Fast atom bombardment mass spectrometry for the determination of the molecular weight distribution of poly(ethylene glycols) and their derivatives

Separation of polyethylene glycols and their fluorescein-labeled compounds depending on the hydrophobic interaction by high-performance liquid chromatography

The separation and characterization of fluorescein-labeled polyethylene glycols (PEG) is described. Firstly, the polyethylene glycols labeled with fluorescein isothiocyanate (FITC) were synthesized and separated using Sephadextrade mark LH-20 medium by a step gradient. Secondly, a TSK GEL G4000 PW XL column was developed for determining the FITC derivatives of PEG. The retention mechanism is based on the hydrophobic interaction between the FITC derivatives of PEG and the packing material of the TSK GEL G4000PW XL column. The retention time of the PEG compounds increased by adding of salts in the mobile phase and decreased by adding of organic modifier. In addition, various salts in the eluent can also change the chromatographic behavior of these compounds. Finally, the pH of the mobile phase can have an impact on the retention time of the PEG compounds.

Comparison of mass spectrometric techniques for generating molecular weight information on a class of ethoxylated oligomers

The results of fast atom bombardment (FAB), time-of-flight secondary ion mass spectrometry (ToF-SIMS), matrix-assisted laser desorption/ionization (MALD/I), electrospray ionization (ESI), and field desorption (FD) analyses of ethoxylated oligomers of 2,4,7,9-tetramethyl-5-decyne-4,7-diol (Surfynol(®) 104) were compared.Each of these desorption mass spectrometry (MS) techniques can produce spectra of unfragmented cationized oligomers. From the observed ion series we calculate average molecular weight information. We have compared the results of mass spectrometric analyses of a series of ethoxylated Surfynol surfactants. Our data indicate that FAB, ToF-SIMS, MALDI/I, and ESI produce similar results for the lower molecular weight species, but that as the average molecular weight increases FAB and SIMS produce slightly lower results than MALD/I and FD. This could be due to increased fragmentation. ESI produced a result similar to FAB and SIMS for the highest average molecular weight material. Further experiments compare the mass spectral results with gas chromatographic quantitative data. Although gas chromatography is not expected to accurately analyze the higher mass oligomers, we observe significant differences in intensities of the short-chain oligomers (especially the 0- and 1-mers) when compared to the desorption mass spectrometer results. These differences may reflect poor cationization efficiency for very short oligomer chains in the mass spectrometric analyses.