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  • Simultaneous analysis of basic, acidic and neutral compounds on an endcapped octadecylsilane silica-based monolith by pressure-assisted capillary electrochromatography.

Simultaneous analysis of basic, acidic and neutral compounds on an endcapped octadecylsilane silica-based monolith by pressure-assisted capillary electrochromatography.

Electrophoresis (2008-01-24)
Tong Zhang, Ibrahim Khadra, Melvin R Euerby, Graham G Skellern, David G Watson, Justice N A Tettey
ABSTRACT

This simultaneous separation of basic, acidic and neutral analytes by pressure-assisted CEC (pCEC) using a hybrid (tetramethoxysilane and methyltrimethoxysilane) silica-based monolith, chemically modified with octadecyldimethylchlorosilane followed by endcapping with hexamethyldisilazane is described. The endcapping resulted in near Gaussian peaks for highly basic analytes such as nortriptyline without a significant loss in the EOF. The migration behaviour of analytes on this phase could be rationalised based on hydrophobicity, electrophoretic mobility and ion-exchange interactions. The high porosity of the monolith allowed manipulation of the linear velocity of mobile phases by the addition of varying amounts of pressure at the inlet to reduce analysis times and overcome the reversed migration of anionic species towards the detection window in cathodic EOF mode. The concomitant programmed application of pressure (2-4 bar) and voltage (27 kV) facilitated the simultaneous separation of four cationic, four neutral and two anionic compounds in 6 min with efficiencies ranging from 41 000 to 94 000, 57 000 to 77 000 and 180 000 to 210 000 theoretical plates/metre, respectively. The % RSD values of migration times and efficiencies in pCEC mode were less than 3.6 and 7.9%, respectively (n = 5).

MATERIALS
Product Number
Brand
Product Description

Sigma-Aldrich
Hexamethyldisilazane, reagent grade, ≥99%
Sigma-Aldrich
Lithium bis(trimethylsilyl)amide solution, 1.0 M in THF
Sigma-Aldrich
Sodium bis(trimethylsilyl)amide solution, 1.0 M in THF
Sigma-Aldrich
Potassium bis(trimethylsilyl)amide solution, 1 M in THF
Sigma-Aldrich
Lithium bis(trimethylsilyl)amide, 97%
Sigma-Aldrich
Potassium bis(trimethylsilyl)amide, 95%
Sigma-Aldrich
Hexamethyldisilazane, ReagentPlus®, 99.9%
Supelco
Hexamethyldisilazane, for GC derivatization, LiChropur, ≥99.0% (GC)
Sigma-Aldrich
Tetramethyl orthosilicate, ≥99%
Sigma-Aldrich
Potassium bis(trimethylsilyl)amide solution, 0.5 M in toluene
Sigma-Aldrich
Trimethoxymethylsilane, 98%
Sigma-Aldrich
Lithium bis(trimethylsilyl)amide solution, 1 M in toluene
Sigma-Aldrich
Tetramethyl orthosilicate, 98%
Sigma-Aldrich
Trimethoxymethylsilane, 95%
Sigma-Aldrich
Sodium bis(trimethylsilyl)amide, 95%
Sigma-Aldrich
Lithium bis(trimethylsilyl)amide solution, 1.5 M in THF
Sigma-Aldrich
Hexamethyldisilazane, produced by Wacker Chemie AG, Burghausen, Germany, ≥97.0% (GC)
Sigma-Aldrich
Lithium bis(trimethylsilyl)amide solution, 1.0 M in hexanes
Sigma-Aldrich
Sodium bis(trimethylsilyl)amide solution, produced by Wacker Chemie AG, Burghausen, Germany, 40% in THF
Sigma-Aldrich
Sodium bis(trimethylsilyl)amide solution, 0.6 M in toluene
Sigma-Aldrich
Octadecylsilane, 97%
Sigma-Aldrich
Tetramethyl orthosilicate, purum, ≥98.0% (GC)
Sigma-Aldrich
Tris[N,N-bis(trimethylsilyl)amide]yttrium
Sigma-Aldrich
Trimethoxymethylsilane, purum, ≥98.0% (GC)
Sigma-Aldrich
Tris[N,N-Bis(trimethylsilyl)amide]gadolinium(III), 98%
Sigma-Aldrich
Trimethoxymethylsilane, deposition grade, ≥98%
Sigma-Aldrich
Lithium bis(trimethylsilyl)amide solution, 1 M in tert-butyl methyl ether
Sigma-Aldrich
Potassium bis(trimethylsilyl)amide solution, 1.0 M in methyl tert-butyl ether
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Tris[N,N-bis(trimethylsilyl)amide]samarium(III), 98%
Sigma-Aldrich
Tris[N,N-bis(trimethylsilyl)amide]europium(III), 98%