Patent ID: 12259374

DETAILED DESCRIPTION

The present disclosure will be further described in details by combining with the accompanying drawings.

FIG.1is the schematic diagram of working principle of the electronic nose instrument in a method for multi-information fusion of gas sensitivity and chromatography and on-site detection and analysis of flavor substances using an electronic nose instrument provided in the present disclosure. Main constructional units of the electronic nose instrument include a gas sensor array module I, a capillary gas chromatographic column module II, an automatic headspace sampling module III, a computer control and data analysis module IV, an automatic lifter V, a large-volume headspace vapor generation device VI, a hydrogen bottle VII-1and a dry air bottle VII-2.FIG.1shows a headspace sampling state of the gas sensor array module I. Hydrogen H2is used both as the carrier gas for the capillary gas chromatographic column module II and as the fuel gas for a Hydrogen flame ionization detector (FID). The dry air is used not only as the combustion-supporting gas of FID in the capillary chromatographic column module II, but also as the calibration gas (not combusted) in the gas sensor array module I.

FIG.2is the schematic diagram of working principle of the electronic nose instrument in the headspace sampling state of the capillary gas chromatographic column, in the present disclosure.

Main constructional units of the gas sensor array module I include the gas sensor array I-1, the annular working chamber I-2, the thermal insulation layer I-3, the partition plate I-4, the fan I-5and the resistance heating element I-6, and is located in the middle right part of the electronic nose instrument. Main constructional units of the capillary gas chromatographic column module II include the capillary gas chromatographic column II-1, the detector II-2, the amplifier II-3, the recorder II-4, a thermal insulation layer II-5, the fan II-6, the resistance heating wire II-7and the inlet port II-8, and is located in the right upper part of the electronic nose instrument. The gas sensor array module I and the capillary gas chromatographic column module II are used for converting the chemical and physical information of an odor into the electric signals online.

The constructional units of the automatic headspace sampling module III include the first micro vacuum pump III-1, the first flowmeter III-2, the first throttle valve III-3, the first two-position two-port electromagnetic valve III-4, the second two-position two-port electromagnetic valve III-5, the two-position three-port electromagnetic valve III-6, a second micro vacuum pump III-7, the third two-position two-port electromagnetic valve III-8, the fourth two-position two-port electromagnetic valve III-9, the side-hole sampling needle III-10, the first pressure relief valve III-11, the first purifier III-12, the second throttle valve III-13, the second pressure relief valve III-14and the second purifier III-15, the third throttle valve III-16, the second flowmeter III-17, the fourth throttle valve III-18and the fifth throttle valve III-19, and is located in the right lower part of the electronic nose instrument.

Main constructional units of the computer control and data analysis module IV include an A/D data acquisition card IV-1, a driving and control circuit board IV-2, a computer mainboard IV-3, a 4-path precision DC stabilized power supply IV-4, a WIFI board card IV-5and a displayer IV-6, and is located in the left side of the electronic nose instrument. The role of the WIFI board card IV-5is to real-time transmit the sensitive information of the gas sensor array module I and the capillary gas chromatographic column module II to multiple specified fixed/mobile terminals.

Main constructional units of the automatic lifter V include the support disc V-1, the step motor V-2, the screw mechanism V-3and the gear transmission mechanism V-4, and is located in the right front lower part of the electronic nose instrument. Main constructional units of the large-volume headspace vapor generation device VI include the thermal insulation layer VI-1, the resistance heating wire VI-2, the heat conduction sleeve VI-3, the temperature sensor VI-4, the tested sample VI-5, the 250 ml glass sample bottle VI-6, the silicone rubber sealing sheet VI-7and the cup cover VI-8. One electronic nose instrument is equipped with 4-6 large-volume headspace vapor generation devices VI. The role of the large-volume headspace vapor generation device VI is to make 10 ml-30 ml tested sample within the 250 ml glass sample bottle VI-6at the constant temperature of 40-80±0.1° C. for about 30 min in a certain test site and generate 220 ml-240 ml headspace vapor. The role of the automatic lifter V is to make the headspace vapor generation device VI up 20 mm within 3 s, in order the side-hole sampling needle III-10fixed under the inlet port of the annular working chamber I-2penetrate through the silicone rubber sealing sheet VI-7on 250 ml glass sample bottle VI-6and thus contact with the headspace vapor in the glass sample bottle VI-6.

FIG.3is the schematic diagram of working principle of an electronic nose instrument, i.e., the schematic diagram of the rough recovery state of the gas sensor array and the separation state of the capillary gas chromatographic column.FIG.4is the schematic diagram of the gas sensor array module I and the capillary gas chromatographic column module II, which may be easily replaced as needed. At this moment, under the action of the automatic lifter V, the large-volume headspace vapor generation device VI descends 20 mm to the original position along with the support disc V-1and then is taken away by an operator, and the preparation is made for replacing a new headspace vapor generation device and detecting a new sample.

FIG.5gives the detailed structure of the automatic lifter V. The ratio of gear tooth numbers in the gear transmission mechanism V-4is 17:73, and the gear module is 1 mm. The step motor V-2drives the screw of the screw mechanism V-3to ascend through the gear transmission mechanism V-4, so that the large-volume headspace vapor generation device VI placed on the support disc V-1ascends.

FIG.6is the schematic diagram of the mutual positional relationship and the detailed structure of the large-volume headspace vapor generation device VI. When testing, the operator takes 10-30 ml liquid or solid tested sample VI-5to place in the 250 ml glass sample bottle VI-6, covers the bottle mouth with the silicone rubber seal sheet VI-7, and tightens the cup cover VI-8. Under the heating action of the resistance heating wire VI-2which is controlled by the computer control and data analysis module IV, the tested sample VI-5is kept at the constant temperature of 40-80±0.1° C. about 30 min to ensure the consistency of multiple tests.

FIG.7are the schematic diagrams of changes about the gas sampling time lengths, the flow rates and the responses of a specified gas sensor given by the gas sensor array module I and the capillary gas chromatographic column module II in the electronic nose instrument in the gas sampling period T=480 s. The gas sampling period may be adjusted in the range of T=5 min and T=10 min.FIG.7only uses the default gas sampling period T=480 s as an example. The adjustable time length is mainly the flushing stage of the ambient air or the rough recovery stage of the gas sensor array module I, and the separation stage of the capillary gas chromatographic column module II. For the gas sensor array module I and the capillary gas chromatographic column module II, the information selection and analysis are performed simultaneously in the last lOs stage of the gas sampling period T.

FIG.7(a)shows the change of cyclical gas sampling cases for the capillary chromatographic column module II, which includes such 3 stage: (i) the tested gas sampling stage, (ii) the tested gas separation stage, and (iii) the chromatographic column discharging stage. The tested gas sampling stage (i) is at a beginning stage of the gas sampling period with a sampling duration of 0.5 s˜1.0 s, and is by default. The range of the sampling flow rates is 1.5 ml/min˜15 ml/min, 6 ml/min by default.

Referring toFIG.7, and in combination withFIG.2, Table 2 shows the operation parameters and the on-off states of the related electromagnetic valves of the capillary gas chromatographic column module II in the gas sampling period T=480 s. In the tested gas sampling stage (i), the two-position three-port electromagnetic valve III-6is located at “1”, the third two-position two-port electromagnetic valve III-8is on, and the second two-position two-port electromagnetic valve III-5and the fourth two-position two-port electromagnetic valve III-9are off, and the on-off status of the first two-position two-port electromagnetic valve III-4is irrelevant to at this stage. Under the suction action of the second micro vacuum pump III-7, the headspace vapor of the tested sample VI-5flows through, at a flow rate of 6 ml/min, the third two-position two-port electromagnetic valve III-8, the two-position three-port electromagnetic valve III-6and the fourth throttle valve III-18in order, and then mixes with the carrier gas H2at the inlet port II-8, flows into the capillary gas chromatographic column II-1accordingly for 1.0 s. If the sampling flow rate is 6 ml/min and the duration is 1 s, then the accumulated sampling volume for a tested odor is 0.1 ml, which meets the requirement of the optimal sampling volume of the capillary gas chromatographic column. In the tested gas separation stage (ii) and the chromatographic column discharging stage (iii), since the two-position three-port electromagnetic valve III-6is located at “2”, and whether the other two-position two-port electromagnetic valves are on or off is not critical. During this period, under the pushing action of the carrier gas H2, the tested odor is separated in the capillary gas chromatographic column II-1.

Referring toFIG.6and in combination withFIG.1andFIG.3, Table 3 shows the operating parameters and the on-off status of the related electromagnetic valve for the gas sensor array module I in the gas sampling period T.

Several main working states of the gas sensor array module I are described below in details by taking the gas sampling period T=480 s as an example.

TABLE 2Operation parameters and on-off status of the related electromagnetic valves for the capillary gaschromatographic column module II in the gas sampling period T = 300 s-600 s (480 s by default)2-position2-position2-position2-position2-positionInitialFlow3-port2-port2-port2-port2-portDurationtime-rateGasvalvevalvevalvevalvevalveStageDescription(s)point (s)(ml/min)typeIII-6III-8III-4III-5III-9(i)Gas sampling0.5-1.501.5~15Tested odor“1”OnIrrelevantOffOff(ii)Chromatographic289-589130~50Tested odor +“2”IrrelevantIrrelevantIrrelevantIrrelevantseparationH2(iii)Chromatographic10290-59030~50H2“2”IrrelevantIrrelevantIrrelevantIrrelevantcolumndischarging

TABLE 3Operation parameters and on-off status of the electromagnetic valves for the gas sensorarray module I in the gas sampling period T = 300 s-600 s (480 s by default)2-position2-position2-position2-position2-positionFlow2-port2-port2-port2-port2-portDurationInitialrateGasvalvevalvevalvevalvevalveStageDescription(s)moment (s)(ml/min)typeIII-5III-4III-6III-8III-9(i)Headspace6011,000Tested odorOnOffIrrelevantOffOffsampling(ii)Transition4611,000Purified airOnOffIrrelevantOnOff(iii)Rough recovery175-475656,500Purified airOnOnIrrelevantIrrelevantOff(iv)Clean air40255-5551,000Clean airOffIrrelevantIrrelevantIrrelevantOncalibration(v)Balance5295-5950—OffIrrelevantIrrelevantOffOff

In the headspace sampling stage (i) for the tested odor, namely, the [1 s, 61 s] time stage with a duration of 60 s in the gas sampling period T, the second two-position two-port electromagnetic valve III-5is on, the first two-position two-port electromagnetic valve III-4, the third two-position two-port electromagnetic valve III-8and fourth two-position two-port electromagnetic valve III-9are all off, and the on-off status of the two-position three-port electromagnetic valve III-6has not effect. Under the suction action of the first micro vacuum pump III-1, headspace vapor of the tested sample flows through, at a flow rate of 1,000 ml/min, the side-hole sampling needle III-10, the gas sensor array I-1inside the annular working chamber I-2, the second two-position two-port electromagnetic valve III-5, the first throttle valve III-3and the first flowmeter III-2in order, and finally is discharged to outdoor for 60 s. During this stage, the gas sensor array I-1generates a sensitive response to the tested odor.

In the rough recovery stage of the gas sensor array, namely, the clean ambient air flushing stage (iii), and the second two-position two-port electromagnetic valve III-5and the first two-position two-port electromagnetic valve III-4are on, the fourth two-position two-port electromagnetic valve III-9is off, and the on-off status of the third two-position two-port electromagnetic valve III-8and the two-position three-port electromagnetic valve III-6has not effect at this stage. The ambient air flows through, at a flow rate of 6,500 ml/min, the side-hole sampling needle III-10, the gas sensor array I-1inside the annular working chamber I-2, the second two-position two-port electromagnetic valve III-5, the first two-position two-port electromagnetic valve III-4and the first flowmeter III-2in order, and finally is discharged to outdoor for 370 s. During this stage, the residual odor molecules on an inner walls of the relevant gas pipelines are washed away, the accumulated heat by the gas sensor array is taken away, and the gas sensor array I-1is roughly recovered to the reference state under the action of the ambient air.

In the accurate dry air calibration stage (iv), namely the time stage of from 435thsec to the 475thsec of the gas sampling period T, the fourth two-position two-port electromagnetic valve III-9is on and the second two-position two-port electromagnetic valve III-5is off, and the on-off status of the other electromagnetic valves is irrelevant. The dry air in the dry air bottle VII-2flows through, at the flow rate of 1,000 ml/min, the first pressure reducing valve III-11, the first purifier III-12, the second throttle valve III-13, the fourth two-position two-port electromagnetic valve III-9, the gas sensor array I-1and the side-hole sampling needle III-10inside the annular working chamber I-2in order, and finally is discharged to outdoor for 40 s. During this stage, the gas sensor array I-1is accurately recovered to the reference state under the role of the dry air.

According toFIGS.7(a) and7(d), in the last 10 s stage of the gas sampling period T, the gas sensor array module I and the capillary gas chromatographic column module II enter the information selection and analysis operation region simultaneously for 10 s.

FIG.8is the schematic diagram of information selection of the semi-separated chromatogram in the gas sampling period T=480 s. In the information selection and analysis region of 10 s in the gas sampling period T, the computer control and data analysis module IV sequentially selects 21 feature variables: 10 pairs of {peak height hgcj, retention time point tgcj} (j=1, 2, . . . , 10) and one under-curve area Agcfrom the semi-separated chromatogram with the appointed 460 s time length, which are the basic sensitive information of the capillary chromatographic column module II to the tested odor and are recorded as xgc={(hgc1, hgc2, . . . , hgc10); (tgc1, tgc2, . . . , tgc10); Agc}.

FIG.9is the schematic diagram of feature selection of two semi-separated chromatograms in the gas sampling period T=480 s. The semi-separated chromatogram inFIG.9(a)has only 8 chromatographic peaks, or only 8 peaks hgci(i=1, 2, . . . , 8) and the corresponding 8 retention time values tgci(i=1, 2, . . . , 8) and plus the under-curve area Agcare obtained from the semi-separated chromatogram. Our practice is to fill ‘0’s elements for the insufficient chromatographic peaks and the corresponding retention time values. Through doing so, the final chromatographic sensitive information is xgc={(hgc1, hgc2, . . . , hgc8, 0, 0); (tgc1, tgc2, . . . , tgc8, 0, 0); Agc} according toFIG.9(a). The semi-separated chromatogram inFIG.9(b)has more than 10 chromatographic peaks, and thus the top 10 maximum chromatographic peaks are selected from them.

FIG.10is the schematic diagram of multi-feature selection of response curves of gas sensors in the gas sampling period T=480 s. Three illustrations inFIG.10respectively show the response curves of 3 gas sensors, TGS822, TGS826 and TGS832, for a petroleum wax sample, a 2,000 ppm ethylene gas and a 5,000 ppm ethanol vapor. The steady-state maximum voltage response values inFIGS.10(b) and10(c)are equal, or vb=vc. According to the conventional feature selection method of the single steady-state maximum value from a single voltage response curve, the electronic nose instrument cannot distinguish the 2,000 ppm ethylene gas and the 5,000 ppm ethanol vapor at that time. After careful observation, it is found thatFIG.10(b)andFIG.10(c)show such a case, called ‘Case 1’: although the voltage response steady-state maximum response values in the two diagrams are equal, the corresponding peak time values and the under-curve area are not equal. Similarly, Case 2 shows that the corresponding peak time values are equal to one another, but their peak values and the under-curve areas are not equal. Case 3 shows that the under-curve areas are equal to one another, but their peak values and the corresponding peak time values are not equal.

TABLE 4Comparison of the main operation parameters between the gas sensor array module I and the capillarygas chromatographic column module II (taking the gas sampling period T = 8 min as an example)InformationHeadspaceStartingFlowChamberselection andMeaning ofModuledurationtime-pointrateSamplingFueltemperatureanalysis timeinformationsizeModule name(s)(s)(ml/min)mannerCarriergas(° C.)length (s)components(mm)capillary gas0.5-1.501.5-15AutomaticH2H2200-250470-48010 peak heights,300 ×chromatographic10 retention time-points,300 ×columnone under-curve area120Gas sensor array30~6011,000AutomaticNoneNone55470-48016 peak voltages,300 ×16 peak time-points,300 ×16 under-curve areas100

According toFIG.10, the present disclosure proposes the following viewpoint: three pieces of information, i.e., a steady-state maximum voltage response vgsi, a corresponding peak time value tgsifrom the starting moment of the headspace sampling, and an area Agsiunder the curve in the 60 s headspace sampling time stage, are selected simultaneously from the response curve of the gas sensor i. If the gas sensor array is composed of 16 sensitive elements, then in the lOs information selection and analysis region of the gas sampling period T, the computer control and data analysis module IV sequentially selects 3*16=48 feature values from 16 response curves as the basic sensitive information of the gas sensor array module I to the tested odor, which is recorded as xgs={(vgs1, vgs2, . . . , vgs16); (tgs1, tgs2, . . . , tgs16); (Agc1, Agc2, . . . , Agc16)}.

In the 10 s information selection and analysis region of the gas sampling period T, the computer control and data analysis module IV fuses the sensitive information of the gas sensor array module I and the capillary chromatographic column module II in different time stages to the tested odor, and then performs the normalization pretreatment to obtain a sensitive information vector of the electronic nose instrument to the tested sample, i.e., x=xgs+xgc={(vgs1, vgs2, . . . , vgs16); (tgs1, tgs2, . . . , tgs16); (Agc1, Agc2, . . . , Agc16); (hgc1, hgc2, . . . , hgc10); (tgc1, tgc2, . . . , tgc10); Agc}∈R69. The sensitive vector x∈R69is the basis of online identification of types and quantitative prediction of main components by the electronic nose instrument for foods, condiments, fragrances and flavors, and petroleum waxes.

Table 4 shows the comparison of the main operation parameters between the gas sensor array module I and the capillary gas chromatographic column module II by taking the gas sampling period T=8 min as an example. In comparison with the 60 s sampling duration and the 1,000 ml/min flow rate of the former, the corresponding terms of the latter are only 1 s and 6 ml/min. According to the above data, the gas sampling volume of the gas sensor array module I is 1,000 ml, but that of the capillary gas chromatographic column module II is only 0.1 ml, or the difference between the two is 10,000 times.

In the present disclosure, the semi-separated chromatogram is regarded as a part of the sensitive information or pattern of the electronic nose instrument, and thus the big odor data is established by combining with the sensitive information of the gas sensor array. Furthermore, the recognition, qualitative analysis and main component quantitative prediction of an undermined odor are realized by means of the artificial intelligence or machine learning method.FIG.11is the schematic diagram of offline learning and online decision-making process of the modular cascade machine learning model adopted in the present disclosure.

In the offline learning stage of the modular cascade machine learning model, the primary task is to establish the big odor data, including the online sensitive data of the gas sensor array module I and the capillary gas chromatographic column module II for a large number of foods, condiments, fragrances and flavors, and petroleum waxes, the offline measuring data of the conventional instruments such as gas chromatography/mass spectrometry; the label data and the sensory evaluation data for the known types and constituents of odors.

Next, the sensitive data of both the gas sensor array and the capillary gas chromatographic column are fused, including the normalization and dimensionality reduction preprocessing. In order to reduce the analysis difficulty of the big odor data, the present disclosure employs the “divide and conquer” strategy, (i), a complex multi-type recognition problem is decomposed into multiple simpler two-odor recognition problems, that is, one n-class problem is decomposed into n(n−1)/2 binary-class problems {Xj, Xk} and then solved by n(n−1)/2 single-output machine learning models {ωjk}n, where j, k=1, 2 . . . , n and j≠k, one by one; and (ii) a complex multi-component estimation problem is decomposed into multiple simpler single-component quantitative prediction problems, one by one, that is, a q-curve/q-surface fitting problem is decomposed into q curve/surface fitting problems, and q single-output machine learning models are used for solving them, one by one.

The n(n−1)/2 single-output machine learning models ωjk(j, k=1, 2, . . . , n and j≠k) in the first level and the q single-output machine learning models in the second level form the modular cascade machine learning model. Among them, each single-output machine learning model both in the first level and in the second level may be one single-output single-hidden-layer neural network, one decision tree, one support vector machine, etc. Here, the present disclosure employs single-output single-hidden-layer neural networks. The offline learning algorithm of the modular cascade machine learning model is mainly the error back-propagation algorithm, which mainly learns the labeled data and the data with the known constituents in the big odor data.

In the decision-making stage, the n(n−1)/2 single-output machine learning models in the first level form n vote recognition groups {Ωj}n, j=1, 2, . . . , n. A single-output machine learning model takes and only takes part in two vote recognition groups. For example, the single-output single-hidden-layer neural network ωjkvotes not only in the vote recognition group Ωjbut also in the group Ωk. The undetermined pattern x belongs to the class represented by the vote recognition group with the most votes, i.e., the winning vote recognition group. Then, the quantitative prediction group corresponding to the winning vote recognition group in the second level predicts multiple quantitative indicator values of the tested odor x, i.e., the overall intensity, the quality grade and the concentrations of multiple main components.