U.S. patent application number 13/266005 was filed with the patent office on 2012-02-16 for total organic carbon meter provided with system blank function.
This patent application is currently assigned to SHIMADZU CORPORATION. Invention is credited to Masahito Yahata.
Application Number | 20120039750 13/266005 |
Document ID | / |
Family ID | 43010791 |
Filed Date | 2012-02-16 |
United States Patent
Application |
20120039750 |
Kind Code |
A1 |
Yahata; Masahito |
February 16, 2012 |
TOTAL ORGANIC CARBON METER PROVIDED WITH SYSTEM BLANK FUNCTION
Abstract
A total organic carbon measuring device comprises: a sample
supply unit that collects and supplies sample water; an oxidative
decomposition unit that is connected to the sample supply unit and
oxidizes organic matter contained in the sample water supplied from
the sample supply unit to carbon dioxide; a carbon dioxide
separation unit that transfers carbon dioxide from the sample water
that has passed through the oxidative decomposition unit to
measurement water consisting of deionized water; a conductivity
measuring unit that measures the conductivity of the measurement
water flowing from the carbon dioxide separation unit; and an
arithmetic processing unit that calculates the TOC concentration of
the sample water from a measured value obtained by the conductivity
measuring unit. A measured value obtained by the conductivity
measuring unit when pure water subjected to aeration treatment is
allowed to pass through the oxidative decomposition unit of which
oxidative decomposition function is turned off and then flows
through a sample water channel is defined as a system blank
value.
Inventors: |
Yahata; Masahito; (Shiga,
JP) |
Assignee: |
SHIMADZU CORPORATION
Kyoto
JP
|
Family ID: |
43010791 |
Appl. No.: |
13/266005 |
Filed: |
April 24, 2009 |
PCT Filed: |
April 24, 2009 |
PCT NO: |
PCT/JP2009/058122 |
371 Date: |
October 24, 2011 |
Current U.S.
Class: |
422/80 |
Current CPC
Class: |
G01N 33/1846 20130101;
Y10T 436/235 20150115; G01N 27/06 20130101 |
Class at
Publication: |
422/80 |
International
Class: |
G01N 31/00 20060101
G01N031/00 |
Claims
1. A total organic carbon measuring device comprising: a sample
supply unit that has a system for collecting and supplying sample
water and subjecting the collected sample water to aeration
treatment using a gas containing no carbon dioxide; an oxidative
decomposition unit that is connected to the sample supply unit, has
oxidative decomposition function that oxidizes organic matter
contained in the sample water supplied from the sample supply unit
to carbon dioxide, and is capable of turning on and off the
oxidative decomposition function; a carbon dioxide separation unit
that includes a sample water channel through which the sample water
that has passed through the oxidative decomposition unit flows, a
measurement water channel through which measurement water
consisting of deionized water flows, and a gas permeable membrane
interposed between the sample water channel and the measurement
water channel to allow carbon dioxide to be transferred
therethrough; a conductivity measuring unit that measures a
conductivity of the measurement water flowing from the carbon
dioxide separation unit; and an arithmetic processing unit that
includes a system blank holding section that holds, as a system
blank value, a measured value obtained by the conductivity
measuring unit when pure water collected in the sample supply unit
and subjected to aeration treatment is allowed to pass through the
oxidative decomposition unit of which oxidative decomposition
function is turned off and then flows through the sample water
channel, and an arithmetic section that calculates a total organic
carbon concentration of the sample water from a system blank value
held in the system blank holding section and a measured value
obtained by the conductivity measuring unit when the sample water
is allowed to pass through the oxidative decomposition unit of
which oxidative decomposition function is turned on and then flows
through the sample water channel.
2. The total organic carbon measuring device according to claim 1,
wherein the oxidative decomposition unit includes an oxidation
channel made of a UV-permeable material through which the sample
water flows and an ultraviolet light source that irradiates the
sample water with ultraviolet light from an outside of the
oxidation channel, and wherein the oxidative decomposition function
is turned on and off by the ultraviolet light source.
3. The total organic carbon measuring device according to claim 1,
wherein the oxidative decomposition unit includes an oxidation
channel made of a UV-permeable material through which the sample
water flows, an ultraviolet light source that irradiates the sample
water with ultraviolet light from an outside of the oxidation
channel, and a shutter provided between the oxidation channel and
the ultraviolet light source, and wherein the oxidative
decomposition function is turned on and off by opening and closing
the shutter.
4. The total organic carbon measuring device according to claim 1,
wherein the arithmetic section holds calibration curve data
representing a relationship between a measured value obtained by
the conductivity measuring unit and a total organic carbon
concentration of the sample water supplied from the sample supply
unit, and wherein the calibration curve data is corrected using a
system blank value held in the system blank holding section to
obtain corrected calibration curve data, and a total organic carbon
concentration of the sample water is calculated from the corrected
calibration curve data and a measured value obtained by the
conductivity measuring unit when the sample water is measured.
5. The total organic carbon measuring device according to claim 4,
wherein the corrected calibration curve data is obtained by
shifting the calibration curve data obtained from a measured value
so that its intercept value becomes a system blank value held in
the system blank holding unit.
6. The total organic carbon measuring device according to claim 1,
wherein the sample supply unit comprises: a multi-port valve having
at least a port connected to a channel for supplying sample water,
a port connected to a channel for supplying pure water, a port
connected to the oxidative decomposition unit, a port opened to the
atmosphere, and a common port connected to any one of these ports
by switching; a syringe connected to the common port of the
multi-port valve and collects and sends the sample water by
slidably moving a piston in a cylinder in a vertical direction; and
a gas supply channel connected to a lower end portion of the
cylinder at a position above the piston in a state where the piston
is located at a lower end of the cylinder to supply a gas
containing no carbon dioxide into the cylinder.
7. The total organic carbon measuring device according to claim 6,
wherein the multi-port valve further has another port connected to
an acid supply channel for supplying an acid for acidifying the
sample water collected in the syringe.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a total organic carbon
measuring device (also referred to as a "TOC meter") for measuring
the total organic carbon (TOC) content, total carbon (TC) content,
or inorganic carbon (IC) content of sample water, for example, a
total organic carbon measuring device in which organic matter is
separated from water containing few impurities, called pure water
or ultrapure water, by a carbon dioxide separation unit to assay
the TOC concentration of the water based on conductivity.
[0003] 2. Description of the Related Art
[0004] For the purpose of management of water containing few
impurities, such as water for manufacturing drugs, process water
for semiconductor manufacturing, cooling water, boiler water, or
tap water, the organic matter (TOC) content of a sample of such
water is measured.
[0005] As a TOC measuring device, a TOC meter comprising a total
carbon combustion unit using an oxidation catalyst is widely used.
The TOC meter measures TOC by converting TOC contained in sample
water to CO.sub.2 gas and measuring the CO.sub.2 concentration in
the gas phase by a nondispersive infrared analyzer.
[0006] On the other hand, a device that measures the TOC
concentration of sample water while keeping the sample water in the
liquid phase has also been developed. In the case of such a device
that measures sample water while keeping it in the liquid phase,
organic matter contained in sample water is converted to carbon
dioxide by an oxidation reactor. The sample water is kept in the
liquid phase and is allowed to flow through a sample water channel.
The sample water channel is in contact with a measurement water
channel, through which measurement water flows, with a gas
permeable membrane being interposed therebetween, and therefore
carbon dioxide contained in the sample water is transferred to
measurement water. The measurement water containing carbon dioxide
transferred from the sample water is sent to a conductivity meter
to measure the conductivity thereof. The carbon dioxide
concentration of the sample water can be determined from the
measured conductivity of the measurement water, and a
previously-prepared calibration curve representing the relationship
between the conductivity of measurement water and the carbon
dioxide concentration of sample water (see Patent Document 1).
[0007] The present invention is directed to such a device that
measures the TOC concentration of sample water while keeping the
sample water in the liquid phase.
[0008] In the measurement of TOC, a measuring device needs to have
a blank value of its own, that is, a system blank value. The system
blank value of a TOC meter is a signal obtained by measuring, as a
sample, pure water whose organic carbon content is infinitely close
to zero, and is used as a reference for measurement by the TOC
meter. Such a system blank value is essential to quantitative
measurement of very low TOC levels of pure water and the like.
[0009] In pure water that is in contact with air, CO.sub.2
contained in air is dissolved. Therefore, it is difficult to obtain
pure water whose carbon content is infinitely close to zero when
the pure water is exposed to the atmosphere. In the case of a
conventional TOC meter that comprises a total carbon combustion
unit using an oxidation catalyst and measures TOC by converting TOC
contained in sample water to CO.sub.2 gas and measuring the
CO.sub.2 concentration in the gas phase, pure water is vaporized
while TOC contained in the pure water is decomposed to CO.sub.2 gas
by oxidation and removed, and then remaining water vapor is
condensed to recover the pure water. The cycle of vaporization,
oxidative decomposition, and recovery is repeated in this device to
obtain pure water whose organic carbon content is infinitely close
to zero. The conventional TOC meter uses the measured value of the
thus obtained pure water as a system blank value. Patent Document
1: WO2008/047405
[0010] The present invention is directed to a TOC measuring device
that is not provided with, as a channel for measurement, a channel
for performing vaporization and oxidative decomposition of sample
water at the same time and then condensing the remaining water
vapor. In order to provide a channel for preparing blank water used
to obtain a system blank value, it is necessary to provide not only
a channel different from a channel for measurement but also a
container intended for exclusive use as a pure water trap. Even
when such a channel for preparing blank water is provided, it takes
a long time to obtain pure water whose organic carbon content is
infinitely close to zero by repeated cycles of vaporization and
oxidative decomposition of sample water and condensation of water
vapor.
SUMMARY OF THE INVENTION
[0011] It is therefore an object of the present invention to
provide a device that measures the TOC concentration of sample
water while keeping the sample water in the liquid phase and is
capable of easily obtaining a system blank value.
[0012] The present invention is directed to a TOC meter comprising:
a sample supply unit that collects and supplies sample water; an
oxidative decomposition unit that is connected to the sample supply
unit and oxidizes organic matter contained in the sample water
supplied from the sample supply unit to carbon dioxide; a carbon
dioxide separation unit that transfers carbon dioxide contained in
the sample water that has passed through the oxidative
decomposition unit to measurement water consisting of deionized
water; a conductivity measuring unit that measures the conductivity
of the measurement water flowing from the carbon dioxide separation
unit; and an arithmetic processing unit that calculates the TOC
concentration of the sample water from a measured value obtained by
the conductivity measuring unit.
[0013] The sample supply unit has a system for subjecting the
collected sample water to aeration treatment using a gas containing
no carbon dioxide.
[0014] The oxidative decomposition unit has oxidative decomposition
function that oxidizes organic matter contained in the supplied
sample water to carbon dioxide and is capable of turning on and off
the oxidative decomposition function.
[0015] The carbon dioxide separation unit includes: a sample water
channel through which the sample water that has passed through the
oxidative decomposition unit flows; a measurement water channel
through which measurement water consisting of deionized water
flows; and a gas permeable membrane interposed between the sample
water channel and the measurement water channel to allow carbon
dioxide to be transferred therethrough.
[0016] The arithmetic processing unit includes: a system blank
holding section that holds, as a system blank value, a measured
value obtained by the conductivity measuring unit when pure water
collected in the sample supply unit and subjected to aeration
treatment is allowed to pass through the oxidative decomposition
unit of which oxidative decomposition function is turned off and
then flows through the sample water channel; and an arithmetic
section that calculates the total organic carbon concentration of
sample water from a system blank value held in the system blank
holding section and a measured value obtained by the conductivity
measuring unit when the sample water is allowed to pass through the
oxidative decomposition unit of which oxidative decomposition
function is turned on and then flows through the sample water
channel.
[0017] In the case of a conventional TOC meter that measures TOC by
oxidative decomposition of TOC to gas-phase CO.sub.2 gas, it is
necessary to repeat the cycle of vaporization and oxidative
decomposition of pure water and recovery of water vapor into a pure
water trap by cooling many times to obtain pure water whose organic
carbon content is infinitely close to zero. During this operation,
TOC contained in pure water is decomposed to CO.sub.2 (inorganic
carbon) by oxidation, vaporized into a gas, and discharged to the
outside of the system together with a carrier gas. However,
gas-liquid equilibrium is established between gasified CO.sub.2 and
recovered pure water, and part of the gasified CO.sub.2 is
dissolved in the pure water. In this case, however, the empty space
of the pure water trap containing the recovered pure water is
aerated by a carrier gas containing little CO.sub.2 such as
high-purity air so that part of the dissolved CO.sub.2 is
distributed to the carrier gas. In this way, TOC contained in pure
water is converted to CO.sub.2 and removed by repeated cycles of
vaporization and oxidative decomposition of pure water and
recovery, and finally, pure water containing dissolved CO.sub.2
(inorganic carbon) whose concentration depends on the partial
pressure of CO.sub.2 in a carrier gas is recovered. The measured
intensity of the obtained pure water is conventionally used as a
system blank value. That is, the obtained system blank value is
equivalent to the measured intensity of CO.sub.2 (inorganic carbon)
remaining in pure water subjected to aeration treatment using a
carrier gas until CO.sub.2 is removed.
[0018] When the CO.sub.2 concentration of a carrier gas is zero,
CO.sub.2 contained in recovered pure water is eventually completely
removed by repeated cycles of vaporization, oxidative
decomposition, and recovery. However, even when high-purity air is
used as a carrier gas, it contains CO.sub.2 or hydrocarbons
although its amount is as small as less than 1 ppm, and therefore,
a system blank intensity has a certain value.
[0019] In the case of the TOC meter according to the present
invention, only
[0020] CO.sub.2 transferred from sample water to measurement water
through the gas permeable membrane in the carbon dioxide separation
unit is detected by the conductivity measuring unit. When pure
water is collected as sample water in the sample supply unit and
subjected to aeration treatment using a gas containing no CO.sub.2,
CO.sub.2 (inorganic carbon) contained in the sample water is
removed and only ionized TOC remains in the sample water. Even when
remaining in the sample water, the TOC is kept in its ionic state
when the oxidative decomposition function of the oxidative
decomposition unit is turned off, and therefore, the TOC is not
transferred to measurement water through the gas permeable membrane
in the carbon dioxide separation unit. Therefore, the pure water
flowing through the sample water channel is equivalent to one
containing no CO.sub.2 gas component.
[0021] The oxidative decomposition unit may include: an organic
matter oxidation part made of a UV-permeable material comprising a
channel through which sample water flows; and an ultraviolet light
source that irradiates sample water with ultraviolet light from the
outside of the organic matter oxidation part. In this case, the
oxidative decomposition function of the oxidative decomposition
unit is turned on and off by the ultraviolet light source.
[0022] Alternatively, the oxidative decomposition unit may include
an organic matter oxidation part made of a UV-permeable material
comprising a channel through which sample water flows, an
ultraviolet light source that irradiates sample water with
ultraviolet light from the outside of the organic matter oxidation
part, and a shutter interposed between the organic matter oxidation
part and the ultraviolet light source. In this case, the oxidative
decomposition function of the oxidative decomposition unit is
turned on and off by opening and closing the shutter.
[0023] The arithmetic section of the arithmetic processing unit may
hold calibration curve data representing the relationship between a
measured value obtained by the conductivity measuring unit and the
total organic carbon concentration of sample water supplied from
the sample supply unit. In this case, the arithmetic processing
unit corrects the calibration curve data using a system blank value
held in the system blank holding section to obtain corrected
calibration curve data, and calculates the total organic carbon
concentration of sample water from the corrected calibration curve
data and a measured value obtained by the conductivity measuring
unit when the sample water is measured.
[0024] The corrected calibration curve data may be obtained by, for
example, shifting the calibration curve data obtained from a
measured value so that its intercept value becomes a system blank
value held in the system blank holding section.
[0025] The sample supply unit may include a multi-port valve having
at least a port connected to a channel for supplying sample water,
a port connected to a channel for supplying pure water, a port
connected to the oxidative decomposition unit, a port opened to the
atmosphere, and a common port connected to any one of the ports by
switching, a syringe that is connected to the common port of the
multi-port valve and collects and sends sample water by slidably
moving a piston in a cylinder in a vertical direction, and a gas
supply channel that is connected to the lower end portion of the
cylinder of the syringe at a position above the piston in a state
where the piston is located at the lower end of the cylinder to
supply a gas containing no carbon dioxide into the cylinder.
[0026] In order to remove a CO.sub.2 gas component contained in
sample water by subjecting the sample water to aeration treatment,
the sample water is preferably acidified. Therefore, it is
preferred that the multi-port valve further has another port
connected to an acid supply channel for supplying an acid for
acidifying sample water collected in the syringe.
[0027] According to the present invention, commercially-available
pure water is subjected to aeration treatment using a gas
containing no carbon dioxide such as high-purity air and is
measured in a state where the oxidative decomposition function of
the oxidative decomposition unit is turned off, which makes it
possible to obtain a system blank value without preparing pure
water containing no organic carbon by repeated cycles of
vaporization, oxidative decomposition, and recovery. As compared to
a conventional method by which only a small amount of pure water
containing no organic carbon can be obtained despite its
complicated operation, a method according to the present invention
makes it possible to easily perform measurement any time and any
number of times.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] FIG. 1 is a block diagram schematically showing one
embodiment of the present invention.
[0029] FIG. 2 is a block diagram showing a first embodiment of an
oxidative decomposition unit, a carbon dioxide separation unit, and
a conductivity measuring unit.
[0030] FIG. 3 is a block diagram showing a second embodiment of the
oxidative decomposition unit, the carbon dioxide separation unit,
and the conductivity measuring unit.
[0031] FIG. 4 is a block diagram showing a third embodiment of the
oxidative decomposition unit, the carbon dioxide separation unit,
and the conductivity measuring unit.
[0032] FIG. 5 is a block diagram showing a fourth embodiment of the
oxidative decomposition unit, the carbon dioxide separation unit,
and the conductivity measuring unit.
[0033] FIG. 6 is a graph showing a calibration curve.
DESCRIPTION OF THE REFERENCE NUMERALS
[0034] 2: sample water channel
[0035] 4: intermediate water channel
[0036] 6: measurement water channel
[0037] 8, 10: gas permeable membranes
[0038] 20, 40: carbon dioxide separation units
[0039] 24: organic matter oxidation part
[0040] 26: ultraviolet lamp
[0041] 27: shutter
[0042] 34: conductivity meter
[0043] 102: sample supply unit
[0044] 104: channel switching valve
[0045] 106: syringe
[0046] 118: oxidative decomposition unit
[0047] 120: gas supply channel
[0048] 124: carbon dioxide separation unit
[0049] 128: arithmetic processing unit
[0050] 130: system blank holding section
[0051] 132: arithmetic section
DETAILED DESCRIPTION OF THE INVENTION
[0052] FIG. 1 is a schematic view of a TOC meter according to one
embodiment of the present invention. It is to be noted that in FIG.
1, components surrounded by a dashed-line box are housed in a
housing of a TOC meter 100 and the area outside the dashed-line box
represents the outside of the housing.
[0053] In the TOO meter 100, a sample supply unit 102 is provided.
The sample supply unit 102 includes a channel switching valve 104
constituted from a multi-port valve such as a 6-port valve or an
8-port valve, a water sampling syringe 106 connected to a common
port of the valve 104, and a gas supply channel 120 through which a
gas containing no carbon dioxide is supplied into the cylinder
106.
[0054] A channel 110 is connected to one of the ports of the valve
104 to receive sample water from the outside of the housing of the
TOC meter. A channel 112 is connected to another one of the ports
of the valve 104 to receive pure water from the outside of the
housing. A channel 114 is connected to yet another one of the ports
of the valve 104 to receive an acid for acidifying sample water or
pure water collected in the syringe 106 from the outside of the
housing. A channel 116 connected to an oxidative decomposition unit
118 is connected to yet another one of the ports of the valve 104.
Yet another one of the ports of the valve 104 can be opened to the
atmosphere.
[0055] As the acid, an inorganic acid such as hydrochloric acid,
sulfuric acid, or phosphoric acid is used. The pH of sample water
or pure water contained in the syringe 106 is preferably adjusted
to 4 or less by adding such an acid.
[0056] The valve 104 includes a stator having a plurality of ports,
and channel switching is performed by rotating a rotor so that the
syringe 106 connected to the common port of the valve 104 is
connected to any one of the ports.
[0057] The syringe 106 includes a cylinder and a piston 108, and
sample water or pure water and, in addition, an acid can be
introduced into the syringe 106 by slidably moving the piston 108
in a vertical direction while the inside of the cylinder is kept
liquid-tight. The sample water or pure water collected in the
syringe 106 can be supplied to the oxidative decomposition unit 118
through the valve 104 and the channel 116 by pushing the piston 108
upward. The piston 108 is attached to the tip of a plunger 107. The
piston 108 is slidably moved in the cylinder in a vertical
direction by driving the plunger 107 by a syringe driving unit 109
driven by a motor.
[0058] The gas supply channel 120 is connected to the lower end
portion of the cylinder of the syringe 106 to supply a gas
containing no carbon dioxide into the syringe 106 for aeration
treatment. The position at which the gas supply channel 120 is
connected to the cylinder is above the piston 108 in a state where
the piston 108 is located at the lower end of the cylinder.
Examples of the gas containing no carbon dioxide include, but are
not limited to, high-purity air contained in a bomb 119 and
high-purity air supplied through a column filled with a filler that
absorbs carbon dioxide gas.
[0059] When flowing through a channel in an organic matter
oxidation part of the oxidative decomposition unit 118, sample
water or pure water (hereinafter, when only the term "sample water"
is used, it refers to sample water or pure water) is irradiated
with ultraviolet light to decompose organic matter contained in the
sample water by oxidation to carbon dioxide gas.
[0060] The sample water that has passed through the oxidative
decomposition unit 118 is introduced into a carbon dioxide
separation unit 124.
[0061] In the carbon dioxide separation unit 124, a carbon dioxide
gas component contained in the sample water is transferred to
measurement water through a gas permeable membrane. The sample
water that has passed through the carbon dioxide separation unit
124 is disposed of.
[0062] The measurement water that has passed through the carbon
dioxide separation unit 124 is introduced into a conductivity
measuring unit 126. The conductivity measuring unit 126 is provided
with an electrode, and the measurement water is brought into
contact with the electrode to detect the conductivity thereof. The
conductivity of the measurement water varies depending on the
concentration of the carbon dioxide gas component transferred from
the sample water to the measurement water in the carbon dioxide
separation unit 124, and therefore, the concentration of the carbon
dioxide gas component of the sample water can be determined based
on the detected value of conductivity of the measurement water. The
carbon dioxide gas component is a component generated by the
oxidative decomposition unit 118 through oxidative decomposition of
a TOC component contained in the sample water, and therefore, the
TOC concentration of the sample water can be determined.
[0063] An arithmetic processing unit 128 is connected to the
electrode of the conductivity measuring unit 126 for measuring
conductivity to calculate the TOC concentration of sample water
based on conductivity detected by the conductivity measuring unit
126. The arithmetic processing unit 128 includes a system blank
holding section 130 and an arithmetic section 132.
[0064] The system blank holding section 130 holds, as a system
blank value, a measured value obtained by the conductivity
measuring unit 126 when pure water collected in the syringe 106 and
subjected to aeration treatment is allowed to pass through the
oxidative decomposition unit 118 whose oxidative decomposition
function is turned off and then flow through a sample water channel
in the carbon dioxide separation unit 118.
[0065] The arithmetic section 132 calculates the TOC concentration
of sample water from a system blank value held in the system blank
holding section 130 and a measured value obtained by the
conductivity measuring unit 126 when the sample water is allowed to
pass through the oxidative decomposition unit 118 whose oxidative
decomposition function is turned on and then flows through the
sample water channel in the carbon dioxide separation unit 118.
[0066] When a system blank value is measured by the TOC meter, the
valve 104 is set so that the channel 112 for receiving pure water
is connected to the syringe 106 to collect an appropriate amount of
pure water (e.g., 3 mL of pure water) in the syringe 106. Then, the
valve 104 is rotated so that the syringe 106 is connected to the
port connected to the channel 114 for supplying an acid, and a
predetermined amount of acid is suctioned into the syringe 106 by
further withdrawing the piston 108 of the syringe 106 to adjust the
pH of the pure water to 4 or less. After this, the valve 104 is
rotated so that the syringe 106 is connected to the port opened to
the atmosphere, and in this state, the piston 108 is withdrawn so
as to be located at the lower end of the cylinder. In this state,
high-purity air is supplied to the syringe 106 through the channel
120 at a flow rate of, for example, 100 mL/min for 90 seconds to
subject the pure water collected in the syringe 106 to aeration
treatment so that inorganic carbon is removed from the pure water
and released into the atmosphere.
[0067] After the completion of the aeration treatment, the valve
104 is rotated so that the syringe 106 is connected to the channel
116 to supply the pure water collected in the syringe 106 to the
oxidative decomposition unit 118. At this time, an ultraviolet lamp
provided in the oxidative decomposition unit 118 is turned off or a
shutter is interposed between an ultraviolet lamp and the oxidative
decomposition unit 118, and therefore, even when passing through
the oxidative decomposition unit 118, the sample water is not
irradiated with ultraviolet light. Therefore, even when remaining
in the pure water, an ionized TOC component is not decomposed by
oxidation, and the TOC component is sent to the carbon dioxide
separation unit 124 while being kept in its ionic state. In the
carbon dioxide separation unit 124, the pure water is brought into
contact with measurement water with a gas permeable membrane being
interposed therebetween. Then, the conductivity of the measurement
water is detected by the conductivity measuring unit 126.
[0068] As shown in FIG. 1, sample water (or pure water) collected
in the syringe 106 is supplied to the oxidative decomposition unit
118 through the channel 116. Hereinbelow, some embodiments of the
oxidative decomposition unit 118, the carbon dioxide separation
unit 124, and the conductivity measuring unit 126 will be
described.
[0069] According to an embodiment shown in FIG. 2, the oxidative
decomposition unit 118 includes an organic matter oxidation part 24
and an ultraviolet lamp 26. The organic matter oxidation part 24 is
made of a UV-permeable material and comprises a channel through
which sample water flows. The ultraviolet lamp 26 irradiates sample
water with ultraviolet light from the outside of the organic matter
oxidation part 24. The organic matter oxidation part 24 is provided
with a UV-irradiated portion in which sample water is irradiated
with ultraviolet light emitted from the ultraviolet lamp 26.
Therefore, organic matter contained in sample water is oxidized to
carbon dioxide by UV irradiation while the sample water flows
through the UV-irradiated portion. The oxidative decomposition
function of the oxidative decomposition unit 118 is turned on and
off by the ultraviolet lamp 26.
[0070] The oxidative decomposition unit 118 may include a shutter
27 interposed between the organic matter oxidation part 24 and the
ultraviolet lamp 26 as shown by a dashed line in FIG. 2. In this
case, the oxidative decomposition function of the oxidative
decomposition unit 118 can be turned on and off by opening and
closing the shutter 27.
[0071] Also in the case of other embodiments, the oxidative
decomposition unit 118 may have the same structure as that of the
embodiment shown in FIG. 2.
[0072] The sample water that has passed through the oxidative
decomposition unit 118 is supplied to a carbon dioxide separation
unit 20 that is one example of the carbon dioxide separation unit
124. The carbon dioxide separation unit 20 includes a sample water
channel 2, a measurement water channel 6, and an intermediate water
part 4 interposed between the sample water channel 2 and the
measurement water channel 6. The sample water channel 2, the
intermediate water part 4, and the measurement water channel 6 are
stacked in a vertical direction and integrated together. The sample
water that has passed through the organic matter oxidation part 24
is allowed to flow through the sample water channel 2. Intermediate
water whose pH is in the neutral range and higher than that of the
sample water is allowed to flow through or is enclosed in the
intermediate water part 4. The intermediate water part 4 is
preferably provided as a channel through which the intermediate
water flows. Measurement water comprising deionized water is
allowed to flow through the measurement water channel 6. The sample
water channel 2 and the intermediate water part 4 are in contact
with each other with a gas permeable membrane 8 being interposed
therebetween, and the intermediate water part 4 and the measurement
water channel 6 are also in contact with each other with a gas
permeable membrane 10 being interposed therebetween. As the gas
permeable membranes 8 and 10, membranes not having carbon dioxide
selectivity, such as porous membranes usually used to achieve
high-speed measurement, are used.
[0073] Ion-exchange water is supplied as deionized water to the
measurement water channel 6 of the carbon dioxide separation unit
20. More specifically, pure water stored in a liquid storage tank
28 is suctioned by a pump 32 and is allowed to pass through the
ion-exchange resin 30 to obtain ion-exchange water, and the
obtained ion-exchange water is supplied to the measurement water
channel 6 of the carbon dioxide separation unit 20. The
conductivity of the measurement water that has flowed through the
measurement water channel 6 is measured by a conductivity meter 34
provided as the conductivity measuring unit 126. The conductivity
is derived from carbon dioxide transferred from the intermediate
water to the measurement water in the carbon dioxide separation
unit 20. The measurement water that has passed through the
conductivity meter 34 is returned to the liquid storage tank 28 and
reused. The conductivity meter 34 may be integrated with the carbon
dioxide separation unit 20 or may be provided separately from the
carbon dioxide separation unit 20. In the latter case, the
conductivity meter 34 is connected to the carbon dioxide separation
unit 20 through a channel. The sample water that has flowed through
the sample water channel 2 of the carbon dioxide separation unit 20
is discharged from the carbon dioxide separation unit 20.
[0074] As the intermediate water, pure water or deionized water is
supplied to the intermediate water channel 4. Deionized water that
has passed through the ion-exchange resin 30 can also be supplied
as the intermediate water. The intermediate water and the sample
water are in contact with each other with the sample water
channel-side gas permeable membrane 8 being interposed
therebetween, and the intermediate water and the measurement water
are also in contact with each other with the measurement water
channel-side gas permeable membrane 10 being interposed
therebetween. The intermediate water that has flowed through the
intermediate water channel 4 is discharged from the carbon dioxide
separation unit 20.
[0075] FIG. 3 shows another embodiment. As shown in FIG. 3, a
carbon dioxide separation unit 40 that is another example of the
carbon dioxide separation unit 124 is separated into a sample
water-side gas exchange part 40a and a measurement water-side gas
exchange part 40b. The intermediate water channel is separated into
a sample water-side intermediate water channel 4a and a measurement
water-side intermediate water channel 4b, and the channel 4a and
the channel 4b are connected to each other through a connecting
channel. The units other than the carbon dioxide separation unit 40
shown in FIG. 3 have the same structure as those shown in FIG.
2.
[0076] FIG. 4 shows yet another embodiment in which a common
syringe pump is used to maintain a constant ratio between the flow
rate of intermediate water and the flow rate of measurement water.
The carbon dioxide separation unit 20 shown in FIG. 4 is the same
as that according to the embodiment shown in FIG. 2, but may be
separated into a sample water-side gas exchange part and a
measurement water-side gas exchange part as shown in FIG. 3. As
intermediate water and measurement water, the same ion-exchange
water supplied by the pump 32 through the ion-exchange resin 30 is
used. The measurement water is allowed to flow through the
measurement water channel 6 to the conductivity meter 34. The
intermediate water is allowed to flow through the intermediate
water channel 4. A channel for returning the intermediate water to
the liquid storage tank 28 is provided with a valve 48, and a
channel for returning the measurement water to the liquid storage
tank 28 is provided with a valve 50, and two syringes 42 and 44 of
one syringe pump 46 are connected to these channels respectively to
adjust the flow rates of the intermediate water and the measurement
water. When the intermediate water and the measurement water are
allowed to flow, the valves 48 and 50 are closed and the
intermediate water and the measurement water are simultaneously
suctioned into the syringes 42 and 44, respectively. Therefore, the
intermediate water is allowed to flow at a flow rate determined by
the inner diameter of the syringe 42, and the measurement water is
allowed to flow at a flow rate determined by the inner diameter of
the syringe 44. After the completion of measurement, the valves 48
and 50 are opened, and the intermediate water and the measurement
water suctioned into the syringes 42 and 44 are ejected from the
syringes 42 and 44 and returned to the liquid storage tank 28.
[0077] As described above, when the intermediate water discharged
from the intermediate water channel 4 and the measurement water
discharged from the measurement water channel 6 are simultaneously
suctioned into the two syringes 42 and 44 fixed to the single
syringe pump 46, the ratio between the flow rate of the
intermediate water and the flow rate of the measurement water can
be maintained at a predetermined constant value by selecting the
diameters of the syringes 42 and 44. By maintaining a constant
ratio between the flow rate of the intermediate water and the flow
rate of the measurement water, it is possible to maintain a
constant distribution ratio of a gas component from the
intermediate water to the measurement water and therefore to
achieve high measurement reproducibility.
[0078] Hereinbelow, yet another embodiment in which the organic
matter oxidation part 24, the carbon dioxide separation unit 20,
and the conductivity meter 34 are integrated together will be
described with reference to FIG. 5. It is to be noted that when it
is necessary to differentiate between the front surface and the
back surface of each substrate shown in FIG. 5, the upper surface
and the lower surface thereof are referred to as "front surface"
and "back surface" respectively.
[0079] The organic matter oxidation part 24 is constituted from a
UV light-incident-side substrate 60 and a substrate 62 bonded to
the substrate 60. The substrate 60 is formed from a UV
light-permeable quartz substrate to decompose organic matter by
ultraviolet light. Part of the substrate 60 is a UV light incident
portion on which ultraviolet light is incident. The substrate 60
has a through hole 64 serving as a sample water inlet and a through
hole 66 serving as a sample water outlet. The other substrate 62 is
also formed from a quartz substrate. The substrate 62 has an
oxidation part channel 68 formed in the front surface thereof, and
one end of the oxidation part channel 68 is located at a position
corresponding to the sample water inlet 64. Further, the substrate
62 has the sample water channel 2 formed in the back surface
thereof, and one end of the sample water channel 2 is located at a
position corresponding to the sample water outlet 66. The substrate
62 has a through hole 70 for connecting the other end of the
oxidation part channel 68 and the other end of the sample water
channel 2 together and a through hole 72 for connecting the one end
of the sample water channel 2 and the sample water outlet 66
together. On the back surface of the substrate 62, that is, on the
surface opposite to the surface of the substrate 62 bonded to the
substrate 60, a light-blocking metal film 33 is provided to define
a UV light-irradiated region. The light-blocking metal film 33 is,
for example, a Pt/Ti film (a film obtained by forming a platinum
film on a titanium film formed as a contact layer) having a
thickness of 0.05 .mu.m or more.
[0080] The size of each of the oxidation part channel 68 and the
sample water channel 2 is not particularly limited, but the
oxidation part channel 68 and the sample water channel 2 each have,
for example, a width of about 1 mm, a depth of about 0.2 mm, and a
length of about 200 mm, and can be formed by processing such as wet
etching or dry etching. The through holes 64, 66, and 70 can be
formed by, for example, sandblasting. The substrates 60 and 62 can
be bonded together by hydrofluoric acid bonding.
[0081] The conductivity meter 34 is formed by bonding the back
surface of a quartz substrate 80 onto an electrode pattern 76
formed by a Pt/Ti film on a quartz substrate 74 with a film 78,
from which a channel portion has been cut out, being interposed
therebetween.
[0082] Examples of the film 78 to be used include an adhesive
fluorine resin film (e.g., NEOFLON (which is a trademark of Daikin
Industries, Ltd.) EFEP having a thickness of 100 .mu.m) and a PDMS
(polydimethylsiloxane) film (e.g., SYLGARD.RTM. 184 having a
thickness of 100 .mu.m and manufactured by Dow Corning). On the
electrode pattern 76, a channel through which measurement water
flows is formed by the film 78.
[0083] The electrode pattern 76 can be formed by forming a Pt/Ti
film by sputtering and subjecting the film to patterning by
photolithography and etching used in semiconductor manufacturing
processes or the field of micro processing. However, a method for
forming the electrode pattern 76 is not particularly limited. The
film for forming a channel on the electrode pattern 76 is not
limited to a NEOFLON film or a PDMS film, and an adhesive organic
film or an adhesive-coated thin film may be used.
[0084] In the front surface of the quartz substrate 80, the
measurement water channel 6 is formed. The quartz substrate 80 has
a measurement water branch channel 82 connected to one end of the
measurement water channel 6 and a through hole 84 for connecting
the other end of the measurement water channel 6 to the channel
provided with the electrode pattern 76 of the conductivity meter
34. The quartz substrate 80 also has a through hole 86 serving as
an intermediate water branch channel for introducing intermediate
water and a through hole 88 serving as an intermediate water outlet
for discharging intermediate water. The thickness of the quartz
substrate 80 is not particularly limited, but is, for example, 1
mm.
[0085] The quartz substrate 74 has a through hole 90 serving as an
ion-exchange water inlet for supplying ion-exchange water as
deionized water and a through hole 92 serving as an ion-exchange
water outlet for discharging excess ion-exchange water. The
ion-exchange water inlet 90 is connected to the measurement water
branch channel 82, the intermediate water branch channel 86, and
the ion-exchange water outlet 92 through a channel formed by the
PDMS film 78 sandwiched between the substrates 74 and 80.
[0086] The quartz substrate 74 also has a through hole 94 serving
as a measurement water outlet for discharging measurement water
from the channel provided with the electrode pattern 76 of the
conductivity meter 34 after conductivity detection and a through
hole 96 that is connected to the through hole 88 provided in the
quartz substrate 80 to discharge intermediate water and serves as
an intermediate water outlet for discharging intermediate
water.
[0087] The back surface of the substrate 62 constituting the
organic matter oxidation unit 24 and the front surface of the
substrate 80 constituting a unit of the conductivity meter 34 are
bonded together with the two gas permeable membranes 8 and 10
constituting the carbon dioxide separation unit being interposed
therebetween. A PDMS film 98 is interposed between the gas
permeable membranes 8 and 10 so that a gap is formed by the
thickness of the PDMS film 98. Therefore, the intermediate water
channel 4 is formed by patterning the PDMS film 98. The
intermediate water channel 4 is configured so that one end of the
intermediate water channel 4 is connected to the intermediate water
branch channel 86 provided in the quartz substrate 80 to introduce
intermediate water and the other end of the intermediate water
channel 4 is connected to the through hole 88 for discharging
intermediate water.
[0088] The gap between the gas permeable membranes 8 and 10 and the
gap between the substrates 62 and 80 are sealed with film such as
PDMS film so that the sample water channel 2 is formed between the
gas permeable membrane 8 and the substrate 62 and the measurement
water channel 6 is formed between the gas permeable membrane 10 and
the substrate 80.
[0089] The gas permeable membranes 8 and 10 are not particularly
limited, and membranes not having carbon dioxide selectivity are
used. Examples of such gas permeable membranes 8 and 10 include
porous fluorine resin membranes (e.g., POREFLON having a thickness
of 30 .mu.m and manufactured by Sumitomo Electric Industries,
Ltd.).
[0090] According to this embodiment, sample water is introduced
through the sample water inlet 64 of the substrate 60, flows
through the oxidation part channel 68 and the sample water channel
2, and is discharged through the sample water outlet 66. During
that time, the sample water is oxidized by the oxidation part 24 by
UV irradiation, and is brought into contact with intermediate water
with the gas permeable membrane 8 of the carbon dioxide separation
unit 20 being interposed therebetween so that a gas component such
as carbon dioxide is distributed to the intermediate water.
[0091] Ion-exchange water is produced outside this device and is
introduced through the ion-exchange water inlet 90. Most of the
introduced ion-exchange water is directly discharged through the
ion-exchange water outlet 92, and only the needed amount of
ion-exchange water is supplied to the measurement water channel 6
through the measurement water branch channel 82 and to the
intermediate water channel 4 through the intermediate water branch
channel 86.
[0092] The intermediate water channel 4 is in contact with both the
gas permeable membrane 8 to be brought into contact with sample
water and the gas permeable membrane 10 to be brought into contact
with measurement water, and therefore, a gas component transferred
from sample water to intermediate water is distributed to
measurement water while reaching equilibrium with its ions, and
then the intermediate water is discharged to the outside through
the intermediate water outlets 88 and 96. The measurement water
receives the gas component while flowing through the measurement
water channel 6, passes through the conductivity meter 34, and is
discharged through the measurement water outlet 94.
[0093] Hereinbelow, the results of measurement using the embodiment
shown in FIGS. 1 and 2 will be described.
[0094] About 3 mL of pure water was collected as sample water in
the syringe 106, and then phosphoric acid was added to adjust the
pH of the pure water to about 4. Then, high-purity air was
introduced into the syringe 106 at a flow rate of about 100 ml/min
for 90 seconds, and then the pure water was sent to the organic
matter oxidation part 24 of the oxidative decomposition unit 118.
At this time, the oxidative decomposition function of the oxidative
decomposition unit 118 was turned off by turning off the
ultraviolet lamp 26 of the oxidative decomposition unit 118 or by
blocking UV light with the shutter 27 provided in the oxidative
decomposition unit 118 so that only the remaining CO.sub.2
(inorganic carbon) in the pure water sample could be measured. The
pure water sample that had passed through the oxidative
decomposition unit 118 whose oxidative decomposition function was
turned off was supplied to the carbon dioxide separation unit 118,
and the conductivity of measurement water that had passed through
the carbon dioxide separation unit 118 was measured by the
conductivity measuring unit 126. In this way, a signal derived from
CO.sub.2 remaining in the pure water subjected to aeration
treatment was detected and processed to obtain a system blank
value.
[0095] The TOC of each of pure water and two potassium hydrogen
phthalate standard solutions (500 .mu.gC/L and 1000 .mu.gC/L) was
measured in a state where the oxidative decomposition function of
the oxidative decomposition unit 118 was turned on. The TOC of each
of these samples was measured five times.
[0096] The measurement results are shown in Table 1.
TABLE-US-00001 TABLE 1 Signal values of samples System blank Pure
water 500 ppb 1000 ppb 4.65 5.04 27.4 54.5 4.66 5.03 27.4 52.5 4.67
5.03 27.2 53.2 4.66 5.06 27.8 53.7 4.67 5.06 27.0 53.8 4.66 5.04
27.4 53.5
[0097] FIG. 6 shows a calibration curve obtained from these
measurement results. This calibration curve was prepared using
averages of five TOC measurements shown in Table 1. The data of the
calibration curve is held in the arithmetic section 132 of the
arithmetic processing unit 128. The data of the calibration curve
directly obtained from the measurement results shown in Table 1 is
represented by the following formula: y=0.0485x+5.04, wherein y is
a signal value and x is a sample concentration (TOC value).
[0098] The data of the calibration curve directly obtained from the
measurement results is shifted so that its intercept value becomes
the above system blank value to obtain the data of a corrected
calibration curve. The data of the corrected calibration curve is
represented by the following formula:
y=0.0485x+4.66.
[0099] The TOC concentration of sample water can be determined from
the corrected calibration curve and a measured value obtained by
measuring the sample water in a state where the oxidative
decomposition function of the oxidative decomposition unit 118 is
turned on.
[0100] The TOC value of pure water can be estimated as follows
using the system blank value and the calibration curve obtained
using this embodiment:
[0101] TOC value=(signal value of pure water-system blank
value)/0.0485=(5.04-4.66)/0.0485=7.84 .mu.gC/L
[0102] On the other hand, a TOC meter different from the TOC meter
according to the present invention, that is, a TOC meter provided
with a total carbon combustion unit for converting TOC contained in
sample water into CO.sub.2 gas using an oxidation catalyst to
measure the CO.sub.2 concentration in the gas phase was used to
determine the TOC value of a pure water sample using a system blank
value obtained by repeated cycles of oxidative decomposition and
recovery of pure water that was the same as the pure water sample.
As a result, the TOC value of the pure water sample was 6.6
.mu.gC/L.
[0103] As described above, the TOC value of pure water determined
by the TOC meter according to the embodiment of the present
invention was 7.84 .mu.gC/L, which was close to the TOC value of
pure water determined using the conventional TOC meter. This
indicates that the measurement of a system blank based on the
system according to the present invention has high validity.
* * * * *