Trace elements in human cancerous and healthy tissues: A comparative study by EDXRF,TXRF, synchrotron radiation and PIXE

It is known that trace elements play an important role in a number of biological processes. These include the activation or inhibition of enzymatic reactions, competition between elements and metal proteins for binding positions and modifications in the permeability of cellular membranes. These elements may also influence carcinogenic processes, thus the knowledge of trace element concentrations in healthy and neoplastic tissues might help in diagnostic and in the etiology and development of cancer.     

Heavy metal analysis of rainwaters: A comparison of TXRF and ASV analytical capabilities

The aim of this work consisted on the implementation of sufficiently accurate and sensitive analytical procedure for the analysis of metal concentration in rainwater. Different sample preparation procedures were tested to achieve the required concentration prior to direct total reflection X-ray fluorescence (TXRF) analysis. TXRF and anodic stripping voltammetry (ASV) were compared in regard to achieved detection limits, precision and accuracy.     

Analysis of geological standards with PIXE and PIGE technioues applications to volcanic rocks

Geological standards are analyzed using PIXE and PIGE techniques. The concentrations of up to 26 elements are determined and compared with those obtained by other methods. PIXE and PIGE techniques are also applied to different volcanic rock samples. Their sensitivity, accuracy, and speed of data collection and reduction, are of great interest in the study of volcanic phenomena.     

Calorimetric sensing in bioanalytical chemistry: Principles, applications and trends

Calorimetry has shown great potential in bioanalytical chemistry as most biochemical processes involve a change in enthalpy. Two types of approach have been developed: (1) adiabatic calorimetry, which relies on the absence of heat exchange between the reaction vessel and the external environment, and (2) heat conduction calorimetry, involving measurement of the heat transferred from the vessel to a surrounding heat sink. Both principles, with their respective advantages and drawbacks, have been applied to microcalorimetry for the analysis of (bio)chemical compounds. Immobilization of the biomaterial in the vicinity of, or directly onto a small temperature or heat sensitive transducer has led to the concept of a calorimetric biosensor. In comparison to the traditional calorimeter, the calorimetric biosensor is better suited to continuous monitoring and size reduction. This simplified but sensitive device is expected to solve numerous problems in various fields of analytical chemistry.     

Principles and analytical applications of acousto-optic tunable filters, an overview

Advantages of acousto-optic tunable filters have been exploited to develop novel analytical instruments which are not feasible otherwise. The instrumentation development and unique features of such AOTF based instruments including the multidimensional fluorimeter, the multiwavelength thermal lens spectrometer, the near-infrared spectrometer based on erbium doped fiber amplifier (EDFA), and detectors for high performance liquid chromatography (HPLC) and flow injection analysis (FIA), will be described.     

Principles,methodologies, and applications of photon activation analysis: a review

This review describes the basic principles of photon activation analysis (PAA) and gives an extensive overview of its numerous applications. Uses of PAA for environmental, biological, geological, archeological, and forensic samples are reviewed. Both scientific and industrial applications of PAA are covered. Potential future uses of PAA are addressed.     

Principles and applications of electrochemical and optical biosensors

The principles of biocatalytic and bioaffinity biosensors are reviewed with emphasis on electron transfer-type enzyme sensors, optical enzyme sensors and optical immunosensors for homogeneous immunoassay. An enzyme sensor for ethanol was fabricated by electrochemical polymerization of pyrrole onto the surface of platinized platinum-adsorbed alcohol dehydrogenase—NAD—Meldola Blue. Ethanol was determined amperometrically by measuring the oxidative current through polypyrrole. An optical enzyme sensor is exemplified by an acethylcholine sensor based on an optical pH fibre sensor using a thin polyaniline film. The optical immunosensor for homogeneous immunoassay consists of an optical fibre, the end of the which is coated with an optically transparent platinum electrode. With using luminol as a label, highly sensitive homogeneous immunoassay is carried out by measuring the electrochemical luminescence of the label.     

Quantitative X-ray fluorescence analysis of an Egyptian faience pendant and comparison with PIXE

The X-ray fluorescence (XRF) technique is a common choice in the archaeometric field for in situ investigations with portable instruments. This work shows that XRF portable systems can be used for quantitative analyses using appropriate software, obtaining a similar accuracy to that provided with other techniques such as particle-induced X-ray emission (PIXE), as shown for an Egyptian faience pendant and for two glass standards.     

Principles, developments and applications of on-line coupling of extraction with chromatography

On-line coupling of extraction and chromatographic separation allows the whole analysis to be performed in a closed system. On-line systems are particularly useful when the analytes are labile, the amount of sample is limited, or very high sensitivity is required. Many on-line systems have been developed both for liquid and for solid samples. This review discusses the different instruments that have been constructed and the factors that need to be considered in the coupling. Selected illustrative applications are described to illustrate the potential of the on-line systems.     

Principles and applications of comprehensive two-dimensional gas chromatography

This issue of Trends in Analytical Chemistry celebrates 50 years of gas chromatography (GC) — the greatest enabling technology for chemical analysis of volatile compounds. However, what may be considered the most powerful separation tool in GC — comprehensive two-dimensional gas chromatography (GC×GC) — is a development born of the 1990s. It was first described and almost fully established in the last decade of the twentieth century. The coming decades can be expected to see it flourish into a major operating mode of GC, when applications and fundamental principles will be further expanded, and, most importantly, its universal acceptance will be unquestioned. This article describes why the pioneers of GC×GC have so much faith in the new opportunities afforded by this exciting technology.     

Principles and applications of wavelet transformation to chemometrics

This paper aims at serving two purposes: firstly, it gives a quick summary of aspects and properties of wavelets and wavelet transforms which are needed in order to understand how to (pre-)process data from spectrometry with wavelet methods. Secondly, it shows on a typical example (wheat NIR spectra) how wavelet transforms can be used in order to extract quantitative information. In contrast to other approaches in the literature, we use special types of wavelets which allow analysing finitely extended signals without introducing artifacts near the boundaries, and we introduce a new way of wavelet coefficient regression in order to build our chemometrical models.     

Principles and applications of fluorescence techniques in biophysical chemistry

Abstract— Fluorescence is widely used as a probe of the properties of ligand-biopolymer complexes or adducts, proteins, nucleic acids and membranes. The principles and techniques utilized in characterizing the basic fluorescence properties of a system of fluorophore-biopolymer complexes are outlined. The different approaches utilized include a correlation of fluorescence decay profiles obtained by time-correlated single photon counting techniques with (1)steady-state fluorescence excitation and emission spectra, (2)relative fluorescence quantum yields, (3)fluorophore-accessibilities investigated by quenching techniques, and (4)ligand-macromolecule binding equilibria.     

Low Level Lead Determination After Membrane Complexation and TXRF Analysis

New membranes containing a few micrograms of various complexing reagents in a Nafion^® matrix were produced on the surface of quartz glasses (reflectors). The reflectors were immersed in standard water solutions containing various, very low concentrations of lead salts (1–50ngmL^–1). The reflectors were left in 5–500mL solutions for many hours; when the equilibration stage was complete, they were cleaned with ultrapure water and left to dry. The stability (adhesion) of the membranes was tested. Analysis of the samples was performed by Total Reflection X-Ray Fluorescence and cross-evaluated by Atomic Absorption Spectrometry. A few ngmL^–1 of the lead were determined. The effect of various experimental parameters (complexing agent, membrane composition, equilibrium time, sample volume etc.) was examined.     

Zeolite analysis: PIXE,XRF or neutron activation

The determination of aluminium-to-silicon ratios in zeolites is of great benefit to catalyst technology and of general interest to mineralogists. However, such determinations tend to be open to error because of interferences that are due mainly to the juxtaposition of these elements in the Periodic Table. The capabilities of neutron activation, both with isotopic sources and accelerator based, of PIXE and of XRF were evaluated to establish which of these instrumental methods was best suited especially for routine on-line usage.     

Development and comparison of biosensors for in-vivo applications

Electrochemical biosensors have been of increasing interest, especially those developed to be directly applied in diagnostic areas, such as neuroscience. We have been interested in developing a range of biosensors for monitoring glucose, lactate, pyruvate, and glutamate in order to study on-line both brain function in the laboratory and to monitor brain health in neurointensive care. For a biosensor to function effectively in these situations, it has to combine the following characteristics: quick response and high sensitivity, good reproducibility and adequate stability. In this study we compared the performance of a number of different amperometric biosensors strategies. These included ferrocene mediation of immobilised enzymes (system A), a redox hydrogel based system (system B), and a conducting polymer approach using polyaniline (system C). All assays were operated as flow-injection systems with upstream immobilised enzyme beds if necessary. When calibrated for H2O2 systems A and B reacted quickly enough to give quantitative conversion up to 0.2 mM. Above this concentration the response was limited by horseradish peroxidase enzyme kinetics and eventually enzyme loading. System C showed a restricted H2O2 response. When calibrated for glucose (by use of immobilised glucose oxidase) system B exhibited the highest sensitivity but its analytical range was restricted because the system became limited by H2O2 response. System A had low sensitivity for analyte compared to H2O2 and system B, but a greater useful range. Problems of mediator cycling between the immobilised enzymes are discussed. System C gave an excellent linear range but sensitivity was limited by background noise. Stability and reproducibility of the systems are also described. In conclusion, from this study the ferrocene system proved to be overall most useful and has now been used in the first dual on-line monitoring of glucose and lactate in patients in neurointensive care.     

Group transfer and anionic polymerization: A critical comparison

The mechanism of group transfer polymerization (GTP) of methacrylates in THF is investigated by using data on kinetics of homo- and copolymerization, polymer microstructure and molecular weight distribution. By comparison with corresponding data on anionic polymerization it is concluded that the mechanisms of monomer addition to the active chain end is very similar for both anionic and group transfer polymerization and that GTP is ionic in character. On the other hand, GTP uniquely is characterized by the existence of a catalyst exchange equilibrium. The position of this equilibrium determines the rates of polymerization, and the dynamics determine the molecular weight distribution.     

Study of Br,Zn, Cu and Fe concentrations in healthy and cancer breast tissues by TXRF

Tissue samples of fifteen breasts were analyzed by X-ray fluorescence spectrometry in order to compare the elemental concentration in healthy and carcinoma regions of the same individual. Five women were from Germany and ten from Portugal living in big cities. The elemental distribution of P, S, K, Ca, Fe, Ni, Zn, Cu and Br present in both normal and cancerous breast tissues were studied. Several contiguous thin sections (up to 10 μm thickness) of each tissue were analyzed by TXRF in order to study the homogeneity in the elemental concentration along each tissue. Correlations between elemental concentrations were established.