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The effect of temperature, water content, and the type of reagent on the silylation of fused silica capillaries was studied by 29Si and 13C CP‐MAS NMR. Fumed silica (Cab‐O‐Sil M5), which is essentially a highly dispersed vitreous quartz with a surface comparable to that of fused silica capillary columns, was selected as a model material. Hexamethyldisilazane (HMDS) and 1,2‐diphenyl‐1,1,3,3‐tetraphenyldisilazane (DPTMDS), which were used as silylation reagents, yielded trimethyl‐ and dimethylphenylsilyl surface groups respectively at lower temperatures (< 350°C and <250°C respectively). At higher temperatures, increasingly more dimethylsilyl groups are formed, with the silicon bound to two oxygen atoms. This process occurs for DPTMDS at a considerably lower temperature than for HMDS. The formation of silyl groups on the surface and the disappearance of hydroxyl groups are followed independently. The 13C NMR and GC‐MS of the reaction products showed that with DPTMDS, the formation of two Si‐O‐Si links is accompanied by a loss of phenyl groups rather than of methyl groups. After the Cab‐O‐Sil had been dried over P2O5, the formation of these double links occurred for HMDS only at temperatures above 460°C and for DPTMDS at 400°C. Thus we concluded that water supplies oxygen atoms for double Si‐O‐Si links (possibly crosslinks) necessary for efficient deactivation. This may explain the less successful silanization of fused silica capillaries because their water content is lower than that of glass capillaries.

. (1985). A study of some deactivation methods for fused silica capillary columns by CP-MAS NMR and capillary gas chromatography. Please check the document version of this publication:• A submitted manuscript is the version of the article upon submission and before peer-review. There can be important differences between the submitted version and the official published version of record. People interested in the research are advised to contact the author for the final version of the publication, or visit the DOI to the publisher's website.• The final author version and the galley proof are versions of the publication after peer review.• The final published version features the final layout of the paper including the volume, issue and page numbers. Link to publication General rightsCopyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.• Users may download and print one copy of any publication from the public portal for the purpose of private study or research.• You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal.If the publication is distributed under the terms of Article 25fa of the Dutch Copyright Act, indicated by the "Taverne" license above, please follow below link for the End User Agreement: www.tue.nl/taverne Take down policy If you believe that this document breaches copyright please contact us at:openaccess@tue.nl providing details and we will investigate your claim.Download date: 27. Apr. 2019Linear "Breakthrough Gradients" ConclusionsThe model system shown here effectively generates linear breakthrough-gradients with volumes between 40-550 pl, suitable for 200-400 pm i.d. micro-HPLC columns. This work shows that gradient volumes can be readily changed. Decreasing gradient-generator column lengths, column cross-sectional areas, porous particle diameters or flush flow rates all decrease gradient volumes. Thus breakthrough-gradients may be the best approach for generating gradients with packed ultra-micro-HPLC systems [l 11 using 100-200 pm i.d. packed columns or open-tubular systems [12] using ca. 50 pm i.d. columns (both withflowsca. 1 plknin). Conversely, 1 mm i.d. columns have employed gradient volumes ranging from 800-4,000 pl [l], and it may be possible that linear breakthroughgradients can be extended to these larger columns. As Figure 9 shows, the possibility ever1 exists for making nonlinear gradients by using fast flush flows with small porous particle gradient-generator columns. CP-MAS NMR SummaryTheeffect of deactivatingafusedsilicasurface bysilylation with 1 ,I ,3,3-tetraphenyl-l,3-dimethylsilazane (TPDMDS), triphenylsilylamine (TPSA), and octamethylcyclotetrasiloxane (D4) and by polydimethylsiloxane degradation (PSD) is studied. Rehydrat...

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