Determination of multiple pesticides in Eucommia ulmoides followed by gas chromatography mass spectrometry based on a solid-phase extraction method.

Eucommia ulmoides, a precious Chinese herbal medicine, lack of studies on the detection of its pesticide residues. A simple sample preparation based on the solid-phase extraction (SPE) procedure was established for the analysis of 16 kinds of pesticides in Eucommia ulmoides by gas chromatography mass spectrometry (GC-MS) with selective ion monitoring mode. Here, the type and volume of extraction solvent and eluent, the kinds of sorbents in SPE Cleanert column, were optimized. Under the optimal conditions, a good linear relationship was obtained in the range of 0.005 to 5.0 mg/L with correlation coefficient (r) higher than 0.9990, and the average recoveries (AR) of 16 pesticides ranged from 79.6 to 109.2% at the spiking levels of 0.01, 0.1, and 0.5 mg/kg. The relative standard deviations (RSD) were 0.78 to 9.56% (n = 6). The results show that the established method can not only fully meet the analytical requirements of various pesticides in Eucommia ulmoides, but also have the potential to be applied in the detection of pesticide residues in others Chinese herbal medicine.

A Novel High-Frequency Vibration Error Estimation and Compensation Algorithm for THz-SAR Imaging Based on Local FrFT.

Compared with microwave synthetic aperture radar (SAR), terahertz SAR (THz-SAR) is easier to achieve ultrahigh-resolution image due to its higher frequency and shorter wavelength. However, higher carrier frequency makes THz-SAR image quality very sensitive to high-frequency vibration error of motion platform. Therefore, this paper proposes a novel high-frequency vibration error estimation and compensation algorithm for THz-SAR imaging based on local fractional Fourier transform (LFrFT). Firstly, the high-frequency vibration error of the motion platform is modeled as a simple harmonic motion and THz-SAR echo signal received in each range pixel can be considered as a sinusoidal frequency modulation (SFM) signal. A novel algorithm for the parameter estimation of the SFM signal based on LFrFT is proposed. The instantaneous chirp rate of the SFM signal is estimated by determining the matched order of LFrFT in a sliding small-time window and the vibration acceleration is obtained. Hence, the vibration frequency can be estimated by the spectrum analysis of estimated vibration acceleration. With the estimated vibration acceleration and vibration frequency, the SFM signal is reconstructed. Then, the corresponding THz-SAR imaging algorithm is proposed to estimate and compensate the phase error caused by the high-frequency vibration error of the motion platform and realize high-frequency vibration error estimation and compensation for THz-SAR imaging. Finally, the effectiveness of the novel algorithm proposed in this paper is demonstrated by simulation results.

Pesticide residues in rice planted in South and Southwest China.

In 2019 and 2020, 70 paddy and 70 brown rice samples were collected from South China and Southwest China, wherein the residues of 15 target pesticides were investigated. A gas chromatography-mass spectrometry (GC-MS) method was established for the simultaneous detection of 15 pesticides, which achieved good linear relationship with limits of detection (LODs) of 0.10-4.00 µg kg-1. The average recoveries and relative standard deviations (RSD) were satisfied for the pesticide residues detection. Analysis results showed that the detection rates of 15 typical pesticides in paddy and brown rice were 0%-12.9% and 0%-1.4%, respectively. None of the 15 pesticides exceed their maximum residue limit (MRL) stipulated by China. The pesticide with the highest detection rate and concentration was chlorpyrifos. This study can provide data support for the control of pesticide residues in rice and the realisation of the improving the efficiency of pesticide and fertiliser while reducing their application.