Free radical photopolymerization initiated by UV and LED: Towards UV stabilized,tack free coatings

UV stabilizers (UV absorbers and Hindered Amine Light Stabilizers‐HALS) are added to UV‐curable formulations to provide long‐term durability. The influence of HALS and the filtering effect of UV absorbers are investigated under UV and LED irradiation by using different photoinitiating systems in free radical photopolymerization. The contribution of irradiation conditions and initiating systems on the filtering effect is discussed by performing Real‐Time Fourier Transform Infrared Spectroscopy (RT‐FTIR) and Confocal Raman Microscopy. Additionally, to get quantitative information about the light absorbed by the photoinitiator, without and with the filtering issue arising from UV stabilizers, series of calculations are carried out by taking into account the amount of light absorbed by the compounds and the intensity of the incident light. Finally, formulations are optimized with respect to surface inhibition to obtain tack free coatings in air atmosphere in the presence of UV stabilizers under visible light. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 3597–3607     

Reduced UV light scattering in PDMS microfluidic devices

Microfluidic devices which consist of polydimethylsiloxane (PDMS) are used extensively for the production of polymer microparticles through the use of droplet templating and on-chip photopolymerization. However, in existing methods, spatial confinement of the photochemical droplet solidification is impaired by UV light scattering inside the PDMS elastomer. We present a technique to load PDMS microfluidic devices with a fluorescent dye that absorbs the scattered UV light and shifts it to longer wavelengths. By this means, the stray light is no longer harmful, and UV exposure can be limited to a desired region on the microfluidic chip.     

Direct comparison between the angular distributions of the erythemal and eye-damaging UV irradiances: a pilot study

Several broadband ultraviolet (UV) radiation angular distribution investigations have been previously presented. As the biologically damaging effectiveness of UV radiation is known to be wavelength dependent, it is necessary to expand this research into the distribution of the spectral UV. UV radiation is also susceptible to Rayleigh and Mie scattering processes, both of which are completely wavelength dependent. Additionally, the majority of previous measurements detailing the biologically damaging effect of spectral UV radiation have been oriented with respect to the horizontal plane or in a plane directed towards the sun (sun-normal), with the irradiance weighted against action spectra formulated specifically for human skin and tissue. However, the human body consists of very few horizontal or sun-normal surfaces. Extending the previous research by measuring the distribution of the spectral irradiance across the sky for the complete terrestrial solar UV waveband and weighting it against erythemal, photoconjunctivital and photokeratital action spectra allowed for the analysis of the differences between the biologically effective irradiance (UV(BE)) values intercepted at different orientations and the effect of scattering processes upon the homogeneity of these UV(BE) distributions. It was established that under the local atmospheric environment, the distribution profile of the UV(BE) for each biological response was anisotropic, with the highest intensities generally intercepted at inclination angles situated between the horizontal and vertical planes along orientations closely coinciding with the sun-normal. A finding from this was that the angular distributions of the erythemal UV(BE) and the photoconjunctivital UV(BE) were different, due to the differential scattering between the shorter and longer UV wavelengths within the atmosphere.     

Rapid estimation of global sugars by UV photodegradation and UV spectrophotometry

The UV/UV method developed for the measurement of specific wastewater pollution parameters (ammonium, Kjeldahl nitrogen, total phosphorus) is adapted to the determination of sugars in fruit juices and soft drinks. The procedure is based on the UV spectrophotometric detection of by-products of UV photodegradation of carbohydrates. Time of analysis is greatly reduced by using specific pH conditions and diluted samples.     

Rapid,on-site identification of explosives in nanoliter droplets using a UV reflected fiber optic sensor

A portable UV (190–400 nm) spectrophotometric based reflected fiber optic sensor system is presented for the on-site detection and identification of explosives. A reflected fiber optic sensor for explosives analysis was developed, with low sample consumption (20–100 nL) and a wide concentration quantification range (1.1–250 mg L⁻¹). Seven common explosives [pentaerythritol tetranitrate (PETN), trinitrophenylmethylnitramine (CE), trinitrotoluene (TNT), dinitrotoluene (DNT), picric acid (PA), cyclotetramethylenetetranitramine (HMX), cyclotrimethylenetrinitramine (RDX)] and a PETN–RDX mixture (to simulate the Semtex used in many terrorist bombings) were quantitatively analyzed and identified by the proposed system in less than 3 s per test, with limits of detection (LOD) of 0.3 mg L⁻¹. Due to chemical interference problems in the UV wavelengths range, a novel feature matching algorithm (FMA) was proposed for explosive identification, which was proved to have higher specificity and better anti-interference ability. Real post-blast debris samples were analyzed by the proposed method, and the results were validated against an LC/MS/MS method. The rapid, cost-effective detection with low sample consumption and wide applicability achieved by this system is highly suitable for homeland security on-site applications, such as rapid sample screening in post-blast debris.     

Investigations of oxidative UV photolysis

Summary Oxidative UV photolysis according to DIN standard 38406 E 16 [1] has been investigated as a sample preparation method for voltammetry. UV photolysis has decisive advantages compared with mineral acid digestion owing to the simple procedure and the very low blank values, which in turn are due to the minimal reagent addition required. For UV photolysis with a high pressure mercury lamp, an apparatus has been used that employs a new type of sample cooling and that allows the simultaneous irradiation of 12 samples. The sample preparation for the voltammetric determination of zinc, cadmium, lead, copper, nickel and cobalt has been optimized using a model water solution and subsequently tested with real matrices. The type of organic matrix and the irradiation temperature determine the irradiation time required. To digest aromatic compounds, it is advantageous to work at reaction temperatures of ca. 90°C. The application of UV photolysis centers on water samples slightly polluted with organic compounds; however, it can also be used with more heavily polluted wastewaters. As the digestion times are at most 60 min, the method is of interest for routine analysis.     

Interaction between UV radiation and filled polytetrafluoroethylene (PTFE). II. A multiple scattering analysis

The second part of the series, this article analyzes the way UV light propagates through pure and filled PTFE. We investigated the diffusiveness of the semicrystalline matrix as well as the effect of scattering and absorbing fillers (CaF₂ and TiO₂) on the attenuation. The UV-visible absorption curves have been determined by spectrophotometry. A theoretical calculation based on a four-flux multiple scattering approach allowed us to satisfactorily reproduce the experimental results, highlighting the respective importance of the coherent and the diffuse fields. In light of this model, we discuss the influence of multiple scattering on the extent of degradation when PTFE is exposed to a high energy UV radiation. This approach provides of a comprehensive view of the damaging effect of UV light on PTFE, showing a good agreement with the experimental results of the previous article. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 2069–2083, 1998     

Capillary zone electrophoretic analysis of carbohydrates by direct and indirect UV detection

Summary The analysis of carbohydrates has been always hampered by their lack of UV absorbance above 200 nm, which is an especially challenging problem in capillary electrophoresis due to the very small (nl) sample volumes injected. The introduction of 2-aminopyridine as derivatizing agent allows sensitive direct UV detection of saccharides in the fmol range. However, due to the requirement of the presence of a free aldehyde group only aldoses and uronic acids can be determined. This limitation was recently overcome by means of precolumn derivatization withp-aminobenzoic acid or ethylp-aminobenzoate, which permits the analysis of fructose with a lower mass detection limit of 0.3 and 0.14 pmol, respectively. The detection limits for aldoses were even as low as 15 and 7 fmol. A more universal approach is the use of indirect UV detection, which permits the analysis of carbohydrates, including (1–2)-linked disaccharides and aldonic acids, at the lower pmol level without the need for derivatization.Dedicated to Professor Leslie S. Ettre on the occasion of his 70th birthday.     

UV and H2O2/UV degradation of a pharmaceutical intermediate in aqueous solution

The degradation of 5-methyl-1,3,4-thiadiazole-2-thiol (MMTD), a pharmaceutical intermediate found in some aquifers of Northern Italy, has been investigated by means of UV and UV/H2O2 treatments. The study has been carried out with a 17 W low pressure mercury lamp at room temperature, using a (100)/(1) (H2O2)/(MMTD) molar ratio. The results have demonstrated that: (i) with an initial MMTD concentration of 1 mg/l, 90% MMTD removal can be achieved within 1 hour or less than 5 minutes by UV or UV/H2O2 respectively; (ii) the sole UV irradiation does not cause any MMTD mineralization; (iii) with an initial MMTD concentration of 50 mg/l, 4 hours of UV/H2O2 treatment lead to an almost complete mineralization of the MMTD organic sulfur and to a partial mineralization of carbon (59%) and nitrogen (14%). The identification of degradation by-products, performed by HPLC-UV-MS analysis, revealed that the sole UV irradiation gives rise to the MMTD transformation into a single by-product that continuously accumulates in the solution. Conversely, the UV/H2O2 treatment forms seven intermediates that undergo further degradation through the breakdown of the thiadiazole ring. On the basis of the obtained results a degradation pathway has been proposed.     

Physical properties of organic particulate UV absorbers used in sunscreens II. UV-attenuating efficiency as function of particle size

In this study the UV-attenuating properties of microparticles consisting of a benzotriazole derivative were investigated, which are used as absorbers for UV radiation in cosmetic sunscreens. The particles were micronized in presence of a dispersing agent by means of a ball milling process. According to the energy input different particle sizes were produced in the range of 0.16 to 4 microm. In order to study even smaller particles, the sample with particle size 0.16 microm was fractionated further by centrifugation. Particle sizes were measured using fiberoptic quasi-elastic light scattering (FOQELS) and laser diffractometry. The UV-attenuating properties of the dispersions with different particle sizes were assessed using UV spectroscopy. With decreasing particle size the efficiency of the UV extinction of the dispersion increases up to a particle size of 80 nm. For particles smaller than 80 nm the UV extinction decreases again indicating an optimum at 80 nm. From reflection spectroscopic measurements it was found that scattering makes about 10%, and absorption 90%, of the UV-attenuating effect of the particles, which are obtained at the end of the milling process.     

UV辐照接枝聚合制备亲水性纳滤膜

用紫外光引发自由基共聚接枝的方法对酚酞基聚芳醚酮(PEK-C)超滤膜表面进行改性制备了亲水性荷电纳滤膜. 研究了用不同单体接枝改性膜对盐溶液的截留性能, 证明了Donnan电荷效应对纳滤膜分离性能的影响. 在此基础上, 通过丙烯酸(AA)与对苯乙烯磺酸钠(SSS)的共聚接枝, 并改变它们在接枝液中的相对含量, 成功地制备出膜的表观截留率和渗透通量都较高的纳滤膜.     

The UV Index on the Spanish Mediterranean coast

An analysis is made of measured ultraviolet erythemal solar radiation (UVER) data recorded during the year 2003 by the networks of the Catalan Weather Service and the Environment Department of Valencia (both on the Spanish Mediterranean coast). Results show a latitudinal variation at sea level, of 3-4% per degree and an increase with altitude of 10% per km. Based on these data the UV Index has been evaluated for the measuring stations. The maximum experimental value of the UV Index was around 9 during the summer, although higher values were recorded at two stations, one at the highest elevation and the other at the lowest latitude. The annual accumulated doses of irradiation on a horizontal plane have been presented as well as the evolution through the year in units of energy, Standard Erythemal Doses and Minimum Erythemal Doses according to different phototypes. Lastly, the UV Index forecast, determined with a multiple scattering radiative transfer model, has been analyzed. Total agreement or only one unit of difference between measured and modelled values was found in 94% of cloud-free cases.     

Solar UV dose patterns in Italy

Since 1992 solar ultraviolet (UV) spectral irradiance (290-325 nm) has been measured at two Italian stations of Rome (urban site) and Ispra (semirural site) using Brewer spectrophotometry. The data collected under all sky conditions, are compared with the output of a sophisticated radiative transfer model (System for Transfer of Atmospheric Radiation--STAR model). The STAR multiple scattering scheme is able to cope with all physical processes relevant to the UV transfer through the atmosphere. The experience so far acquired indicates that, in spite of the unavoidable uncertainties in the input parameters (ozone, aerosol, surface albedo, pressure, temperature, relative humidity, cloud cover), measured and computed clear sky iradiances are in reasonable agreement. The STAR model is applied to build up the solar UV geographic patterns in Italy: the daily dose in the range 290-325 nm is computed at about 70 sites where a thorough and homogeneous climatology is available. For each month the concept of an idealized "standard day" is introduced and the surface distribution of solar UV field determined. The map of solar UV patterns for Italy, available for the first time, meets the study requirements in the field of skin and eye epidemiology, as well as in other investigations dealing with the impact of UV on the biosphere. The results are interpreted in terms of atmospheric and meteorological parameters modulating UV radiation reaching the ground.     

Identification of free radicals induced by UV irradiation in collagen water solutions

Electron paramagnetic resonance (EPR) method has shown that hydrogen atoms and acetic acid free radicals appear in surrounding acetic acid-water solution of collagen under ultraviolet (UV) irradiation. These free radicals interact with the collagen molecule; consequently, seven superfine components of EPR spectrum with the split of aH = 11.3G and g-factor 2.001 appear. It is assumed that this spectrum is related to the free radical occurred on the proline residue in collagen molecule. In order to discover .OH hydroxyl radicals even in minor concentration, spin trap 5.5-dimethyl-1-pyrroline N-oxide (DMPO) has been applied. During the irradiation of collagen water solution in the presence of spin trap, EPR spectrum of the DMPO/.OH adduct has not been identified, while the above mentioned spectrum has been observed once the hydrogen peroxide H2O2 and FeSO4 were added to the sample. That means that water photolysis does not take place in collagen water-solution due to UV irradiation. It was suggested that occurrence of hydrogen radical is connected with the electron transmission to the hydrogen ion. The possible source of free electrons can be aromatic residues, photo ionization of which takes place in collagen molecule due to UV irradiation.     

Solid-phase extraction followed by liquid chromatography-tandem mass spectrometry for the determination of hydroxylated benzophenone UV absorbers in environmental water samples

A procedure for the determination of six derivatives of 2-hydroxybenzophenone, used as UV absorbers, in water samples is presented. Compounds were first concentrated using a solid-phase extraction (SPE) cartridge and then selectively determined by liquid chromatography-tandem mass spectrometry (LC-MS/MS) using electrospray ionization (ESI). The effect of different parameters on the performance of concentration and determination steps is discussed. The highly polar and acidic 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid (BP-4) required the use of ammonium acetate as modifier during desorption of SPE cartridges and also to improve the performance of its separation in the LC column. Under optimized conditions, the proposed method provided limits of quantification from less than 1 to 32 ng L⁻¹, depending on the compound and the type of water sample. Recoveries from the SPE step (83-105%) remained unaffected by the nature of the matrix; however, the efficiency of electrospray ionization was compound and sample dependant. Real sample analysis reflected the presence of three of the six investigated species (BP-4, 2-hydroxy-4-methoxybenzophenone, BP-3, and 2,4-dihydroxybenzophenone, BP-1) in the aquatic environment, particularly in raw wastewater samples. In this latter matrix, BP-4 was the compound presenting the highest concentrations; moreover, it was poorly removed in sewage treatment plants and consequently it also appeared in river water.     

Determination of Pesticide Residues in Cereals by Liquid Chromatography and UV Detection

Abstract

A chromatographic method to determine pesticide residues in cereals by high-performance liquid chromatography (HPLC) and ultraviolet (UV) detection has been described. The study focused on the preliminary purification procedure because of the analytical problems associated with the presence in these food matrices of high-molecular-weight compounds, such as lipids, triglycerides, celluloses, and starch, which can interfere and reduce the chromatographic separation efficiency of the analytes. The method proposed is based on the extraction of pesticide residues from 5 g of sample extracted with the use of petroleum ether and on cleanup with a C18 cartridge. The pesticides were eluted with acetonitrile. The column packed with solid support was eluted with a suitable solvent, and only a portion of flow outlet side of the UV detector was collected. Using the information of standard UV trace, it was possible to establish an appropriate portion and to ensure the collection of all pesticides analyzed. The simple and rapid proposal method has shown good recovery (70–110%) for different spiked levels of samples (0.025–0.1 mg/Kg) and could be applied to other food matrices that containing high-molecular-weight compounds.     

Sensitive determination of phenylarsenic compounds based on a dual preconcentration method with capillary electrophoresis/UV detection

A novel method based on off-line hollow fiber based liquid liquid liquid microextraction (HF-LLLME) combined with on-column anion selective exhaustive injection (ASEI)-capillary electrophoresis/ultraviolet (CE/UV) detection was proposed for the speciation of five phenylarsenic compounds including phenylarsonic acid (PAA), 4-aminophenylarsonic acid (4-APAA), 4-hydroxyphenylarsonic acid (4-HPAA), 4-nitrophenylarsonic acid (4-NPAA) and 3-nitro-4-hydroxyphenylarsonic acid (NHPAA) in this paper. In HF-LLLME, the target analytes were extracted from 5 mL aqueous samples (donor solution pH 2.15) through a thin phase of tributyl phosphate (TBP) inside the pores of a polypropylene hollow fiber and finally into an 18 μL 0.8 mmol/L Tris acceptor solution inside the lumen of the hollow fiber. Following HF-LLLME, the acceptor solutions were directly analyzed by ASEI-CE/UV. For ASEI, a large plug of water (91% length of total capillary) was introduced into the separation capillary before sample injection in order to prolong the sample injection time, and thus enhance the stacking efficiency. Under the optimized ASEI conditions, up to 236-fold of enrichment factor (EF) was obtained for the ASEI-CE/UV determination of target phenylarsenic compounds. By combining HF-LLLME with ASEI-CE/UV, EFs ranging from 155 to 1780-fold were achieved and the limits of detection (LODs) (at a signal-to-noise ratio of 3) were in the range of 0.68-6.90 μg/L for five phenylarsenic compounds; the relative standard deviations (RSDs) of corrected peak area were 5.6-11.8%. The proposed HF-LLLME-ASEI-CE/UV method was applied for the determination of five target phenylarsenic compounds in pig feed from a local pig farm, and storage pig litter, soil in agricultural field and lake water collected near this pig farm, the recoveries for the spiked samples were in the range of 85.7-104.5%, 66.7-96.2%, 28.9-46.9% and 86.9-107.8% for pig feed, pig litter, soil and lake water, respectively.     

紫外光辐射对TiO2溶胶的影响研究

用紫外-可见吸收光谱、动态光散射与透射电镜研究紫外光辐射对T₂溶胶的影响,结果表明,光辐射使T₂溶胶在可见光区的吸收减少,紫外区吸收增加,吸收带隙增大.与非光辐射的T₂溶胶粒子相比,光辐射使T₂溶胶粒子分布均匀且平均粒径减小,提高了T₂纳米粒子在室温下的晶化程度.     

Effect of the UV Modification of α-Crystallin on Its Ability to Suppress Nonspecific Aggregation

Recent studies have shown that structural modifications of α-crystallin during lens aging decrease it's effectiveness as a molecular chaperone. Some of these posttranslational modifications have been linked to UV radiation, and this study was undertaken to investigate the effect of UV irradiation on the ability of α-crystallin to suppress nonspecific aggregation. The effect of 3-hydroxykynurenine (3-HK) was also investigated as a model for its glucoside (3-HKG), a main lens chromophore that has been linked to photochemical changes in the human lens. Alpha- and γ-crystallin solutions (1 mg/mL, 1:0.125 wt/wt) were photolyzed (transmission above 295 nm) for various time intervals. Thermal denaturation of γ-crystallin with or without α-crystallin was carried out at 70°C and increases in light scattering were measured at 360 nm. We found that (1) irradiation of γ-crystallin increased its susceptibility to heat-induced scattering. The addition of α-crystallin protects it against thermal denaturation, although its ability to do so decreases the longer γ-crystallin is irradiated and (2) irradiation of α-crystallin decreases its ability to suppress nonspecific aggregation and the presence of 3-HK during irradiation decreases it further. Our results indicate that posttranslational modifications of α-crystallin due to UV irradiation affect the sites and mechanisms by which it interacts with γ-crystallin. The kinetics of γ-crystallin unfolding during thermal denaturation were also analyzed. We found that a simple two state model applies for nonirradiated γ-crystallin. This model does not hold when γ-crystallin is irradiated in the presence or absence of α-crystallin. In these cases, two step or multistep mechanisms are more likely.