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[Display omitted] • PVC-diphenylamine modified cellulose was proposed as sorptive phase. • The synthesis, using the dip-coating technique, is simple and cost-effective. • Opioids interact with the membrane by a mixed-mode interaction. • Direct infusion mass spectrometry allows to reduce the time of analysis. • The approach was successfully applied to real saliva samples containing codeine and tramadol. This article evaluates the potential of cellulose paper as a substrate for preparing a polyvinylchloride (PVC)-diphenylamine sorptive phase that can be used under the thin film microextraction (TFME) format. This phase was easily synthesized using the dip-coating technique to coat the filter paper with PVC, followed by the covalent bonding of diphenylamine. As a result, aromatics rings are available on paper surface to isolate the target analytes by a mixed-mode interaction at physiological pH. The resulting material was characterized by infrared spectroscopy, UV–Vis diffuse reflection spectroscopy, and scanning electron microscopy. As analytical problem, three opioids (methadone, codeine, and tramadol) were determined in saliva samples by direct infusion mass spectrometry. Different variables involved in the extraction procedure have been optimized (e.g. sample pH, extraction time, and sample dilution). The proposed method provides good linearity (R2 > 0.9817) and sensitivity (detection limits in the range from 1.5 µg L−1 to 15 µg L−1). The intra-day and inter-day precision, expressed as relative standard deviation, were better than 16.4 % and 18.5 % respectively. The accuracy, expressed as relative recovery, provides values in the interval from 82 % to 105 %. Finally, the proposed approach has been successfully applied to real saliva samples of patients under codeine and tramadol medical prescription. [ABSTRACT FROM AUTHOR]

[Display omitted] • An visual distance-based paper analytical device has been developed for on-site detection of Pb(II). • Pb(II) can inhibit the catalytic activity of G4/hemin DNAzyme induced by K+. • The biosensor can sensitively detect Pb(II) with a lowest detection limit of 1 nM. • The biosensor can be applied to detect Pb(II) in real samples. A simple, inexpensive, fast, and visual distance-based paper analytical device has been developed for on-site detection of Pb(II). Pb(II) can inhibit the catalytic activity of G-quadruplex/hemin (G4/hemin) DNAzyme induced by K+, which catalyzes 3,3,5,5-tetramethyl benzidine (TMB) immobilized on paper to produce a visible blue band. The factors affecting Pb(II) detection have been optimized with PS concentration of 3 μM, K+ concentration of 10 mM, and hemin concentration of 10 μM, as well as the straight channel width of 2.0 mm. It can be well found that the formed length correlates with the concentration of Pb(II) with a linear detection range of 0.02 μM − 50 μM. A fitting linear equation of Y = 20.793–5.391Log C (R2 = 0.9788) can be obtained with a lowest detection limit of 1 nM. Additionally, the method is capable of selectively detecting Pb(II) and works well for Pb(II) detection in real samples. Overall, the visual distance-based paper analytical device offers an ideal platform for on-site detection of heavy metal ions, especially in resource-limited areas. [ABSTRACT FROM AUTHOR]