Sieve mechanism of microfiltration separation

A theoretical model of dead-end microfiltration (MF) of dilute suspensions is proposed. The model is based on a sieve mechanism of MF and takes into account the probability of membrane pore blocking during MF of dilute colloidal suspensions. An integro-differential equation (IDE) that includes both the membrane pore size and the particle size distributions is deduced. According to the suggested model a similarity property is applicable, which allows one to predict the flux through the membrane as a function of time for any pressure, and dilute concentration, based on one experiment at a single pressure and concentration. The suggested model includes only one fitting parameter, β>1, which takes into account the range of the hydrodynamic influence of a single pore. For a narrow pore size distribution in which one pore diameter predominates (track-etched membranes), the IDE is solved analytically and the derived equation is in good agreement with the measurements on different track-etched membranes. A simple approximate solution of the IDE is derived and that approximate solution, as well as the similarity principal of MF processes, is in good agreement with measurements using a commercial Teflon microfiltration membrane. The theory was further developed to take into account the presence of multiple pores (double, triple and so on pores) on a track-etched membrane surface.

A series of new dead-end filtration experiments are compared with the proposed initial and modified pore blocking models. The challenge suspension used was nearly monodispersed suspension of latex particles of 0.45 μm filtered on a track-etched membrane with similar sized pores 0.4 μm. The filtered suspension concentration ranged from 0.00006 to 0.01% (w/w) and the cross-membrane pressures varied from 1000 to 20,000 Pa. Three stages of microfiltration have been observed. The initial stage is well described by the proposed pore blocking model. The model required only a single parameter that was found to fit all the data under different experimental operational conditions. The second stage corresponds to the transition from the blocking mechanism to the third stage, which is cake filtration. The latter stage occurred after approximately 10–12 particle layers were deposited (mass = 0.006 g) on the surface of the microfiltration membrane.     

Imaging the Belousov-Zhabotinsky reaction in real time using an ion sensitive array

We show how an array of ion-sensitive-field-effect-transistors can be used to both spatially and temporally image the oscillating pH/ion waves produced by the Belousov-Zhabotinsky (BZ) reaction with high resolution.     

Monolayers of rod-shaped and disc-shaped liquid crystalline compounds at the air-water interface

Calamitic (rod-shaped) and discotic (disc-shaped) thermotropic liquid crystalline (LC) compounds were spread at the air-water interface, and their ability to form monolayers was studied. The calamitic LCs investigated were found to form monolayers which behave analogously to conventional amphiphiles such as fatty acids. The spreading of the discotic LCs produced monolayers as well, but with a behaviour different from classical amphiphiles. The areas occupied per molecule are too small to allow the contact of all hydrophilic groups with the water surface and the packing of all hydrophobic chains. Various molecular arrangements of the discotics at the water surface to fit the spreading data are discussed.     

Selenium intake of Australian breast fed infants

A series of 20 mother-infant pairs were studied in Brisbane, Australia at 6–12 weeks post-partum. Mean breast milk selenium concentration (±SD) was 11.9±3.5 ng/g; infants' mean 24 hour selenium intakes (±SD) were 10.7±4.1 g. Mean selenium concentration in material blood was 101 (±SD 19) ng/g and in material serum 81 (±15) ng/g.     

Mathematical analysis for impedance change with proteolytic digestion of gelatin

A mathematical analysis is proposed to demonstrate an inter-relationship between the proteolytic digestion of gelatin on the surface of an interdigitated gold electrode and the resulting rate of impedance change, at different collagenase concentrations, in a biosensor used to detect protease in solution. The impedance change due to digestion of the gelatin layer by collagenase for the overall digestion process was expressed in two different stages: an initial exponential period where the rate of impedance change with enzymic digestion was slow, leading to a critical thickness; after which there was a greater change in impedance associated with subsequent dissolution of the layer and partial or complete uncoating of the digits on the electrode surface. An inter-relationship between the rate of impedance change and collagenase concentration within the range 0.2-0.6 mg ml-1 was predicted for the early stages of the digestion process. A kinetic theory for the rapid rate of impedance change with collagenase concentrations could not be developed owing to the rate remaining almost constant for all concentrations of collagenase, after the critical thickness had been reached. An inter-relationship between the rate of impedance change and stirrer speed was also demonstrated.     

Thermal analysis of fluidised bed combustion residues containing limestone scavenger

A method has been developed using thermoanalytical techniques for the analysis of residues from coal-burning fluidised bed plant where limestone is used as a sulphur scavenger. This completely eliminates the need for lengthy wet chemical analyses and allows the derivation of parameters necessary for efficient plant operation, such as limestone addition rate, calcium utilisation efficiency and calcium to sulphur mole ratio. The method also gives values for the unburned carbon content and the ratio of coal ash to limestone derivatives in the sample.     

Highly Enantiomerically Enriched Planar Chiral Naphthalene Tricarbonylchromium Complexes

Lithiation/electrophile trapping reactions were carried out with the highly enantiomerically enriched complex [Cr(5‐bromonaphthalene)(CO)₃]. Electrophile quenching with ClPPh₂, PhCHO, and (Me₃SiO)₂ afforded the enantiomerically enriched (>97 % ee) planar chiral 5‐substituted naphthalene complexes with PPh₂, CH(Ph)OH, and OH substituents, respectively. Very mild Pd‐catalyzed Suzuki–Miyaura cross‐coupling reactions were developed and applied to the highly labile [Cr(5‐bromonaphthalene)(CO)₃] to give nine new planar chiral aryl‐, heteroaryl‐, alkynyl‐, and alkenylnaphthalene chromium complexes with high enantiomeric purity. The efficient ambient‐temperature coupling reactions with borinates prepared in situ were also applied to a number of chlorobenzene complexes and to aryl and vinyl halides.     

Isolation of naturally occurring aluminium ligands using immobilized metal affinity chromatography for analysis by ESI-MS

Aluminium (iii) is one of the most abundant metal ions found in soil. Typically, Al(+3) is bound to minerals, but its bioavailability and toxicity toward vascular plants increases with increasing soil acidity. Ectomycorrhizal fungi, which live symbiotically on the roots of numerous woody plants, often confer Al(+3) resistance to host plants by reducing metal availability to the plant by unknown mechanisms. A potential mechanism of detoxification is binding of the Al(+3) by organic compounds that are exuded by the fungi into the surrounding soil and solution. A novel method has been developed to purify and characterize Al(+3) binding ligands from Pisolithus tinctorius exudate solutions using Al(+3) immobilized metal affinity chromatography (IMAC), reversed phase chromatography, and mass spectrometry. Fungal exudates produced by P. tinctorius exhibit a strong binding capacity for Al(+3), allowing their selective enrichment and collection using this IMAC method. Elution of the ligands requires the use of high pH. RP-HPLC separation and elemental analysis of the IMAC elutent indicates that the Al(+3) and the exudate ligands both elute from the column but are not bound in a complex. Thus, reversed phase HPLC at pH 10 is used for separation of the ligands and Al(+3) prior to MS analysis. The strongest binding IMAC fraction is analyzed by electrospray ionization mass spectrometry in positive and negative ion modes. This report provides new methods for the direct purification and analysis of naturally occurring ligands that bind hard metal ions.