Patent Publication Number: US-2023136954-A1

Title: Total organic carbon measurement device and total organic carbon measurement method

Description:
TECHNICAL FIELD 
     The present invention relates to a total organic carbon measurement device and a total organic carbon measurement method. 
     BACKGROUND ART 
     In order to measure total organic carbon (TOC) contained in a sample, a total organic carbon measurement device is used. A sample may contain inorganic carbon (IC) in addition to total organic carbon. TOC and IC are collectively referred to as total carbon (TC). 
     As an example of a method of measuring TOC, a method of measuring TC and IC, and calculating a difference between them (TC—IC) as TOC is known (see, for example, Patent Document 1 below). TC is measured as carbon dioxide generated when a sample is burned in a combustion tube is detected by a detection unit. On the other hand, IC is measured as carbon dioxide generated when a sample is added with acid and aerated is detected by a detection unit. 
     Further, as another method for measuring TOC, a method of measuring TOC in which acid is added to a sample and then the sample is aerated so that IC is converted into carbon dioxide and the carbon dioxide is removed, and carbon dioxide generated when the sample from which the IC is removed is burned in a combustion tube is detected by a detection unit. 
     In either of the above two methods, carrier gas is introduced into a combustion tube, and a mixture of the carrier gas and a sample is burned in the combustion tube. As the carrier gas, high purity air or the like is used. The carrier gas has not only a function of sending carbon dioxide generated from a sample to a detection unit, but also a function as combustion supporting gas when the sample is burned in the combustion tube. 
     PRIOR ART DOCUMENT 
     Patent Document 
     
         
         Patent Document 1: Japanese Patent Laid-Open No. 2007-93209 
       
    
     SUMMARY OF THE INVENTION 
     Problems to be Solved by the Invention 
     In the conventional total organic carbon measurement device, since carrier gas also has a function as combustion supporting gas, it has been difficult to use inert gas as the carrier gas. That is, in a case where inert gas is used as carrier gas, carbon dioxide generated from a sample can be sent to a detection unit by the carrier gas, but it is difficult to efficiently burn the sample in a combustion tube. 
     The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a total organic carbon measurement device and a total organic carbon measurement method in which inert gas can be used as carrier gas. 
     Means for Solving the Problems 
     A first aspect of the present invention is a total organic carbon measurement device including a sample heating unit, a carrier gas introduction unit, and a detection unit. The sample heating unit has a space in which an oxidation catalyst is arranged, and heats a sample arranged in the space. The carrier gas introduction unit introduces inert gas containing water vapor as carrier gas into the sample heating unit. The detection unit detects carbon dioxide generated by steam reforming reaction of organic carbon in a sample in the sample heating unit. 
     A second aspect of the present invention is a total organic carbon measurement method including a carrier gas introduction step, a sample heating step, and a detection step. In the carrier gas introduction step, inert gas containing water vapor is introduced as carrier gas into a sample heating unit having a space in which an oxidation catalyst is arranged. In the sample heating step, a sample arranged in the space is heated in the sample heating unit, and organic carbon in the sample is caused to undergo steam reforming reaction, so that carbon dioxide is generated. In the detection step, the carbon dioxide that is generated is detected. 
     Effects of the Invention 
     According to the present invention, carbon dioxide can be generated from total organic carbon in a sample by an action of water vapor contained in carrier gas, and therefore inert gas can be used as the carrier gas. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic view illustrating a configuration example of a total organic carbon measurement device. 
         FIG.  2    is a schematic cross-sectional view illustrating a configuration example of a humidifier. 
         FIG.  3    is a flowchart for explaining a method for measuring total organic carbon. 
     
    
    
     MODE FOR CARRYING OUT THE INVENTION 
     1. Overall Configuration of Total Organic Carbon Measurement Device 
       FIG.  1    is a schematic view illustrating a configuration example of a total organic carbon measurement device. The total organic carbon measurement device includes a syringe  1 , a flow path switching unit  2 , a total organic carbon measurement unit (TOC measurement unit)  3 , a gas source  4 , a flow controller  5 , a humidifier  6 , a control unit  7 , a display unit  8 , and the like. 
     The syringe  1  includes, for example, a cylindrical body  11  and a plunger  12 . The plunger  12  is inserted into the cylindrical body  11 , and liquid can be sucked into an internal space of the syringe  1  enclosed by an inner surface of the cylindrical body  11  and the plunger  12 . Specifically, by displacing the plunger  12  with respect to the cylindrical body  11 , suction operation of liquid into the syringe  1  and discharge operation of liquid from the syringe  1  are performed. The plunger  12  is displaced by driving of a drive unit (not illustrated) including, for example, a motor. 
     The syringe  1  is fluidly connected to the flow path switching unit  2 . The flow path switching unit  2  includes, for example, a multi-port valve that allows optional communication of a plurality of ports. Pipes  21 A,  22 A,  23 A,  24 A, and  25 A are fluidly connected to ports of the flow path switching unit  2 , and any one of the pipes  21 A,  22 A,  23 A,  24 A, and  25 A can communicate with the syringe  1  by switching of the flow path switching unit  2 . 
     When suction operation by the syringe  1  is performed in a state where the pipe  21 A communicates with the syringe  1 , a sample to be analyzed is sucked into the syringe  1  from a sample storage unit  21 B storing the sample. Further, in a case where suction operation by the syringe  1  is performed in a state where the pipe  22 A communicates with the syringe  1 , acid is sucked into the syringe  1  from an acid storage unit  22 B storing the acid. 
     In this manner, a sample or acid can be selectively sucked into the syringe  1 . As the acid, hydrochloric acid can be exemplified, but the acid is not limited to hydrochloric acid. The pipe  21 A and the sample storage unit  21 B constitute a sample supply unit  21  for supplying a sample. The pipe  22 A and the acid storage unit  22 B constitute an addition unit  22  for adding acid to a sample by introducing the acid into the syringe  1 . 
     The pipe  23 A fluidly connects the flow path switching unit  2  and the TOC measurement unit  3 . In a case where discharge operation by the syringe  1  is performed in a state where the pipe  23 A communicates with the syringe  1 , liquid in the syringe  1  is supplied to the TOC measurement unit  3  via the pipe  23 A. The pipe  24 A communicates with the drain. The pipe  25 A communicates with the atmosphere for degassing the syringe  1 . 
     The TOC measurement unit  3  includes a sample injection mechanism  31 , a reaction tube  32 , an electric furnace  33 , a dehumidifier  34 , a detection unit  35 , and the like. The pipe  23 A communicates with the sample injection mechanism  31  in the TOC measurement unit  3 . Therefore, liquid in the syringe  1  can be supplied from the pipe  23 A to the sample injection mechanism  31  by discharge operation by the syringe  1 . 
     In addition to the pipe  23 A as a sample supply path, a pipe  41  as a carrier gas supply path is fluidly connected to the sample injection mechanism  31 . The pipe  41  communicates the gas source  4  and the sample injection mechanism  31 , and carrier gas supplied from the gas source  4  is introduced into the sample injection mechanism  31  via the pipe  41 . Carrier gas supplied from the gas source  4  is, for example, inert gas such as high-purity nitrogen. However, the carrier gas is not limited to nitrogen, and may be another type of inert gas. 
     The flow controller  5  and the humidifier  6  are provided in the pipe  41 . The humidifier  6  constitutes a water vapor generation unit that generates water vapor. By providing the humidifier  6  in the pipe  41  and allowing carrier gas to pass through the humidifier  6 , water vapor generated in the humidifier  6  can be mixed with the carrier gas. In this manner, carrier gas mixed with water vapor can be introduced into the sample injection mechanism  31 . 
     At least part of the pipe  41  is heated by a pipe heating unit  41 A. The pipe heating unit  41 A may heat at least part of the pipe  41  between the humidifier  6  and the sample injection mechanism  31 . In this manner, water vapor in the carrier gas flowing in the pipe  41  can be heated by the pipe heating unit  41 A. Temperature of the pipe  41  in a portion heated by the pipe heating unit  41 A is adjusted to, for example, about 50° C. The pipe  41  is formed of, for example, metal such as stainless steel, and the pipe heating unit  41 A is provided so as to be in contact with or close to the pipe  41  from the outside. 
     The pipe heating unit  41 A can be composed of, for example, a sheath heater, but is not limited to a sheath heater. Further, it is also possible to omit the pipe heating unit  41 A. That is, water vapor in carrier gas flowing in the pipe  41  does not need to be heated. In this case, temperature of water vapor may be 0° C. or higher, and may be, for example, a temperature similar to room temperature. 
     The reaction tube  32  communicates with the sample injection mechanism  31 , and a sample supplied from the syringe  1  to the sample injection mechanism  31  is injected into the reaction tube  32  together with carrier gas from the sample injection mechanism  31 . The gas source  4 , the flow controller  5 , the humidifier  6 , the sample injection mechanism  31 , the pipe  41 , and the pipe heating unit  41 A constitute a carrier gas introduction unit  40  that introduces carrier gas into the reaction tube  32 . 
     The reaction tube  32  is formed of, for example, quartz glass or ceramic, and an oxidation catalyst  322  is arranged in a space  321  formed inside. As the oxidation catalyst, for example, a platinum-supported alumina catalyst is used. The reaction tube  32  is externally heated by the electric furnace  33 . The electric furnace  33  heats a sample arranged in the space  321  of the reaction tube  32  by heating the reaction tube  32  at a high temperature of about 680° C. The reaction tube  32  and the electric furnace  33  constitute a sample heating unit  30  for heating a sample. However, the sample heating unit  30  is not limited to one composed of the reaction tube  32  and the electric furnace  33 , and may be composed of other members. 
     A sample injected into the reaction tube  32  from the sample injection mechanism  31  generates carbon dioxide as an organic substance contained in the sample is oxidized. An amount of carbon dioxide generated from a sample is an amount corresponding to an amount of an organic substance contained in the sample. Carbon dioxide generated in the reaction tube  32  is sent to the dehumidifier  34  together with carrier gas, dehumidified in the dehumidifier  34 , and then guided to the detection unit  35 . 
     The detection unit  35  can be composed of, for example, a non-dispersive infrared absorption type sensor (NDIR type sensor), but is not limited to a non-dispersive infrared absorption type sensor. The detection unit  35  detects carbon dioxide generated from a sample in the reaction tube  32 . A carbon dioxide detection signal in the detection unit  35  is input to the control unit  7 . 
     The control unit  7  includes, for example, a processor including a central processing unit (CPU). The control unit  7  calculates TOC contained in a sample by performing calculation based on a carbon dioxide detection signal input from the detection unit  35 . Further, the control unit  7  controls operation of each unit such as the flow controller  5  provided in the total organic carbon measurement device. 
     The display unit  8  is composed of, for example, a liquid crystal display. Display on the display unit  8  is controlled by the control unit  7 . The display unit  8  displays various types of information such as a measurement result of TOC, for example. 
     A pipe  51  communicating with the syringe  1  is connected to the flow controller  5  separately from the pipe  41  communicating with the sample injection mechanism  31 . The flow controller  5  is a two-system flow controller capable of individually controlling a flow rate of carrier gas toward the sample injection mechanism  31  via the pipe  41  and a flow rate of carrier gas toward the syringe  1  via the pipe  51 . The flow controller  5  constantly supplies carrier gas from the gas source  4  to the sample injection mechanism  31  via the pipe  41  by controlling a flow rate of the carrier gas toward the sample injection mechanism  31  (TOC measurement state). Further, the flow controller  5  temporarily supplies carrier gas from the gas source  4  to the syringe  1  via the pipe  51  by controlling a flow rate of the carrier gas to the syringe  1  side (IC removal state). 
     After a sample is sucked into the syringe  1  from the sample storage unit  21 B, acid is added into the syringe  1  from the acid storage unit  22 B, and the flow controller  5  is brought into the IC removal state. Then, liquid (mixed liquid of the sample and the acid) in the syringe  1  is aerated by carrier gas supplied into the syringe  1 . In this manner, IC contained in the sample in the syringe  1  can be converted into carbon dioxide and removed. At this time, carbon dioxide generated in the syringe  1  is released into the atmosphere through the pipe  25 A. 
     After the above, in a state where carrier gas is supplied from the flow controller  5  to the sample injection mechanism  31  side via the pipe  41  (TOC measurement state), the sample from which IC is removed is injected from the syringe  1  into the reaction tube  32  via the sample injection mechanism  31 . In this way, the sample from which IC is removed is caused to react in the reaction tube  32 , and carbon dioxide generated in the reaction tube  32  is detected by the detection unit  35 , so that TOC can be measured. 
     2. Specific Configuration of Humidifier 
       FIG.  2    is a schematic cross-sectional view illustrating a configuration example of the humidifier  6 . The humidifier  6  is of a steam type, and generates water vapor by heating water. The humidifier  6  includes a water storage unit  61 , a heater  62 , a heat insulating material  63 , and the like. 
     The water storage unit  61  is a hollow member, and can store water (for example, pure water) in the inside. The water storage unit  61  may be formed of a material having high thermal conductivity such as metal, for example. A water supply port  611  for supplying water into the water storage unit  61  is formed in an upper portion of the water storage unit  61 . A cap  612  is detachably attached to the water supply port  611 . Water in the water storage unit  61  decreases as the humidifier  6  is used. Therefore, the user periodically performs work of detaching the cap  612  to open the water supply port  611 , supplying water from the water supply port  611  into the water storage unit  61 , and then attaching the cap  612  to the water supply port  611 . 
     The heater  62  constitutes a water heating unit for heating water in the water storage unit  61  by heating the water storage unit  61  from the outside. In this manner, temperature of the water in the water storage unit  61  is adjusted to, for example, about 45° C. For example, the heater  62  heats a bottom surface of the water storage unit  61 . However, the heater  62  may be configured to heat a surface (for example, a side surface) other than the bottom surface of the water storage unit  61 . 
     A side surface of the water storage unit  61  is enclosed by the heat insulating material  63 , and the heat insulating material  63  can prevent heat of water in the water storage unit  61  from escaping to the outside. A material of the heat insulating material  63  is not particularly limited, but for example, urethane foam or the like is used. Note that the heat insulating material  63  may be omitted. 
     Water is stored in the water storage unit  61  such that a space S is formed in an upper portion of the water storage unit  61 . Therefore, the space S is filled with water vapor generated as water in the water storage unit  61  is heated by the heater  62 . A gas inflow pipe  613  and a gas outflow pipe  614  communicate with the space S in the water storage unit  61 . Positions at which the gas inflow pipe  613  and the gas outflow pipe  614  communicate with the space S are not particularly limited, but as illustrated in  FIG.  2   , the gas outflow pipe  614  may communicate with the space S above the gas inflow pipe  613 . 
     The gas inflow pipe  613  and the gas outflow pipe  614  constitute a part of the pipe  41 . That is, carrier gas from the gas source  4  flows into the space S in the water storage unit  61  via the gas inflow pipe  613 , then flows out of the water storage unit  61  from the gas outflow pipe  614  through the space S, and is introduced into the reaction tube  32  via the sample injection mechanism  31 . 
     Water vapor filling the space S is mixed with carrier gas in a process of passing through the space S in the water storage unit  61 . In this manner, carrier gas introduced into the reaction tube  32  becomes inert gas containing water vapor. Since water vapor generated from the steam type humidifier  6  does not contain impurities, it is possible to prevent generation of detection noise due to introduction of TOC contained in water in the water storage unit  61  into the reaction tube  32 . 
     By use of the humidifier  6  as described above, water vapor can be continuously and stably mixed with carrier gas introduced into the reaction tube  32 . In this manner, an amount of water vapor in the carrier gas introduced into the reaction tube  32  can be maintained at a predetermined value or more. Humidity of the carrier gas introduced into the reaction tube  32  may be 10 to 80 g/m 3 . Note that, in a case where a sample is water, water vapor is generated only by introduction of the sample into the reaction tube  32 . However, since the water vapor generated from the sample quickly flows out of the reaction tube  32  due to carrier gas, it is difficult to stably secure a necessary amount of water vapor over general oxidation reaction time (for example, about two to five minutes). 
     3. Generation Principle of Carbon Dioxide 
     In the present embodiment, organic carbon in a sample undergoes steam reforming reaction so that carbon dioxide is generated. Specifically, in a case where inert gas containing water vapor is introduced into the reaction tube  32  as carrier gas, reaction represented by Equation (1) below occurs in the reaction tube  32  having an oxidation catalyst. At this time, the reaction tube  32  is heated to, for example, 500 to 1100° C. In 
     Equation (1) below, C m H n  is TOC (total organic carbon) contained in a sample. 
     
       
         
           
             [ 
             
               Equation 
               ⁢ 
                   
               1 
             
             ] 
           
         
       
       
         
           
             
               
                 
                   
                     
                       
                         C 
                         m 
                       
                       ⁢ 
                       
                         H 
                         n 
                       
                     
                     + 
                     
                       
                         
                           m 
                           ⁢ 
                           H 
                         
                         2 
                       
                       ⁢ 
                       O 
                     
                   
                   ⇄ 
                   
                     
                       m 
                       ⁢ 
                       CO 
                     
                     + 
                     
                       
                         ( 
                         
                           m 
                           + 
                           
                             n 
                             2 
                           
                         
                         ) 
                       
                       ⁢ 
                       
                         
                           H 
                           2 
                         
                         . 
                       
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
     Since the carrier gas contains water vapor (H 2 O), TOC contained in the sample reacts with water vapor in the reaction tube  32 . This reaction does not require oxygen. Further, carbon dioxide (CO 2 ) and hydrogen (H 2 ) are finally obtained by generation of reaction (aqueous gas shift reaction) represented by Equation (2) in association with the reaction represented by Equation (1) above. 
       [Equation 2] 
       CO+H 2 O⇄CO 2 +H 2   (2)
 
     In Equation (1), a mole ratio of water vapor to carbon is called a steam/carbon ratio (S/C ratio), and in a case where this value is smaller than a stoichiometric ratio, reaction is not completed, and TOC remains on an oxidation catalyst in the reaction tube  32 . Therefore, when water vapor having an S/C ratio or more is contained in carrier gas, the whole TOC in a sample react. 
     For example, assuming that a flow rate of carrier gas is 150 mL/min, in a case where 100 μL of a sample containing 50 mg/L of TOC is introduced into the reaction tube  32 , an amount of carbon introduced into the reaction tube  32  is 0.005 mg, that is, 0.005/12 mmol. A water vapor amount equivalent to the carbon amount is 0.005/12λ18=0.0075 mg. This amount of water vapor needs to be always present in the carrier gas introduced into the reaction tube  32  at 150 mL/min. For this purpose, an amount of water vapor in the carrier gas only needs to be 0.0075/150×1000 3 =50 g/m 3  or more. This water vapor amount corresponds to a saturated water vapor amount at an air temperature of about 40° C. 
     Note that hydrogen generated by the reactions of Equations (1) and (2) described above is about several ppm and is an extremely small amount, and thus there is no risk of explosion. Therefore, the generated hydrogen may be discharged without further processing, or a processing unit for performing specific processing on the generated hydrogen may be provided. 
     4. Specific Example of Total Organic Carbon Measurement Method 
       FIG.  3    is a flowchart for explaining a method for measuring total organic carbon. In a case of measuring TOC contained in a sample, first, the sample is sucked into the syringe  1 , and after that, acid is sucked into the syringe  1  (Step S 101 : acid addition step). An amount of the sample sucked into the syringe  1  is, for example, 500 μL. On the other hand, an amount of acid sucked into the syringe  1  is smaller than an amount of the sample, and is, for example, 10 μL· 
     After the above, when carrier gas is supplied into the syringe  1 , liquid (mixed liquid of the sample and the acid) in the syringe  1  is aerated for about 90 seconds. In this manner, IC contained in the sample in the syringe  1  is removed (Step S 102 : aeration step). 
     The sample from which IC is removed in this manner is supplied from the syringe  1  to the reaction tube  32 . A supply amount of the sample to the reaction tube  32  is, for example, 100 μL. At this time, carrier gas containing water vapor is introduced into the reaction tube  32  from the gas source  4  via the humidifier  6  (Step S 103 : carrier gas introduction step). Note that the carrier gas is not introduced into the reaction tube  32  for the first time at this time, but is continuously supplied to the detection unit  35  via the reaction tube  32  from when the device is turned on to when the device is turned off. 
     As a result, the sample is heated in the reaction tube  32 , and TOC contained in the sample reacts with water vapor, so that carbon dioxide is generated from the sample (Step S 104 : sample heating step). Carbon dioxide generated from the sample is guided to the detection unit  35  by the carrier gas and detected by the detection unit  35  (Step S 105 : detection step). 
     5. Variation 
     In the above embodiment, the configuration in which the heater  62  indirectly heats water in the water storage unit  61  by heating the water storage unit  61  from the outside is described. However, the present invention is not limited to such a configuration. For example, a configuration in which the heater  62  is provided in the water storage unit  61  to directly heat water in the water storage unit  61  may be employed. 
     The humidifier  6  is not limited to one of a steam type, and may have another configuration such as an ultrasonic type. It is also possible to downsize the humidifier  6  and downsize the entire device depending on a system to be employed. In a humidifier of an ultrasonic type, water is atomized as vibration is applied to water using an ultrasonic wave so that water vapor is generated. However, in a case of the configuration in which water is atomized and mixed with carrier gas, detection noise may occur due to TOC contained in the water being introduced into the reaction tube  32 , and thus, it may be difficult to employ the configuration depending on a condition such as a type of a sample. 
     The sample is not limited to liquid, and may be a solid. Even in such a case, inert gas containing water vapor only needs to be introduced as carrier gas into a reaction tube in which a solid sample is heated to generate carbon dioxide. 
     In the above embodiment, the configuration in which IC is converted into carbon dioxide and removed by adding acid to a sample and aerating the sample, and carbon dioxide generated when the sample from which IC is removed caused to react in the reaction tube  32  is detected by the detection unit  35 . However, the present invention is also applicable to a configuration in which TC and IC are measured, and a difference between them (TC-IC) is calculated as TOC. In this case, when TC is measured, carrier gas containing water vapor may be introduced into the reaction tube together with the sample. 
     6. Aspect 
     It is to be understood by those skilled in the art that a plurality of the exemplary embodiments described above are specific examples of an aspect described below. 
     (Item 1) A total organic carbon measurement device according to one aspect may include: 
     a sample heating unit that has a space in which an oxidation catalyst is arranged and heats a sample arranged in the space; 
     a carrier gas introduction unit that introduces inert gas containing water vapor as carrier gas into the sample heating unit; and 
     a detection unit for detecting carbon dioxide generated by steam reforming reaction of organic carbon in a sample in the sample heating unit. 
     According to the total organic carbon measurement device described in Item 1, carbon dioxide can be generated from total organic carbon in a sample by an action of water vapor contained in carrier gas, and therefore inert gas can be used as the carrier gas. 
     (Item 2) In the total organic carbon measurement device according to Item 1, the carrier gas introduction unit may include a water vapor generation unit that generates water vapor, and cause carrier gas mixed with water vapor generated in the water vapor generation unit to be introduced into the sample heating unit. 
     According to the total organic carbon measurement device described in Item 2, carrier gas containing water vapor can be introduced into the sample heating unit only by mixing of water vapor generated in the water vapor generation unit with the carrier gas. 
     (Item 3) In the total organic carbon measurement device according to Item 2, the carrier gas introduction unit may include a pipe that allows the water vapor generation unit and the sample heating unit to communicate with each other, and a pipe heating unit that heats the pipe. 
     According to the total organic carbon measurement device described in Item 3, since carrier gas mixed with water vapor can be introduced into the sample heating unit while being heated, it is possible to prevent water vapor in the carrier gas from being reduced in amount before being introduced into the sample heating unit. 
     (Item 4) In the total organic carbon measurement device according to Item 2 or 3, the water vapor generation unit may include a water storage unit for storing water and a water heating unit for heating water in the water storage unit, and water vapor generated as water in the water storage unit is heated may be mixed with carrier gas passing through the water storage unit. 
     According to the total organic carbon measurement device described in Item 4, it is possible to generate water vapor with a simple configuration of only heating water in the water storage unit, mix the water vapor with carrier gas, and introduce the mixture into the sample heating unit. 
     (Item 5) A total organic carbon measurement method according to one aspect may include: 
     a carrier gas introduction step of introducing inert gas containing water vapor as carrier gas into a sample heating unit having a space in which an oxidation catalyst is arranged; 
     a sample heating step of heating a sample arranged in the space in the sample heating unit and causing organic carbon in the sample to undergo steam reforming reaction to generate carbon dioxide; and a detection step of detecting the carbon dioxide that is generated. 
     According to the total organic carbon measurement method described in Item 5, carbon dioxide can be generated from total organic carbon in a sample by an action of water vapor contained in carrier gas, and therefore inert gas can be used as the carrier gas. 
     (Item 6) In the total organic carbon measurement method according to Item 5, in the sample heating step, carbon dioxide may be generated based on reaction of total organic carbon contained in a sample with water vapor. 
     According to the total organic carbon measurement method described in Item 6, total organic carbon can be measured by detection of carbon dioxide generated based on reaction of total organic carbon contained in a sample with water vapor. 
     (Item 7) In the total organic carbon measurement method according to Item 5 or 6, in the carrier gas introduction step, water vapor may be generated in a water vapor generation unit, and carrier gas mixed with water vapor generated in the water vapor generation unit may be introduced into the sample heating unit. 
     According to the total organic carbon measurement method described in Item 7, carrier gas containing water vapor can be introduced into the sample heating unit only by mixing of water vapor generated in the water vapor generation unit with the carrier gas. 
     (Item 8) In the total organic carbon measurement method according to Item 7, in the carrier gas introduction step, while a pipe that causes the water vapor generation unit and the sample heating unit to communicate with each other is heated, carrier gas mixed with water vapor may be introduced into the sample heating unit through the pipe. 
     According to the total organic carbon measurement method described in Item 8, since carrier gas mixed with water vapor can be introduced into the sample heating unit while being heated, it is possible to prevent water vapor in the carrier gas from being reduced in amount before being introduced into the sample heating unit. 
     (Item 9) In the total organic carbon measurement method according to Item 7 or 8, the water vapor generation unit may include a water storage unit for storing water and a water heating unit for heating water in the water storage unit, and in the carrier gas introduction step, water vapor generated as water in the water storage unit is heated may be mixed with carrier gas passing through the water storage unit. 
     According to the total organic carbon measurement method described in Item 9, it is possible to generate water vapor with a simple configuration of only heating water in the water storage unit, mix the water vapor with carrier gas, and introduce the mixture into the sample heating unit. 
     DESCRIPTION OF REFERENCE SIGNS 
     
         
           1  syringe 
           2  flow path switching unit 
           3  TOC measurement unit 
           4  gas source 
           5  flow controller 
           6  humidifier 
           7  control unit 
           8  display unit 
           21  sample supply unit 
           22  addition unit 
           30  sample heating unit 
           31  sample injection mechanism 
           32  reaction tube 
           33  electric furnace 
           34  dehumidifier 
           35  detection unit 
           40  carrier gas introduction unit 
           41  pipe 
           41   a  pipe heating unit 
           61  water storage unit 
           62  heater 
           63  heat insulating material