Layered double hydroxide intercalated with tyrosine for ultrasonic-assisted microextraction of tramadol and methadone from biological samples followed by GC/MS analysis.

A magnetic nanocomposite adsorbent based on Zn-Al layered double hydroxide (LDH) intercalated with tyrosine has been synthesized for ultrasound-assisted extraction of two drugs of abuse: tramadol (TRA) and methadone (MET). Analysis was carried out using gas chromatography-mass spectrometry. The synthesized LDH was characterized by Fourier transform-infrared spectroscopy, X-ray diffraction, field emission scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The most important extraction parameters such as type of the elution solvent, pH value of the sample solution, and the amount of the adsorbent were optimized. With assistance of ultrasound radiation, the maximum extraction of target drugs using the fabricated LDH was achieved within 5 min. Under the optimized conditions, the limits of determination were 0.45, 0.45, 2.5, and 0.8 µg L-1 for TRA and 0.15, 0.15, 1.2, and 0.5 µg L-1 for MET in water, urine, plasma, and saliva samples, respectively. The preconcentration factors obtained were in the range of 50-145. The matrix effect for MET and TRA is considerable in plasma (66%, 18%) and saliva (72%, 34%), respectively. The precision was found to be better 11% RSD. The maximum adsorption capacity is 4.84 (mg g-1) (L mg-1)1/n based on the Freundlich isotherm. The proposed method presents good results for trace determination of tramadol and methadone in biological samples with satisfactory repeatability. Graphical abstract.

A glassy carbon electrode modified with a nanocomposite prepared from Pd/Al layered double hydroxide and carboxymethyl cellulose for voltammetric sensing of hydrogen peroxide.

A Pd/Al layered double hydroxide/carboxymethyl cellulose nanocomposite (CMC@Pd/Al-LDH) was fabricated using carboxymethyl cellulose as a green substrate via co-precipitation method. The synthesized nanocomposite was characterized using different methods such as scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray powder diffraction, transmission electron microscopy, and electrochemical techniques. A glassy carbon electrode (GCE) was then modified with the suspended composite to obtain an electrochemical sensor for hydrogen peroxide (H2O2). The voltammetric (cathodic) current of the modified GCE was measured at -380 mV (vs. Ag/AgCl), at the scan rate of 50 mV.s-1. Results show a linear dynamic range of 1 to 120 µM, and a 0.3 µM limit of detection (at S/N = 3). Intraday and interday relative standard deviations are in the ranges of 4.9-5.4% and 6.8-7.3%, respectively. The sensor was applied for the determination of H2O2 in basil extracts, milk, and spiked river water samples. The recoveries are between 96.60 and 102.30%. Graphical abstractA Pd/Al layered double hydroxide/carboxymethyl cellulose nanocomposite (CMC@Pd/Al-LDH) was fabricated via co-precipitation method and was characterized using scanning electron microscopy, Energy-dispersive X-ray spectroscopy, X-ray powder diffraction, transmission electron microscopy and electrochemical techniques. CMC@Pd/Al-LDH was used to fabricate H2O2 electrochemical sensor.

Development of a new pH assisted homogeneous liquid-liquid microextraction by a solvent with switchable hydrophilicity: Application for GC-MS determination of methamphetamine.

In this study, a new method based on homogeneous liquid-phase microextraction was developed for the determination of methamphetamine (MA) in urine samples. Dipropylamine (DPA), as a solvent with switchable hydrophilicity, was used as the extraction solvent and can be miscible/immiscible based on variable pH values of the aqueous sample solution. The effects of operational extraction parameters such as DPA volume, temperature, the amount of added acid and base solutions, and NaCl content of the sample were investigated. Under optimal conditions the preconcentration factor, limit of detection and linearity of the method were achieved in the ranges of 98.8, 1.5 µgL-1 and 5-1500 µgL-1, respectively. Also, within-run precision, between-run precision and robustness of the method were investigated. Finally, the proposed method was successfully applied to the analysis of MA in urine sample.

Switchable-hydrophilicity solvent-based microextraction combined with gas chromatography for the determination of nitroaromatic compounds in water samples.

A simple, fast, sensitive, and low-cost method was developed for the quantification of nitroaromatic compounds in water samples based on CO2 -assisted liquid-phase microextraction using a switchable-hydrophilicity solvent followed by gas chromatography detection. Dipropylamine was used as extraction solvent with switchable hydrophilicity that can be miscible or immiscible upon the addition or removal of CO2 as a reagent. Experimental parameters affecting the extraction efficiency such as the volume of acceptor phase, the volume of donor phase, pH of donor phase, ionic strength, and extraction time were investigated. Under the optimal conditions, detection limits and preconcentration factors were obtained in the ranges of 0.9-1.8 µg/L and 132-138, respectively. Also, the extraction recoveries of water samples were above 88%. Finally, the developed method was successfully applied to the determination of nitroaromatic compounds in real water samples.

Application of a new fiber coating based on electrochemically reduced graphene oxide for the cold-fiber headspace solid-phase microextraction of tricyclic antidepressants.

A new fiber based on the electrochemical reduction of graphene oxide was prepared on a copper wire for solid-phase microextraction (SPME) applications. The prepared fiber was used for the SPME and gas chromatographic analysis of tricyclic antidepressants (TCADs), including amitriptyline, trimipramine, and clomipramine. The feasibility of direct-immersion and headspace modes of SPME for the determination of TCADs was studied. The effects of four parameters including pH, salt content, extraction temperature with and without cooling the fiber, and extraction time were investigated. The comparison showed that headspace cold fiber SPME results in the best outcome for the extraction of TCADs. Under the optimized conditions of this mode, the calibration curves were linear between 2.0 and 500 ng/mL and the detection limits were between 0.30 and 0.53 ng/mL. The intraday and interday RSDs obtained at 20 ng/mL (n = 5), using a single fiber, were 5.5-9.0 and 7.5-9.8, respectively. The fiber to fiber repeatability (n = 4), expressed as the RSD, was between 12.8 and 13.2% at a 20 ng/mL concentration level. The method was successfully applied to the analysis of TCADs in plasma samples showing recoveries from 73 to 96%.

A new platform for sensing urinary morphine based on carrier assisted electromembrane extraction followed by adsorptive stripping voltammetric detection on screen-printed electrode.

Electromembrane extraction (EME) coupled with electrochemical detection on screen-printed carbon electrode has been developed for the quantification of morphine in urine samples. Charged morphine molecules were extracted from an aqueous sample by applying an electrical potential through a thin supported liquid membrane (SLM) into an acidic aqueous acceptor solution (20 µL) placed inside the lumen of a hollow fiber. Then, the acceptor solution was mixed with 20 µL of NaOH solution (0.1 M) and analyzed using screen printed electrochemical strip. Differential pulse voltammetry (DPV) peak current at 0.18 V was selected as the signal and the influences of experimental parameters were investigated and optimized using Box-behnken design and also one-variable-at-a-time methodology as follows: adsorptive accumulation time, 40 s; SLM, 2-nitrophenyl octyl ether+10% tris-(2-ethylhexyl) phosphate+10% di-(2-ethylhexyl) phosphate; pH of the sample solution, 6.0; pH of the acceptor solution, 1.0; EME time, 24 min; EME potential, 90 V and stirring rate, 1000 rpm. The calibration curve which was plotted by the variation of DPV currents as a function of morphine concentration was linear within the range of 0.005-2.0 µg mL(-1). The limit of detection and the limit of quantification were 0.0015 (S/N=3) and 0.005 µg mL(-1), respectively. Finally, the proposed method was able to determine morphine simply and effectively at concentration levels encountered in toxicology and doping.

A new method for the enhancement of electromembrane extraction efficiency using carbon nanotube reinforced hollow fiber for the determination of acidic drugs in spiked plasma, urine, breast milk and wastewater samples.

A new design of low voltage electromembrane extraction (EME) using carbon nanotube reinforced hollow fiber was developed for the determination of acidic drugs in biological and wastewater samples. The supported liquid membrane (SLM) with carbon nanotubes as the sorbent interface was used in this research. CNTs have large surface area and high adsorption capacity for a wide range of organic and inorganic species. Therefore, the presence of CNTs in SLM increased the overall analyte partition coefficient in the membrane and lead to enhancement in analyte transport. Optimization of the variables affecting this method was carried out in order to achieve the best extraction efficiency. Ibuprofen and naproxen, nonsteroid anti-inflammatory drugs (NSAIDs), were selected as model acidic drugs. Optimal extractions were accomplished with 1-octanol with 3.0 mg mL(-1) CNTs as the SLM, with 5V as the driving force, and with pH 7.4 in donor and pH 12 in acceptor solutions. Equilibrium extraction conditions were obtained after 10 min of operation with the whole assembly agitated at 500 rpm. Under the optimized extraction conditions, the proposed EME technique provided good linearity (>0.998), repeatability (RSD=2.7-3.2), low limits of detection (1-3 ng mL(-1)), excellent preconcentration (PF=180-188) and high recoveries (90-94%). In comparison with the conventional EME method, this method showed better results (lower voltage, higher preconcentration factors and higher recoveries). Finally, the developed method was successfully used for the determination of ibuprofen and naproxen in different spiked matrices including plasma, urine, breast milk and wastewater samples.

Electrosynthesis of an imidazole derivative and its application as a bifunctional electrocatalyst for simultaneous determination of ascorbic acid, adrenaline, acetaminophen, and tryptophan at a multi-wall carbon nanotubes modified electrode surface.

In this research, the electrosynthesis of 4-(1H-benzo[d]imidazol-2-ylthio)-5-methylbenze-1,2-diol (as an imidazole derivative) is reported. An imidazole derivative multi-wall carbon nanotube modified glassy carbon electrode (IMWCNT-GCE) was constructed and used as an excellent bifunctional electrocatalyst for oxidation of ascorbic acid (AA) and adrenaline (AD). Cyclic voltammetry was used to calculate the surface electron transfer rate constant, k(s), and the electron transfer coefficient, α, for the electron transfer between MWCNT-GCE and the electrodeposited imidazole derivative. The kinetic parameters such as the electron transfer coefficient, α, and the heterogeneous rate constant, k', for the oxidation of AA and AD at the IMWCNT-GCE surface were estimated. The modified electrode was found quite effective for the simultaneous determination of AA, AD, acetaminophen (AC), and tryptophan (Trp) in a mixture solution. The detection limits of AA and AD were calculated as 0.96 µM and 0.38 µM, respectively. Finally, IMWCNT-GCE was satisfactorily used for the determination of AA, AD, and AC in pharmaceutical samples.

A novel electrochemical sensor based on metal-organic framework for electro-catalytic oxidation of L-cysteine.

A novel electrochemical sensor based on Au-SH-SiO2 nanoparticles supported on metal-organic framework (Au-SH-SiO2@Cu-MOF) has been developed for electrocatalytic oxidation and determination of L-cysteine. The Au-SH-SiO2@Cu-MOF was characterized by scanning electron microscopy, transmission electron microscopy, x-ray diffraction and cyclic voltammetry. The electrochemical behavior of L-cysteine at the Au-SH-SiO2@Cu-MOF was investigated by cyclic voltammetry. The Au-SH-SiO2@Cu-MOF showed a very efficient electrocatalytic activity for the oxidation of L-cysteine in 0.1 M phosphate buffer solution (pH 5.0). The oxidation overpotentials of L-cysteine decreased significantly and their oxidation peak currents increased dramatically at Au-SH-SiO2@Cu-MOF. The potential utility of the sensor was demonstrated by applying it to the analytical determination of L-cysteine concentration. The results showed that the electrocatalytic current increased linearly with the L-cysteine concentration in the range of 0.02-300 µM and the detection limit was 0.008 µM. Finally, the sensor was applied to determine L-cysteine in water and biological samples.