Diode Array Spectrophotometer Research Articles

Smartphone-based procedure to determine content of single synthetic dyes in food using the Arata-Possetto extraction method

The use of additives, including dyes, is common in the preparation of food products. The analytical control of artificial food dye content is relevant since some, such as azo dyes, may produce cancer and attention deficit disorders and hyperactivity in children. Consequently, the maximum permitted concentration of azo dyes in food is regulated by current legislation. Therefore, it is of interest to find simple and fast procedures for the control of these compounds. The aim of this study is to determine the concentration of azo dyes in food samples by the Arata-Possetto method – based on the extraction of azo dyes employing natural wool –, followed by the analysis of an image captured by a smartphone camera. After experimentally determining the optimal extraction conditions, the calibration curves for standard solutions of different food dyes and the color of the dyed wool were obtained. Results from dyed wool image processing were compared with the absorbance spectra of the solutions before extraction as measured by a diode array spectrophotometer. The spectrophotometric and the image processing procedures were employed to obtain the calibration curves for different food dyes, which were subsequently employed to analyze food samples. Statistical treatment shows that the results of both methods are comparable.

Targeted Drug Administration onto Cancer Cells Using Hyaluronic Acid-Quercetin-Conjugated Silver Nanoparticles.

Quercetin (QtN) displays low systemic bioavailability caused by poor water solubility and instability. Consequently, it exerts limited anticancer action in vivo. One solution to increase the anticancer efficacy of QtN is the use of appropriate functionalized nanocarriers that preferentially target and deliver the drug to the tumor location. Herein, a direct advanced method was designed to develop water-soluble hyaluronic acid (HA)-QtN-conjugated silver nanoparticles (AgNPs). HA-QtN reduced silver nitrate (AgNO3) while acting as a stabilizing agent to produce AgNPs. Further, HA-QtN#AgNPs served as an anchor for folate/folic acid (FA) conjugated with polyethylene glycol (PEG). The resulting PEG-FA-HA-QtN#AgNPs (further abbreviated as PF/HA-QtN#AgNPs) were characterized both in vitro and ex vivo. Physical characterizations included UV-visible (UV-Vis) spectroscopy, Fourier transform infrared (FTIR) spectroscopy, transmission electron microscopy (TEM), particle size (PS) and zeta potential (ZP) measurements, and biopharmaceutical evaluations. The biopharmaceutical evaluations included analyses of the cytotoxic effects on the HeLa and Caco-2 cancer cell lines using the MTT assay; cellular drug intake into cancer cells using flow cytometry and confocal microscopy; and blood compatibility using an automatic hematology analyzer, a diode array spectrophotometer, and an enzyme-linked immunosorbent assay (ELISA). The prepared hybrid delivery nanosystem was hemocompatible and more oncocytotoxic than the free, pure QtN. Therefore, PF/HA-QtN#AgNPs represent a smart nano-based drug delivery system (NDDS) and could be a promising oncotherapeutic option if the data are validated in vivo.

The Photochemical Chlorate-Iodide Clock Reaction.

Mixing iodide and perchloric acid solutions with an excess of chlorate inside a diode-array spectrophotometer led to the observation of an abrupt decrease of the absorbance at the 215 nm isosbestic point after an induction period. The clock time decreases by increasing the initial concentrations of chlorate and acid, but increasing the initial iodide concentration has an opposite effect. The proposed mechanism simulates the experimental results and considers the interaction of UV light with iodide, producing iodine and triiodide ion. The autocatalytic core of this mechanism is the same as that employed to explain the autocatalytic behavior of chlorine dioxide-iodine reaction, but considering H2IO+ as the reactive species rather than HOI, being a more realistic mechanism for acid conditions.

Sequential Injection System for Analysis of Degree Brix, Orthophosphate and pH in Raw Sugarcane Juice Applicable to Sugar Industry.

This work presents, for the first time, a new sequential injection analysis (SIA) method to simultaneously analyze degree Brix, orthophosphate and pH in raw cane juice. These key parameters relate to price of harvested sugarcane and quality of cane juice for sugar production. The SIA system employed two detectors: the first detector is a diode-array spectrophotometer, equipped with a regular flow cell, for measurements of degree Brix and orthophosphate. Quantitative of degree Brix (°Bx; ca. % (w/w) sucrose) was based on manipulation of the schlieren effect at the interface between plugs of sample and water. Orthophosphate analysis was carried out based on the molybdenum blue method with significant reduction in consumption of the reagents. Compensation of the schlieren effect from sucrose for determination of orthophosphate was achieved by using a dual-wavelength spectrometric detection. Second detector is a pH-sensing device, called ion-selective field-effect transistors (ISFET). The ISFET is based on the current through the ISFET arising according to the H+ concentration in solution. Our developed SIA system provides linear calibration graphs fitting for purpose in analysis of sugarcane juice (pH: 0–14, °Bx: 1.0–7.0 and P2O5: 20–200 mg L−1). Simultaneous analysis of sugarcane juice for pH, °Bx and P2O5 is carried out within 5 min (12 sample per h). Precision of SIA system is acceptable (RSD < 3%). Our SIA system gave quantitative results insignificantly different, as compared with conventional methods for analysis of pH, °Bx and P2O5 in sugarcane juice.

A kinetic study of the photooxidation of water by aqueous cerium(IV) in sulfuric acid using a diode array spectrophotometer

The photooxidation of water by aqueous cerium(IV) has been investigated in dilute sulfuric acid quantitatively using a diode array spectrophotometer. An overview of experimental data on the speciation of cerium(IV) showed that several different absorbing species are present under almost all conditions, which makes straightforward interpretation of photochemical data very difficult. At submillimolar levels of cerium(IV) in 0.10 mol dm–3 sulfuric acid, a consistent quantum yield of 0.12 for the loss of cerium(IV) could be determined, but even under these conditions, clear evidence of a parallel non-photochemical pathway was obtained. At higher concentrations of the metal ion, significant deviations from the expected direct proportionality between the illumination ratio and the initial rate were confirmed, which can only be interpreted by a complicated system of parallel, coupled photochemical and non-photochemical pathways. The inhibitory effect of aqueous cerium(III) in the process was also demonstrated. Based on indirect evidence, it seems likely that sulfate ion radicals play a significant role in the mechanism.

Electrochromic Property of Adsorbed Carboxylated Viologen on Zinc Oxide

Electrochromic displays (ECD) are non-emissive, reflective, non-volatile and energy-saving, as they are based on reversible color change by electrochemical redox reactions. Unlike the electrophoretic e-ink displays already used in book readers, which can only switch between two tones (black and white), ECD can produce gray tones. While the established inorganic WO3 EC device used as automatic antiglare mirror is monotonous, full color ECD can be envisioned by employing reversible color change of organic chromophore. However, most of solid thin films of organic dye molecules cannot achieve electrical conduction and associated ion exchange needed for near-complete redox. A promising strategy is to use mesoporous inorganic electrode with adsorbed monolayer of organic dyes, just like that used in dye-sensitized solar cells. While sufficient color density can be assured by the virtue of high surface area, electrical conduction and ionic transport are also facilitated. The challenge is to find combination of the organic chromophore which undergo reversible color change, preferably in W/Y, W/M, W/C to achieve full color, and suitable electrolyte to prevent dye desorption from the electrode surface. In this study, we have synthesized carboxylated viologen derivatives (N,N’-bis(2-carboxyethyl)-4,4’-bipyridinium dichloride (CE2V) and 3-[4-(N-methyl-4-pyridino)-1-pyridinio]carboxyethyl diiodide (CEMV)) (Fig. 1a), which are adsorbed onto mesoporous ZnO nanoparticulate electrode to test their electrochromism. Viologens are known to exhibit a sharp color change from colorless to deep blue upon its reduction to its cation radical that is stable and reversibly oxidized. In situ spectroelctrochemical measurements were performed to evaluate the capabilities of the newly developed systems. CE2V was synthesized by carboxylation of 4,4’-bipyridine with acrylic acid and subsequent conversion to chloride with hydrochloric acid (yield 73%). CEMV was prepared by monomethylation of 4,4’-bipyridine with methyl iodide and subsequent carboxylation with acrylic acid (yield 46%). Mesoporous ZnO film (10 μm thick) prepared by doctor blading was soaked in ethanolic solution 500 µM of CE2V or CEMV for 3 hours. Transmission absorption spectra were measured in situ by Otsuka Electronics MDPC-7000 diode array spectrophotometer during cyclic voltammetry on the viologen modified ZnO electrodes in a 0.1 M tetrabuthylammonium hexafluorophosphate (TPAPF6) in acetonitrile under N2. The amounts of CE2V and CEMV adsorbed on ZnO were 1.31×10-7, 7.28×10-8 mol cm-2, respectively, indicating superior adsorption stability of double anchor molecule. Both of them exhibited stable reversible redox in two-steps (Fig. 1b). Associated color changes were observed from colorless to purplish blue and yellow to purple for CE2V and CEMV, respectively, which were then bleached in the second reduction. Singly reduced cation radicals intensely absorb in the visible, but doubly reduced states are not colored. The oxidation back to the singly reduced state regenerated the color, which was again bleached on its oxidation back to the original dication state. The in situ spectra monitored for the reversible color change are shown for ZnO/CE2V electrode (Figs. 1c,d). The charges consumed in the primary reduction were calculated from the integral of the peak areas to determine the redox active fractions as 6.83×10-8 and 4.48×10-8 mol cm-2 for CE2V and CEMV, respectively, which correspond to 52 and 62% of the totally adsorbed amounts. Although the spectra of cation radicals of viologens developed in the present study are bit too broad to serve as white to “cyan” chromic device, the relatively fast and stable reversible electrochromism has been achieved by combination of porous inorganic electrode and adsorbed monolayer of organic chromophore. Figure 1

Near-infrared spectroscopy-based methods for quantitative determination of active pharmaceutical ingredient in transdermal gel formulations

Semi-solid pharmaceutical forms, like topical and transdermal products, are widely used for medical purposes since they provide convenient and pain-free treatment for patients. In this study, two transdermal gel formulations with different active pharmaceutical ingredients were analyzed with near-infrared spectrophotometers with three distinct optical arrangements (dispersive, Fourier transform, and diode-array spectrophotometers) for the measurement of active pharmaceutical ingredient concentration. The reference concentrations were measured with high-performance liquid chromatography methods.The developing of calibration for reference concentrations based on near-infrared spectra was performed using partial least squares regression. The spectra from near-infrared spectrophotometer with diode-array optical arrangement presented the best root mean square error of cross-validation results with 0.045% and 0.144% for the two active pharmaceutical ingredients. The root mean square error of cross-validation using dispersive spectra were 0.125% and 0.193% and using Fourier transform spectra were 0.130% and 0.344% for the active pharmaceutical ingredients. The results of partial least squares regression were confirmed using simulated spectra based on the measured datasets.Near-infrared spectroscopy can be used successfully for the quantitative measurement of active pharmaceutical ingredient concentration in transdermal gel formulations. The type of optical arrangements of spectrophotometers can influence the performance of calibrations and have to be optimized case by case.

Some physical parameters influencing the comprehensive evaluation of kinetic data in photochemical reactions and its application in the periodate-chemistry

Quantitative treatment of photochemical processes requires precise knowledge of the amount of photons reaching the sample. A possible and probably the most convenient way is to investigate a photochemical reaction subject to be studied by conventional or diode-array spectrophotometers. The self-test mode of the given instrument usually provides an opportunity for any user to obtain the measurable components of the emission spectrum of the lamp. This spectrum may then be used to determine the rate of primary photochemical processes as recently proposed by Fábián and Lente, alongside with molar absorbance, concentration of the absorbing species, quantum yield, and the absorbance measured itself. However, in some cases, the spectrum obtained by this way has to be treated with special circumspection because the amount of light may significantly differ from each other in the sample compartment and in other parts of the instrument as well. The most important technical factors influencing the emission spectrum of the light are discussed and their suitable utilization may straightforwardly provide a comparable amount of photons reaching the sample. To present it, different light sources of several spectrophotometers were systematically surveyed and some feasible corrections were as well highlighted. The considerations illustrated here are applied and demonstrated in case of sodium periodate providing a solid basis for a sound quantitative description of its photochemical decomposition.

Comparison of antioxidant activity, content of polyphenols and flavonoids in liturgical and common wines

This article deals with the comparison of biologically active substances (antioxidant capacity, content of polyphenols and flavonoids) in samples of common and liturgical wines. For determination were chosen these varieties Pinot Noir, Red Traminer and Chardonnay. The total content of polyphenols and flavonoids were found by visible diode array spectrophotometer. For determination of total antioxidant capacity was used the DPPH test. Results of this paper did not prove a general difference between liturgical and common wines, although between individual samples a statistically significant difference was found. Furthermore, the results show considerably higher values of biologically active substances in red wines Pinot Noir against white wine Red Traminer and Chardonnay - the total antioxidant capacity was considerably in excess of values up to 30 times, the total content of polyphenols up to 50 times and the total content of flavonoids up to 50 times. From the content of biologically active substances point of view, the red wine is recommended for human health.

Study of Some Qualitative and Quantitative Characters of the Grapes of Indigenous Greek Grapevine Varieties (Vitis vinifera L.) using HPLC and Spectrophotometric Analyses

Grape skins and seeds are sources of various quality characters of grapevine varieties, such as phenolic compounds, anthocyanins, resveratrol etc. The Greek vineyard is characterized by a large number of indigenous grapevine varieties which remain almost unexploited in terms of their different phenolic content. The aim of this study was to assay the polyphenolic content of seven red native Greek grapevine varieties (‘Kolliniatiko’, ‘Bekari’, ‘Bakouri’, ‘Kountoura mavri’, ‘Doubrena mavri’, ‘Thrapsa’, and ‘Mavro Spetson’) using high performance liquid chromatography (HPLC) coupled with a diode array detector and spectrophotometer. All studied varieties were cultivated in the same area and under the same conditions. The results revealed that despite the fact that anthocyanins and phenolic compounds content were in high levels for all varieties, statistically significant differences were recorded among them. The highest anthocyanins concentration was recorded in ‘Kolliniatiko’, while the lowest anthocyanins concentration was recorded in ‘Mavro Spetson’. Grapevine variety ‘Mavro Spetson’ presented the highest concentration of total phenolic compounds, with statistically significant difference compared to ‘Kountoura mavri’ and ‘Bekari’. Grapevine varieties ‘Kolliniatiko’ and ‘Bekari’ presented the highest concentrations in trans-resveratrol and piceid content, while grapevine variety ‘Doubrena mavri’ presented the highest concentration in vanillin content. These unexploited rare native cultivated varieties contained appreciable amounts of non-colored phenols as well as anthocyanins, meaning that they would be worthy of further study and use for the production of quality wines.

On-line SPE chromatography with spectrophotometric diode array detection as a simple and advantageous choice for the selective trace analysis of benzo(a)anthracene degradation products from microalgae

In this work, a methodology based on on-line solid phase extraction (SPE) chromatography with spectrophotometric diode array detection was optimized and validated for the trace analysis of benzo(a)anthracene dihydrodiol degradation products from microalgae cultures 5,6-dihydrodiol, 8,9-dihydrodiol and 10,11-dihydrodiol. The two on-line methods for the constituents of the culture, an SPE/on-line SPE chromatographic method for liquid medium and a matrix solid phase dispersion (MSPD)/on-line SPE chromatographic method for biomass presented good linearity in the ranges of 0.5−47ngmL−1 and 2−80ngmg−1 of samples, respectively, with correlation coefficients r>0.99. The percent relative standard deviation (RSD%) values were ≤4.9%. For the liquid medium and biomass methods, the global recoveries were between 84% and 90% and between 67% and 78%, and the limit of detection LODs were ≤0.3ngmL−1 and ≤0.8ngmg−1 respectively. The methodology was applied to exposure bioassays, and for the first time the three metabolites were detected and quantified individually by their appearance in the biomass and when they were excreted into the liquid medium. The metabolite formed in the greatest amount was 10,11-dihydrodiol, and the maximum production of all metabolites was at 6h of exposure. This work contributes to the study of the degradation route of BaA, which has not been elucidated for microalgae until now.

P11. Dose verification for high-dose bulk industrial 60Co irradiators with chemical dosimeters and gafchromic media

Introduction Dosimetry and dose verification at bulk industrial irradiator facilities is subject to numerous challenges, most notably due to their high volume, high throughput design and operations. Industries such as the Sterile Insect Technique (SIT), a biological control practice for the management of insect pests of agricultural and medical or veterinary significance, rely on annually derived output factors to deliver sterilization doses to organisms within strict parameters. Routine dose verification should therefore constitute an integral part of the quality control system. Materials and methods Two distinct dosimeter types were employed in this study. Firstly a chemical solution, Fricke’s solution made up of 1 mM Fe(NH4)2(SO4)2, 0.8 N H 2 SO 4 , 1 mM NaCl high purity chemicals, decanted in 2 ml ampules, secondly enveloped 1 cm 2 EBT2 radiochromic media sections. Dosimeters were exposed in a reference 60Co field under charged particle equilibrium conditions to incremental doses up to 100 Gy. Dosimeter absorbance measurements were conducted with a diode array spectrophotometer, resolution of 1 nm, at 304 nm and 676 nm for the Fricke and EBT2 dosimeters respectively. Results Dosimeter absorbance unit (AU) readings for the Fricke (0.06–0.35) and EBT2 (0.05–1.36) dosimetry systems were recorded for the dose range 0–100 Gy. Linear dose response relationships were noted for both the Fricke (dose range 20–100 Gy, r 2 = 0.9992 ) and EBT2 (2–100 Gy, r 2 = 0.9868 ) dosimetry systems. The dose–response relationship of the Fricke dosimetry system ( 3.6 × 10 - 3 ± 2.42 × 10 - 5 ) is roughly one order of magnitude lower compared to the EBT2 ( 1.35 × 10 - 2 ± 3.67 × 10 - 4 ) system. Conclusion Both dosimetry systems prove to be reliable dose verification tools for bulk industrial irradiator applications. The Fricke dosimetry system, a primary dosimeter, remains the preferred dosimeter due to its superior linear dose response and higher dose range capabilities.

Mechanistic insight into chromium(VI) reduction by oxalic acid in the presence of manganese(II)

Over the past few decades, reduction of hexavalent chromium (Cr(VI)) has been studied in many physicochemical contexts. In this research, we reveal the mechanism underlying the favorable effect of Mn(II) observed during Cr(VI) reduction by oxalic acid using liquid chromatography with spectrophotometric diode array detector (HPLC–DAD), nitrogen microwave plasma atomic emission spectrometry (HPLC–MP-AES), and high resolution mass spectrometry (ESI–QTOFMS). Both reaction mixtures contained potassium dichromate (0.67mM Cr(VI)) and oxalic acid (13.3mM), pH 3, one reaction mixture contained manganese sulfate (0.33mM Mn(II)). In the absence of Mn(II) only trace amounts of reaction intermediates were generated, most likely in the following pathways: (1) Cr(VI)→Cr(IV) and (2) Cr(VI)+Cr(IV)→2Cr(V). In the presence of Mn(II), the active reducing species appeared to be Mn(II) bis-oxalato complex (J); the proposed reaction mechanism involves a one-electron transfer from J to any chromium compound containing CrO bond, which is reduced to CrOH, and the generation of Mn(III) bis-oxalato complex (K). Conversion of K to J was observed, confirming the catalytic role of Mn(II). Since no additional acidification was required, the results obtained in this study may be helpful in designing a new, environmentally friendly strategy for the remediation of environments contaminated with Cr(VI).

A chemometric-assisted method for the simultaneous determination of malachite green and crystal violet in water based on absorbance–pH data generated by a homemade pH gradient apparatus

An attractive method of generating second-order data was developed by a dropping technique to generate pH gradient simultaneously coupled with diode-array spectrophotometer scanning. A homemade apparatus designed for the pH gradient. The method and the homemade apparatus were used to simultaneously determine malachite green (MG) and crystal violet (CV) in water samples. The absorbance–pH second-order data of MG or CV were obtained from the spectra of MG or CV in a series of pH values of HCl–KCl solution. The second-order data of mixtures containing MG and CV that coexisted with interferents were analyzed using multidimensional partial least-squares with residual bilinearization. The method and homemade apparatus were used to simultaneously determine MG and CV in fish farming water samples and in river ones with satisfactory results. The presented method and the homemade apparatus could serve as an alternative tool to handle some analysis problems.

Vis/NIR spectroscopic measurement of selected soil fertility parameters of Cuban agricultural Cambisols

The conventional methods frequently used in Cuba to determine some fertility parameters important for sugarcane production, such as organic matter (OM), available phosphorus (P) and potassium (K2O), are difficult, costly, and time-consuming procedures. This study was undertaken to build and validate Visible/Near Infrared Reflectance (Vis/NIR) calibration models of these parameters at landscape level and within a field, by taking into consideration their correlation coefficients with the OM. The parameters P and K2O, which are not spectrally active in the Vis/NIR range should be better predicted when are highly correlated with OM. Also, the wavelength intervals to simplify this methodology were selected. Samples were air-dried before scanning using a diode array spectrophotometer covering the wavelength range from 399 to 1697 nm. The regression models were built by using the linear multivariate regression method Partial Least Squares (PLS), and the nonlinear multivariate regression methods Support Vector Machines (SVM) and Locally Weighted Regression (LWR). At landscape level the best correlations between soil spectra and OM (0.90 ≤ R2 ≤ 0.93; 0.12 ≤ RMSEP≤0.14) were obtained with LWR, followed by K2O with LWR (0.77 ≤ R2 ≤ 0.79; 3.47 ≤ RMSEP≤3.62), Olsen P (0.69 ≤ R2 ≤ 0.81; 0.27 ≤ RMSEP≤0.35) and Oniani P (0.64 ≤ R2 ≤ 0.65; 3.31 ≤ RMSEP≤3.61) both with SVM. Also, the nonlinear regression models gave the best results within a field. The higher values for OM (R2 = 0.92; RMSEP = 0.14) and Olsen P (0.68 ≤ R2 ≤ 0.83; 0.27 ≤ RMSEP≤0.34) were observed with SVM, while for K2O (0.16 ≤ R2 ≤ 0.63; 5.13 ≤ RMSEP≤5.88), and Oniani P (0.70 ≤ R2 ≤ 0.72; 2.32 ≤ RMSEP≤2.52) were obtained with LWR. The soil fertility parameters studied at landscape level and within a field were best estimated by using nonlinear regression models.

Low-cost and portable absorbance measuring system to carbamate and organophosphate pesticides

This manuscript describes the development of a low-cost and portable solid-state absorbance measuring system that detects the thiocoline after the hydrolysis of substrates acetylthiocholine (ACTh) by acetylcholinesterase. Consisting in measure the relation between the amount of light transmitted through and absorbed by the enzymatic reaction that is carried out in the cuvette and expressed in voltage value. The proposed system indicated a detection limit of the enzyme (6.91×10−4 absorbance units/s) that is lower than the commercial diode-array spectrophotometer (2.29×10−3 absorbance units/s) equipment model 8452A from Hewlett–Packard. The working ranges for the developed system were 6.58mM to 36.5μM and 19.8mM to 349μM for the spectrophotometer, respectively. In addition, the system was employed to calculate the kinetic inhibition constants of three different enzymes (Electric Eel, Drosophila melanogaster and Genetically-modified D. melanogaster) toward paraoxon, carbofuran and malaoxon pesticides.

Aqueous photochemical reactions of chloride, bromide, and iodide ions in a diode-array spectrophotometer. Autoinhibition in the photolysis of iodide ions

The aqueous photoreactions of three halide ions (chloride, bromide and iodide) were studied using a diode array spectrophotometer to drive and detect the process at the same time. The concentration and pH dependences of the halogen formation rates were studied in detail. The experimental data were interpreted by improving earlier models where the cage complex of a halogen atom and an electron has a central role. The triiodide ion was shown to exert a strong inhibiting effect on the reaction sequence leading to its own formation. An assumed chemical reaction between the triiodide ion and the cage complex interpreted the strong autoinhibition effect. It is shown that there is a real danger of unwanted interference from the photoreactions of halide ions when halide salts are used as supporting electrolytes in spectrophotometric experiments using a relatively high intensity UV light source.

Ferrioxalate actinometry with online spectrophotometric detection

Abstract The best methods to study the stoichiometries of photochemical reactions are those that provide a continuous monitoring of the changes e.g. by measuring the spectral changes in the UV–vis region. Although the light of a diode array spectrophotometer or other lamp (UV lamp, LED, etc.) is not intense enough to generate the excited state in measurable quantities, it is enough to drive reactions, thus diode array spectrophotometers or LED-driven photoreactors with spectrophotometric detection are useful tools for these measurements. However, their illuminating light intensities need to be calibrated. The classical ferrioxalate actinometric method uses a separate complexation and spectrophotometric steps to determine the concentration of the Fe(II) formed during illumination. Decomposition of ferrioxalate is also accompanied by reproducible spectral changes, which are measured if the above mentioned techniques are used. This renders complexation and spectrophotometric Fe(II) concentration determination unnecessary. The present work introduces a simplified actinometric method, which was developed for photoreactors with spectrophotometric detection and used to calibrate such photoreactors with different arrangements. The method can be used for both polychromatic and monochromatic illuminating light sources. The relative error of the developed actinometric method is smaller than that of the classical actinometry.

Construction of a photochemical reactor combining a CCD spectrophotometer and a LED radiation source

An inexpensive photoreactor using LED light sources and a fibre-optic CCD spectrophotometer as a detector was built by designing a special cell holder for standard 1.000 cm cuvettes. The use of this device was demonstrated by studying the aqueous photochemical reaction of 2,5-dichloro-1,4-benzoquinone. The developed method combines the highly quantitative data collection of CCD spectrophotometers with the possibility of illuminating the sample independently of the detecting light beam, which is a substantial improvement of the method using diode array spectrophotometers as photoreactors.

β-Carboline Alkaloid Constituents from a Thermoactinomyces SP. Strain Isolated from Livingston Island, Antarctica

ABSTRACTTwo natural β-carboline alkaloids were isolated from the culture filtrate of Thermoactinomyces sp. imbas-14 strain. The organism was isolated from penguin excrements collected on the Antarctic Livingston Island. Based on the effect of temperature on its growth rate, the strain is thermophilic with an optimal growth temperature at 50°C. The compounds were purified by solvent extraction, silica gel column chromatography and preparative TLC and HPLC consecutively. The structures of the two compounds were elucidated by using high-performance liquid chromatography, using double online detection with a diode array spectrophotometer and a mass spectrometer (HPLC-DAD-ESI-MS), and extensive one- and two-dimensional NMR experiments. Both substances—1-methyl-β-carboline (harmane)(1) and 1-acetyl-4-methyl-β-carboline (2), are natural products and are isolated for the first time from the culture filtrate of the antarctic strain Thermoactinomyces sp. imbas-14. These compounds showed activity against important Gram-positive (Bacillus mycoides, Bacillus subtilis) and Gram-negative bacteria (Escherichia coli), yeasts (Candida tropicalis) and filamentous fungi (Penicillium notatum).