Hatsuichi Ohta

Fullerenes separation with monomeric type C30 stationary phase in high-performance liquid chromatography

The temperature effect on the separation of fullerenes in LC was examined using monomeric type C30, C18 and C8 alkyl bonded stationary phases. It appears that the C30 phase exhibits superior separation ability for fullerenes. It is observed that the maximum retention temperature of fullerenes on the C30 phase is around 20 degrees C. A strong correlation between the changes in NMR spectra and the retention behavior of the solutes was found. The interpretation of the retention behavior of fullerenes on the alkyl bonded stationary phases, including the behavior in subambient temperature, is discussed using the information obtained by CP-MAS solid-state NMR spectroscopy and LC.

Dimethoxyphenylpropyl bonded silica phase for higher fullerenes separation by high-performance liquid chromatography

Fullerenes were separated using three chemically bonded phases, dimethoxyphenylpropyl (DMP), monomeric octadecyl and polymeric octadecyl modified silicas (ODS), with n-hexane as the mobile phase. DMP and the monomeric ODS are the best choices for the separation of C60 and C70 compounds, while DMP is the only phase that has high temperature stability while maintaining the resolution. For the separation of higher fullerenes, DMP offers faster analysis at higher temperatures while maintaining its high resolution, whereas ODS phases cannot provide similar run times while offering the same resolution. In conclusion, DMP is the most suitable and promising stationary phase for fullerenes analysis because of the short run time and its superior separation efficiency.

Separation and identification of higher fullerenes in soot extract by liquid chromatography-mass spectrometry

SummaryTwo-step liquid chromatographic separation (LC) has been applied to soot extract and the identification of higher fullerenes has been accomplished by LC-MS measurements using an ESI interface. The first separation step is preparative-scale LC using a 50 mm i.d. column packed with monomeric octadecylisilica (ODS) because elution is mainly controlled by relative molecular mass. 39 batches of five fractions each were collected and then as the second separation step each fraction was analysed by analytical-scale LC using a conventional column of a polymeric ODS phase which can elute fullerenes according to shape and structure. This stationary phase can also separate many isomers of higher fullerenes, consequently the existence of several higher fullerenes larger than C86 has been confirmed and their UV-Vis spectra were obtained by the photodiode array detection system coupled to the analytical LC.

Effect of temperature on the mechanism of retention of fullerenes in liquid chromatography using various alkyl bonded stationary phases

SummaryThe temperature-dependency of the separation of fullerenes in liquid chromatography (LC) has been examined using various alkyl bonded stationary phases. It has been found that a maximum retention temperature exists with long alkyl bonded stationary phases, whereas there is no similar effect with the newly synthesized alkyl bonded phases which have two phenyl groups at the base of the bonded phase. The interpretation of the retention behavior of fullerenes in the low temperature region on alkyl bonded stationary phases is discussed using information obtained by CP-MAS solid-state NMR spectroscopy and LC.

Temperature effect in separation of fullerene by high-performance liquid chromatography

SummaryThe effect of column temperature, especially at low temperatures, on the separation of fullerenes on monomeric and polymeric octadecyl silica (ODS) bonded phases has been studied. Decreasing the column temperature induces an increase in selectivity. The best temperature for the separation of fullerenes was determined for both types of ODS phase with n-hexane eluent. The selectivity for higher fullerenes on monomeric phases becomes similar to that on polymeric phases to low temperature. It has been found that as the carbon content of monomeric phases is increased, the selectivity also becomes similar to polymeric phases.

Nano-scale design of novel stationary phases to enhance selectivity for molecular shape and size in liquid chromatography

Abstract The design of novel stationary phases in liquid chromatography (LC) which offer enhanced selectivity or better resolution of fullerenes is described. Fullerene molecules have been chosen due to their recent popularity and importance in both chemistry and the materials science fields. From the previous studies on octadecyl modified silica (ODS) stationary phases in LC an important structural requirement for stationary phases that can effectively separate fullerenes has been identified. The distance between each bonded functional group on the silica surface that is best-fit to the fullerene diameter (e.g. C60 has ca. 7 A diameter and inter-ligand distance 7.1 A of ODS phase is the best-fit size) is the key to improve the separation performance. A phenyl ligand contribution to fullerenes retention has also been found to be important. The size and shape of the cavity-like multilegged phenyl bonded phases is the dominant parameter for the structural recognition of fullerenes. By utilizing these factors a novel stationary phase structure is proposed.

Retention of Fullerenes by Octadecyl Silica. Correlation with NMR Spectra at Low Temperatures

SummaryThe temperature effect on the retention of fullerenes in the range 80°C to −70°C in liquid chromatography (LC) has been examined using octadecylsilica stationary phases (ODS). It has been found that the maximum retention temperature lies around −10°C with a highly carbon loaded ODS phase. Solid state CPMAS NMR measurements on the stationary phases indicated that the relaxation time at the 30 ppm methylene signal changes with the temperature and has a minimum relaxation time at the temperature which closely matches the maximum retention temperature observed in chromatography. The interpretation of both NMR spectroscopic and LC chromatographic data are discussed.

Peer Reviewed: Chromatographic Separation of Fullerenes

Not only are they distinctive and fun to look at, but their PAH-like behavior can also be used to characterize chromatography stationary phases.

Separation of fullerenes with novel stationary phases in microcolumn high performance liquid chromatography

Abstract Newly designed bonded phases have been synthesized and evaluated for the separation of fullerene molecules. Further investigations about the retention behaviour of fullerenes with these phases have been carried out systematically. In this study we describe the separation of fullerenes with novel bonded stationary phases in microcolumn high performance liquid chromatography (micro-HPLC) and also propose the basic separation mechanism of those molecules obtained from the preliminary chromatographic observations. The results indicate that the octadecyldiphenyl bonded silica phases, which have been synthesized from octadecyldiphenylchlorosilane as the silanization reagent, possess a better retentivity for fullerenes than the octadecyldimethylsilica phase (i.e. monomeric ODS phase) having a similar surface coverage value.

Separation of C60 and C70 Fullerenes with a Triphenyl Bonded Silica Phase in Microcolumn Liquid Chromatography

Abstract C60 and C70 fullerenes were chromatographically separated with triphenyl, diphenyl and monophenyl bonded silica phases in microcolumn liquid chromatography. The results indicate that the triphenyl bonded phase having the narrowest pore size possesses the best separation performance among the evaluated phases. The retention power of the triphenyl bonded phase for C60 and C70 was much greater than that of typical octadecylsilica (ODS) phases, although the separation factor between C60 and C70 was almost comparable to that of ODS phases. With the triphenyl bonded phase, a smaller temperature dependence than ODS phases was observed for the separation of C60 and C70.