CN203870077U - Secondary cold trap enrichment device and GC-FID (Gas Chromatography-Flame Ionization Detector) combined device for detecting trace phosphine - Google Patents

Abstract

The utility model belongs to the technical field of phosphine detection and discloses a secondary cold trap enrichment device and GC-FID (Gas Chromatography-Flame Ionization Detector) combined device for detecting trace phosphine. In the secondary cold trap enrichment device and GC-FID combined device, a carrier gas system of a GC-FID analysis system is connected with a six-way valve of a secondary cold trap enrichment system, and an outlet of a secondary cold trap is connected with a gas phase sampler injector of the GC-FID analysis system through a capillary tube. The combined device has the benefits that carrier gas in the secondary cold trap enrichment system and the GC-FID analysis system is set and controlled by the carrier gas system of the GC-FID analysis system, the gas pressure and the gas flow rate are more accurate and more stable to control, and meanwhile, a good fit with the GC-FID analysis system can be realized, so that the reproducibility and the stability of the system are greatly improved.

Description

A secondary cold trap enrichment and GC-FID combined device for detecting trace phosphine

technical field

The utility model belongs to the technical field of phosphine detection, in particular to a secondary cold trap enrichment and GC-FID combined device for detecting trace phosphine.

Background technique

It is generally accepted that phosphine (PH ₃ ) is an important reduced form of phosphorus in the natural environment. Since Devai et al first detected the presence of phosphine in the volatiles of sewage plants in 1988, more and more researchers have participated in the research of phosphine related fields. The study of phosphine not only has important geochemical significance for understanding the cycle of phosphorus in nature, but also provides a new solution direction for the increasingly serious problem of water eutrophication.

Phosphine quantitative and qualitative analysis methods mainly include molybdenum blue colorimetry and gas chromatography. The former is complicated to operate, takes a long time, and has low sensitivity and is not suitable for the determination of a large number of samples and low-concentration samples; the latter is convenient and fast, but the sample pretreatment is complicated, and because phosphine is easily affected by external factors such as light and oxygen, etc., currently It is still not accepted as a standard method for phosphine analysis. The principle of molybdenum blue spectrophotometric determination of phosphine is to contact other phosphine with a strong oxidant to form orthophosphate, and then indirectly detect the content of phosphine with a spectrophotometer. Due to the low accuracy and many interference factors, this method is only suitable for the occasions with high concentration.

The content of phosphine in the natural environment is very low, and it is almost undetectable by the molybdenum blue colorimetric method. This also caused the research on phosphine in the environmental field to start late before the appearance of gas chromatography. However, after decades of development, the application and continuous progress of gas chromatography have driven the continuous improvement of phosphine detection technology.

Utility model content

In order to solve the shortcomings and deficiencies of the prior art, the purpose of the utility model is to provide a secondary cold trap enrichment and GC-FID combined device.

The utility model purpose is realized through the following technical solutions:

A secondary cold trap enrichment and GC-FID combined device for detecting trace amounts of phosphine, comprising a cold trap secondary enrichment system and a GC-FID analysis system, the cold trap secondary enrichment system consists of The sample injection device, a six-way valve, a primary cold trap and a secondary cold trap are composed of an online temperature detector set in the primary cold trap and the secondary cold trap; the GC-FID analysis system consists of a gas phase sampler, a chromatographic column, The flame ionization detector (FID) and the carrier gas system of the GC-FID analysis system are composed. The interface of the six-way valve is respectively connected to the sample injection device, the inlet and outlet of the primary cold trap, the inlet of the secondary cold trap and GC-FID The carrier gas system of the analysis system, the outlet of the secondary cold trap is connected to the gas phase sampler of the GC-FID analysis system through a capillary tube.

The primary cold trap or the secondary cold trap is composed of an enrichment capillary column and a cold trap cup. The capillary column is placed in the cold trap cup, and liquid nitrogen is poured into the cold trap cup. The cold trap cup can be placed on a lifting platform, and The temperature of the cold trap is kept constant by adjusting the distance between the liquid nitrogen liquid level in the cold trap cup and the capillary column through the lifting platform. The enrichment capillary column is preferably 100 cm in length, 0.53 mm in diameter, and filled with Al ₂ O ₃ -Na ₂ SO ₄ capillary column (Kromat Corporation); the temperature on-line detector control system uses a Pt100 thermal resistance temperature detector.

Before the sample injection device of the cold trap secondary enrichment system, a pretreatment device for phosphine enrichment can be arranged, and the pretreatment device is two drying tubes (50mm * 4mm) connected in series, and the drying tube is equipped with porous Carrier NaOH granular desiccant.

A method for detecting trace amounts of phosphine using the above-mentioned secondary cold trap enrichment and GC-FID combined device, the specific detection steps are: setting and controlling the carrier gas system in the GC-FID analysis system. The gas flow rate is 1.5mL/min, and then the phosphine detection sample enters the six-way valve through the sample injection device, and enters the primary cold trap under the drive of the carrier gas for a first enrichment. After the first enrichment, turn the six-way valve to the corresponding position, the enriched phosphine detection sample is subjected to thermal analysis and driven by the carrier gas into the secondary cold trap through the six-way valve for secondary enrichment. The temperature of the primary cold trap and the secondary cold trap are both controlled at -90 ℃, thermal analysis is carried out after the secondary enrichment is completed, and the test sample after thermal analysis is driven by the carrier gas from the gas phase sampler of the GC-FID analysis system into the chromatographic column, separated at a column temperature of 90 °C, and finally enters the chromatographic column. Flame ionization detector (FID) was used for detection at 220°C.

The device of the present utility model has the following advantages and beneficial effects:

(1) In the detection device of the present utility model, the carrier gas is set and controlled by the carrier gas system of the GC-FID analysis system. Compared with the external carrier gas in the prior art, the control of air pressure and gas flow rate is more accurate and stable. Moreover, it can better cooperate with the GC-FID analysis system, which greatly improves the reproducibility and stability of the system;

(2) adopting the device of the utility model can reduce the detection limit of phosphine and greatly improve the precision of phosphine detection;

(3) The GC-FID analysis system of the present utility model adopts a flame ionization detector (FID), which has the advantages of simple structure, convenient operation, and economical price, and is insensitive to changes in gas flow rate, pressure and temperature at the same time, reducing environmental pollution. The operational difficulty and economic cost of the detection and analysis of trace amounts of phosphine provide convenience for more researchers to participate in the study of phosphine in the environment.

Description of drawings

Fig. 1 is a schematic diagram of the main structure of the secondary cold trap enrichment and GC-FID combined device in Example 1 of the present utility model.

The markings in the figure are explained as follows: 1-sample injection device; 2-six-way valve; 3-primary cold trap; 4-secondary cold trap; 5-on-line temperature monitor; 6-gas phase sampler; 7-chromatographic column ; 8-flame ionization detector (FID); 9-the carrier gas system of the GC-FID analysis system; ①-⑥represent the 6 ports of the six-way valve.

Detailed ways

The utility model will be further described in detail below in conjunction with the examples, but the implementation of the utility model is not limited thereto.

Example 1

As shown in Figure 1, a secondary cold trap enrichment and GC-FID combined device for detecting trace amounts of phosphine in this embodiment includes a cold trap secondary enrichment system and a GC-FID analysis system, The cold trap secondary enrichment system is composed of a sample sampling device 1, a six-way valve 2, a primary cold trap 3 and a secondary cold trap 4, and a temperature online detector 5 is arranged in the primary cold trap and the secondary cold trap; The GC-FID analysis system is composed of a gas phase sampler 6, a chromatographic column 7, a flame ionization detector (FID) 8 and a carrier gas system 9 of the GC-FID analysis system. The port is connected to the sample injection device, port ② is the exhaust gas discharge port, port ③ is connected to the inlet of the secondary cold trap, port ④ is connected to the carrier gas system of the GC-FID analysis system, port ⑤ is connected to the outlet of the primary cold trap, The port ⑥ is connected to the inlet of the primary cold trap, and the outlet of the secondary cold trap is connected to the gas phase sampler of the GC-FID analysis system through a capillary tube.

The method that the secondary cold trap enrichment and GC-FID combined device of this embodiment is used to detect trace amounts of phosphine:

Before the gas detection sample is injected into the six-way valve, the carrier gas flow rate in the gas path is set to 1.5mL/min through the carrier gas system of the GC-FID analysis system. It enters the first-stage cold trap driven by air, and performs a first enrichment in the first-stage cold trap. After the first enrichment, turn the six-way valve to the corresponding position, thermally analyze the enriched sample and pass it through the The six-way valve enters the secondary cold trap for enrichment in the secondary cold trap. The temperature of the primary cold trap and the secondary cold trap are both controlled at -90°C. After the secondary enrichment, the gas chromatograph is triggered to make it in the collection state. The gas sample after the second enrichment by thermal analysis is driven by the carrier gas from the gas phase sampler of the GC-FID analysis system into the chromatographic column, separated at the column temperature of 90°C, and finally enters the flame ionization detector (FID ) was detected at 220°C.

Example 2

A secondary cold trap enrichment and GC-FID combined device for detecting trace amounts of phosphine in this embodiment includes a cold trap secondary enrichment system and a GC-FID analysis system, and the cold trap secondary enrichment The system consists of a sample sampling device, a six-way valve, a primary cold trap and a secondary cold trap. A Pt100 thermal resistance temperature detector is installed in the primary cold trap and the secondary cold trap. The length of the primary cold trap and the secondary cold trap is 100cm , with a diameter of 0.53mm, filled with Al ₂ O ₃ -Na ₂ SO ₄ enrichment capillary column and cold trap cup, the capillary column is placed in the cold trap cup, liquid nitrogen is poured into the cold trap cup, and the cold trap cup is placed On the lifting platform, the distance between the liquid nitrogen liquid level in the cold trap cup and the capillary column is adjusted by the lifting platform to realize the constant temperature of the cold trap; the GC-FID analysis system consists of a gas phase sampler, a chromatographic column, and a flame ionization detection The interface of the six-way valve is connected to the sample injection device, the inlet of the secondary cold trap, the carrier gas system of the GC-FID analysis system, the inlet of the primary cold trap and the carrier gas system of the GC-FID analysis system. Outlet, the outlet of the secondary cold trap is connected to the gas phase sampler of the GC-FID analysis system through a capillary tube. Two series-connected drying tubes with a size of 50mm×4mm were set before the sample injection device of the combined device, and the drying tubes were equipped with a porous carrier NaOH particle desiccant (MerekKGaA, 64271Darmstadt, Germany).

In this embodiment, the secondary cold trap enrichment and GC-FID combined device is used to detect trace amounts of phosphine, and the specific detection steps are:

(1) Preparation before the test

Firstly, check the periphery of the equipment, including gas samples, liquid nitrogen and hydrogen used in gas chromatography, high-purity nitrogen and dry air. Check the capacity of liquid nitrogen tanks and gas cylinders to ensure that the use process will not be interrupted. At the same time, check the valves regularly to ensure the safety of the experiment. Turn on the machine to preheat, turn on the GC, download the experimental program method after ignition, preheat for 1-2 hours, and observe that the GC baseline is stable before starting to test samples. After the baseline is stable, prepare the cold trap. First, pour liquid nitrogen into the cold trap cup, place the cold trap on the lifting platform, slowly raise the cold trap so that the capillary is immersed in the cold trap, and wait until the temperature drops to minus 90°C. Injection can begin.

(2) Injection and first enrichment

Before the gas detection sample is injected into the sample injection device, it first passes through two series-connected drying tubes with a size of 50 mm × 4 mm. The tubes are filled with porous carrier NaOH particles (Merek KGaA, 64271 Darmstadt, Germany) to remove CO ₂ , H ₂ O, _H2S gas. Through the carrier gas system of the GC-FID analysis system, the flow rate of the carrier gas in the gas circuit is controlled to be 1.5mL/min. After the filtered gas passes through the six-way valve, it enters the primary cold trap driven by the carrier gas. Enrichment is carried out in the enrichment capillary column (enrichment behavior includes adsorption on the capillary surface at low temperature and liquefaction after reaching the boiling point), the enrichment column is a section with a length of 100cm and a diameter of 0.53mm, filled with Al ₂ O ₃ - Capillary of Na ₂ SO ₄ (Kromat Corporation), this enrichment separates phosphine from hydrocarbons, oxygen, nitrogen and other gases with lower boiling points. The timing starts after the injection, and the enrichment time is 1 min.

(3) Secondary enrichment

After the first enrichment, turn the six-way valve to the corresponding position, lower the cold trap cup of the primary cold trap to expose the enrichment capillary column, blow the surface of the enrichment capillary column evenly with warm air to raise the temperature to room temperature, and enrich in the The phosphine in the capillary column desorbs and vaporizes rapidly from the capillary after the temperature rises, and is driven by the carrier gas through the six-way valve into the enrichment capillary column of the secondary cold trap for enrichment in the secondary cold trap. Trap enrichment improves the enrichment rate of phosphine and increases the response signal value. Start timing from warm air blowing, enrichment time 1min.

(4) into the gas chromatograph

After the secondary enrichment, trigger the gas chromatograph to make it in the acquisition state, lower the cold trap cup of the secondary cold trap to expose the enrichment capillary column, and evenly blow the surface of the enrichment capillary column with warm air to raise the temperature to room temperature. The phosphine originally enriched in the capillary is quickly desorbed and gasified from the capillary after the temperature rises, and driven by the carrier gas, it enters the chromatographic column from the gas phase sampler of the GC-FID analysis system and is separated at a column temperature of 90°C. Into the flame ionization detector (FID) at 220 ° C for detection. Before measuring the actual sample, it is necessary to test the phosphine standard calibration sample to determine the peak time of phosphine, and to make a standard curve for the detection of phosphine concentration. When measuring the actual sample, compare the peak value of the sample measured by the gas chromatograph with the standard curve to obtain the concentration value of the sample.

The detection equipment and method of this embodiment were used to detect the content of paddy soil bound phosphine (MBP) in typical paddy fields in Guangzhou when the rice was in each growth stage. Before the detection, the paddy soil was prepared as a gas detection sample, specifically The preparation steps are as follows: collect fresh paddy soil samples, put 1g of the samples into the digestion tube, use 5mL of _{H2SO4 solution} with a concentration of 0.5mol/L to heat and digest them in the digestion tube, and use high-purity nitrogen to carry out the digestion to obtain Finally, these gases (that is, the gas phosphine released from the combined phosphine) are detected by this detection system. The test results are shown in Table 1.

Table 1 Detection results of bound phosphine (MBP) content in paddy soil

System Repeatability and Stability Verification:

Experimental group: choose the phosphine concentration to be ^1.39ng /m The standard sample and the jointing stage sample in the embodiment 2 adopt the equipment and the method in the embodiment 2 to measure, the sample size is 60ml, and the sample is repeatedly measured 4 times, The coefficient of variation of each sample was analyzed, and the results were expressed as relative standard deviations (RSDs) of peak areas.

Comparison group: The difference between the detection equipment and method and Example 2 is that the secondary cold trap enrichment system is powered by an external carrier gas and is not connected to the carrier gas system of the GC-FID analysis system.

The results of the experimental group and the comparison group are shown in Table 2.

Table 2 Experimental group and comparison group system repeatability and stability verification results

As can be seen from the results in Table 2, the relative standard deviations of the peak areas of the experimental group samples were 4.289% and 5.367%, and the obtained coefficients of variation were all within the acceptable range, indicating that the method had good repeatability and stability, and compared with the comparison group Compared with the device and method of the utility model, the repeatability and stability are better.

Detection Limit Verification:

Concentration is 1.39ng/m The phosphine standard gas is measured by the equipment and method of embodiment ² , sample injection volume is 30mL, 60mL, 90mL, 120mL and 150mL, phosphine peak area and sample injection volume between The linear equation is: y=579.773x-221.000, where x is the injection volume of phosphine (mL), y is the peak area (pA), the fitting coefficient (R Square)=0.9996, and the detection limit is 0.0417pg.

The above-mentioned embodiment is a preferred implementation mode of the present utility model, but the implementation mode of the present utility model is not limited by the above-mentioned embodiment, and any other changes, modifications and substitutions made without departing from the spirit and principle of the present utility model , combination, and simplification, all should be equivalent replacement methods, and are all included in the protection scope of the present utility model.

Claims (4)

1. the secondary cold-trap enrichment for detection of trace hydrogen phosphide and GC-FID combined apparatus, comprise cold-trap secondary enrichment system and GC-FID analytic system, it is characterized in that: described cold-trap secondary enrichment system is comprised of sample feeding device, six-way valve, cold-trap and secondary cold-trap, in cold-trap and secondary cold-trap, set temperature is at thread detector; Described GC-FID analytic system is comprised of the carrier gas system of gas phase injector, chromatographic column, flame ionization detector and GC-FID analytic system, the interface of six-way valve connects respectively import and outlet, the import of secondary cold-trap and the carrier gas system of GC-FID analytic system of sample feeding device, a cold-trap, and the outlet of secondary cold-trap is connected to the gas phase injector of GC-FID analytic system by kapillary.

2. a kind of secondary cold-trap according to claim 1 enrichment and GC-FID combined apparatus, it is characterized in that: cold-trap or secondary cold-trap are comprised of enrichment capillary column and cold-trap cup, capillary column is placed in cold-trap cup, in cold-trap cup, pours liquid nitrogen into, and cold-trap cup is placed on lifting table.

3. a kind of secondary cold-trap according to claim 2 enrichment and GC-FID combined apparatus, is characterized in that: it is 100cm that described enrichment capillary column refers to long, and diameter is 0.53mm, interior filling Al ₂o ₃-Na ₂sO ₄enrichment capillary column.

4. a kind of secondary cold-trap according to claim 1 enrichment and GC-FID combined apparatus, is characterized in that: the drying tube of two series connection is set before the sample feeding device of described cold-trap secondary enrichment system, porous carrier NaOH particle dry agent is housed in drying tube.