STUDY OF OUTER PHASES IN CAPILLARY CHROMATOGRAPHY BASED ON TUBE RADIAL DISTRIBUTION OF CARRIER SOLVENTS UNDER LAMINAR FLOW CONDITIONS

Phase-separation multiphase flow: preliminary application to analytical chemistry

A two-phase separation mixed solution can undergo phase separation from one phase to two phases (i.e., upper and lower phases) in a batch vessel in response to changes in temperature and/or pressure. This phase separation is reversible. When the mixed solution undergoes a phase change while being fed into a microspace region, a dynamic liquid-liquid interface is formed, leading to a multiphase structure. This flow is called a phase-separation multiphase flow. Annular flow in a microspace, which is one such phase-separation multiphase flow, is interesting and has been applied to chromatography, extraction, reaction fields, and mixing. Here, research papers related to phase-separation multiphase flows-ranging from the discovery of the phenomenon to basic and technical research from the viewpoint of analytical science-are reviewed. In addition, the development of a new separation mode in a high-performance liquid chromatography system based on phase-separation multiphase flow is introduced.

Development of a HPLC system using a phase-separation multiphase flow as an eluent coupled to a silica-particle packed column

The study reports the development of a high-performance liquid chromatography (HPLC) system in which a phase-separation multiphase flow as the eluent and a silica-particle based packed column as the separation column were combined to form the phase separation mode. Twenty-four types of mixed solutions of water/acetonitrile/ethyl acetate and water/acetonitrile were applied as eluents to the system at 20 °C. 2,6-Naphthalenedisulfonic acid (NDS) and 1-naphthol (NA) were injected as model analytes into the system. They showed separation tendency in organic solvent-rich eluents in normal-phase mode and NA was detected earlier than NDS. Subsequently, seven types of the ternary mixed solutions were examined as eluents in the HPLC system at 20 °C and 0 °C. These mixed solutions worked as a two-phase separation mixed solution, providing a phase-separation multiphase flow at 0 °C in the separation column. In the organic solvent-rich eluent, the mixture of analytes was separated at both 20 °C (normal-phase mode) and 0 °C (phase-separation mode), with NA being detected earlier than NDS. The separation at 0 °C was more efficient than at 20 °C. In the water-rich eluent, the mixture of NDS and NA was not separated at 20 °C but was separated at 0 °C (phase-separation mode), with NDS being detected earlier than NA. We also discussed the separation mechanism of phase-separation mode in HPLC together with the computer simulation for the multiphase flow in the cylindrical tube having sub-μm inner diameter.

Consecutive Sample Injection Analysis in Tube Radial Distribution Chromatography

Tube radial distribution chromatography based on the tube radial distribution flow, or annular flow, in an open-tubular capillary has been reported, where the annular flow is created through phase-separation multiphase flow. We have proposed the first-ever procedure for consecutive sample injection analysis using chromatography. In basic terms, a commercially available HPLC system could be used with a sample injector (0.2 μL volume) and a fused-silica capillary tube (250 cm long) as a separation column instead of a normal packed one, while the built-in detection cell was replaced by improved on-capillary detection. A ternary mixed solution of water/acetonitrile/ethyl acetate (3:8:4 volume ratio) was delivered into the capillary tube as an eluent at a flow rate of 2.0 μL min^-1. Model sample solutions of 1-naphthol and 2,6-naphthalenedisulfonic acid were consecutively analyzed by the present chromatography with a processing rate of 6 samples per hour. Simple and rapid consecutive analysis could be performed because washing and initialization of the separation tube was no longer necessary. The obtained results provide clues to developing new methodologies which combine features of both chromatography (separation) and the flow injection method (consecutive analysis).

Development of Tube Radial Distribution Chromatography Based on Phase-Separation Multiphase Flow Created via Pressure Loss

A tube radial distribution chromatography (TRDC) method based on phase-separated multiphase flow created through phase transformation via temperature change has been developed. These systems typically required a temperature-controlling device containing a water bath and a stirrer. Herein, we proposed a novel TRDC system without a cooling device, where the phase transformation was achieved via pressure loss in a capillary tube of 50 μm inner diameter and 550 cm length. Model analytes were successfully separated with the developed TRDC system, which provided a simplified platform and helped to clarify the operating principle of TRDC based on phase transformation in a capillary tube.

Recent advances in open tubular capillary liquid chromatography

This review covers advances and applications of open tubular capillary liquid chromatography (OT-LC) over the period 2007–2018.