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Measurements of Electron Paramagnetic Resonance (EPR) signal intensity of free radicals generated in solid γ-irradiated sugar (sucrose) showed variation in the amplitude of the signal within hours, days and years after irradiation. After that it was “stabilized” but how long is unknown. The subject of the present work was to study more deeply the time stability of the free radicals generated in solid sugar during irradiation by EPR spectroscopy and by means of UV spectrometry their recombination products obtained after dissolution in water in a more extended period (up to six years). Very good time stability of irradiated sugar was found, to some extent dependent on the storage conditions. Thus, the obtained high stability of the radiation induced products in sugar suggest that it can be used very successfully not only for regular and accidental dosimetry but also for retrospective dosimetry even six years after irradiation.

The results of electron paramagnetic resonance (EPR) study on commercially available juices from various fruits and different fruit contents: 25%, 40%, 50%, and 100%, homemade juices, nectars and concentrated fruit syrups, before and after gamma-irradiation are reported. In order to remove water from non- and irradiated samples all juices and nectars were filtered; the solid residue was washed with alcohol and dried at room temperature. Only concentrated fruit syrups were dried for 60 min at 40 °C in a standard laboratory oven. All samples under study show a singlet EPR line with g =2.0025 before irradiation with exception of concentrated fruit syrups, which are EPR silent. Irradiation of juice samples gives rise to complex EPR spectra which gradually transferred to “cellulose-like” EPR spectrum from 25% to 100% fruit content. Concentrated fruit syrups show typical “sugar-like“ spectra due to added saccharides. All EPR spectra are characteristic and can prove radiation treatment. The fading kinetics of radiation-induced EPR signals were studied for a period of 60 days after irradiation.

Nutritive supplements Enoviton, Enoviton C and Enoviton CE containing standardized anthocyanins from lyophilized red wine, vitamins (some of them) and excipients were investigated by EPR spectrometry before and after gamma-irradiation. Non-irradiated samples exhibit one singlet line with g=2.0039±0.0002, most probably due to free radicals from anthocyanins. After irradiation with 10 kGy gamma-rays, tablets of Еnoviton, Еnoviton С and Еnoviton СЕ, all exhibit complex EPR signals centered at a g-value of g=2.0034. The EPR spectrum of irradiated Enoviton is different from that of Еnoviton С or Еnoviton СЕ due to the overlap of the spectra of microcrystalline cellulose and the background singlet spectrum present in all tablets with the EPR resonance due to irradiated ascorbic acid (in Еnoviton С and Еnoviton СЕ). Gamma-induced free radicals exhibit long time stability—for a six months period the intensity of central peak decrease with 30–40%.

The time stability and dose response of the free radicals produced in various types of “less-studied” mono- and disaccharides by γ-radiation is studied by EPR (Electron Paramagnetic Resonance) and UV spectrometry. The time evolution of the shape of the EPR spectra of irradiated saccharides is investigated from 5 min to 5 months after irradiation. The intensity of the stable EPR signal is studied as a function of the absorbed γ-dose in the range 0.5–20 kGy. Aqueous solutions of irradiated solid saccharides exhibit a UV absorption maximum in the range 250–290 nm. A linear dependency is found between the magnitude of the UV absorption maximum and the absorbed γ-dose. The time stability of the UV absorption maximum is also studied for every saccharide. The results are compared with those obtained for irradiated sucrose.

Crystalline sucrose irradiated with C and Si ions is investigated with EPR and UV spectroscopy. Samples are treated at different doses of radiation in the region 20–300 Gy and linear energy transfer (LET) values of 39.6, 49 and 58 keV μm−1 for C ions and 60 keV μm−1 for Si ions. All samples exhibit identical EPR spectra due to radiation-induced stable sucrose radicals. At given constant LET the EPR signal responses are linear to the absorbed doses of Si and C ions. Water solutions of irradiated sucrose exhibit UV absorption maximum at 267 nm due to the product of radical recombination. The intensity of this band is stronger at irradiation with Si than with C ions. UV absorption is more sensitive to heavy-ion species irradiation than the EPR signals.

The results of electron paramagnetic resonance (EPR) study on fresh fruits (whole pulp of pears, apples, peaches, apricots, avocado, kiwi and mango) before and after gamma-irradiation are reported using two drying procedures before EPR investigation. In order to remove water from non-irradiated and irradiated samples of the first batch, the pulp of fresh fruits is pressed, and the solid residue is washed with alcohol and dried at room temperature. The fruits of the second batch are pressed and dried in a standard laboratory oven at 40 °C. The results obtained with both drying procedures are compared. All samples under study show a singlet EPR line with g=2.0048±0.0005 before irradiation. Irradiation gives rise to typical “cellulose-like” EPR spectrum featuring one intensive line with g=2.0048±0.0005 and two very weak satellite lines situated 3 mT at left and right of the central line. Only mango samples show a singlet line after irradiation. The fading kinetics of radiation-induced EPR signal is studied for a period of 50 days after irradiation. When the irradiated fruit samples are stored in their natural state and dried just before each EPR measurement, the satellite lines are measurable for less than 17 days of storage. Irradiated fruit samples, when stored dried, lose for 50 days ca. 40% of their radiation-induced radicals if treated with alcohol or ca. 70% if dried in an oven. The reported results unambiguously show that the presence of the satellite lines in the EPR spectra could be used for identification of radiation processing of fresh fruits, thus extending the validity of European Protocol EN 1787 (2000). Foodstuffs—Detection of Irradiated Food Containing Cellulose by EPR Spectroscopy. European Committee for Standardisation. Brussels for dry herbs.

The paper is a study on the formation and properties of mixed-chelate copper(II) complexes, in which one ligand is strongly covalently bound diselenocarbamate (dsc), and the other belongs to a series of differently substituted acetylacetonates (acac), all forming weak covalent bonds. Thenoyltrifluoro- and trifluoro- substituted acetylacetonates only partly form mixed-chelate complexes, stable in toluene, benzene or dichloromethane, but gradually decomposing in chloroform or carbontetrachloride by analogy with Cu(Et 2 dsc) 2 behavior in these solvents. Hexafluoro-acetylacetonato copper(II) completely turns into a mixed-chelate Cu(dsc)(hfacac), which remains unchanged for more than 8 months of monitoring in all solvents used. The stability of Cu(dsc)(hfacac) is attributed to the reduced remaining negative charge on selenium atom embarrassing the formation of weak D–A complex with haloalkanes. The obtained EPR parameters suggest significant lowering of the contribution of the 4s AO of copper(II) in the mixed-chelate complexes. It is shown that Cu(acac) 2 does not react with Cu(Et 2 dsc) 2 .

Sucrose irradiated with N-ions and gamma-rays is investigated by EPR and UV spectroscopy. Irradiation doses are in the range of 20–380 Gy and linear energy transfer (LET) for N-ions of 90, 125 and 160 keV μ m - 1 . All EPR spectra recorded in irradiated solid samples are identical, suggesting that generated free radicals are not sensitive to the radiation quality. The EPR response of free radicals linearly depends on the absorbed dose but when generated by N-ions it is always lower than that obtained by irradiation with the same absorbed dose from gamma-rays. Water solutions of irradiated sucrose exhibit UV absorption at 267 nm due to the product of free radicals recombination, which spectrum remains independent on the radiation quality. The intensity of this band however depends on the absorbed dose and for equal doses it is higher for samples irradiated with N-ions than with gamma-rays. For different high LET-radiations with N-ions and low-LET radiation from gamma rays is found an excellent linearity between the EPR signal intensity and the UV absorbance of the obtained water solution. The relation between EPR and UV response of N-ions irradiated samples is reciprocal as well as between them and gamma-irradiated samples suggesting different impact of the high-energy photons and heavy particles on the solid state. For low LET photon radiation with moderate dose rate the probability for a successful hitting of two neighboring molecules is low. Therefore, only a small part of low LET radiation-induced free radicals may be expected to recombine giving an UV detectable product. In opposite, because of the dense ionizations and heaviness of N-ions almost all molecules in the core of the track are ionized yielding mainly products of the recombined free radicals. In the outer part of the track delta particles, which are more like low LET radiation electrons, stands for ionizations and produces a small number of free radicals situated far from each other. Therefore, we can expect higher EPR response of sugar irradiated with a certain dose of gamma-rays than of heavy particles. Just the opposite behavior should be expected for the UV absorption, which should be higher in the irradiation with heavy particles than with gamma-rays. The reported observations suggest that a sucrose/UV/EPR dosimetric system seems to be very promising for dose determinations from both gamma and heavy particle radiation and indicate a method for simultaneous determination of absorbed dose and LET. It also seems to be a new way for calibration of EPR dosimeters irradiated with N-ions via UV spectrometry.

The results, obtained by six independent electron paramagnetic resonance (EPR) laboratories, of the dose response coefficients ( K dr ) of “self-calibrated” solid-state EPR dosimeters containing alanine as a radiation-sensitive material and Mn 2+ /MgO as an internal reference material, are reported. The intercomparison trial was divided into three steps. It started with the distribution of dosimeters among the participating EPR laboratories with the purpose of irradiating them with known doses of γ -rays and to estimate the K dr . The percentage standard deviation (PSD) of the K dr obtained at individual labs was in the range of 1.4–4.6%. The interlaboratory PSD of the K dr was 8%, primarily pointing to variations in irradiation procedures and EPR spectrometer settings. Further investigations showed that the main source of the interlaboratory PSD is differences in the calibrations of irradiators and settings of EPR acquisition parameters. In order to provide reproducible estimates of the K dr , low microwave power and modulation amplitude using a combination of sweep time and time constant that gives a distortion-free EPR spectrum should be utilized. In the third step following such a procedure, measuring the same irradiated alanine dosimeter at the respective laboratories, spectrometers (12 instruments of 6 different models and 3 producers) and 10 operators gave an interlaboratory PSD of 3.1%. In conclusion, EPR dosimetry using “self-calibrated” alanine dosimeters may be used as a secondary standard, although a careful calibration of the EPR spectrometer must be performed in order to further reduce the uncertainty.

Summary EPR studies of free radicals generated in roasting process of peanut, almond, walnut and apricot are reported separately for the kernels and flakes. The raw flakes exhibit a weak singlet EPR signal, whereas raw kernels are EPR silent. Two different EPR signals are recorded in the course of roasting. One in flakes with g = 2.0040, which is independent of temperature and time of roasting and is attributed to C-centered free radical. The same C-centered (g = 2.0040) free radical is recorded at high temperature (>140 °C) and for extended time (>20 min) of roasted kernels connected with burning of the material. However, an O-centered (g = 2.0048) free radical of ‘lipid’ type appears in kernels at roasting temperature of 100–140 °C and short time (5–20 min). On the contrary, free radical concentration in kernels and flakes increases with increase in roasting temperature and decreases with the time after that. The kinetics of the decay of free radicals concentration in flakes and kernels is followed at room temperature under the storage environment (air or argon).

X-, K- and Q-band EPR studies on lyophilized whole pulp parts of blue plum, apricot, peach, melon as well as achens and pulp separately of strawberry before and after X–ray irradiation are reported. Before irradiation all samples show in X band a weak singlet EPR line with g = 2.0030 ± 0.0005 , except melon, which is EPR silent. Immediately after irradiation all samples exhibit complex fruit-depending spectra, which decay with time and change to give, in ca. 50 days, an asymmetric singlet EPR line with g = 2.0041 ± 0.0005 . Only apricot pulp gave a typical “sugar-like” EPR spectrum. Singlet EPR lines recorded after irradiation in X -band are K- and Q-band resolved as typical anisotropic EPR spectra with g | | = 2.0023 ± 0.0003 and g ⊥ = 2.0041 ± 0.0005 . In addition, K- and Q-band EPR spectra of all samples show a superposition with the six EPR lines of Mn2+ naturally present in the fruits. The saturation behavior of the EPR spectra of achens of lyophilized and fresh strawberry is also studied. The differences in g factors of samples before and after X-ray irradiation might be used for the identification of radiation processing of fruits in the case of pulp and the differences in the EPR saturation behavior might be used for the achens of strawberry.

EPR study on the ligand-exchange reaction between bis(diethyldiselenocarbamato)copper(II), Cu(Et 2 dsc) 2 , and bis(octyldithiocarbonato)copper(II), Cu(octxant) 2 , in CH 2 Cl 2 , CHCl 3 , CCl 4 , C 6 H 6 and C 6 H 5 ·CH 3 is reported for the first time. Mixing of equimolar amounts of the parents (chromophores CuSe 4 and CuS 4 , respectively) in C 6 H 6 , C 6 H 5 ·CH 3 and CH 2 Cl 2 makes EPR signals of both parents superimposed by the spectrum of a mixed-chelate Cu(xant)(dsc) complex (chromophore CuS 2 Se 2 ). A new additional EPR spectrum appears in CHCl 3 or CCl 4 due to a five-coordinate mixed-ligand complex with the chromophore Cu(S 3 Se)S as follows by comparing the g -values of parents and mixed-ligand complexes. The appearance of this complex could be explained having in mind donor–acceptor properties of complexes, solvents and the resultant reaction of Cu(octxant) 2 with the ester of diselenocarbamic acid yielded in Cu(Et 2 dsc) 2 destruction by CCl 4 or CHCl 3 .

The influence of the shape and size of dosimeters used in solid state-EPR (SS/EPR) dosimetry on their response is reported. It is shown that for commonly used cylindrical (rod) shaped dosimeters of equal height, prepared of low ( e ⩽ 3 ) dielectric constant materials, linearity between their volume and the EPR response is observed when their diameter varies between 3 and 5 mm. Further increase of the dosimeter's diameter is not recommended since the increased penetration of the dosimeter material into the electric component of the microwave field in the EPR cavity increases the dielectric losses and decreases the EPR response. In an attempt to improve the sensitivity of the SS/EPR dosimetry we have prepared and tested new, flat-shaped, dosimeters of low ( e ≈ 2 ) dielectric constant materials which were found to exhibit: (i) linear EPR response within 1–5 mm thickness; (ii) higher sensitivity than cylindrical dosimeters at equal sample volume; (iii) increased by ca. 270% EPR sensitivity at 5 mm thickness compared to the cylindrical dosimeters with the same diameter (ca. 1.7 times increased sample volume). Using flat shape dosimeters of suitable size provides 2.7 times higher EPR sensitivity of single estimation.

EPR spectra of dry, sugar containing fruits—raisins, sultanas, figs, dates, peaches, blue plums and chokeberry recorded before and after irradiation with gamma-rays, are reported. It is shown that weak singlet EPR line with 2.0031 ± 0.0005 can be recorded before irradiation of seeds, stones or skin of chokeberry, figs and raisins as well as flesh of blue plum, raisins and peaches. EPR signals of various shape are distinguished after irradiation in different parts of the fruits, as well as in randomly cut pieces of them: • Seeds of raisins, chokeberry and figs give a singlet line. Stones from blue plums and peaches exhibit typical “cellulose-like” EPR signal consisting of an intense singlet line with g = 2.0033 ± 0.0005 and 2 week satellite lines situated ca. 30 G left and right to it. Stones of dates are the only sample in which “sugar-like” spectrum is recorded. • Skin of raisins and figs exhibits “sugar-like” EPR spectrum whereas that of dates and chokeberry—a singlet line. Under the same experimental conditions skin of sultanas, peaches and blue plums are EPR silent. • Flesh of raisins, sultanas, figs, dates and peaches exhibits “sugar-like” EPR spectrum, flesh of blue plums gives a singlet EPR line and that of chokeberry is EPR silent. As a result, randomly cut pieces of dry fruits suitable for EPR studies, containing various constituents, exhibit different in shape and intensity EPR spectra. Kinetic studies followed for 1 year on the time stability of all reported EPR signals indicate that intensity ratio between the simultaneously appearing EPR signals in particular fruit varies from 1:20 immediately after irradiation to 1:0.5 at the end of the period. These observations open a new possibility for identification of irradiated fruits – using the magnitude of the intensity ratio to find the approximate date of radiation processing in the first ca. 30–100 days.

Polycrystalline phenyl-alanine and perdeuterated l - α -alanine ( l - α -alanine-d 4 ) were studied as potential high-energy radiation-sensitive materials (RSM) for solid state/EPR dosimetry. It was found that phenyl-alanine exhibits a linear dose response in the dose region 0.1–17 kGy. However, phenyl-alanine is about 10 times less sensitive to γ -irradiation than standard l - α -alanine irradiated at the same doses. Moreover, the EPR response from phenyl-alanine is unstable and, independent of the absorbed dose, decreases by about 50% within 20 days after irradiation upon storage at room temperature. γ -irradiated polycrystalline perdeuterated l - α -alanine (CD 3 CD(NH 2 )COOH) has not previously been studied at room temperature by EPR spectroscopy. The first part of the present analysis was with respect to the structure of the EPR spectrum. By spectrum simulations, the presence of at least two radiation induced free radicals, R 1 =CH 3 C • (H)COOH and R 2 =H 3 N + −C • (CH 3 )COO − , was confirmed very clearly. Both these radicals were suggested previously from EPR and ENDOR studies of standard alanine crystals. The further investigations into the potential use of alanine-d 4 as RSM, after choosing optimal EPR spectrometer settings parameters for this purpose, show that it is ca. two times more sensitive than standard l - α -alanine.

The reported EPR studies on the dependence of the microwave saturation behavior as a function of temperature (up to 60 °C) and heating time of some dry plants demonstrate the possibility to distinguish naturally present from radiation induced EPR signals independently of the fact that they have equal g -factors in X- and Q-band spectra. Using these properties of the dry plants a new approach for identification of their previous radiation processing is considered. It is based on the fact that the intensity of the EPR line appearing after irradiation increases at high microwave power (for example 100 mW) and decreases at low microwave power (for example 1 mW) when the irradiated sample is recorded after thermal treatment (up to 60 °C, 60 min). The intensity of the naturally present EPR signal observed in non-irradiated samples remains, meanwhile, unchanged.

The features of the recorded EPR spectra of paramagnetic species formed in bread and rusk are reported. The appearance of free radicals in them is only connected with their thermal treatment since the starting materials (flour and grains) exhibit very weak EPR signal. The obtained EPR spectra are complex and indicate that: (i) the relative number of paramagnetic species depends on the temperature and treating time of the raw product; (ii) the g-values are strongly temperature dependent with a tendency to coincide at tor = 220 degrees C. Because of the relatively low (150-220 degrees C) temperature of thermal treatment, the studied free radicals can be assumed to appear in the course of the browning (Maillard) reaction and not to the carbonization of the material.

The EPR and UV spectral properties of gamma-irradiated white and burned sugar, fructose and glucose are studied with the accent on their suitability as dosimetric materials. It is shown that gamma-irradiation of solid samples of white sugar and fructose yields stable EPR spectra whereas glucose signal remains time-dependent even 11 months later. Sugar and glucose exhibit linear EPR dose response in the region 0.44-21 kGy and fructose only up to ca. 10 kGy. The relative radiation sensitivity obtained for sugar and fructose is up to 10 kGy and slightly lower for glucose. Burned saccharides provide 2-3 orders of magnitude lower EPR radiation sensitivity making them not suitable for the proposed designation. According to the UV spectra water solutions of gamma-irradiated solid white saccharides show well pronounced absorption bands at 267 and 286 nm for sugar and fructose with time-dependent intensities reaching steady values ca. 11 days after dissolution. The intensities of these absorption bands are in linear relation with the absorbed dose of gamma-radiation. Glucose shows low sensitively because irradiation with 5.5 kGy yields only a shoulder at about 260-280 nm with decreasing to ca. 40% intensity in the first few days after dissolution. Excellent correlation between the intensities of the EPR- and UV-absorbed dose response is found for sugar and fructose in the region 0.44-10 kGy. This opens new possibilities for independent calibration the EPR dose response. Finally, the comparison suggests sugar as the best, universal material for EPR- and/or UV-dosimetry in the region 0.44-160 kGy.

The EPR response of γ -irradiated ammonium tartrate on the absorbed dose of γ -rays up to 22 kGy as well as the changes in the shape of the EPR spectrum upon applied modulation amplitude and microwave power are reported. Also the possibility to use ammonium tartrate together with Mn 2+ magnetically diluted in MgO as an internal reference material is evaluated. The influence of the microwave power and the modulation amplitude on their dose response is investigated. The results show that the radiation-induced EPR spectrum of ammonium tartrate, obtained at a low microwave power is complex consisting several patterns and is more easily saturated than the Mn 2+ EPR spectrum. In this case the following settings of the EPR parameters are recommended: H mod ⩽0.05 mT and 10⩽ P MW ⩽13 mW. Using these parameters the dosimeters can be considered for use in intercomparisons.

X- and Q-band EPR studies after γ -irradiation of some dry spices and aromatic herbs are reported. Before irradiation all samples show only one singlet line in X-band EPR, whereas the Q-band EPR spectrum of the same samples is a superposition of two individual spectra—one corresponding to the above EPR signal, with an anisotropic spectrum, and a second one consisting of six lines due to the Mn 2+ naturally present in plants. The radiation induced EPR signal due to cellulose free radicals was not detected after γ -irradiation, but only the increase of the natural signal present before the irradiation. The fading kinetic of this EPR signal was monitored in three cases—when samples were kept in plastic bags without any special conditioning after irradiation, when samples were covered with paraffin before irradiation and when samples were dried at 60°C for 1 h before irradiation. The studies show that stability of radiation induced EPR signals decreases in the order of: paraffin covered > heated before irradiation > kept at room conditions. The two EPR spectra in the Q-band—one with radiation dependent intensity and a second due to Mn 2+ , which is radiation independent allow identification of previous radiation treatment based on the fact that Mn 2+ quantity in the sample is constant whereas the quantity of radiation-induced free radicals is temperature dependent. It was found that for irradiated samples the ratio between EPR intensity of the free radicals and that of Mn 2+ before and after heating decreases with 50–60% whereas for non-irradiated samples it is ca. 10–15%.

The possibilities for the estimation of the absorbed dose for high-energy radiation with a new self-calibrated dosimeter containing table sugar as a radiation-sensitive material and Mn 2+ /MgO as an internal standard by the method of electron paramagnetic resonance (EPR) is reported. The dose response of this dosimeter is represented as the ratio between the EPR signal intensities of sugar and Mn 2+ versus absorbed dose. Because the EPR spectra of both substances are simultaneously recorded, the influence of some related instrumental setting parameters were investigated. UV spectral studies on water solutions of irradiated solid sugar were also performed. In all solutions of irradiated sugar samples a band at 267 nm was recorded as linearly increasing intensity with the absorbed dose. The minimum detectable dose using the UV spectrum of water solutions of irradiated sugar is 100 Gy. Combination of EPR and UV spectral data is possible to use for independent internal or international calibration and control of dose estimations.

Photolysis of the ternary system consisting of diethyldithiocarbamate (Et 2 dtc), diethyldiselenocarbamate (Et 2 dsc) and copper(II) (1:1:1) has been studied in isobutylmethylketone (IBMK), toluene, chloromethane and chloromethane/ROH solutions (chloromethane=CCl 4 , CHCl 3 or CH 2 Cl 2 and ROH=EtOH or i-PrOH). The results obtained by EPR techniques and UV–Vis data indicate that a homolytic CuS bond cleavage involving the dithiocarbamate (dtc) ligand appears as the primary photo-process in Cu(Et 2 dtc)(Et 2 dsc) photolysis. Further conversion of the primary photoproduct Cu I (Et 2 dsc) is discussed in terms of a specific interaction with the solvent. In chloromethanes and chloromethane/ROH Cu I (Et 2 dsc) is oxidised by the solvent to give the corresponding paramagnetic mixed-ligand Cu II (Et 2 dsc)Cl complex and/or its chloride-bridged and EPR silent dimer Cu 2 (Et 2 dsc) 2 Cl 2 . The formation of the monomeric species occurs through a co-ordination of the alcohol molecule in the xy plane of the complex. Because of its co-ordination inertness, toluene poorly stabilises the primary photoproduct Cu I (Et 2 dsc), thus providing an effective primary recombination process and lower efficiency of Cu(Et 2 dtc)(Et 2 dsc) photolysis. The formation of the bis-solvated mixed-ligand complex Cu II (Et 2 dsc) + in IBMK is also discussed.

The magnitude of the continuous wave electron paramagnetic resonance (CW-EPR) response of a given sample is governed by several cavity parameters. Two of them are the distribution of the modulation magnetic flux density and the microwave magnetic component over the sample length. Their mutual configuration could have a significant influence on quantitative EPR estimations. In the present paper, we report the results obtained with 14 different cavities of TE 102 ,T E 104 ,T M 110 and TM011 modes commercially available and used in many EPR laboratories with respect to the magnitude of their EPR response as a function of the sample length. The results show that due to their technical construction the widely used cavities in CW-EPR spectroscopy could be classified into three types in which: (i) the distribution of the microwave magnetic component in the cavity coincides with the modulation magnetic flux; (ii) the modulation magnetic flux is wider than the microwave magnetic component in the cavity. In this type, the magnitude of the EPR response along the sample length is governed only by the distribution of the microwave magnetic component in the cavity, (iii) the modulation magnetic flux is narrower than to the microwave magnetic component in the cavity. In the cavities of this type, the magnitude of the EPR response is governed by the distribution of the modulation magnetic flux. Whereas, in both former types, the EPR response corresponds to the full length of the sample along the z-axis of the cavity, an EPR silent zone appears in the latter type. In some of them this zone takes ca. 40% of their full length. Therefore, the assumption that the EPR active zone corresponds to the full cavity length (along the sample axis) is not valid for the latter type cavities. Their use will give 2–3% error within a series of samples, but the results will be burdened by a systematic error and could not be compared with the data obtained with another cavity even on the same spectrometer. In view of this, we should be familiar with the features of every cavity before using it for quantitative EPR estimations. Two ways are recommended to overcome the effect of EPR silent zones of an unknown cavity in order to get comparable results in quantitative EPR estimations: (i) to use samples of less than 5–6 mm length, symmetrically situated with respect to the cavity center in consecutive procedures of estimations independently of the cavity type, (ii) in the cases of simultaneous recording of unknown sample and a standard they both should be homogeneously mixed or coaxially situated along their full length. © 2002 Elsevier Science B.V. All rights reserved.

Consecutive estimation of nitrate and nitrite in vegetables and fruits by electron paramagnetic resonance (EPR) spectrometry is described, based on the selective reactions of nitrate and nitrite ions to yield a stoichiometric amount of the EPR-active mononitrosyldiethyldithiocarbamate complex of iron in aerobic conditions. Since, nitrogen monoxide and dioxide (which may be present in the air) give the same reaction, the detection limit depends on their background concentration in the air. The EPR response is found to be linear up to 2500 μg of NO2− and 16 000 μg of NO3−. The applicability of EPR spectrometry for estimation of both nitrate and nitrite content is demonstrated by the analysis of 18 vegetables and fruits, available in the local markets, grown with the use of mineral fertilizers. The results obtained are compared with those for some “home-grown” vegetables with the use of organic fertilizers.

The photochemical reactions of bis(diethyl-diselenocarbamato)copper(II), Cu(Et2dsc)2, complex have been studied in toluene, CH2Cl2, CHCl3 and chloroalkane/EtOH mixed solvents. Charge-transfer irradiation induces intramolecular oxidation of the ligand and reduction of copper(II) to copper(I) as evidenced by EPR and UV-Vis spectra of the complex as well as quantum yield results. When photolysis is carried out in CHCl3 or CH2Cl2 or in the solvent mixture CHCl3/EtOH resp. CH2Cl2/EtOH of lower than 1:1 EtOH content, the primary photoproduct CuI(Et2dsc) is further oxidised in a dark reaction with the chloroalkane producing the corresponding paramagnetic mixed-ligand CuII(Et2dsc)Cl complex in equilibrium with its chloride-bridged and EPR silent, dimeric form Cu2(Et2dsc)2Cl2. At low concentration of EtOH the equilibrium is shifted to the dimeric form whereas at higher than 1:1 EtOH content in the mixed solvent CHCl3/EtOH it is shifted to CuII(Et2dsc)Cl. A reaction mechanism is proposed and the role of ethanol is discussed.

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.

The dependence of the direct and relative (to reference standard situated outside the sample) EPR response estimations on the sample’s dielectric constant, the sample container’s internal diameter and the frequency of the magnetic field modulation in quantitative EPR estimations is studied. It is shown that it is possible to compare with good accuracy and reproducibility quantitative results obtained with samples of different dielectric constants and inserted in sample containers of different internal and outer dimensions if: (a) reference standard and unknown sample are simultaneously recorded making all calculations with the ratio I uk /I st ; (b) the reference standard is situated outside the sample; (c) EPR spectrometer settings do not affect both the unknown sample and the standard spectra; (d) low frequency (12.5 kHz or less) modulation of the magnetic field is used all the time.

Some physico-technical parameters of the self-calibrated alanine/EPR dosimeters are described. Principally, this new type of solid state/EPR dosimeter contains radiation sensitive diamagnetic material (in the present case, alanine), some quantity of EPR active, but radiation insensitive, substance (for example, Mn2+/MgO) playing roles of an internal standard and a binding material. Thus with this dosimeter the EPR spectra of alanine and the internal standard Mn2+ are recorded simultaneously and the dose response is represented as a ratio of EPR signal intensities of alanine versus Mn2+ as a function of absorbed dose. As a result, the data of the present study have shown that there is practically no interference of the dosimeter EPR response (expressed as the ratio I alanine/I Mn) from the way of preparation (homogeneity), behavior after irradiation (fading of EPR signals with time, influence of different meteorological conditions) as well as specific spectrometer setting conditions. These dosimeters show satisfactory reproducibility of preparation and reading as well as stability on keeping. Thus, fulfilling the described physico-technical data of this type of dosimeters, the reproducibility of the readings is significantly improved particularly when intercomparison among different laboratories is performed. This conclusion is confirmed by independent studies of the described self-calibrated alanine/EPR dosimeters in several laboratories in Europe. Results of which are also reported.

The results from the EPR studies on fresh, air-dried and lyophilized tomato samples before and after gamma-irradiation are reported. Before irradiation fresh and air-dried tomatoes exhibit one singlet EPR line characterized with common g -factor of 2.0048±0.0005, whereas freeze-dried tomato does not show any EPR spectrum. After irradiation, a typical “cellulose-like” triplet EPR spectrum appears in all samples, attributed to cellulose free radicals, generated by gamma-irradiation. It consists of intense central line with g =2.0048±0.0005 and two weak satellite lines separated ca. 3 mT left and right of it. In air-dried and lyophilized tomatoes the “cellulose-like” EPR spectrum is superimposed by an additional partly resolved carbohydrate spectrum. Fading measurements of the radiation-induced EPR signals indicate that the intensity of the EPR spectra of air-dried and freeze-dried tomato are reduced to about 50% after 50 days, whereas those of fresh irradiated tomatoes kept at 4 °C fade completely in 15 days. The reported results unambiguously show that the presence of two satellite lines in the EPR “cellulose-like” spectra of tomato samples can be used for identification of radiation processing.

EPR-spectroscopic properties (line-intensity,-width, andg-factors) of pyrolized at 550°C sucrose, MgO and MgO doped with Mn2+ ions (500∶1) remain unchanged after high-dose (1–100 kGy) irradiation, whereas CaO gives an EPR signal. These properties of these materials make it possible to use them as internal reference EPR standards in the work under conditions of strong ionisation environment, for precise determination of theG-values of other materials, for obtaining exact magnitudes of increase of the EPR response when the method of additional dose is applied, to follow the kinetics of decay of some radiation induced defects.

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.

A comparative study of irradiated pork meat containing bone was made by the methods of electron paramagnetic resonance (EPR) and gas chromatography (GC). In this investigation EPR has the advantage to be a very fast and unambiguous method even in the cases of thermal treatment of bones. On the other hand, GC analysis is a time consuming procedure however, it becomes very valuable for meat samples that contain no bones.

Interactions of the complex bis(diethyl–diselenocarbamato)copper(II), (Cu(dsc) 2 ) with some copper(II) salts in solution have been studied by EPR and electronic spectroscopy. The complex interacts with copper salts (CuX 2 , X = Cl, Br, NO 3 ) to produce EPR silent dimers of the type [(dsc)CuX 2 Cu(dsc)] which are formed in equilibrium with mixed-ligand Cu(dsc)X complexes. The same dimers are found to be formed in the course of the exchange reaction between the zinc diselenocarbamate and copper chloride. The electronic spectrum of the bis-chelate has a characteristic absorption band at 20,200 cm −1 (e = 11,800 m −1 dm 3 cm −1 ) whereas the dimers are characterized by a band at 22,600 cm −1 (e = 23,800 m −1 dm 3 cm −1 ). This property of complex could be used in analytical practice for increasing sensitivity of photometric estimations.

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.

A first simultaneous EPR- and VIS-spectrophotometric study is reported on the interaction of the stable free radical 1,1-diphenyl-2-picryl-hydrazyl (DPPH) dissolved in ethanol with thioglycolic acid (HSCH2CO2H, TGA). The results of the kinetic studies at room temperature permit to assume 1:1 stoichiometry of the reaction between DPPH and TGA giving 1,1-diphenyl-2-picryl-hydrazine (DPPH2) and thioglycolic disulphide. The linear plots of EPR- and UV/Vis responses vs. the quantity of added TGA are used to find the DPPH molar absorptivity at 520 nm to be 12350 ± 3% l · mol–1· cm–1 which may be used as a criterion for the purity of the material itself. It was also found that the paramagnetic and optical properties of a 30 year old sample give results suggesting that in the solid state DPPH is a fairly stable material.

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.

The method of EPR spectroscopy is applied for the first time in the systematic quantitative estimations of carbonaceous solids present as aerosols in the urban air. The quantitative data obtained are in concert with the estimations using other conventional methods. The advantage of the EPR method in such estimations is that it is not destructive, exhibit selectivity only to paramagnetic species which are in fact the pyrolyzed products and not to other polycyclic aromatic hydrocarbons, the analyses are simple, time saving and inexpensive.

The powder EPR spectra of some ammonium and potassium salts of dithiophosphoric acid, (RO)2P(S)SH, irradiated with X-rays at 77 K have been recorded and analyzed in respect to their distinguishable EPR-active components. In general each EPR spectrum is a superposition of isotropic and anisotropic features from a number of carbon- and phosphorus-centered radicals. Whereas carbon-centered radicals are practically isotropic the phosphorus-centered species exhibit threefold anisotropy with a large (700–800 G) isotropic31P hyperfine splitting. The identification of the latter is based on the magnitudes of the31P splitting as well as on the phosphorous 3p/3s spin densities ratio. The experimentally obtained EPR parameters of the studied radicals are refined using computer simulation procedure.

The results obtained on the examination of different instrumental parameter settings as well as the influence of the accuracy of sample positioning on the EPR parameters for two types of EPR spectrometers — Bruker ER 200D SRC and a portable PS 100.X — are reported. The results obtained show good agreement between the EPR signal parameters and relative values of the spectrometer settings. The reproducibility of the results on re-inserting of one and the same sample in the cavity was evaluated with and without a holder fixed in the cavity.

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.

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.

The present studies are concerned with the influence of the nature of the solvent on the time-dependent stability of the absorption maxima of the free radical 1,1-diphenyl-2-picrylhydrazyl (DPPH) at 520 nm as well as the intensity of its EPR spectrum. The correlation between these two characteristics of DPPH, the behaviour of which is found to be unpredictably strange, unambiguously shows that the problem for calibration of DPPH in order to be used as a primary standard for quantitative EPR spectrometry purpose is not solved yet. This problem needs additional studies in order to find exact methods for examination of the data concerning DPPH quantitative characteristics before its use.

Two copper(II) complexes in equilibrium contribute to the solution EMR (EPR) spectrum of bis(ethylacetoacetato)copper(II). In the present paper, EMR line-widths have been analysed to obtain better insight into the nature of these two paramagnetic species. The analysis shows that the EMR anisotropy and rotational correlation times of the two paramagnetic species are similar in magnitude. The EMR anisotropy determined from linewidth studies is compared with that obtained from a frozen solution EMR spectrum.

X irradiation of sucrose single crystals at room temperature leads to the production of stable radicals, which give rise to the dosimetric electron paramagnetic resonance (EPR) signal. In the first few hours after irradiation, however, the shape of the EPR spectrum changes drastically. Based on two-dimensional field-frequency electron nuclear double resonance (FF-ENDOR) measurements, we demonstrate that, after high-dose ( approximately 5 kGy) and high-dose-rate irradiation, several species with limited stability at room temperature are produced next to the stable radicals. For two of these species, the main characteristics could be determined. Analysis of the time evolution of the FF-ENDOR and room-temperature EPR spectra in the first few hours after irradiation leads to the conclusion that these meta-stable radicals mainly recombine into diamagnetic species, while transformation into stable radicals is at most a marginal process.

Alanine/EPR dosimeters are well established as secondary, reference dosimeters for high-energy radiation. However, there are various sources of uncertainty in the evaluation of absorbed dose. This arises primarily from the necessity to calibrate each EPR spectrometer and each batch of dosimeters before their use. In order to overcome this disadvantage, a new generation alanine/EPR dosimeter has been developed, and its possibilities as a radiation detector are reported. Principally, it is a mixture of alanine, some quantity of EPR active substance, and a binding material. The EPR active substance, acting as an internal EPR standard, is chosen to have EPR parameters which are independent of the irradiation dose. The simultaneous recording of the spectra of both the sample and the standard under the same experimental conditions and the estimation of the ratioIalanine/IMn as a function of the absorbed dose strongly reduces the uncertainties. The response of these dosimeters for60Co γ-radiation exhibits excellent linearity and reproducibility in the range of absorbed dose, 102−5·104 Gy.

The spectral properties of bis(diaryl-dithiophosphato)copper(II) complexes, [Cu(S(2)P(OR)(2))(2)], with R = o-cresyl (complex I) and 2,6-dimethylphenyl (complex II) are studied by EPR- and vis spectroscopy. In solid (powder) state both complexes exhibit dark brown colour and are paramagnetic. Room temperature EPR spectra of the complexes dissolved in non-coordinating (C(6)H(5)CH(3), C(5)H(12), C(6)H(14)), acceptor (CHCl(3), CCl(4)) or donor (DMFA, DMSO) solvents have typical features of the chromophore CuS(4). In non-coordinating and acceptor solvents their isotropic EPR parameters are: g(iso)=2.047+/-0.003, (Cu)A(iso) = 7.2+/-0.1 mT and (P)A = 0.95+/-0.1 mT. An absorption band characterizes the vis spectra in these solvents with a maximum at 427 nm, due to a ligand-to-metal charge-transfer transition. One hour after dissolution the absorbance at 427 nm follows Beer's law with molar absorptivity (epsilon) about 11000, which does not change significantly after 24 h staying at room temperature or after 30 min heating at 50 degrees C. Both DMFA and DMSO exhibit specific solute-solvent interaction with the acceptor centre of copper complex yielding an axial adduct, with increased g-factor and decreased (hf)A compared to the initial complex. An additional EPR signal with unresolved hyperfine structure is also detected in DMSO. EPR and vis intensities of both bis(diaryl-dtp)Cu(II) complexes decrease after dissolution in both solvents. Moreover, they are EPR silent in pyridine and do not show any absorption in the vis spectra.

The results are presented of an electron magnetic resonance analysis at 110 K of radiation-induced defects in sucrose single crystals X-irradiated at room temperature, yielding a total of nine 1H hyperfine coupling tensors assigned to three different radical species. Comparisons are made with results previously reported in the literature. By means of electron paramagnetic resonance and electron nuclear double resonance temperature variation scans, most of the discrepancies between the present 110 K study and a previous 295 K study by Sagstuen and co-workers are shown to originate from the temperature dependence of proton relaxation times and hyperfine coupling constants. Finally, radical models previously suggested in the literature are convincingly refuted by means of quantum chemical density functional theory calculations.

Several types of laboratory glasses such as: “Jena”, “Rasotherm”, “Thuring” as well as window and windscreen glasses were studied by the method of EPR spectroscopy as possible emergency radiation dosimeters for γ-ray irradiation. The most appropriate values of modulation amplitude and microwave power were found to obtain best sensitivity for the measured signals. Dose measurements have shown a linear dependence between the EPR signal intensity of radiation created defects in glasses and applied dose in the dose range 50–500 Gy. “Thuring” glass was found to be the most sensitive sample to radiation. The magnitude of window glass absorbed dose was evaluated as the difference between the intensity of its EPR signal recorded after irradiation and the background signal, obtained after thermal relaxation of the former.

The content of soot in home dust collected from eight different flats or homes situated in different areas of Sofia, Bulgaria, is studied for a period of 14 months by using EPR spectrometry. The results obtained show two different areas in respect to the in-door pollution with soot which in one area is three to five times lower in comparison to the another. The characteristic features of both places are the intensive automotive traffic and central heating in the first part and less intensive automotive traffic but local heating facilities in the second area. These results are fully coinciding with previous studies on the soot content in urban aerosols and strongly suggest that main source of soot in air (in form of aerosols or precipitated as home dust) are the local heating facilities.

The self-redox reaction proceeding between two molecules of the complex bis(disubstituted-dithiophosphato)copper(II), CuII(R2-dtp)2, is studied by EPR and UV-VIS spectroscopy in DMFA, DMSO and pyridine. The effect of temperature and disulphide concentration in the solutions is also evaluated. The EPR spectra show that the g-values of CuII(R2-dtp)2 increase when it is dissolved in co-ordinating solvents, whereas the copper hyperfine splitting decreases compared to the corresponding values in non-co-ordinating solvents. Under the same conditions, a hypsochromic shift is observed in the maximal absorption at 420 nm of the electronic spectra which corresponds to the ligand-to-metal charge-transfer (LMCT) transition of the complex. The results are explained with the formation of axial or equatorial adducts between CuII(R2-dtp)2 and the co-ordinating solvents used. On the other hand, the molar absorptivity of the LMCT band and the intensity of the EPR spectrum increase strongly with the nature of the used co-ordinating solvent, the time after dissolution and the quantity of added disulphide. Both also depend on the size and shape of remote ligand substituents and they increase in the order MeEti-Pr. Beer's law is not obeyed immediately after dissolution of copper bis-dithiophosphate complexes. However, after standing for 24 h in the dark, DMFA solutions exhibit linear absorption/concentration dependence with approximately 70% higher molar absorptivity. An additional increase of the LMCT band and EPR intensity is found after heating the solution up to 50 degrees C for a short time, as well as after addition of the corresponding disulphide of dithiophosphate [(RO)2P(S)S-S(S)P(RO)2] to the CuII(R2-dtp)2 solution. As a result, the molar absorptivity value at the maximum of the LMCT band of Cu[(i-PrO)2-dtp]2 increases from 7.9 x 10(3) m(-1) dm3 cm(-1) immediately after dissolution to 2.9 x 10(4) m(-1) dm3 cm(-1). In DMSO and pyridine, the intensity of both the EPR signal and LMCT band of CuII(R2-dtp)2 continuously decrease after the preparation of the solutions. A small increase is only observed immediately after the addition of the corresponding disulphide of dithiophosphate. While DMFA forms stable adducts with Cu[(i-PrO)2-dtp]2, adduct formation with DMSO and pyridine destroys the initial complex.