Ingrid Hintersteiner

Characterization of hindered amine light stabilizers employing capillary electrophoresis coupled to quadrupole time-of-flight mass spectrometry.

In the current work, a fast and reliable CE method for characterizing of six hindered amine light stabilizers (HALS), technical products commonly employed as UV‐stabilizing agents for various polymeric materials, is presented. These compounds can be monomeric or oligomeric species whereby there is no or only limited information available concerning purity or actual structural composition of the respective stabilizer. Using a BGE based on formic acid with 10% acetonitrile, different constituents of several HALS could be separated by CE and identified employing QTOF/MS detection. In the case of Cyasorb 3529, ten different oligomers were discovered and possible structures were suggested based on exact mass measurements. The majority of the elucidated structures is not fully congruent with the information provided by the manufacturers. Furthermore, in the case of Chimassorb 119 and Tinuvin 770 impurities or unreacted compounds remaining from the manufacturing process could be identified. Besides performing such basic characterizations of technical grade HALS, the presented method is also shown to be suitable for a reliable identification of these stabilizers in real polymer samples.

Quantitative analysis of hindered amine light stabilizers by CZE with UV detection and quadrupole TOF mass spectrometric detection

The current work describes the development of a CZE method with quadrupole QTOF‐MS detection and UV detection for the quantitation of Cyasorb 3529, a common hindered amine light stabilizer (HALS), in polymer materials. Analysis of real polymer samples revealed that the oligomer composition of Cyasorb 3529 changes during processing, a fact hampering the development of a straightforward method for quantitation based on calibration with a Cyasorb 3529 standard. To overcome this obstacle in‐depth investigations of the oligomer composition of this HALS using QTOF‐MS and QTOF‐MS/MS had to be performed whereby 22 new oligomer structures, in addition to the ten structures already described, were identified. Finally, a CZE method for quantitative analysis of this HALS was developed starting with a comprehensive characterization of a Cyasorb 3529 standard using CZE‐QTOF‐MS, subsequently allowing the correct assignment of most Cyasorb 3529 oligomers in an electropherogram with UV detection. Employing the latter detection technique and hexamethyl‐melamine as internal standard, peak areas obtained for the melamine could be correlated with those from the triazine ring, the UV‐absorbing unit present in the HALS. This approach finally allowed proper quantitation of the single oligomers of Cyasorb 3529, an imperative for the quantitative assessment of this HALS in real polymer samples.

Damp Heat Aging Behavior of a Polyamide-Based Backsheet for Photovoltaic Modules

This paper describes and evaluates accelerated aging of a titanium dioxide (TiO2) filled polyamide (PA) based backsheet film for photovoltaic (PV) modules. Damp heat exposure (85%RH, 85 °C) was carried out up to 2000 hrs. The backsheet was characterized using microscopic, spectroscopic, thermoanalytic, chromatographic, and mechanical methods. While Raman microscopy, infrared spectroscopy in attenuated total reflection mode (IR-ATR), scanning calorimetry (DSC), and thermal gravimetric analysis did not reveal aging-induced changes, significant yellowing was detected by ultraviolet visible near infrared (UV/VIS/NIR) spectroscopy. Depending on the stabilizer type (UV-absorbers, hindered amine light stabilizers (HALSs), and antioxidants), rather different consumption rates were ascertained by high-performance liquid chromatography (HPLC) and gas chromatography (GC). Although the ultimate mechanical properties decreased significantly, no full embrittlement was obtained after damp heat exposure of up to 2000 hrs. The observed physical and chemical aging mechanisms were classified as within the induction period without premature failure.

DIRECT ANALYSIS IN REAL TIME/TIME-OF-FLIGHT MASS SPECTROMETRY: INVESTIGATIONS ON PARAMETERS FOR THE COUPLING WITH LIQUID-PHASE SAMPLE INTRODUCTION TECHNIQUES

□ Studies for the evaluation of a lab made liquid jet interface designed for the coupling of direct analysis in real time (DART) time-of-flight mass spectrometry (TOF-MS) with liquid-phase sample introduction systems such as flow injection analysis (FIA) or high performance liquid chromatography (HPLC) have been performed. Thereby a substantial influence of parameters like surface/volume ratio (determined by the inner diameter of the capillary employed) of the liquid jet as well as the composition of the eluent (with respect to the concentration of electrolyte and organic solvent) on signal intensities could be detected. Comparison of the developed interface with other more common interface types (based on electrospray ionization, atmospheric pressure chemical ionization, and atmospheric pressure photoionization) was carried out on the example of a test mixture containing four parabens spiked into biological fluid samples. DART ionization proved superior when employed in combination with FIA as it was less affected by matrix effects resulting in ionization suppression. On the other hand if at least partial separation of the matrix/analytes was performed by using short chromatographic columns, the other ionization techniques turned out to be the better choice primarily due to their increased sensitivity.

Characterization of polyoxymethylene for backsheets of photovoltaic modules

This article describes and evaluates the basic properties and the damp heat (85%RH, 85℃) aging behaviour of a 400 µm thick titanium dioxide filled polyoxymethylene film for potential use as backsheet in photovoltaic (PV) modules. The polyoxymethylene monolayer was characterized using analytical methods and technological tests. The stabilizer package contained Tinuvin 234, Tinuvin 770 and Irganox 245. The less than 1 wt% pigmentation resulted in 0.680 solar optical reflectance. The slightly anisotropic mechanical properties elastic modulus and strength were within the requirements for backsheets. Damp heat exposure triggered degradation, stabilizer loss and lead to optical properties degrading (yellowing). However, neither premature embrittlement nor a critical loss of ultimate mechanical properties was found after 5005 h of aging. Hence, polyoxymethylene was classified as a potential candidate for backsheet core layers.