Endcapping reagent

When the sorbent is endcapped, which is typically done with trimethylsi-lane, the trimethylsilane will increase the carbon loading by bonding to any available silanol sites that have not been derivatized by the C-8 or C-18. Because of the smaller size of the endcapping reagent, it can derivatize the more sterically hindered sites on the silica. This process makes the sorbent more hydrophobic and increases the carbon loading as much as several percent. 

If, in a stoichiometric reaction, a perfluoralkyl substituted endcapper group is added to a diene and a catalytic ADMET reaction of ot,co-diene follows, which is stopped by addition of some perfluoralkyl substituted endcapping reagent, high molecular weight... 

Although a second reaction step to bond more silanols with a smaller endcapping reagent to HPLC sorbents is routine today, only one stage of bonding is done with the sorbents for TLC, which saves cost and time in making the bonded sorbent. 

A monofunctional phosphine oxide containing the endcapping reagent, 4-car-boxyl-phenyl-diphenylphosphine oxide, was prepared for applications in the synthesis of telechelic polyester oligomers. The diphenyl-4-methylphenyl phosphine oxide obtained in Grignard reaction was subjected to oxidation to afford the carboxyl-phenyl derivative (Scheme 47). 

Coverage is 3.0 timol on 200 m g silica (12% C). The phase is endcapped with a small silylating reagent in the conventional way. Ascentis RP-amide columns are the latest version of the Supelco amido column bonded on higher surface area 450 m g pure silica (25% C). A polymeric bonding is used to increase the stability and reduce bleed, especially for MS work. 

Dimethy 1-4,4 -diamino-1,1 -biphenyl dihydrochloride was obtained from Professor Lorraine Deck at the University of New Mexico and used as received. Maleic anhydride was obtained from Eastman Kodak and p-aminobenzoic was obtained from National Starch. The other anhydrides, diols, and reagents were purchased from Aldrich Chemical. All reagents were used without further purification. The monomers were synthesized via a Schotten-Baumann type procedure using the appropriate acid chloride endcap and diamines or diols. Triethylamine was used as a scavenger for HC1. The monomers were recrystallized from appropriate solvents in yields of approximately 70%. 

It is quite important to know the pore size of the silica gel (which controls surface area), the amount of liquid phase or functional groups bonded to the silica, the type of derivatization reagent (mono- or trifunctional), and the extent of endcapping. This information was realized by some of the manufacturers of SPE products thus, they supply customers with quality control and quality assurance (QA) data of their SPE products. Figure 2.8 shows an example of such a QA report from 1ST (International Sorbent Technology). 

Separation of ionic soiutes what works out best - endcapped phases, inert phases, phosphate bu er or ion pairing reagents Part I... 

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