Cellulose microfibrils from banana farming residues: isolation and characterization

Cellulose microfibrils have been prepared from banana rachis using a combination of chemical and mechanical treatments. The morphology and structure of the samples were characterized using transmission electron microscopy, atomic force microscopy, and X-ray diffraction. Fourier-transformed infrared spectroscopy (FTIR) was used to characterize the chemical modifications of the samples after each treatment. Suspensions of bundled or individualized 5-nm-wide microfibrils were obtained after homogenization (PH) whereas an organosolv (PO) treatment resulted in shorter aggregates of parallel cellulose microcrystallites. The sharper rings in the X-ray diffraction pattern of the PO-treated sample suggest a higher crystallinity due to a more efficient removal of hemicelluloses and dissolution of amorphous zones by the acid treatment. Both microfibrils and microcrystals prepared by both methods can be used as reinforcing filler in nanocomposite materials.     

A way of establishing quality of measurements in gas analysis—national and international aspects

Standardising quality of measurements at both the national and international level results in a unity in measurement that may be regarded a synonym of traceability. In gas analysis, the key issue in achieving this aim is production of gaseous reference materials. Establishing a network of secondary measurement standards at gaseous CRM producers’ sites in Ukraine might be interesting for those involved in gas analysis activities. Inevitably, problems concerning the recognition of measuring capabilities of both national metrological institutes and local CRM producers are now an international issue. Thus, the problems of national adoption of international standards, as well as harmonisation between different international documents are currently relevant, and Ukrainian experience may be useful to others in this field. Presented at the 3rd International Conference on Metrology, November 2006, Tel Aviv, Israel.     

New In-situ Sampling and Analysis of the Production of CeO<Subscript>2</Subscript> Powders from Liquid Precursors using a Novel Wet Collection System in a rf Inductively Coupled Thermal Plasma Reactor. Part 1: Reactor System and Sampling Probe

A new reactor and a novel in-situ sampling technique were developed for the study of the synthesis of CeO₂ powders produced from dissolved cerium nitrate salts. The conical reactor minimized particle recirculation and provided a highly symmetrical and undisturbed plasma flow suitable for the analysis of the phenomena affecting the formation of CeO₂ powders. Both a calorimetric study of the reactor and a thermodynamic analysis of CeO₂ formation were conducted. The sampling probe is described and near-isokinetic sampling was achieved. The sampled particles were collected using a miniature wet collection system, i.e. a mist atomizer and a custom-made spray chamber. A numerical simulation of the velocity and temperature fields of the plasma gas in the reactor was done using Fluent. A comprehensive droplet-to-particle formation mechanism presented elsewhere is revisited and expanded based on calorimetry, thermodynamics of CeO₂ formation, numerical simulations and collected particles. No traces of other oxidation states other than CeO₂ were found.     

A.C. Cyclic voltammetry: A digital simulation study of the slow scan limit condition for a reversible electrode process

Rate laws presented to date for analysis of a.c. cyclic voltammetric data have invoked the so-called “slow scan limit approximation” which requires that ΔEω ? v, where Δ E and ω are the applied a.c. potential amplitude and angular frequency, respectively, and v is the d.c. potential scan rate. To provide a more useful guideline for the experimentalist than this qualitative condition, a pure digital simulation approach has been used to compute the a.c. cyclic time domain waveform for a reversible process under small amplitude conditions. The a.c. content of this waveform is extracted by the digital FFT alogirthm. Results of this study are presented here. Among the conclusions reached are more quantitative limitations for the slow scan limit rate laws describing the fundamental and second harmonic responses (approximately 128 a.c. cycles/d.c. cyclic sweep and 512 a.c. cycles/d.c. cyclic sweep, respectively) and an interesting prediction that the latter limitations can be relaxed further by a current waveform subtraction strategy, to as low as about 16 a.c. cycles/d.c. cyclic sweep for the fundamental and second harmonics. The cycles/sweep values assume one triangular wave potential scan of ±200 mV is encompassed.     

Atomic force microscopy study for supermolecular microstructures in side-chain liquid crystalline polymer films

Atomic force microscopy (AFM) is employed to study the supermolecular microstructures of disclinations and inversion walls in thin films of a smectic side-chain liquid crystalline polymer. Two-dimensional nanostripes are formed in thin films when the material enters the smectic phase. A possible mechanism for their formation is also suggested. The stripes run parallel to the local director and thus decorate the overall patterns of nematic director around the disclinations and inversion walls. Three patterns involving radial, spiral, and circular supermolecular microstructures of a positive disclination with s = +1 and one hyperbolic pattern of a negative disclination with s = -1 are observed. The cores of all these microstructures exhibit circular dark centers in AFM height images. It is found that the specific configurations of a pair of (+1, -1) disclinations form during the late stage of annihilation and inversion walls always separate a pair of (+1, +1) disclinations. The analysis on the director fields around disclinations and inversion walls shows that the bend and splay elastic constants are of the same order of magnitude in the side-chain liquid crystalline polymer.     

Preconcentration of Cadmium and Zinc on a Chelating Sorbent and Their Determination by Flame Atomic Absorption Spectrometry

A method is developed for cadmium and zinc preconcentration on a minicolumn packed with a new chelating polymer sorbent. The effects of the test solution pH and volume, the sample matrix composition, the eluent volume, and the sample and eluent flow rates are studied. Zinc and cadmium in the eluate are determined by flame atomic absorption spectrometry. Under optimal conditions, the determined ion recovery is more than 95%. The detection limits (3σ, n = 20) are found to be 15.0 (Cd) and 17.2 (Zn) ng/mL. The developed method is employed for cadmium and zinc determination in samples of seawater and water obtained after oil pumping.     

Flow-injection analysis with a small cylindrical wire type electrode

An amperometric detector with a small thin mercury film electrode is described. The device demonstrates advantageous operational characteristics such as small dispersion (D<2) and “memory effect” (me<0.6%), extensive maximum sample frequency (msf −200 samples/h), and high sensitivity. It has been proven useful in flow-injection analysis at a constant potential under hydrodynamic conditions.     

Case Study: Doping Substances in Equestrian Food Supplements

In the course of investigations on equestrian supplemental products for the presence of doping substances, two products were found to contain forbidden substances. As reported earlier a plant extract (Mexican cactus extract) named “Energy 5” contained the anabolic androgenic steroids (AAS) stanozolol, 17β-hydroxy-17α-methyl-5α-androstane-3β-ol (3β,5α-THMT) as well as mestanolone not declared on the label. In the present study, a product called “Super Kalm Paste” was tested. Analysis by gas chromatography - mass spectrometry (GC-MS) revealed that the preparation contained the class I anti-arrhythmics quinine (trade names Kinidin^TM, Durules) and cinchonine. The samples were prepared according to a sample preparation procedure established for anabolic steroids in nutritional supplements for humans. The sample treatment comprised the extraction and purification of the analytes as well as the chemical conversion with N-methyl-N-trimethylsilyl-trifluoracetamide (MSTFA) to yield the trimethylsilyl (TMS)-derivatives. To verify whether the administration of such products could lead to positive doping tests, a pilot excretion study on “Energy 5” was conducted with two geldings, and urine samples were collected. Gas chromatography - high resolution mass spectrometry (GC-HRMS) after solid phase extraction and mixed derivatisation has demonstrated the presence of the stanozolol metabolite 16β-hydroxy-stanozolol in urine samples after “Energy 5” application.     

Styrene emulsion polymerization: Particle-size distributions

Data are presented on the time evolution of particle-size distributions (PSDs) in seeded and ab initio styrene emulsion polymerization systems. Initiation was by chemical reagent (potassium persulfate) or γ-radiation. The unswollen PSDs at various times during interval II of the polymerization were obtained by direct measurement of calibrated electron micrographs. Experimental results were fitted with the equations that describe the time evolution of an initial PSD. Analytic solutions to these equations that allow for entry, exit, and propagation of free radicals were obtained. The values of the rate coefficients for these processes used to fit the experimental data were in excellent agreement with those obtained from dilatometric kinetics experiments.