Volker Ribitsch

Application of Mid-Infrared Spectroscopy: Measuring Hydrogen Peroxide Concentrations in Bleaching Baths

The presented work applies mid-infrared attenuated total reflection (ATR) spectroscopy to the measurment of hydrogen peroxide in aqueous matrices. The performance of different ATR crystals mounted in flow cells was investigated in the presence of aqueous hydrogen peroxide solutions. Quantitative determination has been achieved by evaluation of specific OH stretching and deformation vibrations with linear correlation between peak areas or peak heights and hydrogen peroxide concentration in the range of 1–10% (weight in water). Important aspects such as chemical stability of the waveguide material and influences of pH and ionic strength on the performance are discussed. Feasibility for the investigation of real world samples is demonstrated by measuring industrial bleaching solutions with known concentrations of hydrogen peroxide fitting well with calibration graphs established with neat hydrogen peroxide solutions. The presented sensor system is capable of determining hydrogen peroxide within complex matrices and clearly corroborates the potential of providing an in situ measurement concept for on-line hydrogen peroxide detection.

The influence of structural and morphological changes on the electrokinetic properties of PA 6 fibres

Abstract A two-phase model composed of alternating crystalline and amorphous regions is usually used to describe the structure of fibre-forming polymers. Different changes in fibre fine structure influence the entire morphological character of the polymer. The ratio between the fibres crystalline and amorphous area (accessible part of the polymer) defines their adsorption character. In the present paper, we tried to analyse the interdependence between fibre structure and their electrokinetic character. The structure and the adsorption abilities of PA 6 fibres were modified by thermal treatment. The accessibility of free adsorption places in the amorphous part of PA 6 polymers was investigated by the determination of electrokinetic properties, which were analysed by ζ-potential determination. It was determined by streaming-potential measurements as a function of the pH and the surfactant concentration in the liquid phase. From the ζ-pH functions the adsorption potential for all ionic species Φ i (i.e. Φ K+ , Φ H+ , Φ Cl− , Φ OH− , in the case of potassium chloride solutions), the charge densities σ k and the pK values were calculated according to the Borner and Jacobasch model. From the ζ-surfactant concentration functions the adsorption isotherms were calculated. The results show that the modifications to the polymer structure cause different electrokinetic properties that correlate with the changes in the fine structure and morphology. After thermal treatments the crystallinity of the samples increases, which causes the increase in negativity of ZP plateau (pH=9).

Optochemical hydrogen peroxide sensor based on oxygen detection

Abstract A novel hydrogen peroxide sensor based on an optochemical oxygen sensor is presented. An oxygen sensitive membrane is covered with an additional layer containing inorganic catalysts which decompose hydrogen peroxide to water and oxygen. The oxygen is detected in the underlying oxygen sensitive membrane via luminescence quenching. The investigated concentration range for the reported sensor was between 0.1 and 2xa0wt.% hydrogen peroxide in water. Several catalysts were tested for this application with manganese dioxide being the preferred material. In addition to this, it was shown that by coating the sensor with a proper polymer layer, the hydrogen peroxide sensitivity could be improved up to five times compared to an uncoated sensor. The response times of the sensors depends on the type of covering layer, with the shortest response times being similar to that of uncoated sensors ( t 95 was approximately 1xa0min for a change from 0 to 0.2xa0wt.% hydrogen peroxide in water).

Combined sensing platform for advanced diagnostics in exhaled mouse breath

Breath analysis is an attractive non-invasive strategy for early disease recognition or diagnosis, and for therapeutic progression monitoring, as quantitative compositional analysis of breath can be related to biomarker panels provided by a specific physiological condition invoked by e.g., pulmonary diseases, lung cancer, breast cancer, and others. As exhaled breath contains comprehensive information on e.g., the metabolic state, and since in particular volatile organic constituents (VOCs) in exhaled breath may be indicative of certain disease states, analytical techniques for advanced breath diagnostics should be capable of sufficient molecular discrimination and quantification of constituents at ppm-ppb - or even lower - concentration levels. While individual analytical techniques such as e.g., mid-infrared spectroscopy may provide access to a range of relevant molecules, some IR-inactive constituents require the combination of IR sensing schemes with orthogonal analytical tools for extended molecular coverage. Combining mid-infrared hollow waveguides (HWGs) with luminescence sensors (LS) appears particularly attractive, as these complementary analytical techniques allow to simultaneously analyze total CO2 (via luminescence), the 12CO2/13CO2 tracer-to-tracee (TTR) ratio (via IR), selected VOCs (via IR) and O2 (via luminescence) in exhaled breath, yet, establishing a single diagnostic platform as both sensors simultaneously interact with the same breath sample volume. In the present study, we take advantage of a particularly compact (shoebox-size) FTIR spectrometer combined with novel substrate-integrated hollow waveguide (iHWG) recently developed by our research team, and miniaturized fiberoptic luminescence sensors for establishing a multi-constituent breath analysis tool that is ideally compatible with mouse intensive care stations (MICU). Given the low tidal volume and flow of exhaled mouse breath, the TTR is usually determined after sample collection via gas chromatography coupled to mass spectrometric detection. Here, we aim at potentially continuously analyzing the TTR via iHWGs and LS flow-through sensors requiring only minute (< 1 mL) sample volumes. Furthermore, this study explores non-linearities observed for the calibration functions of 12CO2 and 13CO2 potentially resulting from effects related to optical collision diameters e.g., in presence of molecular oxygen. It is anticipated that the simultaneous continuous analysis of oxygen via LS will facilitate the correction of these effects after inclusion within appropriate multivariate calibration models, thus providing more reliable and robust calibration schemes for continuously monitoring relevant breath constituents.

Opto-chemical method for ultra-low oxygen transmission rate measurement

A highly sensitive alternative to established methods for measuring oxygen transmission rates of ultra-barrier membranes is presented. The key idea is the employment of an opto-chemical sensor (a luminescent dye immobilized in a matrix) which has vital advantages over electrochemical sensors, such as consumption-less detection and extraordinary sensitivity. The luminescent response to modulated light, which is altered in the presence of oxygen, is recorded by an opto-electronic instrument in a non-invasive manner. Provided with said sensing system, a reusable stand-alone permeation cell was developed. Unlike in conventional devices, the permeating oxygen is accumulated while being simultaneously monitored. The demonstrator unit achieves a limit of detection in the 10−5 cm3 m−2 day−1 bar−1 regime. It is therefore among the most sensitive O2 permeability testers, outperforming commercial instruments by two orders of magnitude, yet offering reusability and similar convenience in operation.

New developments of an optochemical measurement system for the continuous monitoring in subcutaneous tissue by microdialysis

The monitoring of dissolved 02 in blood and organic tissues is extremely useful for physiological and respiratory studies and for monitoring the health conditions of hospitalized patients. Based on these demands an optochemical measurement system for the continuous monitoring of 02 in subcutaneous adipose tissue of critically ill patients is reported The system consists of a miniaturized flow trough cell including an 02 sensitive layer, an optoelectronic measuring unit and a microdialysis catheter for the extraction of the biological fluid. The measurement principle is the phase modulation fluorometry. The sensor allows the 02 measurement in the range 0-300 mmHg, with a resolution better than 1 mmHg and an accuracy better than plusmn1 mmHg. With respect to a previously reported instrumentation, this measurement system shows a high degree of miniaturization and an improved production reproducibility of the optochemical sensing layers. This new instrumentation has been extensively validated in laboratory and in-vivo tests.

Adsorption of surfactants on polymer surfaces investigated with a novel zeta-potential measurement system

The determination of electrokinetic properties such as the zeta-potential of polymer samples with classical methods is laborious and time-consuming. For this reasons, a reliable, fast, and easy to use measurement system based on streaming potential measurement was developed. In this novel measurement system, streaming potential is created by an oscillating flow of a small amount of electrolyte solution through the sample media. In addition, this setup allows direct titration and therefore time-resolved monitoring of changes in zeta-potential in a seconds timescale. With this instrument, the concentration- as well as the time-dependent adsorption behaviour of various non-ionic, anionic and cationic surfactants on a novel, regenerated cellulosic polymer was investigated. This new cellulose-based, fibrous textile polymer is permanently cationised, not only at the surface but throughout the whole fibre. The results show that even very low concentrations of surfactant, due to its charge and chemical composition, highly influence the surface charge of the polymer in a large range. Furthermore, the results for this new textile material are compared with other textile fibres, e. g. wool.

Simultaneously monitoring of tissue O 2 and CO 2 partial pressures by means of miniaturized implanted fiber optical sensors

A novel opto-chemical sensor instrumentation based on fiber optical micro-sensors for the simultaneous detection of pO2 and pCO2 in tissues is presented. The adopted sensing principle for both parameters is the measurement of luminescence lifetime via phase modulation fluorometry. Respect to currently used blood-gas analysers that require blood sampling and are associated with blood loss, this instrumentation allows on-line continuous measurements. Compared to electrochemical micro sensors, it is advantageous because of intrinsic higher sensitivity, no analyte consumption and less electromagnetic interferences. The results of the laboratory characterization and of tests in in vivo experiments of the proposed instrumentation are reported.

Stable Dispersions of Aromatic Hydrocarbon Colloidal Particles by Laser Ablation

Dispersions of colloidal particles of polycyclic aromatic hydrocarbons were obtained by nanosecond laser ablation. Aqueous suspensions of micron-sized crystals were irradiated with the second harmonic output of a Nd:YAG laser and converted into colloidal particles. Ionic and nonionic surfactants were used in the ablation process to stabilise the particles. Dispersions with good long term stability were obtained. A strong dependence of particle formation rate on laser fluence was found and the particle formation process is discussed on the basis of UV-Vis spectra and microscopic examination of the crystals.

Measurements of Zeta Potential of Poly(Tetrafluoroethylene) Foils

Zeta potential (ZP) of poly-tetrafluoroethylen (PTFE) and polyamide 6 (PA 6) foils was measured using the streaming potential method. All measurements were carried out in a flat cell where PTFE foils are usually used in electrokinetic measurements as a part of the measuring device, to form the channel and to achieve a proper distance between the foils surface of measured samples. The primary interest of the present work was to investigate the influence of pretreatment of PTFE foils on their electrokinetic properties in order to find out to what extent such pretreatment may affect measuring results of other samples and to develop a procedure of PTFE foils preparation with purpose to achieve the same initial conditions for all measurements.