Photophysics of Push–Pull Distyrylfurans,Thiophenes and Pyridines by Fast and Ultrafast Techniques

Time‐resolved transient absorption and fluorescence spectroscopy with nano‐ and femtosecond time resolution were used to investigate the deactivation pathways of the excited states of distyrylfuran, thiophene and pyridine derivatives in several organic solvents of different polarity in detail. The rate constant of the main decay processes (fluorescence, singlet–triplet intersystem crossing, isomerisation and internal conversion) are strongly affected by the nature [locally excited (LE) or charge transfer (CT)] and selective position of the lowest excited singlet states. In particular, the heteroaromatic central ring significantly enhances the intramolecular charge‐transfer process, which is operative even in a non‐polar solvent. Both the thiophene and pyridine moieties enhance the S₁→T₁ rate with respect to the furan one. This is due to the heavy‐atom effect (thiophene compounds) and to the ¹(π,π)*→³(n,π)* transition (pyridine compounds), which enhance the spin‐orbit coupling. Moreover, the solvent polarity also plays a significant role in the photophysical properties of these push–pull compounds: in fact, a particularly fast ¹LE*→¹CT* process was found for dimethylamino derivatives in the most polar solvents (time constant, τ≤400 fs), while it takes place in tens of picoseconds in non‐polar solvents. It was also shown that the CT character of the lowest excited singlet state decreased by replacing the dimethylamino side group with a methoxy one. The latter causes a decrease in the emissive decay and an enhancement of triplet‐state formation. The photoisomerisation mechanism (singlet/triplet) is also discussed.     

Pesticide residues analysis in honey using ethyl acetate extraction method: validation and pilot survey in real samples

This paper presents a cost-effective and validated multi residue confirmatory method for the determination of 167 chemically different pesticides and a survey study on Cyprus honey samples. This method uses ethyl acetate for the extraction of pesticides from honey and the determination is performed with liquid chromatography (LC) coupled to mass spectrometry (MS) operating in tandem mode (MS/MS) and with GC–ECD (gas chromatography with electron capture detector) analysis. The LC-MS/MS analytical system is especially important in the analysis of polar and non-volatile pesticides. For the validation of the method, blank honey samples were spiked with 146 pesticides (organophosphorous, carbamates, triazoles, amides, neonicodinoids, strobilurines, phenylureas, bendimidazoles and others) for the LC-MS/MS analysis at three levels: 0.01, 0.05 and 0.1 mg kg^?1 and with 21 pesticides for the GC-ECD analysis at two levels: 0.01 and 0.05 mg kg^?1for organochlorines and 0.05 and 0.2 mg kg^?1for the pyrethroids. As blank sample, a sample of honey which did not contain detectable levels of the analytes sought was used. The validation study was in accordance to the DG SANCO guidelines. The scope of validation included recovery, linearity, limits of quantification and precision. Linearity is demonstrated all along the range of concentration that was investigated with correlation coefficients ≥0.98. Recoveries of the majority of compounds were in the 70%–120% range and were characterised by precision lower or equal to 20%. The validated method was used for a survey of 36 samples of honey produced in different areas of Cyprus and this is the first work on Cypriot honey samples investigating a broad range of pesticides. Only coumaphos was detected at concentrations higher than 0.01 mg kg^?1 in the 58.6% of the honey samples analysed for Coumaphos. The results were evaluated in accordance to the provisions of the Commission Regulation (EU) No 37/2010 on pharmacologically active substances and their classification regarding maximum residue limits (MRLs) in foodstuffs of animal origin. The concentrations of coumaphos in all positive samples were at levels much lower than the MRL.     

Development and validation of a rapid HPLC method for the determination of five banned fat-soluble colorants in spices using a narrow-bore monolithic column

This work reports a fast and simple liquid chromatographic method for the simultaneous determination of five banned fat-soluble synthetic colorants, namely Sudan I-IV and Para-Red, in spice samples. The analytes were successfully separated isocratically in less than 5 min on the new narrow bore monolithic column, FastGradient^® Chromolith (50 mm × 2.0 mm i.d.) using a mobile phase of 0.1% (v/v) HCOOH/acetonitrile (35/65%, v/v) at a flow rate of 1.5 mL min⁻¹. All colorants were detected at 506 nm. The main parameters (mobile phase composition, flow rate, injection volume) affecting the separation were studied. The proposed method was thoroughly validated in terms of linearity, LODs, precision and accuracy. The method was applied to the determination of the studied azo-dyes in various spices (paprika, chilli and mixed spice powders) after ultrasound-assisted extraction. Satisfactory recoveries, ranging from 92% to 109% were obtained.     

Review of analytical methods for the determination of chlorine dioxide

The present study reviews more than twenty years (1985-present) of published research on the development and application of analytical procedures for the determination of chlorine dioxide, a widely used disinfectant and bleaching agent. The review covers a variety of techniques including batch and automated spectrophotometry and fluorimetry, electroanalysis and chromatography. The analytical figures of merit to the methods are presented, while critical discussion regarding their advantages and disadvantages is addressed.      

Gas-diffusion flow injection assay for the selective determination of chlorine dioxide based on the fluorescence quenching of chromotropic acid

The present work reports the first spectrofluorimetric gas-diffusion flow injection (GD-FI) assay for the determination of chlorine dioxide in water samples (tap, mineral and soda water). The method is based on the fluorescence quenching of chromotropic acid (CA) (λ_ex. = 347 nm, λ_em. = 371 nm) caused by the analyte. The chemical and instrumental variables of the system were studied in terms of maximum sensitivity. The gas-diffusion cell was thermostated at 40 °C to enhance the vaporization of chlorine dioxide and thus the sensitivity of the method. The quenching effect of chlorine dioxide on CA was linear in the range 0.09-3.41 mg l^− 1, while the precisions either close to the quantitation limit or near to the middle of the linear section of the calibration graph were satisfactory in both cases (s_r = 2.6% and 1.5% (n = 10) at 0.17 and 1.71 mg l^− 1 level, respectively). The developed method proved to be adequately selective and sensitive with 3σ limit of detection equal to c_L = 0.03 mg l^− 1. The application of the assay to spiked tap, mineral and soda water samples yielded accurate results with recovery values in the range 94.1-105.9%.     

Flow-injection manifold for the simultaneous spectrophotometric determination of Fe(II) and Fe(III) using 2,2''-dipyridyl-2-pyridylhydrazone and a single-line double injection approach

A simple and rapid flow-injection (FI) method is reported for the simultaneous spectrophotometric determination of Fe(II) and Fe(III) in pharmaceutical products. The method is based on the reaction of Fe(II) with 2,2'-dipyridyl-2-pyridylhydrazone (DPPH) in acidic medium to form a water-soluble reddish complex (lambdamax=535 nm). Fe(III) reacts with DPPH under flow conditions only after its on-line reduction by ascorbic acid (AsA). Both analytes were determined in the same run via a double-injection valve, which enabled the simultaneous injection of two sample volumes in the same carrier stream (,,single-line double-injection" approach). The two well-defined peaks produced corresponded to total iron [Fe(II)+Fe(III)] and Fe(II). Speciation of the analytes in their mixtures was achieved by multiple regression analysis. The calibration curves obtained were linear over the ranges 0-30 and 0-50 mg L(-1) for Fe(II) and Fe(II), respectively, and the precision [s(r)=1.0% for Fe(II) and 1.5% for Fe(III)] was satisfactory. The method proved to be selective and adequately sensitive (cL=0.25 and 0.17 mg L(-1) for Fe(III) and Fe(II), respectively, in mixtures). Application of the method to the analysis of pharmaceutical samples resulted in excellent accuracy; the percent mean recoveries were in the range 99.0-102.0% for both Fe(II) and Fe(III) and the mean relative error was e(r)=1.0%.     

On-line dilution flow injection manifold for the selective spectrophotometric determination of ascorbic acid based on the Fe(II)-2,2'-dipyridyl-2-pyridylhydrazone complex formation

A new simple and rapid FI method for the accurate and precise spectrophotometric determination of ascorbic acid (AsA) in pharmaceutical formulations is reported. The method is based on the reduction of Fe(III) to Fe(II) by the analyte, and the subsequent reaction of the produced Fe(II) with 2,2'-dipyridyl-2-pyridylhydrazone (DPPH) in acidic medium (pH ca. 2.5) to form a colored complex (lambda(max)=535 nm). An on-line dilution mode using a binary inlet static mixer (BISM) was incorporated in the FI system, allowing the determination of the analyte in a wide concentration range. The calibration graph was linear in the range of 5.7-600.0 mg l(-1) AsA, at a sampling rate of 120 injections h(-1). The method was found to be very precise [s(r)=0.1% at 300 mg l(-1) AsA (n=12)] and the 3delta detection limit (c(L)=1.7 mg l(-1)) was quite satisfactory. The detailed study of various interferences confirmed the high selectivity of the proposed method. Its application to a variety of pharmaceuticals produced excellent results, with a mean relative error of e(r)<1.0%.     

Quantitative determination of jatrophone in "cachaça" prepared with Jatropha elliptica

A method for sample preparation and analysis by high performance liquid chromatography with UV detection (HPLC-UV) was developed for analysis of jatrophone in "cacha?a" prepared with Jatropha elliptica, administered orally, employed in Brazil for the treatment of venomous snake bites. The linearity, accuracy, precision of the procedure was evaluated. Analytical curve for jatrophone was linear in the range of 16.24-81.20 microg ml(-1). The recovery of the jatrophone in the samples analyzed was 98.99-99.89%. The percent coefficient of variation for the quantitative analysis of the "cacha?a" in the analyses was under 2%.     

A method for quantitative determination of furanocoumarins in capsules and tablets of phytochemical preparations

A method for sample preparation and analysis by high-performance liquid chromatography with UV detection (HPLC-UV) was developed for analysis of psoralen, bergapten and 5-[3-(4,5-dihydro-5,5-dimethyl-4-oxo-2-furanyl)-butoxy]-7H-furo[3-2-g][1]benzopyran-7-one in capsules and tablets employed in Brazil for certain illnesses. The linearity, accuracy, the inter- and intra-day precision of the procedure were evaluated. Analytical curves for furanocoumarins were linear in the range of 1.0-50.0 microg/ml. The recoveries of the furanocoumarins in the products analyzed were 97.3-99.5%, and the percent coefficient of variation for the quantitative analysis of the furanocoumarins in the analyses was under 5%. For inter-equipment study gas chromatography (GC) was employed.