Paper on Novel Spectroelectrochemical Technique

A windowless electrochemical cell for the spectroscopic investigation of the liquid-liquid interface, using a dual droplet configuration, has been designed. The setup permits in situ probing of the bulk solutions and the interfacial region by fibre-optic UV-vis spectroscopy, microfocus X-ray fluorescence (XRF) elemental mapping, and microfocus X-ray absorption near-edge structure (micro-XANES) spectroscopy. The electrodeposition of Au, induced by ion transfer of the tetrachloroaurate complex from a halogenated solvent (containing a weak reducing agent) to the aqueous phase, has been monitored by a combination of the three techniques. The reaction can be followed in-situ by UV-vis spectroscopy by detecting the oxidised form of the reducing agent. Voltammetric evidence suggests the formation of interfacial Au(I) species, whereas micro-XANES detect the presence of metallic Au(0).

In Situ Spectroelectrochemistry at Free-Standing Liquid-Liquid Interfaces: UV-vis Spectroscopy, Microfocus X-ray Absorption Spectroscopy and Fluorescence Imaging
Y. Gründer, J.F.W. Mosselmans, S.L.M. Schroeder & R.A.W. Dryfe
Journal of Physical Chemistry C 117 (2013), 5765–5773.
DOI:10.1021/jp312060f

Review in Angewandte Chemie: Nucleation of Organic Crystals

Roger and Sven, together with Joop ter Horst (University of Delft), have published a review in Angewandte Chemie:

Nucleation of Organic Crystals – A Molecular Perspective
R.J. Davey, S.L.M. Schroeder & J.H. ter Horst
Angewandte Chemie – International Edition 52 (2013) 2166–2179.
DOI:10.1002/anie.201204824

German version:

Keimbildung organischer Kristalle aus molekularer Sichtweise
R.J. Davey, S.L.M. Schroeder & J.H. ter Horst
Angewandte Chemie 125 (2013) 2220–2234.
DOI:10.1002/ange.201204824

Paper on Uranium/Plutonium Dioxide Dissolution in Nitric Acid

A joint paper with NNL on uranium/plutonium dioxide dissolution in nitric acid has been published.

The Chemistry of (U,Pu)O2 Dissolution in Nitric Acid
M.J. Carrott, P.M.A. Cook, O.D. Fox, C.J. Maher & S.L.M. Schroeder
Procedia Chemistry 7 (2012) 92-97.
DOI:10.1016/j.proche.2012.10.017

Sin-Yuen Wins Chemical Engineering Course Prize

Congratulations are in order to our team member Sin-Yuen Chang, who has just been awarded the Course Prize for being the highest performing student on the MEng Chemical Engineering degree programme of the School. Sin-Yuen has just completed her MEng final year dissertation research with us, carrying out mechanistic studies of Au-catalysed aerobic oxidations of halogenated organic wastewater components. She has recently also been awarded a President’s Scholarship to continue her work with us as a PhD student from September 2012. Congratulations Sin-Yuen!

Sven’s Quick Guide to Measuring a Good Absorption Spectrum

The rule to remember is this:

When you measure absorption spectra (X-ray, UV, Vis, IR…) in transmission mode then you must not have any feature in the spectrum with an absorbance higher than approximately 1.2.

The principles from which this follows are nicely explained here:

http://www.chemguide.co.uk/analysis/uvvisible/beerlambert.html

For an absorbance of 1 90% of the incident light is absorbed. So 10% of the light transmits the sample and is detected. This ensures that the detector for the transmitted light has a signal with reliable intensity.

If you have an absorbance of 2 then 99% of the light is absorbed by your sample – so the transmission detector only sees 1% of the original intensity, which is usually not quite enough to ensure low noise and a linear response of the detector.

For an absorbance of 3 the detector only gets 0.1% of the original light intensity. This intensity is already approaching the noise level in many laboratory spectrometers. So what you are measuring is probably not significant – you are probably just seeing a flat noise line due to … – electronic noise.

So if the concentration of your substance is so that the absorbance is >1.2 then you must dilute your sample or shorten the thickness of the sample.

Most of the time dilution is the better way to do it:*

Just take a defined volume (in practice usually 1 mL or 10 mL) from your solution with a volumetric pipette and fill it up to 100 mL or perhaps even 1000 mL, in a clean volumetric flask. Use clean glassware for all of this – plastics may introduce contaminants.

Accuracy is important here – especially in pipetting. A 10% error in the pipette volume will mean a 10% error in the absorbance. You should aim for 1% accuracy.

Good luck!

*Those of you interested in molecular interactions at high concentrations can’t dilute of course – you will need to get special cuvettes providing a low sample thickness.