JP5505293B2 - Nitrogen analysis sample processing method and processing apparatus - Google Patents

Description

  The present invention relates to a processing method and a processing apparatus for a sample for nitrogen analysis, and more particularly to a processing method and a processing apparatus suitable as a sample pretreatment in quantitative analysis of nitrogen compounds contained in foods and the like. .

  In quantitative analysis of nitrogen in samples containing nitrogen compounds such as proteins in foods, a so-called Dumas method is used in which nitrogen is extracted by combustion decomposition of the sample. In the analysis of nitrogen by the Dumas method, nitrogen oxides are generated by combustion decomposition of a sample, and this is reacted with metallic copper as a reducing agent to generate nitrogen, which is then used as a carrier such as helium or carbon dioxide. It introduce | transduces into a detector with gas and measures a density | concentration (refer patent document 1, 2).

In the above nitrogen analysis, the pretreatment mechanism for generating the sample gas from the sample is as shown in FIG. That is, in the generation of the sample gas, first, the sample is combusted and decomposed by heating while supplying oxygen (O ₂ ) in a heating device (heating furnace), and nitrogen oxide (NOx) is generated as the sample gas. Next, in a reducing device, nitrogen oxide (NOx) is brought into contact with copper (Cu) to be reduced to nitrogen (N ₂ ). At the same time, in the above reducing device, excess oxygen (O ₂ ) that has not been spent on combustion by the heating device is reacted with copper (Cu) to be removed.

JP 2003-107071 A JP 2005-300550 A

  By the way, in the treatment by the Dumas method, copper as a reducing agent reacts with nitrogen oxides and surplus oxygen and is consumed as copper oxide. Therefore, it is necessary to replenish expensive copper sequentially for each analysis. Actually, a column filled with copper is exchanged at an appropriate timing in the reducing device. In other words, in the nitrogen analysis pretreatment as described above, it is difficult to reduce the analysis cost due to the consumption of copper, and much labor is required for handling the reducing device.

  The present invention has been made in view of the above circumstances, and its purpose is to provide a sample processing method and a processing apparatus for extracting nitrogen from a sample in analyzing nitrogen in a nitrogen compound-containing sample, An object of the present invention is to provide a nitrogen analysis sample processing method and processing apparatus that can further reduce analysis costs and labor.

  In the present invention, in extracting nitrogen from the sample gas obtained by burning the sample, that is, the sample gas containing nitrogen oxide and surplus oxygen, the sample gas is previously brought into contact with graphite, and the surplus oxygen is converted into carbon monoxide and After conversion to carbon dioxide, this is brought into contact with metallic copper to reduce nitrogen oxides to produce nitrogen. At the same time, copper oxide produced by the reduction reaction is reduced with carbon monoxide. Regenerate and convert carbon monoxide to carbon dioxide. As a result, the components of the sample gas were nitrogen and carbon dioxide, and consumption of copper as a reducing agent was eliminated.

  That is, the first gist of the present invention is a nitrogen analysis sample processing method for extracting nitrogen by reducing nitrogen oxide in a sample gas obtained by combustion decomposition of a sample. After contacting the sample gas containing nitrogen with graphite and converting surplus oxygen into carbon monoxide and carbon dioxide, the sample gas containing nitrogen oxide, carbon monoxide and carbon dioxide is brought into contact with copper by copper. A method for treating a sample for nitrogen analysis is characterized in that nitrogen oxides are converted into nitrogen, and the produced copper oxide is regenerated into copper with carbon monoxide in a sample gas.

  The second gist of the present invention is a sample processing apparatus for nitrogen analysis for extracting nitrogen by reducing nitrogen oxide in a sample gas obtained by combustion decomposition of a sample, and configured to supply oxygen A heating device that generates a sample gas containing nitrogen oxides and surplus oxygen by burning and decomposing the sample, and surplus oxygen in the sample gas filled with graphite and obtained by the heating device is converted into carbon monoxide and carbon dioxide. An oxygen removing device for converting to carbon, and nitrogen oxide in a sample gas filled with copper and processed by the oxygen removing device is converted to nitrogen, and the resulting copper oxide is converted to copper by carbon monoxide in the sample gas. And a reducing apparatus for regenerating the nitrogen analysis sample processing apparatus.

  According to the present invention, the sample gas obtained by burning the sample is previously brought into contact with graphite, and excess oxygen in the sample gas is converted into carbon monoxide and carbon dioxide, thereby being used as a nitrogen oxide reducing agent. Since the copper can always be regenerated with carbon monoxide, there is no consumption of expensive copper, the analysis cost can be further reduced, and it is not necessary to replenish the reduction device with copper, so that the labor of analysis can be further reduced.

It is a flowchart which shows the main structures of the processing apparatus of the sample for nitrogen analysis which concerns on this invention. It is explanatory drawing which shows the basic principle of the processing method of the sample for nitrogen analysis which concerns on this invention. It is explanatory drawing which shows the basic principle of the processing method of the sample by the conventional Dumas method.

  Embodiments of a method for processing a sample for nitrogen analysis (hereinafter referred to as “processing method”) and a processing apparatus (hereinafter referred to as “processing apparatus”) according to the present invention will be described with reference to the drawings. The present invention is applied to a pretreatment for extracting nitrogen by reducing nitrogen oxide in a sample gas obtained by combustion decomposition of a sample with copper in quantitative analysis of nitrogen contained in a sample containing nitrogen compounds such as food. . In the present invention, the gas handled after the combustion decomposition step is referred to as “sample gas”.

  First, a processing apparatus suitable for carrying out the processing method of the present invention will be described. As shown in FIG. 1, the processing apparatus of the present invention is configured to be able to supply oxygen, and a heating apparatus 1 that generates a sample gas by burning and decomposing a sample, and is obtained by the heating apparatus 1 that is filled with graphite 72. The oxygen removal device 2 that removes excess oxygen from the sample gas, and the reduction device 3 that converts the nitrogen oxide in the sample gas filled with copper 73 and processed by the oxygen removal device 2 into nitrogen. The

  The heating device 1 is a device that generates a sample gas containing nitrogen oxides and surplus oxygen by burning and decomposing a sample, and a heating tube 11 made of stainless steel into which the sample is charged and oxygen and carrier gas are supplied. And a heating furnace 12 for heating the heating tube. The heating tube 11 accommodates, for example, a bottomed cylindrical stainless steel inner tube 13 for accommodating a sample, and is arranged vertically. The inner tube 13 is designed to have an outer diameter smaller than the inner diameter of the heating tube 11 and shorter than the length of the heating tube 11 in order to secure a clearance for ventilation between the inner tube 13 and the inner peripheral surface of the heating tube 11. For example, the diameter of the heating tube 11 is about 20 to 50 mm, the length of the heating tube 11 is about 300 to 450 mm, the diameter of the inner tube 13 is about 15 to 40 mm, and the length of the inner tube 13 is about 100 to 200 mm. Is done.

  The head of the heating tube 11 is provided with a lid 14 for inserting the inner tube 13 containing the sample and sealing the heating tube 11 in an airtight manner. The lid 14 is mounted via a flow path connection ring 15 for connecting a flow path 62 described later to the heating tube 11. The flow path connection ring 15 is a short-axis cylindrical member having a pipe connection port, and a flow path 62 for supplying carbon dioxide as a carrier gas to the heating pipe 11 is connected to the connection port. The flow path 62 is connected to a flow path 61 for supplying combustion oxygen to the heating pipe 11. And although not shown in figure, the heating pipe | tube 11 is comprised so that these gas may be supplied with the fixed flow volume through the flow paths 61 and 62 from the container of oxygen and a carbon dioxide by control by a flow controller.

  Further, below the inner tube 13 of the heating tube 11, that is, on the bottom side of the heating tube 11, granular copper oxide 71 for promoting combustion is filled as an oxidation catalyst. Furthermore, a nonwoven fabric made of alumina fibers may be inserted into the upper portion of the copper oxide 71 in order to prevent the copper oxide from moving. And the flow path 64 for taking out the sample gas obtained by combustion and supplying it to the oxygen removal apparatus 2 is connected to the bottom part of the heating pipe 11, and nitrogen oxide, A sample gas containing surplus oxygen and carbon dioxide as a carrier is supplied.

  The heating furnace 12 of the heating device 1 is configured by a cylindrical electric furnace provided with a heating tube insertion hole at the center. Specifically, the heating furnace 12 accommodates a heat insulating material made of a ceramic fiber molded body or a mixed fiber of ceramic fiber and alumina fiber in a cylindrical casing, and a plurality of heat insulating materials are contained inside the heat insulating material. In other words, for example, a seeded heater in which a cantal heating element, a nichrome heating element, a silver heating element and the like are accommodated in a metal tube is embedded. In the heating device 1, the temperature of the heating tube 11 is detected and the power supply to the heater of the heating furnace 12 is controlled so that the temperature of the heating tube 11 becomes a predetermined temperature, for example, 800 to 1000 ° C. ing.

  In the present invention, in order to remove in advance oxygen contained in the sample gas obtained by the heating device 1, that is, excess oxygen that has been supplied to the heating device 1 and has not been consumed, the downstream side of the heating device 1 is used. The oxygen removing device 2 is disposed in the middle. The oxygen removing device 2 is a device that converts surplus oxygen into carbon monoxide and carbon dioxide, and includes a reaction tube 21 made of quartz glass filled with graphite 72 and a heating furnace 22 that heats the reaction tube. The The size of the reaction tube 21 is designed in substantially the same manner as the heating tube 11 of the heating apparatus 1 described above. Further, the heating furnace 22 is configured in the same manner as the heating furnace 12 described above, and in the oxygen removing apparatus 2, the temperature of the reaction tube 21 is detected so that the temperature of the reaction tube 21 is, for example, 500 to 1000 ° C. Thus, energization to the heater of the heating furnace 22 is controlled.

  Examples of the graphite filled in the reaction tube 21 of the oxygen removing device 2 include granular graphite. In particular, from the viewpoint of increasing the contact efficiency with oxygen, those having a particle size of about 1 to 2 mm are preferable.

  A flow path 64 extended from the heating tube 11 of the heating device 1 is connected to the bottom of the reaction tube 21 of the oxygen removing device 2, and a sample processed in the reaction tube 21 is connected to the head of the reaction tube 21. A flow path 65 is connected to take out the gas and supply it to the reduction device 3. That is, in the oxygen removing device 2, surplus oxygen contained in the sample gas reacts with the graphite 72 to convert oxygen into carbon monoxide and carbon dioxide, and through the channel 65, nitrogen oxide, carbon monoxide and carbon dioxide are converted. A sample gas containing carbon is supplied to the reduction device 3.

  The reducing device 3 converts nitrogen oxides in the sample gas treated by the oxygen removing device 2 into nitrogen, regenerates the generated copper oxide with carbon monoxide in the sample gas, and converts the carbon monoxide into carbon dioxide. A reaction tube 31 made of quartz glass filled with copper 73 and a heating furnace 32 for heating the reaction tube. The size of the reaction tube 31 is designed to be substantially the same as that of the heating tube 11 of the heating device 1 described above, and the heating furnace 32 is configured similarly to that of the heating device 1. In the reduction device 3, the temperature of the reaction tube 31 is detected and the energization of the heater of the heating furnace 32 is controlled so that the temperature of the reaction tube 31 is 500 to 800 ° C., for example. .

  Examples of the copper filled in the reaction tube 31 of the reducing device 3 include linear copper. In particular, from the viewpoint of increasing the contact efficiency with the sample gas, those having a wire diameter (φ) of about 0.5 to 1 mm and a length of about 2 to 8 mm are preferable.

  A flow path 65 extended from the reaction tube 21 of the oxygen removing device 2 is connected to the head of the reaction tube 31 of the reducing device 3, and a sample processed in the reaction tube 31 is connected to the bottom of the reaction tube 31. A flow path 66 for taking out the gas and supplying it to the detector 5 is connected. That is, in the reduction device 3, the nitrogen oxide contained in the sample gas and the copper 73 as the reducing agent are reacted to convert the nitrogen oxide into nitrogen, and at the same time, the produced copper oxide is converted into the sample gas. The carbon monoxide is regenerated into copper 73, thereby converting the carbon monoxide in the sample gas into carbon dioxide, and the sample gas containing nitrogen and carbon dioxide is sent to the detector 5 through the flow path 66. It is made like that.

  By the way, in the present invention, excess oxygen in the sample gas is reacted with graphite 72 in the oxygen removing device 2 to convert it into carbon monoxide and carbon dioxide. The amount of oxygen initially introduced into the heating device 1 and Depending on the amount of nitrogen oxides in the sample gas produced by the heating device 1, that is, the amount of copper oxide produced in the reducing device 3, excess carbon monoxide is discharged from the reducing device 3, thereby detecting the subsequent stage. There is a possibility that nitrogen cannot be accurately quantified in the vessel 5. Therefore, in the present invention, in order to reliably convert carbon monoxide into carbon dioxide in the reducing device 3, an excess is provided below the reaction tube 31 of the reducing device 3, that is, downstream of the copper 73 as the reducing agent. Copper oxide 74 is filled as an oxidizing agent that converts carbon monoxide into carbon dioxide. In addition, as the copper oxide 74, the thing similar to the above-mentioned copper 73, and a wire diameter (phi) of about 0.5-1 mm and length of about 2-8 mm is used.

  Further, as described above, when the oxidation treatment of carbon monoxide with the copper oxide 74 is continued, the copper oxide 74 changes to copper, and the copper oxide 74 gradually decreases. Therefore, in the present invention, when the analysis is stopped, such as during maintenance or batch analysis processing, the copper oxide 74 as the oxidant is regenerated, so that the reaction tube 31 of the reduction device 3 is used for introducing oxygen. The flow path 69 is attached. The channel 69 is normally connected to a boundary portion between the copper 73 accommodating portion and the copper oxide 74 accommodating portion. Thus, the reaction tube 31 is configured to be able to supply oxygen at a constant flow rate from the oxygen container through the flow channel 69 under the control of the flow rate controller.

  In the reducing apparatus 3, the ratio of the copper 73 and the copper oxide 74 filled in the reaction tube 31 is such that the copper 73 as a reducing agent that can reliably convert nitrogen oxides into nitrogen and excess carbon monoxide are reliably trapped. Although it is determined in consideration of a quantitative balance with copper oxide 74 as a possible oxidizing agent, the volume ratio is usually 1: 1 to 1: 2.

  The processing apparatus of the present invention sends a sample gas containing nitrogen and carbon dioxide from the reducing apparatus 3 to the dehumidifying agent column 41 through the flow path 66 and supplies the dehumidifying agent column to the detector 5 through the flow path 67. Configured as follows. Further, a part of, for example, carbon dioxide supplied as a carrier gas from the flow path 62 to the heating apparatus 1 is sent to the dehumidifying agent column 42 through the flow path 63, and supplied from the dehumidifying agent column to the detector 5 through the flow path 68. Configured as follows.

  The dehumidifying agent columns 41 and 42 are arranged to remove moisture from the sample gas, and are configured to accommodate the dehumidifying agent. As such a dehumidifying agent, for example, a mixture of an indicator that changes color depending on the amount of water and particles of diphosphorus pentoxide is used. Moreover, as the detector 5, a thermal conductivity detector in which a constant temperature bath is provided in the sample gas introduction part is usually used. As is well known, the thermal conductivity detector includes a pair of heating filaments and a resistance measurement circuit, and the same gas as the carrier gas is supplied to one filament as a reference gas, and the sample gas containing the carrier gas is supplied to the other filament. This is a measuring device that detects the change in the thermal conductivity of the sample gas by comparing the difference in electrical resistance between both filaments, and analyzes the nitrogen concentration by a computer based on the change in the thermal conductivity. Can do. Although illustration is omitted, trap channels for capturing moisture in the sample gas may be disposed in the flow paths 64 to 66.

Next, the processing method of the present invention using the above processing apparatus will be described. In the quantitative analysis of nitrogen, first, in the heating apparatus 1 shown in FIG. 1, a sample is accommodated in the inner tube 13, the inner tube is inserted into the heating tube 11, and then oxygen is added to the heating tube 11 at 100 to 500 ml / min. While supplying at a flow rate, the inside of the heating tube 11 is heated to 800 to 1000 ° C. by the heating furnace 12 to burn and decompose the sample to generate a sample gas. As shown in FIG. 2, the obtained sample gas includes nitrogen oxide (NOx) generated from nitrogen compounds in the sample, surplus oxygen (O ₂ ) not consumed, and carbon dioxide (CO ₂₎ (not shown). ) Is included.

Next, the sample gas obtained by combustion decomposition of the sample is introduced into the reaction tube 21 of the oxygen removing apparatus 2 shown in FIG. At that time, the inside of the reaction tube 21 is kept in a state heated to 500 to 1000 ° C. by the heating furnace 22. Thereby, surplus oxygen is converted into carbon monoxide and carbon dioxide. That is, in the oxygen removing device 2, as shown in FIG. 2, the sample gas is brought into contact with the graphite (C), thereby causing the excess oxygen (O ₂ ) in the sample gas to react with the graphite (C). Of oxygen (O ₂ ) is converted into carbon monoxide (CO), and other oxygen (O ₂ ) is converted into carbon dioxide (CO ₂ ).

Subsequently, the above-described sample gas brought into contact with the graphite 72, that is, the gas containing nitrogen oxide (NOx), carbon monoxide (CO), and carbon dioxide (CO ₂ ) is used in the reaction tube of the reducing device 3 shown in FIG. The sample gas is brought into contact with copper 73 and nitrogen oxide is converted into nitrogen by copper 73. At that time, the inside of the reaction tube 31 is kept in a state heated to 500 to 800 ° C. by the heating furnace 32. That is, in the reduction device 3, as shown in FIG. 2, by bringing the sample gas into contact with copper (Cu), nitrogen oxide (NOx) in the sample gas is reduced with copper (Cu), and nitrogen (N ₂ ) is generated.

In the reducing device 3 described above, the copper oxide generated by the reduction treatment of nitrogen oxides is regenerated into copper 73. That is, in the reduction device 3, as shown in FIG. 2, copper oxide (CuO) is generated by reduction of nitrogen oxides (NOx), but the sample gas is generated by the oxygen removal device 2 in the previous stage. Since carbon oxide (CO) is contained, such carbon monoxide (CO) and copper oxide (CuO) can be reacted to reduce and regenerate copper oxide (CuO) to copper (Cu). Then, by regenerating copper (Cu), in other words, carbon monoxide (CO) in the sample gas can be converted into carbon dioxide (CO ₂ ) by the generated copper oxide (CuO).

Moreover, in the reducing device 3, the reaction tube 31 is filled with copper oxide 74 as an oxidant, and when carbon monoxide is excessively generated in the oxygen removing device 2, the copper oxide 74 causes the sample gas to be contained in the sample gas. Can convert carbon monoxide to carbon dioxide. As a result, in the reduction device 3, a sample gas composed of nitrogen (N ₂ ) and carbon dioxide (CO ₂ ) can be obtained. And sample gas can be introduce | transduced into the detector 5 through the flow path 66, the dehumidifier column 41, and the flow path 67, and the nitrogen concentration in sample gas can be measured.

  As described above, in the present invention, in extracting nitrogen from the sample gas obtained by burning the sample with the heating device 1, that is, the sample gas containing nitrogen oxides and surplus oxygen, in the oxygen removing device 2 in advance. After contacting the sample gas with graphite 72 and converting surplus oxygen into carbon monoxide and carbon dioxide, this is brought into contact with copper 73 in the reduction device 3, thereby reducing nitrogen oxides to generate nitrogen, Then, by reducing the copper oxide produced by the reduction reaction with carbon monoxide, the copper 73 is regenerated and the carbon monoxide is converted to carbon dioxide, and the components of the sample gas are changed to nitrogen and carbon dioxide. Therefore, according to the present invention, it is not necessary to sequentially replenish expensive copper 73 in the reducing device 3, and the analysis can be continued only by replenishing the relatively low-cost graphite 72 in the oxygen removing device 2. The labor can be further reduced.

  Further, in the present invention, even when the amount of carbon monoxide produced in the oxygen removing device 2 is large and treatment cannot be performed in the regeneration of the copper 73 of the reducing device 3, the reducing device 3 is filled with copper oxide 74 as an oxidizing agent. Therefore, excessively generated carbon monoxide can be reliably captured. In addition, since the reaction tube 31 of the reduction device 3 is configured to be able to supply oxygen through the flow path 69, when the copper oxide 74 has decreased, oxygen is supplied during batch analysis processing or during maintenance. By doing so, the copper oxide 74 can be regenerated. Therefore, it is not necessary to replace the copper oxide 74 of the reduction device 3 and the maintenance labor can be reduced.

1: Heating device 11: Heating tube 12: Heating furnace 13: Inner tube 14: Lid 15: Flow path connecting ring 2: Oxygen removing device 21: Reaction tube 22: Heating furnace 3: Reducing device 31: Reaction tube 32: Heating furnace 41: Dehumidifier column 42: Dehumidifier column 5: Detector (thermal conductivity detector)
61-69: Channel 71: Copper oxide (oxidation catalyst)
72: Graphite 73: Copper (reducing agent)
74: Copper oxide (oxidant)

Claims (5)

  A method for treating a sample for nitrogen analysis, which extracts nitrogen by reducing nitrogen oxide in a sample gas obtained by combustion decomposition of the sample, wherein the sample gas containing nitrogen oxide and surplus oxygen is brought into contact with graphite, After converting surplus oxygen into carbon monoxide and carbon dioxide, the sample gas containing nitrogen oxides, carbon monoxide and carbon dioxide is brought into contact with copper to convert the nitrogen oxides into nitrogen with copper, and A method for treating a sample for nitrogen analysis, wherein the produced copper oxide is regenerated into copper with carbon monoxide in a sample gas.   The treatment method according to claim 1, wherein the excessively generated carbon monoxide is further converted into carbon dioxide by copper oxide.   A processing apparatus for a sample for nitrogen analysis that extracts nitrogen by reducing nitrogen oxide in a sample gas obtained by combustion decomposition of the sample, and configured to supply oxygen, and the sample is subjected to combustion decomposition for nitrogen oxide And a heating device that generates a sample gas containing surplus oxygen, an oxygen removing device that is filled with graphite and converts surplus oxygen in the sample gas obtained by the heating device into carbon monoxide and carbon dioxide, and copper A reduction device that converts nitrogen oxide in the sample gas that has been filled and processed by the oxygen removal device into nitrogen, and that regenerates the copper oxide that is produced into carbon with carbon monoxide in the sample gas. An apparatus for processing a sample for nitrogen analysis characterized by the following.   The processing apparatus according to claim 3, wherein the reducing apparatus is filled with copper oxide as an oxidizing agent that converts excess carbon monoxide into carbon dioxide.   The processing apparatus according to claim 4, wherein oxygen for regenerating copper oxide as an oxidizing agent is supplied to the reducing apparatus.

Images