Determination of molecular mass distribution of silicone oils by supercritical fluid chromatography, matrix‐assisted laser desorption ionization time‐of‐flight mass spectrometry and their off‐line combination

Abstract

Silicone oil samples were characterized by supercritical fluid chromatography (SFC), matrix-assisted laser desorption ionization-time-of-flight mass spectrometry (MALDI--TOF MS), and their off-line combination. SFC was used to separate samples of silicone oils on micropacked capillary columns. The fractions for the identification studies were obtained from SFC runs at defined time intervals, when the restrictor was pulled out from the chromatographic flame ionization detector (FID) and inserted into a glass vial with acetone. MALDI--TOF MS was used for the identification of individual oligomers in the fractions separated. The molecular mass distributions determined based on SFC and MALDI--TOF MS measurements were compared. From this comparison, it follows that the results are in good agreement. However, certain differences were observed: MALDI--TOF MS was capable of detecting somewhat larger oligomers than the SFC-FID, but the lower molecular mass oligomers were not present in the MALDI spectra. Differences in the region of lower molecular masses can be explained by evaporation of the more volatile low molecular mass oligomers resulting from heating of the sample during the MALDI--TOF MS measurements as a result of the absorption of the laser shot energy. The fact that no high mass discrimination effects of the MALDI--TOF MS measurements, compared with SFC, were observed is very promising for further applications of MALDI--TOF MS in characterizing synthetic polymers of moderate polydispersity.

Oligomeric carbon and siloxane series observed by matrix‐assisted laser desorption/ionisation and laser desorption/ionisation mass spectrometry during the analysis of soot formed in fuel‐rich flames

“…The mass spectrometry of silicones has not been extensive. Chmelik and co‐workers have characterised silicone oils by MALDI‐MS3,4 and compared these results with data from super‐critical fluid chromatography; the distributions of oligomers identified by the two methods were comparable. Silicone rubber extracts have also been examined by gel permeation chromatography (GPC) using toluene as eluent, MALDI‐MS using dithranol as matrix doped with sodium nitrate, and by other methods 5.…”

Development of packed capillary columns using carbon dioxide slurries

“…30 minutes. The prepared columns were also used for the separation of waxes in objects of art [18], and for a SFC-MALDI study of polymer distribution [19,20].…”

Fluidos supercríticos em química analítica. III.: aplicações

“…Jordan et al 53 descreveram o uso "on-line" de extração e cromatografia com fluido supercrítico acoplado com espectroscopia vibracional na região do infravermelho com transformada de Fourier (SFE-SFC-FT/IR) para extração, separação e identificação de extratos em Nylon e poliestirenos, usando condições de extração relativamente brandas. Chmelik et al 54 determinaram a distribuição da massa molar de óleo de silicone por SFC e compararam os resultados com espectrometria de massas por tempo de vôo com desorção à laser e ionização assistida por matriz (MALDI-TOF MS, "matrix-assisted laser desorption ionization time-of-flight mass spectrometry") e verificaram que as duas abordagens apresentaram uma boa correlação dos resultados com grande vantagem para SFC na detecção de oligômeros menores, os quais são subestimados na análise por espectrometria de massas. MALDI-TOF MS foi relativamente melhor na detecção de oligômeros de massa molares mais elevadas, conseguindo detectar oligômeros com 70 unidades, enquanto que SFC foi até 60 unidades, como pode ser visto na Figura 6.…”