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The matrix effects of ethyl acetate extracts from seven different citrus fruits on the determination of 80 pesticide residues using liquid chromatography coupled to high-resolution time-of-flight mass spectrometry (UHPLC-(ESI)-HR-TOF) at 4 GHz resolution mode were studied. Only 20% of the evaluated pesticides showed noticeable matrix effects (ME) due to coelution with natural products between t = 3 and 11 min. Principal component analysis (PCA) of the detected coextractives grouped the mandarins and the orange varieties, but separated lemon, oranges, and mandarins from each other. Matrix effects were different among species but similar between varieties, forcing the determination of pesticide residues through matrix-matched calibration curves with the same fruit. Twenty-three natural products (synephrine, naringin, poncirin, glycosides of hesperitin, limonin, nomilin, and a few fatty acids, among others) were identified in the analyzed extracts. Twelve of the identified compounds coeluted with 28 of the pesticides under study, causing different matrix effects.

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The validation of an analytical procedure for the determination of pesticide residues in beeswax, an interesting matrix for environmental pollution monitoring, is presented. Using the QuEChERS template, the impacts of wax particle size, sample amount, and cleanup procedure (water addition, dispersive solid phase extraction, freeze-out, and combinations thereof) on extraction yield and coextractive load were studied. Sample preparation through liquid-liquid partitioning between acetonitrile and melted wax (∼80 °C), followed by freeze-out and primary-secondary amine dispersive cleanup, was performed on incurred and pesticide-free samples for 51 residues. Determinations were made through LC-MS/MS and GC×GC-TOF, and the whole procedure was validated. Matrix effects were evaluated, with recoveries between 70 and 120% and RSDs below 20% in almost all cases. LC-MS/MS LOQs ranged from 0.01 to 0.1 mg/kg for most pesticides, but for GC-amenable pesticides, GC×GC-TOF sensitivity was lower (0.1-0.2 mg/kg). This methodology can be applied for routine analysis of pesticide residues in beeswax.

The results of an experiment to study the occurrence and distribution of pesticide residues during rice cropping and processing are reported. Four herbicides, nine fungicides, and two insecticides (azoxystrobin, byspiribac-sodium, carbendazim, clomazone, difenoconazole, epoxiconazole, isoprothiolane, kresoxim-methyl, propanil, quinclorac, tebuconazole, thiamethoxam, tricyclazole, trifloxystrobin, λ-cyhalotrin) were applied to an isolated rice-crop plot under controlled conditions, during the 2009–2010 cropping season in Uruguay. Paddy rice was harvested and industrially processed to brown rice, white rice, and rice bran, which were analyzed for pesticide residues using the original QuEChERS methodology and its citrate variation by LC-MS/MS and GC-MS. The distribution of pesticide residues was uneven among the different matrices. Ten different pesticide residues were found in paddy rice, seven in brown rice, and eight in rice bran. The highest concentrations were detected in paddy rice. These results provide information regarding the fate of pesticides in the rice food chain and its safety for consumers.

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