Ágnes Keszler

Influence of extraction parameters and medium on efficiency of solid-phase microextraction sampling in analysis of aliphatic aldehydes

Abstract The main sorption conditions were optimized in the solid-phase microextraction (SPME) analysis of aldehydes that have different degrees of saturation. Aliphatic aldehydes were analyzed quantitatively in oil matrix and in aqueous solution by GC–MS using SPME sampling. The effectiveness of the immersion and the headspace techniques was compared in water. Samples were analyzed by gas chromatography with mass spectral detection using a medium polar CP WAX 52 CB column. The optimal exposure time was 30 min at 40°C using a 100 μm poly(dimethylsiloxane) coating. A ratio of liquid to headspace volume of 1:1 resulted in the best extraction in headspace analysis. Principal component analysis (PCA) was carried out to find similarities among various aldehydes and among conditions of optimization. The PCA identifies three clusters corresponding to analysis conditions (immersion in water, headspace above water and headspace above oil). The aldehydes behave similarly with the exception of dienals.

Principal component analysis of measured quantities during degradation of hydroperoxides in oxidized vegetable oils

Decomposition of hydroperoxides in sunflower oil under strictly oxygen-free conditions was followed by measuring peroxide values against time, absorbance values at 232 and 268 nm, para-anisidine values, and by quantitative analyses of volatile products using various additives. The results were arranged in a matrix form and subjected to principal component analysis. Three principal components explained 89–97% of the total variance in the data. The measured quantities and the effect of additives were closely related. Characteristic plots showed similarities among the measured quantities (loading plots) and among the additives (score plots). Initial decomposition rate of hydroperoxides and the amount of volatile products formed were similar to each other. The outliers, the absorbance values, were similar to each other but carried independent information from the other quantities. Para-anisidine value (PAV) was a unique parameter. Since PAV behaved differently during the course of hydroperoxide degradation, it served as a kinetic indicator. Most additives were similar in their effects on the mentioned quantities, but two outliers were also observed. Rotation of the principal component axes did not change the dominant patterns observed. The investigations clearly showed which variables were worth measuring to evaluate different additives.

Quantitative analysis of aliphatic aldehydes by headspace SPME sampling and ion-trap GC-MS

SummaryA fast and simple headspace SPME sampling method has been developed for quantification of volatile aliphatic aldehydes in sunflower oil. Analysis has been performed by gas chromatography, on a 30m×0.25 mm i.d. ×0.25 μm CP-Wax 52CB column, with mass spectrometric detection. Carryover from the SPME fiber could be eliminated by heating the fiber in the injection port between runs. Response factors of all the compounds were linear for concentrations up to 100 ng μL−1. The slopes of the calibration curves decrease with the amount of saturation of the aldehydes. The average responses for unsaturated aldehydes were twice as high as those for the saturated variety. Responses for dienes were approximately one order of magnitude higher than for saturated aldehydes. Depletion of the analyte was examined by repeated extraction from the same vial. SPME was optimized—after 30 min extraction most components were found to have reached equilibration. The detection limit for the compounds studied varied between 0.1 and 1 ng μL−1. Distribution constants were determined for ten different aldehydes and Henrys constants were calculated for unsaturated aldehydes. There was a definite relationship between the response factors and the amount of saturation of the aldehydes.

Three Reagents in One: Ammonium Permanganate in the Oxidation of Benzyl Alcohol

The oxidation or consecutive ammoxidation reaction of benzyl alcohol with solid ammonium permanganate was studied. The first oxidation step leads to the formation of benzaldehyde, ammonia, and MnO2. The MnO2 is present in the system in a colloidal form which facilitates the reaction between aldehyde and ammonia, and this latter reaction then yields benzonitrile. All these products are formed in a heterogeneous system under relatively mild conditions. The yield of benzaldehyde has an optimum at room temperature and increases with increasing reaction time. At higher temperature (e.g. 80 °C) benzonitrile is formed together with minor amounts of benzyl benzoate

Type III photosensitization: attempt for quantification and a way toward new sensitizers

Earlier results studying the effect of excited triplet photosensitizer on the zymosan-stimulated and luminol- dependent chemiluminescence of macrophages have been quantitatively re-evaluated and rate constant data indicate that the effect is due to triplet-doublet interactions between sensitizer and free radicals generated. Such interactions, named Type III mechanism, compete with Type I and Type II mechanisms depending on the experimental environment. This suggestion resulted in the synthesis of new sensitizers being the first members of the Antioxidant Carrier Sensitizer (ACS) group of molecules. According to preliminary experiments the PDT treatment of tumor bearing mice seems promising with two of such compounds which demonstrate an inhibitory effect in chemical systems already in their ground state.

Study on the Existence of Hydrogen Bonds in Ammonium Permanganate

The crystal structures of ammonium permanganate and ammonium perchlorate at 293 K were determined and compared. X-ray and vibrational spectroscopic data confirmed the existence of weak hydrogen bonds in NH4MnO4. These hydrogen bonds proved to be slightly stronger than H-bonds in ammonium perchlorate. Difference between the results of diffuse reflectance and KBr matrix pellet IR spectra of NH4MnO4 has been explained. Untersuchung uber die Existenz von Wasserstoffbruckenbindungen in Ammoniumpermanganat Die Kristallstrukturen von Ammoniumpermanganat und -perchlorat wurden bei 293 K bestimmt und miteinander verglichen. Die Rontgen- und schwingungsspektroskopischen Daten bestatigen die Existenz von schwachen Wasserstoffbruckenbindungen im NH4MnO4. Diese sind etwas starker als die H-Brucken im Ammoniumperchlorat. Unterschiede zwischen den Ergebnissen der Reflexions- und IR-Spektren von NH4MnO4 werden erklart.

Evidence for quasi-intramolecular acid-base reactions in solutions of transition metal ammine complexes

We have investigated the effect of temperature on the postulated quasi-intramolecular acid-base reactions in aqueous solutions of Cu(NH3)4(MnO4)2 and Ag(NH3)2ClO4. Pure ammonium permanganate and perchlorate were obtained above 5 ∘C and at room temperature, respectively, due to quasi-intramolecular acid-base reactions.

Studies on the thermal behavior of ammonium permanganate

The thermal decomposition of ammonium permanganate was studied by thermogravimetry-mass spectrometry (TG-MS). A Perkin Elmer TGS-2 thermobalance and a Hiden’s HAL 3F/PIC mass spectrometer equipped with a fast ion counter was used. Products of thermal decomposition of ammonium permanganate are oxygen, manganese oxides, water and ammonia. There is no gas phase oxidation of ammonia by oxygen. The possible intermediates of low-temperature decomposition reaction are ammonium nitrite or nitrate which transform into N2 ,N 2O, or H2O. The oxidation of adsorbed ammonia by manganese oxides via the superoxide active centers takes place on the surface of manganese oxide. # 1999 Elsevier Science B.V. All rights reserved.

In situ chlorination of poly(vinyl chloride) in aqueous hydrochloric acid

Based on environmental, safety, corrosion and technological considerations a new method has been developed for chlorination of PVC in aqueous hydrochloric acid solvent by controlled electrolytic in situ generation of chlorine using graphite and chlorine-selective Ti-RuO2 electrodes. The byproduct, HCl gas, is dissolved at the moment of its formation and acts as starting material of further chlorination. This way, the application of corrosive chlorine gas is avoided. The chlorination conditions have been optimized. The highest chlorine content was found at 5.5 h reaction time using a graphite electrode. The obtained chlorinated PVC did not contain any CCl2 units. Aufgrund von Uberlegungen zu Umweltschutz, Sicherheit, Korrosion und Verfahrenstechnik wurde eine neue Methode zur Chlorierung von PVC entwickelt, wobei Chlor mit Graphit- und chlorselektiven Ti-RuO2-Elektroden in wasseriger Salzsaure elektrolytisch in situ erzeugt wird. Als Nebenprodukt entsteht Chlorwasserstoff, der im Moment der Entstehung gelost wird und als Ausgangsmaterial fur weitere Chlorierung dient. Dadurch wird die Verwendung von korrosivem Chlorgas vermieden. Die Bedingungen der Chlorierung wurden optimiert. Der hochste Chlorgehalt wurde bei einer Reaktionszeit von 5,5 h mit einer Graphitelektrode erhalten. Das chlorierte PVC enthielt keine CCl2-Einheiten.

Quantitative studies on photodynamic effects

According to our hypothesis the interactions of triplet photosensitizer molecules with doublet free radicals generated in vivo (native free radicals) play an important role in the overall photodynamic effect (MTO mechanism). In order to support this mechanism, experiments have been performed recently in vivo, in vitro and in chemical model systems. The precondition of such studies, however, is the measurement of the kinetic parameters of various native free radicals generated in the systems investigated. Experimental results and their kinetic evaluation indicate that the triplet-doublet interactions may actually take place in the overall processes under study.