Headspace single-drop microextraction coupled with microvolume fluorospectrometry for highly sensitive determination of bromide

Waterproof Cellulose-Based Substrates for In-Drop Plasmonic Colorimetric Sensing of Volatiles: Application to Acid-Labile Sulfide Determination in Waters

The present work reports on the assessment of widely available waterproof cellulose-based substrates for the development of sensitive in-drop plasmonic sensing approaches. The applicability of three inexpensive substrates, namely, Whatman 1PS, polyethylene-coated filter paper, and tracing paper, as holders for microvolumes of colloidal solutions was evaluated. Waterproof cellulose-based substrates demonstrated to be highly convenient platforms for analytical purposes, as they enabled in situ generation of volatiles and syringeless drop exposure unlike conventional single-drop microextraction approaches and can behave as sample compartments for smartphone-based colorimetric sensing in an integrated way. Remarkably, large drop volumes (≥20 μL) of colloidal solutions can be employed for enrichment processes when using Whatman 1PS as holder. In addition, the stability and potential applicability of spherical, rod-shaped, and core-shell metallic NPs onto waterproof cellulose-based substrates was evaluated. In particular, Au@AgNPs showed potential for the colorimetric detection of in situ generated H₂S, I₂, and Br₂, whereas AuNRs hold promise for I₂, Br₂, and Hg⁰ colorimetric sensing. As a proof of concept, a smartphone-based colorimetric assay for determination of acid-labile sulfide in environmental water samples was developed with the proposed approach taking advantage of the ability of Au@AgNPs for H₂S sensing. The assay showed a limit of detection of 0.46 μM and a repeatability of 4.4% (N = 8), yielding satisfactory recoveries (91-107%) when applied to the analysis of environmental waters.

Application of atmospheric pressure glow discharge generated in contact with liquids for determination of chloride and bromide in water and juice samples by optical emission spectrometry

Novel atmospheric pressure glow discharge (APGD) microplasma systems, sustained between a miniaturized flowing anode (FLA) or cathode (FLC) and a He jet, were investigated for the direct determination of Br and Cl, using optical emission spectrometry (OES). The impact of the most crucial operating parameters, i.e., the acid type and its concentration, the discharge current, the gas flow rate, and the sample flow rate, was studied for each of the proposed APGD-based systems. Under the optimized conditions, the analytical figures of merit were determined. The susceptibility to the matrix effects of both developed methods was verified as well. It was found that the mechanism of the analytes transport into the discharge likely relied on the cathode sputtering in the case of FLC-APGD and the formation of the volatile Br and Cl species for FLA-APGD. The DLs of Br and Cl were established to be relatively high, i.e., 0.15 and 1.5 mg L^-1 for FLA-APGD and 2.1 and 18 mg L^-1 for FLC-APGD. However, both studied methods turned out to be resistant to the presence of foreign ions in a sample, at relatively high concentrations. Hence, the proposed methods could be successfully applied for the determination of Br and Cl in water and juices samples and no major differences between the results obtained using the external standard calibration and the standard addition method were found.

Single-drop microextraction technique for the determination of antibiotics in environmental water

Growing concerns related to antibiotic residues in environmental water have encouraged the development of rapid, sensitive, and accurate analytical methods. Single-drop microextraction has been recognized as an efficient approach for the isolation and preconcentration of several analytes from a complex sample matrix. Thus, single-drop microextraction techniques are cost-effective and less harmful to the environment, subscribing to green analytical chemistry principles. Herein, an overview and the current advances in single-drop microextraction for the determination of antibiotics in environmental water are presented were included. In particular, two main approaches used to perform single-drop microextraction (direct immersion-single-drop microextraction and headspace-single-drop microextraction) are reviewed. Furthermore, the impressive analytical features and future perspectives of single-drop microextraction are discussed in this review. This article is protected by copyright. All rights reserved.

Single bubble in-tube microextraction coupled with capillary electrophoresis

Headspace (HS) extraction is a sample pretreatment technique for volatile and semivolatile organic compounds in a complex matrix. Recently, in-tube microextraction (ITME) coupled with CE using an acceptor plug placed in the capillary inlet was developed as a simple but powerful HS extraction method. Here, we present single bubble (SB) ITME using a bubble hanging to the capillary inlet immersed in a sample donor solution as a HS of submicroliter volume (∼200 nL). The analytes evaporated to the bubble were extracted into the acceptor phase through the capillary opening, then electrophoresis of the enriched extract was carried out. Since the bubble volume was much smaller than a conventional HS volume (∼1 mL), it was filled with the evaporated analytes rapidly and the analytes could be enriched much faster compared to conventional HS-ITME. Owing to the high surface-to-volume ratio of the SB, 5 min SB-ITME yielded the enrichment factor values similar to those of 10 min HS-ITME. When 5 min SB-ITME at room temperature was applied to a tap water sample, the enrichment factors of 2,4,6-trichlorophenol (TCP), 2,3,6-TCP, and 2,6-dichlorophenol were 53, 41, and 60, respectively, and the LOQs obtained by monitoring the absorbance at 214 nm were 5.6-8.3 ppb, much lower than 200 ppb, the World Health Organization guideline for the maximum permissible concentration of 2,4,6-TCP in drinking water.

An improved step-by-step airflow/paper-based colorimetric method for highly selective determination of halides in complex matrices

An improved step-by-step colorimetric method for determination of halides has been developed. The method is based on successive selective oxidation of iodide, bromide and chloride into corresponding free halogens, their extraction by airflow and colorimetric detection with different paper test-strips. This procedure can be performed in a single analyzed solution and possesses high selectivity and good sensitivity due to the extraction step. Three types of paper test-strips were examined: paper modified with tetramethylammonium iodide and starch, paper modified with methyl orange and paper modified with silver triangular nanoplates. Limits of detection for iodide, bromide and chloride are 0.01, 0.02, and 0.04 mg L^-1 respectively in case of the last mentioned paper. The method was applied to the analysis of samples having complex matrices, such as various seafood, preserves, bread, and natural waters, showing good accuracy of the analysis with recoveries of 95-105% and relative standard deviations not higher than 6%.

Solid-phase colorimetric sensing probe for bromide based on a tough hydrogel embedded with silver nanoprisms

Sharp-tipped anisotropic silver (Ag) nanostructures are attracting increasing attention because of their unusual optical properties. However, the sharp tips make such nanostructures thermodynamically unstable; thus, they have been considered unsuitable for use in colorimetric sensing because of their tendency to aggregate or transform in a solution state. In the present study, a colorimetric sensing platform for detecting bromide (Br^-) in an aqueous medium was developed. The platform is based on the localized surface plasmon resonance (LSPR) properties of Ag nanoprisms with sharp tips. The key to using such Ag nanocrystals with extreme anisotropic structures is to adopt a solid-phase sensing platform. A Ag-nanoprism-embedded tough hydrogel with interpenetrating polymer networks was synthesized via aqueous-phase polymerization and crosslinking processes. The Ag nanoprisms immobilized inside the hydrogel were stable and did not exhibit aggregation or degradation over time; specifically, when the hydrogel was dried, the nanoprisms retained their inherent LSPR properties for an extended period. By taking advantage of the rapid and spontaneous morphological transformation of Ag nanoprisms inside the hybrid hydrogel exposed to Br^- and the corresponding changes in their LSPR properties, we designed a plasmonic sensing platform for the sensitive and selective detection of Br^- in an aqueous medium. The proposed colorimetric sensing platform was found to exhibit a wide sensing range and high selectivity, with a low limit of detection (LOD) of 10 μM, and offers substantial advantages over previously developed systems; specifically, it is portable, eco-friendly, safe to use and handle, stable for extended periods, and enables naked-eye detection. We believe that the as-proposed sensing platform can be used as a point-of-care analytical tool for detecting Br^- in a broad range of samples.

Highly sensitive, selective and naked-eye detection of bromide and bromate using distance-based paper analytical device

Bromine (Br) can usually be found as a bromide (Br‾) form contained in drinking water. Bromate (BrO₃‾) formation often occurred during the ozonation process in the presence of Br‾. BrO₃‾ is classified as a potential human carcinogen, so both the Br‾ and BrO₃‾ concentrations must be strictly controlled before and after an ozone-based treatment procedure, respectively. This work reports on distance-based paper analytical devices (dPADs) that have been modified with silver hexagonal nanoprisms (AgNPrs) for highly sensitive and selective determination of both Br‾ and BrO₃‾. The measurement of BrO₃‾ is based upon its conversion to bromine vapor (Br₂) when gauged with a paper-based headspace extractor (PAD-HS) that is coupled with dPADs (PAD-HS-dPADs). For Br‾ analysis, O₂ plays an important role in the change from Br‾ to Br₂ within an acid media. Br₂ changes rapidly in water to give us HBrO which is a strong oxidizing agent of AgNPrs. Then, the oxidative reaction of the AgNPrs (pink color) within the presence of Br‾ and BrO₃‾ establishes both silver bromide (AgBr) and the silver nanosphere (AgNPs, yellow color), which can then be easily observed as a change of a pink color band to a yellow color band by the naked eye. Quantification of Br‾ and BrO₃‾ is then achieved by measuring the length of the yellow color band. Under the optimal conditions, the calibration curve will be linear in the range of 25 μg L^-1 to 2 mg L^-1, and from 0.5 to 50 μg L^-1 for Br‾ and BrO₃‾, respectively. The naked-eye detection limits were found to be 10 and 0.5 μg L^-1 for Br‾ and BrO₃‾, respectively. The proposed dPADs for the Br‾ and BrO₃‾ detection exhibited an exceptional sensor performance combined with a low detection limit. They also have the benefits of ease of use, an instrument-free convenience, coupled with portability and a low-cost efficiency. Consequently, our sensing device should be applied to the low-level detection of Br‾ and BrO₃‾ in real samples, including drinking water, rice, and flour.

A novel immobilization fluorescence capillary analysis method and its applications

Fluorescence capillary analysis (FCA) realizes trace-level analysis of micro-volume samples; it is easy to operate, extremely low in analytical cost and can significantly lessen environmental pollution from analytical chemistry waste. FCA has the characteristics of green analytical chemistry and has been applied in clinical, biochemical, pharmaceutical, food safety and other fields. FCA basically involves a micro-volume glass capillary, a capillary holder and an ordinary fluorescence detector. The capillary is not only a container for chemical reaction and detection but also functions as a carrier to immobilize enzymes, gene probes or reagents; it can be used repeatedly or can be disposable. In analysis, the capillary which is modified with functional reagents sucks in a measured liquid for the reaction and is then inserted into the holder within the fluorescent detector for measurement. The immobilized FCA method has been successfully used in the determination of reduced coenzyme I, ethanol in liqueur, lactic acid in dairy products, pyruvic acid and glucose in serum, trace-level sulfated bile acid in urine, the ratio of pyruvic/lactic acid in serum, and pyruvic acid in cells as well as in DNA end-labeling and dyeing methods. Further, FCA can also be extended to capillary arrays to complete multipurpose simultaneous determinations and can be combined with mobile phones as fluorescence detectors for use in mobile health analytical technology. FCA will produce considerable social benefits in medicine, pharmacy, fermentation of food, environmental protection and other fields. Therefore, the relevant contents are presented in this tutorial review.