Decrease of Pirimiphos-Methyl and Deltamethrin Residues in Stored Rice with Post-Harvest Treatment

A modified quick, easy, cheap, effective, rugged (QuEChERS) method with multi-walled carbon nanotubes (MWCNTs) as reversed-dispersive solid phase extraction (r-DSPE) material was applied to the analysis of pirimiphos-methyl and deltamethrin residues in stored rice. Two dustable powder (DP) formulations (2% pirimiphos-methyl and deltamethrin DP; 5% pirimiphos-methyl DP) were applied in simulated storehouse trials in the lab. The residues and dissipation of the two pesticides in stored rice were investigated. Slow dissipation of both pesticides was observed in stored rice. The half-lives of pirimiphos-methyl were 23.9–28.9 days, and those of deltamethrin were 23.9–24.8 days. Residues of pirimiphos-methyl from application rates of 4.5–6.75 a.i. mg/kg (active ingredient milligram per kilogram) and 10–15 a.i. mg/kg were 1.6–3.8 mg/kg and 3.0–4.5 mg/kg at 60 days Pre-harvest Interval (PHI). Residues of deltamethrin from an application rate of 0.5–0.75 a.i. mg/kg were 0.13–0.14 mg/kg at 60 days PHI. Both pesticides residues were below the Maximum Residue Limits (MRLs) established by the Codex Alimentarius Commission (CAC). Therefore, at the recommended dosages they are safe for use on stored rice

Ionic Liquid-Dispersive Micro-Extraction and Detection by High Performance Liquid Chromatography–Mass Spectrometry for Antifouling Biocides in Water

A simple analytical method was developed and evaluated for the determination of two antifouling biocides using an ionic liquid-dispersive liquid–liquid micro-extraction (IL-DLLME) and a high-performance liquid chromatography–electrospray ionization mass spectrometry (LC-ESI-MS) analysis. Irgarol 1051 and Sea-Nine 211 were extracted from deionized water, lake water, and seawater using IL 1-hexyl-3-methylimidazolium hexafluorophosphate ([HMIm][PF6]) and ethyl acetate as the extraction solvent and the dispersion solvent. Several factors were considered, including the type and volume of extraction and dispersive solvent, IL amount, sample pH, salt effect, and cooling temperature. The developed method resulted in a recovery range of 78.7–90.3%, with a relative standard deviation (RSD, n = 3) less than 7.5%. The analytes were enriched greater than 40-fold, and the limits of detection (LOD) for two antifouling biocides were 0.01–0.1 μg L−1. The method was effectively applied for the analysis of real samples of freshwater as well as samples of seawater

Decrease of Pirimiphos-Methyl and Deltamethrin Residues in Stored Rice with Post-Harvest Treatment

A modified quick, easy, cheap, effective, rugged (QuEChERS) method with multi-walled carbon nanotubes (MWCNTs) as reversed-dispersive solid phase extraction (r-DSPE) material was applied to the analysis of pirimiphos-methyl and deltamethrin residues in stored rice. Two dustable powder (DP) formulations (2% pirimiphos-methyl and deltamethrin DP; 5% pirimiphos-methyl DP) were applied in simulated storehouse trials in the lab. The residues and dissipation of the two pesticides in stored rice were investigated. Slow dissipation of both pesticides was observed in stored rice. The half-lives of pirimiphos-methyl were 23.9–28.9 days, and those of deltamethrin were 23.9–24.8 days. Residues of pirimiphos-methyl from application rates of 4.5–6.75 a.i. mg/kg (active ingredient milligram per kilogram) and 10–15 a.i. mg/kg were 1.6–3.8 mg/kg and 3.0–4.5 mg/kg at 60 days Pre-harvest Interval (PHI). Residues of deltamethrin from an application rate of 0.5–0.75 a.i. mg/kg were 0.13–0.14 mg/kg at 60 days PHI. Both pesticides residues were below the Maximum Residue Limits (MRLs) established by the Codex Alimentarius Commission (CAC). Therefore, at the recommended dosages they are safe for use on stored rice

Dissipation and Residues of Thiram in Potato and Soil

The residue levels of thiram during potato cultivation in open field were evaluated. Thiram residues were determined by methylation derivation method with high performance liquid chromatography (HPLC). Wettable powder (WP) formulation containing 25% thiram was applied at 2320 g active gradient hm−2 (a.i. hm−2) dosage for the dissipation study. The decline rate in potato leave and soil followed first-order kinetics equation, and the half-life ranged from 2.8 to 5.4 days and 2.6 to 9.9 days, respectively. In terminal residue, the thiram was sprayed at 580 g a.i. hm−2 (low concentration, recommended dosage) and 1160 g a.i. hm−2 (high concentration, double of recommended dosage). The residues of thiram in potato and soil samples collected in the field at preharvest interval of 21 days and 30 days were all below 0.02 mg kg−1. The results show that thiram possesses low dietary risk in potato at harvest according to supervised residue field trial. It may be safe when used at recommended rate of application

Surface pH and Ion Affinity at the Alcohol-Monolayer/Water Interface Studied by Sum-Frequency Spectroscopy

Phase-sensitive sum-frequency vibrational spectroscopy was used to probe interfaces of a long-chain alcohol monolayer with various electrolytic solutions, chosen as a prototype for <i>nonionic</i> organic/water interfaces. Spectra in the OH stretching range were observed to be under the influence of ions emerging at the interfaces. Analysis of the spectra with the help of Levin’s theory allowed us to quantitatively find the surface densities of various ions and, hence, the ion affinities and surface pH/pOH at the alcohol/water interface. For the ions studied, the interface affinity has the ranking order of OH^– > I^– > Cl^– ∼ H₃O⁺ > Na⁺, the same as that at the air/water interface except that OH^– and H₃O⁺ have their places interchanged. Significantly stronger affinity of OH^– than H₃O⁺ with the result of surface pH/pOH extrapolating to bulk pH 7 suggests that the alcohol/neutral water interface is weakly basic

Sharing of Na⁺ by Three −COO^– Groups at Deprotonated Carboxyl-Terminated Self-Assembled Monolayer-Charged Aqueous Interface

By combining theoretical calculations and experimental observations, we show that Na⁺ can be shared by three charged −COO^– groups of the deprotonated carboxyl-terminated self-assembled monolayers in aqueous solution at lipid–aqueous interface. This is similar to the sharing structure of Na⁺ usually found in crystals. Notably, this ionic configuration leads to a hydroxyl orientation distribution of interfacial water molecules, showing a maximum toward the bulk solution, in addition to the maximum toward the charged surface expected based on the structure of one-to-one ion-pair formation between Na⁺ and −COO^–. Our results provide new insights for a better understanding of electrochemically and biologically related charged interfaces at the molecular level and should be helpful to design the nanodevices and bioinspired human-made nanomaterials