A new and less destructive laboratory procedure for the physical separation of distal glass tephra shards from sediments

Tephrochronology, a key tool in the correlation of Quaternary sequences, relies on the extraction of tephra shards from sediments for visual identification and high-precision geochemical comparison. A prerequisite for the reliable correlation of tephra layers is that the geochemical composition of glass shards remains unaltered by natural processes (e.g. chemical exchange in the sedimentary environment) and/or by laboratory analytical procedures. However, natural glasses, particularly when in the form of small shards with a high surface to volume ratio, are prone to chemical alteration in both acidic and basic environments. Current techniques for the extraction of distal tephra from sediments involve the ‘cleaning’ of samples in precisely such environments and at elevated temperatures. The acid phase of the ‘cleaning’ process risks alteration of the geochemical signature of the shards, while the basic phase leads to considerable sample loss through dissolution of the silica network. Here, we illustrate the degree of alteration and loss to which distal tephras may be prone, and introduce a less destructive procedure for their extraction. This method is based on stepped heavy liquid flotation and which results in samples of sufficient quality for analysis while preserving their geochemical integrity. In trials, this method out-performed chemical extraction procedures in terms of the number of shards recovered and has resulted in the detection of new tephra layers with low shard concentrations. The implications of this study are highly significant because (i) the current database of distal tephra records and their corresponding geochemical signatures may require refinement and (ii) the record of distal tephras may be incomplete due to sample loss induced by corrosive laboratory procedures. It is therefore vital that less corrosive laboratory procedures are developed to make the detection and classification of distal glass tephra more secure.

Polymeric complexesSynthesis, Characterization and Analytical Applications

As the application of polymeric complexes is enormous, there exists a continuing interest in the synthesis and characterization of these complexes. The synthetic and characterization parts are very important in an academic point of view. Further in an application point of view also polymeric ligands/complexes are gaining attention.The thesis is divided in to six chapters, in which the first chapter gives an introduction along with a brief review on polymeric ligands/ complexes. The second chapter explains the different procedure adopted for the whole work along with the details of the reagents/ instruments used. The third chapter gives a report of the detailed study regarding the synthesis and characterization of eighteen complexes. While the fourth chapter is a report of the ion removal studies using three polymeric ligands, the fifth chapter explains the development of a polymeric complex as ion selective electrode material for the fabrication of a CC ion selective electrode. The sixth chapter presents the summary and tables, figures and references are given separately at the end.

Analytical potentials for triatomic molecules IX. The prediction of anharmonic force constants from potential energy surfaces based on harmonic force fields and dissociation energies for SO2 and O3

Analytical potential energy functions which are valid at all dissociation limits have been derived for the ground states of SO2 and O3. The procedure involves minimizing the errors between the observed vibrational spectra and spectra calculated by a variational procedure. Good agreement is obtained between the observed and calculated spectra for both molecules. Comparisons are made between anharmonic force fields, previously determined from the spectral data, and the force fields obtained by differentiating the derived analytical functions at the equilibrium configurations.

Contact angle of a hemispherical bubble: an analytical approach

We have calculated the equilibrium shape of the axially symmetric Plateau border along which a spherical bubble contacts a flat wall, by analytically integrating Laplace’s equation in the presence of gravity, in the limit of small Plateau border sizes. This method has the advantage that it provides closed-form expressions for the positions and orientations of the Plateau border surfaces. Results are in very good overall agreement with those obtained from a numerical solution procedure, and are consistent with experimental data. In particular we find that the effect of gravity on Plateau border shape is relatively small for typical bubble sizes, leading to a widening of the Plateau border for sessile bubbles and to a narrowing for pendant bubbles. The contact angle of the bubble is found to depend even more weakly on gravity.

A green flow-based procedure for fluorimetric determination of acid-dissociable cyanide in natural waters exploiting multicommutation

A flow system designed with solenoid valves is proposed for determination of weak acid dissociable cyanide, based on the reaction with o-phthalaldehyde (OPA) and glycine yielding a highly fluorescent isoindole derivative. The proposed procedure minimizes the main drawbacks related to the reference batch procedure, based on reaction with barbituric acid and pyridine followed by spectrophotometric detection, i.e., use of toxic reagents, high reagent consumption and waste generation, low sampling rate, and poor sensitivity. Retention of the sample zone was exploited to increase the conversion rate of the analyte with minimized sample dispersion. Linear response (r=0.999) was observed for cyanide concentrations in the range 1-200 mu g L(-1), with a detection limit (99.7% confidence level) of 0.5 mu g L(-1)(19 nmol L(-1)). The sampling rate and coefficient of variation (n=10) were estimated as 22 measurements per hour and 1.4%, respectively. The results of determination of weak acid dissociable cyanide in natural water samples were in agreement with those achieved by the batch reference procedure at the 95% confidence level. Additionally to the improvement in the analytical features in comparison with those of the flow system with continuous reagent addition (sensitivity and sampling rate 90 and 83% higher, respectively), the consumption of OPA was 230-fold lower.

Development of a spectrophotometric Sequential Injection Analysis (SIA) procedure for determination of ammonium: A Response Surface Methodology (RSM) approach

This paper describes the optimization and use of a Sequential Injection Analysis (SIA) procedure for ammonium determination in waters. Response Surface Methodology (RSM) was used as a tool for optimization of a procedure based on the modified Berthelot reaction. The SIA system was designed to (i) prepare the reaction media by injecting an air-segmented zone containing the reagents in a mixing chamber, (ii) to aspirate the mixture back to the holding coil after homogenization, (iii) drive it to a thermostated reaction coil, where the flow is stopped for a previously established time, and (iv) to pump the mixture toward the detector flow cell for the spectrophotometric measurements. Using a 100 mu mol L(-1) ammonium solution, the following factors were considered for optimization: reaction temperature (25 - 45 degrees C), reaction time (30 - 90 s), hypochlorite concentration (20 - 40 mmol L(-1)) nitroprusside concentration (10 - 40 mmol L(-1)) and salicylate concentration (0.1 - 0.3 mol L(-1)). The proposed system fed the statistical program with absorbance data for fast construction of response surface plots. After optimization of the method, figures of merit were evaluated, as well as the ammonium concentration in some water samples. No evidence of statistical difference was observed in the results obtained by the proposed method in comparison to those obtained by a reference method based on the phenol reaction. (C) 2010 Elsevier B.V. All rights reserved.

Graphite-silicone rubber composite electrode: Preparation and possibilities of analytical application

Composite electrodes were prepared using graphite powder and silicone rubber in different compositions. The use of such hydrophopic materials interned to diminish the swallowing observed in other cases when the electrodes are used in aqueous solutions for a long time. The composite was characterized for the response reproducibility, ohmic resistance, thermal behavior and active area. The voltammetric response in relation to analytes with known voltammetric behavior was also evaluated, always in comparison with the glassy carbon. The 70% (graphite, w/w) composite electrode was used in the quantitative determination of hydroquinone (HQ) in a DPV procedure in which a detection limit of 5.1 x 10(-8) mol L-1 was observed. HQ was determined in a photographic developer sample with errors lower then 1% in relation to the label value. (c) 2007 Elsevier B.V. All rights reserved.

Development of a new analytical approach based on cellulose membrane and chelator for differentiation of labile and inert metal species in aquatic systems

A new procedure was developed in this study, based on a system equipped with a cellulose membrane and a tetraethylenepentamine hexaacetate chelator (MD-TEPHA) for in situ characterization of the lability of metal species in aquatic systems. To this end, the DM-TEPHA system was prepared by adding TEPHA chelator to cellulose bags pre-purified with 1.0 mol L-1 of HCl and NaOH solutions. After the MD-TEPHA system was sealed, it was examined in the laboratory to evaluate the influence of complexation time (0-24 h), pH (3.0, 4.0, 5.0, 6.0 and 7.0), metal ions (Cu, Cd, Fe, Mn and Ni) and concentration of organic matter (15, 30 and 60 mg L-1) on the relative lability of metal species by TEPHA chelator. The results showed that Fe and Cu metals were complexed more slowly by TEPHA chelator in the MD-TEPHA system than were Cd, Ni and Mn in all pH used. It was also found that the pH strongly influences the process of metal complexation by the MD-TEPHA system. At all the pH levels, Cd, Mn and Ni showed greater complexation with TEPHA chelator (recovery of about 95-75%) than did Cu and Fe metals. Time also affects the lability of metal species complexed by aquatic humic substances (AHS); while Cd, Ni and Mn showed a faster kinetics, reaching equilibrium after about 100 min, and Cu and Fe approached equilibrium after 400 min. Increasing the AHS concentration decreases the lability of metal species by shifting the equilibrium to AHS-metal complexes. Our results indicate that the system under study offers an interesting alternative that can be applied to in situ experiments for differentiation of labile and inert metal species in aquatic systems. (c) 2006 Elsevier B.V. All rights reserved.

Procedure optimization of silicate rocks dissolution in open vessels for ICP-AES analysis.

The main variables found on procedure of the dissolution silicate rocks using acid dissolution in teflon open vessel for analysis of micro elements by ICP-AES has been determined. The results obtained for some samples showed strong dependence of the rock mineralogical composition, then it was recommended an alkaline fusion step after acid dissolution. The decomposition procedure use 20 mi of an acid mixture of HF:HNO3 in the proportion 3:1 for a fraction of 250 mg pulverized sample. The recommended temperatures were 60 degrees C for attack and 90 degrees C for acid volatilization. The fusion step with 50 mg LiBO2 at 1000 degrees C may be used if non-attacked residue is observed in the solution. The whole time was 6 h per sample. Nine types os silicate rocks that show mineralogical and chemical different compositions were chosen for obtaining the optimization of the variables. The elements used were Ce, Y, Yb and Zr. In addition, ultrassonic nebulization has been used. The percentual standard deviations obtained for five determinations were 0.7 and 1.4 for triplicate samples. The mineralogical and textural information from the petrographical analysis of the samples indicated the need of increasing the fusion step on the optimized procedure.

Analytical model for heterogeneous crystallization kinetics of spherical glass particles

An analytical model developed to describe the crystallization kinetics of spherical glass particles has been derived in this work. A continuous phase transition from three-dimensional (3D)-like to 1D-like crystal growth has been considered and a procedure for the quantitative evaluation of the critical time for this 3D-1D transition is proposed. This model also allows straightforward determination of the density of surface nucleation sites on glass powders using differential scanning calorimetry data obtained under different thermal conditions. © 2009 The American Ceramic Society.

Analytical procedures for cadmium determination in facial make-up samples by graphite furnace AAS

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Development of instrumental and sensory analytical methods of food obtained by traditional and emerging technologies

The consumer demand for natural, minimally processed, fresh like and functional food has lead to an increasing interest in emerging technologies. The aim of this PhD project was to study three innovative food processing technologies currently used in the food sector. Ultrasound-assisted freezing, vacuum impregnation and pulsed electric field have been investigated through laboratory scale systems and semi-industrial pilot plants. Furthermore, analytical and sensory techniques have been developed to evaluate the quality of food and vegetable matrix obtained by traditional and emerging processes. Ultrasound was found to be a valuable technique to improve the freezing process of potatoes, anticipating the beginning of the nucleation process, mainly when applied during the supercooling phase. A study of the effects of pulsed electric fields on phenol and enzymatic profile of melon juice has been realized and the statistical treatment of data was carried out through a response surface method. Next, flavour enrichment of apple sticks has been realized applying different techniques, as atmospheric, vacuum, ultrasound technologies and their combinations. The second section of the thesis deals with the development of analytical methods for the discrimination and quantification of phenol compounds in vegetable matrix, as chestnut bark extracts and olive mill waste water. The management of waste disposal in mill sector has been approached with the aim of reducing the amount of waste, and at the same time recovering valuable by-products, to be used in different industrial sectors. Finally, the sensory analysis of boiled potatoes has been carried out through the development of a quantitative descriptive procedure for the study of Italian and Mexican potato varieties. An update on flavour development in fresh and cooked potatoes has been realized and a sensory glossary, including general and specific definitions related to organic products, used in the European project Ecropolis, has been drafted.

Pyrolysis of peptides and proteins. Analytical study and environmental applications

Analytical pyrolysis was used to investigate the formation of diketopiperazines (DKPs) which are cyclic dipeptides formed from the thermal degradation of proteins. A quali/quantitative procedure was developed combining microscale flash pyrolysis at 500 °C with gas chromatography-mass spectrometry (GC-MS) of DKPs trapped onto an adsorbent phase. Polar DKPs were silylated prior to GC-MS. Particular attention was paid to the identification of proline (Pro) containing DKPs due to their greater facility of formation. The GC-MS characteristics of more than 80 original and silylated DKPs were collected from the pyrolysis of sixteen linear dipeptides and four model proteins (e.g. bovine serum albumin, BSA). The structure of a novel DKP, cyclo(pyroglutamic-Pro) was established by NMR and ESI-MS analysis, while the structures of other novel DKPs remained tentative. DKPs resulted rather specific markers of amino acid sequence in proteins, even though the thermal degradation of DKPs should be taken into account. Structural information of DKPs gathered from the pyrolysis of model compounds was employed to the identification of these compounds in the pyrolysate of proteinaceous samples, including intrinsecally unfolded protein (IUP). Analysis of the liquid fraction (bio-oil) obtained from the pyrolysis of microalgae Nannochloropsis gaditana, Scenedesmus spp with a bench scale reactor showed that DKPs constituted an important pool of nitrogen-containing compounds. Conversely, the level of DKPs was rather low in the bio-oil of Botryococcus braunii. The developed micropyrolysis procedure was applied in combination with thermogravimetry (TGA) and infrared spectroscopy (FT-IR) to investigate surface interaction between BSA and synthetic chrysotile. The results showed that the thermal behavior of BSA (e.g. DKPs formation) was affected by the different form of doped synthetic chrysotile. The typical DKPs evolved from collagen were quantified in the pyrolysates of archaeological bones from Vicenne Necropolis in order to evaluate their conservation status in combination with TGA, FTIR and XRD analysis.

Ultrasensitive chemiluminescence bioassays based on microfluidics in miniaturized analytical devices

The activity carried out during my PhD was principally addressed to the development of portable microfluidic analytical devices based on biospecific molecular recognition reactions and CL detection. In particular, the development of biosensors required the study of different materials and procedures for their construction, with particular attention to the development of suitable immobilization procedures, fluidic systems and the selection of the suitable detectors. Different methods were exploited, such as gene probe hybridization assay or immunoassay, based on different platform (functionalized glass slide or nitrocellulose membrane) trying to improve the simplicity of the assay procedure. Different CL detectors were also employed and compared with each other in the search for the best compromise between portability and sensitivity. The work was therefore aimed at miniaturization and simplification of analytical devices and the study involved all aspects of the system, from the analytical methodology to the type of detector, in order to combine high sensitivity with easiness-of-use and rapidity. The latest development involving the use of smartphone as chemiluminescent detector paves the way for a new generation of analytical devices in the clinical diagnostic field thanks to the ideal combination of sensibility a simplicity of the CL with the day-by-day increase in the performance of the new generation smartphone camera. Moreover, the connectivity and data processing offered by smartphones can be exploited to perform analysis directly at home with simple procedures. The system could eventually be used to monitor patient health and directly notify the physician of the analysis results allowing a decrease in costs and an increase in the healthcare availability and accessibility.

Study of and design procedure for dual circularly polarized waveguide slot arrays

For the past sixty years, waveguide slot radiator arrays have played a critical role in microwave radar and communication systems. They feature a well-characterized antenna element capable of direct integration into a low-loss feed structure with highly developed and inexpensive manufacturing processes. Waveguide slot radiators comprise some of the highest performance—in terms of side-lobe-level, efficiency, etc. — antenna arrays ever constructed. A wealth of information is available in the open literature regarding design procedures for linearly polarized waveguide slots. By contrast, despite their presence in some of the earliest published reports, little has been presented to date on array designs for circularly polarized (CP) waveguide slots. Moreover, that which has been presented features a classic traveling wave, efficiency-reducing beam tilt. This work proposes a unique CP waveguide slot architecture which mitigates these problems and a thorough design procedure employing widely available, modern computational tools. The proposed array topology features simultaneous dual-CP operation with grating-lobe-free, broadside radiation, high aperture efficiency, and good return loss. A traditional X-Slot CP element is employed with the inclusion of a slow wave structure passive phase shifter to ensure broadside radiation without the need for performance-limiting dielectric loading. It is anticipated this technology will be advantageous for upcoming polarimetric radar and Ka-band SatCom systems. The presented design methodology represents a philosophical shift away from traditional waveguide slot radiator design practices. Rather than providing design curves and/or analytical expressions for equivalent circuit models, simple first-order design rules – generated via parametric studies — are presented with the understanding that device optimization and design will be carried out computationally. A unit-cell, S-parameter based approach provides a sufficient reduction of complexity to permit efficient, accurate device design with attention to realistic, application-specific mechanical tolerances. A transparent, start-to-finish example of the design procedure for a linear sub-array at X-Band is presented. Both unit cell and array performance is calculated via finite element method simulations. Results are confirmed via good agreement with finite difference, time domain calculations. Array performance exhibiting grating-lobe-free, broadside-scanned, dual-CP radiation with better than 20 dB return loss and over 75% aperture efficiency is presented.