Chemical Actinometer Research Articles

Polarographic Study of the Photodecomposition of Nimodipine

Nimodipine, a calcium antagonist belonging to the dihydropyridine family, produces a well‐defined polarographic peak due to the four‐electron reduction of the nitro group. This peak was used to track the photodecomposition of nimodipine induced by UV light and daylight. Nimodipine was modified by UV irradiation with degradation following first‐order kinetics. A degradation rate constant of 0.099 min−1, with a half‐life of 7.78min, for UV irradiation without a filter was obtained. Furthermore, a quantum yield of 1.32 × 10−3 molecules/quantum absorbed was measured with a chemical actinometer. The UV degradation product, which was isolated and identified, showed that irradiation of nimodipine causes oxidation of the dihydropyridine ring and transmutation of the nitro group in the nitrobenzene moiety.

Photoelectrochemical (PEC) cell: riboflavin-Na 2EDTA system as an actinometer

Photoexcited riboflavin (B 2 *) can be quenched by electron transfer to Na 2EDTA to B 2 .− irreversibly in the photoelectrochemical (PEC) cell. B 2 .− can be oxidized at a suitable anode, and the electron transferred via an external circuit to a cathode dipped in acid reduces H + to H 2. The generated photocurrents ( i) are linearly dependent on the intensity of the incident light (I 0 λ). A kinetic model for the variation of i with I 0 λ has been derived. Conditions for the operation of the cell as an actinometer, which is useful for the wavelength region 350 nm ⩽ λ ⩽ 450 nm, are given in detail. The reproducibility of the cell is comparable to that observed with a conventional chemical actinometer, namely a potassium ferrioxalate actinometer.

Actinometer and Eppley radiometer measurements of the NO2 photolysis rate coefficient during the Mauna Loa Observatory photochemistry experiment

Measurements of the apparent first‐order rate coefficient for NO2 photodissociation (jNO2) were made using a chemical actinometer during the month of May 1988 at the Mauna Loa Observatory, Hawaii. Simultaneous measurements of the ultraviolet irradiance (E), obtained with an Eppley radiometer, allowed extensive testing of the semi‐empirical relationships between E and jNO2 proposed by Madronich (1987a). More than 3700 simultaneous measurements of jNO2 and E were obtained for solar zenith angles ranging from 4–90 degrees, and for different sky conditions (including clear skies, partial cloud cover, arid valley clouds below the horizon). For overhead clear skies, the NO2 photodissociation rate coefficient derived from Eppley radiometer data, here denoted j′, was in good agreement with actinometric measurements, j′/jNO2=1.01±0.05(1σ). The actinometer‐radiometer relationship holds reasonably well even when low‐lying valley clouds are present. For the periods of overhead intermittent clouds, the j′values track jNO2 values well, but the observed ratio shows significantly more scatter and the average is somewhat less than unity: 0.93 ± 0.09 (1σ). Measurements taken with and without upward scattered and reflected radiation show that valley clouds can contribute to the jNO2 values for the conditions encountered during the Mauna Loa Observatory Photochemistry Experiment.

Electrochemical actinometry using the assembled monolayer film of an azo compound

A simple, convenient chemical actinometer based on an assembled monolayer film of an amphiphilic azo compound is proposed. In contrast to spectrophotometric quantification in conventional chemical actinometries, an electrochemical approach was employed.

Chemical actinometers in the 250–270 nm region

Both γ-1,t-2,t-3,c-4-tetraphenylcyclobutane (TPCB) and 2,4-dimethoxy-6-phenoxy-s-triazine (DMPT) can be used as chemical actinometers for laser pulses (less than 10 17 photons pulse −1) and steady state light in the 250–270 nm range. The photocycloreversion of TPCB occurs to give trans-stilbene with a reaction quantum yield of 0.29 ± 0.01 in methylcyclohexane or n-butyl chloride at room temperature. The photo-Fries rearrangement of DMPT takes place to give the corresponding ortho and para isomers; the reaction quantum yield for the ortho isomer is 0.12 in ethanol or 0.15 in methylcyclohexane. Actinometry with these compounds can be carried out easily using spectrophotometry.

Actinometry of an excimer laser with a ferrioxalate chemical actinometer.

Actinometry of intense UV lights from ArF, KrF and XeF excimer lasers has been studied with a ferrioxalate chemical actionometer. The relation between the number of photons per pulse (N) and the absorbance change per pulse (ΔA) at 510 nm is expressed by using a first-order function, N=a·ΔA-b. (a, b: numerical constants characterized by a laser-wavelength). The experimental errors in this method were 4.8, 5.2, and 1.6% for ArF, KrF and XeF excimer lasers, respectively. The results prove that the ferrioxalate chemical actinometer is satisfactorily usable as an actinometer for excimer lasers.

Formation of low molecular weight carbonyl compounds by sensitized photochemical decomposition of aliphatic hydrocarbons in seawater

Anthraquinone has been found to be a compound occuring frequently in seawater. Excited by solar radiation it acts as one of many natural and man-made photosensitizers and can thus be used as a model substance for the study of sensitized photochemical reactions of environmental chemicals. Experimentally it has been shown to mediate the oxidative photochemical decomposition of aliphatic hydrocarbons which, lacking absorption bands in the solar UV range at sea level, are by themselves photochemically inert. Formaldehyde, smaller amounts of acetaldehyde and acetone as well as a still unidentified carbonyl compound are the principal low molecular weight products generated in the anthraquinone-sensitized photooxidation, with natural as well as artificial sunlight, of straight chain saturated hydrocarbons accommodated in high purity water. Qualitatively the same results were obtained in natural seawater as reaction medium from which particles were removed by glass fiber filtration and organic compounds by adsorption on activated charcoal. The concomittant generation of homologous series of methylketones and terminal alkenes suggest a decomposition mechanism involving cyclic electron rearrangement in a 6-membered transition state. Based on HPLC analysis of their 2,4-dinitrophenylhydrazones, the rates of volatile carbonyl generation in the sensitized photo-oxidation of n-tetradecane was determined in the liquid phase. Also determined was the rate of formaldehyde formation in the gas phase from n-tetradecane and from two Brazilian crude oils. The rates of generation of acetaldehyde and acetone could not be determined in the experiments with crude oils because of irregular changes of concentrations with time. The rate of concentration increase of formaldehyde in the vapour phase over the hydrocarbon surface film was similar to that in the water underneath. The artifical light source was a high pressure xenon lamp whose emission spectrum closely resembles that of natural sunlight at sea level. It was calibrated against the intensity of natural sunlight using pnitroacetophenone/pyridine as binary chemical actinometer.

A chemical actinometer for the wavelength range 610 – 670 nm

The methylene-blue-sensitized photo-oxygenation of mesodiphenylhelianthrene can be used as a chemical actinometer in the wavelength region 610 – 670 nm. The system has the advantage of high sensitivity and accuracy and can be used as a quantum counter for polychromatic light in the range 620 – 670 nm.

Complementary study on the use of the potassium Reinecke's salt as a chemical actinometer

Aqueous solutions of K[Cr(NH3)2(SCN)4].H2O (the potassium Reinecke's salt) can be used as a photochemical reference system for radiations in the visible region. The results of complementary studies on the improvement of analytical procedures, the direct synthesis of the salt and its thermal reactivity are reported. The possibilities of the application of the system are also discussed.

Two wavelength-independent chemical actinometers which together cover the range 334 – 560 nm

The self-sensitized photo-oxygenation reactions of 9,10-dimethyl-anthracene and 5,12-diphenyltetracene can be used as actinometers and quantum counters for polychromatic light in the wavelength regions 334 - 395 nm and 405 - 500 nm respectively. Both systems have the advantages of wavelength independent quantum yields, high reproducibility, high accuracy and convenient analysis.

A convenient method of measuring quantum yields of photoisomerization of trans-stilbene

Abstract A novel and convenient method of measuring quantum yields of photoisomerization of trans -stilbene was developed by using a monochromic nitrogen laser light source and a pulsed energy meter. The method has high accuracy without the need to employ chemical actinometers.

Measurement of attenuation coefficients in natural water columns

Light scattering and light absorption by particulates and humic substances in natural waters can significantly affect the photoreaction rates of chemicals in aquatic systems. These scattering and absorption processes are quantitatively described by the use of an empirical parameter, the diffuse attenuation coefficient, K. We have tested actinometric and radiometric methods for measuring the diffuse attenuation coefficient K which can be used to calculate the depth averaged rate constant (kpavg) in a specific water body. The two methods were found to give excellent agreement. We found the method using a chemical actinometer system to be the most practical and convenient for use in field studies, but that more studies in other water systems and with other test cheimcals are needed to more rigorously test the method. We calculated kpavg equal to 0.33 ±0.17d−1 for carbazole in a 1-m test pond.

Direct Determination of Absolute Light Intensity in UV-Transmitting and UV-Dispersive Fluoro Polymer Tubes

Abstract To determine the absolute light intensity (including the reflective, scattered, and incident light intensity) in a UV-transmitting and UV-dispersive fluoro polymer tube, a new chemical actinometer, DPOF system, was introduced which was composed of dilute potassium tris(oxalato)ferrate(III), 0.03 mol m−3; 1,10-phenanthroline, 0.135 mol m−3; and potassium oxalate, 1.5 mol m−3. The overall light intensity was determined with a simple procedure based on a precise analysis of the photochemical kinetics of a DPOF system. The absolute intensities at 366 nm in the UV-transmitting and UV-dispersive Teflon FEP and Folaflon PVdF tubes were detected to be higher than that in a fused-silica tube of similar size while the incident light intensities in the former tubes were always lower than that in the latter. In addition, the dispersive effect of a Teflon FEP tube was rather independent of the wall thickness and the tube diameter under the experimental conditions studied, owing to its high dispersibility of light. The dispersive effect was much more remarkable for the Folaflon PVdF tube. The property of light transmission with dispersion, with the characteristic of antifouling, would make the fluoro polymer tubes useful for novel photoreactors in various areas.

Potassium Ferrioxalate as Chemical Actinometer in Ultraviolet Reactors

The ultraviolet doses delivered by a quartz‐sleeve and a Teflon‐tube design ultraviolet disinfection reactor at various flow rates are estimated using a Bacillus subtilis bioassay and compared to dose estimates made using a potassium ferrioxalate chemical actinometric technique. The volumetric dose estimates obtained with the potassium ferrioxalate actinometer are converted to areal dose estimates by multiplying them by the irradiated volume to irradiated surface area ratio. Conservative estimates of dose are consistently achieved by assuming 100% reflectance of UV radiation off of reactor walls when approximating the irradiated surface area. Potassium ferrioxalate actinometry is found to provide reproduceable dose estimates but is sensitive to procedural variation. The relatively high cost of potassium ferrioxalate actinometry combined with the difficulties associated with preparing and using the actinometer suggest that it is impractical for regular use in field situations. However, potassium ferrioxalate actinometry does appear to have the potential for being a useful tool in design evaluations and comparative studies of UV system efficiencies.

Sensitive chemical actinometry with acetone-hydrogen chloride mixtures

The 2850, 3000 and 3130 Å photolysis of acetone-hydrogen chloride mixtures was studied at 130 °C. The effect of HCl pressure (1 – 8 Torr), CH 3COCH 3 pressure (5 – 60 Torr) and incident light intensity on the formation of CO and CH 4 was examined. Under the conditions employed, methyl radicals are completely scavenged by HCl and Φ CH 4 /φ CO = 2. Based on this finding and the availability of sensitive techniques for CH 4 detection, it is suggested that the CH 3COCH 3-HCl system can be used as a convenient and sensitive chemical actinometer. The potential advantages and applications of this method are discussed.

A new liquid phase actinometer: quantum yield and photo-CIDNP study of phenylglyoxylic acid in aqueous solution

Phenylglyoxylic acid ( 1) in aqueous solution is recommended as a convenient chemical actinometer (φ ≈ 0.6 – 0.8) for the region 250 – 400 nm. UV spectroscopy, nuclear magnetic resonance spectroscopy, gas chromatography, high performance liquid chromatography and titrimetry are suitable analytical methods for monitoring the photodecarboxylation of 1 and the formation of benzaldehyde ( 2). Quantum yield φ determinations and 1H photochemically induced dynamic nuclear polarization (photo-CIDNP) experiments in different media reveal that the photochemistry of 1 is strongly dependent on the nature, water content and pH value of the solvent. Photodecarboxylation of 1 requires the presence of water, and φ is drastically enhanced by increasing the water concentration in acidic solution. On the basis of photo-CIDNP results it is suggested that the photoreduction of 1 in 2-propanol, yielding a 1:1 mixture of meso- and D, L-2,3-diphenyl-tartaric acid, proceeds via a radical-pair mechanism. Two pathways are discussed for the formation of 2 by photodecarboxylation of 1. The main reaction is proposed to occur without polarization under photo-CIDNP conditions while side reactions give rise to polarized benzoin and benzaldehyde proton nuclear magnetic resonance spectra.

Quantum yields for the photodecomposition of polychlorinated dibenzo- [formula omitted]-dioxins (PCDDs) in water-acetonitrile solution

The quantum yields for the phototransformation of 1,2,3,4,7-penta-, 1,2,3,4,7,8-hexa-, 1,2,3,4,6,7,8-hepta-, and 1,2,3,4,6,7,8,9-octachlorodibenzo- p -dioxin in H 2O-CH 3CN (2:3 v/v), measured at 313 nm through the utilization of o -nitrobenzaldehyde in CH 3CN as a chemical actinometer, were (9.781 ± 2.376) × 10 −5, (1.096 ± 0.020) × 10 −4, (1.526 ± 0.165) × 10 −5, and (2.257 ± 0.331) × 10 −5, respectively.

Determination of wavelength-averaged, near UV quantum yields for environmental chemicals

The present study describes a procedure for determination of an average quantum yield for the wavelength range of 310 to 410 nm. Solutions of the pollutant in sealed Pyrex tubes are irradiated in a Rayonet photoreactor fitted with fluorescent lamps emitting maximally at 355 nm. The integrated spectral overlap and the photolysis half-life for both the chemical actinometer and the pollutant are determined and from these data the quantum yield is calculated. The method has been evaluated by measuring quantum yields for organophosphorus, chlorinated hydrocarbon, and dinitroaniline pesticides and p -nitroanisole/pyridine mixtures. Corrected quantum yields are obtained on simultaneous irradiation of the trifluralin actinometer.

A NEW REUSABLE CHEMICAL ACTINOMETER FOR UV IRRADIATION IN THE 248 ‐ 334 nm RANGE

AbstractThe highly reversible thermally stable photochromic system consisting of heterocoerdianthrone‐endoperoxide (HCDPO) and its parent compounds HCD and 02 is proposed as a new reusable liquid chemical actinometer in the UV region 248 ≤λ≤ 334 nm. The foremost advantageous features of this new system are: (1) high reproducibility and accuracy, (2) high sensitivity, (3) almost wavelength independent quantum yields, (4) no loss in accuracy even after 100 repeated actinometric cycles and (5) very easy handling and straightforward calculability of the radiation quantum flux.

Photochemical reduction of iron. I. light reactions

Abstract The role of spectral quality in the photochemical reduction of Fe3+ in vitro was investigated under various lamps to determine the basis for severe chlorosis observed in certain species and cultivars under low pressure sodium (LPS) lamps when used as a sole source of artificial light in plant growth chambers. The comparative efficacy of LPS and cool white fluorescent (CWF) lamps was evaluated by means of an automated spectroradiometer with capability of measuring spectral irradiance every nanometer from 250 nm to 840 nm; by visible appearance of the plants (e.g., extent of greening and morphological development); by physiological measurements (e.g., of biomass and chlorophyll content); and by use of ferrozine as a chemical actinometer. Reduction of Fe3+ to Fe2+, measured as Fe2+ ferrozine (at 562 nm) was more than 4 times as great under CWF lamps, which emit appreciable amounts of UV and blue irradiance, as under LPS lamps, which are deficient in these wavelengths. By use of appropriate filters to selectively remove the UV or UV + blue wavelengths from CWF lamps or other light sources, it was possible to greatly reduce or prevent the in vitro photoreduction of ferrous iron. Conversely, the addition of CWF lamps to a LPS growth room greatly enchanced Fe3+ photoreduction in solution. Citrate was found to be required for the in vitro photoreduction of 59FeC13 solutions. Further studies are needed, however, to relate photochemical and biochemical changes in the intact plant in order to determine the precise role of UV and blue radiation in the photochemical reduction of Fe3+ in vivo.