This work presents a surface-enhanced Raman scattering (SERS) and density functional theory (DFT) study of a fipronil adsorbed on colloidal silver nanoparticles (AgNPs). A standard curve was established to quantify fipronil within a range of 0.0001–0.1 ppm (r2 ≥ 0.985), relying on the unique fipronil Raman shift at ~2236 cm−1 adsorbed on AgNPs. DFT calculations suggest that the nitrile moiety (C≡N) binding should be slightly more favorable, by 1.92 kcal/mol, than those of the nitrogen atom of the pyrazole in fipronil and Ag6 atom clusters. The characteristic peaks of the SERS spectrum were identified, and both the calculated vibrational wavenumbers and the Raman intensity pattern were considered. The vibrational spectra of fipronil were obtained from the potential energy distribution (PED) analysis and selective Raman band enhancement.

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Wine oxidation is reported to be linked to the iron species present in the wine, but spectrophotometric speciation is plagued by unstable measurements due to alterations to the reduction potential of iron by complexing agents. Ferrozine raises the reduction potential of iron by complexing preferentially to iron(II), inducing the reduction of iron(III) during analysis; here, EDTA is added to chelate iron(III) and to stabilize the forms of iron. Bisulfite addition allows the use of ferrozine for red wine analysis by mitigating color interference. Measurements agree with values from a previous method for iron(II) and from FAAS for total iron. Spike recoveries were in the range of 103.5−110.1%. The method is linear for iron concentrations in the range of 0.10−6.00 mg L −1 and offers good precision (CV 0.4−10.1%) and low limits of detection (0.02 mg L −1 ) and quantification (0.06 mg L −1 ). The method demonstrated changes to iron speciation during the oxygenation of red wines.

Micro-oxygenation (Mox) is a common technique used to stabilize color and reduce harsh astringency in red wines. Here, we investigate the role of residual sugars, phenolics, SO 2 , and yeast on the oxidation of wine in three studies. In a Mox experiment, populations of yeasts emerged after the loss of SO 2 , and this was associated with sharp increases in oxygen consumption and acetaldehyde production. No acetaldehyde production was observed without the presence of yeast. In an oxygen saturation experiment, unfiltered wines, in particular those with residual sugar >3 g/L, consumed oxygen more quickly and produced more acetaldehyde than filtered wines. In a final experiment, the reincorporation of oxygen and glucose immediately after the completion of fermentation of an otherwise dry synthetic wine resulted in significant acetaldehyde production. These experiments highlighted the importance of yeast metabolism in determining a wine's response to Mox and suggested that the role of chemical oxidation to produce acetaldehyde during Mox may not be very important. It appears that control of microbial populations and residual sugar levels may be key to managing Mox treatments in winemaking, and production scale experiments should be conducted.

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