Development of a gas diffusion probe for the rapid measurement of pCO2 in aquatic samples

A capillary electrophoresis (CE) procedure with contactless conductivity detection (C(4)D) has been developed for monitoring of neutral mono- and disaccharides in drinks and foodstuffs. The separation of a mixture of seven neutral saccharides (glucose, fructose, galactose, mannose, ribose, sucrose and lactose) employed a quartz capillary, 5 μm i.d., with an effective length of 18.3 cm, and 75 mM NaOH (pH 12.8) as the background electrolyte (BGE). The limit of detection (LOD) values obtained lied within a range from 0.4 μmol L(-1) for lactose to 0.9 μmol L(-1) for ribose, with a separation time shorter than 140 s. The procedure was successfully applied to determinations of saccharides in fruit juices, Coca-Cola, milk, red and white wines, yoghurts, honey and a foodstuff additive.     

Near-infrared spectroscopy of LiNH3: first observation of the electronic spectrum

Electronic spectra of LiNH(3) and its partially and fully deuterated analogues are reported for the first time. The spectra have been recorded in the near-infrared and are consistent with two electronic transitions in close proximity, the ?(2)E-X(2)A(1) and B(2)A(1)-X(2)A(1) systems. Vibrational structure is seen in both systems, with the Li-N-H bending vibration (ν(6)) dominant in the ?(2)E-X(2)A(1) system and the Li-N stretch (ν(3)) in the B(2)A(1)-X(2)A(1) system. The prominence of the 6(0)(1) band in the ?(2)E-X(2)A(1) spectrum is attributed to Herzberg-Teller coupling. The proximity of the B(2)A(1) state, which lies a little more than 200 cm(-1) above the ?(2)E state, is likely to be the primary contributor to this strong vibronic coupling.     

Thermal and odd–even behaviour in a homologous series of lithium n-alkanoates

Thermotropic phase transition temperatures, enthalpies and entropies of phase changes and odd–even alternation, in a homologous series of anhydrous lithium n-alkanoates, LiC_nH_2n?1O₂ (LiC_8–19 inclusive), have been investigated by differential scanning calorimetry (d.s.c.), hot stage polarizing microscopy and solid state ¹³C NMR spectroscopy. The number of phases observed, between the room temperature microcrystalline solid and isotropic melt, shows a clear dependence on chain length. For LiC_8–13, only one intermediate lamellar II crystalline phase is observed. For LiC_14–19, a lamellar II and high temperature phase are evident. The high temperature phase is characterized by pre-melting and disordering of hydrocarbon chains as they change from nearly all-trans to one with increased gauche conformers. It is probably a solid rotator phase. Odd–even alternation in melting temperature, density and some thermodynamic data result from the relative distance between methyl groups, from opposite layers in a bi-layer. Molecular models indicate that the methyl groups in odd chains are more favourably orientated which lead to a more energetically favoured staggered conformer. As a consequence, the methyl groups, for odd chains, are in closer proximity than even chains. This subtle change in the molecular lattice could account for the presence of polymorphic structures on cooling from the melt.     

Laser microperforated biodegradable microbial polyhydroxyalkanoate substrates for tissue repair strategies: an infrared microspectroscopy study

Flexible and biodegradable film substrates prepared by solvent casting from poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBHV) solutions in chloroform were microperforated by ultraviolet laser ablation and subsequently characterized using infrared (IR) microspectroscopy and imaging techniques and scanning electron microscopy (SEM). Both transmission synchrotron IR microspectroscopy and attenuated total reflectance microspectroscopy measurements demonstrate variations in the polymer at the ablated pore rims, including evidence for changes in chemical structure and crystallinity. SEM results on microperforated PHBHV substrates after cell culture demonstrated that the physical and chemical changes observed in the biomaterial did not hinder cell migration through the pores.     

Flow analysis methods for the direct ultra-violet spectrophotometric measurement of nitrate and total nitrogen in freshwaters

Allergy to tree nuts represents an acute health problem. Sensitized people can be inadvertently exposed to hidden allergens resulting from cross-contamination of foods. For this reason, reliable and highly sensitive analytical methods are needed to be developed for control and labeling of food ingredients and products. In the present paper we have proposed a new allergen specific sandwich-ELISA for hazelnut operated in optical and electrochemical modes. The ELISA was based on chicken egg yolk antibodies raised against a major hazelnut allergen, Cor a 9. The developed ELISA has a limit of detection in phosphate buffer of 4 ng mL(-1). No significant cross-reactivity with peanut, wheat or other food ingredients has been detected. Extracts of blank control cookies did not show any false positive response and the limit of detection in cookies was estimated to be 0.1 μg of hazelnut protein per g of food (0.1 ppm). The ELISA protocol was successfully adapted to operate in electrochemical mode and it was applied for the detection of hazelnut traces in cookies.     

The complex spectrum of a "simple" free radical: the Ã-X̃ band system of the jet-cooled boron difluoride free radical

The near-ultraviolet band system of the jet-cooled boron difluoride free radical has been studied by a combination of laser-induced fluorescence and single vibronic level wavelength resolved emission spectroscopies. The radical was produced in a supersonic discharge jet using a precursor mixture of 1%-3% of BF(3) or (10)BF(3) in high pressure argon. A large number of bands were found in the 340-286 nm region and assigned as transitions from the X?(2)A(1) ground state to the lower Renner-Teller component of the A?(2)Π excited state, based on our previous ab initio potential energy surface predictions, matching the emission spectra Franck-Condon profiles of (11)BF(2) and (10)BF(2), and comparison of observed and calculated boron isotope effects. Several bands have been rotationally analyzed providing ground state structural parameters of r(0)(') (BF) = 1.3102(9) ? and θ(0)(') (FBF) = 119.7(6)°. The ground state totally symmetric vibrational energy levels of both boron isotopologues have also been measured and assigned up to energies of more than 8000 cm(-1). Although BF(2) might be considered to be a "simple" free radical, understanding the details of its electronic spectrum remains a major challenge for both theory and experiment.     

Core-shell effects in the ionization of doped helium nanodroplets

Core-shell particles with water clusters as the core and surrounded by an atomic or molecular shell have been synthesized for the first time by adding water and a co-dopant sequentially to helium nanodroplets. The co-dopants chosen for investigation were Ar, O(2), N(2), CO, CO(2), NO and C(6)D(6). These co-dopants have been used to investigate the effect of an outer shell on the ionization of the core material by charge transfer in helium nanodroplets. The specific aim was to determine how the identity of the shell material affects the fragmentation of water cluster ions, i.e. whether it helps to stabilize parent ion ((H(2)O)(n)(+)) formation or increases fragmentation (to form (H(2)O)(n)H(+)). N(2), O(2), CO(2) and C(6)D(6) all show a marked softening effect, which is consistent with the formation of a protective shell around the water cluster core. For CO and NO co-dopants, the response is complicated by secondary reactions which actually favour water cluster ion fragmentation for some water cluster sizes.