk and infant formulas. LC–EC determination provides linear responses in the range from 0.03 to 0.7 μg Vitamin D 3 /ml, with inter- and intra-day variations (R.S.D.%) of 4.1 and 4.4, respectively, and detection and quantification limits of 0.012 ng in assay (48 ng/100 g of sample) and 0.039 ng in assay (156 ng/100 g of sample), respectively. Application of the method to a set of infant formulas and fortified milk confirmed its usefulness.

Density Functional Theory Calculated Raman Spectra of Ergocalciferol (Vitamin D2) and Cholecalciferol (D3)

2021

Density functional theory (DFT)-calculated Infrared and Raman spectra of Vitamin D2 and D3 are presented. The calculated results are compared with each other and with available experimental data. Applicability of Raman spectra for non-invasive optical Vitamin D sensors is discussed.

Structural-relaxation phenomena in As–S glasses as probed by combined PAL/DBAR technique

2015

Abstract Experimental techniques exploring phenomena of positron–electron interaction, namely the positron annihilation lifetime spectroscopy and Doppler broadening of annihilation radiation, are shown to be very informative tools to study radiation- and thermally-induced phenomena in chalcogenide glasses of binary As–S system. Time-dependent processes of free-volume voids agglomeration (expansion), fragmentation (refining) and disappearing (contraction) are identified as main stages of physical aging in S-rich glasses, while a competitive channel of coordination topological defects formation associated with void charging becomes significant in a vicinity of near-stoichiometric glass compos…

Protein dynamics: conformational disorder, vibrational coupling and anharmonicity in deoxy-hemoglobin and myoglobin.

1993

In this work we study the temperature dependence of the Soret band lineshape of deoxymyoglobin and deoxyhemoglobin, in the range 300-20 K. To fit the measured spectra we use an approach originally proposed by Champion and coworkers (Srajer et al. 1986; Srajer and Champion 1991). The band profile is modelled as a Voigt function that accounts for the coupling with low frequency vibrational modes, whereas the coupling with high frequency modes is responsible for the vibronic structure of the spectra. Moreover, owing to the position of the iron atom out of the mean heme plane, inhomogeneous broadening brings about a non-Gaussian distribution of 0-0 electronic transition frequencies. The reporte…

Structure-dynamics-function relationships in Asian elephant (Elephas maximus) myoglobin. An optical spectroscopy and flash photolysis study on functi…

1993

In this work we report the thermal behavior (10–300 K) of the Soret band lineshape of deoxy and carbonmonoxy derivatives of Asian elephant (Elephas maximus) and horse myoglobins together with their carbon monoxide recombination kinetics after flash photolysis; the results are compared to analogous data relative to sperm whale myoglobin. The Soret band profile is modeled as a Voigt function that accounts for the coupling with high and low frequency vibrational modes, while inhomogeneous broadening is taken into account with suitable distributions of purely electronic transition frequencies. This analysis makes it possible to isolate the various contributions to the overall lineshape that; in…

Tests of atomic charge-exchange cells for collinear laser spectroscopy

2012

Abstract The performance characteristics of two charge-exchange cells (CECs) with horizontal and vertical cell configurations were determined by neutralizing a 10-keV rubidium ion beam in a potassium vapor. The neutralization efficiency and the fluorescence line shape of the 5s 2 S 1 / 2 ↔ 5 p 2P3/2 (D2) transition in neutral 85Rb were investigated as a function of the reservoir temperature used to control the potassium vapor density. The CECs exhibited similar neutralization performance and at neutralization efficiencies greater than 25–50% an asymmetric line shape of the rubidium D2 fluorescent signal was observed. The asymmetry was attributed to inelastic channels in the charge-exchange …