Silke Matysik

Determination of volatile metabolites originating from mould growth on wall paper and synthetic media

Microbial volatile organic compounds (MVOCs) emitted from the mould species Penicillium expansum, P. chrysogenum, Aspergillus versicolor, A. fumigatus, A. niger and Cladosporium cladosporoides were analyzed by means of solid phase microextraction (SPME) and GCMS. The mould species were cultivated on the synthetic agar dichloran chloramphenicol (DG 18) and on wet wall paper. The production of MVOCs was monitored over several weeks to detect changes in the emission rates between the initial stage and later periods of growth. The cultivation on the synthetic agar resulted in MVOC patterns with a wide variety of signals. In contrast, the growth on wet wall paper led to changed MVOC patterns with less signals. The emission rates were drastically reduced. Components emitted by all six fungi species on wall paper were 2-pentanol and 2-pentanone. 1-Octen-3-ol was emitted by five fungi species. 2-Pentanol was only detected in considerable amounts during the first days of growth whereas 1-octen-3-ol had a more constant emission rate over the whole period of growth. On the basis of our studies some MVOCs could be proposed as specific for single fungi on wall paper, e.g. 1,3-dimethoxybenzene for A. versicolor and 2,4-pentandione for A. fumigatus.

Nafion-coated mercury thin film electrodes for batch-injection analysis with anodic stripping voltammetry.

Batch-injection analysis exhibits the advantages of rapid and simple electroanalysis of microlitre samples. Nafion-coated mercury thin film electrodes have been evaluated for use in batch-injection analysis with anodic stripping voltammetry (BIA-ASV). The advantages of Nafion-coated electrodes in reducing electrode contamination by components of complex matrices are combined with the analysis of small microlitre sample volumes. The measurement of traces of lead and cadmium is used to illustrate the approach. An optimised procedure for formation of Nafion-coated mercury thin film electrodes is evolved. The relative sensitivity for BIA-ASV at electrodes with and without Nafion coatings is 0.9 and 0.8 for cadmium and lead respectively; detection limits are 2 x 10(-9) M and 4 x 10(-9) M. Studies were done concerning the influence of surfactants and their effect was found to be much less with the Nafion film coating. Applications to real environmental samples are demonstrated.

Determination of microbial volatile organic compounds (MVOCs) by passive sampling onto charcoal sorbents.

Passive sampling combined with GC-MS was applied for the detection of microbial volatile organic compounds (MVOCs) emitted by mould cultures. The fungi species Penicillium expansum, Penicillium chrysogenum, Penicillium brevicompactum, Aspergillus fumigatus, Aspergillus versicolor, Aspergillus niger, and Cladosporium cladosporoides were cultivated on dichloran glycerol agar. The emitted volatiles were collected by charcoal-based passive diffusion monitors during the first four weeks of growth. Several alcohols, mainly 2-methyl-1-propanol and 3-methyl-1-butanol, alkenes, ketones, ethers and esters could be identified and quantified after external calibration. Species-specific compounds like 1,3-dimethoxybenzene for A. versicolor could be proposed. Associations between the concentrations of some of the identified MVOCs (e.g. methylfurans and dimethyldisulfide) and indoor mould exposure in dwellings were found in a field study comprising more than 500 dwellings in Leipzig/Germany. It could be concluded that passive sampling onto charcoal adsorbents for the determination of MVOCs is particularly suitable in epidemiological studies with a high number of participants.

Application of zeolite-polydimethylsiloxane electrodes to potentiometric studies of cationic species

Potentiometric electrodes based on the incorporation of zeolite particles into polydimethylsiloxane (PDMS) membranes are described. The electrode characteristics are evaluated regarding the response towards alkali metal cations. Zeolite/PDMS-coated iridium disk electrodes offer lower limits of detection (3 × 10−5 M for Cs+) and a more extended concentration range with Nernstian slope than zeolite-PDMS electrodes with inner reference solution. Both types of electrodes respond rapidly to concentration changes (within a few seconds or less). Zeolite-PDMS electrodes exhibit almost the same sensitivity towards all alkali metal cations independent of the use of either zeolite X or zeolite A. Furthermore, zeolite-PDMS electrodes are applied to the determination of ionic surfactants. In contrast to the results obtained for alkali metal cations zeolites of the faujasite type (X and Y) lead to superior electrode function when compared to A zeolites. The determination of surfactants is accomplished by potentiometric titration using a zeolite-PDMS indicator electrode. Practical applications of surfactant determination in commercial detergents are presented and verified by performing the two-phase titration as independent reference method.

A disposable electrode based on zeolite–polymer membranes for potentiometric titrations of ionic surfactants

Abstract A planar all-solid-state electrode for the titrimetric analysis of ionic surfactants has been developed and characterised. The electrode is fabricated by lamination of suitable electrode structures that are sandwiched between flexible plastic foils. The zeolite–polymer membrane containing 50% (w/w) zeolite of the faujasite type is cast onto an exposed gold film surface to form the surfactant-sensitive electrode. The very fast potentiometric response of the sensor can be exploited for potentiometric titrations of surfactants. Without any further pre-treatment, reproducible and well-defined titration curves are obtained for the titrimetric analysis of anionic surfactants using a cationic surfactant and vice versa. According to the fabrication strategy applied, the developed devices have the character of disposable electrodes. The electrode assembly exhibits shelf-lives longer than 3 months under room temperature and dry conditions. The practical utility of the disposable all-solid-state electrodes is demonstrated in terms of titrimetric determinations of anionic surfactants in commercial detergents.

Sonoelectrochemical analysis of trace metals

Ultrasonically-enhanced mass transport was exploited to increase preconcentration efficiency in anodic stripping voltammetry. We developed a Nafion-coated mercury thin-film working electrode which is stable under ultrasonic irradiation, making it possible to achieve very low limits of detection for relatively short preconcentration times. This allows the investigation of a variety of biological and environmental samples.

Adsorption of water on ZSM-5 zeolites☆

The non-isothermal desorption of water adsorbed on ZSM-5 zeolites at room temperature shows, depending on the cation type (H+, Na+), differently structured desorption curves. A kinetic analysis based on various methods shows that the course of desorption is well described by a first order rate equation considering a distribution function for the desorption energy. In addition, adsorption isotherms were measured at room temperature. The adsorption energy distribution functions calculated with a regularization method can be correlated with the desorption energy distributions. FTIR investigations of water-loaded zeolites enables the assignment of desorption steps to different adsorbate complexes.

Potential of gas chromatography–atmospheric pressure chemical ionization–time-of-flight mass spectrometry for the determination of sterols in human plasma

The application of Gas Chromatography (GC)-Atmospheric Pressure Chemical Ionization (APCI)-Time-of-Flight Mass Spectrometry (TOF-MS) is presented for sterol analysis in human plasma. A commercial APCI interface was modified to ensure a well-defined humidity which is essential for controlled ionization. In the first step, optimization regarding flow rates of auxiliary gases was performed by using a mixture of model analytes. Secondly, the qualitative and quantitative analysis of sterols including oxysterols, cholesterol precursors, and plant sterols as trimethylsilyl-derivatives was successfully carried out. The characteristics of APCI together with the very good mass accuracy of TOF-MS data enable the reliable identification of relevant sterols in complex matrices. Linear calibration lines and plausible results for healthy volunteers and patients could be obtained whereas all mass signals were extracted with an extraction width of 20 ppm from the full mass data set. One advantage of high mass accuracy can be seen in the fact that from one recorded run any search for m/z can be performed.

Impedance spectroscopic investigations of zeolite polydimethylsiloxane electrodes

Abstract Electrochemical impedance spectroscopy (EIS) was applied to study charge transfer and ion diffusion processes of all-solid-state ion-sensitive electrodes based on zeolite–polydimethylsiloxane (PDMS) membranes. In order to investigate the effects of zeolites embedded into a polymer matrix membranes with different types and contents of zeolites were characterised. On the basis of EIS studies, zeolites of the faujasite type were found most suitable for potentiometric determinations. This result can be attributed to the large pore size of 7.4 A and a low Si/Al ratio. The differences in selectivity of potentiometric responses towards alkali metal cations and tetrabutylammonium cations were found to be reflected by differences in the bulk resistance of the membrane. The impedance behaviour of the zeolite–polymer electrodes was modelled by an appropriate equivalent electrical circuit.

Adsorption of Water and Methanol on a NaZSM-5 Zeolite. A temperature-programmed desorption (TPD) study

Using temperature-programmed desorption (TPD), we have investigated the desorption behavior after subsequent co-adsorption of methanol and water and after adsorption of their mixtures on a NaZSM-5 zeolite. The course of desorption indicates that a strong mutual displacement of both components occurs. However, on the strongest adsorption sites methanol is preferentially adsorbed, and already the addition of small amounts of methanol leads to a displacement of water. Our results support the idea of a subdivision of the pore space for adsorption of water/methanol mixtures. Above all, the experiments show that in the part of the pore space where both components are adsorbed, different sites are of importance which vary significantly in their interaction strength.