TECHNICAL FIELD

The present invention belongs to the field of pesticides detection, relates to a spectrogram automatic comparison and identification system and method for pesticides and chemical pollutants, and particularly to an intelligent mass spectrogram comparison and identification system and method for pesticides and chemical pollutants based on cloud platform.

BACKGROUND ART

The pesticide residue detection technique is an import research content related to food safety. Scientists from all around the world have dedicated to the research of pesticide residue detection technology in food for a long time. Earlier pesticide residue detection is based on gas chromatography (GC), and the number of pesticides was relatively small, usually several or more than a dozen. With the application of gas chromatography-mass spectrometry (GC-MS), dozens of pesticides could be detected. With the application of gas chromatography-tandem mass spectrometry (GC-MS/MS), the detection technique for pesticide residue in food reaches a higher level, and about 200 pesticides could be detected. Meanwhile, liquid chromatography-tandem mass spectrometry (LC-MS/MS) technique has been wildly used due to its advantage in detection of highly polar and thermally instable pesticides over GC-MS and GC-MS/MS. Researchers generally applies both techniques in pesticide residue detection at the same time because they are complementary. Since 2001, mass spectrometry detection techniques related to GC and LC have become the leading technique in pesticide multi-residues detection.

According to report, there are more than 1,000 pesticides commonly used in the world, and the number is still increasing. Faced with so many pesticides with different properties, and various complex sample matrices, the application of low-resolution mass spectrometry for the routine detection of target compounds could not meet the actual needs. The application of high-resolution mass spectrometry could solve the problems encountered in low-resolution mass spectrometry, and the representatives thereof are time-of-flight mass spectrometry (TOF) and orbit ion trap mass spectrometry (Orbitrap). The high-resolution mass spectrometry applied in the present invention includes liquid chromatography-quadrupole-time of flight mass spectrometry (LC-Q-TOFMS), gas chromatography-quadrupole-time of flight mass spectrometry (GC-Q-TOFMS), linear ion trap-electric field cyclotron resonance orbit trap combined mass spectrometry (LC-LTQ-Orbitrap), liquid chromatography-quadrupole-electrostatic field orbit trap mass spectrometry (LC-Q-Orbitrap-MS) and gas chromatography-quadrupole-electrostatic field orbit trap mass spectrometry (GC-Q-Orbitrap-MS), the greatest advantage in pesticide multi-residues detection is to provide enough sensitivity under full scan mode and to collect as much compound information as possible. At the same time, the compounds can be further confirmed.

There are two problems need to be solved for the application of the above mass spectrometry techniques. First, the mass spectrometry information of the reference standard is required during the establishment of the method; second, the confirmation of the detection result requires comparison with the standard mass spectrum, which is especially important for high-resolution mass spectrometry. In the actual work, there are two ways to obtain the standard mass spectrum, either to use the standard to collect by oneself, or to use commercial mass spectrums provided by instrument company, however, both require large amount of manpower, material resources and financial resources, resulting in big limitations. This is also one of the problems that trouble the researchers.

CONTENT OF INVENTION

To solve the above problems, the present invention applies mainstream mass spectrometers (liquid chromatography-tandem mass spectrometry (LC-MS/MS), gas chromatography-tandem mass spectrometry (GC-MS/MS), liquid chromatography-quadrupole-time of flight mass spectrometry (LC-Q-TOFMS), gas chromatography-quadrupole-time of flight mass spectrometry (GC-Q-TOFMS), linear ion trap-electric field cyclotron resonance orbit trap combined mass spectrometry (LTQ-Orbitrap-MS) liquid chromatography-quadrupole-electrostatic field orbit trap mass spectrometry (LC-Q-Orbitrap-MS) and gas chromatography-quadrupole-electrostatic field orbit trap mass spectrometry (GC-Q-Orbitrap-MS)) to create an electronic ID card for each pesticide in the database. Mass spectrum information is acquired by image processing technique, the detected mass spectrum is classified and modeled by applying deep convolutional neural network, and the image model system is arranged in the background cloud server end, the users can login in the system, upload spectrums of detected pesticide residues on the browser end, and use the intelligent comparison system and method to know what pesticide has been detected according to detection data.

The present invention provides a cloud-platform based spectrum comparison and identification system and method for pesticides and chemical pollutants; can achieve accurate and rapid comparison and identification of the pesticides and the chemical pollutants. The system includes a cloud server platform end and a user platform end;

wherein, the cloud server platform end includes:

a spectrum acquisition unit, which is used to acquire mass spectrum;

a spectrum parameter acquisition unit, which is used to acquire the experiment environment, experiment condition, and experiment parameter data corresponding to the mass spectrum;

a spectrum device acquisition unit, which is used to acquire information of the spectrum detection device corresponding to the mass spectrum;

a spectrum pretreatment unit, which is used to longitudinally splice and pretreat the acquired mass spectrum and extract the spectrum features;

a spectrum classification model unit, which is used to acquire the change value of fitting angle at the pixel point where the highest peak inside the mass spectrum is located and construct mass spectrum classification model.

a pesticide species classification model unit, which is used to train the extracted spectrum features, spectrum detection device information and experimental parameter data by neural network model and to obtain the classification model which can identify the species and/or names of pesticides and chemical pollutants;

the user platform end includes:

a spectrum data uploading unit, which is used to upload the mass spectrum, spectrum description data and experiment parameter data to the system for detection;

a spectrum pretreatment unit, which is used to longitudinally splice and pretreat the mass spectrum to be detected and extract the mass spectrum features;

a spectrum species identification unit, which is used to classify the mass spectrum according to the change value of fitting angle at the pixel point where the highest peak inside the mass spectrum is located;

a spectrum identification unit, which is used to input the extracted spectrum features, spectrum description data and experiment parameter data to the pesticide species classification model, to identify the species and/or names of the corresponding pesticides and chemical pollutants,

Preferably,

the neural network model is a layer-by-layer refinement convolutional neural network model, the design or usage method thereof is: each pretreated spectrum is inputted to the layer-by-layer refinement convolutional neural network model, to train the spectrum classification model. After pretreatment, the size of the mass spectrum inputted to the layer-by-layer refinement convolutional neural network model for training is 1×1×1626×1626, the meaning of each parameter is: one sample is selected at a time in training set to update the weight, the number of channel for input of image (binary image) is 1, the inputted image size (height×width) is 1626×1626.

The first convolutional layer Conv1 uses the convolution kernel with the size of 11×11×1, which represents that after each convolution operation, the convolution kernel moves 4 pixels. The edge complement pixel p is 0, representing that the image edge is not filled. After Conv1 layer operation, the feature image is outputted, which reflects information such as the spectrum edge contour. The Relu activation function is used to map the convoluted result and control the data range. Next, the local response normalization layer LRN1 normalizes the feature data outputted from the convolutional layer Conv1, and creates a competitive mechanism for the activity of the local neurons, such that the values with larger response become relatively larger and other neurons with smaller feedback is suppressed, so as to enhance model generalization ability. After the calculation of this layer, the size of the feature image remains unchanged. Next, pooling layer Pool1 uses the kernel with the size of 3×3×64 to maximally pool the feature image outputted by the LRN1 layer and reduces calculation and parameter number by sampling.

Convolutional layers Conv2-Conv5 respectively perform corresponding convolution operation for the feature image outputted from the previous layer, the convolutional kernel size is reduced layer by layer, respectively 9×9×64, 7×7×128, 5×5×256, 3×3×512, wherein 64, 128, 256 and 512 respectively correspond to the number of convolution kernels used by the convolutional layer. The more the convolutional kernel used, the higher the obtained feature dimension. After the layer-by-layer convolution operation, the lower-layer features are abstracted into higher dimensional and more refined convolution activation features. The step size and the edge complement pixel size in each convolutional layer are shown inFIG. 3. The local response normalization layer LRN2 normalizes the feature data outputted from the convolutional layer Conv2. The pooling layers Pool2-Pool5 respectively use the kernel with the size of 3×3×128, 3×3×256, 3×3×512 and 3×3×512 to maximally pool the feature image outputted by the previous layer.

The fully connected layer Fc6 connects the local features outputted by the Conv5, three fully connected layers, Fc6-Fc8, filter the features which perform well in the classification task by learning all the weights during the training process, and send the features into the Softmax-loss layers. The Dropout layers, Dop6 and Drop7, are used in the calculation results of Fc6 and Fc7 respectively, and randomly disable partial nodes of the hidden layer to speed up the training speed and prevent overfitting. The Softmax-loss layer is like a classifier, and calculates the value of loss function. In the training process, the stochastic gradient descent algorithm is used to update the weight and the initial learning rate is set as 0.0001. By minimizing the loss function, the classification effect is gradually improved, and a layer-by-layer refinement convolutional neural network classification model having better classification effect is obtained.

Preferably,

the spectrum includes the mass spectrum and/or chromatographs.

Preferably,

the spectrums include one or more of the followings: liquid chromatography-tandem mass spectrum, gas chromatography-tandem mass spectrum, liquid chromatography-quadrupole-time of flight mass spectrum, gas chromatography-quadrupole-time of flight mass spectrum, linear ion trap-electric field cyclotron resonance orbit trap combined mass spectrum, liquid chromatography-quadrupole-electrostatic field orbit trap mass spectrum and gas chromatography-quadrupole-electrostatic field orbit trap mass spectrum.

Preferably,

the mass spectrum classification model unit classifies, according to the change value of angle at the pixel point where the highest peak inside the mass spectrum is located: the change value of fitting angle of the ion chromatogram in liquid chromatography-tandem mass spectrum is in the range of x11-x12, and the change value of fitting angle of ion mass spectrum under 4 collision energies is in the range of x13-x14; the change value of fitting angle of the ion chromatogram in liquid chromatography-quadrupole-time of flight mass spectrometry is in the range of x21-x22, and the value of fitting angle of ion mass spectrum under 4 collision energies is x23; the change value of fitting angle of the ion chromatogram in linear ion trap-electric field cyclotron resonance orbit trap combined mass spectrum, is in the range of x31-x32, the value of fitting angle of full scan mass spectrum under ionization mode is x33; the change value of fitting angle of the primary mass spectrum in gas chromatography-tandem mass spectrum is x41, the value of fitting angle of ion mass spectrum under 4 collision energies is x43; the change value of fitting angle of the ion chromatogram in liquid chromatography-quadrupole-electrostatic field orbit trap mass spectrometry is x51, the value of fitting angle of fragment ion mass spectrum is x53; the value of fitting angle of the mass spectrum in gas chromatography-quadrupole-time of flight mass spectrum is x61; the change value of fitting angle of the total ion chromatogram in gas chromatography-quadrupole-electrostatic field orbit trap mass spectrometry is in the range of x71-x72, the value of fitting angle of full scan mass spectrum under ionization mode is x73. Wherein value range of x11-x73is 0°-40°.

Preferably,

the mass spectrum classification model unit converts the grayscale image of mass spectrum into binary image and assigns the image values to a two-dimensional matrix; according to the matrix value, the position of the pixel point (the row and column of matrix) where the highest peak of the image (the highest peak of the spectrum) is located is determined. With this point as the center, traversal is performed to the lower-left and lower-right area to obtain the row and column of a matrix with the corresponding matrix value of 1, and the image angle of the highest peak after fitting is recorded and stored.

Preferably,

the change value of angle at the pixel point, where the highest peak inside the mass spectrum is located, is calculated according to the gradient vector. Around a straight line or a curve, the gradient vector is perpendicular to the straight line or the curve, the angle could be calculated by the orientation change of gradient vector. The gradient vector at a point on the curve is the vertical line of the curve segment passing through the point. A short line segment near the point replaces the curve segment, and the vertical line of the line segment is calculated as the gradient vector. The line segment near the point is determined by the neighborhood chain length, and for different chain length, the calculated gradient vector is slightly different. The orientation of the gradient vector is its angle size.

Preferably,

Pn={p1, . . . , pn} is the ordered points set on a curve or a straight line. Ln={l1, . . . , ln} is a short line segment near the ordered points on a curve or a straight line, li(i=1, . . . , n) represents the line segment with point pias the center and having a neighborhood chain length of m (i.e., connecting points pi−mand pi+m). In this system, the value of m can be the value between 1 and 5. Sn={s1, . . . , sn} represents the set of slopes of the vertical line of line segment li. An={a1, . . . , an} represents the set of angle of the vertical line of linear point pi, aishould be in the range of [0, 360°].

the slope of the line segment linear the point pi(xi,yi) (connecting the point pi−m(xi−m, yi−m) and the point pi+m(xi+m, yi+m)) is:
gi=(yi+m−yi−m)/(xi+m−xi−m)

the slope of vertical line of line segment liis (−1/gi), i.e.:
si=(xi+m−xi−m)/(yi+m−yi−m)

the calculation method of aiis shown in table 2.

TABLE 2No SlopeSlope = 0Slope > 0Slope < 0aiai= π/2ai= πai= arctankiai= π + arctanki

Preferably,

the spectrum identification unit screens the mass spectrum data which may be similar to the species of mass spectrum to be detected from the existing mass spectrum database, according to the mass spectrum description data, experiment parameters and number of mass spectrums before inputting the mass spectrum to be detected into the classification model. The Fc7 layer features are extracted from the mass spectrum to be detected, and the cosine similarity between this Fc7 layer feature and the Fc7 layer features of all pretreated mass spectrum selected from the database to find the spectrum with the highest degree of similarity to the current mass spectrum to be detected and determine whether the similarity is higher than 50%. If the similarity is higher than 50%, the mass spectrum inputted by the user is identified successfully.

Preferably,

the cosine similarity is calculated as following:

cos⁢⁢θ=∑1dn⁢(Ai×Bi)∑1dn⁢Ai2×∑1dn⁢Bi2

wherein, Airepresents the ith feature value of spectrum A; Birepresents the ith feature value of spectrum B; dnrepresents the total dimension number of the features;

Correspondingly, the present invention also provides a cloud-platform based identification method of seven types of mass spectrum for pesticides and chemical pollutants, including:

to acquire mass spectrum from the cloud server platform end and to acquire the experiment environment, experiment condition and experiment parameter data corresponding to the mass spectrum;

to acquire the detection device information corresponding to the mass spectrum;

to longitudinally splice and pretreat the acquired mass spectrum and to extract the features thereof;

to acquire a change value of fitting angle at a pixel point where the highest peak inside the mass spectrum is located, and to construct a mass spectrum classification model;

to use the neural network model to train the extracted mass spectrum feature, spectrum detection device information and experiment parameter data, and to obtain a pesticide species classification model which can identify the species and/or name of pesticides and chemical pollutants.

to upload the mass spectrum to be detected, mass spectrum description data and experimental parameter data to the system at the user platform end.

to longitudinally splice and pretreat the mass spectrum to be detected, and to extract the features of the mass spectrum;

to classify the mass spectrum according to the change value of fitting angle at the pixel point where the highest peak inside the mass spectrum is located;

to input the extracted spectrum features, mass spectrum description data and experiment parameter data into the pesticide species classification model to identify the species and/or name of corresponding pesticides and chemical pollutants.

The cloud-platform based spectrum comparison and identification method for the pesticides and the chemical pollutants provided in the present invention constructs the spectrum classification model on the cloud server platform end, extracts the spectrum data features and constructs the training model of the convolutional neural network. The user platform end is used for the user to upload the mass spectrum, experiment condition and device data. Based on the mass spectrum classification model of the cloud server platform end, the mass spectrum species are identified. Based on the neural network model obtained by training in the cloud server platform, end, the species and name of pesticides are automatically compared and identified, and the comparison result is fed back to the user. This system solves the restriction on the purchase of standard material for the user, the use of the system is not limited by location, and it can detect the pesticides and the chemical pollutants rapidly and accurately.

The beneficial effects of the present invention:

1. The present invention covers seven types of mainstream chromatography-mass spectrometry techniques, i.e. liquid chromatography-tandem mass spectrometry LC-MS/MS (605 species), gas chromatography-tandem mass spectrometry GC-MS/MS (619 species), liquid chromatography-quadrupole-time of flight mass spectrometry LC-Q-TOFMS (510 species), gas chromatopaphy-quadrupole-time of flight mass spectrometry GC-Q-TOFMS (753 species), linear ion trap-electric field cyclotron resonance orbit trap combined mass spectrometry LC-LTQ-Orbitrap-MS (378 species), liquid chromatography-quadrupole-electrostatic field orbit trap mass spectrometry LC-Q-Orbitrap-MS (570 species) and gas chromatography-quadrupole-electrostatic field orbit trap mass spectrometry OC-Q-Orbitrap-MS (664 species). The unique electronic identity card information of over 1,200 pesticides and chemical pollutants has been established; necessary parameters for chromatography-mass spectrometry analysis and identification, such as the mass spectrum information database (exact mass number, isotope distribution, isotope abundance) and feature spectrum database of mass spectrum (total ion chromatogram and fragment ion mass spectrum under different collision energies). It establishes theoretical and methodological basis for research and development of high-throughput pesticide multi-residues detection techniques. It has technique innovation, and is nowadays the most accurate, sensitive and reliable detection technique. It is the only accurate detection technique which can achieve the largest single-pass pesticide cluster detection.

2. The present invention can realize intelligent matching, comparison and identification, and qualitative identification for mass spectrum of over 1,200 pesticides and chemical pollutants commonly used in the world. Classification search can be performed according to the compound composition, including organohalogen pesticides, organophosphorus pesticides, pyrethroid pesticides, carbamate pesticides, organic nitrogen pesticides, organic sulfur pesticides etc.; according to pesticide function, including insecticides, fungicides, herbicides, acaricides, nematicides, insect growth regulators, plant growth regulators, and persistent environmental pollutants such as polychlorinated biphenyls and polycyclic aromatic hydrocarbons; according to pesticide toxicity, including slight toxic, low toxic, medium toxicity, high toxicity, extreme toxicity, and prohibited pesticides. For the identification of known compounds, comprehensive chromatography-mass spectrum information such as the molecular structure of the compound and fragment ions under different conditions can be quickly obtained by chromatography-mass spectrum atlas. The detection and identification method can be established scientifically, reasonably and quickly, to ensure the accuracy and reliability of the detection and identification results for targets.

3. The present invention can realize the identification of the unknown compounds. The unknown compounds are measured under the assigned chromatography-mass spectrometry condition, to acquire the chromatography-mass spectrum information, such as the exact mass number, total ion chromatogram and secondary fragment ion mass spectrum; through the comparison with the system information, the nature of unknown compound can be rapidly and accurately determined.

4. The present invention can confirm the same compound on different devices, which improves the identification and confirmation ability. The detection of residues of pesticide and chemical pollutant in complex matrices is often interfered by the co-extracted matrix, and false positive result easily occur, and sometimes different types of instruments are needed for confirmation. The present invention comprises chromatographs-mass spectrums of 7 different chromatography-mass spectrometry instruments under different condition, which are complementary to each other, expand the application field, is in line with actual work, and has strong reference.

5. The standard high resolution mass spectrum in the present invention provides basis for confirmation of pesticide multi-residues detection result, there is no need to purchase a large amount of real reference standards for collecting mass spectrums by oneself. Then intelligent and automatic spectrum retrieval and comparison is achieved, the cost of pesticide residues detection is saved, and the ability of market-oriented rapid detection is improved. Meanwhile, it greatly facilitates the detection of the pesticides and chemical pollutants, so that the analysts have a reference basis when establishing methods, and have a query tool when confirming the result. It has important application value and high economic benefit.

6. The present invention realizes the electronization of spectrum data and automation of data retrieval, and develops a relatively complete and globally advanced detection database of pesticide information and pesticide residues with completely independent intellectual property rights in China. It is not only a major contribution to the chromatography-mass spectrometry in the world, but also has great scientific and social significance to the pesticide residue analysis, food safety and environment safety detection, and import-export inspection and quarantine in China.

7. Through the integration, development and utilization of the chromatography-mass spectrum information bases in the present invention, the construction of pesticide residues detection laboratories in China will be rapidly improved, and the overall level and detection efficiency of pesticide identification and pesticide residue detection will be improved, which has high social significance. The construction of retrieval system will greatly improve the data analysis ability of samples and identification ability of pesticides and the screening detection ability of the target pesticides, and has a good application prospect and economic value.

8. The present invention has four major functions: a guidebook for the development of new technique of pesticide residues detection, a reference book for the identification of unknown compound, a textbook for technical training, and a handbook for daily work. These four major functions will play a greater role when the automatic identification system of seven types of chromatography-mass spectrums for the pesticides and chemical pollutants commonly used in the world is established.

