Online trace enrichment to determine pyrethroids in river water by HPLC with column switching and photochemical induced fluorescence detection

The potential of online trace enrichment on a highly apolar short column in LC was evaluated for the determination of pyrethroids in river water. Twelve millilitres of water samples, modified with 8 mL ACN (ACN/water 40:60, v/v), were passed through 50 x 4.6 mm ID first separation column packed with 5 microm Hypersil Elite C18. Pesticides were preconcentrated in this column while the matrix background was eluted to waste. Separation of pesticides was performed on a 3.5 microm symmetric C18 column (250 x 4.6 mm ID) with an ACN step gradient as mobile phase and fluorescence detection was used after postcolumn derivatization by using UV light. The use of photochemically induced fluorescence for detection improved sensitivity and selectivity. Quantification limits ranged from 0.05 to 0.1 microg/L and pesticide recoveries at two concentration levels (0.1 and 0.5 microg/L) were between 93.1 and 118.6%, with RSD between 2.5 and 7.5% (n = 3) in river water samples. No matrix effect was detected.     

Aliphatic organolithiums by fluorine-lithium exchange: n-octyllithium

The reaction of 1-fluorooctane (1) with an excess of lithium powder (4-10 equiv.) and DTBB (2-4 equiv.) in THP at 0°C for 5 min gives a solution of the corresponding 1-octyllithium (2), which reacts then with different electrophiles at 0°C (D₂O, MeSiCl, Bu^tCHO, Et₂CO), or −78°C [ClCO₂Me, (PhCH₂S)₂] or −40°C (CO₂) to room temperature to give, after hydrolysis, the expected products (3). The same process applied to 2-fluorooctane gives mainly octane as reaction product, independently on the electrophile used, resulting from a proton abstraction by 2-lithiooctane formed from the reaction medium before addition of the electrophilic reagent.     

[All]-S,S-dioxide Oligo-Thienylenevinylenes: Synthesis and Structural/Electronic Shapes from Their Molecular Force Fields

Oligo-S,S-dioxothienylenevinylenes have been prepared by transferring oxygen atoms to the sulfur atoms using the HOF ⋅ CH₃CN complex. Their photophysical properties are presented in comparison with their thiophenevinylene congeners. Together with their vibrational properties and molecular force fields, this study allows for the interpretation of the alteration of aromaticity and inter-ring exocyclic π-conjugation in this series.     

Estimating regression parameters with imprecise input data in an appraisal context

Traditional valuation models, such as capitalization or comparative, share the common principle of using exact information in their calculations. However, in the professional field, it is difficult to find situations characterized by the wealth and precision of the information available. Within the professional context, it is usually necessary to carry out estimates on some of the explanatory variables of pricing, even though consciously introducing an important degree of subjectivity. The model proposed in this paper, which uses the goal programming optimization technique, is capable of dealing with imprecise information, since it allows to consider intervals to define the values of the explanatory variables. Additionally, this paper presents and demonstrates several propositions that increase the informative capacity of the model presented.     

Determination of paraquat by flow-injection spectrophotometry

The flow-injection determination of Paraquat (1,1′-dimethyl-4,4′-bipyridinium) is based on its reduction with sodium dithionite in alkaline medium and detection at 605 nm. Linear calibration plots are obtained for 0.1–1.0, 1.0–10 and 5.0–30.0 mg l^?1 Paraquat, the lower limit being 40 times less than that of the usual spectrophotometric method. The method is applied to determine Paraquat in spiked potable water and potatoes after preconcentration by column ion-exchange. The determination of Paraquat in different herbicide samples yielded results in good agreement with those obtained by polarographic and manual spectrophotometric methods.     

Understanding Surface Recombination Processes Using Intensity-Modulated Photovoltage Spectroscopy on Hematite Photoanodes for Solar Water Splitting

Converting solar energy into hydrogen through photoelectrochemical (PEC) water splitting offers a promising route towards a fully renewable energy economy. A fundamental understanding of photogenerated charge recombination processes in semiconducting photoelectrodes is a key consideration in optimizing solar water splitting cells and intensity-modulated photovoltage spectroscopy (IMVS) has recently emerged as a promising technique for gaining new insight. However, the interpretation of IMVS data under various conditions (that is, when photoelectrodes are in sacrificial electrolytes or employ catalytic overlayers) is not complete. Using IMVS data we present herein an analysis of charge recombination processes under open circuit conditions on a model photoanode system: nanostructured hematite. Employing two sacrificial oxidation conditions compared to standard water oxidation conditions, our IMVS results establish a direct correlation between surface recombination processes and the low frequency IMVS response. We found that surface intermediate states for water oxidation under open circuit condition exhibit a lifetime of 229 ms under standard illumination conditions. Applying a nickel iron oxide overlayer also gives insight into surface passivation effects through IMVS analysis of photoanode system.     

Microwave-assisted solvent-free synthesis of enantiomerically pure N-(tert-butylsulfinyl)imines

A simple, environmentally friendly, and very efficient procedure for the synthesis of optically pure N-(tert-butylsulfinyl)imines has been developed with microwave-promoted condensation of aldehydes and ketones using (R)-2-methylpropane-2-sulfinamide in the presence of Ti(OEt)(4), under solvent-free conditions. This procedure allows for the preparation of a variety of sulfinyl aldimines with excellent yields and purities in only 10 min, making any further purification of the imines unnecessary. Several sulfinyl ketimines have also been prepared in good yields by extension of the reaction times to 1 h. This methodology has proved to be equally efficient for the synthesis of aromatic, heteroaromatic, and aliphatic N-(tert-butylsulfinyl)imines. Conventional heating has also been shown to be useful to promote these reactions, especially for the synthesis of aldimines.     

ID29: a high‐intensity highly automated ESRF beamline for macromolecular crystallography experiments exploiting anomalous scattering

ID29 is an ESRF undulator beamline with a routinely accessible energy range of between 20.0 keV and 6.0 keV (λ = 0.62 Å to 2.07 Å) dedicated to the use of anomalous dispersion techniques in macromolecular crystallography. Since the beamline was first commissioned in 2001, ID29 has, in order to provide an improved service to both its academic and proprietary users, been the subject of almost continuous upgrade and refurbishment. It is now also the home to the ESRF Cryobench facility, ID29S. Here, the current status of the beamline is described and plans for its future are briefly outlined.