Photostimulated luminescence detection of irradiated shellfish: international interlaboratory trial

An interlaboratory trial was conducted to validate photostimulated luminescence (PSL) detection of irradiated shellfish. Five species of shellfish (Nephrops norvegicus, mussels, black tiger prawns, brown shrimps, and king scallops) were presented blind as nonirradiated and irradiated to 0.5 and 2.5 kGy. Precharacterization analysis of each product and treatment was performed on both whole (including shell) and intestinal samples. The results for whole samples (including shell) confirmed that the method was able to distinguish between nonirradiated and irradiated samples, regardless of dose. Intestinal data have identified that the method is dependent on the quantity and sensitivity of grits present within the intestinal tract, which can be assessed using calibration by normalization to 1 kGy. Five laboratories returned both initial screening and calibrated data and sample classification. All laboratories correctly identified all irradiated products using the screening criteria. There were no false positives. The results confirm the validity of the PSL method for shellfish, which has been adopted as a European standard method and by the Codex Alimentarius Commission. Calibration is required where only intestinal material is available. For whole samples with shell, screening alone is sufficient.     

Photostimulated luminescence detection of irradiated herbs, spices, and seasonings: international interlaboratory trial

An interlaboratory trial was conducted to validate photostimulated luminescence (PSL) methods for herbs, spices, and seasonings. Forty products (11 herbs, 17 spices, and 12 seasonings) were purchased from a local commercial source, and randomly selected samples were irradiated with 10 kGy. Four blended products were prepared at Scottish Universities Research and Reactor Centre, mixing varying proportions of irradiated material with the untreated product. Precharacterization against a predefined threshold identified low sensitivity products (black and white peppers) and products with high natural signals (thyme, sage, parsley, and mixed herbs), both of which might be susceptible to misclassification. Precharacterization also revealed whether calibration was likely to resolve overlap between classification categories. Eight sets of screening data and 5 sets of calibrated data were returned by participants. Of the 840 samples sent, 1593 screening measurements and 788 calibrated measurements were received from 662 samples. In screening mode, participants reached definitive conclusions in 87% of cases, 99% of which were correct. Of the remaining 13%, calibration to identify low-sensitivity resolved 60% of cases. Overall, 94% of samples were correctly identified by either screening alone, or screening plus calibration; 6% remained unclassified and therefore required further investigation by thermoluminescence. The results confirm the validity of the PSL method for herbs, spices, seasonings, and blends, and emphasize the need for calibration to identify low-sensitivity samples. This method has now been adopted by the European Committee for Standardization (CEN) and the Codex Alimentarius Commission.     

Examination of covalently bound polymeric stationary phases by luminescence spectroscopy

Luminescnce spectroscopy is used to prove silica-gel surfaces derivatized with [3-(3-pyrenyl)propyl]methyldichlorisilane. Evidence of solution pre-polymerizatiln and subsequent derivatization to acceisibl surface silanols is presented. Conformatonal changes of the bound ligands in polar and non-polar solvents indicate a dynamic surface which minimized its surface area in hostile solvents.     

Preliminary study on application of impregnated synthetic peptide TLC stationary phases for the pre-screening of 5-HT1A ligands

Chromatographic parameters (deltaR(f)), defined as a difference in the migration of tested compound on the control and peptide impregnated silica gel TLC plates, were determined for 42 arylpiperazine derivatives. An amino acid sequence of the peptide used for impregnation was derived from the III transmembrane segment of the 5-HT(1A) receptor in the close vicinity of aspartic acid (Asp 166) residue. It was found that the deltaR(f) values obtained in a model employing tetrapeptide P4LA (ADVL), as well as the calculated logP correlate with 5-HT(1A) receptor affinity of the studied compounds.     

Exciplex luminescence studies of the surface polarity of end-capped bonded phases

The fluorescence intensities and emission maxima of surface-bound exciplexes were studied to determine the relative polarity of microparticulate silica before and after derivatization with trimethylchlorosilane (TMCS) and hexamethyldisilazane (HMDS). The results indicate that HMDS yields a bonded phase with greater average polarity relative to TMCS at equivalent surface coverages. This difference is attributed to the formation of basic sites on the surface by chemisorption of ammonia generated during derivatization with HMDS. The observation of exciplex emission on silica gel is novel and strongly supports clustering of surface-bound molecules into high-density regions.     

Reversible thermal and photochemical switching of liquid crystalline phases and luminescence in diphenylbutadiene-based mesogenic dimers

The synthesis and study of the photo- and thermoresponsive behavior of a series of novel asymmetric mesogenic dimers, consisting of a cholesterol moiety linked to a diphenylbutadiene chromophore via flexible alkyl chains are reported. These mesogenic dimers possess the combined glass forming properties of the cholesterol moiety and the photochromic and luminescent properties of the butadiene moiety. Photoinduced cis/trans isomerization of the butadiene chromophore in these materials could be utilized to bring about an isothermal phase transition from the smectic to the cholesteric state. By photochemically controlling the cis/trans isomer ratio, the pitch of the cholesteric could be continuously varied making it possible to tune the color of the film over the entire visible region, and the color images thus generated could be stabilized by converting them to N* glasses. These materials were also polymorphic, exhibiting two crystalline forms possessing distinctly different fluorescence properties. The ability to thermally switch these materials from one crystalline form to the other in a reversible manner also makes them useful for recording fluorescent images.     

Some new algorithms applicable to potentiometric titration in acid-base systems

The paper describes some regression equations adaptable for determination of parameters such as concentrations, equilibrium constants and hydrogen-ion activity coefficients in systems comprising hydrolysable salts of type MeB(u) and monoprotic and polyprotic acids or their salts. These equations are based on the charge and mass balances. Two unconventional types of regression equations are applied: (i) Padé functions W = G(1)(h)/G(2)(h) relating the sum (W) of V(0) ml of titrand and V ml of titrant, W = V(0) + V, to polynomial functions G(1)(h) and G(2)(h) of the hydrogen-ion activity, h, and (ii) functions of the type 1/W = phi(h), based on the Simms titration constants involved. The latter functions are notable for determination of acids and/or their salts in mixtures. The regression equations are developed for systems at constant ionic strength. The parameters of the system can be calculated by means of the computer program MINUITS. Other possibilities of the method, e.g., application to mixed complexes and extraction systems, are also presented.     

1,4-Anthraquinonoid dienophiles applicable to synthesis of linear tetracycles

Derivatives of 1,4-anthraquinones (3), (21) are shown to be good dienophiles for achieving strongly regiocontrolled synthesis of linear tetracycles, a property greatly enhanced by their ease of formation and of subsequent replacement of the chloride.     

Linear calibration graph applicable to the indirect determination of sulphate

Equations based on the equilibrium relationship between a sulphate-containing solution and solid lead sulphate were derived and applied to calibration graphs for the determination of sulphate. The special character of the linear graphs extends not only the applicability of linear calibration and standard addition procedures to the indirect determination of sulphate, but also the reliability of the analytical results. Experiments with the flow-injection technique confirmed the applicability of the proposed linear graphs.     

Photosensitized electron transfer processes of nanocarbons applicable to solar cells

Photosensitized electron-transfer processes of nanocarbon materials hybridized with electron donating or electron accepting molecules have been surveyed in this tutorial review on the basis of the recent results reported mainly from our laboratories. As nano-carbon materials, fullerenes and single wall carbon nanotubes (SWCNTs) have been employed. Fullerenes act as photo-sensitizing electron acceptors with respect to a wide variety of electron donors; in addition, the fullerenes act as good ground state electron acceptors in the presence of light-absorbing electron donors such as porphyrins and phthalocyanines. In the case of SWCNTs, their ground states act as electron acceptor and electron donors, depending on the photosensitizers. For example, with respect to the photoexcited porphyrins and phthalocyanines, SWCNTs usually act as electron acceptors, whereas for the photoexcited fullerenes, SWCNTs act as electron donors. The diameter sorted semi-conductive SWCNTs have been used to verify the size-dependent electron transfer rates. For the confirmation of the electron transfer processes, the transient absorption methods have been widely used, in addition to the time-resolved fluorescence spectral measurements. The kinetic data thus obtained in solution are found to be quite useful to predict the efficiencies of photovoltaic cells constructed on semiconductor nanoparticle modified electrodes and their photocatalytic processes.     

A theory of field-induced birefringence applicable to systems of large molecules

We consider a molecule in an external constant field interacting with a linearly polarized photon. When the field is chosen to be magnetic and directed along the wave vector of the photon (longitudinal), we find that the time dependence of the state function implies a rotation of the plane of polarization of the photon characteristic of the Faraday effect. Similarly when the field is transverse, the time evolution of the state corresponds to the Kerr effect in the case of an electric, and the Cotton—Mouton effect in the case of a magnetic field. The theory is applicable to a dilute system of freely oriented molecules of any size: the long-wavelength approximation is not invoked. The general procedure for averaging over all molecular orientations is carried out explicitly in the case of the Faraday effect.     

Experimental verification of the modified Gran methods applicable to redox systems

This study describes the application of the modified Gran I and II methods for determination of equivalence volume in redox titrations and for calibration, i.e. for determination of the correct slope of the redox indicator electrodes, which appears to be a major problem in using these electrodes. The four new versions of the Gran II method, denoted as MG(II)B, MG(II)C, MG(II)D and MG(II)E methods, in which the problem of calibration and determination of equivalence volume are considered simultaneously are suggested and compared with MG(I)S and MG(II)A methods known hitherto. All the methods are experimentally tested and discussed.     

Experimental evaluation of different precision criteria applicable to microbiological counting methods

The dispersion of microbiological counting measurements, when repeating the analysis on the same material both within a laboratory (repeatability) and between laboratories (reproducibility) can be characterized by the organization of interlaboratory studies, where several sets of identical test materials are sent to several laboratories. Using the example of data generated by an interlaboratory study on enumeration of Listeria monocytogenes in foods by the standardized reference method (colony-count technique), 2 types of robust estimators of reproducibility standard deviations, based on the median, were examined, in comparison with the classical estimators, based on the mean. Experimental evaluation indicated that the 3 approaches gave consistent results for most of the combinations. The usual log10 transformation of the enumeration results was also questioned before these calculations were conducted.     

A simple perturbed-hard-sphere equation of state applicable to subcritical and supercritical temperatures

A Carnahan—Starling—van der Waals equation of state is applied to eight fluids, including ammonia and water. The two constants are evaluated from supercritical-density data, subcritical saturated-liquid densities and vapor pressures; both constants decrease weakly as temperature rises. Good agreement with experiment is obtained over a wide range of conditions but, because of inherent weaknesses in perturbed-hard-sphere theory, agreement in the immediate critical region is poor and calculated second virial coefficients tend to be too positive. Nevertheless, this simple equation may be useful for engineering calculations.     

Application of luminescence to the determination of trace copper

A review of Russian and foreign literature on the luminescence determination of copper in a large group of materials is presented.     

Application of time-resolved luminescence to dry reagent chemical technology

A time-resolved luminescence method describing the use of terbium(III) in the dry reagent format is presented for the first time. Paper strips previously treated with sucrose are used as solid substrates where terbium(III) is immobilised by adsorption. The strips are stable for at least 6 months and they can be easily stored under a desiccant medium. Only the addition of the buffered sample is required for the analysis. This methodology has been applied to the determination of two local anaesthetics, namely benzocaine and procaine. These compounds release p-aminobenzoic acid after a hydrolysis step in alkaline medium, which reacts to terbium(III) giving a luminescent chelate. The luminescence intensity measurements are obtained at λ_ex 286 and λ_em 545 nm by using the time-resolved mode of the instrument. The method presents a linear range from 1.1 to 21.9 μM and the calculated LOD is 0.4 μM. It has been satisfactorily applied to the analysis of pharmaceutical samples and the recoveries obtained are in the range 88-108%.