Search

CN-121994976-A - Volatile organic compound air on-line detection method based on gas chromatography

CN121994976ACN 121994976 ACN121994976 ACN 121994976ACN-121994976-A

Abstract

The invention discloses a gas chromatography-based volatile organic compound air on-line detection method, which relates to the technical field of gas chromatography analysis. And then, carrying the analytic substances into a gas chromatographic separation column by carrier gas, and realizing time sequence separation of each component by temperature programming, wherein the separated components are detected by a flame ionization detector to generate an original spectrogram containing retention time and peak area data. And finally, comparing the original spectrogram data with a pre-stored volatile organic compound fingerprint feature library, matching the types of the target objects according to the retention time, directly inverting and calculating the concentration by using the standard peak area response coefficient in the library, and outputting a detection result. The method improves the enrichment and analysis efficiency through spiral condensation and instantaneous thermal analysis, realizes quick qualitative and quantitative analysis by utilizing a fingerprint feature library, and improves the automation level and analysis efficiency of online monitoring.

Inventors

  • SHEN SHUTING

Assignees

  • 上海谱诺检测技术有限公司

Dates

Publication Date
20260508
Application Date
20260410

Claims (10)

  1. 1. The volatile organic compound air on-line detection method based on gas chromatography is characterized by comprising the following steps of: Introducing an air sample to be tested into a pretreatment pipeline, carrying out low-temperature enrichment on the air sample to be tested by utilizing a spiral condensing pipe arranged in the pretreatment pipeline, and transferring concentrate in the spiral condensing pipe to an analysis chamber through instantaneous heating after enrichment is finished; Loading the concentrate in the analysis chamber into a gas chromatographic separation column along with carrier gas, and utilizing a temperature gradient control program of the gas chromatographic separation column to realize time sequence separation of volatile organic compounds with different boiling points in the gas chromatographic separation column so as to form separated component peak groups; Scanning the separated component peak groups one by one through a flame ionization detector, and collecting the retention time and peak area intensity of each component peak to generate original spectrogram data; Inputting the original spectrogram data into a preset volatile organic compound fingerprint feature library for comparison, wherein the standard retention time of known volatile organic compounds and corresponding standard peak area response coefficients are stored in the volatile organic compound fingerprint feature library; And screening target volatile organic compound types with the retention time deviation within an allowable range from the original spectrogram data according to the comparison result, and carrying out concentration inversion calculation on the peak area intensity in the original spectrogram data by utilizing standard peak area response coefficients corresponding to the target volatile organic compound types to output a final volatile organic compound concentration detection result.
  2. 2. The gas chromatography-based volatile organic compound air on-line detection method according to claim 1, wherein the low-temperature enrichment of the air sample to be detected by using a spiral condenser tube arranged in the pretreatment pipeline comprises the following steps: Starting a semiconductor refrigerating sheet arranged on the outer side of the spiral condensing tube, and reducing the tube wall temperature of the spiral condensing tube to a preset low-temperature capturing zone; Opening an air inlet valve of the air sample to be detected, and controlling the air sample to be detected to flow through the cavity in the spiral condensing tube at a constant low flow rate, so that volatile organic compounds in the air are condensed and adsorbed on the inner wall of the spiral condensing tube; After the enrichment timing reaches a preset time length, closing the air inlet valve and stopping conveying the air sample to be detected; Starting an instantaneous heating program of the spiral condensing tube, and heating the spiral condensing tube by using a pulse heating wire wound on the outer wall of the spiral condensing tube to heat the spiral condensing tube in millisecond level so as to promote instantaneous vaporization and desorption of volatile organic matters adsorbed on the inner wall of the spiral condensing tube, wherein the winding density of the pulse heating wire from a sample inlet to a sample outlet of the spiral condensing tube is gradually reduced, so that the heating power density of the sample inlet is higher than that of the sample outlet; and simultaneously, switching an air inlet electromagnetic valve of the analysis chamber to a conducting state, and carrying the vaporized and desorbed volatile organic compounds into the analysis chamber by utilizing reverse purging of carrier gas.
  3. 3. The gas chromatography-based volatile organic compound air on-line detection method according to claim 1, wherein the time sequence separation of the volatile organic compounds with different boiling points in the gas chromatography separation column is realized by using a temperature gradient control program of the gas chromatography separation column, comprising: Setting a column incubator initial temperature of the gas chromatographic separation column to a minimum value below the boiling point of all target volatile organics prior to loading the concentrate in the resolving chamber into the gas chromatographic separation column; Maintaining the initial temperature for a fixed period of time after the concentrate enters the gas chromatographic separation column with a carrier gas to ensure that low boiling point components completely enter the gas chromatographic separation column; Then, linearly heating a column temperature box of the gas chromatographic separation column according to a preset heating rate, wherein volatile organic compounds with different boiling points sequentially move forwards in the gas chromatographic separation column due to the difference of gasification rates in the heating process; Monitoring the gas components flowing through the outlet of the gas chromatographic separation column in real time, when detecting that a certain volatile organic compound flows out, recording the temperature of the column incubator and the outflow time point at the moment, and confirming the outflow time point as the retention time of the volatile organic compound; And continuing heating until all volatile organic compounds in the gas chromatographic separation column flow out, and ending the separation procedure.
  4. 4. The gas chromatography-based volatile organic compound air on-line detection method according to claim 1, wherein the scanning of the separated component peak groups one by a flame ionization detector, collecting the retention time and peak area intensity of each component peak, comprises: hydrogen and air are respectively introduced into the combustion head of the flame ionization detector, and are ignited to form stable hydrogen flame; Introducing the gas component flowing out of the gas chromatographic separation column directly into the root of the hydrogen flame to enable the organic compound to generate ionization reaction in the high-temperature flame; applying a constant voltage to a collector of the flame ionization detector, collecting a flow of charged ions generated by the ionization reaction, and converting it into a current signal; the current signal is subjected to uninterrupted sampling by utilizing a high-speed analog-to-digital conversion module, and a current intensity curve which changes along with time is obtained; Carrying out digital filtering denoising treatment on the current intensity curve, identifying and extracting a peak area in the current intensity curve, recording a time span between a starting point and an ending point of each peak as retention time of a component peak corresponding to the peak, and determining an area integral value enclosed by the peak as peak area intensity of the component peak corresponding to the peak; The raw spectrogram data comprises the acquired retention time and peak area intensity.
  5. 5. The gas chromatography-based volatile organic compound air on-line detection method according to claim 1, wherein the step of inputting the original spectrogram data into a preset volatile organic compound fingerprint feature library for comparison comprises the steps of: extracting the retention time of all component peaks from the original spectrogram data, and sequencing according to the sequence of the retention time to generate a retention time sequence to be matched; Traversing each standard record in the volatile organic compound fingerprint feature library, wherein the standard record comprises standard retention time and standard peak area response coefficient of a single volatile organic compound; calculating the absolute value of the difference value of each retention time in the retention time sequence to be matched and the standard retention time in the standard record; Judging whether the absolute difference value is smaller than a preset time tolerance threshold value or not, and if a plurality of continuous absolute difference values are smaller than the time tolerance threshold value, judging that the volatile organic species corresponding to the standard record is a potential matching object; and packaging and outputting all the volatile organic species judged as potential matching objects and the corresponding standard peak area response coefficients thereof, and taking the volatile organic species and the corresponding standard peak area response coefficients as input parameters of subsequent concentration inversion calculation.
  6. 6. The gas chromatography-based volatile organic compound air on-line detection method according to claim 1, wherein the concentration inversion calculation of the peak area intensity in the raw spectrogram data by using the standard peak area response coefficient corresponding to the target volatile organic compound type comprises: reading the corresponding standard peak area response coefficient from the volatile organic compound fingerprint feature library aiming at each screened target volatile organic compound, wherein the standard peak area response coefficient represents the peak area output capacity of the volatile organic compound with unit concentration under the condition of a specific detector; finding a component peak matched with the target volatile organic species in the original spectrogram data, and reading the peak area intensity of the component peak obtained by matching; dividing the peak area intensity by the standard peak area response coefficient to obtain an actual measurement concentration value of the target volatile organic compound; the measured concentration values of all the target volatile organic compound species are summed to generate a detection result data set containing all the detected volatile organic compound concentrations.
  7. 7. The method for online detection of volatile organic compound air based on gas chromatography according to claim 1, wherein the step of constructing the volatile organic compound fingerprint feature library comprises the following steps: Selecting a plurality of representative known volatile organic compound standard samples, wherein the concentration range of each standard sample covers the actual concentration level of the expected detection environment; Under the same gas chromatography detection condition, respectively carrying out enrichment, separation and flame ionization detection on each standard sample to obtain corresponding standard spectrogram data; extracting retention time and peak area intensity of each volatile organic component from each standard spectrogram data, and taking the ratio of the peak area intensity to the concentration under the same concentration as a standard peak area response coefficient of the volatile organic component; Storing the standard retention time, standard peak area response coefficient and corresponding chemical name or number of each volatile organic compound in a correlated manner to form a standard record; and carrying out classified indexing on all standard records, arranging according to the ascending order of the retention time, and adding version numbers and generation dates to generate the volatile organic compound fingerprint feature library.
  8. 8. The gas chromatography-based volatile organic compound air on-line detection method according to claim 5, further comprising the step of periodically self-checking the performance of the gas chromatography separation column: Before the beginning of each formal detection flow, cutting off an air inlet passage of an air sample to be detected, and introducing a calibration sample gas containing trace propane gas into the gas chromatographic separation column instead; Starting a simplified gas chromatographic separation procedure, and recording the retention time of the propane component in the calibration sample gas at the outlet of the gas chromatographic separation column; Comparing the retention time with a propane standard retention time stored in a system, and calculating a difference between the retention time and the propane standard retention time; if the difference exceeds a preset performance drift threshold, triggering a chromatographic column aging cleaning instruction, and prolonging a subsequent detection period until the difference returns to a normal range; after said comparing said retention time with a propane standard retention time stored in the system, calculating a difference between said retention time and said propane standard retention time, said method further comprises the step of dynamically time-correcting the fingerprint feature library comparison process based on said difference: If the difference value does not exceed the preset performance drift threshold value, directly using a preset volatile organic compound fingerprint feature library to carry out subsequent comparison; If the difference exceeds the preset performance drift threshold but is within an acceptable correction range, temporarily generating a corrected comparison time sequence when the step of inputting the original spectrogram data into a preset volatile organic compound fingerprint feature library for comparison is executed subsequently; generating the corrected alignment time sequence includes: Reading standard retention time in each standard record from the volatile organic compound fingerprint feature library, adding the difference value to each standard retention time, and generating corresponding temporary correction retention time, wherein all the temporary correction retention time forms the corrected comparison time sequence; The absolute value of the difference value is calculated and the time tolerance threshold value is judged according to the comparison time sequence which is extracted from the original spectrogram data and is to be matched with the corrected comparison time sequence, so that the screening of the target volatile organic compound types is completed; And stopping using the corrected comparison time sequence after the chromatographic column aging cleaning instruction is executed and the difference value returns to the normal range after the follow-up self-check is confirmed, and recovering to use the original volatile organic compound fingerprint feature library for comparison.
  9. 9. The gas chromatography-based volatile organic compound air online detection method according to claim 1, further comprising a sampling flow rate adaptive adjustment step based on meteorological parameters: Collecting an ambient temperature value and an atmospheric pressure value of a deployment site in real time, substituting the ambient temperature value and the atmospheric pressure value into a gas state equation conversion model, and calculating a current air density correction factor; According to the air density correction factor, dynamically adjusting the rotating speed of an air inlet sampling pump of the air sample to be tested so as to maintain the air quality entering the system in unit time to be constant; Meanwhile, the average value of the concentration of the volatile organic compounds detected in the previous period is read, if the average value of the concentration of the volatile organic compounds is higher than a high concentration warning threshold value, the air inlet sampling flow rate of the air sample to be detected is temporarily reduced, and the single enrichment time is prolonged to ensure the detection precision; And after the high concentration detection is finished, recovering the air inlet sampling flow rate of the air sample to be detected to a conventional set value.
  10. 10. The gas chromatography-based volatile organic compound air on-line detection method according to claim 1, further comprising the step of drift calibration of the detection data: Regularly extracting standard gas with known concentration, introducing the standard gas into a detection system, and executing a complete process from enrichment to detection to obtain a group of measured peak area intensities under the standard concentration; Calculating the ratio of the measured peak area intensity to the theoretical peak area intensity to generate a current detector sensitivity drift coefficient; the sensitivity drift coefficient of the history detector stored last time is called, and the relative variation between the two coefficients is calculated; Comparing the relative variation with a preset drift alarm threshold, and if the relative variation exceeds the drift alarm threshold, applying the currently generated detector sensitivity drift coefficient to all subsequent concentration inversion calculations to replace the original coefficient; If the drift alarm threshold is not exceeded, the original coefficient is maintained unchanged, and only the calibration data is recorded.

Description

Volatile organic compound air on-line detection method based on gas chromatography Technical Field The invention belongs to the technical field of gas chromatography analysis, and particularly relates to a volatile organic compound air on-line detection method based on gas chromatography. Background The monitoring of volatile organic compounds in the air is important for environmental assessment, health early warning and pollution source analysis. At present, on-line monitoring based on gas chromatography technology is a mainstream means, and the key links of the on-line monitoring are rapid pretreatment of samples and accurate analysis of components. In the aspect of sample pretreatment, the conventional technology mostly adopts adsorption tubes for normal-temperature adsorption or conventional cold trap trapping. The former has limited trapping efficiency on low boiling point components, and the adsorbent can possibly introduce background interference or generate irreversible adsorption, while the latter can realize low-temperature concentration, but the common straight tube type or simple coil type cold trap has limited condensation surface area and air path length, and still has room for improving the enrichment efficiency of trace volatile organic compounds in complex air matrixes. More importantly, when the enriched target is transferred to a chromatographic system, the conventional temperature programming analysis speed is low, so that chromatographic peak broadening can be possibly caused, the subsequent rapid analysis with high separation degree is influenced, and the analysis speed becomes one of bottlenecks limiting analysis flux under a continuous online monitoring scene. In the data analysis and quantification link, the existing methods generally rely on external standard methods or internal standard methods. For each detection, standard gas with known concentration is used for instrument calibration so as to establish a retention time window and a peak area-concentration correction curve of each target object. The process needs to frequently prepare and use standard substances, is complex in operation and increases operation and maintenance cost and complexity. For application scenes of which tens or even hundreds of volatile organic compounds need to be monitored simultaneously, the workload of building and maintaining a complete calibration system is huge, and the identification of unknown spectrum peaks is difficult to quickly respond. There is a contradiction between real-time requirements of online monitoring and offline and time-consuming calibration procedures, and a data analysis strategy capable of reducing dependence on frequent calibration and rapidly realizing multi-component qualitative and quantitative is needed. Disclosure of Invention The present invention aims to solve at least one of the technical problems existing in the prior art. Therefore, the invention provides a volatile organic compound air on-line detection method based on gas chromatography, which comprises the following steps: Introducing an air sample to be tested into a pretreatment pipeline, carrying out low-temperature enrichment on the air sample to be tested by utilizing a spiral condensing pipe arranged in the pretreatment pipeline, and transferring concentrate in the spiral condensing pipe to an analysis chamber through instantaneous heating after enrichment is finished; Loading the concentrate in the analysis chamber into a gas chromatographic separation column along with carrier gas, and utilizing a temperature gradient control program of the gas chromatographic separation column to realize time sequence separation of volatile organic compounds with different boiling points in the gas chromatographic separation column so as to form separated component peak groups; Scanning the separated component peak groups one by one through a flame ionization detector, and collecting the retention time and peak area intensity of each component peak to generate original spectrogram data; Inputting the original spectrogram data into a preset volatile organic compound fingerprint feature library for comparison, wherein the standard retention time of known volatile organic compounds and corresponding standard peak area response coefficients are stored in the volatile organic compound fingerprint feature library; And screening target volatile organic compound types with the retention time deviation within an allowable range from the original spectrogram data according to the comparison result, and carrying out concentration inversion calculation on the peak area intensity in the original spectrogram data by utilizing standard peak area response coefficients corresponding to the target volatile organic compound types to output a final volatile organic compound concentration detection result. Further, the low-temperature enrichment of the air sample to be tested is performed by using a spiral condensing tube arranged in the pr