Analysis device and method for measuring contents of hydrogen sulfide and phosphine

文档序号:1435046 发布日期:2020-03-20 浏览:11次 中文

阅读说明:本技术 一种测定硫化氢和磷化氢含量的分析装置及其方法 (Analysis device and method for measuring contents of hydrogen sulfide and phosphine ) 是由 张东华 栾粹东 韩小龙 朱凤蛟 邢燕 温丽霞 陈梅梅 闫志 王贤新 于 2019-12-30 设计创作,主要内容包括:本发明公开了一种测定硫化氢和磷化氢含量的分析装置及方法,该装置包括:载气装置、燃气装置、助燃气装置、六通阀、火焰光度检测器和显示器;载气装置经过第一过滤器连接至六通阀;燃气装置经过第三过滤器与火焰光度检测器相连接,助燃气装置经过第二过滤器后分两路空气管路连接至火焰光度检测器,六通阀连接至色谱柱,色谱柱连接至火焰光度检测器,火焰光度检测器为双光电倍增管检测器,并在其出口处分别设置有硫滤光片和磷滤光片,并检测得到响应信号分别与第一微电流放大器及第二微电流放大器相连接后传输至显示器用于谱出色谱图。本发明能有效对混合气体中硫化氢和磷化氢进行分离,并测定其含量。(The invention discloses an analysis device and a method for measuring the content of hydrogen sulfide and phosphine, wherein the device comprises: the device comprises a gas carrier device, a gas device, a combustion-supporting gas device, a six-way valve, a flame luminosity detector and a display; the carrier gas device is connected to the six-way valve through a first filter; the gas device is connected with the flame photometric detector through a third filter, the combustion-supporting gas device is connected to the flame photometric detector through two air pipelines after passing through a second filter, the six-way valve is connected to the chromatographic column, the chromatographic column is connected to the flame photometric detector, the flame photometric detector is a double-photomultiplier detector, a sulfur filter and a phosphorus filter are arranged at the outlets of the flame photometric detector respectively, response signals obtained through detection are respectively connected with the first micro-current amplifier and the second micro-current amplifier, and then the response signals are transmitted to the display for chromatogram spectrum. The invention can effectively separate hydrogen sulfide and phosphine in the mixed gas and measure the content of the hydrogen sulfide and the phosphine.)

1. An analytical device for determining the content of hydrogen sulfide and phosphine, comprising: the device comprises a gas carrier device (1), a gas burning device (3), a combustion-supporting gas device (2), a six-way valve (8), a flame luminosity detector (11) and a display (15);

the carrier gas device (1) is connected to an inlet (8a) of a six-way valve (8) through a first filter (5a), a first flow stabilizing valve (6a) and a second pressure stabilizing valve (7a) are arranged on a pipeline between the first filter (5a) and the six-way valve (8) and used for controlling the flow rate and the pressure of the carrier gas device (1), and the pressure of the carrier gas device (1) is displayed by a first pressure gauge (4 a); the outlet (8a) of the six-way valve (8) is connected with a flame photometric detector (11); a first control valve (9a) is arranged on a pipeline between the six-way valve (8) and the flame photometric detector (11) and is used for adjusting make-up gas;

the gas device (3) is connected with the flame luminosity detector (11) through a third filter (5c), a third flow stabilizing valve (6c) and a third pressure stabilizing valve (7c) are arranged on a pipeline between the third filter (5c) and the flame luminosity FPD detector (11) and used for controlling the flow rate and the pressure of the gas device (3), and the pressure of the gas device (3) is displayed by a third pressure gauge (4 c);

the combustion-supporting gas device (2) is divided into two air pipelines after passing through a second filter (5b) and is connected to the flame luminosity detector (11), a second flow stabilizing valve (6b) and a second pressure stabilizing valve (7b) are arranged on a pipeline between the second filter (5b) and the flame luminosity detector (11) and are used for controlling the flow rate and the pressure of the combustion-supporting gas device (2), the pressure of the combustion-supporting gas device (2) is displayed by a second pressure gauge (4b), and a second control valve (9b) and a third control valve (9c) are respectively arranged in the two air pipelines;

the outlet (8b) of the six-way valve (8) is connected to the inlet of a chromatography column (10); the outlet of the chromatographic column (10) is connected to the flame photometric detector (11);

the flame photometric detector (11) is a double-photomultiplier detector, and a sulfur filter (13a) and a phosphorus filter (13b) are respectively arranged at the outlets of the double-photomultiplier detector and are used for detecting hydrogen sulfide and phosphine in a sample to be detected, and obtained detection response signals respectively pass through a first photomultiplier (12a) and a second photomultiplier (12b) and then are respectively connected with a first micro-current amplifier (14a) and a second micro-current amplifier (14b) for signal amplification, so that the obtained amplified signals are connected to the display (15) for chromatogram spectrum.

2. The analyzer according to claim 1, wherein: all the pressure stabilizing valves, the flow stabilizing valve, the control valve, the six-way valve and the air path pipe are made of polytetrafluoroethylene materials.

3. The analyzer according to claim 1, wherein: the stationary phase filler adopted by the chromatographic column (10) is a high-molecular porous pellet made of quartz glass.

4. The analytical method of an analytical device for determining the contents of hydrogen sulfide and phosphine according to claim 1, which is characterized by comprising the steps of:

step 1, calibrating a standard method:

step 1.1, setting relevant parameters of an analysis device;

step 1.2, wait forAfter the device is stabilized, standard gas is converted and injected through the six-way valve (8) and then is carried in carrier gas N of the carrier gas device (1)2The hydrogen sulfide and the phosphine in the sample are separated after the sample and the stationary phase are repeatedly adsorbed and desorbed for a plurality of times under the action, and the separated sample flows out of the chromatographic column (10) according to the size of the adsorption coefficient and flows into a flame photometric detector (11) in sequence;

step 1.3, the flame photometric detector (11) utilizes the combined action of a sulfur filter (13a), a phosphorus filter (13b), a first photomultiplier (12a) and a second photomultiplier (12b) to complete the detection of the content of hydrogen sulfide and phosphine, and a display (15) is used for spectrum chromatogram after the generated response value is amplified by a first micro-current amplifier (14a) and a second micro-current amplifier (14 b);

step 1.4, repeatedly injecting samples for N times under the same condition, and selecting a group with the best linearity as a calibration standard under the condition that the error is not more than +/-0.2 ppm;

step 1.5, carrying out quantification by utilizing peak areas, and determining relative correction factors of hydrogen sulfide and phosphine;

step 2, determination of samples:

step 2.1, a sample to be detected in the production process is obtained by using a sampling air bag, and the sampling air bag is replaced by the sample for 2-3 times before sampling;

and 2.2, after the device is stabilized, detecting the sample to be detected under the same condition, and after a chromatogram is obtained, detecting the content of hydrogen sulfide and phosphine in the sample to be detected by using a calibrated standard method to obtain the unit of an analysis result, namely the concentration ppm per million.

5. The analytical method of claim 4, wherein: the step 1.1 is carried out according to the following processes:

the temperature rise program of the analysis device was set as follows: the initial temperature is 60 ℃, the temperature is kept for 2min, the temperature is increased to 130 ℃ at the speed of 30 ℃/min, and the temperature is kept for 3 min;

the temperature of the sample injector, namely the six-way valve (8) is set as follows: 150 ℃;

setting the temperature of the flame photometric detector (11) to: 150 ℃;

the carrier gas of the carrier gas device (1) is high-purity nitrogen, and the flow rates of the carrier gas and the carrier gas supplement gas are set as follows: 30 ml/min;

the fuel gas of the fuel gas device (3) is high-purity hydrogen, and the flow rate of the high-purity hydrogen is set as follows: 140 ml/min;

the combustion-supporting gas of the combustion-supporting gas device (2) is air: setting air with different flow rates, wherein one flow rate is as follows: 80 ml/min; the other flow rate is: 170 ml/min.

6. The analytical method of claim 1, wherein: in step 1.5, the relative correction factors of hydrogen sulfide and phosphine are determined by using the formula (1):

Figure FDA0002346210980000021

in the formula (1), the reaction mixture is,

Figure FDA0002346210980000022

7. The analytical method of claim 1, wherein: in the step 2.2, the contents of hydrogen sulfide and phosphine are obtained by using a formula (2):

Figure FDA0002346210980000031

in the formula (2), wsRepresenting the mass concentration of the external standard; w is aiRepresenting the mass concentration of the component to be measured; wsRepresenting the mass of the external standard; wiIndicating the measuredThe mass of the components; a. theiRepresenting the peak area of the component to be measured; gwi/sRepresenting the relative mass correction factor of the component to be detected to the external standard; k represents the mass fraction of the external standard corresponding to the peak area of the external standard unit, and

Figure FDA0002346210980000032

Technical Field

The invention relates to an analysis method and device for measuring the content of hydrogen sulfide and phosphine.

Background

The hydrogen sulfide is colorless, extremely toxic and acidic gas, has special odor of the egg, is unstable in chemical property, easy to decompose, combustible and reductive when being heated, and easy to explode when being mixed with air or oxygen in a proper proportion (4.3% -4.6%); gaseous Phosphine (PH)3) Called phosphine, colorless gas, has peculiar smell of mustard and garlic, has rotten fish-like smell of industrial product, is extremely toxic, and has an explosion lower limit of 1.79% (26 g/m)3). The industries which are easy to generate hydrogen sulfide and phosphine gases include sewage treatment, paper making, petrochemical industry, chemical fertilizer manufacturing and chemical fiber manufacturing. The content of hydrogen sulfide and phosphine in the air is too high, so that not only is the potential safety hazard of explosion existed, but also the poisoning accident can be caused after the excessive inhalation of human body, and the environment can be polluted to a certain extent when the hydrogen sulfide is discharged into the atmosphereIf acid rain is formed, the method for detecting the content of hydrogen sulfide and phosphine is advanced, and can provide high-efficiency guarantee for environment, life and production.

Through literature retrieval, the existing methods for measuring the contents of hydrogen sulfide and phosphine in domestic industrial gas or atmosphere are different, and a chemical inspection method mainly adopts silver nitrate solution to detect through a colorimetric method, but cannot quantitatively measure the contents of hydrogen sulfide and phosphine. The physical inspection method is mainly gas chromatography, and adopts a pulse type flame photometric detector, but the detector only uses a phosphorus optical filter for detection, so that the sensitivity of hydrogen sulfide detection is greatly reduced, and the content of hydrogen sulfide cannot be accurately measured.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provides an analysis device and method for measuring the content of hydrogen sulfide and phosphine, so that the content of hydrogen sulfide and phosphine in industrial gas or atmosphere can be effectively separated and accurately measured.

In order to achieve the purpose, the invention adopts the following technical scheme:

the invention relates to an analysis device for measuring the content of hydrogen sulfide and phosphine, which is characterized by comprising the following components: the device comprises a gas carrier device, a gas device, a combustion-supporting gas device, a six-way valve, a flame luminosity detector and a display;

the carrier gas device is connected to an inlet of the six-way valve through a first filter, a first flow stabilizing valve and a second pressure stabilizing valve are arranged on a pipeline between the first filter and the six-way valve and used for controlling the flow rate and the pressure of the carrier gas device, and the pressure of the carrier gas device is displayed by a first pressure gauge; the outlet of the six-way valve is connected with a flame photometric detector; a first control valve is arranged on a pipeline between the six-way valve and the flame photometric detector and used for adjusting make-up gas;

the gas device is connected with the flame luminosity detector through a third filter, a third flow stabilizing valve and a third pressure stabilizing valve are arranged on a pipeline between the third filter and the flame luminosity FPD detector and used for controlling the flow rate and the pressure of the gas device, and the pressure of the gas device is displayed by a third pressure gauge;

the combustion-supporting gas device passes through a second filter and then is divided into two air pipelines and is connected to the flame luminosity detector, a second flow stabilizing valve and a second pressure stabilizing valve are arranged on a pipeline between the second filter and the flame luminosity detector and are used for controlling the flow rate and the pressure of the combustion-supporting gas device, the pressure of the combustion-supporting gas device is displayed by a second pressure gauge, and a second control valve and a third control valve are respectively arranged in the two air pipelines;

the outlet of the six-way valve is connected to the inlet of the chromatographic column; the outlet of the chromatographic column is connected to the flame photometric detector;

the flame photometric detector is a double-photomultiplier detector, and a sulfur filter and a phosphorus filter are respectively arranged at the outlets of the flame photometric detector, and are used for detecting hydrogen sulfide and phosphine in a sample to be detected, and detecting response signals obtained respectively pass through a first photomultiplier and a second photomultiplier and then are respectively connected with a first micro-current amplifier and a second micro-current amplifier for signal amplification, so that the amplified signals are connected to the display for spectrum chromatogram.

The analysis device of the present invention is also characterized in that: all the pressure stabilizing valves, the flow stabilizing valve, the control valve, the six-way valve and the air path pipe are made of polytetrafluoroethylene materials.

The stationary phase filler adopted by the chromatographic column is a high-molecular porous pellet made of quartz glass.

The analysis method of the analysis device for determining the content of the hydrogen sulfide and the content of the phosphine is characterized by comprising the following steps of:

step 1, calibrating a standard method:

step 1.1, setting relevant parameters of an analysis device;

step 1.2, after the device is stabilized, the standard gas is converted and injected through the six-way valve, and the carrier gas N in the carrier gas device2Entering into a chromatographic column under the action of the hydrogen sulfide, separating the hydrogen sulfide and the phosphine in the sample after the sample and the stationary phase are repeatedly adsorbed and desorbed for a plurality of times, and separatingEnabling the separated samples to flow out of the chromatographic column in sequence according to the size of the adsorption coefficient and flow into a flame photometric detector;

step 1.3, the flame photometric detector utilizes the combined action of a sulfur optical filter, a phosphorus optical filter, a first photomultiplier and a second photomultiplier to complete the detection of the contents of hydrogen sulfide and phosphine, and a display is used for spectrum chromatogram after the generated response value is amplified by a first micro-current amplifier and a second micro-current amplifier;

step 1.4, repeatedly injecting samples for N times under the same condition, and selecting a group with the best linearity as a calibration standard under the condition that the error is not more than +/-0.2 ppm;

step 1.5, carrying out quantification by utilizing peak areas, and determining relative correction factors of hydrogen sulfide and phosphine;

step 2, determination of samples:

step 2.1, a sample to be detected in the production process is obtained by using a sampling air bag, and the sampling air bag is replaced by the sample for 2-3 times before sampling;

and 2.2, after the device is stabilized, detecting the sample to be detected under the same condition, and after a chromatogram is obtained, detecting the content of hydrogen sulfide and phosphine in the sample to be detected by using a calibrated standard method to obtain the unit of an analysis result, namely the concentration ppm per million.

The analysis method of the present invention is also characterized in that: the step 1.1 is carried out according to the following processes:

the temperature rise program of the analysis device was set as follows: the initial temperature is 60 ℃, the temperature is kept for 2min, the temperature is increased to 130 ℃ at the speed of 30 ℃/min, and the temperature is kept for 3 min;

the temperature of the sample injector, i.e. the six-way valve, is set to be: 150 ℃;

setting the temperature of the flame photometric detector to be: 150 ℃;

the carrier gas of the carrier gas device is high-purity nitrogen, and the flow rates of the carrier gas and the carrier gas supplement airflow are set as follows: 30 ml/min;

the fuel gas of the fuel gas device is high-purity hydrogen, and the flow rate of the high-purity hydrogen is set as follows: 140 ml/min;

the combustion-supporting gas of the combustion-supporting gas device is air: setting air with different flow rates, wherein one flow rate is as follows: 80 ml/min; the other flow rate is: 170 ml/min.

In step 1.5, the relative correction factors of hydrogen sulfide and phosphine are determined by using the formula (1):

Figure BDA0002346210990000031

in the formula (1), the reaction mixture is,

Figure BDA0002346210990000032

representing the relative mass correction factor of the component to be detected to the standard; gwiAn absolute correction factor representing the component to be measured; gwsAn absolute correction factor representing a composition of the standard; m isiIndicating the concentration in parts per million of the component to be measured; m issRepresents the parts per million concentration of external standard; a. theiRepresenting the peak area of the component to be measured; a. thesThe peak area of the external standard is indicated.

In the step 2.2, the contents of hydrogen sulfide and phosphine are obtained by using a formula (2):

Figure BDA0002346210990000033

in the formula (2), wsRepresenting the mass concentration of the external standard; w is aiRepresenting the mass concentration of the component to be measured; wsRepresenting the mass of the external standard; wiRepresenting the mass of the measured component; a. theiRepresenting the peak area of the component to be measured; gwi/sRepresenting the relative mass correction factor of the component to be detected to the external standard; k represents the mass fraction of the external standard corresponding to the peak area of the external standard unit, and

Figure BDA0002346210990000034

compared with the prior art, the invention has the beneficial effects that:

1. the invention is provided with the double detectors and the inspection method, can determine the accurate concentration of the component to be measured, avoids the error of a chemical analysis method, and has high detection precision and good repeatability.

2. The invention selects the gas chromatograph, the detector adopts a flame photometric sulfur-phosphorus dual detector to measure the content of hydrogen sulfide and phosphine in mixed industrial gas or atmosphere, the operation is simple and convenient, the analysis speed is high, the accuracy of the detection result is high, and the production can be effectively guided in time.

3. The device of the invention avoids the volatilization of gas, and the use of chemical reagents and chemical equipment, and meets the requirements of economic operation and environmental protection.

4. The application of the invention can not only improve the analysis speed and ensure the accuracy of the analysis result, but also greatly reduce the consumption of chemical reagents and chemical equipment and the discharge of chemical waste liquid, realize economic operation and simultaneously meet the national environmental protection requirement.

Drawings

FIG. 1 is a schematic view of the apparatus of the present invention;

FIG. 2a is a schematic representation of a chromatographic peak of hydrogen sulfide standard gas in accordance with the present invention;

FIG. 2b is a schematic diagram of a chromatographic peak of a phosphine standard gas according to the present invention;

FIG. 3a is a schematic diagram of a chromatographic peak of a hydrogen sulfide sample to be tested according to the present invention;

FIG. 3b is a schematic diagram of a chromatographic peak of a phosphine to be detected sample according to the present invention;

reference numbers in fig. 1: 1 a carrier gas device; 2, a combustion-supporting gas device; 3, a gas device; 4a first pressure gauge; 4b a second pressure gauge; 4c a third pressure gauge; 5a first filter; 5b a second filter; 5c a third filter; 6a first flow stabilizing valve; 6b a second flow stabilizing valve; 6c a third flow stabilizing valve; 7a first pressure maintaining valve; 7b a second pressure maintaining valve; 7c a third pressure maintaining valve; 8a six-way valve; 8a six-way valve inlet; 8b six-way valve outlet; the 8C six-way valve is emptied; 9a first control valve; 9b a second control valve; 9c a third control valve; 10 chromatographic columns; 11 a flame photometric detector; 12a first photomultiplier tube; 12b a second photomultiplier tube; 13a sulfur filter; 13b a phosphor filter; 14a first micro-current amplifier; 14b a second micro-current amplifier; 15 a display;

Detailed Description

In this embodiment, an analysis device for determining the content of hydrogen sulfide and phosphine is a selective gas chromatograph, and a detector uses a flamephotometric sulfur-phosphorus dual-optical filter and a double photomultiplier detector to determine the content of hydrogen sulfide and phosphine in a mixed industrial gas or atmosphere, as shown in fig. 1, the analysis device includes: the system comprises a gas path system, a sample introduction system, a separation system, a detection system and a display system.

The gas circuit system includes: a gas carrier device 1, a gas device 3 and a combustion-supporting gas device 2;

the carrier gas is filtered by the carrier gas device 1 through the first filter 5a and then is connected to an inlet 8a of the six-way valve 8, a first flow stabilizing valve 6a and a second pressure stabilizing valve 7a are arranged on a pipeline between the first filter 5a and the six-way valve 8 and used for controlling the flow rate and the pressure of the carrier gas device 1, and the pressure of the carrier gas device 1 is displayed by the first pressure gauge 4 a; the outlet 8a of the six-way valve 8 is connected with a flame photometric detector 11; a supplementary gas is arranged on a pipeline between the six-way valve 8 and the flame photometric detector 11, and a first control valve 9a is arranged for adjusting the supplementary gas; nitrogen (N) in carrier gas device 12) After passing through the sample injector, i.e. the six-way valve 8, the carrier gas is supplemented by connecting the detector through the control valve 9 a.

The gas device 3 is connected with a flame luminosity detector 11 through a third filter 5c, a third flow stabilizing valve 6c and a third pressure stabilizing valve 7c are arranged on a pipeline between the third filter 5c and the flame luminosity FPD detector 11 and used for controlling the flow rate and the pressure of the gas device 3, and the pressure of the gas device 3 is displayed by a third pressure gauge 4 c; the hydrogen in the gas device 3 is connected with a flame luminosity (FPD) detector 11 through a third filter 5c, a third flow stabilizing valve 6c and a third pressure stabilizing valve 7c, and the FPD detector is used for detecting hydrogen sulfide and phosphine in a sample by using the hydrogen as gas.

The combustion-supporting gas device 2 is divided into two air pipelines after being filtered by a second filter 5b and is connected to a flame luminosity detector 11, a second flow stabilizing valve 6b and a second pressure stabilizing valve 7b are arranged on a pipeline between the second filter 5b and the flame luminosity detector 11 and are used for controlling the flow rate and the pressure of the combustion-supporting gas device 2, the pressure of the combustion-supporting gas device 2 is displayed by a second pressure gauge 4b, and a second control valve 9b and a third control valve 9c are respectively arranged in the two air pipelines; the air in the combustion-supporting air device 2 is divided into two paths through a second filter 5b, a second flow stabilizing valve 6b and a second pressure stabilizing valve 7b and is connected with a flame luminosity (FPD) detector 11 through a second control valve 9b and a third control valve 9c, and the air is used as the combustion-supporting air to assist the FPD detector to finish the determination of hydrogen sulfide and phosphine in a sample.

A sample injector of the sample injection system is a six-way valve 8; the sample to be measured is converted and injected through the six-way valve 8, the sample to be measured is accurately measured, and surplus gas is discharged through the emptying 8c of the six-way valve; an inlet 8a of the six-way valve 8 is connected with an outlet of the carrier gas device 1, and an outlet 8b of the six-way valve 8 is connected to the chromatographic column 10; the inlet of a chromatographic column 10 of the separation system is connected with the outlet of the six-way valve 8, and the outlet of the chromatographic column 10 is connected with a Flame Photometric (FPD) detector 11; the measured sample to be detected is brought into a chromatographic column 10 under the action of a mobile phase (carrier gas), the chromatographic column 10 is used for separating hydrogen sulfide and hydrogen phosphide in the sample, and the separated components flow out of the chromatographic column and then enter a flame photometric detector 11;

the stationary phase filler adopted by the chromatographic column 10 is a porous polymer bead and is made of quartz glass, so that the condition of adsorbing sulfur (S) in a sample is avoided, and the accuracy of analysis data is improved.

The detection system is a Flame Photometric (FPD) detector 11; the display system is a display 15;

the flame photometric detector 11 is a double photomultiplier detector, the inlet of the flame photometric detector 11 is connected with the outlet of the chromatographic column 10, and the outlet thereof is connected with the first micro-current amplifier 14a and the second micro-current amplifier 14 b;

a sulfur filter 13a and a phosphorus filter 13b are respectively arranged at the outlets of the flame photometric detector 11, so that the first photomultiplier 12a, the second photomultiplier 12b, the sulfur filter 13a and the phosphorus filter 13b are used for detecting hydrogen sulfide and phosphine in a sample to be detected, sulfur and phosphorus electric signals generated by the flame photometric detector 11 are used as detection response signals and are respectively amplified by the first micro-current amplifier 14a and the second micro-current amplifier 14b, so that the amplified signals are connected to the display 15 for spectrum chromatogram, and finally, the content of two components of hydrogen sulfide and hydrogen phosphide is determined by using a calibrated standard method.

The display 15 of the display system is provided with a gas chromatography workstation, and the chromatogram obtained by the chromatogram is displayed in the display 15 through the gas chromatography workstation, as shown in fig. 2a and fig. 2b, which are chromatograms of standard samples of hydrogen sulfide and phosphine, respectively, wherein the standard sample content of hydrogen sulfide in fig. 2a is 280.00ppm, and the standard sample content of phosphine in fig. 2b is 102.00 ppm. According to the standard sample content calibration standard method, the standard method is introduced to determine the content of the hydrogen sulfide and phosphine components in the sample to be detected, as shown in fig. 3a and fig. 3b, which are the chromatogram of the hydrogen sulfide and phosphine in the sample to be detected, respectively, the content of the hydrogen sulfide component in the sample to be detected in fig. 3a is 215.30ppm, and the content of the hydrogen phosphide component in the sample to be detected in fig. 3b is 11.87 ppm.

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