Ulrich Just

Chromatographic investigations of macromolecules in the “critical range” of liquid chromatography: II. Two-dimensional separations of poly(ethylene oxide-block-propylene oxide)

Abstract A polyethylene oxide-polypropylene oxide block polymer was characterized with respect to molar mass distribution and block length of the individual blocks using two-dimensional chromatographic techniques. In the first dimension the block polymer was separated according to the length of the polypropylene oxide block by liquid chromatography at the critical point of adsorption. The resulting polypropylene oxide uniform fractions were subjected to supercritical fluid chromatography or size-exclusion chromatography and the average length and the molar mass of the polyethylene oxide blocks were determined for every fraction.

Molar mass determination of oligomeric ethylene oxide adducts using supercritical fluid chromatography and matrix-assisted laser desorption—ionization time-of-flight mass spectrometry

Abstract Supercritical fluid chromatography (SFC) and matrix-assisted laser desorption—ionization time-of-flight mass spectrometry [MALDI-MS (TOF)] are suitable, mutually complementary methods for characterizing oligomeric ethylene oxide adducts. While SFC is successfully applicable in the low-molecular-size range up to molar masses of ca. 1000 g/mol, MALDI-MS facilitates proper differentiation also in higher molar mass ranges. In the lower molar mass ranges down to approximately degree of polymerization n = 6, the problem of discrimination arises when MALDI-MS is applied; this problem is reduced considerably through the addition of lithium chloride instead of sodium or potassium ions, a measure which also eases identification of the molar peak. Provided that the ethylene oxide chain is known, it is also possible to definitely determine substituents in the molecule (e.g., alkyl or arylalkyl chains). By-products, which may arise, for example, when water is split off during the reaction or during storage, can be detected.

Analysis of benzyloxy-terminated poly(1,3,6-trioxocane)s by supercritical fluid chromatography

Abstract Benzyloxy-terminated poly(1,3,6-trioxocane)s are separated into oligomers by supercritical fluid chromatography. Depending on the chemical structure of the polytrioxocane, two to three peaks are obtained for each degree of polymerization, corresponding to different types of functionality. Up to a degree of polymerization of n = 7 the α, ω-dihydroxy, α-hydroxy-ω-benzyloxy and α,ω-dibenzyloxy species are well separated.

Analysis of a mixture of linear and cyclic siloxanes by cryo-gas chromatography-Fourier transform infrared spectroscopy and gas chromatography-mass spectrometry

Abstract A mixture of linear and cyclic methylsiloxanes was analysed to characterize the different types of siloxane structures using gas chromatography (GC), mass spectrometry (MS) and Fourier transform infrared (FT-IR) spectroscopy. Siloxane structures are formed by hydrolysis of dimethyldichlorosilane under controlled conditions in technical applications. In the presence of methyltrichlorosilane or even trimethylchlorosilane, linear polydimethylsiloxanes and mono-, bi- or polycyclic methylsiloxanes are synthesized depending on the reaction conditions. The main structural units are ( CH 3 ) 3 SiO 3 2 , (CH3)2SiO and ( CH 3 ) SiO 3 2 . GC-MS may provide molecular mass information, but it is not able to identify isomeric structures, which are also formed in lower quantities by the mentioned reactions. Coupling GC with FT-IR enables the determination of group frequencies to assign specific structures. Thus, combination of GC with MS and FT-IR may be used in elucidating complex cyclosiloxane compounds. FT-IR measurements were performed with a Tracer unit.

Enzymatic hydrolysis of the cytotoxic triterpenoid glycoside virgaureasaponin 1

The cytotoxic compound, virgaureasaponin 1, was converted using several optimized enzymecatalysed hydrolyses to the 28-O-beta-D-xylopyranosyl (1-->4)-alpha-L-rhamnopyranosyl-(1-->2)-beta-D-fucopyranoside (2), and the 28-O-alpha-L-rhamnopyranosyl-(1-->3)-beta-D-xylopyranosyl-(1-->4)-alpha- L- rhamnopyranosyl-(1-->2)-beta-D-fucopyranoside (3) and 28-O-beta-D-xylyopyranosyl-(1-->4)-alpha-L-rhamnopyranosyl-(1-->2) - beta-D-fucopyranoside (4) both lacking the glucose moiety at C-3 of the aglycone. The terminal rhamnose of the acylglycosidic bonded tetrasaccharide was cleaved by naringinase to give compound 2. The new acylglycosides 3 and 4 were obtained with the help of a relatively crude beta-glucuronidase preparation, but the cleavage of the sapogenin bonded glucose was impossible using several beta-glucosidase preparations directly. These derivatives were used for the investigation of the relationship between the saponin carbohydrate structure and their cytotoxic activity.

Simultaneous determination of functionality type and molar mass distribution of oligo (1,3,6-trioxocane)s by supercritical fluid chromatography

Abstract Benzyloxy terminated oligo (1,3,6-trioxocane)s are separated into components of single molar mass and functionality by supercritical fluid chromatography. The assignment and quantification of the components is described. It is shown that molar mass and functionality type distribution may be determined simultaneously from one chromatogram.

Polymer Reference Materials: Round-Robin Tests for the Determination of Molar Masses

Abstract This article reports round-robin tests dealing with static light scattering (LS), size exclusion chromatography (SEC), and viscometry measurements of 10 reference materials of various polymer classes: poly(styrene)s (PS), poly(methyl methacrylate)s (PMMA), poly(ethylene oxide)s (PEO), and poly(lactide)s (PLA). In the certificates, molar masses and intrinsic viscosities as well as their uncertainties are specified. Additional values from nuclear magnetic resonance (NMR), infrared spectroscopy (IR), differential scanning calorimetry (DSC), melt flow index (MFR), and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS), which were determined exclusively in BAM laboratories are given, as well. These results represent the base for the BAM certification work of creating polymer reference materials according to the BAM Guidelines for the Production and Certification of BAM Reference Materials, a version of the European guidelines (BCR/01/97). These samples are available for third-party user.

Static Light Scattering of Polystyrene Reference Materials: Round-RobinTest

Abstract This paper reports a round-robin test dealing with static light scattering (LS) measurements of three polystyrene standard materials with narrow distributions. Low-angle laser light scattering (LALLS) and multi-angle laser light scattering (MALLS) instruments, as well as other types of goniometers, were used. The results of the two samples with higher molar masses are in good agreement if one and the same Rayleigh ratio value was used for calibrating multi-angle instruments, and refractive indices, and refractive index increments were adjusted. The values of LS measurements for the oligomeric sample exhibited greater deviations in this test.

Supercritical fluid chromatography-mass spectrometry and matrix-assisted laser-desorption ionisation mass spectrometry of cyclic siloxanes in technical silicone oils and silicone rubbers

Abstract Supercritical fluid chromatography in combination with mass spectrometry is used for determining cyclic siloxanes beside linear methyl and hydroxyl “end-capped” siloxanes. Electron impact ionisation and chemical ionisation techniques are utilized for identifying cyclic siloxanes in technical silicone oils and silicone rubber. Ammonia as reagent gas is preferred in the higher-molecular-mass range. Matrix-assisted laser-desorption ionisation mass spectrometry can be useful as a supplementary method for characterizing smaller amounts of both cyclic and linear siloxanes as well as silanols in the higher-molecular-mass range.

Characterization of Polymers Using Supercritical Fluid Chromatography: Application of adsorption chromatography, size exclusion chromatography and adsorption chromatography at critical conditions

Abstract Supercritical fluid chromatography (SFC) utilizes fluids or mixtures of fluids above their critical temperature and critical pressure which exhibit greater solvating properties with simultaneously reduced viscosities and higher diffusion coefficients compared with their liquid state; supercritical fluids, thus, offer new possibilities for characterizing polymers. The three modes of liquid chromatography are applied in the analysis of polystyrenes, using supercritical fluids (mixtures of dichloromethane with carbon dioxide) in each mode: adsorption chromatography for the separation of oligomers, size exclusion chromatography for the determination of molar mass distribution, and adsorption chromatography at critical conditions for the characterization of functionality type distribution. Advantages and disadvantages of size exclusion chromatography with fluids in their supercritical, subcritical and liquid phase are discussed with the system polystyrene in dichloromethane.