U.S. patent application number 15/896734 was filed with the patent office on 2018-08-16 for electrolysis device.
This patent application is currently assigned to ARKRAY, Inc.. The applicant listed for this patent is ARKRAY, Inc.. Invention is credited to Tokuo Kasai.
Application Number | 20180230608 15/896734 |
Document ID | / |
Family ID | 61226452 |
Filed Date | 2018-08-16 |
United States Patent
Application |
20180230608 |
Kind Code |
A1 |
Kasai; Tokuo |
August 16, 2018 |
Electrolysis Device
Abstract
An electrolysis device comprising a cell containing a solution,
a pair of electrodes installed in the cell, and a voltage
application device connected to the pair of electrodes. One
electrode of the pair of electrodes is a small electrode, and
another electrode of the pair of electroeds is a large electrode.
An area of a liquid-contacting portion of the small electrode with
the solution is smaller than an area of a liquid-contacting portion
of the large electrode with the solution. In a state in which the
solution is contained in the cell, only the solution is present
between the liquid-contacting portion of the small electrode and a
liquid surface of the solution vertically above the
liquid-contacting portion of the small electrode.
Inventors: |
Kasai; Tokuo; (Kyoto-shi,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ARKRAY, Inc. |
Kyoto |
|
JP |
|
|
Assignee: |
ARKRAY, Inc.
Kyoto
JP
|
Family ID: |
61226452 |
Appl. No.: |
15/896734 |
Filed: |
February 14, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01J 3/443 20130101;
C25B 9/06 20130101; C25B 11/02 20130101; G01N 21/67 20130101; C25B
9/16 20130101; C25B 11/12 20130101; G01N 21/69 20130101 |
International
Class: |
C25B 9/16 20060101
C25B009/16; C25B 11/02 20060101 C25B011/02 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 16, 2017 |
JP |
2017-026678 |
Claims
1. An electrolysis device comprising: a cell containing a solution;
a pair of electrodes installed in the cell; and a voltage
application device connected to the pair of electrodes, wherein one
electrode of the pair of electrodes is a small electrode, and
another electrode of the pair of electrodes is a large electrode,
wherein a liquid-contacting portion of the small electrode, which
is a portion of the small electrode that makes contact with the
solution, has a smaller area than an area of a liquid-contacting
portion of the large electrode, which is a portion of the large
electrode that makes contact with the solution, and wherein only
the solution is present between the liquid-contacting portion of
the small electrode and a liquid surface of the solution vertically
above the liquid-contacting portion of the small electrode in a
state in which the solution is contained in the cell.
2. The electrolysis device of claim 1, wherein: a part of the small
electrode is covered by an insulator; a portion of the small
electrode exposed from the insulator is the liquid-contacting
portion of the small electrode; and the small electrode is
installed so that an end edge of the insulator at the
liquid-contacting portion is perpendicular to the liquid surface of
the solution or faces upward.
3. The electrolysis device of claim 1, wherein the large electrode
is installed at a position other than vertically above the
liquid-contacting portion of the small electrode.
4. The electrolysis device of claim 1, further comprising: a
light-transmissive portion that is provided in an outer wall of the
cell, in a vicinity of a tip end of the small electrode, and that
is transmissive to light from the cell to outside; and a light
receiver that is disposed outside the light-transmissive portion
and receives light transmitted through the light-transmissive
portion, wherein a charge carrying detection substance is included
in the solution contained in the cell, wherein the detection
substance is concentrated in the cell at the small electrode by
applying a voltage from the voltage application device across the
pair of electrodes, wherein plasma is generated at the small
electrode by applying a higher voltage from the voltage application
device across the pair of electrodes than the voltage when
concentrating the detection substance, and wherein luminescence of
the detection substance generated by the plasma is detectable by
the light receiver through the light-transmissive portion.
5. The electrolysis device of claim 4, wherein: the voltage
application device is capable of switching a direction of current
when applying voltage; and a direction of current when generating
plasma is an opposite direction to a direction of current when
concentrating the detection substance.
6. The electrolysis device of claim 1, wherein the area of the
liquid-contacting portion of the small electrode is from 0.01
mm.sup.2 to 6 mm.sup.2.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims priority under 35 U.S.C.
.sctn.119 to Japanese Patent Application No. 2017-026678, filed on
Feb. 16, 2017. The contents of this application are incorporated
herein by reference in their entirety.
BACKGROUND
Technical Field
[0002] The present invention relates to an electrolysis device in
which a pair of electrodes make contact with a solution contained
in the device.
Related Art
[0003] During electrolysis, bubbles are generated from electrodes
when anions (for example, chlorine ions) which donate electrons to
a positive electrode, or cations (for example, hydrogen ions) which
receive electrons from a negative electrode, become gaseous
molecules. Normally, the bubbles rise toward the surface of the
solution and are released into the atmosphere. However, depending
on the structure of the electrodes, sometimes bubbles stay on the
surface of the electrode. This decreases a surface area of the
electrode that makes contact with the solution, and sometimes
obstructs the reaction from proceeding. In particular, when the
electrode is small compared to a volume of a gas generated, i.e.,
when a small quantity of specimen solution is analyzed in a
reaction system in which a pair of electrodes are provided in a
minute cell having a volume less than 1 cm.sup.3, due to minute
diameters of the electrodes, the progress of electrochemical
reactions is seriously obstructed by the generated bubbles staying
on the electrodes. This is a problem that needs to be considered
when unitizing plasma spectrometry analysis instruments as
disclosed, for example, in JP 2016-130734 A.
[0004] Note that, although the disclosure of JP 2013-257147 A makes
reference to prevention of obstruction of electrochemical reactions
due to bubbles generated from electrodes adhering to ion-sensitive
films, the technology therein does not consider the adherence of
bubbles to electrodes.
[0005] Exemplary embodiments of the present invention are related
to preventing bubbles from adhering to an electrode in an
electrolysis device.
SUMMARY
[0006] An electrolysis device according to the present disclosure
includes a cell containing a solution, a pair of electrodes
installed in the cell, and a voltage application device connected
to the pair of electrodes. One electrode out of the pair of
electrodes is a small electrode and the other is a large electrode.
A liquid-contacting portion of the small electrode, which is a
portion of the small electrode that makes contact with the solution
has a smaller area than an surface area of a liquid-contact portion
of the large electrode, which is a portion of the large electrode
that makes contact with the solution. Moreover, only the solution
is present between the liquid-contacting portion of the small
electrode and a liquid surface of the solution vertically above the
liquid-contacting portion of the small electrode in a state in
which the solution is contained in the cell. Note that the word
"vertically" mentioned herein means a direction of gravity, or a
direction perpendicular to a horizontal plane.
[0007] In the electrolysis device according to the present
disclosure, there is no structure at all present vertically above
the liquid-contacting portion of the small electrode in the
solution, other than the solution itself. Any bubbles arising due
to the reaction accordingly rise directly to the liquid surface of
the solution, and do not stay on the small electrode or on any
other structure (for example, the large electrode). This enables
the prevention of obstruction of electrochemical reactions caused
by bubbles from the reaction staying on the surface of an
electrode, or caused by a reduction in the effective surface area
of an electrode surface area.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1A is a schematic see-through perspective view of
relevant portions of an electrolysis device according to an
exemplary embodiment of the present invention, and FIG. 1B is a
schematic cross-section of FIG. 1A, taken along line I-I.
[0009] FIG. 2A is a schematic cross-section illustrating an outline
of a concentration process in plasma spectroscopy analysis using
the electrolysis device of FIG. 1A, and FIG. 2B is a schematic
cross-section illustrating an outline of a detection process in
plasma spectroscopy analysis using the electrolysis device of FIG.
1A.
[0010] FIG. 3A and FIG. 3D are schematic diagrams illustrating
examples of unsuitable installation orientations for a small
electrode, and FIG. 3B, FIG. 3C, and FIG. 3E are schematic diagrams
illustrating examples of suitable installation orientations for a
small electrode.
[0011] FIG. 4A is a schematic diagram of an example of unsuitable
positional relationships between electrodes, and FIG. 4B to FIG. 4D
are schematic diagrams illustrating examples of suitable positional
relationships between electrodes.
[0012] FIGS. 5A to 5D are schematic diagrams each illustrating an
example of a shape of an end edge of an insulator at a tip end of a
small electrode.
[0013] FIG. 6A is a graph illustrating results of a comparative
example of plasma spectroscopy analysis using the electrolysis
device according to an exemplary embodiment of the present
invention, and FIG. 6B is a graph illustrating results of an
exemplary embodiment of plasma spectroscopy analysis using the
electrolysis device according to an exemplary embodiment of the
present disclosure.
DETAILED DESCRIPTION
[0014] A first aspect of an electrolysis device according to the
present disclosure includes, as stated above, a cell containing a
solution, a pair of electrodes installed in the cell, and a voltage
application device connected to the pair of electrodes. One
electrode out of the pair of electrodes is a small electrode and
another electrode of the pair of electrodes is a large electrode.
The liquid-contacting portion of the small electrode, which is a
portion of the small electrode that makes contact with the solution
has a smaller area than an area of a liquid-contacting portion of
the large electrode, which is a portion of the large electrode that
makes contact with the solution. Moreover, only the solution is
present between the liquid-contacting portion of the small
electrode and a liquid surface of the solution vertically above the
liquid-contacting portion of the small electrode in a state in
which the solution is contained in the cell.
[0015] This means that there is no structure of the electrolysis
device at all (for example, the large electrode) present vertically
above the liquid-contacting portion of the small electrode in the
solution, other than the solution itself. The liquid-contacting
portion mentioned herein is a material portion of the small
electrode that makes contact with the solution, thereby electrons
are actually transferred between the electrode and ions in the
solution. For example, in cases in which there is a structure (for
example, an insulator) covering and protecting the material forming
the small electrode, the portion projecting from the structure and
actually making contact with the solution is the liquid-contacting
portion. Thus in such cases, suppose that there were, for example,
to be an end edge of the structure present at a boundary between
the structure and the projecting portion of the small electrode,
then this would mean that no part of the end edge at all must be
present vertically above the liquid-contacting portion. For
example, in cases in which the small electrode including such an
end edge is installed facing downward with respect to a horizontal
plane, then such an end edge would be present vertically above the
vicinity of the base of the small electrode, and so the present
aspect of this disclosure would not adopt such an installation
position. The reason therefor is that there would be a possibility
of bubbles generated by the small electrode staying at the end
edge.
[0016] In a second aspect of the electrolysis device of the present
disclosure, in addition to the configuration of the first aspect, a
part of the small electrode is covered by an insulator, a portion
of the small electrode exposed from the insulator is the
liquid-contacting portion of the small electrode, and the small
electrode is installed so that an end edge of the insulator at the
liquid-contacting portion is perpendicular to the liquid surface of
the solution or faces upward facing.
[0017] In other words, for example, in cases in which the small
electrode projects out perpendicular to an end edge of the
insulator, the small electrode is installed so as to face any
direction from parallel to the liquid surface of the solution
(namely, to a horizontal plane) to vertically upward. Due to the
small electrode being installed in this manner, the end edge is not
positioned vertically above the liquid-contacting portion of the
small electrode, and so bubbles do not stay at the end edge.
[0018] In a third aspect of an electrolysis device of the present
disclosure, in addition to the configuration of the first aspect or
the second aspect, the large electrode is installed at a position
other than vertically above the liquid-contacting portion of the
small electrode.
[0019] Namely, no portion at all of the large electrode is present
vertically above the liquid-contacting portion of the small
electrode. Thus, when bubbles generated from the small electrode
rise vertically upward, the bubbles do not stay due to not making
direct contact with the large electrode.
[0020] A fourth aspect of an electrolysis device of the present
disclosure includes, in addition to the configuration of any one of
the first to the third aspects, a light-transmissive portion that
is provided in an outer wall of the cell in a vicinity of a tip end
of the small electrode, and that is transmissive to light from the
cell to outside, and a light receiver that is disposed outside the
light-transmissive portion and receives light transmitted through
the light-transmissive portion. The electrolysis device is
configured such that a charge carrying detection substance is
included in the solution contained in the cell, that the detection
substance is concentrated in the cell at the small electrode by
applying a voltage from the voltage application device across the
pair of electrodes, that plasma is generated at the small electrode
by applying a higher voltage from the voltage application device
across the pair of electrodes than the voltage when concentrating
the detection substance, and that luminescence of the detection
substance generated by the plasma is detectable by the light
receiver through the light-transmissive portion.
[0021] An electrolysis device according to the present aspect is,
for example, employable in a plasma spectrometry analysis method.
Such a plasma spectrometry analysis method includes a concentration
process and a detection process. In the concentration process, a
voltage is applied to the small electrode in the presence of the
solution, serving as a sample, so as to concentrate the detection
substance in the solution at least in the vicinity of the small
electrode. In the detection process, plasma is generated by
applying a higher voltage across the pair of electrodes than during
the concentration process, and luminescence of the detection
substance generated by the plasma is detected. This analysis method
includes the concentration process and the detection process, and
there are no particular limitations to any other processes or
conditions.
[0022] In this analysis method, the solution may, for example, be a
liquid specimen, or may be a diluent of a solid specimen that has
been, for example, suspended, dispersed, or dissolved in a medium.
A neat solution of the specimen may, for example, be employed as it
is as the liquid specimen, or the neat solution may be employed
with a medium as the liquid specimen, for example, in a diluent in
which the neat solution of the specimen is suspended, dispersed, or
dissolved in the medium. So long as the medium is able to suspend,
disperse, or dissolve the specimen, there are no particular
limitations thereto, and examples of the medium include water and
buffers. Examples of the specimen include specimens (samples) taken
from biological bodies, environmental specimens (samples), metals,
chemical substances, pharmaceutical products, and so on. There are
no particular limitations to specimens taken from biological
bodies, and examples thereof include urine, blood, hair, saliva,
sweat, nails, and the like. The blood specimen may, for example, be
erythrocytes, whole blood, serum, blood plasma, or the like.
Examples of the biological body include a human, a non-human
animal, a plant, or the like. The non-human animal may, for
example, be a mammal other than a human, a reptile, an amphibian, a
fish, an insect, or the like. The environmental specimen is not
particularly limited, and examples thereof include food, water,
soil, the atmosphere, an air sample, or the like. Examples of the
food include fresh foods, and processed foods. Examples of the
water include drinking water, underground water, river water, sea
water, household effluent, and the like.
[0023] There are no particular limitations to the detection
substance so long as the detection substance has electric charge,
and examples of the detection substance include metals, chemical
substances, and the like. The metal is not particularly limited,
and examples of the metal include aluminum (Al), antimony (Sb),
arsenic (As), barium (Ba), beryllium (Be), bismuth (Bi), cadmium
(Cd), caesium (Cs), gadolinium (Gd), lead (Pb), mercury (Hg),
nickel (Ni), palladium (Pd), platinum (Pt), tellurium (Te),
thallium (Tl), thorium (Th), tin (Sn), tungsten (W), and uranium
(U). Examples of the chemical substance include reagents,
agricultural chemicals, and cosmetics. There may, for example, be a
single type or two or more types of the detection substance.
[0024] In cases in which the detection substance is a metal, the
liquid may, for example, include a reagent for separating the metal
in the specimen. Examples of the reagent include chelating agents,
masking agents, and the like. Examples of the chelating agent
include dithizone, tiopronin, meso-2,3-dimercaptosuccinic acid
(DMSA), sodium 2,3-dimercapto-l-propane sulfonate (DMPS),
ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid
(NTA), ethylenediamine-N,N'-disuccinic acid (EDDS), and alpha
lipoic acid. "Masking" in an analysis method mentioned herein
deactivating the reactivity of SH groups, and may, for example, be
performed by chemically modifying SH groups. Examples of the
masking agent include maleimide, N-methylmaleimide,
N-ethylmaleimide, N-phenylmaleimide, maleimidopropionic acid,
iodoacetamide, and iodoacetic acid.
[0025] The liquid may, for example, be a liquid that regulates pH.
The pH in such cases is not particularly limited so long as it is a
pH that is conducive to detection of the detection substance. The
pH of the liquid can, for example, be regulated by a pH-regulating
reagent that is an alkaline reagent, an acid reagent, or the
like.
[0026] Examples of the alkaline reagent include alkalis and aqueous
solutions of alkalis. The alkali is not particularly limited, and
examples include sodium hydroxide, lithium hydroxide, potassium
hydroxide, and ammonia. Examples of the aqueous solutions of
alkalis include aqueous solutions in which alkali is diluted by
water or a buffer. The concentration of the alkali in the alkaline
aqueous solution is not particularly limited, and may, for example,
be from 0.01 mol/L to 5 mol/L.
[0027] Examples of the acid reagent include acids and aqueous
solutions of acids. The acid is not particularly limited, and
examples include hydrochloric acid, sulfuric acid, acetic acid,
boric acid, phosphoric acid, citric acid, malic acid, succinic
acid, and nitric acid. Examples of the acid aqueous solutions
include aqueous solutions in which acid is diluted by water or a
buffer. The concentration of acid in the acid aqueous solution is
not particularly limited, and may, for example, be from 0.01 mol/L
to 5 mol/L.
[0028] The electrodes are solid electrodes, and specific examples
thereof include rod electrodes. The material of the electrodes is
not particularly limited, and as long as the material is a solid,
conductive material, the material can be appropriately set
according to the type of the detection substance, for example. The
material of the electrodes may, for example, be a non-metal, may be
a metal, or may be a mixture thereof. When the material of the
electrodes includes a non-metal, then the material of the
electrodes may, for example, include one type of non-metal, or may
include two or more types of non-metal. Examples of the non-metal
include carbon. When the material of the electrodes includes a
metal, the material of the electrodes may, for example, include one
type of metal, or may include two or more types of metal. Examples
of the metal include gold, platinum, copper, zinc, tin, nickel,
palladium, titanium, molybdenum, chromium, and iron. When the
material of the electrodes includes two or more types of metal, the
material of the electrodes may be an alloy. Examples of the alloy
include brass, steel, INCONEL (registered trademark), Nichrome, and
stainless steel. The pair of electrodes may, for example, be the
same material or may be different materials.
[0029] The sizes of the electrodes are not particularly limited, as
long as at least a portion of each of the electrodes can be placed
in the cell and an area of the liquid-contacting portion of the
small electrode is smaller than that of the large electrode. Note
that in cases in which the cell is, for example, to be made into a
cartridge to enable mass production, the size of the cell is
preferably made as small as possible. In such cases, the area of
the liquid-contacting portion of the small electrode in the
electrolysis device according to each of the above aspects is
preferably from 0.01 mm.sup.2 to 6 mm.sup.2. More specifically, in
cases in which the liquid-contacting portion of the small electrode
is formed in a circular pillar shape with a diameter and a length
of 0.05 mm, the area of the liquid-contacting portion is about 0.01
mm.sup.2. Moreover, in cases in which the liquid-contacting portion
thereof is formed in a circular pillar shape with a diameter of 1.0
mm and a length of 1.66 mm, area of the liquid-contacting portion
about 6 mm.sup.2. In consideration of the above circumstances, in
cases in which the shape of the liquid-contacting portion of the
small electrode is a circular pillar shape, the diameter thereof is
preferably from 0.05 mm to 1.0 mm (and more preferably 0.1 mm) and
the length thereof is preferably 0.05 mm to 1.66 mm (and more
preferably 0.5 mm).
[0030] The concentration process, as stated above, is a process in
which a voltage is applied across the pair of electrodes in the
presence of a liquid so as to concentrate the detection substance
in the liquid at least in the vicinity of the small electrode. The
pair of electrodes are in contact with the liquid. In the
concentration process, the vicinity of the small electrode is not
particularly limited, and examples thereof include a region where
plasma is generated in a detection process, described later, for
example the surface of the small electrode.
[0031] In the concentration process, for example, some of the
detection substance in the solution may be concentrated in the
vicinity of the small electrode, or all of the detection substance
may be concentrated in the vicinity of the small electrode.
[0032] In the concentration process, the charge condition of the
electrode is preferably set such that the detection substance
concentrates at the electrode used to detect the detection
substance in a detection process, described later, namely, the
electrode where plasma is generated (also referred to as the
"plasma generation electrode" hereinafter). The charge condition is
not particularly limited; however, in cases in which the detection
substance has positive charge, such as a metal ion, the plasma
generation electrode may be set with a current direction from the
voltage application device such that the plasma generation
electrode becomes the negative electrode in the concentration
process. On the other hand, in cases in which the detection
substance has negative charge, the plasma generation electrode may
be set with a current direction from the voltage application device
such that the plasma generation electrode becomes the positive
electrode.
[0033] The concentration of the detection substance can, for
example, be adjusted using the voltage. Thus, the voltage to
generate the concentration (referred to as the "concentration
voltage" hereinafter) can be appropriately set by a person of
ordinary skill in the art. The concentration voltage is, for
example, 1 mV or more, and is preferably 400 mV or more. The upper
limit of the concentration voltage is not particularly limited. The
concentration voltage may be fixed, or may fluctuate, for example.
The concentration voltage may, for example, be a voltage at which
plasma is not generated.
[0034] The duration over which the concentration voltage is applied
is not particularly limited, and may be appropriately set according
to the concentration voltage. The duration of concentration voltage
application is, for example, from 0.2 minutes to 40 minutes, and is
preferably from 5 minutes to 20 minutes. The voltage applied across
the pair of electrodes may, for example, by applied continuously,
or may be applied intermittently. An example of the intermittent
application is pulse application. In cases in which the voltage
application is intermittent, the duration of concentration voltage
application may, for example, be a total duration of the time the
concentration voltage is applied, or may be a total duration of the
time the concentration voltage is applied and the time the
concentration voltage is not applied.
[0035] A voltage application device that applies the voltage across
the pair of electrodes is not particularly limited. Any known
device such as a voltage source may be employed therefor as long as
it is capable of applying a voltage across the pair of electrodes.
In the concentration process, the current flowing between the
electrodes may, for example, be set to 0.01 mA to 200 mA, is
preferably set to 10 mA to 60 mA, and is more preferably set to 10
mA to 40 mA.
[0036] In the detection process, as stated above, plasma is
generated by applying a higher voltage across the pair of
electrodes than during the concentration process, and luminescence
of the detection substance generated by the plasma is detected.
[0037] The direction of current in the detection process may be the
same direction as that of the direction of current in the
concentration process. However, the voltage application device is
preferably configured so as to be capable of switching the
direction of current when applying voltage, and the direction of
the current when generating plasma is preferably the opposite
direction to the direction of current when concentrating the
detection substance.
[0038] More specifically, in cases in which the detection substance
has a positive charge in the concentration process, in the
detection process, the current direction from the voltage
application device is preferably set so as to make the plasma
generation electrode the positive electrode. On the other hand, in
cases in which the detection substance has a negative charge, the
voltage application device is preferably set with a current
direction in the detection process that makes the plasma generation
electrode the negative electrode.
[0039] The detection process may be performed so as to be
contiguous to the concentration process, or may be non-contiguous
thereto. The detection process of the former case is a detection
process performed as soon as the concentration process ends. The
detection process of the latter case is a detection process
performed within a predetermined time from when the concentration
process ends. The predetermined time is, for example, from 0.001
seconds to 1000 seconds after the concentration process, and is
preferably from 1 second to 10 seconds thereafter.
[0040] In the detection process, "generating plasma" mentioned
herein means generating plasma at a practical level, and, more
specifically, with regard to detection of plasma emission, means
causing plasma to be generated that gives a practically detectable
level of luminescence. As a specific example, this may be said to
be a level at which plasma emission is detectable by a plasma
emission detector.
[0041] The generation of plasma at a practical level can be
adjusted by, for example, the voltage. Thus the voltage to cause
plasma to be generated so as to give a practically detectable
luminescence (also referred to as the "plasma generation voltage"
hereinafter) can be appropriately set by a person of ordinary skill
in the art. The plasma generation voltage is, for example, 10 V or
greater, and is preferably 100 V or greater. There is no particular
limitation to the upper limit thereof. The plasma generation
voltage is, for example, a relatively high voltage compared to a
voltage used to cause the concentration. Thus, the plasma
generation voltage is preferably a higher voltage than the
concentration voltage. The plasma generation voltage may be fixed,
or may fluctuate, for example.
[0042] The duration over which the plasma generation voltage is
applied for is not particularly limited, and may be appropriately
set according to the plasma generation voltage. The duration over
which the plasma generation voltage is applied may, for example, be
from 0.001 seconds to 0.02 seconds, and is preferably from 0.001
seconds to 0.01 seconds. The voltage application across the pair of
electrodes may, for example, by continuous application, or may be
intermittent application. An example of the intermittent
application is pulse application. In cases in which the voltage
application is intermittent, the duration of plasma generation
voltage application may, for example, be the duration of one time
of the plasma generation voltage application, may be the total
duration of the time the plasma generation voltage is applied, or
may be the total duration of the time the plasma generation voltage
is applied and the time the plasma generation voltage is not
applied.
[0043] In the detection process, the luminescence of the generated
plasma may be detected continuously or may be detected
intermittently, for example. Examples of the luminescence detection
include detection of the presence or absence of luminescence,
detection of the intensity of the luminescence, detection of a
particular wavelength, and detection of a spectrum. Examples of the
detection of a particular wavelength include, for example,
detection of a characteristic wavelength emitted by the detection
substance during plasma emission. The method of detecting
luminescence is not particularly limited and, for example, a known
optical measurement instrument such as a charge coupled device
(CCD) or a spectroscopy instrument may be utilized therefor.
[0044] The voltage application across the pair of electrodes in the
detection process is performed by the voltage application device
employed in the concentration process, and can be performed at a
higher voltage and preferably with the opposite direction to the
current direction thereof. In the detection process, the current
across the electrodes may be set, for example, to 0.01 mA to 100000
mA, and is preferably set to 50 mA to 2000 mA.
[0045] The analysis method may further include a computation
process in which a concentration of a detection substance in the
solution is computed from the detection results of the detection
process. Examples of the detection results include the intensity of
the luminescence, as described above. In the computation process,
the concentration of the detection substance may, for example, be
computed based on detection results, and correspondence
relationships between detection results and concentrations of the
detection substance in the solution. Such correspondence
relationships may be found, for example, by taking standard samples
of known concentrations of the detection substance, and plotting
detection results obtained by the analysis method against the
concentrations of the detection substance of the standard samples.
The standard samples are preferably a dilution series of the
detection substance. A high degree of reliability can be achieved
by performing such computations.
[0046] In the analysis method, the pair of electrodes may be placed
inside the cell that has been configured to include a transmissive
portion. In such cases, the luminescence may be detected in the
detection process by a light receiver disposed so as to be capable
of receiving luminescence emitted by the detection substance and
passes through the transmissive portion.
[0047] In the analysis method, due to employing the electrolysis
device of the present disclosure, any bubbles (for example,
hydrogen gas) generated from the small electrode in the analysis
process are not prevented from rising from the surface of the small
electrode and do not stay thereon. Moreover, the bubbles that have
risen do not stay on the large electrode. Thus, any bubbles caused
by electrochemical reactions do not interfere with the analysis
process in the analysis method. This suppresses variation in
measurement results and the like caused by bubbles, so that stable
analysis results are obtained.
[0048] Description follows regarding exemplary embodiments of an
electrolysis device of the present disclosure, with reference to
the drawings. For ease of explanation, in these figures, the
structure of each section is simplified as appropriate and
illustrated schematically such that the dimensional ratios and so
on of each section differ from their actual dimensional ratios.
[0049] FIG. 1A is a schematic see-through perspective view of
relevant portions of an electrolysis device 1 of an exemplary
embodiment, and FIG. 1B is a schematic cross-section of FIG. 1A
taken on line I-I. As illustrated in FIG. 1A and FIG. 1B, the
electrolysis device 1 of the present exemplary embodiment includes
a cell 10, a pair of electrodes (a small electrode 20 and a large
electrode 30), and a light receiver 40. The cell 10 exhibits a
substantially cylindrical shape, having a portion of its side face
as if truncated to form a flat face shape. A circular,
light-transmissive portion 11 is included in the flat face portion.
Luminescence generated by applying a voltage to the small electrode
20 and the large electrode 30 passes through the light-transmissive
portion 11, and the light receiver 40 is disposed outside the cell
10 so as to be capable of receiving the luminescence emitted by the
detection substance. The small electrode 20 is disposed parallel to
a liquid surface 61 of a solution 60, and a tip end of the small
electrode 20 is disposed so as to abut the light-transmissive
portion 11. The large electrode 30 having a cylindrical shape is
disposed with its side face portion in the side face of the cell 10
on a side of the cell 10 facing the circular light-transmissive
portion 11, such that the large electrode 30 intersects the
vertical direction at right angles, and this portion of the large
electrode 30 is exposed to the interior of the cell 10. Namely, the
length direction of the large electrode 30 and the length direction
of the small electrode 20 are at skew-line positions with respect
to each other. The small electrode 20 is covered by an insulator
22. In the electrolysis device 1 of the present exemplary
embodiment, the solution 60 containing the detection substance is
introduced into the tube of the cell 10 such that the solution 60
makes contact with the small electrode 20 and the large electrode
30.
[0050] In the present exemplary embodiment, most of the surface of
the small electrode 20 is covered by the insulator 22. The portion
not covered by the insulator 22 is a liquid-contacting portion 21
that projects out perpendicular to an end edge 23 of the insulator
22. The liquid-contacting portion 21 is parallel to the liquid
surface 61 of the solution 60. There is no structure of the
electrolysis device 1 at all, including the end edge 23 of the
insulator 22, present at a portion in the solution 60 that is
vertically above the liquid-contacting portion 21 (the region
indicated by the reference sign "A" in FIG. 1B), other than the
solution 60 itself. The surface area of the liquid-contacting
portion 21 contacting the solution 60 is smaller than the exposed
surface area of the large electrode 30 inside the cell 10 and in
contact with the solution 60.
[0051] In the present exemplary embodiment, the small electrode 20
and the light-transmissive portion 11 contact each other; however,
the present embodiment is not limited thereto, and for example, the
small electrode 20 may not make contact with the light-transmissive
portion 11. The distance between the small electrode 20 and the
light-transmissive portion 11 is not particularly limited, and may,
for example, be from 0 cm to 0.5 cm.
[0052] The material of the light-transmissive portion 11 is not
particularly limited, and may, for example, be set as appropriate
according to the wavelength of the luminescence, so long as it is a
material that transmits luminescence generated by applying voltage
to the small electrode 20 and the large electrode 30. Examples of
the material of the light-transmissive portion 11 include quartz
glass, acrylic resin (PMMA), borosilicate glass, polycarbonate
(PC), cyclo-olefin polymer (COP), and polymethylpentene (TPX
(registered trademark)). The size of the light-transmissive portion
11 is not particularly limited, so long as it is a size that
enables transmission of luminescence generated by applying voltage
to the small electrode 20 and the large electrode 30.
[0053] In the present exemplary embodiment, the cell 10 is a
bottomed cylindrical shape having a portion of its side face
truncated to form a flat face shape running along its length
direction; however, the shape of the cell 10 is not limited
thereto, and may be any desired shape. The material of cell 10 is
not particularly limited, and examples include acrylic resin
(PMMA), polypropylene (PP), polyethylene (PE), polyvinyl chloride
(PVC), polyethylene terephthalate (PET), and polystyrene (PS). In
cases in which the cell 10 has a bottomed tube shape, the diameter
of the cell 10 is, for example, from 0.3 cm to 1 cm, and the height
of the cell 10 is, for example, from 0.9 cm to 5 cm. Into the cell
10 is introduced 0.3 cm.sup.3 to 0.8 cm.sup.3 of the solution
60.
[0054] The light receiver 40 is not particularly limited, and
examples include known optical measurement instruments such as
CCDs, spectroscopy instruments, and so on. The light receiver 40
may, for example, be a transmitter that transmits the generated
luminescence to the optical measurement instrument disposed outside
the electrolysis device 1. Examples of the transmitter include a
transmission path such as an optical fiber.
[0055] The method of manufacturing the cell 10 is not particularly
limited and the cell 10 may be a molded body manufactured by
injection-molding or the like, or may be manufactured by forming a
recess in a substrate such as a plate. The manufacturing method of
the cell 10 is not particularly limited, and other examples thereof
include lithography and machine cutting.
[0056] Explanation follows regarding a case in which metal ions
(such as mercury ions, lead ions, etc.) present in the solution 60,
serving as an acidic aqueous solution, are the detection substance,
so as to summarize a spectroscopy analysis method employing the
electrolysis device 1 of the present exemplary embodiment.
[0057] First, as the concentration process, in a state in which the
solution 60 has been introduced into the cell 10, a voltage is
applied by a voltage application device 50 such that the small
electrode 20 acts as the cathode and the large electrode 30 acts as
the anode, as illustrated in FIG. 2A. Then, metal ions present in
the solution 60 are attracted to the small electrode 20, this being
the cathode. At the same time, hydrogen ions in the solution 60 are
also attracted to the small electrode 20 and gain electrons there
to form hydrogen gas, resulting in bubbles 62 arising from the
small electrode 20.
[0058] There is no structure (that is, the large electrode 30 or
the end edge 23 of the insulator 22) at all present at a region in
the solution 60 corresponding to vertically above the
liquid-contacting portion 21 of the small electrode 20 (the region
indicated by the reference sign "A" in FIG. 1B), other than the
solution 60 itself. The generated bubbles 62 accordingly are not
interfered with by any structure, quickly rise toward the liquid
surface 61, and do not stay on the surface of the small electrode
20.
[0059] Next, as the detection process, a voltage is applied by the
voltage application device 50 such that the small electrode 20 then
acts as the anode and the large electrode 30 acts as the cathode,
as illustrated in FIG. 2B. Then, plasma is generated from the metal
ions that were attracted around the small electrode 20 by the prior
concentration process, and the light generated as a result passes
through the light-transmissive portion 11 and is received and
detected by the light receiver 40. Since the generated bubbles 62
generated in the prior concentration process do not stay on the
surface of the small electrode 20, generation of plasma is not
obstructed by such bubbles 62.
[0060] Supplementary explanation follows regarding the installation
orientation of the small electrode 20 in the solution 60, based on
FIG. 3A to FIG. 3E. Note that in FIG. 3A to FIG. 3E, the top of the
figure is the liquid surface 61 side of the solution 60 (see FIG.
1B; the same applies below), and the large electrode 30 is not
present between the liquid-contacting portion 21 of the small
electrode 20 and the liquid surface 61 (see FIG. 1B).
[0061] As illustrated in FIG. 3A, in a state in which the
liquid-contacting portion 21 of the small electrode 20 is installed
pointing directly downward with respect to the liquid surface 61,
the end edge 23 of the insulator 22 also faces downward with
respect to the liquid surface 61. In this state, the small
electrode 20 itself is present in the region "A" vertically above
the liquid-contacting portion 21. Thus, in this state, bubbles 62
stay at the end edge 23, and at least a portion of the
liquid-contacting portion 21 is covered by the bubbles 62.
[0062] As illustrated in FIG. 3B, in a state in which the
liquid-contacting portion 21 of the small electrode 20 is installed
parallel to the liquid surface 61, the end edge 23 of the insulator
22 is perpendicular to the liquid surface 61. In this state, there
is nothing present in the region "A" that is vertically above the
liquid-contacting portion 21 up to the liquid surface 61, other
than the solution 60 itself. Thus, in this state, the bubbles 62
are not impeded by anything, and rise vertically upward.
[0063] As illustrated in FIG. 3C, in a state in which the
liquid-contacting portion 21 of the small electrode 20 is installed
slanting upward with respect to the liquid surface 61, the end edge
23 of the insulator 22 also slants upward with respect to the
liquid surface 61. Also in this state, there is nothing present in
the region "A" vertically above the liquid-contacting portion 21 up
to the liquid surface 61, other than the solution 60 itself. Thus,
also in this state, the bubbles 62 are not impeded by anything, and
continue to rise vertically upward.
[0064] As illustrated in FIG. 3D, in a state in which the
liquid-contacting portion 21 of the small electrode 20 is installed
slanting downward with respect to the liquid surface 61, the end
edge 23 of the insulator 22 also slants downward with respect to
the liquid surface 61. In this state, a portion of the end edge 23
of the insulator 22 is caught up in the region "A" vertically above
the liquid-contacting portion 21. Thus, in this state, the bubbles
62 stay at the end edge 23 caught up in the region "A", and at
least a portion of the liquid-contacting portion 21 is covered by
the bubbles 62.
[0065] As illustrated in FIG. 3E, in a state in which the
liquid-contacting portion 21 of the small electrode 20 is installed
facing directly upward with respect to the liquid surface 61, the
end edge 23 of the insulator 22 also faces upward with respect to
the liquid surface 61. In this state, there is nothing present in
the region "A" vertically above the liquid-contacting portion 21
and between the liquid-contacting portion 21 and the liquid surface
61, other than the solution 60. Thus, in this state, the bubbles 62
are not impeded by anything, and continue to rise vertically
upward.
[0066] It is apparent from the above explanation that, as
illustrated in FIG. 3B, FIG. 3C, and FIG. 3E, when the small
electrode 20 is installed such that the end edge 23 of the
insulator 22 faces any direction from perpendicular to the liquid
surface 61 of the solution 60 to upward (including slanting
upward), then the bubbles 62 arising at the liquid-contacting
portion 21 of the small electrode 20 quickly rise vertically upward
and do not obstruct the electrolytic reaction at the small
electrode 20.
[0067] Next, supplementary explanation follows regarding the
positional relationship of the small electrode 20 to the large
electrode 30 when the small electrode 20 is installed such that the
end edge 23 of the insulator 22 faces any direction from
perpendicular to the liquid surface 61 of the solution 60 to upward
(including slanting upward), with reference to FIG. 4A to FIG.
4D.
[0068] As illustrated in FIG. 4A, when the large electrode 30 is
present in the region "A" vertically above the liquid-contacting
portion 21 of the small electrode 20, the bubbles 62 stay at the
lower side of the large electrode 30, and there is a possibility
that the bubbles 62 obstruct the electrochemical reactions at the
large electrode 30.
[0069] On the other side, when, as illustrated in FIG. 4B to FIG.
4D, the large electrode 30 is not present in the region "A"
vertically above the liquid-contacting portion 21 of the small
electrode 20, the bubbles 62 do not stay at the lower side of the
large electrode 30, and the bubbles 62 accordingly do not obstruct
the electrochemical reactions at the large electrode 30.
[0070] Note that even in the case illustrated in FIG. 4A, the
bubbles 62 do not stay at the lower side of the large electrode 30
in cases in which the large electrode 30 is outside of the region
"A" in plan view, and in such cases the bubbles 62 accordingly do
not obstruct the electrochemical reactions at the large electrode
30.
[0071] Supplementary explanation now follows regarding measures
taken such that bubbles do not stay at the end edge 23 of the
insulator 22 even in cases in which the liquid-contacting portion
21 of the small electrode 20 is installed facing downward
(including slanting downward), with reference to FIG. 5A to FIG.
5D.
[0072] As illustrated in FIG. 5A, even in cases in which the
liquid-contacting portion 21 of the small electrode 20 faces
directly downward, forming the end edge 23 of the insulator 22 with
a tapered shape enables the bubbles 62 to readily escape upward.
When formed in such a shape, as illustrated in FIG. 5B, placing the
liquid-contacting portion 21 of the small electrode 20 facing
downward at an angle is effective in making the bubbles 62 less
susceptible to contacting the end edge 23.
[0073] Moreover, as illustrated in FIG. 5C, when the
liquid-contacting portion 21 of the small electrode 20 faces
directly downward, forming the end edge 23 of the insulator 22 as a
convex face enables the bubbles 62 to readily escape upward.
However, there is still some concern that the bubbles 62 might stay
in the vicinity of the boundary between the end edge 23 and the
liquid-contacting portion 21 due to the end edge 23 being close to
perpendicular to the liquid-contacting portion 21. In order that
such a situation does not arise, when the insulator 22 is formed in
a cylindrical shape, the radius of curvature of the convex face of
the end edge 23 is preferably set to two or more times the radius
of the insulator 22.
[0074] Moreover, as illustrated in FIG. 5D, when the
liquid-contacting portion 21 of the small electrode 20 faces
directly downward, forming the end edge 23 of the insulator 22 as a
concave face also enables the bubbles 62 to readily escape upward.
However, due to the end edge 23 being close to perpendicular to the
side faces in the vicinity of the boundary between the end edge 23
and the side faces of the insulator 22, there is still some concern
that the bubbles 62 might stay in this area. In order that such a
situation does not arise, when the insulator 22 is formed in a
cylindrical shape, the radius of curvature of the concave face of
the end edge 23 is preferably set to two or more times the radius
of the insulator 22.
[0075] Examples of the present invention will now be described.
Note that the present invention is not limited to the following
examples.
EXAMPLE 1
[0076] Confirmation was made that lead could be analyzed with good
sensitivity using the electrolysis device of the present
example.
[0077] (1) Plasma Spectrometry Analysis Instrument
[0078] An analysis instrument of the present exemplary embodiment
as shown above was prepared. Specifically, a bottomed tubular
shaped cell 10 manufactured from transparent PMMA was prepared
(height 28 m.times.diameter (at maximum diameter portion) 7 mm).
Quartz glass (diameter 4.5 mm, thickness 0.3 mm), serving as the
light-transmissive portion 11, was disposed in the vicinity of the
lower end of the flat face portion on the side face of the cell 10.
The small electrode 20 and the large electrode 30 were disposed in
the cell 10. The small electrode 20 was disposed parallel to the
liquid surface 61. The tip end of the small electrode 20 was
disposed so as to contact the light-transmissive portion 11. The
small electrode 20 employed a Nichrome wire with a diameter of 0.1
mm. The small electrode 20 employed was covered with a glass tube,
serving as the insulator 22, over regions other than a region from
a tip end of the small electrode 20 up to 0.5 mm from the tip end
where the small electrode 20 was exposed. The large electrode 30
employed was a carbon rod with a diameter of 4.0 mm. The large
electrode 30 was disposed with a portion of its side face in the
side face of the cell 10 on a side of the cell 10 facing the
circular light-transmissive portion 11, such that the large
electrode 30 intersected the vertical direction at a right angle,
and this portion of the large electrode 30 was exposed to the
interior of the cell 10. Namely, the length direction of the large
electrode 30 and the length direction of the small electrode 20
were at skew-line positions with respect to each other. Moreover,
an optical fiber, serving as the light receiver 40, was disposed so
as to oppose the tip end of the small electrode 20 across the
light-transmissive portion 11. The optical fiber employed had a 400
.mu.m diameter single core. The optical fiber was connected to a
concave grating type of spectrometer (not illustrated in the
drawings).
[0079] (2) Plasma Spectroscopy Analysis
[0080] Lead nitrate was dissolved at 100 ppb in 0.4 mL of a 2 mol/L
solution of lithium hydroxide to give a lead sample as the solution
60. The lead sample was then introduced into the cell 10 of the
electrolysis device.
[0081] Then first, as a concentration process, a voltage was
applied across the small electrode 20 and the large electrode 30
such that the small electrode 20 acted as the negative electrode
(cathode) and the large electrode 30 acted as the positive
electrode (anode) (see FIG. 2A) under the following concentration
conditions. Thereby lead in the solution 60 was concentrated in the
vicinity of the small electrode 20.
[0082] Concentration Conditions
[0083] Applied Voltage: 5V
[0084] Applied Current: 10 mA to 60 mA
[0085] Current ON/OFF period: 25 microseconds or greater
[0086] Current ON/OFF duty: 50% to 80%
[0087] Application duration: 300 seconds
[0088] Immediately after concentrating, as the detection process, a
further voltage was applied across the small electrode 20 and the
large electrode 30 such that current flowed with the small
electrode 20 acting as the positive electrode and the large
electrode 30 acting as the negative electrode (see FIG. 2B) under
the following plasma generation conditions. The intensity (count
values) of luminescence was measured at each wavelength of the
plasma emission thereby generated.
[0089] Plasma Generation Conditions
[0090] Applied Voltage: 500V
[0091] Applied Current: 1A
[0092] Applied Voltage Switching Period: 50 microseconds
[0093] Applied Voltage Switching Duty: 50%
[0094] Application duration: 5 milliseconds
[0095] Note that as a control (comparative example), the
light-transmissive portion 11 was installed in the bottom face of
the cell 10, and the small electrode 20 was installed facing
directly downward (see FIG. 3A). With these exceptions, the
concentration conditions and plasma generation conditions employed
were similar, and the spectrum of the generated plasma emission was
measured in a similar manner.
[0096] Results are illustrated in FIG. 6A and FIG. 6B. FIG. 6A and
FIG. 6B are graphs illustrating measurement results of the spectrum
in the vicinity of a lead peak which was measured five times for
both the example and the comparative example. In FIG. 6A and FIG.
6B, the horizontal axis indicates the wavelength, and the vertical
axis indicates the intensity (count value) of luminescence.
Moreover, FIG. 6A illustrates the results of the comparative
example, and FIG. 6B illustrates the results of the example.
[0097] These results apparently confirmed that, in comparison to
the comparative example, the example showed a smaller variation in
count values at a peak in the vicinity of 368.3 nm, this being the
wavelength of plasma emission characteristic of lead.
[0098] Note that count values at this peak and the results of
statistical processing based on these count values are listed in
the flowing Table 1.
TABLE-US-00001 TABLE 1 Example/Comparative Example Comparative
Example Example Count Values 10430 8238 9425 7631 8594 7615 7626
7115 7448 7018 Average 8705 7523 Variance 1250127 190568 Standard
Deviation 1118 437 F-test (P) 0.096 Unequal Variances t-test (P)
0.104
[0099] First, an equal variance test (F-test) between the
comparative example group and the example group, each containing
five specimens, gave a significance level (P) of 0.096, and this
exceeded P=0.05. Thus, there was a statistically significant
difference in the variances between the two groups. Namely, the
fact that the variation (variance) in the comparative examples was
clearly greater than the variation in the examples was also
confirmed by the results of statistical processing. This difference
in variation is hypothesized to be due to the orientation of the
small electrode 20. Namely, in the comparative examples, the small
electrode 20 faced directly downward, and the generated bubbles 62
stayed at the end edge 23 of the insulator 22 (see FIG. 3A). It is
thought that variation arises in the count values due to the
staying bubbles 62 covering the liquid-contacting portion 21 of the
small electrode 20 according to the way in which the bubbles 62
stay. However, in the examples, the end edge 23 of the insulator 22
is perpendicular to the liquid surface 61 due to the small
electrode 20 being parallel to the liquid surface 61. The bubbles
62 are not liable to stay at the end edge 23, and it is thought
that the variation in the count values due to the bubbles 62 is
accordingly smaller.
[0100] Moreover, an unequal variances t-test performed between the
average value of the comparative examples (8705) and the average
value of the examples (7523) showed the significance level (P) of
0.104, which exceeds P=0.05. The result demonstrates a
statistically significant difference between the average values.
The bubbles 62 staying at the small electrode 20 might normally
also have a large effect on the average values representing plural
measurement results, and therefore this suggests that there is also
a possibility that they have an effect on the explanation and
interpretation of these results.
INDUSTRIAL APPLICABILITY
[0101] The present invention may be utilized as an electrolysis
device to execute electrochemical reactions in which bubbles are
generated from electrodes. The present invention may accordingly be
utilized as an electrolysis device employed for plasma spectroscopy
analysis using minute cells that are highly influenced by bubbles
from electrodes.
* * * * *