Chris G. de Koster

Determination of Block Length Distributions of Poly(oxypropylene) and Poly(oxyethylene) Block Copolymers by MALDI-FTICR Mass Spectrometry.

Matrix-assisted laser desorption/ionization (MALDI) was performed on an external ion source Fourier transform ion cyclotron resonance mass spectrometer (FTICR-MS) to analyze the block length distributions of triblock polymers of poly(oxypropylene) and poly(oxyethylene). The first series of results presented demonstrate that the apparent molecular weight distributions are distorted. This distortion is induced by the flight-time-induced mass discrimination inherent in the experimental technique, the variation of isotopic patterns over the measured mass range, and the overlap of peaks in the spectrum. Subsequently, a method for the treatment of molecular weight distributions measured by MALDI on an external ion source FTICR-MS is developed to yield the actual molecular weight distribution and, from that, the individual block length distributions. For the first time, detailed and accurate molecular weight data were obtained on a complex sample using this methodology, which independently validates the data provided by the manufacturer. The experimentally verified random coupling hypothesis proves the validity of the methodology.

Electron capture and collisionally activated dissociation mass spectrometry of doubly charged hyperbranched polyesteramides

Electron capture dissociation (ECD) of doubly protonated hyperbranched polyesteramide oligomers (1100–1900 Da) was examined and compared with the structural information obtained by low energy collisionally activated dissociation (CAD). Both the ester and amide bonds of the protonated species were cleaved easily upon ECD with the formation of odd electron (OE·+) or even electron (EE+) fragment ions. Several mechanistic schemes are proposed that describe the complex ECD fragmentation behavior of the multiply charged oligomers. In contrast to studies of biomolecules, the present results indicate that consecutive cleavages induced by intramolecular H-shifts are significant for ECD and of less importance for low energy CAD. The capture of an electron by the ionized species results in fragmentation associated with a redistribution of the excess internal energy over the products and the subsequent bond cleavage. Low energy, multiple collision CAD is found to be a more selective dissociation method than ECD in view of the observation that only amide bonds are cleaved for most of the hyperbranched polymers examined with CAD in this study. ECD appears not to provide complementary structural information compared to CAD in the study of hyperbranched polymers, even though a significantly more complex ECD fragmentation behavior is observed. ECD is shown to be of use for the structural characterization of large oligomers that may not dissociate upon low energy CAD. This is a direct result of the fact that ECD produces ionized hyperbranched oligomers with a relatively high internal energy.

In-source decay of hyperbranched polyesteramides in matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

Hyperbranched polyesteramides (DA2), prepared from hexahydrophthalic anhydride (D) and diisopropanolamine (A) have been characterized, by use of matrix-assisted laser desorption/ ionization time-of-flight mass spectrometry (MALDI-TOF-MS), field desorption (FD)-MS, and electrospray ionization (ESI)-MS. MALDI of polyesteramides produces protonated molecules. The spectra show a complex chemical composition distribution and end-group distribution which are mainly composed of two series of homologous oligomers DnAn+1 − mzH2O and DnAn − mH2O, where m = 1–2. Signals from protonated molecules DnAn+1 and DnAn are almost absent in the MALDI spectrum, whereas these ions are responsible for the base peak of DnAn+1 − mH2O and DnAn − mH2O (m = 1–2) clusters in the ESI spectrum. The absence of −OH end-groups signals in the MALDI spectrum is due to a metastable decay of protonated DnAn+1 and DnAn ions in the ion source of the MALDI mass spectrometer prior to ion extraction. In-source decay results in the formation of protonated lower DnAn+1 − mH2O and DnAn − mH2O oligomers and their corresponding neutrals, leading to wrong conclusions concerning the relative end-group distribution as a function of the degree of polymerization and the chemical composition.

Laser ablation inductively coupled plasma mass spectrometry as a tool for studying heterogeneity within polymers

The distribution (heterogeneous or homogeneous) of inorganic additives within an organic polymer phase is important because it directly influences the physical and chemical properties of the polymer. Heterogeneity must also be assessed when producing reference materials. When producing a polymer reference material certified for the concentrations of its inorganic additives, assessment of heterogeneity is crucial. In this work the use of LA-ICP-MS to demonstrate the occurrence of heterogeneity in polymers, and polyethylene in particular, is described. The polymers studied were candidate reference materials. The conclusions reached correspond well with those obtained by means of solid sampling-Zeeman atomic absorption spectrometry (SS-ZAAS). As LA-ICP-MS is a multi-elemental technique the data was obtained in a fraction of the time required by SS-ZAAS. Hence, LA-ICP-MS can be used as a screening tool to quickly reject materials on the basis of unacceptable heterogeneity, thereby avoiding unnecessary time-consuming SS-ZAAS analyses.

Structural characterization of hyperbranched polyesteramides: MSn and the origin of species

Four hyperbranched synthetic polyesteramides were synthesized by the polycondensation of the trifunctional diisopropanolamine (D) and difunctional anhydrides (X) of succinic acid, glutaric acid, 1,2-cyclohexane dicarboxylic acid, and phthalic acid. The polymers were analyzed with electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry. The most intense oligomer series observed was XnDn+1 containing diisopropanolamine end groups as expected from the polycondensation conditions. A series of oligomers XnDn+1H2O is observed as well, which can have its origin in the polymerization process or alternatively could result from in-source fragmentation of XnDn+1. Breakdown diagrams of the protonated parent ions X3D4 and additional MSn (n = 1, 2, 3) measurements gave insight in the fragmentation behavior of the polymers. Three main fragmentation pathways have been observed for all polymers of which the loss of H2O to oxazolonium ions has the lowest onset energy followed by the rearrangement of the amide and ester bonds also leading to oxazolonium ions. The loss of a second H2O to allylic or morpholine end groups has highest onset energy. MS3 experiments demonstrated that the presence of a series of oligomers XnDn+1H2O can be attributed to the polymerization process. Most probably an allylic end group has formed from one of the alcohol end groups. The formation of allylic end groups partly terminates the polymerization reaction and results in a change of the composition of the molecular weight distribution and decrease of the number average molecular weight.

On the use of inductively coupled plasma mass spectrometry as an element specific detector for liquid chromatography: optimization of an industrial tellurium removal process

Abstract The current status of inductively coupled plasma mass spectrometry (ICP-MS) can be defined as a versatile element and isotope specific detection technique of high sensitivity and wide element coverage. In conjunction with this type of detector a variety of sample introduction systems is used enabling the introduction of samples in liquid, solid and gaseous form. In addition, ICP-MS instruments are increasingly being used in speciation studies especially as a detector for liquid chromatography (LC). This is demonstrated by the following representative application. A considerable part of the industrial chemicals currently produced by DSM is derived from an (amm)oxidation process on the basis of sophisticated heterogeneous catalysts in which tellurium plays an important role. A drawback of tellurium is its volatility resulting in material losses and a corresponding decay in catalytic properties. These tellurium losses show up in waste water drained at a concentration of 0.5–1.5 mg Te/l. Supply of this waste water to a central waste water purification plant leads to biological methylation of tellurium into dimethyltelluride Te(CH3)2 with an unpleasant garlic smell. Therefore a tellurium removal process was developed based on the cementation of tellurium onto iron. This process showed unacceptably low removal efficiencies when supplied with freshly drained waste water. LC–ICP-MS experiments revealed the occurrence of tellurium compounds that were only slowly converted into tellurite and tellurate. Conversion parameters and conditions were extensively studied by LC–ICP-MS experiments. Process conditions developed on a benchscale were successfully applied in a plantscale tellurium removal process. This process is capable of removing tellurium from a continuous 100 m3/h waste water supply to a concentration level of 0.01–0.03 mg Te/l.