Characterization of Lippia sidoides oil extract-b-cyclodextrin complexes using combined thermoanalytical techniques

Thermoanalytical techniques, being rapid and un-expensive have been used for the investigation of the cyclodextrin inclusion complexes for three decades. The conventional thermoanalytical techniques (TG and DTA/DSC) follow the thermal properties of the uncomplexed compounds. Consequently, the inclusion complex formation as well as the liberation of the entrapped guest cannot be followed. Monitoring the products of the thermal fragmentation of parent cyclodextrin and the included molecule(s), applying TG-MS combined technique provides evidence concerning the inclusion complex formation, and besides, gives selective signal to follow the decomposition of the cyclodextrin inclusion complexes. b-cyclodextrin inclusion complexes of Thymol and Lippia sidoides Cham essential oil extract have been prepared and investigated using conventional and combined (TG-MS) thermoanalytical techniques. The evolved gas analysis proved the inclusion complex formation between the host and guests. By the evaluation of the experimental results the elaboration of the entrapped guests from the cyclodextrin cavity could be followed. This revised version was published online in July 2006 with corrections to the Cover Date.     

An improved method for assay of vitamin C in fish feed and tissues

Summary A method was devised to assay four forms of vitamin C: L-ascorbic acid (AA), dehydroascorbic acid (DHA), ascorbate-2-mono- and polyphosphate (AMP, APP), as well as ascorbate-2-monosulphate (AMS), in sample series of different fish tissues and feed. Direct and indirect detection were combined. Sample extractions were carried out with 0.2 mol L⁻¹ sodium acetate buffer (pH 4.8) and extracts were deproteinized after different chemical or enzymatic reactions, with perchloric acid. The DHA was reduced to AA with dithioerythritol (DTE). Ascorbate oxidase enzyme was used for the detection of background and an acidic phosphatase enzyme for the hydrolysis of different phosphate esters. Ascorbate-2-sulphate was detected directly with help of coinjection of the compound. Chromatographic analysis was carried out with a single column isocratic reverse phase method. The mobile phase was an aqueous buffer of 0.04 M sodium-acetate, 0.05 mM EDTA, 0.5 mM tetrabutylammonium dihydrogen phosphate (TBA) adjusted to pH 3.76 with 85% H₃PO₄ and with 24 mL methanol added to 1000 mL. C-18 columns were used with 0.6 mL min⁻¹ flow rate at 23°C. The vitamin C forms were detected by UV absorption at 250 nm. The determination limit was 1.0–5.0 μg g⁻¹ in AA equivalent. The standard deviations were between 1–6% and depended on the concentrations of vitamin C forms and tissues. Recoveries were between 90–96% in samples. Presented at: Balaton Symposium on High-Performance Separation Methods, Siófok, Hungary, September 3–5, 1997     

Iminodiacetic acid/ethylcellulose as a chelating ion exchanger : Part 1. Determination of trace metals by atomic absorption spectrometry and collection of uranium

A chelate-forming ion exchanger, iminodiacetic acid/ethylcellulose, is used for the separation of trace metals from waters and different organic solvents. Added uranium was collected from sea waters with recoveries of about 97%. Graphite-furnace atomic absorption spectrometry and solution spectrophotometry were used to quantify the metals. For the direct determination of trace metals in waters by the graphite-furnace method, a simple matrix-matching method is described. The detection limit for cadmium was 0.1 μg l^?1 and for lead 1 μg^?1 in drinking water.     

Analysis of actinides in the primary coolant of a WWER-440 type reactor

A simple and effective method has been developed for the determination of the transuranium isotopes in primary coolant samples of WWER-440 type reactors. Membrane filters containing undissolved particles from about one liter coolant were destroyed by mineral acids, then americium-curium isotopes and neptunium-plutonium isotopes were coprecipitated sequentially with NdF₃ based on their different redox behavior. Alpha-spectra were determined by silicon semiconductor detectors connected to multichannel analyzers. Activity ratios measured in a reactor unit with a failed fuel element were compared with calculated values of the same type of reactor under similar conditions. Parameters of the defective fuel (burnup, original enrichment) could be estimated.     

Liner as the Key of Injection Optimization in Pesticide Analysis

Regulations for pesticide residue analysis in food require very low detection limits; thus requiring maximum sensitivity in the gas chromatographic determination. This is accomplished by an overall method optimisation, which includes optimisation of injector parameters. Here we study the effect of the inlet liner design on the optimisation by comparing five liner designs in splitless and pulsed splitless injection modes, using a test mixture of fifteen pesticides analyzed by GC-ECD. Possible links between the injection parameters and liner types were evaluated, with the result that, accurate choice of inlet liner and injection parameters can reduce detection limits by up to 300%. Revised: 25 October 2005 and 9 January 2006     

Novel separation method for highly sensitive speciation of cancerostatic platinum compounds by HPLC–ICP–MS

A high-performance liquid chromatography–inductively coupled plasma mass spectrometry (HPLC–ICP–MS) method is presented for analysis of cisplatin, monoaquacisplatin, diaquacisplatin, carboplatin, and oxaliplatin in biological and environmental samples. Chromatographic separation was achieved on pentafluorophenylpropyl-functionalized silica gel. For cisplatin, carboplatin, and oxaliplatin limits of detection of 0.09, 0.10, and 0.15 g L^–1, respectively, were calculated at m/z 194, using aqueous standard solutions. (3 L injection volume). The method was utilized for model experiments studying the stability of carboplatin and oxaliplatin at different chloride concentrations simulating wastewater and surface water conditions. It was found that a high fraction of carboplatin is stable in ultrapure water and in solutions containing 1.5 mol L^–1 Cl^–, whereas oxaliplatin degradation was increased by increasing the chloride concentration. In order to support the assessment of oxaliplatin eco-toxicology, the method was tested for speciation of patient urine. The urine sample contained more than 17 different reaction products, which demonstrates the extensive biotransformation of the compound. In a second step of the study the method was successfully evaluated for monitoring cancerostatic platinum compounds in hospital waste water.     

A New Gamma-Ray Spectrum Catalog for PGAA

A major obstacle to the use of the prompt gamma activation analysis (PGAA) method has so far been the lack of a suitable library. Therefore, new measurements have been performed at the PGAA facility at Budapest Research Reactor (BRR) in order to create a prompt -ray catalog for qualitative and quantitative analysis. Prompt -ray energies and associated k ₀-factors have been determined by internal standardization. The resulting catalog contains prompt -ray data from neutron capture and other reactions such as (n,), and decay -ray data from short-lived reaction products. Data have been measured for nearly all stable elements, from hydrogen to uranium. Generally, data for several isotopes are given, to enable isotopic analysis as well.     

Potentiometric detection in flow analysis

Special aspects of ion-selective electrodes relevant to applications in flow-through systems are discussed. The predominant role of the dynamic response characteristics of the sensor, especially in flow-injection analysis, is emphasized. Indirectly, these characteristics can affect the linear response range, the detection limit and the selectivity properties of the sensors. As examples, flow-injection methods are described for the determination of fluoride in rain-water samples and of potassium ion activity in blood sera.     

Vibrational spectroscopic detection of H-bonded β- and γ-turns in cyclic peptides and glycopeptides

The conformation of N-glycoproteins and N-glycopeptides has been the subject of many spectroscopic studies over the past decades. However, except for some preliminary data, no detailed study on the vibrational spectroscopy of glycosylated peptides has been published until recently.

This paper reports FTIR spectroscopic properties in DMSO and TFE of the N-glycosylated cyclic peptides cyclo[Gly-Pro-Xxx(GlcNAc)-Gly-δ-Ava] 3a and 3b in comparison with data on the non-glycosylated parent peptides cyclo(Gly-Pro-Xxx-Gly-δ-Ava) 2a and 2b [a, Xxx = Asn; b, Xxx = Gln; δ-Ava = NH-(CH₂)₄-CO] and N-acetyl 2-acetamido-2-deoxy-β- -gluco pyranosylamine (GlcNAc-NHAc, 4). The assignment of amide I band frequencies to conformation is based on ROESY experiments and determination of the temperature coefficients in DMSO-d₆ solution. (For the synthesis and NMR characterization of 2a and 3a see Ref. [19].)

Cyclic peptides are expected to adopt folded (β- and/or γ-turn) conformations which may be fixed by intramolecular H-bonding(s). A comparison of the temperature coefficients of the NH protons and amide I band frequencies and intensities suggests that in DMSO there is no significant difference in the backbone conformation and H-bond system of the N-glycosylated models and their parent cyclic peptides. The common feature of the backbone conformation of models 2 and 3 is the predominance of a 1 ← 4 (C₁₀) H-bonded type II β-turn encompassing Pro-Xxx or Pro-Xxx(GlcNAc), respectively. The ROESY connectivities in the Asn(GlcNAc) model (3a) have not been found to reflect intramolecular H-bondings between the peptide and the sugar.

The unique feature of the FTIR spectra in DMSO of the cyclic models is the lack or weakness of low-frequency (< 1640 cm⁻¹) amide I component bands. In TFE the amide I region of the FTIR spectra shows an increased number of components below 1650 cm⁻¹ reflecting a mixture of open and H-bonded β- and γ-turn conformers.

Because of its destabilizing effect upon γ-turns and other weakly H-bonded structures, DMSO decreases the number of backbone conformers. DMSO also destroys side-chain-backbone H-bondings of type C₇, C₆ or C₈. Possible ‘glyco’ C₇ H-bondings in GlcNAc-NHAc (4) or in glycopeptides 3a and 3b cannot resist the effect of DMSO either.

The FTIR data in TFE of models 2–4 suggest that the acceptor amide group of strong C₇ H-bondings in peptides and glycopeptides absorbs at 1630 ± 5 cm⁻¹ and that of bifurcated H-bondings between 1600–1620 cm⁻¹.     

Fitting the boron peak and resolving interferences in the 450–490 keV region of PGAA spectra

Prompt gamma activation analysis (PGAA) is one of the most powerful analytical methods for the determination of boron because of its very large neutron capture cross section. The peak of boron in the PGAA spectra is highly broadened due to the Doppler-effect. An improved method is presented to fit the boron peak, and to resolve interference with the gamma-rays of sodium and other matrix components. The method has been checked on test samples and on geological samples as well.