Alkali Metal Modification of Silica Gel-Based Stationary Phase in Gas Chromatography

Ashraf Yehia El-Naggar

doi:10.1155/2013/982029

Abstract

Modification of the precipitated silica gel was done by treatment with alkali metal (NaCl) before and after calcination. The silica surfaces before and after modification were confirmed by infrared spectroscopy in order to observe the strength and abundance of the acidic surface OH group bands which play an important role in the adsorption properties of polar and nonpolar solutes. The surface-modified silica gels were tested as GC solid stationary phases in terms of the separation efficiency for various groups of non-polar and polar solutes. Also, thermodynamic parameters (<svg style="vertical-align:-0.0pt;width:25.924999px;" id="M1" height="11.425" version="1.1" viewBox="0 0 25.924999 11.425" width="25.924999" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns="http://www.w3.org/2000/svg"> <g transform="matrix(.017,-0,0,-.017,.062,11.363)"><path id="x394" d="M600 0h-557v24l268 633l28 8l261 -641v-24zM497 50l-194 489l-196 -489h390z" /></g><g transform="matrix(.017,-0,0,-.017,10.959,11.363)"><path id="x1D43B" d="M865 650q-1 -4 -4 -14t-4 -14q-62 -5 -77 -19.5t-29 -82.5l-74 -394q-12 -61 -0.5 -77t75.5 -21l-6 -28h-273l8 28q64 5 82 21t29 76l36 198h-380l-37 -197q-11 -64 0.5 -78.5t79.5 -19.5l-6 -28h-268l6 28q60 6 75.5 21.5t26.5 76.5l75 394q13 66 2 81.5t-77 20.5l8 28
h263l-6 -28q-58 -5 -75.5 -21t-30.5 -81l-26 -153h377l29 153q12 67 2 81t-74 21l5 28h268z" /></g> </svg>, <svg style="vertical-align:-0.23206pt;width:23.325001px;" id="M2" height="11.75" version="1.1" viewBox="0 0 23.325001 11.75" width="23.325001" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns="http://www.w3.org/2000/svg"> <g transform="matrix(.017,-0,0,-.017,.062,11.4)"><use xlink:href="#x394"/></g><g transform="matrix(.017,-0,0,-.017,10.959,11.4)"><path id="x1D43A" d="M713 296l-5 -25q-47 -7 -59 -20t-23 -72l-15 -79q-9 -48 -3 -74q-15 -3 -55 -13t-63 -15t-59.5 -10t-70.5 -5q-149 0 -243 80t-94 220q0 169 127.5 276.5t336.5 107.5q91 0 206 -36l-10 -165l-29 -1q1 85 -47.5 126t-146.5 41q-153 0 -243.5 -97t-90.5 -242
q0 -122 68.5 -198.5t188.5 -76.5q121 0 139 75l20 86q13 58 -1.5 70.5t-99.5 20.5l5 26h267z" /></g> </svg>, and <svg style="vertical-align:-0.23206pt;width:19.174999px;" id="M3" height="11.75" version="1.1" viewBox="0 0 19.174999 11.75" width="19.174999" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns="http://www.w3.org/2000/svg"> <g transform="matrix(.017,-0,0,-.017,.062,11.4)"><use xlink:href="#x394"/></g><g transform="matrix(.017,-0,0,-.017,10.959,11.4)"><path id="x1D446" d="M457 488l-30 -3q-17 148 -131 148q-53 0 -84.5 -34.5t-31.5 -82.5q0 -42 25.5 -72t74.5 -62l33 -22q63 -42 95 -85t32 -102q0 -84 -67 -137t-163 -53q-58 0 -113 22t-70 43l-4 152l27 4q4 -32 15 -62.5t31 -59.5t53.5 -47t76.5 -18q56 0 92 35t36 96q0 39 -25 70t-78 68
l-31 22q-32 23 -53.5 41.5t-45 57t-23.5 77.5q0 82 58 132.5t156 50.5q46 0 101 -17l18.5 -6t17 -6t8.5 -3q-4 -55 0 -147z" /></g> </svg>) were determined using <i >n</i>-hexane as a probe in order to show the adsorbate-adsorbent interaction. It was observed that the non-polar solutes could be separated Independent on the reactivity and porosity of the silica surfaces. The efficiency of the surface-modified silica gels to separate the aromatic hydrocarbons seemed to be strongly influenced by the density of the surface hydroxyls.

Highlights

The technique of bonding with transition metal complexesinvolves bonding the transition metals to support surface with the help of suitable ligand having their hydrocarbon chain terminated with appropriate functional group in order to form π-complexes [1]
Wasiak et al [18,19,20,21,22] produced selective complexing sorbent which solves many analytical problems such as (i) the use of Ni and Co complexes bonded to the silica surface via β-diketonate groups to elute alkane-alkene pairs [18] or via thiol groups for separation of cyclic hydrocarbons, cyclic ethers, and chloro derivatives of aliphatic hydrocarbons [19] and (ii) bonded Cu, Ni, and Cr to the silica surface via ketoamino groups to elute halogenated hydrocarbons, geometric isomers, olefin, ethers, thioethers, cyclic hydrocarbons, aromatic, and ketones [20,21,22]
All parent and modified samples were subject to an inverse gas chromatography to evaluate their efficiency when used as a solid stationary phases or solid support

Summary

Introduction

The technique of bonding with transition metal complexesinvolves bonding the transition metals to support surface with the help of suitable ligand (mostly silanes) having their hydrocarbon chain terminated with appropriate functional group in order to form π-complexes [1]. Using such complexes in GC is characterized by high selectivity to separate compounds of similar chemical structure and boiling temperatures (like separation of different types of isomers and isotopes), thermal stability, and high resistance to external factors [2]. Enantioselective complexation gas chromatography has been reviewed [25]

Experimental

Modification Methods

Treating with Alkali Metal

Result and Discussion

Conclusion