Headspace single-drop microextraction coupled to microchip-photothermal lens microscopy for highly sensitive determination of captopril in human serum and pharmaceuticals

Application of Extraction and Determination Based on Deep Eutectic Solvents in Different Types of Environmental Samples

Water sources are an indispensable resource for human survival. Monitoring the pollution status of the surrounding environment is necessary to protect water sources. Research on the environmental matrix of deep eutectic solvents (DESs) has expanded rapidly because of their high extraction efficiency for various target analytes, controllable synthesis, and versatile structure. Following the synthesis of hydrophobic deep eutectic solvents (HDESs), their application in aqueous matrices broadened greatly. The present review conducted a survey on the pollutant extraction methods based DESs in environmental matrices from two aspects, application methods and matrix types; discussed the potential risk of DESs to the environment and future development trends; and provided some references for researchers to choose DES-based extraction methods for environmental research.

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.

Fluorescence resonance energy transfer-thermal lens spectrometry (FRET-TLS) as molecular counting of methamphetamine

A novel and sensitive approach has been presented for the determination of methamphetamine (METH) based on fluorescence resonance energy transfer-thermal lens spectrometry (FRET-TLS). Due to the affinity of fluorescein molecules to the surface of AuNPs through the electrostatic interaction and thereby caused reduction of the distance between fluorescein and AuNPs, the best way for de-excitation of excited fluorescein is FRET. The energy absorbed by fluorescein transferred to AuNPs causes enhancement of the thermal lens effect. The thermal lens of the fluorescence molecule could be enhanced through a proper acceptor. Upon the addition of methamphetamine, the fluorescein molecules are detached from the surface of AuNPs, due to the stronger adsorption of methamphetamine. As a result, the fluorescence of fluorescein recovered, and the thermal lens effect of fluorescein decreased. The mechanism of energy transfer was evaluated by two different methods including time-resolved spectroscopy and thermal lens spectrometry. Under the optimal conditions, the thermal lens signal was linearly proportional to methamphetamine concentration in the range 5 - 80 nM. The limit of detection and limit of quantitation were 1.5 nM and 4.5 nM, respectively. The detection volume and limit of molecules in the detection volume were 960 attoliter and 87 molecules, respectively. The method was successfully applied for the determination of methamphetamine in human blood plasma and urine.

Combining gold nanoparticle-based headspace single-drop microextraction and a paper-based colorimetric assay for selenium determination

A novel method combining headspace single-drop microextraction with a paper-based colorimetric assay was developed. Headspace single-drop microextraction using a microdrop containing unmodified gold nanoparticles (AuNPs) as both the extractant and the colorimetric probe was used for the sensitive and selective determination of Se(IV). The method relies on the color change of the microdrop solution caused by the adsorption of in situ-generated hydrogen selenide on the surface of AuNPs. Following extraction, the microdrop was spotted onto cellulose paper, and scanometric-assisted digital image analysis was used for selenium quantification. The analytical variables affecting the method sensitivity, including the drop volume, the concentrations of KBH₄, HCl, and AuNP solutions, and the extraction time, were studied. Under the optimal conditions, a linear correlation between the colorimetric signal and Se(IV) concentration in the range from 15-100 μg L^-1 with a limit of quantification of 12 μg L^-1 was achieved. The repeatability of the method was studied by the calculation of intraday and interday precision for the standard solutions at concentrations of 20 and 70 μg L^-1. The batch-to-batch reproducibility of the AuNPs synthesized under the same conditions was also assessed. The relative standard deviations were less than 7%. The method provided satisfactory results for the determination of selenium in real samples.

Photoluminescent coral-like carbon-branched polymers as nanoprobe for fluorometric determination of captopril

The authors describe the synthesis of fluorescent coral-like carbon nano-branched polymers (PCNBPs) co-doped with nitrogen and phosphorus. Uric acid and phosphoric acid act as nitrogen and phosphorus sources, respectively. The PCNBPs have a coral-like branched structure, are cross-connected, and < 20 nm in skeleton diameter. Their blue fluorescence, best measured at excitation/emission wavelengths of 330/425 nm, is quenched by mercury (II) ions due to the specifically restricted rigid conformation caused by the interaction of phosphorus, nitrogen, and oxygen groups on the surface of the PCNBPs. Fluorescence is selectivity quenched by Hg(II) but restored in addition of the hypertension drug captopril (CAP) in the range 50 nM to 40 μM concentration range. Fluorescence recovery is attributed to the effectively specific interactions between the thiol group of CAP and Hg(II). The method was applied to the determination of the concentration of Cap in pharmaceutical samples, and recoveries were between 97.6 and 105.1%. Graphical abstract Fluorescent coral-like carbon nano-branched polymers (PCNBPs) co-doped with nitrogen and phosphorus are described. Their fluorescence is selectivity quenched by Hg(II) but restored in addition of the hypertension drug captopril (Cap) in the range 50 nM to 40 μM concentration range.