CN102866224B - A gas chromatographic detection method for the determination of carbon-containing compounds based on carbon atomic emission spectroscopy - Google Patents

Abstract

The invention discloses a gas chromatographic detection method for determining a carbon-containing compound based on carbon atomic emission spectroscopy. A dielectric barrier discharge (DBD) device is used as an atomizer and an excitation source of a carbon element in the carbon-containing compound, 193.0nm is selected as a detection wavelength, a charge-coupled device is used for quantitative detection, and detection sensitivity is improved by adopting an auxiliary heating method. The method has the characteristics of high selectivity, high analysis speed, high stability and the like for the detection of the carbon element.

Description

A gas chromatographic detection method for the determination of carbon-containing compounds based on carbon atomic emission spectroscopy

technical field

The invention belongs to a new technology of gas chromatography detection in analytical chemistry and relates to a gas chromatography detection method with high selectivity for carbon elements. the

Background technique

In a gas chromatograph, the detector is an important component of the detection method. At present, there are dozens of known gas chromatographic detectors, the most common of which include thermal conductivity detector (TCD), hydrogen flame ionization detector (FID), nitrogen phosphorus detector (NPD), electron capture detector (ECD) ), Flame Photometric Detector (FPD), etc. These detectors are used as different gas chromatography detection methods because of their different detection principles. TCD is based on the principle that different analytical components and carrier gases have different thermal conductivity. It is a general-purpose non-destructive concentration detector, which can be applied to the detection of any component in theory, but the sensitivity is low; FID is based on the detection The target is ionized in the hydrogen flame, and the generated ions are detected by moving under the action of an electric field to form an ion flow. The detection target is combustible organic matter, but there is no response to non-combustible targets such as carbon dioxide; NPD is used for determination Nitrogen- and phosphorus-containing organic compounds, ECD is used to analyze some compounds with high electronegativity such as halogen compounds and polycyclic aromatic hydrocarbons, and FPD is mainly used to determine sulfur- and phosphorus-containing compounds. At present, there is no report on a gas chromatographic detection method that is selective for carbon. the

Dielectric Barrier Discharge (DBD) is a non-equilibrium gas discharge in which an insulating medium is inserted into the discharge space. DBD has many advantages, including low operating temperature, low energy consumption, simple device structure, and can work under atmospheric pressure. Currently, DBD is widely used in industry for surface modification and pollutant treatment, etc. In analytical chemistry, DBDs have been used as atomizers and ion sources. For example, Miclea et al. used DBD as an atomizer for laser atomic absorption spectroscopy (Miclea, M.; Kunze, K.; Musa, G.; Franzke, J.; Niemax, K. Spectrochim. Acta Part B, 2001,56,37-43); patent (ZL-200510086518.2) designed a DBD-based atomizer, which can be used for the atomization of arsenic, selenium, tin, antimony and other elements that can generate hydrides; patent (ZL- 200610011548.1) designed a DBD-based chemical ionization method and mass spectrometry ion source, which can be used in conjunction with mass spectrometry detectors for organic detection. DBD is used as a gas chromatographic detection method also reported in the literature, Kunze et al. used a DBD-based laser atomic absorption spectrometer as a gas chromatographic detector for the detection of halogen-containing gas analytes (Kunze, K.; Miclea, M.; Franzke, J.; Niemax, K. Spectrochim. Acta Part B, 2003, 58, 1435-1443); Li et al. found that DBD can excite the molecular emission spectrum of halogenated hydrocarbons and use it as a gas chromatography Detectors to detect halogenated hydrocarbons (Li, W.; Zheng, C.; Fan, G.; Tang, L.; Xu, K.; Lv, Y.; Hou, X. Anal. Chem. 2011, 83, 5050 -5055). As an atomizer, the DBD device is only used for easily atomized elements, such as mercury, arsenic, selenium, tin, antimony and other elements; for organic substances, it can only excite the emission spectra of molecules with low energy requirements, such as halogenated hydrocarbons; currently There is no report on using DBD to excite carbon atomic emission spectroscopy. the

Contents of the invention

The purpose of the present invention is to use heating-assisted DBD plasma to excite carbon atom emission spectrum and develop it into a gas chromatography detection method with high selectivity, high stability and high sensitivity for carbon for gas chromatography of carbon-containing compounds detection. the

Technical solutions

In the present invention, a dielectric barrier discharge device is used as an atomizer and an excitation source for carbon elements in carbon-containing compounds, and a charge-coupled device is used as a detector of carbon atomic emission spectrum. The dielectric barrier discharge device uses a hollow quartz tube as an insulating medium. Copper wire is wound outside as the external electrode, copper wire is inserted inside as the internal electrode, heating and temperature control equipment is installed on the quartz tube of the dielectric barrier discharge device, argon gas is introduced as the discharge gas, and a transformer is used to adjust the voltage of the internal and external electrodes to contain carbon The compound is used as the detection object, and the specific atomic emission line of 193.0nm carbon is selected for quantitative detection. The detection steps are:

⑴The sample enters from the gas chromatograph inlet, and after separation, enters the dielectric barrier discharge device from the discharge gas inlet;

(2) The voltage of the inner and outer electrodes of the dielectric barrier discharge device is controlled at 1.84~3.25kV;

⑶ The discharge gas argon enters through the discharge gas port at 300-900mL min ^-1 ;

⑷By controlling the voltage of the electric heating wire, the temperature of the dielectric barrier discharge device is controlled to be 25-300°C;

(5) After the sample enters the heated dielectric barrier discharge device, it is atomized in the dielectric barrier discharge plasma to generate free atoms of carbon elements;

⑹The free atoms of carbon element are excited by dielectric barrier discharge plasma to produce the characteristic atomic emission line of carbon element at 193.0nm, which is detected by charge-coupled device to realize the quantitative analysis of carbon-containing compounds. the

The dielectric barrier discharge-based gas chromatographic detector of the present invention, as shown in FIG. 1 , has a structure consisting of a dielectric barrier discharge plasma excitation device, a heating temperature control device, and an optical detection device. the

The carbon-containing compound mentioned in the present invention refers to a carbon-containing compound that can be gasified in gas chromatography. The optimum temperature of the dielectric barrier discharge device is 200-300°C, the optimum internal and external electrode voltage of the dielectric barrier discharge device is 2.54-3.25kV, and the optimum argon flow rate is 300-600mL min ^-1 .

Invention effect

Compared with the existing gas chromatography detection method, the present invention mainly has the following characteristics/advantages: (1) the carbon atom emission spectrum is obtained by exciting the DBD plasma device; (2) the DBD plasma device is assisted by heating to improve the detection method. Stability, and enhance the sensitivity of its detection; (3) choose 193.0nm carbon-specific atomic emission line, less interference and high sensitivity; (4) analysis is fast and simple; (5) the detection method only needs argon as the discharge gas, argon The gas consumption is small, green and environmental protection; (6) The measurement range is wide, suitable for organic and inorganic carbon-containing compounds. the

Description of drawings

Fig. 1 Schematic diagram of gas chromatographic detection device for heating-assisted-DBD plasma-atomic emission spectrometry. 1: copper outer electrode; 2: copper inner electrode; 3: sealing plug; 4: quartz tube; 5: discharge gas inlet; 6: heating temperature control device; 7: charge coupled detector; 8: discharge gas outlet. Wherein, the length of the quartz tube 4 is 50mm, the inner diameter is 3.0mm, and the outer diameter is 5.0mm; the outside of the quartz tube is tightly wound with a copper wire (1.0mm in diameter) for a section of about 25mm as the copper outer electrode 1; a copper electrode 1 is inserted inside. The wire (1.5mm in diameter and 30mm in length) is used as the copper inner electrode 2; on the left side of the quartz tube, high-temperature-resistant silica gel is used as the sealing plug 3; the left and right ends of the quartz tube have a leg of 7.5 mm respectively as the discharge gas inlet 5 and Outlet 8 also uses high-temperature-resistant silica gel as the sealing plug 3; the heating temperature control device 6 includes a resistance wire heater and a temperature controller, and controls the heating temperature by adjusting the voltage of the resistance wire heating device; the right end of the quartz tube is a sealing plug 3. Ensure that the characteristic emission spectrum of the detection object is collected smoothly, and at the same time, the substance in the quartz tube does not contaminate the charge-coupled detector 7; the atomic emission line of the carbon in the detection object is recorded by the charge-coupled detector 7. the

Figure 2 is the atomic emission spectrum at 193.0nm for carbon-containing compounds and carbon-free compounds in this method. In the figure, the abscissa is the wavelength in nm; the ordinate is the signal response intensity; the 15 substances are: 1, blank, 2, hydrogen peroxide, 3, water, 4, ammonia, 5, carbon dioxide, 6, methane, 7 , formaldehyde, 8, methanol, 9, ether, 10, acetonitrile, 11, acetone, 12, n-butanol, 13, ethyl acetate, 14, n-hexane, 15, tert-butylamine. the

Fig. 3 The effect of discharge voltage on the sensitivity of seven carbon-containing compounds in this method. The working conditions are: injection volume: 1 μL, argon flow rate: 300 mL min ⁻¹ , heating temperature: 300° C. In the figure, the abscissa is the discharge voltage in kV; the ordinate is the peak area; the seven substances are: 1, formaldehyde, 2, ethyl acetate, 3, methanol, 4, ethanol, 5, n-propanol, 6 , n-butanol, 7, n-pentanol.

Fig. 4 The effect of argon flow rate on the sensitivity of seven carbon-containing compounds in this method. The working conditions are: injection volume: 1 μL, discharge voltage: 2.95kV, heating temperature: 300°C. In the figure, the abscissa is the flow rate of argon, and the unit is mL min ^-1 ; the ordinate is the peak area; the seven substances are: 1, formaldehyde, 2, ethyl acetate, 3, methanol, 4, ethanol, 5, n- Propanol, 6, n-butanol, 7, n-pentanol.

Fig. 5 The effect of heating temperature on the sensitivity of seven carbon-containing compounds in this method. The working conditions are: injection volume: 1 μL, discharge voltage: 2.95kV, argon flow rate: 300mL min ^-1 . In the figure, the abscissa is the temperature in °C; the ordinate is the peak area; the seven substances are: 1, formaldehyde, 2, ethyl acetate, 3, methanol, 4, ethanol, 5, n-propanol, 6, n-butanol, 7, n-pentanol.

Fig. 6 The gas chromatograms of standard samples and beer samples of four kinds of liquid carbon-containing components in beer determined by this method. In the figure, the abscissa is the retention time in seconds; the ordinate is the signal response intensity; Figure A is the standard sample, and Figure B is the beer sample; the four components are: 1, formaldehyde; 2, ethyl acetate; 3 , methanol; 4, ethanol. the

Figure 7: Gas chromatograms of standard samples of carbon-containing components in three gases measured by this method. In the figure, the abscissa is the retention time in seconds; the ordinate is the signal response intensity; the three components are: 1, CO; 2, CH ₄ ; 3, CO ₂ .

Detailed ways

Embodiment one:

In this embodiment, various common volatile organic and inorganic carbon-containing compound samples are selected, and the characteristic atomic emission line of carbon element at 193.0nm produced after DBD is detected, and the carbon-containing compound is mixed with ammonia, water, hydrogen peroxide and other non-carbon-containing compounds. Compound samples are compared to confirm the detection ability of the present invention for carbon-containing compounds. The specific operation steps are: ⑴The sample enters from the gas chromatograph inlet, and enters the DBD device from the discharge gas inlet after separation; ⑵The voltage of the internal and external electrodes of the DBD device is controlled at 2.95kV; ⑶The discharge gas argon passes through the discharge gas port to 400mL min ^-1 enters; ⑷By controlling the voltage of the electric heating wire, the temperature of the DBD device is controlled to 300°C; ⑸After the sample enters the heated DBD device, it is atomized in the DBD plasma to generate free atoms of carbon element; ⑹The carbon element is The free atoms are excited by the DBD plasma to produce the characteristic atomic emission line of carbon at 193.0nm, which is detected by a charge-coupled device to realize the quantitative analysis of carbon-containing compounds. Various carbon-containing compounds analyzed include tert-butylamine, n-hexane, ethyl acetate, n-butanol, acetone, acetonitrile, ether, methanol, formaldehyde, methane and carbon dioxide, etc. The atomic emission spectrum at 193.0nm is shown in Figure 2 .

Embodiment two:

This example examines the influence of the internal and external electrode voltages on the detection sensitivity of carbon-containing compounds in a DBD device. Referring to the operation steps of Example 1, taking formaldehyde, ethyl acetate, methanol, ethanol, n-propanol, n-butanol and n-pentanol as test objects, the test range of the inner and outer electrode voltages is 1.84-3.25kV. The experimental results of this embodiment are shown in Fig. 3, from which it is determined that the optimum excitation voltage of the present invention is 2.54-3.25 kV. the

Embodiment three:

In this embodiment, the effect of the argon flow rate of the discharge gas in the DBD device on the detection sensitivity of carbon-containing compounds is investigated. Referring to the operation steps of Example 1, formaldehyde, ethyl acetate, methanol, ethanol, n-propanol, n-butanol and n-pentanol were used as test objects, and the test range of argon flow rate was 300-900mL min ^-1 . The experimental results of this embodiment are shown in Fig. 4, from which it is determined that the optimum argon flow rate of the present invention is 300-600 mL min ^-1 .

Embodiment four:

This embodiment examines the influence of the temperature of the heating and temperature control device in the DBD device on the detection sensitivity of carbon-containing compounds. Referring to the operation steps of Example 1, formaldehyde, ethyl acetate, methanol, ethanol, n-propanol, n-butanol and n-pentanol were used as test objects, and the temperature range of the DBD device was 25-300°C. The experimental results of this embodiment are shown in the accompanying drawing 5, thus it is determined that the optimum working temperature of the present invention is 200-300°C. the

Embodiment five:

The content of low-carbon aldehydes, esters and alcohols is one of the important indicators for evaluating the quality of wine samples. In this embodiment, the carbon-containing liquid components in the beer sample are analyzed, and the selected analytes include formaldehyde, ethyl acetate, methanol and ethanol. The sample is injected from the gas chromatograph with an injection volume of 0.02μL; the excitation voltage of the inner and outer electrodes is 2.95kV, the flow rate of the discharge gas argon is 400mL min ^-1 , and the temperature of the heating device is adjusted to 300°C. This method is successfully applied to the determination of formaldehyde, ethyl acetate, methanol and ethanol in beer samples, and the chromatograms of standard samples and beer samples are shown in Figure 6. The relative standard deviation (RSD) and limit of detection (LOD) of the four carbon-containing compounds are shown in Table 1.

Table 1 This method measures the detection limit of 4 kinds of carbon-containing compounds

Embodiment six:

Quantitative detection of carbon-containing gases is an important problem in analysis work, involving oil and gas, garbage disposal, chemical catalysis, organic synthesis and other aspects. In this embodiment, a carbon-containing gas sample is analyzed, and the selected analytes include CO ₂ , CH ₄ and CO. The sample is injected from the gas chromatograph with an injection volume of 0.50mL; the excitation voltage of the inner and outer electrodes is 2.95kV, the flow rate of the discharge gas argon is 400mL min ^-1 , and the temperature of the heating device is adjusted to 300°C. This method has been successfully applied to the detection of CO ₂ , CH ₄ and CO 3 mixed gases, and the chromatograms of the standard substances of the detected components are shown in Figure 7. The relative standard deviation (RSD) and limit of detection (LOD) of the three gaseous carbon compounds are shown in Table 2.

Table 2 This method measures the detection limit of 3 kinds of carbon-containing compounds

Claims (4)

1. the gas-chromatography detection method based on carbon atom emission spectrometry carbon compound, atomizer and the excitaton source of carbon in it is characterized in that using dielectric barrier discharge device as carbon compound, dielectric barrier discharge device adopts hollow quartz ampoule as insulating medium, be wound around copper wire as external electrode in quartz ampoule outside, the inner copper wire that inserts is as interior electrode, heated for controlling temperature equipment is installed on the quartz ampoule of dielectric barrier discharge device, pass into argon gas as discharge gas, use transformer to regulate the voltage of internal and external electrode; Detecting device using charge-coupled image sensor as carbon atom emission spectrum, using carbon compound as detecting thing, selects the specific atoms emission line of 193.0 nm carbon quantitatively to detect, and its detecting step is:

(1) sample enters from gas chromatograph injection port, after separating, enters into dielectric barrier discharge device from discharge gas import;

(2) dielectric barrier discharge device internal and external electrode Control of Voltage is at 1.84 ~ 3.25 kV;

(3) discharge gas argon gas through discharge gas mouth with 300 ~ 900 mL min ^-1enter;

(4) by controlling the voltage of electrical heating wire, regulating dielectric barrier discharge unit temp is 25 ~ 300 DEG C;

(5) sample enters after the dielectric barrier discharge device of heating, produces the free atom of carbon in dielectric barrier discharge plasma Atomization;

(6) free atom of carbon excites through dielectric barrier discharge plasma, produces the characteristic atomic spectral line of emission of 193.0 nm of carbon, detects through charge-coupled image sensor, realizes the quantitative test of carbon compound.

2. the internal and external electrode voltage that in accordance with the method for claim 1, it is characterized in that dielectric barrier discharge device is 2.54 ~ 3.25 kV.

3. in accordance with the method for claim 1, it is characterized in that argon gas flow velocity is 300 ~ 600 mL min ^-1.

4. the temperature that in accordance with the method for claim 1, it is characterized in that dielectric barrier discharge device is 200 ~ 300 DEG C.