Rapid determination of oligomeric hindered amine light stabilizers in polymeric materials.

Hindered amine light stabilizers are essential for the stabilization of synthetic polymers, particularly for materials used for outdoor applications. Although up to now a considerable number of studies dealing with the analytics of this class of stabilizers had been published, especially the determination of oligomeric hindered amine light stabilizers is still an analytical challenge. In the current work, a fast and simple liquid chromatographic method for the quantitative determination of oligomeric hindered amine light stabilizers is presented. A key aspect of this method is their completely different retention behavior depending on the pH, enabling a single peak elution approach by a pH gradient run. This allows a quantitation with simple UV detection independent of the actual oligomeric composition. Calibration curves within the concentration range relevant for the analysis of real polymer samples (LOQ = 70 mg/L) were constructed with R2 values above 0.99. Spiked extracts from polyolefin samples showed recovery rates between 97.3 and 102.9% for five different commercial hindered amine light stabilizers. Relative standard deviations were between 2.0 and 3.9%. Furthermore, it was demonstrated that the employed approach can be easily adapted for mass spectrometry detection.

Investigation of photochemical reaction products of glucose formed during direct UV detection in CE.

In CE, saccharides are accessible to direct UV detection due to a photochemical reaction in the detection window of the separation capillary resulting in the formation of UV absorbing substances. Employing a CE method that allows long in-capillary irradiation with subsequent UV and MS detection, the present study could identify several reaction products of glucose. Among these were UV absorbing substances so far unknown to be formed during direct UV detection with the chemical formulas C4 H6 O2 , C5 H6 O4 , C5 H8 O3, and C6 H8 O5 . Investigations of the impact of the irradiation time revealed differences between these reaction products suggesting differing reaction mechanisms especially for the smallest products. More detailed information could be obtained by experiments with isotope-labeled substrates performed to determine the parts of glucose that are converted to the particular reaction products. In addition, structural formulas for the reaction products were suggested based on HPLC-MS/MS measurements of off-line irradiated glucose solutions which revealed the existence of functional groups such as carboxylic acid or aldehyde groups.

Characterization and quantitation of polyolefin microplastics in personal-care products using high-temperature gel-permeation chromatography.

In recent years, the development of reliable methods for the quantitation of microplastics in different samples, including evaluating the particles' adverse effects in the marine environment, has become a great concern. Because polyolefins are the most prevalent type of polymer in personal-care products containing microplastics, this study presents a novel approach for their quantitation. The method is suitable for aqueous and hydrocarbon-based products, and includes a rapid sample clean-up involving twofold density separation and a subsequent quantitation with high-temperature gel-permeation chromatography. In contrast with previous procedures, both errors caused by weighing after insufficient separation of plastics and matrix and time-consuming visual sorting are avoided. In addition to reliable quantitative results, in this investigation a comprehensive characterization of the polymer particles isolated from the product matrix, covering size, shape, molecular weight distribution and stabilization, is provided. Results for seven different personal-care products are presented. Recoveries of this method were in the range of 92-96 %.

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.

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.

Current approaches to trace analysis of pharmaceuticals and personal care products in the environment.

A large number of xenobiotics including pharmaceuticals and personal care products are continuously released into the environment. Effluents from sewage treatment plants are well known to be the major source for introduction of pharmaceuticals and personal care products into the aquatic system. In recent years, reliable methods have been established for residue analysis of these pollutants down to low ng/L levels. In this review, the different approaches to their trace determination are reviewed with special attention being paid to sample preparation procedures, state-of-the-art high-performance separation methods hyphenated with mass spectrometry, and immunochemical methods.

Characterization of mixtures of biocidal oligoguanidines by capillary electrophoresis and high-performance liquid chromatography coupled to mass spectrometry.

The polycondensation of guanidine hydrochloride and 2,2'-(ethylenedioxy)bis(ethylamine) leads to various types of oligomeric guanidines exhibiting a broad spectrum of biocidal activities. In the present work a reversed-phase high-performance liquid chromatographic method with a gradient consisting of aqueous 0.1% trifluoroacetic acid and acetonitrile as mobile phase has been developed to separate these oligoguanidines according to type and chain length. The combination with electrospray mass spectrometry allowed the identification of the various compounds. By this technique, some structures already suggested in the literature could be confirmed, and several additional oligoguanidines not yet reported could be identified. As a complementary technique, capillary zone electrophoresis was investigated. Best results were obtained with carrier electrolytes consisting of phosphoric acid in water/acetonitrile mixtures. Although the number of peaks that could be separated by the electrophoretic method was considerably lower than in case of the chromatographic method, capillary electrophoresis in combination with UV detection at 195nm may still be a fast method suitable for quantitation of some of the major compounds and for monitoring the reaction rate during the polycondensation reaction.

Microemulsion electrokinetic chromatography.

Microemulsion electrokinetic chromatography (MEEKC) is an attractive capillary electrophoretic technique in which a microemulsion is used as carrier electrolyte. Analytes may partition between the aqueous phase of the microemulsion and its oil droplets, which act as a pseudostationary phase. It is well suited for the separation of neutral analytes, but can also be employed for charged analytes. A single set of separation parameters may be sufficient for separation of a wide range of analytes. Fine-tuning of the separation may be achieved by addition of organic solvents to the microemulsion or by changes in the nature of the surfactant used for stabilization of the microemulsion. In this chapter, MEEKC conditions are summarized that have proven their reliability for routine purposes. Furthermore, microemulsions can be used for on-capillary preconcentration of analytes so that the problem of poor concentration sensitivity of ultraviolet detection in capillary electrophoresis is circumvented.

Novel analytical procedures for screening of drug residues in water, waste water, sediment and sludge.

Traces of pharmaceuticals are continuously introduced into the aquatic environment mainly by sewage treatment plant effluents. Final data about their impact on the ecosystem are still partly missing. Progress in instrumental analytical chemistry has resulted in the availability of methods that allow a monitoring of these pollutants at ng L(-1) levels. In this review the state-of-the-art of residue analysis of pharmaceuticals by chromatographic and electrophoretic techniques is summarized. Improvements in detection limits over the past years have mainly been due to sophisticated mass spectrometric detection techniques. Furthermore, robust sample preparation and preconcentration protocols based on solid-phase extraction and related procedures have contributed significantly to the achievements observed so far. This review also covers several immunochemical approaches which may serve as an inexpensive alternative for quick screening of samples.