Research Progress of Terahertz Spectroscopy in the Field of Pesticide Detection

Laser & Optoelectronics Progress, Volume. 57, Issue 13, 130006(2020)

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Figures & Tables(4)

Fig. 1. Instrument light path schematic. (a) THz-TDS; (b) FTIR

System performance	Test system
System performance	THz-TDS	FTIR
Radiation source	High radiation source stability	Radiation source covers a wide frequency range and can detect weak signals
Working frequency/ THz	0.1-4	Switch the beam splitter,can detect 0.1-100
Data collection	Direct access to amplitude, phase, power spectrum	Must perform inverse Fourier transform on the interferogram and the information extraction is relatively complicated
Testing sample	Can extract multi-layer sample internal information	Unable to extract internal information for layered samples^[6]
Instrument resolution/ GHz	3.8/7.6	13.5

Researchdirection	Chemometric method
Researchdirection	Method	Introduction
Qualitativeresearch	PCA	Reduce dimensional optical parameters, simplify samples, and maximize sample characterization
	CA	Classification using the principle of similarity
	SVM	Establish an optimal classification hyperplane to maximize the distance between the samples on both sides and the plane
Quantitativeresearch	PLS	One of the most commonly used quantitative regression methods for situations where there is a correlation between variables
	OLS	Find the best matching function by summing the squared sum of the actual value and the minimum value of the fitted value
	ANN	It is extremely efficient and has a certain fault tolerance. It is a superior unsupervised learning method
	SVR	Find the optimal hyperplane to minimize the total deviation of all sample points from the hyperplane

Pesticide	Absorption peak /THz	Accuracy /%
Carbendazim	1.29、1.52^[19]	97.67
Imidacloprid	0.89、1.13^[19]	98.20
Chlorpyrifos	1.47、1.93、2.73^[28]
Carbofuran	2.72、3.06^[28]
Dimethoate	1.05、1.09、2.92^[28]
Methomyl	1.01、1.65、1.91、2.72、3.20^[28]
Thiabendron	0.99、1.57、2.17、2.66^[28]	94.41
2,4-dichlorophenoxyacetic acid	1.36、1.60、2.38^[30]
Indole acetic acid	2.5^[30]	97.60
Chlorpyrifos	1.77、2.44^[30]	97.60
Thiacloprid	0.65^[31]
Herbicidal ether	0.48、0.98、1.33^[31]
Nitroguanidine	1.08、1.48^[31]
Chlorothalonil	0.75、1.02、1.3、1.72^[32]
Epoxystrobin	1.49、1.93^[32]
Carbofuran	1.88^[32]
Thiophanate	1.28、1.65、2.23^[32]
Procymidone	0.75、1.7、2.23^[32]
Dicofol	0.35、0.65、0.96、1.30、1.57、1.84、2.18^[33]
Trichlorfon	1.18、1.56、2.05^[33]
Imine sulfur	0.90、1.23、1.68、1.84、1.98、2.11^[33]
Hexachlorobenzene	0.64、0.87、1.06、1.23、1.54、1.74、1.93^[33]
Deltamethrin	0.91、1.14、1.34、1.53、1.78、1.92^[34]	92.20
Lacy-cyhalothrin	0.55、1.11、1.59、1.72、1.85、1.97、2.15^[34]	97.27
Beta-cypermethrin	1.01、1.27、1.58、1.72、1.85、2.02、2.16^[34]	96.90
Diflubenzuron	0.65、1.55、1.81、1.98、2.12^[34]	95.23
6-benzylaminopurine	2.07、2.98^[35]	96.00
Sodium p-chlorophenoxyacetate	1.37、1.96、2.13^[35]	95.77
Sodium o-nitrophenolate	0.42、0.51、0.96、1.18^[35]	95.77
Methyl thiophanate	1.05、1.23、1.65^[36]
Benomyl	0.78、1.14、1.35、1.55^[36]
Maleic hydrazide	2.34^[37]	100