A selective chromone‐containing colorimetric chemosensor DOCC ((E)‐N,N‐dimethyl‐2‐((4‐oxo‐4H‐chromen‐3‐yl)methylene)hydr azine‐1‐carbothioamide) was designed for the sequential probing of Cu2+ and cysteine. DOCC exhibited a marked color variation from colorless to pale yellow and had the lowest limit of detection (0.30 μM) among the chromone‐based colorimetric sensors for Cu2+ in near‐perfect aqueous media. DOCC could work to probe and quantify Cu2+ in real water samples with great recovery (98‐102%). DOCC could discriminate Cu2+ using the test kit down to 10 μM. On the other hand, Cu2+‐2⋅DOCC could selectively detect cysteine (Cys) in a sequential step through the demetallation reaction. Cu2+‐2⋅DOCC showed that its color returned from pale yellow to colorless only in the presence of Cys and its limit of detection was calculated to be 6.62 μM. The practical applications for Cys were successfully achieved in water samples with perfect recovery (99–100%) and pH tests at 7–9. FT‐IR, Job plot, ESI‐MS, and DFT calculations were applied to explain the sensing mechanisms of Cu2+ by DOCC and Cys by Cu2+‐2⋅DOCC.

A new nitrobenzoxadiazole (NBD)‐based chemosensor N′‐(7‐nitrobenzo[c][1,2,5]oxadiazol‐4‐yl)thiophene‐2‐carbohydrazide (NTCH) was synthesized for detecting Hg2+. NTCH could sense Hg2+ through a color change method from pale yellow to pink. Binding ratio of NTCH and Hg2+ was determined to be 1:1 with the analysis of electrospray ionization mass spectrometry and Job plot. Detection limit turned out to be 0.69 μM. In addition, NTCH could be successfully utilized for detecting Hg2+ in real water samples and visible color test strips. The probing mechanism of NTCH to Hg2+ was explained with 1H nuclear magnetic resonance (NMR) titration, Job plot, electrospray ionization mass spectrometry (ESI‐MS), and theoretical calculations.

A new naphthol‐based chemosensor NPN ((E)‐2‐(((2‐hydroxynaphthalen‐1‐ylmethylene)amino)isoindoline‐1,3‐dione) was synthesized. NPN could sense Ga3+ by a fluorescence “turn‐on” method from colorless to blue. Detection limit for Ga3+ by NPN was determined to be 0.26 μM. The sensing mode of NPN and Ga3+ turned out to be a 1:1. NPN could also be successfully applied to visible fluorescent test strips. The sensing process of Ga3+ by NPN was illustrated through 1H NMR titration, Job plot, ESI‐MS, and DFT calculations.

Loxoprofen is a non-steroidal anti-inflammatory drug of the 2-arylpropionic acid type, which has used to treat musculoskeletal disorders in the horse racing industry. However, it has also used illicitly to mask clinical signs of inflammation and pain in racehorses. Thus, its accurate analysis has become an important issue in horse doping laboratories. In this study, an analytical method of loxoprofen was developed as tert-butyldimethylsilyl (TBDMS) derivative by gas chromatography-mass spectrometry (GC-MS). Characteristic fragment ions of [M-15], [M-57], and [M-139] permitted the accurate and selective detection of loxoprofen. Under optimal conditions, this method showed good linearity (r ≥ 0.999) in the range of 10-500 ng/mL, repeatability (% relative standard deviation = 5.6-8.5), and accuracy (% relative error = - 0.3-0.9) with a detection limit of 1.0 ng. When applied to the analysis of loxoprofen in tablet and patch products, loxoprofen was positively identified as TBDMS derivative by GC-MS. The present method provided rapid and accurate determination of loxoprofen in patch and tablet products. Levels of loxoprofen were highest in equine urine at 0.5 and 1 h after oral administration with single dose (3 mg/kg) to three horses, and then rapidly reduced to below the lower limit of quantification at 24 h. Therefore, the present method will be useful for the pharmacokinetic study and doping tests for loxoprofen and other similar acidic drugs in horses.

We designed a colorimetric and fluorescent dual-mode chemosensor ADM ((E)-2-(((2-amino-4,5-dichlorophenyl)imino)methyl)-6-methoxyphenol) for detecting fluoride (F À ). The sensor ADM can detect F À by colour and fluorescence changes. The colour change is from colourless to yellow, and the fluorescence change is a yellow turn-on. With the results of Job plot and electrospray ionisation mass spectrometry, the reaction of F À and ADM turned out to be a 1:1 binding. The detection limits for F À of ADM were 5.00 μM in ultraviolet-visible and 4.16 μM in fluorescence. The detecting process of F À by ADM was demonstrated by ultraviolet-visible and fluorescent titrations, electrospray ionisation mass spectrometry, proton nuclear magnetic resonance titration and theoretical calculations.