Microfluidic Behavior of Ternary Mixed Carrier Solvents Based on the Tube Radial Distribution in Triple-Branched Microchannels in a Microchip

doi:10.4236/jasmi.2012.22010

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Journal of Analytical Sciences, Methods and Instrumentation, 2012, 2, 49-53

http://dx.doi.org/10.4236/jasmi.2012.22010 Published Online June 2012 (http://www.SciRP.org/journal/jasmi)

Microfluidic Behavior of Ternary Mixed Carrier Solvents

Based on the Tube Radial Distribution in Triple-Branched

Microchannels in a Microchip

Naoya Jinno, Masahiko Hashimoto, Kazuhiko Tsukagoshi*

Department of Chemical Engineering and Materials Science, Faculty of Science and Engineering, Doshisha University, Kyotanabe,

Japan.

Email: *[email protected]

Received March 1st, 2012; revised March 21st, 2012; accepted April 8th, 2012

ABSTRACT

Microfluidic behavior of ternary mixed carrier solvents of water-acetonitrile-ethyl acetate (2:3:1 volume ratio) was ex-

amined by use of a microchip incorporating microchannels in which one wide channel was separated into three narrow

channels, i.e., triple-branched microchannels. When the ternary carrier solution containing the fluorescent dyes, hydro-

phobic perylene (blue) and relatively hydrophilic Eosin Y (green), was fed into the wide channel under laminar flow

conditions, the carrier solvent molecules or fluorescence dyes were radially distributed in the channel, forming inner

(organic solvent-rich major; blue) and outer (water-rich minor; green) phases in the wide channel. And then, in the nar-

row channels, perylene molecules mostly appeared to flow through the center narrow channel and Eosin Y, which is

distributed in the outer phases in the wide channel, flowed through the both side narrow channels. A metal ion, Cu(II) as

a model, dissolved in the ternary mixed carrier solution was also examined. The Cu(II) showed fluidic behavior, trans-

ferring from the homogeneous carrier solution to the water-rich solution in the side narrow channels through the tri-

ple-branched microchannels.

Keywords: Triple-Branched Microchannels; Ternary Mixed Solvents; Fluorescence Dyes; Metal Ion; Tube Radial

Distribution Phenomenon (TRDP)

1. Introduction

The development of micro total analysis systems that

include a microchip or microfluidic device technology is

an interesting aspect of analytical chemistry [1,2]. Mi-

crofluidics exhibit various types of fluidic behavior of

solvents in a microchannel. The microfluidic behavior

has been examined by varying the channel configuration

and flow rate of the solvents, by using aqueous-organic

solvent mixtures, and by introducing specific obstacles

into the microchannel [3-5]. The fluidic behavior of the

solvents in the microchannel is related to the mixing,

separation, diffusion, and reaction of the solutes. Infor-

mation regarding the flow pattern of the solvents is im-

portant and useful to design microreactors or micro total

analysis systems [6,7].

Recently, we reported that when ternary mixed solvents

of water-hydrophilic/hydrophobic organic solvents are

fed into a microspace, such as microchannels in a micro-

chip or capillary tubes, the solvent molecules are radially

distributed under laminar flow conditions. This is called

the “tube radial distribution phenomenon” (TRDP) [8-

11]. In TRDP, in an organic solvent-rich carrier solution,

the organic solvent-rich major phase is formed around

the center of the microspace as an inner phase, while the

water-rich minor phase is formed near the inner wall as

an outer phase. On the other hand, in the water-rich car-

rier solution, the water-rich major phase is formed as an

inner phase and the organic solvent-rich minor phase as

an outer phase. TRDP forms a specific liquid-liquid

interface, which is not static but kinetic, in a micro-

space.

Until now, TRDP has been investigated by use of mainly

capillary tubes and straight single line microchannels

[8-11]. The triple-branched microchannels in which one

wide channel was separated into three narrow channels in

a microchip was designed and manufactured in our pre-

vious study to conform TRDP, where the ternary mixed

carrier solution was fed from the three narrow channels

to the one wide channels [8]. In this study microfluidic

behavior of the ternary mixed carrier solution in the tri-

ple-branched microchannels was examined with the re-

verse flow direction against the previous paper [8], i.e.,

*Corresponding author.

Microfluidic Behavior of Ternary Mixed Carrier Solvents Based on the Tube Radial Distribution

in Triple-Branched Microchannels in a Microchip

the flow direction form the one wide channel to the three

narrow channels. By the experiments, we could observe

unique fluidic behavior of the solvents and solutes in the

microchannels based on TRDP. The preliminary results

reported in a communication previously [12].

2. Experimental

2.1. Reagents and Materials

Water was purified with an Elix 3 UV system (Millipore

Co., Billerica, MA). All reagents used were obtained

commercially and were of analytical grade. Perylene,

Eosin Y, acetonitrile, ethyl acetate, and Cu(II) chloride

were purchased from Wako Pure Chemical Industries,

Ltd. (Osaka, Japan). Orange G was purchased from

Nacalai Tesque, Inc. (Kyoto, Japan). A microchip made

of quartz incorporating microchannels was manufactured

with Microchemical Technology (Kanagawa, Japan).

Figure 1 illustrates the setup of the microchip in the mi-

crochip holder (Figure 1(a)) and the enlarged view of the

microchip incorporating the triple-branched microchan-

nels (Figure 1(b)). As shown in Figure 1(b)), one wide

channel (300 μm wide × 40 μm deep) denoted as channel

W was separated into three narrow channels (each 100

μm wide × 40 μm deep) designated as channels N1-N3.

2.2. Fluorescence Microscope Equipped with a

CCD Camera System

A microchip incorporating the microchannels was set up

for the fluorescence microscope-CCD camera system.

Fluorescence in the microchannel was monitored using a

fluorescence microscope (BX51; Olympus, Tokyo, Japan)

equipped with an Hg lamp, a filter (U-MWU2, ex. 330 -

385 nm, em. >420 nm), and a CCD camera (JK-TU53H).

The ternary mixed solvents of the water-acetonitrile-

ethyl acetate mixture (3:8:4 volume ratio) contained 0.1

mM perylene and 1 mM Eosin Y. The carrier solution

was fed into the microchannels using a microsyringe

pump.

2.3. Cu(II) Analysis

The homogenous carrier solution of the water–acetone-

trile-ethyl acetate mixture (2:3:1 volume ratio) including

2.0 mM Cu(II) was fed into channel W at a definite flow

rate. 100 μL of the solution in channels N1-N3 was col-

lected through polytetrafluoroethylene (PTFE) tubes into

the corresponding vessel. The solution was dried under a

vacuum, and 0.5 M ammonia solution (100 μL) was

added to the residue for flow absorption measurement at

600 nm (modified SPD-6AV spectrophotometric detector,

Shimadzu Co., Kyoto, Japan).

3. Results and Discussion

3.1. Fundamental Experiments for TRDP in a

Microchannel

Microchips with single-branched microchannels having

widths of 100, 200, 300, and 400 μm and identical channel

depth of 40 μm were also manufactured. The influences

of channel width on TRDP in the microchannels were

examined with fluorescent dyes, perylene and Eosin Y,

dissolved in an organic solvent-rich carrier solution (wa-

ter-acetonitrile-ethyl acetate; 3:8:4 volume ratio). The

fluorescence images of the dyes in the solution fed into

the microchannels were observed with the fluorescence

microscope-CCD camera system (Figure 2). The flow

(a) (b)

Figure 1. Schematic representation of (a) setup of the microchip in the microchip holder and (b) the enlarged view of the mi-

crochip incorporating triple-branched microchannels.

Microfluidic Behavior of Ternary Mixed Carrier Solvents Based on the Tube Radial Distribution

in Triple-Branched Microchannels in a Microchip

rates in all microchannels (100 - 400 μm width) were

adjusted to achieve the same average linear velocity of

25 cm·min–1.

It is evident from Figure 2 that TRDP was observed in

all microchannels regardless of the channel width. Hy-

drophobic perylene molecule (blue) was distributed

around the center of the channel away from the side inner

walls of the channel, while relatively hydrophilic Eosin

Y molecule (green) was distributed near the side inner

walls of the channel. That is, the major inner phase (or-

ganic solvent-rich phase) and the minor outer phase (wa-

ter-rich phase) were formed in the microchannels of 100

- 400 μm width.

3.2. Effects of Flow Rates on TRDP in

Triple-Branched Microchannels

The effects of flow rate on TRDP in the triple-branched

microchannels were examined with an organic solvent-

rich carrier solution (water-acetonitrile-ethyl acetate,

3:8:4 volume ratio) containing Orange G by using the

bright-field microscope-CCD camera system. The Or-

ange G-containing carrier solution was fed at the flow

rates of 2.0 - 50.0 μL·min–1. The images are shown in

Figure 3. The hydrophilic Orange G molecule was dis-

tributed near the channel side inner walls, and the inter-

face between the water-rich outer phase and the organic

solvent-rich inner phase was distinguished because of the

color of Orange G (Figure 3). The TRDP was for the

first time observed with a bright-field microscope-CCD

camera system in our TRDP investigation. The system

was confirmed to be useful for TRDP observation in a

similar way to fluorescence system. At the low flow rates

of 2.0 and 5.0 μL·min–1, the liquid-liquid interface was

unstable, considerably changed, or appeared to instanta-

neously disappear, while the stability was observed at the

flow rates higher than 5 μL·min–1.

Thus, flow rates higher than 5 μL·min–1 created a sta-

ble liquid-liquid interface in the triple-branched micro-

channels under the present conditions.

Figure 2. Fluorescence images of fluorescent dyes dissolved

in a ternary mixed carrier solvent in microchannels with

channel widths of 100, 200, 300, and 400 μm and identical

channel depth of 40 μm. Conditions: Carrier, water-ace-

tonitrile-ethyl acetate (3:8:4 v/v/v) mixture including 0.1

mM perylene and 1 mM Eosin Y; and flow rates, 1, 2, 3,

and 4 μL·min–1 for microchannel widths of 100, 200, 300,

and 400 μm, respectively.

Figure 3. Effects of flow rates of the carrier solution on

TRDP. Conditions: Carrier, water-acetonitrile-ethyl acetate

(3:8:4 v/v/v) mixture containing 2 mM Orange G and flow

rate, 2.0 - 50 μL·min–1 for channel W.

(a) (b)

Figure 4. Fluorescence images of fluorescent dyes dissolved

in a mixed carrier solvent in triple-branched microchannels.

(a) Water-acetonitrile (1:4 v/v) and (b) water-acetonetrile-

ethyl acetate (3:8:4 v/v/v) mixtures. Conditions: Carrier,

aqueous-organic mixtures including 0.1 mM perylene and 1

mM Eosin Y; and flow rate, 6.3 μL·min–1 for channel W.

3.3. Fluorescence Images of the Dyes Based on

TRDP in Triple-Branched Microchannels

The microchip incorporating triple-branched microchannels

was shown in Figure 1(b) with their measurements. The

organic solvent-rich carrier solution (water-acetonitrile-

ethyl acetate, 3:8:4 volume ratio) containing Eosin Y and

perylene was fed into channel W of the microchip at the

flow rate of 6.3 μL·min–1. The mixture carrier solution

excluding ethyl acetate (water-acetonitrile, 1:4 volume

ratio) but containing the dyes was also fed into the

channel as a reference. Figure 4 shows the fluorescence

images of the dyes in the triple-branched microchannels

of the microchip. Figures 4(a) and (b) were obtained

with the water-acetonitrile mixture as a reference and the

water-acetonitrile-ethyl acetate mixture as ternary mixed

solvents, respectively.

The distribution behavior of the dyes, i.e., TRDP, was

not observed in the image of Figure 4(a) with the water-

acetonitrile mixture. On the contrary, the image of

Figure 4(b) with the ternary solvent mixture shows TRDP,

in which the hydrophobic perylene molecule (blue) was

distributed around the center of channel W away from

the channel side inner walls, while relatively hydrophilic

Eosin Y molecule (green) was distributed near the channel

side inner walls. The distribution phenomena of the ternary

mixed carrier solvents fed into the microchannels was

evident in the wide channel. And then, perylene molecules

Microfluidic Behavior of Ternary Mixed Carrier Solvents Based on the Tube Radial Distribution

in Triple-Branched Microchannels in a Microchip

mostly appeared to flow through the center channel

(channel N2) and Eosin Y, which is distributed in the

outer phases in channel W, flowed through channels N1

and N3, as shown in Figure 4(b).

3.4. Distribution of Eosin Y Based on TRDP in

Triple-Branched Microchannels

The homogenous carrier solution of the water–acetone-

trile-ethyl acetate mixture (3:8:4 volume ratio) including

0.5 mM Eosin Y was fed into channel W at a flow rate of

10 μL·min –1. 100 μL of the solution in channels N1-N3

was collected through PTFE tubes into the corresponding

vessel. The solution was subjected to flow absorption

measurement at 517 nm (modified SPD-6AV spectro-

photometric detector, Shimadzu Co., Kyoto, Japan). Eo-

sin Y concentrations in the center channel (channel N2)

and the two side channels (channels N1 and N3) were

0.36, 0.59, and 0.58 mM, respectively (Figure 5). The

concentrations were averages for five measurements. The

experimental data indicated that relatively hydrophilic

Eosin Y was distributed from the homogeneous carrier

solution to the water-rich solution in the side narrow

channels rather than the organic solvent-rich solution in

the central narrow channel. The distribution of the fluo-

rescent dyes in the triple-branched microchannels might

suggested the possibility of extraction or separation for

some solutes by utilizing the phase interface formed by

TRDP in these channels.

3.5. Distribution of Cu(II) Based on TRDP in

Triple-Branched Microchannels

Distribution of Cu(II) was examined in the triple-

branched microchannels by utilizing the kinetic liquid-

liquid or aqueous-organic interface formed by TRDP.

First, the calibration curve of Cu(II) was examined in a

manner similar to that described in the experimental sec-

tion (Sec 2.3). Cu(II) was determined over the concentra-

tion range of 0.5 - 10 mM with good linearity (R2 =

0.999).

Figure 5. Distribution of Eosin Y from the homogeneous

ternary mixed solution into the outer phases in the side

narrow channels by TRDP. Conditions: Carrier, water-

acetonitrile-ethyl acetate (3:8:4 v/v/v) mixture; flow rate, 10

μL·min–1 for channel W; Eosin Y concentration in the ho-

mogeneous solution, 0.50 mM.

The homogenous carrier solution of the water-ace-

tonitrile-ethyl acetate mixture (2:3:1 volume ratio) in-

cluding 2.0 mM Cu(II) was fed into channel W at the

flow rate of 40 μL·min–1. 100 μL of the solution in chan-

nels N1-N3 was collected with PTFE tubes into the cor-

responding vessel. Cu(II) concentrations in the center

wide channel (channel N2) and the two side channels

(channels N1 and N3) were 0.8, 2.5, and 2.7 mM, respec-

tively (Figure 6(a)). The concentrations were averages

for five measurements. As a reference, Cu(II) concentra-

tions were examined with the water-acetonitrile (2:3

volume ratio) carrier solution in a similar manner. Cu(II)

concentrations in channels N1-N3 were 2.1, 2.1, and 2.0

mM, respectively (Figure 6(b)). The experimental data

indicated that Cu(II) was extracted to the water-rich solu-

tion in the side narrow channels from the homogeneous

solution by the formation of a phase interface in the mi-

crochannel; we refer to this process as tube radial distri-

bution extraction (TRDE).

Moreover, we examined the Cu(II) distribution by

TRDE at other flow rates of 32 and 63 μL·min–1 in

channel W. At 32 μL·min–1, Cu(II) concentrations in the

center channel (channel N2) and the two side channels

(channels N1 and N3) were 0.8, 3.0, and 2.9 mM,

whereas, at 63 μL min–1, those were 1.1, 2.9, and 2.7 mM,

respectively. Comparing with the Cu(II) concentration,

2.0 mM, in the homogeneous carrier solution, the Cu(II)

concentration in the solution collected from the center

channel (channel N2) decreased, while that from the two

side channels (channels N1 and N3) increased at every

(a)

(b)

Figure 6. Distribution of Cu(II) in triple-branched micro-

channels. (a) Water-acetonitrile-ethyl acetate (2:3:1 v/v/v)

mixture and (b) water-acetonitrile (2:3 v/v) mixture carrier

solution. Conditions: Flow rate, 40 μL·min−1 for channel W

and Cu(II) concentration in the homogeneous solution, 2.0

mM.

Microfluidic Behavior of Ternary Mixed Carrier Solvents Based on the Tube Radial Distribution

in Triple-Branched Microchannels in a Microchip

flow rates. The obtained data showed that TRDE oc-

curred in the triple-branched microchannels of the mi-

crochip.

4. Conclusion

TRDP has been investigated by use of mainly capillary

tubes and straight single line microchannels. The TRDP

of the ternary mixed carrier solution in the triple-

branched microchannels was observed with fluorescence

microscope-CCD camera system. Consequently, pery-

lene molecules mostly appeared to flow through the cen-

ter narrow channel and Eosin Y flowed through channels

in the side narrow channels. The TRDP was also ob-

served through bright-light microscope-CCD camera

system. We tried to apply the phase interface formed by

TRDP, i.e., inner and outer phases, to the distribution or

extraction procedure of Cu(II) in the triple-branched mi-

crochannels. This process will be helpful for investigat-

ing separation and extraction in a microfluidic device.

5. Acknowledgements

This work was supported by a Grant-in-Aid for Scientific

Research (C) from the Ministry of Education, Culture,

Sports, Science, and Technology, Japan. This work was

also supported by “Advanced Study for Integrated Parti-

cle Science, and Technology,” Strategic Development of

Research Infrastructure for Private Universities, the Mini-

stry of Education, Culture, Sports, Science, and Techno-

logy, Japan.

REFERENCES

[1] K. Ueno, F. Kitagawa and N. Kitamura, “One-Step Elec-

trochemical Cyanation Reaction of Pyrene in Polymer

Microchannel-Electrode Chips,” Bulletin of the Chemical

Society of Japan, Vol. 77, No. 7, 2011, pp. 1331-1338.

doi:10.1246/bcsj.77.1331

[2] D. R. Reyes, D. Iossifidis, P. A. Auroux and A. Manz,

“Micro Total Analysis Systems. 1. Introduction, Theory,

and Technology,” Analytical Chemistry, Vol. 74, No. 12,

2002, pp. 2623-2636. doi:10.1021/ac0202435

[3] Y. Kikutani, H. Hisamoto, M. Tokeshi and T. Kitamori,

“Micro Wet Analysis System Using Multi-Phase Laminar

Flows in Three-Dimensional Microchannel Network,”

Lab on a Chip, Vol. 4, No. 4, 2004, pp. 328-332.

doi:10.1039/b400233d

[4] A. Hibara, M. Tokeshi, K. Uchiyama, H. Hisamoto and T.

Kitamori, “Integrated Multilayer Flow System on a Mi-

crochip,” Analytical Sciences, Vol. 17, No. 1, 2001, pp.

89-93. doi:10.2116/analsci.17.89

[5] N. Kaji, Y. Okamoto, M. Tokeshi and Y. Baba, “Nano-

pillar, Nanoball, and Nanofibers for Highly Efficient

Analysis of Biomolecules,” Chemical Society Reviews,

Vol. 39, No. 3, 2010, pp. 948-956. doi:10.1039/b900410f

[6] H. Nakamura, Y. Yamaguchi, M. Miyazaki, H. Maeda

and M. Uehara, “Preparation of CdSe Nanocrystals in a

Micro-Flow-Reactor,” Chemical Communications, No. 23,

2002, pp. 2844-2845. doi:10.1039/b208992k

[7] H. Kawazumi, A. Tashiro, K. Ogino and H. Maeda, “Ob-

servation of Fluidic Behavior in a Polymethylmethacry-

late-Fabricated Microchannel by a Simple Spectroscopic

Analysis,” Lab on a C h ip, Vol. 2, No. 1, 2002, pp. 8-10.

doi:10.1039/b109058e

[8] N. Jinno, M. Murakami, K. Mizohata, M. Hashimoto and

K. Tsukagoshi, “Fluorescence Observation Supporting

Capillary Chromatography Based on Tube Radial Distri-

bution of Carrier Solvents under Laminar Flow Condi-

tions,” Analyst, Vol. 136, No. 5, 2011, pp. 927-932.

doi:10.1039/c0an00820f

[9] N. Jinno, M. Hashimoto and K. Tsukagoshi, “Experi-

mental Consideration of Capillary Chromatography

Based on Tube Radial Distribution of Ternary Mixture

Carrier Solvents under Laminar Flow Conditions,” Ana-

lytical Sciences, Vol. 27, No. 3, 2011, pp. 259-264.

doi:10.2116/analsci.27.259

[10] M. Murakami, N. Jinno, M. Hashimoto and K. Tsukago-

shi, “Tube Radial Distribution Phenomenon of Ternary

Mixed Solvents in a Microspace under Laminar Flow

Conditions,” Analytical Sciences, Vol. 27, No. 8, 2011,

pp. 793-798. doi:10.2116/analsci.27.793

[11] S. Fujinaga, N. Jinno, M. Hashimoto and K. Tsukagoshi,

“Use of Tube Radial Distribution of Ternary Mixed Car-

rier Solvents for Introduction of Absorption Reagent for

Metal Ion Separation and Online Detection into Capil-

lary,” Journal of Separation Science, Vol. 34, No. 20,

2011, pp. 2833-2839. doi:10.1002/jssc.201100404

[12] N. Jinno, M. Hashimoto and K. Tsukagoshi, “Extraction

of Cu(II) Based on Tube Radial Distribution of Ternary

Mixed Carrier Solvent in Microchannels,” Chemistry

Letters, Vol. 40, No. 6, 2011, pp. 654-655.

doi:10.1246/cl.2011.654