Development of a colorimetric sensor based on the coupling of a microfluidic paper-based analytical device and headspace microextraction for determination of formaldehyde in textile, milk, and wastewater samples.

A user-friendly, cost-effectively, portable, and environmentally friendly colorimetric sensor for the quantitative determination of formaldehyde was developed based on the combining of microfluidic paper-based analytical device (µPAD), headspace microextraction (HSME), and digital image colorimetry. Coupling HSME and µPAD led to enhancements in selectivity and sensitivity of the sensor through sample cleanup and analyte enrichment. To construct the µPAD-HSME device, two pieces of paper as the sample and detection zone were placed facing each other so that a small common and sealed space was created between them. The color change occurred when the analyte in the gaseous form crossed this gap and reached the detection zone. Colorimetric sensing in the detection zone was performed based on the Hantzsch reaction. The color change in the detection zone was recorded by a smartphone and digital images were processed using image analysis software based on the RGB model. The influence of some key variables on the sensitivity of the method including derivatization reagent composition, sample volume, extraction temperature, and extraction time was studied and optimized. The linear dynamic range of the method was obtained in two ranges of 0.10-0.75 and 0.75-5.0 mg L-1 with a limit of detection of 0.03 mg L-1. The recoveries were in the range 80-126% for the quantification of formaldehyde in textile, milk, and wastewater samples.

Solvent holder-assisted liquid-phase microextraction using nano-structure biomass-derived carbonaceous aerogel combined with ion mobility spectrometry for simultaneous determination of ethion and chlorpyrifos.

A biomass-derived sponge-like carbonaceous aerogel was prepared through a two-step procedure, including hydrothermal carbonization and freeze-drying process. The aerogel was employed as the solvent holder for liquid-phase microextraction of organophosphorus pesticides, ethion, and chlorpyrifos (as the model compounds), prior to determination by secondary electrospray ionization-ion mobility spectrometry. The carbonaceous aerogel is an appropriate candidate to be used as the solvent holder due to some properties such as three-dimensional structure, porous nature, and very low density. So, the aerogel, including extraction solvent, can tumble on the top of the sample solution, without loss of solvent during its agitation. A comparison of the extraction efficiency was performed at similar conditions between the proposed method and single-drop microextraction, as well as hollow-fiber solvent bar microextraction. Different parameters affecting the extraction efficiency, such as stirring rate, salt concentration, temperature, and extraction time were investigated by using the response surface methodology. The linear dynamic range was in the ranges 1-30 and 1-70 µg L-1 with regression coefficients of 0.9973 and 0.9956 for ethion and chlorpyrifos, respectively. The limit of detection was 0.09 and 0.21 µg L-1 for ethion and chlorpyrifos, respectively. The method was used for extracting analytes from environmental water and vegetable samples, with the spiking recoveries in the range 80-121%. Graphical abstract Schematic representation of three-dimensional biomass-derived carbonaceous aerogel as the solvent holder in solvent bar microextraction (as a mode of the liquid-phase microextraction method). It was used for the extraction of two kinds of organophosphorus pesticides prior to the determination by ion mobility spectrometry.

Direct molecular imprinting technique to synthesize coated electrospun nanofibers for selective solid-phase microextraction of chlorpyrifos.

Molecularly imprinted-electrospun nanofibers based on the use of poly(vinyl alcohol) were fabricated and used as a new sorbent for solid-phase microextraction of chlorpyrifos. The molecularly imprinted nanofibers were prepared by electrospinning and direct molecular imprinting of polymeric nanofibers. Poly(vinyl alcohol) was used as the functional and electrospun polymer. Chlorpyrifos was used as a template molecule, and glutaraldehyde as the cross-linker. Detection was performed by ion mobility spectrometry equipped with a secondary electrospray ionization source. The molecularly imprinted fiber has a selectivity and extraction efficiency better than the fiber fabricated using the conventional method of encapsulating MIP particles in electrospun nanofibers. Parameters affecting the extraction efficiency such as ionic strength, stirring rate, extraction time, and temperature were evaluated. The dynamic range of the method was in the range of 0.5-200 µg L-1 with the limit of detection of 0.1 µg L-1. The intra- and inter-day relative standard deviations of the method were 4 and 9%, respectively. The fiber-to-fiber reproducibility for three different fibers is 5%. The spiking recoveries from spiked apple, cucumber, and water samples were in the range of 82-112%. Graphical abstract Molecularly imprinted-electrospun nanofibers were fabricated based on the direct molecular imprinting technique and used as a new SPME fiber coating for selective extraction of chlorpyrifos from fruits and water samples prior its determination by secondary electrospray ionization-ion mobility spectrometry.