This review describes analytical methods developed for the separation, identification and quantitation of trans-isomers of unsaturated fatty acids.Although these methods are applicable to a wide variety of food matrices, we have particularly emphasised the analysis of trans unsaturated fatty acids in milk fat.Various methods are described such as infrared spectroscopy, direct gas chromatography, gas chromatography in combination with either thin-layer chromatography or liquid chromatography both impregnated with silver nitrate and gas chromatography coupled with mass spectrometry.The field of application, the advantages and the drawbacks of each method are evaluated and discussed.
We report here on from determination in sea matrix by electrothermal atomic absorption spectrometry. We optimised the experimental conditions of the spectroscopic factors, i.e. entrance monochromator slit height, slit width and lamp current, and of the electrothermal factors, i.e. calcination temperature, calcination duration, atomisation temperature and injected volume, since these two groups are independent. Because of the technical constraints occuring on our experimental domain of study we built a D-optimal experimental design to conduct these optimisations. We monitored three experimental responses, i.e. the standard deviation of the instantaneous specific absorbance, the specific integrated absorbance and the non-specific integrated absorbance. The three of them clearly showed an optimum in three opposed experimental conditions. Consequently, a desirability transformation of the experimental responses permitted us to obtain a better compromise. We, finally, computed a new experimental response which took the raw measurements into account to directly estimate the limits of detection. The optimisation of this computed response showed us that the lowest detection limit was obtained under the same experimental compromise than the one suggested by the desirability study. This result allowed us to validate the computed response as an interesting optimisation criterion in electrothermal atomic absorption spectrometry.
Various soil extraction methods were developed for the determination of total and/or plant-available concentrations of potentially toxic elements. In this experiment, four single extraction procedures ( aqua regia, HNO3, acetic acid, DTPA) were tested for the determination of extractable contents of As, Cd and Zn. 35 soils differing in their physicochemical properties an d in total element contents were used in this experiment. Extractability of elements from soil samples varied following the indi- vidual elements and/or extraction agents used. The strong acids were not able to release the elements tightly bound into the si l- icate sample matrix. However, such techniques remain utilizable for the approximate determination of pseudototal element con- tents in soil, especially if soil samples are affected by anthropogenic contamination. The concentrations of As, Cd, and Zn determined in soil extracts by both mineral and organic acids covered in most cases the element portion representing more than one soil element fraction determined using SM&T sequential extraction procedure. Solutions of acetic acid and DTPA were able to release a part of the element fraction bound in Fe/Mn oxides and organic matter of soil sample. Arsenic represents an excep- tion because it is not released by DTPA.
Disposal of polychlorobiphenyls (PCBs) is a current problem still far from a really satisfactory solution. Because of the wide use and the chemical inactivity, the PCB amount to be treated is considerably large. In this paper, the setting-up of a methodical catalytic pyrolysis of polychlorinated compounds is proposed. The monitoring of the final decomposition products by analytical techniques, such as GC and coupled TG-FTIR, allowed to optimize the reaction temperature: the encouraging results, the lower operative temperatures with respect to previous systems and the favourable prospects regarding the environmental impa ct make this methodology open to practical applications at a relative low cost.
A set of 114 olfactory molecules divided into fruity, ethereal and camphoraceous compounds, was submitted to an analysis by Kohonen Neural Networks, also known as Self Organising Map (SOM). The compounds are represented in a hyperspace derived from their molecular descriptors and SOM gives a useful projection of this hyperspace onto a 2D map. Owing to the complexity of the olfaction mechanism, evidenced by the fact that one compound can exhibit simultaneously different properties, SOM alone is unable to take into account the olfaction diversity of the original 114 compounds, Then, a Fuzzy Partition method was applied on the Kohonen map previously developed. The obtained results allowed delineating different representative zones for the three odours, expressing more closely the olfactory richness. The ability of the Hybrid System combining SO and Fuzzy Partition to model the three odours was validated by dividing the 114 compounds into a training set and a test set, including 86 and 28 molecules, respectively. The most important olfactory characteristics were reproduced satisfactorily for the entire test set compounds.
adducts could well be explained with the dissociation energies (DE) of the complexes [14]. The DE is related to the proton affinity (PA) of the constituent base by DE = a-b ΔPA where a and b are constants and ΔPA is the absolute PA difference [10]. Therefore it can be argued that the DE hypothesis used for the thermospray data can also be used for the explanation of the adduct formation in APCI. As the PA, and consequently the DE, of a molecule is dependent on its structure, the tendency of a molecule to form adduct ions can be used for structural identification purposes. A major problem with this theory is the presence of the collisionally induced dissociation processes occurring in the sampling region of the atmospheric pressure source (somewhat like the effect of the repeller in the thermospray interface) which are, ironically enough, meant to de-cluster the adduct ions. The following, limited study, discusses the data from the acetate adduct ions with steroid molecules (see Fig. 1 for a general structure and the numbering of the C atoms) in the negative ion mode. Abundant adduct ions for these type of molecules have been reported both with the thermospray [7] as with the HN [8,9] interface. These types of compounds are chosen because the MSMS data are considered hard to interpret [15]. That is hydrogen transfer
The staphylococcal enterotoxin research method is a quantitative method, involving a sample preparation and an imunoenzymatic detection. In order to estimate its performance characteristics, a method characterisation is carried out with a single dairy product and for staphyloccal enterotoxin A. Statistical analysis shows that the method is linear over a contamination interval between 0 - 1 ng SEA per gram of cheese. The limit of detection is about 0.01 ng SEA per gram of cheese and the limit of quantification is about 0.04 ng SEA per gram of cheese. The intra laboratory repeatability and intermediate precision are estimated on two levels of contamination. The repeatability coefficient of variation is included between 3.1 % and 6.2 %, the intermediate precision coefficient of variation is included between 4.7 % and 11.0 %.
Reduced cytochrome c UV-visible absorption, ESR spin trapping, hydroethidine fluorescence and lucigenin-enhanced chemiluminescence techniques, were used to study O 2 - production from A23187-stimulated bovine aortic endothelial cells (BAEC). All detected O 2 - release but some lack of sensitivity and specificity in probes and enzymes occured. Cytochrome c prepared with trichloroacetic acid (TCA), TCA-free or acetylated (C2506, C7752, C4186) provided similar superoxide-dismutase (SOD)-inhibitable absorbances at 20 μM. At a higher concentration (100 μM) TCA-prepared cytochrome c could no longer detect O 2 - production whereas TCA-free cytochrome c detected less O 2 - at 100 μM than at 20 μM. Catalase C-40 was not contaminated with SOD-like impurities. Lucigenin provided high artefactual amounts of O 2 - production from stimulated BAEC in the presence of NADH or NADPH. Moreover, even at a low concentration (5μM) lucigenin and NADH (or NADPH) decreased endothelium-dependent relaxation induced by acetylcholine to 50 %. The use of lucigenin is not recommended.
Withdrawing of representative and reliable microsamples down to 1/100th mg is far from trivial, especially for extreme conditions such as high temperature and high pressure conditions or very corrosive media. The new Rapid On-Line Sampler- Injector presented herein was designed and set-up to largely extend sampling capabilities in hazardous media. It is largely use d in our laboratory to measure vapour-liquid equilibria. It has a lot of applications, both in production (process control in pet ro- leum, chemical, nuclear plants, etc.) and academic and industrial researches and development (laboratory instruments, pilot plants…).
Analytical and toxicological aspectsO ver the last 5 years, concerns have increased about chemicals in the environment, which influence the reproductive capabilities of human and animals.Reproductive hormone-receptor systems appear to be especially vulnerable.Hormonal disturbances in wildlife include sex changes in riverine fish and marine snails, reproductive failure in birds, genital tract malformations in mammals.These effects may be attributed to various classes of chemicals such as chlorinated pesticides (DDT, endrin, pentachlorophenol) or chlorinated aromatic compounds (PCBs, dioxins), metals (cadmium, selenium, zinc, mercury, tributyltin), alkylphenols (nonylphenol, pentylphenol, bisphenol), phytooestrogens.The identification of the chemicals responsible of these reproductive alterations is difficult and demands the development of specific procedures to analyse these compounds in complex environmental mixtures.Moreover the causal relationships between the exposure to these substances by wildlife organisms and the adverse effects on reproduction in the environment are not yet clear evidence.
Two recently developed approaches to the subisoform-specific detection and identification of metallothionein (MT) isoforms are compared. They are based on the coupling of capillary electrophoresis with ICP MS and microbore chromatography with electrospray MS. The resolution of HPLC is judged to be slightly better since differently metallated forms of the same sub-isoform can be separated. Detection by electrospray MS is mandatory to avoid the attribution of artefact signals observed in etement-specific chromatograms to different sub-isoforms.
We report in this paper a global and exhaustive overview of the various attempts reported in the literature to develop electrochemical microsensors for the direct determination of nitric oxide (NO) in biological systems. In this compilation, we address the physico-chemical characteristics and the performances tin term of sensitivity) of the numerous chemically modified microelectrodes that were specially designed for the determination of NO, without judging what the biological applications might be.
coastal waters. Due to its economic importance it is extensively cultured in many countries, and particularly in Portugal where its production represents > 80 % of total shellfish production. The selection of the clam R. decussatus as a bioindicator was a consequence of its economic importance and the need to use a filter-feeding bivalve to evaluate environmental changes of metal concentrations [1]. Like many other bivalves, this species resides in sediments and accumulates metal concentrations reflecting gradients of metal contamination in the surrounding environment [2,3,4]. This suggests that its tissues have mechanisms, related to its filter-feeding habit, that inhibit the toxic effects of these contaminants. Like many other molluscs R. decussatus has evolved a number of subcellular systems for accumulation, regulation and immobilization of metals. These include, among others, the binding of essential and pollutant metals to soluble ligands such as MT. These two-domain molecules are low molecular, heat-stable proteins of non-enzymatic nature that occur mainly in the cytoplasm. They have strong affinity to class B metal cations which enable them to be differentiated from most of the other proteins [5]. The induction of these proteins has, therefore, been proposed as a specific indicator and possible “early warning marker” for the detection of detrimental effects caused by exposure to excess of essential and pollutant metals. MT induction has been detected in the whole soft tissues, gills, digestive gland and remaining tissues of the clam R. decussatus after exposure to essential and toxic metals [4,6] and this paper represents an overview of MT function in this bivalve species. MT induction in laboratory experiments
Poly(ethyleneglycol) (PEG) substituted by various organic moieties wee analyzed by electrospray ionization (ESI) mass spectrometry in order to determine the best experimental protocol allowing reproducible, sensitive and informative spectra in the search of completely automated high throughput identification of libraries generated by the liquid-phase methodology. The nature of the eluent and of the PEG derivatization as well as the value of the sampling cone voltage were investigated by comparing the recorded oligomer distributions.
Synthesis of octacalcium phosphate (OCP) by hydrolysis of brushite was studied using a 3 block central composite design including 4 factors and 6 responses. Analysis of the responses allowed the definition of one set of experimental conditions in which OCP was obtained with the highest overall desirability (87.6 %).
The aim of this work is to optimize the degradation yield of an activated sludge and to study the reaction mechanism on a cellulose model compound. This optimization is performed with a Simplex design with four parameters: reaction temperature (280-350 degreesC), injected air pressure (40-60 MPa), reaction time (10-45 minutes) and COD concentration (0.5-5 g L-1). The better yield obtained on TOC concentration is 82 5% at 330 degreesC. Over this temperature, the yield substantially decreases. The use of cellulose as a model compound for activated sludge confirms optimization results and leads to the identification of by-products and free radical species participating in the reaction. Two major organic compounds have been detected: 4-oxo pentanoic acid and 3-oxo butanoic acid, and three types of radicals: HO degrees, CO(2)degrees (-) and degrees CH(OH)CH3.
The analytical performance of the Fast - Protein Liquid Chromatography (FPLC) (on a Mono Q HR 5/5 column) and the conventional Anion-Exchange Chromatography (on a Protein Pak DEAE 5PW column) to realise rabbit liver metallothioneins separations and Cd speciation has been investigated and the results are compared. The Mono Q column was found to provide higher resolution and reproducibility in shorter separation times than Protein Pak DEAE 5PW, a conventional anion-exchange column. Thus, FPLC is proposed as a very useful tool for the study of the polymorphism of metallothioneins.
A new optical temperature sensor based on the fluorescence intensities of the fullerene C-60 immobilized in polymethylmethacrylate (PMMA) film was developed. The fluorescence intensity of the C-60 film decreased with increasing the temperature in the range 260-373 K. Arrhenius plot of ln[(I(T)/I(T-ref))] versus 1/T for the C-60 film exhibits considerable linearity supported by the correlation factor, r(2), estimated to be 0.989 by the least squares method (T-ref = 260 K). The E/R value of the C-60 film is estimated to be 22.3 K. These results indicate that the C-60 film provides a linear temperature response in the range 260-373 K.
A reliable and simple procedure to extract polychlorinated biphenyls (PCBs) from marine mussels using microwave energy is proposed. Freeze-dried mussels were subjected to MASE (Microwave Assisted Solvent Extraction) in a closed-vessel microwave system with n-pentane-sodium hydroxide (5 %) or dichloromethane-pentane (1:1) at different temperatures (70 and 90 degreesC), the extraction time was 10 minutes. Sample extract cleanup procedure was performed by using alumina. Gas chromatography-mass spectrometry and gas chromatography-electron capture detector were employed for individual congener identification and determination. The influence of the following variables on microwave extraction of PCBs has been studied: extraction temperature,, solvent volume, solvent nature, cleanup procedure time and volume of sodium hydroxide solution. Recoveries for PCBs were between 77 and 106 % with relative standard deviation between 2 to 20 %. Validation of the extraction process was carried out by processing a certified reference material. Microwave Assisted Solvent Extraction was compared to Soxhlet extraction.
