Titanium dioxide nanotube fiber using in headspace solid-phase microextraction with GC–MS for BTEX detection

Anodized TiO₂ nanotube fibers using in-headspace solid-phase microextraction (SPME) with gas chromatography–mass spectrometry (GC–MS) have been exploited as an analytical method for volatile organic compounds such as benzene, toluene, ethylbenzene, and xylenes (BTEX) detection. The factors of anodizing time and annealing temperature for TiO₂ nanotube production are studied and the adsorption factors (time, ionic strength, and temperature) and desorption factors (time and temperature) for BTEX analysis are optimized. The limit of detections (LODs) for benzene, toluene, ethylbenzene o-xylene, and m, p-xylene are 0.5, 0.1, 1.0, 1.0, and 2.0 μg L⁻¹, respectively. The linear ranges for BTEX (0.5–15,000 μg L⁻¹) and satisfactory linearity (R² ≥ 0.9954) are obtained. This method is successfully applied in real samples with the recoveries ranging from 92% to 97%. TiO₂ nanotube fiber is a promising technique for BTEX analysis.     

Speciation analysis of vanadium in natural water samples by electrothermal vaporization inductively coupled plasma optical emission spectrometry after separation/preconcentration with thenoyltrifluoroacetone immobilized on microcrystalline naphthalene

A sensitive and simple method for low temperature electrothermal vaporization inductively coupled plasma optical emission spectrometry (ETV-ICP-OES) determination of V(IV) and V(V) after separation/preconcentration by a micro-column packed with immobilized thenoyltrifluoroacetone (TTA) on microcrystalline naphthalene has been developed. Thenoyltrifluoroacetone was used as both a chelating agent for micro-column separation/preconcentration and a chemical modifier for ETV-ICP-OES determination of vanadium. Both vanadium species could be trapped by micro-column at pH 4.0, and the vanadate (VO₂⁺) ion could be collected selectively at pH 2.4. Solid material loaded with analyte in the micro-column was dissolved with 100 μL of acetone containing 2.0 mmol L⁻¹ TTA and the vanadium was determined subsequently by ETV-ICP-OES. The concentration of vanadyl (VO²⁺) ion was calculated by subtracting the vanadate concentration from the total concentration of vanadium. Under the optimized experimental conditions, the detection limit (3σ) for the preconcentration of 5 mL of aqueous solution is 0.068 μg L⁻¹ for both species and the relative standard deviations were 4.3% for vanadium(V) and 4.8% for vanadium(IV) (c=10 μg L⁻¹, n=7), respectively. The method was applied successfully to the determination of vanadium(IV) and vanadium(V) in natural water samples.     

Study on Cd2+ Determination Using Bud-like Poly-L-Tyrosine/Bi Composite Film Modified Glassy Carbon Electrode Combined with Eliminating of Cu2+ Interference by Electrodeposition

A bud-like poly-L-tyrosine/Bi modified glassy carbon electrode (p-Tyr/Bi/GC) was prepared by CV and in situ Bi plating, whose conductivity and membrane morphology were characterized by CV, EIS and SEM, respectively. The p-Tyr membrane can effectively promote the enrichment of Cd²⁺. The optimal Tyr concentration and scanning number for p-Tyr/GC preparation were 2.0 mmol ⋅ L⁻¹ and 35, while the optimal Bi³⁺ concentration, pH and Cd²⁺ accumulation potential in test medium were 3.0 μmol ⋅ L⁻¹, 6.5 and −1.3 V, respectively. The linear equation of p-Tyr/Bi/GC's response to Cd²⁺ (1.0 nmol ⋅ L⁻¹ to 2.0 μmol ⋅ L⁻¹) was i_p (μA) = −0.6809 + 100.2c (μmol ⋅ L⁻¹) (R² = 0.9985) with a detection limit of 0.11 nmol ⋅ L⁻¹ (3S/N). The elimination of interference caused by Cu²⁺ in sample was studied by electrodeposition. The p-Tyr/Bi/GC electrode was successfully used for detecting Cd in rice samples with good reliability and accuracy. The developed Cd²⁺ sensor exhibits high sensitivity, wide linear range and low detection limit, especially the designed method of eliminating Cu²⁺ interference has the characteristics of high selectivity, simple operation and wide application range.     

A new Approach for the Voltammetric Sensing of the Phytoestrogen Genistein at a Non-modified Boron-doped Diamond Electrode

An effective electrochemical sensor was constructed using an unmodified boron-doped diamond electrode for determination of genistein by square-wave voltammetry. Cyclic voltammetric investigations of genistein with HClO₄ solution indicated that irreversible behavior, adsorption-controlled and well-defined two oxidation peaks at about +0.92 (P_A1) & +1.27 V (P_A2). pH, as well as supporting electrolytes, are important in genistein oxidations. Quantification analyses of genistein were conducted using its two oxidation peaks. Using optimized experiments as well as instrumental conditions, the current response with genistein was proportionately linear in the concentrations range of 0.1 to 50.0 μg mL⁻¹ (3.7×10⁻⁷−1.9×10⁻⁴ mol L⁻¹), by the detection limit of 0.023 μg mL⁻¹ (8.5×10⁻⁸ mol L⁻¹) for P_A1 and 0.028 μg mL⁻¹ (1.1×10⁻⁷ mol L⁻¹) for P_A2 in 0.1 mol L⁻¹ HClO₄ solution (in the open circuit condition at 30 s accumulation time). Ultimately, the developed method was effectively applied to detect genistein in model human urine samples by using its second oxidation peak (P_A2).     

Electrophoretic deposition of polyaniline nanofibers on a stainless steel wire as an adsorbent for determination of tamoxifen by SPME/GC–FID in urine samples

Polyaniline nanofiber films were fabricated on the surface of stainless steel wire via a controllable and simple electrophoretic deposition route from a nonaqueous colloidal suspension consisting of polyaniline nanofibers. The prepared coating material was then characterized by field emission scanning electron microscopy equipped with energy dispersive spectroscopy and elemental mapping analysis. The fabricated polyaniline film-coated stainless steel wire was then utilized as an effective and novel sorbent phase for solid-phase microextraction of tamoxifen for subsequent gas chromatography/flame ionization detection of this anticancer drug. Parameters consisting of the temperature, extraction time, salt concentration, agitation speed, pH, temperature and time of desorption were studied and optimized using a one-at-a-time strategy. Under the optimum conditions, detection limit (S/N = 3), the limit of quantification (10/3 limit of detection), linear dynamic range, repeatability and reproducibility values of 0.51 μg L⁻¹, 1.7 μg L⁻¹, 2–1,130 μg L⁻¹, 5.7% and 8.6% were attained, respectively. The prepared fiber can preserve 90% of its efficacy after 20 consecutive cycles, demonstrating the suitable thermal stability and cyclability of the proposed solid-phase microextraction coating material for the determination of tamoxifen by gas chromatography/flame ionization detection. The route was effectively utilized to determine tamoxifen in urine samples, with relative recoveries ranging from 89 to 106%.     

Development of Electroanalytical Methods Using Different Electrodes for the Determination of Progesterone (P4) in Pharmaceutical Formulations and Human,Cow and Goat Milk

For the determination of progesterone (P4) electroanalytical studies were performed using mercury electrode (HMDE) and screen-printed boron-doped diamond electrode (BDD-SPE). The effects of pH, supporting electrolyte, accumulation potential and time (E_acc, t_acc) were studied in both systems. The optimum conditions were: i) HMDE: pH 7,0; E_acc: −0,1 V and t_acc: 40 s, ii) BDD-SPE: 0,5 mol L⁻¹ H₂SO₄; E_acc: 0,0 V and t_acc: 120 s. Under these conditions, the detection limit was 3.1 μg L⁻¹ for HMDE and 45.6 μg L⁻¹ for BDD-SPE. Both methods were validated and applied in the P4 determination on pharmaceutical formulations and milk samples.     

Preconcentration and Successful Selective Detection of Traces of Diclofenac in Water using a Nanostructured Modified Carbon Paste Electrode

A highly sensitive, simple and low cost sensor for the quantification of the diclofenac has been constructed. This sensor consists of a carbon paste nano-structured by Multi-Walled Carbon Nanotubes (G-MWCNT)-CPE. Scanning electron microscopy (SEM) and voltammetry technique were used to characterize the electrode material and to determine the analytical performances of the sensor in comparison with those obtained at a G-CPE. The electrochemical oxidation of diclofenac on both G-CPE and (G-MWCNT)-CPE electrodes is mainly controlled by adsorption, presenting a maximum peak current intensity in H₂SO₄ 0.5 mol L⁻¹. The carbon nanotubes, as well as they provide higher conductivity of the paste, act as spacers between the flake graphite particles and avoid their stacking in order to make the surface of graphite particles more accessible to DCF adsorption. The voltammetric measurements of diclofenac on (G-MWCNT)-CPE provide a large quantification range from 0.02 to 1 μmol L⁻¹, a detection limit of 0.004 μmol L⁻¹ and quantification limit of 0.014 μmol L⁻¹ under the optimized operating conditions (H₂SO₄, 0.25 M+KCl 0.25 M, scan rate of 30 mV s⁻¹, preconcentration time 18 min. and MWNTC% (30 %)). The (G-MWCNT)-CPE sensor was successfully applied to natural water samples, just acidified with sulfuric acid (pH<1). These samples were doped with diclofenac in sub-micromolar range and the developed method was validated with excellent recoveries (within a maximum of 3 % difference from 100 %) for all samples indicating no interference effects of the water matrix.     

Graphdiyne and Ionic Liquid Composite Modified Gold Electrode for Sensitive Voltammetric Analysis of Rutin

It is significant to develop a point-of-care testing (POCT) method for rapid detection of medicinal molecules. In this paper, a graphdiyne (GDY)-ionic liquid (IL) composite was prepared via one-step facile ultrasound preparation process and then modified on gold (Au) electrode surface by simple casting method. Scanning electron microscopy and transmission electron microscopy were used to characterize the morphology of GDY-IL composite. Cyclic voltammetric results proved that GDY-IL composite on the electrode surface could effectively improve electron transfer rate, which meant that GDY-IL composite had high conductivity with big surface area. Finally, the modified electrode exhibited excellent performances for rutin detection with wider linear range (8.0×10⁻⁹ mol L⁻¹–2.0×10⁻⁶ mol L⁻¹ and 2.0×10⁻⁶ mol L⁻¹–1.5×10⁻⁴ mol L⁻¹) and lower detection limit (2.7 nmol L⁻¹, 3S₀/S). The Nafion/GDY-IL/Au electrode showed good sensitivity and high selectivity, which was satisfactory in analytical application to real samples. Therefore, the GDY-IL composite modified electrode has the potential applications in the POCT for electrochemical analysis of various medicinal molecules.     

Nanoporous Gold Microelectrode: A Novel Sensing Platform for Highly Sensitive and Selective Determination of Arsenic (III) using Anodic Stripping Voltammetry

A home‐made gold microelectrode (Au‐μE) was fabricated and its surface was modified with nanoporous gold structures via a facile electrochemical approach (anodization followed by electrochemical reduction method). The fabricated nanoporous Au microelectrode (NPG‐μE) was used as a sensor probe for the determination of As(III) in 1.0 mol L⁻¹ HCl solution using square wave anodic stripping voltammetry (SWASV) technique. Field emission scanning electron microscopy (FE‐SEM) and cyclic voltammetry were used to characterize the surface morphology and assess the electrochemical surface area and the roughness factor of the NPG‐μE. SWASVs recorded with the NPG‐μE in As(III) solutions indicated linear behaviour in the concentration ranges of 10–200 μg L⁻¹ and 2–30 μg L⁻¹, with regression coefficients of 0.996 and 0.999 at a deposition time of 120 s, respectively. The limit of detection (LOD) was found to be 0.62 μg L⁻¹ with high sensitivity of 29.75 μA (μg L⁻¹)⁻¹ cm⁻². Repeatability and reproducibility were also examined and values were determined as 3.2 % and 9.0 %. Negligible interference from major interfering copper ion was noticed, revealing the excellent anti‐interference property of the proposed sensing platform. The developed NPG‐μE was successfully used for As(III) determination in tap water samples.     

Electrodetermination of Gallic Acid Using Multi-walled Carbon Nanotube Paste Electrodes and N-Octylpyridinium Hexafluorophosphate

In this work, the determination of gallic acid was performed using surface-renewable carbon paste electrodes fabricated with multi-walled carbon nanotubes (MWCNT) and a mixture of N-octylpyridinium hexafluorophosphate (OPyPF₆) ionic liquid with mineral oil (MO) as binder. This system shows remarkable amperometric sensor characteristics and promotes a better electronic transfer. An electroanalytical study of gallic acid shows a linear range from 4.98±0.25 to 74.1±2.2 μmol L⁻¹, with R²=0.9958 and an experiment a limit of detection of 2.70±0.08 μmol L⁻¹ (S/N=3), and a sensitivity of 0.029 μA μmol⁻¹ L.     

Sensitive Superoxide Biosensor Based on Silicon Carbide Nanoparticles

Direct electron transfer of immobilized superoxide dismutase (Cu, Zn‐SOD) onto silicon carbide (SiC) nanoparticles displays a pair of well defined and nearly reversible redox peaks with formal potential (E°′) of −0.03 V in pH 7.4. The heterogeneous electron transfer rate constant (k_s) and surface coverage (Γ) of immobilized SOD are 11.0±0.4 s⁻¹ and 1.42×10⁻¹¹ mol cm⁻². Biosensor shows fast amperometric response (3s) with sensitivity and detection limit of 1.416 nA μM⁻¹, 1.66 μM, and 1.375 nA μM⁻¹, 2.1 μM for cathodically or anodically detection of superoxide, respectively. This biosensor also exhibits good stability, reproducibility and long life‐time.     

Electrochemical sensing platform based on the use of ZnONPs and MWCNTs as CPE modifiers for a selective and sensitive determination of polyamine spermine in the urine sample

A simple electroanalytical procedure has been developed for the determination of polyamine spermine using the ZnONPs-MWCNTs-CPE sensor. Spermine has been irreversibly oxidized on a modified electrode at a potential of +0.92 V versus Ag/AgCl (KCl, 3.5 mol L⁻¹). The developed sensor demonstrated a respective linear response in borate buffer pH 8.5 from 2 μmol L⁻¹ to 100 μmol L⁻¹, with a detection limit of 0.300 μmol L⁻¹ and quantification limit of 0.998 μmol L⁻¹. The proposed sensor showed high reproducibility (RSD = 2.58 %), stability, robustness, and no obvious interference effects of several inorganic ions and organic molecules. The obtained results demonstrated excellent performance during the determination of the spermine in human urine samples with satisfactory recovery results (98.41–101.34 %), offering promising opportunities for practical clinical analysis.     

Adsorptive Stripping Determination of Scandium(III) with Mordant Blue 9 on Silver Amalgam Film Electrode

A new adsorptive stripping voltammetric method for the determination of trace scandium(III) based on the adsorption of scandium(III)‐mordant blue 9 complex on the cyclic renewable mercury film silver based electrode (Hg(Ag)FE) is presented. The effects of various factors such as: preconcentration potential and time, pulse height, step potential and supporting electrolyte composition are optimized. The calibration graph is linear from 2 nM (0.09 μg L^?1) to 90 nM (4 μg L^?1) for a preconcentration time of 45 s, with correlation coefficient of 0.9995. For a Hg(Ag)FE with a surface area of 7.9 mm² the detection limit for a preconcentration time of 90 s is as low as 5 ng L^?1. The repeatability of the method at a concentration level of the analyte as low as 0.2 μg L^?1, expressed as RSD is 1.9 % (n=5). The proposed method was successfully applied and validated by studying the certified reference material (CRM 320 – river sediment) and natural samples with simultaneous recovery of Sc(III) from spiked water and sediment samples.     

Development of a Sensor Based on Modified Carbon Paste with Com Iron(III) Protoporphyrin Immobilized on SiNbZn Silica Matrix for L‐tryptophan Determination

In this work, SiO₂/Nb₂O₅/ZnO prepared by the sol‐gel processing method was used as substrate base for immobilization of the protoporphyrin‐IX ion. Iron(III) ion was inserted into the porphyrin ring (SiNbZn‐PPFe). A simple square wave voltammetry method based on a composite sensor carbon paste electrode of this material,designed as EPC‐SiNbZn‐PPFe, was developed and validated successfully for the determination of L‐tryptophan (Trp). The optimum conditions were obtained by using sensor modified with 18.00 mg SiNbZn‐PPFe material, 12.00 mg graphite powder and 6.0 μL mineral oil and phosphate buffer 0.3 mol L⁻¹ pH 7.0. The sensitivity of the sensor was found to be 0.523 AL mol ⁻¹, linear range from 10 to 70 μmol L⁻¹ and limit of detection of 3.28 μmol L⁻¹. Therefore, the developed method was successfully applied for the Trp determination in real samples of pharmaceutical formulation and can be used for routine quality control pharmaceutical formulations containing Trp.     

Photoelectrochemical Sensor for Isoniazid: Application in Drugs Used in the Treatment of Tuberculosis

The present work describes the development of a photoelectrochemical sensor based on titanium dioxide, cadmium telluride quantum dots and the tris (2,2′-bipyridyl) ruthenium(II) chloride complex for detection of Isoniazid (INH). The Ru(bpy)₃²⁺/CdTe-QDs/TiO₂/FTO photoelectrochemical platform was characterized by scanning electrochemical microscopy, electrochemical impedance spectroscopy and amperometry. The photoelectrochemical sensor presented two linear ranges for INH concentrations ranging from 0.5 to 150 μmol L⁻¹ and 150 to 1270 μmol L⁻¹, with a theoretical detection limit of 0.02 μmol L⁻¹. The sensor was successfully applied for the determination of INH in drugs samples used in the treatment of tuberculosis.     

Fabrication of Co3O4 particles-modified multi-walled carbon nanotube and poly(phenosafranine) composite electrode for selective and sensitive rutin detection

The preparation and characterisation of a new composite electrode with Co₃O₄ particles-modified multi-walled carbon nanotube (MWCNT) and poly(phenosafranine), as well as its novel application for the voltammetric detection of rutin was described. The resulting composite electrode was characterised using scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS). In the optimised experimental conditions, the oxidation peak current (I_pa) of rutin showed a linear increase in concentration, between 0.008–0.6 and 0.80–6.0 μmol L⁻¹, with a detection limit of 0.00379 μmol L⁻¹. Due to its good selectivity and stability, the composite electrode was successfully applied in detecting rutin in pharmaceutical formulations.     

Simultaneous Determination of Lipophilic Vitamin Esters Using Square-wave Voltammetry at the Glassy Carbon Electrode

Simple and rapid voltammetric method for simultaneous determination of all-trans-retinyl acetate (RAc) or all-trans-retinyl palmitate (RPa) and α-tocopheryl acetate (α-TOAc) has been proposed. The respective method was based on the anodic oxidation of the compounds of interest by square-wave voltammetry in acetone with 0.1 mol L⁻¹ LiClO₄ at the glassy carbon electrode. The procedure was also beneficial with respect to simple dissolution of sample directly in the supporting electrolyte. The all-trans-retinyl acetate could be quantified in two linear ranges (3.1–140 μmol L⁻¹ and 140–400 μmol L⁻¹) and α-tocopheryl acetate in linear range 5.3–400 μmol L⁻¹ with detection limits of 0.9 μmol L⁻¹ RAc (or 0.8 μmol L⁻¹ RPa) and of 1.6 μmol L⁻¹ α-TOAc. Selected commercial cosmetic products were analysed achieving satisfactory recoveries.     

Electrochemical Glyphosate Sensor Based on Hybrid Material SiO2/Sm2O3/Carbon Modified with Meldola Blue

In this work, we have proposed an electrochemical sensor for the detection of pesticides by using a ceramic composite with a SiO₂ surface modified with Sm₂O₃ nanoparticles and C-graphite (SSMG), obtained by the sol-gel process and immobilized by adsorption in Meldola Blue cationic dye (MB). The composite was called (SSMG/MB), which was characterized by spectroscopic, electrochemical techniques, Fourier-transform infrared spectroscopy, and Cyclic Voltammetry. The proposed sensor was applied for the glyphosate electrochemical detection, using Differential Pulse Voltammetry, and, under optimized parameters has presented the linear response for the pesticide in the concentration range from 0.99 to 7.94 (μmol L⁻¹; R²=0.9963; n=8). The calculated values for the detection limit and the quantification limit were 0.15 and 0.49 μmol L⁻¹, respectively. Therefore, the new electrochemical sensor based on SiO₂, NPsSm₂O_3, C-graphite, and MB hybrid material was developed for the first time for glyphosate determination, which has demonstrated high potential for the development of new hybrid devices for environmental control.     

Fast and Simple Preparation of a Sensor Based on Electrochemically Reduced Graphene Oxide (rGO) for the Determination of Zopiclone in Pharmaceutical Dosage by Square Wave Adsorptive Stripping Voltammetry (SWAdSV)

The interactions of zopiclone with electrochemically reduced graphene oxide (rGO) modified electrode were examined. A comparison of GC/rGO and glassy carbon electrode (GC) by electrochemical impedance spectroscopy and scanning electrochemical microscopy (SECM) shows that the modified surface is much less conductive than GC. The role of rGO is to act as a site of specific adsorption of the analyte. Molecular dynamics showed that the monoanionic form of zopiclone presents more interactions with defects of rGO. The analytical methodology allowed obtaining a linearity of 10–130 μg L⁻¹, with a limit of detection of 2.14 μg L⁻¹ using SWAdSV at pH 10.0.     

Speciation analysis of chromium in water samples using nanometer zirconium dioxide and direct ultrasonic slurry sampling with electrothermal atomic absorption spectrometry

A new analytical procedure for the determination of chromium Cr(III) and Cr(VI) species in different water samples was developed. The method involves solid-phase extraction (SPE), direct ultrasonic slurry sampling (DUSSS), and subsequent electrothermal atomic absorption spectrometry (ETAAS). The nanometer-sized zirconium dioxide (ZrO₂) was used as the sorbent material. The optimal conditions for the proposed solid phase extraction were: 50 mg ZrO₂, 20 min extraction time, pH 2.5 for Cr(VI) and pH 8.0 for Cr(III) and for the ETAAS measurement: 1500°C pyrolysis and 2300°C atomisation temperatures, 1.5 g L^?1 Mg(NO₃)₂ as matrix modifier. The samples were sonicated directly in the autosampler cup, using an ultrasonic probe at 20% power setting for 10 seconds prior to injection into the graphite tube with ?vov platform. In this way, all drawbacks due to the elution procedure were eliminated. The limit of detection and limit of quantification for Cr(III) obtained under optimised conditions were 0.48 μg L^?1, and 1.61 μg L^?1, respectively, and for Cr(VI) 0.27 μg L^?1 and 0.90 μg L^?1. The pre-concentration factors attained for both the species were 25. The effects of alkaline, alkaline earth and some metal ions and some anions were also examined. The relative standard deviation estimated from six replicate measurements at a concentration of 0.4 μg L^?1 for both Cr(III) and Cr(VI) with a pre-concentration factor of 25 was 2.96% and 4.06%, respectively. The accuracy of the method was confirmed by analysis of the standard reference material SRM 1643e “Trace Elements in Water?. The proposed technique is simple, sensitive, environmentally friendly, and the risk of contamination is low. Hence, it was successfully applied to spiked synthetic and real water samples with recoveries ranging from 91.3% to 109.2%