Nicola D. Yordanov

Identification of irradiation treatment of aromatic herbs, spices and fruits by electron paramagnetic resonance and thermoluminescence.

Electron paramagnetic resonance and thermoluminescence signals induced by gamma irradiation in some herbs, spices and fruits were systematically studied in order to detect the treatment. Using European protocols the validity and effectiveness of these two techniques are compared in regard to time of storage after irradiation.

A new approach for extension of the identification period of irradiated cellulose-containing foodstuffs by EPR spectroscopy.

We report on the possibility of identification by EPR spectroscopy of some irradiated cellulose-containing foodstuffs, at a relatively long time after the irradiation, when the characteristic EPR spectral lines of the cellulose free radical have essentially disappeared. In such cases rather expensive and time-consuming methods (e.g. thermoluminescence analysis) have to be applied. The present communication demonstrates with some pre-irradiated spices, dried medicinal and sweet herbs that simply heating the samples to 60 degrees C for one hour leads to a significant (50% or more) decrease of the EPR intensity of the remaining central line of the samples. For comparison, the loss in the intensity of the same line upon heating non-irradiated samples at 60 degrees C for one hour was only about 10%. This inexpensive new procedure will extend the post-irradiation period in which EPR can be used for distinguishing irradiated from non-irradiated samples, of certain cellulose-containing foodstuffs.

Quantitative EPR spectrometry — “State of the art”

The purpose of the present review is to collect some results available in the literature in order to focus the attention of the world EPR community and thus to stimulate their activity on solving the problems of quantitative EPR spectrometry.

Is our knowledge about the chemical and physical properties of DPPH enough to consider it as a primary standard for quantitative EPR spectrometry

The knowledge about the physico-chemical properties of the stable free radical DPPH as a primary standard for the Quantitative EPR spectrometry is summarized. It is shown how to calibrate DPPH in order to use it as a primary EPR standard for quantitative estimations. It is expected that the reported data will be useful for the EPR community specially in calibration and also for periodical checking of the standards used.

Comparative identification of irradiated herbs by the methods of electron paramagnetic resonance and thermoluminescence

Abstract Non irradiated and γ -irradiated dry herbs savoury ( Savoury ), wild thyme ( Thymus serpollorium ) and marjoram ( Origanum ) with absorbed dose of 8 kGy have been investigated by the methods of elecrtron paramagnetic resonance (EPR) and thermoluminescence (TL). Non-irradiated herbs exhibit only one weak siglet EPR signal whereas in irradiated samples its intensity increase and in addition two satelite lines are recorded. This triplet EPR spectrum is attributed to cellulose free radical generated by irradiation. It has been found that upon keeping the samples under the normal stock conditions the life-time of the cellulose free radical in the examined samples is ∼60–80 days. Thus the conclusion has been made that the presence of the EPR signal of cellulose free radical is unambiguous indication that the sample under study has been irradiated but its absence can not be considered as the opposite evidence. In the case when EPR signal was absent the method of TL has been used to give the final decision about the previous radiation treatment of the sample.

The present state of quantitative EPR spectrometry: The results from an international experiment

The present work collects the results obtained from an international experiment carried out during 1991–1992 on quantitative EPR spectrometry. The data from 12 labs in Europe, Asia and America are compared with those obtained from weighing procedure for the same samples. The results from the different labs are characterized with a big variance not permitting to apply a standard statistical procedure. Nevertheless, these data are very helpful to point out the main group of problems in the present state of quantitative EPR spectrometry.

Quantitative electron paramagnetic resonance and spectrophotometric determination of the free radical 4-hydroxy-2,2,6,6-tetramethylpiperidinyloxy.

The first quantitative estimation of the stable free radical 4-hydroxy-2,2,6,6-tetramethylpiperidinyloxy (TEMPOL) simultaneously performed by electron paramagnetic resonance (EPR) and visible spectrophotometric titration is reported. The obtained molar absorptivity of TEMPOL 13.2 +/- 0.1 l(-1) m(-1) cm(-1) at 22,900 cm(-1) may be used as the future criterium about the purity of the EPR active substance. The studied compound may be considered as the second (after 1,1-diphenyl-2-pikrilhydrazil) material calibrated as the primary standard for quantitative EPR spectrometry.

Analysis of some non-linear effects in quantitative electron paramagnetic resonance spectrometry. Non-linear effects due to the use of cavities with TE102 and TM110 modes

Abstract The non-linear effects between the electron paramagnetic resonance (EPR) signal intensity and sample shape (length and diameter) and its positioning in the most commonly accepted cavities operating in TE 102 or TM 110 modes are discussed in detail. These effects are only due to the physical properties of the cavities. It is obvious from both theoretical considerations and experimental results that several precautions must be taken with respect to the physical parameters, like internal diameter of the sample tubes and length of the unknown sample and standard on planning quantitative EPR estimations.

High-field/ high-frequency EPR study on stable free radicals formed in sucrose by gamma-irradiation

The EPR spectrum of sucrose irradiated by high-energy radiation is complex due to the presence of more than one radical species. In order to decompose the spectrum and elucidate the radical magnetic parameters a high-field (HF(-)EPR) study on stable free radicals in γ-irradiated polycrystalline sucrose (table sugar) was performed at three different high frequencies—94, 190 and 285 GHz as well as at the conventional X-band. We suggest a presence of three stable radicals R1, R2 and R3 as the main radical species. Due to the increase of g-factor resolution at high fields the g-tensors of these radicals could be extracted by accurate simulations. The moderate g-anisotropy suggests that all three radicals are carbon-centred. Results from an earlier ENDOR study on X-irradiated sucrose single crystals (Vanhaelewyn et al., Appl Radiat Isot, 52, 1221 (2000)) were used for analyzing of the spectra in more details. It was confirmed that the strongest hyperfine interaction has a relatively small anisotropy, which indicates either the absence of α-protons or a strongly distorted geometry of the radicals.

An improved method for endor study of powdered samples

Abstract A method for ENDOR study of powdered samples is described, giving the polar angle between g∥ and A∥ and the true values of the hyperfine splittings. Using this method Cu(II) complexes ordimethyldithiocarbamate and methyldithiocarbonate magnetically diluted in the corresponding Ni(II) host lattices are studied.