Sulfonamides and fluoroquinolones are two group of antibiotics widely used in the treatment of bacterial infections. Monitoring these residues in live animals and animal products is commonly legislated; however, the environmental occurrence and fate is still sporadically assessed. The development of adequate analytical methods is a key issue to provide accurate data on concentrations of antimicrobial compounds and their residues in different organic matters. This review presents an overview of proposed methods published between 2008 and 2013 for analysis of fluoroquinolones and sulfonamides with special emphasis on sample preparation and detection systems employed. The coupling of high-performance liquid chromatography and mass spectrometry has been the most widely used method to determination of sulfonamides and fluoroquinolones, concomitantly to other antibiotics residues, due to high sensitivity and selectivity. The main drawbacks of this technique are the high cost and the equipment complexity. The coupling high-performance liquid chromatography and fluorescence detection has also been used to fluoroquinolones determination. Their fluorescent properties allowed the development of several methods with limits of detection in ng L⁻¹ range. Sample preparation is an important tool to reach lower detection limits and the online solid-phase extraction has a broader use. The hydrophilic–lipophilic balance polymeric are the mostly applied sorbents for sulfonamides and fluoroquinolones preconcentration. These sorbents have allowed reaching better recoveries and sensitivity improvement. Physico-chemical properties of these antibiotic groups in addition to trends on papers occurrence and frequency of analysis in different types of water (surface water, groundwater, drinking water and wastewater) are discussed.

Fluoroquinolones are in the order of the day concerning environmental contamination through anthropogenic activities, resulting in increased risk for antibiotic resistance dissemination. In this context, accessible, low-cost analytical methods are required for implementation of comprehensive surveillance and screening schemes. In this work, we propose a down-scaled disk-based solid-phase extraction system from which the eluate can be first screened by miniaturized fluorimetric reading, followed by individual determination of target fluoroquinolones (ciprofloxacin, norfloxacin, and enrofloxacin) by liquid chromatography combined to tandem mass spectrometry. The fluorimetric measurement is based on the intrinsic fluorescence of fluoroquinolones. Disk-based retention was performed after sample acidification (pH 4.0) by mixed-mode cation exchange using polystyrene divinylbenzene sulphonated sorbent. Sample loading was precisely controlled in a dedicated flow system operating at 4.0 mL min⁻¹. Different eluent compositions were tested, with elution performed by 1.00 mL of methanol-ammonium hydroxide (98:2, v/v), with subsequent reading of eluate in both detectors. Quantification was attained for 2–25 µg L⁻¹ range, with LOD values at 1 µg L⁻¹. The proposed approach was successfully applied to estuarine waters from the Douro River, with comparable results to a conventional SPE-LC-MS/MS procedure.

A simple and cost-effective screening method for determination of sulfonamides in water is proposed. For this, micro-solid phase extraction based on polystyrene divinylbenzene sulfonated (SDB-RPS) disks was coupled to microplate analysis. Extraction was performed in parallel for up to four samples, and the elution procedure was performed by soaking the SDB-RPS disk in 1 mL of methanol + 0.1% (v/v) ammonia. Miniaturized spectrophotometric determination under microplate format was based on the chromogenic reaction between sulfonamides and p-dimethylaminocinnamaldehyde in organic medium. Several aspects were evaluated, including the derivatization reaction conditions, sample loading rate, and eluent composition using sulfamethoxazole as model compound. Detection of other sulfonamides (sulfadiazine, sulfaquinoxaline, sulfamerazine, sulfanilamide, sulfamethazine, sulfametizole, sulfadimethoxine, sulfapyridine and sulfacetamide) was also evaluated, providing values for limit of detection between 2 and 11 μg L⁻¹ for a sample volume of 100 mL. The proposed method was successfully applied to different types of water, providing a sample throughput of 5.3 samples per hour, making it a suitable, cost effective and environmental friendly approach for screening purposes.

Fluoroquinolones are broad-spectrum bactericidal agents applied for the treatment of human and veterinary diseases. Their common use and their incorrect disposal foster environmental contamination, namely in water resources, increasing the risk of antimicrobial resistance. Hence, a method based on automatic solid-phase extraction coupled to liquid chromatography and fluorimetric detection is proposed for the determination of fluoroquinolones in environmental waters. For the solid-phase extraction procedure, a commercially available molecularly imprinted polymer targeting fluoroquinolones was trapped inside a flow-through extraction column, integrated into a programmable flow injection system using multisyringe flow injection analysis, where all steps concerning sorbent conditioning, sample loading, matrix removal, and analyte elution were performed under computer control. The eluate resulting from the sample preparation was collected and transferred at-line to chromatographic analysis using a reversed-phase monolithic column coupled to a fluorimetric detector, and isocratic elution with methanol–phosphoric acid (pH 3.0; 5.0 mM) (17.5 : 82.5, v/v) at a flow rate of 3.5 mL min⁻¹. Sample treatment and chromatographic analysis were performed in tandem, with sample throughput limited by the sample treatment step. Calibration curves based on fluorescence intensity vs. analyte mass were obtained in the range of 10 to 1000 pg for norfloxacin, ciprofloxacin, and enrofloxacin with LOD values of 6–19 ng L⁻¹ for a sample volume of 100 mL, and RSD < 11% at 0.7 μg L⁻¹. The method was successfully applied to estuarine river water analysis.

Antibiotic resistance is a major health concern of the 21st century. The misuse of antibiotics over the years has led to their increasing presence in the environment, particularly in water resources, which can exacerbate the transmission of resistance genes and facilitate the emergence of resistant microorganisms. The objective of the present work is to develop a chemosensor for screening of sulfonamides in environmental waters, targeting sulfamethoxazole as the model analyte. The methodology was based on the retention of sulfamethoxazole in disks containing polystyrene divinylbenzene sulfonated sorbent particles and reaction with p-dimethylaminocinnamaldehyde, followed by colorimetric detection using a computer-vision algorithm. Several color spaces (RGB, HSV and CIELAB) were evaluated, with the coordinate a_star, from the CIELAB color space, providing the highest sensitivity. Moreover, in order to avoid possible errors due to variations in illumination, a color palette is included in the picture of the analytical disk, and a correction using the a_star value from one of the color patches is proposed. The methodology presented recoveries of 82–101% at 0.1 µg and 0.5 µg of sulfamethoxazole (25 mL), providing a detection limit of 0.08 µg and a quantification limit of 0.26 µg. As a proof of concept, application to in-field analysis was successfully implemented.

A reverse configured flow injection system was developed for the determination of copper in water samples. In this study, a bathocuproine disulfonic acid copper complexing reagent was used. In the presence of a reducing agent (hydroxylamine), the formation of complex was monitored at 484 nm. The determination range extended from 1 to 40 µg L⁻¹, with an applicable determination rate of 40 h⁻¹. The developed method was applied to the determination of copper in water samples (estuarine, river, and drinking water) and showed good accuracy (z-score below 2). The detection limit of 0.7 µg L⁻¹ copper is consistent with the requirement of the target water samples. The developed method was also used for the comparison of different spectrophotometric flow cells. Alternative flow cells (U, Z shaped, and the liquid waveguide capillary cell) were compared in terms of their sensitivity and response to refractive index changes.