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Glyphosate (Gly) is the most widely used herbicide at the moment. It presents a broad spectrum of action, hence its use for many different crops. Regulatory agencies have constantly mentioned the low hazard potential of Gly to mammals. However, the International Agency for Research on Cancer concluded in 2015 that glyphosate is “probably carcinogenic to humans”. For this reason, it is important to develop reliable analytical methods to quantify Gly in food samples. Here, we propose an analytical method that makes use of graphene quantum dots (GQDs) and cysteine-capped silver nanoparticles (AgNPs) for the screening of glyphosate, using QuEChERS as sample treatment. Gly quenched the luminescence of GQDs-AgNPs system, achieving an excellent sensitivity (detection limit of 9 ng mL−1) and selectivity. The method developed was applied to different types of pulses (peas and lupins), obtaining recoveries close to 100% and relative standard deviations lower than 4% in all cases. Its simplicity and rapidity make this method an interesting alternative to other existing methodologies for the analysis of this pesticide in food samples.

A flow-through optosensor is here proposed for the determination of mixtures of two widely used pesticides, carbendazim and o-phenylphenol, in fruits. The pesticides are separated on-line using an additional amount of solid support, C 18 silica gel, in the flow-through cell. The resolution is performed due to the different retention/desorption kinetics of the analytes when interacting with the C 18 microbeads. Therefore, both separation and determination are integrated in the same cell, considerably simplifying the system. In addition, the use of Sequential Injection Analysis provides a high degree of automation and minimum wastes generation. After the analytes are separated, their native fluorescence is measured, obtaining linearity in the 2.0–30 and 1.1–20 mg kg −1 ranges for carbendazim and o-phenylphenol. The detection limits are 0.60 and 0.33 mg kg −1 for carbendazim and o-phenylphenol respectively. The proposed method fulfills the maximum residue limits (MRLs) established in Europe and USA for these pesticides in cherries, pineapple, and mango: 5–10 mg kg −1 . In order to demonstrate the suitability of the method, several samples have been analyzed and the obtained results compared with a chromatographic method.

The determination of thiamethoxam (TMX), a widely known neonicotinoid pesticide, by a multicommutated optosensing device implemented with photochemically induced fluorescence (PIF) has been developed. The combination of both methodologies allows, on one hand a quick on-line photodegradation of TMX and, on the other hand, the preconcentration, quantification and desorption of the fluorescent photoproduct generated once retained on C18 silica gel filling the flow-cell which was monitored at 353 and 407nm for excitation and emission wavelengths, respectively. The proposed analytical method presents a detection limit of 3.6ngmL(-1) by using Multicommutated Flow Injection Analysis (MCFIA) as flow methodology. Recovery experiments have been carried out in different kinds of vegetables at levels same or below the legislated maximum residue limit, demonstrating that this method combines advantages such as simplicity, high sensibility and high selectivity, in addition to fulfill the requirements for its applications in quality control. The obtained results in the analysis of real samples were in good agreement with those provided by a reference liquid chromatography (HPLC) method.

Thiabendazole is a benzimidazole fungicide of general use that is specifically used to control mushroom diseases, mainly cobweb diseases, which is caused by members of the genus Cladobotryum. Although this compound is legislated and its maximum residue limit established at 60mgkg(-1) by Codex Alimentarius, there is almost a complete absence of analytical methods available for its determination in mushrooms. Here, we propose an automated method, using Sequential Injection Analysis with fluorescence detection (λ(exc)/λ(em)=305/345nm) for the determination of thiabendazole in mushrooms. We have developed a flow-through optosensor using C(18) silica gel as solid support placed in the flow-cell where the determination is performed. This method presents a detection limit of 0.5mgkg(-1), and recovery experiments have been carried out in different kinds of mushrooms at levels below the legislated maximum residue limit, demonstrating that the proposed analytical method fulfils the requirements for its applications in quality control of mushrooms.

In this work, we have explored the analytical potential of combining solid-phase optosensing and multicommutation principles, applied to the field of routine analyses of pharmaceuticals. This marriage benefits from the advantaging features of both concepts: the ability of multicommutation to provide increased repeatability, easier sample handling, reduced sample and reagent consumption as well as minor waste generation, combined with the enhancement of both sensitivity and selectivity obtained when a solid support is used to carry out the spectroscopic measurements directly on it. This approach has been evaluated by developing a method for the simultaneous analysis of two active principles (piroxicam and pyridoxine) in pharmaceutical formulations, using a non-polar sorbent as a solid support to attain the separation and subsequent preconcentration/detection of the targeted analytes. A multicommutated flow-through multisensor based on the direct intrinsic solid-phase UV absorbance measurements of the analytes on a packed C(18) silica gel bed was then thoroughly developed. The usefulness of this approach was assessed when it was applied to the determination of piroxicam and pyridoxine in different pharmaceutical formulations obtaining remarkable results.

A rapid and simple flow-through solid phase spectrofluorimetric system is described in this paper for the determination of the diuretic amiloride in physiological fluid (serum) and pharmaceuticals. The sensor was developed in conjunction with a monochannel flow-injection analysis system with fluorimetric transduction. Amiloride was transitorily retained on cationic exchanger gel Sephadex SP-C25 placed in the detection area into the cell. The determination is carried out without any derivatization reaction, by measuring directly the intrinsic fluorescence of the analyte and using the peak height as analytical signal. The wavelengths of excitation and emission were 291 and 419 nm, respectively. Amiloride could be determined in the concentration ranges of 10–600 and 4–250 μg l−1 at a sampling rate of 24 and 30 h−1, respectively with detection limits of 0.92 and 0.33 μg l−1 for 100, and 600 μl of sample volume injected, respectively. The relative standard deviations for ten independent determinations were better than 0.65%. The method was satisfactorily applied to the determination of amiloride in spiked biological fluids (serum) and pharmaceutical preparations without any pretreatment of the samples.