Intermolecular interactions on multiwalled carbon nanotubes in reversed-phase liquid chromatography

Application of Carbonaceous Materials in Separation Science

Porous carbons in the separation sciences occupy an important niche owing to their unique retention characteristics, chemical stability and the ability to control pore structure through template strategies. However, these same synthetic processes utilise oil-based carbonising resins and high temperature, energy-intensive pyrolysis steps to ensure the carbon product has pore-size regularity, minimal micropore content and homogeneous surface chemistry. This chapter will primarily focus on the development of porous carbons for application as chromatographic stationary phases. Discussion will cover the unique characteristics of the porous carbon retention mechanism and its application in separating a broad range of analyte classes. The chapter then moves on to describe the current disadvantages in the manufacture of commercially available carbon phase and then highlight recent efforts aimed at the development of alternative porous carbon stationary phases derived from sustainable carbon precursors.

Evaluating the interactions of organic compounds with multi-walled carbon nanotubes by self-packed HPLC column and linear solvation energy relationship

Understanding the interactions between organic pollutants and carbon nanotubes (CNTs) is critical for fate assessment of both CNTs and organic pollutants. In this study, the chromatographic approach was introduced based on CNTs as stationary phase for the evaluation of such interactions. The pristine multi-walled carbon nanotubes (MWCNTs) were packed into columns of high-pressure liquid chromatography (HPLC) and the retention factors (k') were determined to characterize the adsorption affinity of organic compounds onto MWCNTs. Nine compounds were tested. The results showed that their lnk' values followed the order: benzene < toluene < phenol < chlorobenzene < bromobenzene < aniline < sulfamethoxazole < sulfadiazine ≈ sulfadimidine. The linear solvation energy relationship (LSER) theory was adopted to correlate lnk' with the molecular solvatochromic parameters. We found that lnk' of the studied compounds correlate positively with molecular polarizability (E) significantly, suggesting that the π-/n-electrons-dependent polarizable interactions play a major role for the adsorption. Moreover, the thermodynamic parameters calculated from van't Hoff equations revealed that the interactions between the compounds and MWCNTs were spontaneous and exothermic processes.

Carbon nanoparticles from corn stalk soot and its novel application as stationary phase of hydrophilic interaction chromatography and per aqueous liquid chromatography

Carbon nanoparticles (CNPs) (6-18 nm in size) were prepared by refluxing corn stalk soot in nitric acid. The obtained acid-oxidized CNPs are soluble in water due to the existence of carboxylic and hydroxyl groups. (13)C NMR measurement shows the CNPs are mainly of sp(2) and sp(3) carbon structure different from CNPs obtained from candle soot and natural gas soot. Furthermore, these CNPs exhibit unique photoluminescence properties. Interestingly, the CNPs might be exploited to immobilize on the surface of porous silica particles as chromatographic stationary phase. The resultant packing material was evaluated by high-performance liquid chromatography, indicating that the new stationary phase could be used in hydrophilic interaction liquid chromatography (HILIC) and per aqueous liquid chromatography (PALC) modes. The separation of five nucleosides, four sulfa compounds and safflower injection was achieved by using the new column in the HILIC and PALC modes, respectively.

Enrichment of peptides from plasma for peptidome analysis using multiwalled carbon nanotubes

Human plasma contains a complex matrix of proteolytically derived peptides (plasma peptidome) that may provide a correlate of biological events occurring in the entire organism. Analyzing these peptides from a small amount of serum/ plasma is difficult due to the complexity of the sample and the low levels of these peptides. Here, we describe a novel peptidome analysis approach using multiwalled carbon nanotubes (MWCNTs) as an alternative adsorbent to capture endogenous peptides from human plasma. Harvested peptides were analyzed by using liquid chromatography-mass spectrometry as a means of detecting and assessing the adsorbed molecules. The improved sensitivity and resolution obtained by using liquid chromatography-mass spectrometry allowed detection of 2521 peptide features (m/z 300-1800 range) in about 50 microL of plasma. 374 unique peptides were identified with high confidence by two-dimensional liquid chromatography system coupled to a nano-spray ionization linear ion trap-mass spectrometer. High recovery of BSA digest peptides enriched with MWCNTs, in both standard buffer and high abundance protein solution, was observed. Comparative studies showed that MWCNTs were superior to C18 and C8 for the capture of the smaller peptides. This approach could hold promise of routine plasma peptidome analysis.