Enhanced Retention of Chelating Reagents in Octadecylsilyl Silica Phase by Interaction with Residual Silanol Groups in Solid Phase Extraction of Divalent Metal Ions

Abstract

Solid-phase extraction (SPE) of divalent metal ions with a lipophilic and potentially divalent hexadentate chelating reagent (H2L), with which octadecylsilyl silica (ODS) was impregnated, was studied to gain more insight into and develop the potential of this methodology. This is the first time to demonstrate that this reagent as well as other common nitrogencontaining reagents were retained both by adsorption due to hydrogen bonding between nitrogen atoms of the reagent and residual silanol groups in the ODS phase and by simple distribution into the hydrophobic space. An appreciably large amount of this reagent could be retained by the adsorption mechanism even with a relatively thin loading solution. ) with anion in SPE with H2L. The extractability and selectivity were substantially the same as that in liquid-liquid extraction.

Roles of Residual Silanol in Solid Phase Extraction of Copper to Octadecylsilyl Silica in the Presence of Acetylacetone

“…The silica gel SG showed negligibly small retention. Both the isotherms suggested substantially the same characteristics as those of nitrogen-containing compounds, 12 and were thus fitted by Eq. 3as the sum of a simple distribution term and a Langmuir adsorption term by hydrogen bonding between oxygen atom of R and silanol hydrogen:…”

“…11 In a previous work, we have studied the retention of a certain nitrogen-containing compound in an ODS silica subjected to sufficient endcapping treatment and an ODS silica with silanol intentionally left, under ambient pressure. 12 This study has revealed that residual silanol enhances the wettability of the ODS silica even in the absence of any water-miscible organic solvent, that the retention of the compound may be attributed to the sum of the…”

“…21 These reactions are also expected to contribute to the retention of metal ions in SPE to ODS Silica gel (SG, pour size of 50 Å; specific surface area of 680  50 m 2 g -1 ) was reacted with trichlorooctadecylsilane to give non-endcapped ODS silica (NEC) according to the literature. 12,22 A portion of NEC was thoroughly washed and then endcapped by trimethylchlorosilane to give endcapped ODS silica (EC). After equilibration at 25 C and at a relative humidity of 50%, both NEC and EC were subjected to the determination of the carbon content (CC) by elemental analysis and of the water content (WC) by Karl-Fischer coulometry.…”

“…With regard to EC, in contrast, Cu 2+ was not retained enough for the equilibrium analysis.Since the formation of [aa -] is negligible under the present experimental conditions, the mass balances on Cu 2+ and Haa are expressed by Eqs (11). and(12).…”

Effects of Residual Silanol on Solid Phase Extraction of Organic Compounds to Octadecylsilyl Silica

“…22,23 In a previous work, we demonstrated that a hexadentate chelating reagent dissolved in toluene was retained on ODS silica as the sum (defined afresh as retention including isotherms within this paper) of the simple distribution to the ODS phase and the Langmuir adsorption to residual silanol group mechanism. 24 A large amount of the reagent could be retained on the ODS silica containing a large amount of residual silanol by virtue of the Langmuir adsorption term. In the retention of acetylacetone and its metal complex from the aqueous phase on the ODS phase, it was reported that the residual silanol group improves the wettability of the ODS phase and is the donor of the ligand and the metal complex.…”