E. Peter Maziarz

Comparative studies of poly(dimethyl siloxanes) using automated GPC-MALDI-TOF MS and on-line GPC-ESI-TOF MS

In this study we compare on-line gel permeation chromatography (GPC) electrospray ionization (ESI) time-of-flight (TOF) mass spectrometry (MS) to automated GPC matrix assisted laser desorption ionization (MALDI) TOF MS for poly (dimethylsiloxane) (PDMS) analysis. Average mass values for a hydroxyl-terminated PDMS (OH-PDMS) sample were obtained and compared to traditional GPC that was calibrated with narrow polystyrene standards, by direct ESI and MALDI MS analysis, by a summation of mass spectra of all GPC fractions, and also by the recalibration method determined by both mass spectrometric methods. Quantitatively, the difference noted here between these hyphenated techniques is that GPC-ESI-TOF MS effectively reports the low-mass oligomers and underestimates the high-mass oligomers, while GPC-MALDI-TOF MS effectively reports the high-mass oligomers and underestimates the low-mass oligomers. In the GPC-ESI-TOF MS experiments, ion current suppression was observed in the high molecular weight region. The suppression effect was confirmed by repeatable sample runs and by injecting different PDMS samples. Higher chromatographic resolution was observed for GPC-ESI-TOF MS compared to GPC-MALDI-TOF MS. In fact, truly mono-disperse oligomers were observed in the low molecular weight range from GPC-ESI MS experiments.

Detailed analysis of α,ω-bis(4-hydroxybutyl) poly(dimethylsiloxane) using GPC-MALDI TOF mass spectrometry

In this study the prepolymer α,ω-bis(4-hydroxybutyl) poly(dimethylsiloxane), used in the formulation of oxygen permeable films, is evaluated by gel permeation chromatography (GPC) combined with matrix assisted laser desorption ionization (MALDI) time of flight (TOF) mass spectrometry (MS). Two unexpected mass distributions are observed in the mass spectra. Reaction schemes for the formation of these distributions are proposed. A solution phase trimethylsilane end group modification was performed on the prepolymer to determine whether the unexpected mass distributions occur as impurities from synthesis or as artifacts from the MS process. Evaluation of the TMS modified prepolymer indicates the unexpected mass distributions indeed occur as impurities from the synthetic procedure. Average molecular weight values are determined by traditional GPC, direct MALDI-TOF MS, and GPC-MALDI-TOF MS methods and the results are compared.

A comparison of electrospray versus nanoelectrospray ionization Fourier transform mass spectrometry for the analysis of synthetic poly(dimethylsiloxane)/poly(ethylene glycol) oligomer blends

Abstract The transfer efficiency of synthetic oligomer ions in monocomponent systems of polymer mixtures from solution phase to gas phase is examined here for electrospray ionization (ESI) and nanoelectrospray (nanoES) ionization. For poly(dimethylsiloxane) (PDMS), one sees a significant bias in favor of methyl-terminated (ME) PDMS versus 2-methylpropyl-terminated (MP) PDMS in ESI. This ionization dependence (even for two very similar polymers differing only in end-group functionality) would be problematic for quantification efforts of polymers within blends by ESI. It is known that the surface tension of droplets containing polymer blends and solutions is strongly dependent on molecular weight of the polymer and on potential surface activity of the end groups, which occurs primarily via differential adsorption and depletion at the surface. This theory can be used to describe the solution to gas phase bias for PDMS ions with different end groups. For oligomers of similar mass but very different polarity, such as PDMS and poly(ethylene glycol) (PEG), this preferential bias is even more notable, as the PDMS ion signal is nearly completely attenuated relative to the PEG ion signal in ESI mass spectra when drying gas is applied. This bias against PDMS may be due to thermal denaturation and loss of the lone charge or conformational effects. However, both the drying gas flow rate and the ESI skimmer potential influences the degree of this bias. In the absence of drying gas, the PDMS ion signal in the PEG/PDMS mixtures is readily observable. Furthermore, the PEG signal scales with drying gas flow rates, which is consistent with the notion that higher surface tension hydrophilic PEG becomes more efficiently desolvated and ionized with increasing collisions with drying gas molecules. The observation that nanoES (which uses no drying gas) has far less solution-to-gas-phase transfer bias is indicative of the critical role that heat of vaporization of the solvent plays in ion formation for polymers of very different polarities and surface tensions.

Characterization of silicone rubber extracts using gel- permeation chromatography, matrix-assisted laser desorption/ionization mass spectrometry, electrospray ionization mass spectrometry, Fourier transform infrared spectroscopy and gas chromatography/mass spectrometry

Extracts from a silicone rubber product were characterized by gel-permeation chromatography (GPC), matrix-assisted laser desorption/ionization time-of-flight (MALDI-ToF) mass spectrometry, Fourier transform infrared spectroscopy (FT-IR), electrospray time-of-flight (ESI-ToF) mass spectrometry and gas chromatography/mass spectrometry (GC/MS). The extracted sample was determined to be a complex mixture with a molecular weight ranging from 200 to 210,000 Da as determined from GPC measurements. GPC fractions of the extract sample were further analyzed by MALDI-ToF mass spectrometry, ESI-ToF mass spectrometry, FT-IR spectroscopy and GC/MS. The extracted products were determined to be macrocyclic poly(dimethylsiloxane) oligomers. Two additives known as bis(2-ethylhexyl) adipate and bis(2-ethylhexyl) phthalate were observed in the extract.

Detailed characterization of hyaluronan using aqueous size exclusion chromatography with triple detection and multiangle light scattering detection

Hyaluronan (HA) has attracted great interest and attention from ophthalmic surgical and eye care companies owing to its unique properties. A more complete understanding of HA biopolymers has, therefore, become increasingly critical as thorough characterization of raw materials helps promote product quality and process control. Often, such detailed information requires the use of a combination of analytical techniques. In this study, we compared size exclusion chromatography (SEC) with online multiangle light scattering (SEC-MALS) and SEC with triple detection (SEC-TD) experiments for HA analysis. Three lots of commercially available eye drop grade HA were characterized by SEC-MALS and SEC-TD. The absolute molecular weight averages, molecular weight distribution, radius of gyration, and solution conformation of the three HA lots were determined and compared by the two techniques. In addition, the intrinsic viscosity and intrinsic viscosity distribution were measured by SEC-TD.

A modified thermal deposition unit for gel-permeation chromatography with matrix-assisted laser desorption/ionization and electrospray ionization time-of-flight analysis

We describe a modified commercially available thermal deposition unit that incorporates a post-column mixing cell for gel-permeation chromatography (GPC) effluent and matrix solution prior to continuous deposition onto a matrix-assisted laser desorption/ionization (MALDI) sample target. This modification overcomes the shortcomings of using a prefabricated matrix foil. This GPC MALDI method with time-of-flight (ToF) mass spectrometry is demonstrated by the analysis of a poly(dimethylsiloxane) (PDMS) sample used in the production of implantable device materials.