Multi-element and mineralogical analysis of mineral ores using laser induced breakdown spectroscopy and chemometric analysis

In the mining industry the quality and extent of an ore body is determined on the basis of routine assays conducted on drill core and chip samples. Both the elemental composition and the mineralogical classification are important in the characterisation of an ore body for commercial exploitation. Mining industry laboratories typically analyse large numbers of samples from both exploration and mine production environments.At CSIRO we have explored the application of chemometric methods of analysis in combination with laser induced breakdown spectroscopy (LIBS) in order to produce routine quantitative analysis of several ore types including iron, nickel and lead/zinc ores. In particular, principal components regression (PCR) has been applied to perform multi-element analysis of iron ore samples from Australia and West Africa. Calibration models for iron (4.8% Av. Relative Error), aluminium (2.2%), silicon (3.7%) and potassium (1.4%) were determined for the Australian ores. In addition phosphorous measurements were made at trace level for samples from West Africa (5.5% Av. Relative Error). LIBS measurements of segments of a nickel drill core were also analysed using PCR.Mineralogical classification using a combination of LIBS and principal components analysis (PCA) has also been explored. Broad discrimination of ore mineralogy was demonstrated on the basis of the PCA of LIBS spectra in selected emission wavelength bands. The combination of PCA and PCR offers potential for both broad mineralogical and elemental analysis for the minerals industry in exploration and in mine production for the on-line monitoring of ore quality.     

Host-guest interactions at self-assembled monolayers of cyclodextrins on gold

We have developed synthesis routes for the introduction of short and long dialkylsulfides onto the primary side of alpha-, beta-, and gamma-cyclodextrins. Monolayers of these cyclodextrin adsorbates were characterized by electrochemistry, wettability studies, X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (TOF-SIMS), and atomic force microscopy (AFM). The differences in thickness and polarity of the outerface of the monolayers were measured by electro-chemistry and wettability studies. On average about 70% of the sulfide moieties were used for binding to the gold, as measured by XPS. Tof-SIMS measurements showed that the cyclodextrin adsorbates adsorb without any bond breakage. AFM measurements revealed for beta-cyclodextrin monolayers a quasi-hexagonal lattice with a lattice constant of 20.6 A, which matches the geometrical size of the adsorbate. The alpha-cyclodextrin and gamma-cyclodextrin monolayers are less ordered. Interactions of the anionic guests 1-anilinonaphthalene-8-sulfonic acid (1,8-ANS) and 2-(p-toluidinyl)naphthalene-6-sulfonic acid (2,6-TNS) and the highly ordered monolayers of heptapodant beta-cyclodextrin adsorbates were studied by surface plasmon resonance (SPR) and electrochemical impedance spectroscopy. The SPR measurements clearly showed interactions between a beta-cyclodextrin monolayer and 1,8-ANS. Electrochemical impedance spectroscopy measurements gave high responses even at low guest concentrations (< or = 5 microM). The association constant for the binding of 1,8-ANS (K = 289,000 +/- 13,000M-1) is considerably higher than the corresponding value in solution. (Partial) methylation of the secondary side of the beta-cyclodextrin strongly decreases the binding.     

Multicomponent analyses of chiral samples by use of regression analysis of UV–visible spectra of cyclodextrin guest–host complexes

We report the first combined use of analytical spectroscopy, guest–host chemistry, and multivariate regression analysis for determination of enantiometric composition of multicomponent samples of chiral analytes. Sample solutions containing multicomponent analytes of ephedrine, tryptophan, propranolol, and proline of varying enantiomeric composition with beta-cyclodextrin (BCD) or methyl-beta-cyclodextrin (Me-BCD) as chiral host molecules were investigated using ultraviolet (UV)–visible spectroscopy. The interactions of enantiomers of chiral analytes with chiral hosts resulted in the formation of transient diastereomeric inclusion complexes with varying spectral properties. Multivariate analysis using partial-least-square (PLS) regression was used to correlate subtle changes in the UV–visible spectra of the guest–host complexes with the enantiomeric composition of the calibration samples. These PLS regressions were carefully optimized and then used to predict the enantiomeric composition of multicomponent chiral analytes of validation samples. The results of these validation studies demonstrate the predictive ability of the regression models for determination of future enantiomeric composition of samples. The accuracy of the models to correctly predict the enantiomeric composition of samples, evaluated by use of the root mean square percent relative error (RMS%RE) was analyte and chiral host dependent. In general, better prediction of enantiomeric composition of samples and low RMS%RE values were obtained when Me-BCD was used as the chiral host. The analyses procedure reported here is simple, rapid, and inexpensive. In addition, this approach does not require prior separation of chiral analytes, thus reducing analysis time and eliminating the need for expensive chiral columns.     

Surface-engineered polyelectrolyte multilayer capsules: synthetic vaccines mimicking microbial structure and function

Immunizing: to evoke highly potent immune responses against recombinant antigens, hollow capsules consisting of layers of dextran sulphate and poly-L-arginine that encapsulate the antigen ovalbumin (orange circles) were coated with immune-activating CpG-containing oligonucleotides (green). These capsules were readily internalized by dendritic cells and showed activity in further immunization experiments.     

Reversible three-state switching of luminescence: a new twist to electro- and photochromic behavior

The fully reversible three-state blue/red/off emission from photo-/electrochromic substituted bis-thiaxanthylidenes is reported. The blue luminescence of the most stable (anti-folded) conformer of dimethyl- and dimethoxy-bis-thiaxanthylidene can be switched off by photochemical conversion to the meta-stable (syn-folded) conformer and switched on again by thermal reversion to the anti-folded state. The red luminescence of the bis-thiaxanthylium dication can be switched on by oxidation at approximately 1.0 and 1.2 V vs SCE of the syn- and anti-folded conformers respectively and switched off or to blue by reduction at approximately 0.35 V vs SCE.     

Quantum theory for transition state absorption

A time-dependent quantum model involving two wave packets on two excited-state surfaces is presented to describe absorption (or emission) from the transition state of a chemical reaction. The connection between the quantum result and existing classical theories is shown. The model ia applied to the direct dissociation of ICN* and gives results in good agreement with experiment. The dissociation time - the time to half-maximal absorption - is almost invariant with the pulse width but is dependent on the probe wavelength. A lower absorption plateau and a longer dissociation time is predicted for probe energies above the asymptotic resonance energy.