Minimization of mass interferences in quadrupole inductively coupled plasma mass spectrometric (ICP-MS) determination of palladium using a flow injection on-line displacement solid-phase extraction protocol

A flow injection on-line displacement solid-phase extraction protocol was employed to minimize mass interferences with determination of palladium by inductively coupled plasma mass spectrometry (ICP-MS). The developed method involved in on-line complexing of Ag⁺ with pyrrolidine dithiocarbamate (PDC), presorption of the resultant Ag–PDC onto a microcolumn packed with the cigarette filter, displacement sorption of Pd²⁺ through loading the sample solution onto the microcolumn due to on-line displacement reaction between Pd²⁺ and the presorbed Ag–PDC, elution of the retained Pd²⁺ with 50 μL of ethanol for on-line ICP-MS detection. Interferences from co-existing heavy metal ions with lower stability of their PDC complexes relative to Ag–PDC were minimized/eliminated. No interferences from 5 mg L^− 1 Zn and 3 mg L^− 1 Pb for ¹⁰⁴Pd, 0.4 mg L^− 1 Cu for ¹⁰⁵Pd, 6 mg L^− 1 Zn and 2 mg L^− 1 Cd for ¹⁰⁶Pd, 6 mg L^− 1 Zn and 3 mg L^− 1 Cd for ¹⁰⁸Pd, and 2 mg L^− 1 Cd for ¹¹⁰Pd were observed for the determination of 100 ng L^− 1 Pd. The enhancement factors of 71–75, sample throughput of 23 samples h^− 1 and detection limits of 2.8–3.5 ng L^− 1 were achieved with the consumption of 3.0 mL of sample solution. The precision (RSD) for eleven replicate determinations of Pd at the 100 ng L^− 1 level was 1.8–2.7%. The developed method was applied to the determination of palladium in rock samples.     

A Novel Method of High Sensitive Determination of Prednisolone on Renewable Mercury Film Silver Based Electrode

Fast and sensitive method of prednisolone determination at renewable mercury film electrode using differential pulse adsorptive stripping voltammetry (DPAdSV) was successfully developed. The effects of various factors such as: preconcentration potential and time, pulse height, step potential and supporting electrolyte composition were optimized. A linear voltammetric response for analyte was obtained in the concentration range from 0.05 µmol L⁻¹ (18 µg L⁻¹) to 2.25 µmol L⁻¹ (0.81 mg L⁻¹), with a detection limit of 0.01 µmol L⁻¹ for preconcentration time of 20 s. Repeatability of method was determined as RSD % for prednisolone concentration of 0.04 µmol L⁻¹ as 1.6 % (n=9). The proposed method was successfully applied and validated by recovery parameter of prednisolone in simulated sample and pharmaceutical product.     

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.     

Visible Light Photoelectrochemical Sensor for Acetaminophen Determination using a Glassy Carbon Electrode Modified with BiVO4 Nanoparticles

A new and simple photoelectrochemical (PEC) sensor using a glassy carbon electrode (GCE) modified with bismuth vanadate (BiVO₄) nanoparticles and dihexadecyl phosphate (DHP) film was useful for acetaminophen (AC) determination. In 0.2 mol L⁻¹ phosphate buffer (pH=9), the GCE without modification exhibited the smaller photocurrent (0.86 μA) when compared with GCE modified with 1.0 mg mL⁻¹ or 2.0 mg mL⁻¹ BiVO₄ nanoparticles suspension (5.9 and 34 μA, respectively). Based on the photocurrent signal generated through the interaction between GCE, BiVO₄ and the energy of visible light a chronoamperometric method for AC determination was developed. The AC linear range concentration from 0.099 to 0.99 μmol L⁻¹ and limits of detection and quantification of 0.027 and 0.091 μmol L⁻¹, respectively, was obtained. The proposed method was applied to the AC determination in commercial drugs and tap water with satisfactory accuracy and precision. Moreover, the PEC construction was easy and had a short response time, which might confer higher sample throughput for the method.     

Therapeutic drug monitoring of mitotane: Analytical assay and patient follow‐up

Adrenocortical carcinoma (ACC) is an aggressive malignancy of the adrenal gland. Mitotane (o ,p' ‐DDD) is the most effective chemotherapy for ACC. According to the literature, mitotane plasma trough concentrations within 14–20 mg L⁻¹ are correlated with a higher response rate with acceptable toxicity. Therapeutic drug monitoring (TDM) of mitotane is therefore recommended. The aim of this study was to propose a robust and simple method for mitotane quantification in plasma. The validation procedures were based on international guidelines. Sample preparation consisted of a single protein precipitation with methanol using 100 μL of plasma. The supernatant was submitted to liquid chromatography coupled with ultra‐violet detection at 230 nm. Mitotane retention time was 7.1 min. The limit of detection was 0.1 mg L⁻¹ and the limit of quantification was 0.78 mg L⁻¹. The assay demonstrated a linear range of 0.78–25 mg L⁻¹ with correlation coefficients (r ²) at 0.999. Inter‐ and intra‐assay precision was <4.85%. Evaluation of accuracy showed a deviation <13.69% from target concentration at each quality control level. This method proved easy and rapid to perform mitotane TDM and required a small volume of sample. It was successfully applied to routine TDM in our laboratory.     

Electrochemical Sensor for Selective Detection of Meldonium in Urine by Voltammetry

A highly sensitive electrochemical sensor based on arenediazonium tosylates was designed to detect meldonium in urine. The effect of the concentration of ArN2⁺OTs⁻ arenediazonium tosylate modifier and various substituents was studied. Basic operating parameters for voltammetric meldonium detection were established and the procedure for urine sample preparation was developed. The following values were obtained: limit of detection (LOD) 0.005 mg ⋅ L⁻¹ (P=0.95) and limit of quantification (LOQ) 0.01 mg ⋅ L⁻¹. The relationship between the analytical signal and meldonium concentration in the solution ranging from 0.01 to 400 mg ⋅ L⁻¹ was described by a linear function. The meldonium concentration error did not exceed 18 %. The analysis time for a single urine sample was reduced to 15 minutes.     

Simultaneous Analysis of Isoniazid and Its Impurities by CZE

An alternative methodology for simultaneous determination of isoniazid, isonicotinic acid, 4-cyanopyridine, ethyl isonicotinate and isonicotinamide by capillary zone electrophoresis, within an analysis time of 11 min, is proposed. An electrolyte composed by 50 mmol L⁻¹ of acetic acid/sodium acetate buffer and 12.5 mmol L⁻¹ of Cu²⁺, an analyte dilution in 1 mmol L⁻¹ of Brij 35 and 12.5 mmol L⁻¹ of Cu²⁺ and +20 kV voltage were optimized. After evaluating some figures of merit, such as linearity, precision, recovery and quantification limit, the method was successfully applied to the isoniazid analysis in tablets. The contents found were 99.3 mg of isoniazid and 0.3 mg of isonicotinic acid, corresponding to 0.3 % of impurity regarding the content of the active ingredient in the pharmaceutical formulation.

     

Development and Application of a Voltammetric Biosensor Based on Polypyrrole/uricase/graphene for Uric Acid Determination

In the present paper a voltammetric biosensor based on platinum electrode and polypyrrole / uricase / graphene composite, named Pt‐PPy/UOx/Grap has been successfully prepared and validated for uric acid (UA) determination in real samples. The electrochemical behavior has been evaluated by employing cyclic voltammetric. The charge transfer coefficient, α, and the charge transfer rate constant, κs, for electron transfer between PPy/UOx/Grap and Pt were calculated as 0.71, in average, and 48.3 s⁻¹, respectively. Under optimized conditions for the composite (2.5 U mL⁻¹ of UOx, 0.3 mg mL⁻¹ of Grap and 2.9 mmol L⁻¹ of pyrrole) and for the analysis (pH 7.0 in 0.1 mol L⁻¹ phosphate buffer) the method was validated for UA determination at human urine and showed good linearity to UA from 2 up to 24 nmol L⁻¹ (r=0.993) with limits of detection and quantification of 0.541 and 1.805 nmol L⁻¹, respectively. The results obtained for the UA determination at urine presented a relative error lower than 5 %, showing the good performance of the method developed and potential application in UA clinical analysis.     

Voltammetric Detection of Aqueous Glyphosate on a Copper and Poly(Pyrrole)-electromodified Activated Carbon Fiber

Aqueous glyphosate (GLYP) was voltammetrically detected using a Cu-(poly)pyrrole composite electrochemically deposited on activated carbon fiber for the first time in a single-step method. Differential pulse voltammetry indicated good linearity (R² = 0.9902) in the response over 0.02–12 mg L⁻¹ range, with a low limit of detection (0.01 mg L⁻¹). The sensor exhibited reproducibility for soil and fruit samples (RSD values = 2.41 and 3.87%, respectively). The response showed repeatability over 100 consecutive measurements. The response was also unaffected by the interfering substances containing the same functional groups as in GLYP and its metabolite. The method described in this study is facile.     

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).     

Voltammetric Detection of Ethinylestradiol in Water and Synthetic Urine Samples using a Ni(II) Phthalocyanine/Iron Oxide Nanocomposite Electrode

A novel nickel phthalocyanine/iron oxide nanoparticle (NiTsPc/ION) nanocomposite electrode is proposed for the voltammetric detection of ethinyl estradiol. The method shows a wide linear range (0.07–30 μmol L⁻¹, R² >0.99), sensitivity of 0.308 μA cm⁻²/μmol L⁻¹ and limit of detection of 7.8 nmol L⁻¹ (3.3 Sb/b). Recoveries are above 95 % for quantification in tap and treatment plant water samples and synthetic urine. A single electrode can be used in seven consecutive runs (RSD=2.85 %) and responses of different electrodes vary only 7–9 %. The excellent sensing performance of the proposed sensor is ascribed to its porous morphology and efficient charge-transfer between ION and NiTsPc.     

A New Approach for the Voltammetric Determination of Amoxicillin in the Dosage Form Using Azo Coupling Reaction with Sulphanilamide

The novel method of amoxicillin (AM) determination has been developed using single-sweep polarography. The proposed method is based on the obtaining of yellow coloured azo compound due to azo coupling reaction of previous diazotized sulphanilamide (SA) (in the medium of 0.6 M hydrochloric acid) with amoxicillin at pH=9.0 with the further reduction of the formed analytical form on a dropping mercury electrode. Voltammetric determination of amoxicillin is carried out due to the reduction peak of azo group of the obtained azo compound in the presence of 0.05 mol ⋅ L⁻¹ Na₂B₄O₇ as a background electrolyte at the potential E_c^p2=−0.55 V and potential sweep rate of 2.5 V ⋅ s⁻¹. The developed voltammetric method has two linear ranges of the determined concentrations (0.05–2.0) ⋅ 10⁻⁵ mol ⋅ L⁻¹ and (0.2–1.0) ⋅ 10⁻⁴ mol ⋅ L⁻¹ and the high sensitivity: LOD without the removing of unreacted sodium nitrite is 1.1 ⋅ 10⁻⁶ mol ⋅ L⁻¹, and 7.2 ⋅ 10⁻⁷ mol ⋅ L⁻¹, when NaNO₂ excess is removed using urea. The developed voltammetric technique of AM determination has been approved during the analyses of tablets and oral suspension.     

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.     

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.     

Voltammetric Method for the Simultaneous Determination of Melatonin and Pyridoxine in Dietary Supplements Using a Cathodically Pretreated Boron‐doped Diamond Electrode

The simultaneous voltammetric determination of melatonin (MT) and pyridoxine (PY) has been carried out at a cathodically pretreated boron‐doped diamond electrode. By using cyclic voltammetry, a separation of the oxidation peak potentials of both compounds present in mixture was about 0.47 V in Britton‐Robinson buffer, pH 2. The results obtained by square‐wave voltammetry allowed a method to be developed for determination of MT and PY simultaneously in the ranges 1–100 μg mL⁻¹ (4.3×10⁻⁶–4.3×10⁻⁴ mol L⁻¹) and 10–175 μg mL⁻¹ (4.9×10⁻⁵–8.5×10⁻⁴ mol L⁻¹), with detection limits of 0.14 μg mL⁻¹ (6.0×10⁻⁷ mol L⁻¹) and 1.35 μg mL⁻¹ (6.6×10⁻⁶ mol L⁻¹), respectively. The proposed method was successfully to the dietary supplements samples containing these compounds for health‐caring purposes.     

Amperometric detection of indapamide on glassy carbon electrode

This work describes the development of a fast, precise and reliable voltammetric method for the quantification of indapamide, an orally active diuretic sulfonamide used for hypertensive treatment. This compound acts inhibiting sodium reabsorption and increasing the elimination of water. This characteristic was responsible for its banishment by the International Olympic Committee since 1999. The study begins by finding an adequate potential range (−0.20 to 0.30 V) to avoid poisoning the working glassy carbon electrode (GCE) in phosphate buffer 0.10 mol L⁻¹ (pH=12.0). Utilizing flow injection analysis, linear responses between 2.0 × 10⁻⁶ mol L⁻¹ to 2.5 × 10⁻⁵ mol L⁻¹ of indapamide (R²=0.995), and detection limit (LOD) 3.0 × 10⁻⁷ mol L⁻¹ were obtained. This method was applied for the quantification of indapamide in tablets and in synthetic urine. The same flow system was used for the analysis of commercial drugs and the response obtained corresponded to 98 % of the concentration indicated on the drug label. These tablets were also analyzed by high performance liquid chromatography (HPLC), obtaining a recovery of 103 % and LOD 4.0 × 10⁻⁷ mol L⁻¹. The velocity of analysis using flow methods compares advantageously to the classical chromatographic methods. For synthetic urine, linear responses were obtained in samples spiked in the region from 5.0 × 10⁻⁶ mol L⁻¹ to 30 × 10⁻⁶ mol L⁻¹ (R²=0.991) and LOD 3.0 × 10⁻⁷ mol L⁻¹.     

MDMA Electrochemical Determination and Behavior at Carbon Screen-printed Electrodes: Cheap Tools for Forensic Applications

This article describes a method that uses Carbon Screen-printed Electrodes (C-SPEs) to detect 3,4 – methylenedioxyamphetamine (MDMA) by Linear Sweep Voltammetry in aqueous medium. Major parameters of this technique were evaluated aiming improve the method sensibility. Amines interference were conducted in order to verify disturbs at the MDMA response. The method obtained a linear response from 1×10⁻⁵ mol L⁻¹ to 1×10⁻⁴ mol L⁻¹ with linear correlation coefficient of 0.996, Amperometric Sensitivity (AS) of 0.025 A×mol⁻¹ L, Limit of Detection (LOD) of 1,83×10⁻⁶ mol L⁻¹, and Limit of Quantification (LOQ) of 6,11×10⁻⁶ mol L⁻¹. The method applicability, reproducibility and reproducibility were carried over inter/intra days tests and its application on seized samples.     

Determination of Cr(VI) by Catalytic Adsorptive Stripping Voltammetry with Application of Nitrilotriacetic Acid as a Masking Agent

A selective and sensitive method for determination of traces of Cr(VI) in the presence of a large excess of Cr(III) by differential pulse catalytic adsorptive stripping voltammetry is presented. For minimization of Cr(III) interference nitrilotriacetic acid was used as a masking agent. The determinations were performed in a flow system. The calibration plot was linear from 1×10⁻¹⁰ to 1×10⁻⁸ mol L⁻¹ for accumulation time 60 s. The relative standard deviation for 3×10⁻⁹ mol L⁻¹ Cr(VI) was 4.1% (n=5). The detection limit for an accumulation time of 60 s was 4×10⁻¹¹ mol L⁻¹. The influence of common foreign ions is also presented. The performance of the method was verified by analysis of certified reference material for Cr(VI) and comparing the results of analyses of natural water samples with those obtained by another accepted electrochemical method.     

Extraction and preconcentration of residual solvents in pharmaceuticals using dynamic headspace–liquid phase microextraction and their determination by gas chromatography–flame ionization detection

The present study describes a microextraction and determination method for analyzing residual solvents in pharmaceutical products using dynamic headspace–liquid phase microextraction technique followed by gas chromatography–flame ionization detection. In this method dimethyl sulfoxide (μL level) placed into a GC liner‐shaped extraction vessel is used as a collection/extraction solvent. Then the liner is exposed to the headspace of a vial containing the sample solution. The effect of different parameters influencing the microextraction procedure including collection/extraction solvent type and its volume, ionic strength, extraction time, extraction temperature and concentration of NaOH solution used in dissolving the studied pharmaceuticals are investigated and optimized. Under the optimum extraction conditions, the method showed wide linear ranges between 0.5 and 5000 mg L⁻¹. The other analytical parameters were obtained in the following ranges: enrichment factors 240–327, extraction recoveries 72–98% and limits of detection 0.1–0.8 mg L⁻¹ in solution and 0.6–3.2 μg g⁻¹ in solid. Relative standard deviations for the extraction of 100 mg L⁻¹ of each analyte were obtained in the ranges of 4–7 and 5–8% for intra ‐ day (n = 6) and inter ‐ day (n = 4) respectively. Finally the target analytes were determined in different samples such as erythromycin, azithromycin, cefalexin, amoxicillin and co‐amoxiclav by the proposed method.     

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.