Phase-separation multiphase flow: preliminary application to analytical chemistry

Abstract

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.

Keywords: High-performance liquid chromatography (HPLC); Phase-separation mode; Phase-separation multiphase flow; Tube radial distribution chromatography (TRDC); Tube radial distribution extraction (TRDE); Tube radial distribution flow (TRDF); Tube radial distribution mixing (TRDM); Tube radial distribution reaction (TRDR).

Fig. 1

Phase-separation multiphase flow [1]

Fig. 2

Schematic of a fluorescence microscope CCD camera and the transformation of a fluorescence photograph to a fluorescence profile through the computer. Reproduced from Ref. [21] with permission

Fig. 3

Phase diagram for water–acetonitrile–ethyl acetate mixed solution, including the solubility curves at 20 °C and 0 °C and fluorescence photographs of TRDF in the microchannel (100 µm wide). Flow rate is 1.0 μL min⁻¹ [21, 24]

Fig. 4

Fluorescence photographs of TRDF in the meandering microchannel. The flow rate is 2.0 μL min⁻¹. Reproduced from Ref. [49] with permission

Fig. 5

TRDF image of an ionic liquid–water mixed solution consisting of [C₄mim]Cl and NaOH, as obtained with a bright-field microscope CCD camera system. Nos. 1–5 are as follows: (No. 1) [C₄mim]Cl:NaOH, 48:6 w/w %; (No. 2) 32:8; (No. 3) 25:10; (No. 4) 20:13; and (No. 5) 13:20. Conditions: capillary tube, 120 cm length (effective length: 100 cm) and 75 µm i.d. fused silica; rhodamine B concentration, 5 mM; tube temperature, 15 °C; and flow rate, 1.0 µL min⁻¹. Reproduced from Ref. [53] with permission

Fig. 6

Computer simulated cross-sectional images of TRDC. a Water–acetonitrile–ethyl acetate mixed solution (3:8:4, volume ratio; organic solvent-rich) and b (4:3:1, volume ratio; water-rich). Reproduced from Ref. [58] with permission

Fig. 7

Schematic of an open-tubular capillary chromatography (TRDC system). Reproduced from Ref. [21] with permission

Fig. 8

Illustration of the separation performance in a capillary tube. a Organic solvent-rich carrier solution and b water-rich carrier solution. Reproduced from Ref. [21] with permission

Fig. 9

Chromatogram of a mixture analyte solution, as obtained by the TRDC system. Conditions: Capillary tube, 120 cm (effective length from the inlet: 100 cm) of 75 µm i.d. fused silica; carrier, water–acetonitrile–ethyl acetate (3:8:4 v/v/v) mixture solution; sample injection, 20 cm height (gravity) × 30 s; flow rate, 0.8 µL min⁻¹; temperature, 20 °C; and 1-naphthol, 1-naphthalenesulfonic acid, and 2,6-naphthalenedisulfonic acid, 1 mM, 1,3,6-naphthalenetrisulfonic acid, 2.0 mM, and eosin Y, 0.1 mM. Reproduced from Ref. [60] with permission

Fig. 10

Fluorescence photographs of solvents containing dissolved fluorescence dyes at the microchannel in a microchip. Conditions: carrier for C1, water–acetonitrile (3:2 volume ratio) containing 1.0 mM eosin Y; carrier for C2 and C3, acetonitrile–ethyl acetate (3:2 volume ratio) containing 0.1 mM perylene; flow rate, 20 µL min⁻¹ for C1 and 4.0 µL min⁻¹ for C2 and C3; volume ratio of water–acetonitrile–ethyl acetate in the wide channel, approximately 20:53:27; temperature, 25 °C (room temperature). Reproduced from Ref. [96] with permission

Fig. 11

Consecutive chromatograms obtained by the TRDC system for various concentrations (two measurements) and mixed analytes (four analytes): a 1-naphthol, b 2,6-naphthalenedisulfonic acid, c 1-naphthalenesulfonic acid, and d 1,3,6-naphthalenetrisulfonic acid. Eluent, water–acetonitrile–ethyl acetate mixed solution (3:8:4, volume ratio); flow rate, 2.0 μL min⁻¹; analyte injection volume, 0.2 μL; cooling temperature, 5 °C; and detection wavelength, 254 nm. Reproduced from Ref. [101] with permission

Fig. 12

Bright-field photographs at the tip of the smaller capillary tube (75 µm i.d.) within the larger tube (200 µm i.d.) at 34 °C. The homogeneous aqueous solution containing 12 wt% Triton X-100, 2.4 M KCl, and 5 mM rhodamine B was fed at a flow rate of 20 µL min⁻¹ into the larger capillary tube. Reproduced from Ref. [107] with permission

Fig. 13

Bright-field images of microfluidic flow in a Y-type micro-channel (100 µm wide and 40 µm deep) for solution (PEG 10.0 wt% and dextran 10.0 wt%) containing 0.1 mM rhodamine B at 40 °C and at flow rate of 5.0 µL min⁻¹. a Equal pressure loss and b unequal pressure loss in the separated Y-type channels. Reproduced from Ref. [45] with permission

Fig. 14

Relationship between the migration times and the fluorescence intensities in the micro-flow reaction (TRDR) system as well as between the reaction time and the fluorescence intensity in the batch reaction system [108]. The solutions included 8.3 µM BSA and 0.67 mM FR for derivatization in the systems. TRDR system (water–acetonitrile–ethyl acetate; 1:2:1 volume ratio) at 7.5, 12, and 15 µL min⁻¹ and batch reaction system (water–acetonitrile; 1:2 volume ratio). Reproduced from Ref. [108] with permission

Fig. 15

Fluorescence photographs of the solvents with the dissolved fluorescent dyes at a the combining point of the channels and b 3 cm from the combining point in a wide channel. The white dashed line indicates the combining point between the narrow channel and wide channel. Conditions: carrier, water–acetonitrile (3:2, volume ratio) containing 3.0 mM eosin Y in a center narrow channel and acetonitrile–ethyl acetate (3:2, volume ratio) containing 0.15 mM perylene in side narrow channels; flow rate, 2.0 µL min⁻¹ for narrow channels. The volume ratio of water–acetonitrile–ethyl acetate in the wide channel is 3:8:4. Reproduced from Ref. [109] with permission

Fig. 16

Schematic of the present HPLC system. A PEEK tube of 100 μm i.d. and 40 cm length; B PEEK tube of 130 μm i.d. and 40 cm length; and C fused silica capillary of 250 μm i.d. and 200 cm length. Analytical conditions for NDS and NA: eluent, water–acetonitrile–ethyl acetate mixed solution; flow rate, 100 μL min⁻¹; injection volume, 20 μL; analyte concentration, 0.5 mM, and column temperature, 0 °C; and detection wavelength, 254 nm. Reproduced from Ref. [114] with permission

Fig. 17

Phase diagram for water–acetonitrile–ethyl acetate mixed solution including the solubility curves at 20 °C and 0 °C. A (20:60:20, water–acetonitrile–ethyl acetate volume ratio), B (70:23:7), and C (60:35:5). Reproduced from Refs. [114, 115] with permission

Fig. 18

Effect of phase-separation mode on chromatograms. ODS column (Shim-pack HT-ODS; Shimadzu, Kyoto, Japan: particle type, nonporous silica base; material: octadecyl-modified silica (ODS); particle diameter, 2 µm; column size, 30 mm length × 4.6 mm inner diameter). Solution A (organic solvent-rich) and Solution B (water-rich). Reproduced from Ref. [114] with permission

Fig. 19

Effect of phase-separation mode on chromatograms. Silica column (Shim-pack XR-SIL; Shimadzu, Kyoto, Japan: Particle type, spherical, porous, high-purity silica particles; particle diameter, 2.2 µm; pore size, 12 nm; and column size, 50 mm length × 2.0 mm inner diameter). Solution A (organic solvent-rich) and Solution C (water-rich). Reproduced from Ref. [115] with permission

Fig. 20

Images of the separation mechanism of the phase-separation mode and the conventional normal- and reversed-phase modes in HPLC. Reproduced from Ref. [115] with permission