Exploring Surface-Enhanced Raman Spectroscopy (SERS) Characteristic Peaks Screening Methods for the Rapid Determination of Chlorpyrifos Residues in Rice.

Surface-enhanced Raman spectroscopy (SERS), coupled with characteristic peak screening methods, was developed for analyzing chlorpyrifos (CM) pesticide residues in rice. Au nanoparticles (AuNPs) were prepared as Raman signal enhancement. Magnesium sulfate (MgSO4), primary secondary amine (PSA), and C18 were used to purify the rice extraction. A successive projections algorithm (SPA) was performed to identify the optimal characteristic peaks of CM in rice from full Raman spectroscopy. Support vector machine (SVM) and partial least squares (PLS) were implemented to investigate the quantitative analysis models. The results demonstrated that six Raman peaks such as 671, 834, 1016, 1114, 1436, and 1444 cm-1 were selected by the SPA and SVM models and had better performance using six peaks (only 0.92% of the full spectra variables) with R2p = 0.97, RMSEP = 2.89 and RPD = 4.26, and the experiment time for a sample was accomplished within 10 min. Recovery for five unknown concentration samples was 97.45-103.96%, and T-test results also displayed no obvious differences between the measured value and the predicted value. The study stated that SERS, combined with characteristic peak screening methods, can be applied to rapidly monitor the chlorpyrifos residue in rice.

[Determination of fenbutatin oxide residue in orange products by gas chromatography].

An analytical method for the determination of fenbutatin oxide (FBT) residue in oranges by capillary gas chromatography-flame photometric detection (GC-FPD) was developed. The FBT was extracted with acetone-acetic acid (99:1, v/v) and hexane, filtered and evaporated by nitrogen evaporator in a water bath at 35 degrees C. The residue was dissolved in hexane. The FBT in the solvent was derivatized with ethyl magnesium bromide for 15 min, 1 mol/L hydrochloride was added, the supernatant was collected and the solvent was evaporated to get dry supernatants, then the supernatant was dissolved in hexane and cleaned up with a silica solid phase extraction column, eluted with 5 mL hexane-dichloromethane (4:1, v/v), determined by GC. The standard curve was linear in the range of 0.2-2.0 mg/L. The correlation coefficients (r) were more than 0. 999 5, the average recoveries were 79.6%-109.6% with the relative standard deviations (RSDs) of 3.60%-9.04% at the spiked levels of 0.1-0.4 mg/kg, and the detection limit of fenbutatin oxide was 0.1 mg/kg. This method is suitable for the analysis of fenbutatin oxide residue in orange products.