On‐column titration and investigation of metal complex formation for aminopolycarboxylate functionalised monoliths using scanning contactless conductivity detection

Abstract

The application of scanning capacitively coupled contactless conductivity detection (SC(4)D) for the determination of pH dependant behaviour of two aminopolycarboxylates immobilised onto the surface of a monolithic capillary column is described. The use of SC(4)D to visualise changes in conductivity of the discrete zones of functional groups within monolithic capillary columns allows for the effects of immobilisation on the physicochemical properties of zones to be compared to that of the functional group in solution. The perturbation of the pK(a) values of the functional groups can be attributed to the change in chemical environment experienced by the functional group through the presence of local hydrogen bonding and surface induced effects. These bonds, both between adjacent functional groups and with the monolithic polymethacrylate scaffold, result in a modification of the electron density on the functional group and therefore a change in pK(a). Changes in the pK(a) of N-(2-acetamido)iminodiacetic acid (ADA) from 2.48 to 5.2 for one of the acidic protons, with little change in the pK(a) of the amine group, were observed, which correlates to similar changes in aggregated systems of aminopolycarboxylates. Similar results were obtained for the iminodiacetic acid (IDA) once immobilised onto the surface of the monolith. Furthermore, the ability to measure changes in the charge of such discrete zones of functional groups allows for the visualisation of complexation events occurring directly on-column, where such complexes result in a change in charge of the functional group. This potentially useful technique is illustrated within for the formation of aminopolycarboxylate complexes with a selection of metal ions.

Monitoring gradient profile on-line in micro- and nano-high performance liquid chromatography using conductivity detection

“…Because C 4 D actually measures the admittance of a solution, it is also termed admittance detection [12,13]. C 4 D has been used for characterizing stationary-phases during elutions [14,15], but few have reported using it for monitoring eluent gradient profiles in micro-or nano-HPLC systems.…”

Fabrication and characterisation of capillary polymeric monoliths incorporating continuous stationary phase gradients

“…Monoliths comprising VAL as co-monomer, or monoliths incorporating a grafted layer of azlactone polymer chains have been shown to be an effective means of immobilising proteins via the amine group of exposed lysine residues [27] and more recently for the immobilisation of small molecules which contain a free amine group [22,23]. Reaction between azlactone and amine functional groups has been shown to occur rapidly at room temperature and across the pH range in comparison to the slower epoxy chemistry which generally must be carried out at elevated temperature and pH [25].…”

“…A conductivity profile was collected for Column IDA]1 using a pH 9 buffer (2.5 mM TES/3 mM ethanolamine) during data collection in order to maximise the stationary phase charge due to deprotonation of both carboxylate groups on the immobilised IDA as described by Gillespie et al [23]. A comparison of conductivity profiles before (i) and after (ii) immobilisation of IDA on the azlactone gradient is shown in Fig.…”

Click N-benzyl iminodiacetic acid: Novel silica-based tridentate zwitterionic stationary phase for hydrophilic interaction liquid chromatography

“…Iminodiacetic acid (IDA) is a dicarboxylic acid amine, which can act as a tridentate ligand. Chelex 100 resin, which is a styrenedivinylbenzene copolymer containing IDA groups, has been utilized in ion exchange columns, DNA extraction in preparation for polymerase chain reaction (PCR), trace metal removal, metal analysis, as well as in water testing in environmental and agricultural laboratories [43][44][45]. All of these applications are attributed to the strong interactions between IDA and polar or charged compounds, and these interactions should be stronger than the bidentate ligand such as α, β-amino acid.…”