Dispersive micro solid phase extraction of glibenclamide from plasma, urine, and wastewater using a magnetic molecularly imprinted polymer followed by its determination by a high-performance liquid chromatography-photodiode array detector.

The present study describes the development of a simple and selective analytical method for dispersive micro solid phase extraction and determination of glibenclamide (GLB) using magnetic molecularly imprinted polymer (MMIP) as a sorbent. MMIP was fabricated by the non-covalent method on the surface of silicated Fe3O4 and had a high affinity for glibenclamide; dual monomers, itaconic acid and allylamine, were used for this. Polymerization was achieved by the precipitation method in the presence of glibenclamide as the template and ethylene glycol dimethacrylate as the cross-linker. The morphology and structural properties of the MMIP were characterized by different analytical methods. To achieve maximum extraction efficiency, influencing parameters were optimized. The linearity range was 1-2000 and 12-2000 µg L-1 by high-performance liquid chromatography-photodiode array detector (HPLC-PDA) and UV-vis spectroscopy, respectively. The detection and quantification limits with UV-vis and HPLC-PDA analyses were 4 and 12 µg L-1 and 0.3 and 1 µg L-1, respectively. Under optimized conditions, recovery of glibenclamide spiked in plasma, human urine, and wastewater was between 89.4 and 102.9% at the concentration levels of 25, 250, and 500 µg L-1; relative standard deviations were below 3.7% by HPLC-PDA. The developed method has a favorable pre-concentration factor of 140.0. Equilibrium data and sorption isotherms fitted well with the Langmuir model. A maximum sorption capacity of 24.260 mg g-1 was acquired based on the Langmuir model. The synthesized sorbent with high selectivity was used to separate GLB from complex biological systems and wastewater before measurement with UV-vis or HPLC-PDA.

Polyamidoamine with a hyper-branched structure grafted on modified magnetic graphene oxide for the trace separation of diclofenac and acetaminophen followed by high-performance liquid chromatography determination.

Different generations of polyamidoamine dendrimers were synthesized on a focal core of magnetic graphene oxide modified with 3-aminopropyltriethoxysilane. After the characterization of synthesized dendrimers, its second generation was employed as a suitable sorbent for simultaneous separation/preconcentration of diclofenac and acetaminophen by a dispersive magnetic solid phase microextraction. The extracted analytes were then quantified by high-performance liquid chromatography with ultraviolet detection. Under optimized conditions, the limits of detection were 0.3 µg/L for diclofenac and 0.1 µg/L for acetaminophen. The intra-day relative standard deviations at 50 µg L-1 levels were 1.8% for diclofenac and 2.1% for acetaminophen, while the inter-day relative standard deviations were 3.6% and 4.5% for diclofenac and acetaminophen, respectively. The calibration graphs were linear in ranges of 1.0-500.0 µg/L and 0.5-600.0 µg/L for diclofenac and acetaminophen, respectively, with good coefficients of determination (r2 > 0.998). The method was successfully applied to the determination of diclofenac and acetaminophen in water, milk, and biological samples.

Synthesis of magnetic molecular imprinted polymer with a new functional monomer for dispersive micro solid phase extraction of captopril from wastewater and biological samples and determination by UV-Vis spectrophotometry.

A magnetic molecularly imprinted polymer (MMIP) was fabricated for captopril by surface polymerization of Fe3O4@SiO2 nanoparticles using a new functional monomer of N-(allylcarbamothioyl)-2-chlorobenzamide. It was then employed as a selective nanosorbent for dispersive magnetic micro solid phase extraction (DM-µ-SPE) of captopril from biological and wastewater samples. To characterize the physicochemical properties of the MMIP, different analytical methods such as the vibrating sample magnetometer, field emission scanning electron microscopy, Brunauer-Emmett-Teller, and Fourier transform infrared spectroscopy were utilized. To gain the maximum extraction recovery of captopril, the influence of various operating conditions was investigated and experimental settings optimized. After the extraction step, the concentration of captopril was measured by UV-Vis spectrophotometer at 245 nm. The assessments demonstrated that the MMIP provides higher extraction efficiency in comparison to magnetic non-imprinted polymer, suggesting the establishment of selective recognition binding sites at the MMIP surface. The method depicted desirable figures of merit of a low detection limit of 0.16 µg L-1, a limit of quantification of 0.50 µg L-1, a linear dynamic range of 0.50-22.0 µg L-1, and an acceptable preconcentration factor of 333. The magnetic MIP was successfully employed for preconcentration and extraction of trace amounts of captopril in real samples, such as human blood serum, urine, and wastewater samples, with recoveries in the range 95.7 to 102.6% and relative standard deviations < 5%.

A Selective Fluorescent Nanoprobe Based on Graphene Quantum Dots and Hg2+ for the Determination of Tetracycline in Biological Samples.

A simple, sensitive, and selective fluorometric method based on graphene quantum dots and Hg2+ is presented for the determination of tetracycline. The fluorescence emission of graphene quantum dots at 463 nm decreased in the presence of Hg2+ ions due to its electrostatic interaction with the negatively charged surface of quantum dots at pH = 8.0. The addition of tetracycline to this system resulted in the retrieval of the fluorescence emission of the graphene quantum dots proportional to the tetracycline concentration. This is because of the interaction between tetracycline and Hg2+ that results in the release of the quantum dots' surface. Under the optimized conditions, the calibration curve indicated good linearity in the range of 2.0-44.0 nmol L-1 with a detection limit of 0.52 nmol L-1 for tetracycline. The designed nanoprobe was capable of the determination of tetracycline in serum and urine samples.

Selective and Sensitive Fluorometric Determination of Piroxicam Based on Nitrogen-doped Graphene Quantum Dots and Gold Nanoparticles Coated with Phenylalanine.

In this study, a sensitive fluorimetric method is proposed for the determination of piroxicam using nitrogen graphene quantum dots (N-GQDs) and gold nanoparticles coated with phenylalanine. The fluorescence emission of N-GQDs at 440 nm decreases with the increase of gold nanoparticles coated with phenylalanine. However, the addition of piroxicam causes the release of gold nanoparticles from the surface of quantum dots followed by the retrieval of the fluorescence emission of N-GQDs. Under the optimum conditions, the calibration graph was linear in the concentration range of 2.0-35.0 nmol L-1 for piroxicam with a limit of detection of 0.11 nmol L-1. The developed method was successfully applied for the determination of piroxicam in urine and serum samples.

Chemiluminescence determination of dopamine using N, P-graphene quantum dots after preconcentration on magnetic oxidized nanocellulose modified with graphene quantum dots.

A novel sorbent consisting of magnetic oxidized nanocelluloses modified with graphene quantum dots was prepared and used for the separation and preconcentration of dopamine. The eluted dopamine from the sorbent was determined by a designed chemiluminescence system containing luminol, H2O2, Fe3+, and graphene quantum dots doped with nitrogen and phosphorus. Graphene quantum dots cause an increase in the intensity of the chemiluminescence system of luminol-H2O2, but the presence of Fe3+ ions in this system decreases its intensity because of the sorption of the Fe3+ ions on the surface of P, N-graphene quantum dots. However, the addition of dopamine resulted in the retrieval of P, N-graphene quantum dots, as well as the chemiluminescence intensity, due to the formation of its complex with Fe3+. The sorbent made of magnetic oxidized nanocelluloses modified with graphene quantum dots was characterized by various analytical techniques, and the effective parameters on the extraction of dopamine were investigated and optimized. Under the optimized conditions, the method displayed good linearity in the concentration range 0.25-17.5 µg L-1 for dopamine (R2 = 0.9918) with a limit of detection of 0.054 µg L-1. The intra- and inter-day relative standard deviations at a 10.0 µg L-1 concentration level of dopamine (n = 6) were 2.6 and 4.1%, respectively. This method was successfully applied to the extraction and determination of dopamine in human serum and urine samples.

Determination of lamotrigine by fluorescence quenching of N-doped graphene quantum dots after its solid-phase extraction using magnetic graphene oxide.

A sensitive fluorescent nanoprobe is reported for the determination of lamotrigine after its preconcentration by magnetic graphene oxide nanocomposite. The fluorescent nanoprobe is based on the quenching effect of lamotrigine on the nitrogen graphene quantum dots fluorescence at 440 nm, through strong hydrogen bonding. Under optimum conditions, the quenching fluorescent intensity of nitrogen graphene quantum dots shows linearity with the lamotrigine concentration in the range of 2.0-45.0 µg L-1, limits of detection (LOD), and quantification of 0.39 and 1.28 µg L-1 respectively. The parameters affecting the extraction and determination of lamotrigine were optimized via the central composite design (CCD) and one at the time method, respectively. The developed method was successfully employed for the extraction and quantification of lamotrigine in biological samples.

Fabrication of a sensitive colorimetric nanosensor for determination of cysteine in human serum and urine samples based on magnetic-sulfur, nitrogen graphene quantum dots as a selective platform and Au nanoparticles.

A novel colorimetric nanosensor is reported for the selective and sensitive determination of cysteine using magnetic-sulfur, nitrogen graphene quantum dots (Fe3O4/S, N-GQDs), and gold nanoparticles (Au NPs). Thus, S, N-GQDs was firstly immobilized on Fe3O4 nanoparticles through its magnetization in the presence of Fe3+ in the alkali solution. The prepared Fe3O4/S, N-GQDs were dispersed in cysteine solution resulting in its quick adsorption on the surface of the Fe3O4/S, N-GQDs through hydrogen bonding interaction. Then, Au NPs solution was added to this mixture that after a short time, the color of Au NPs changed from red to blue, the intensity of surface plasmon resonance peak of Au NPs at 530 nm decreased, and a new peak at a higher wavelength of 680 nm appeared. The effective parameters on cysteine quantification were optimized via response surface methodology using the central composite design. Under optimum conditions, the absorbance ratio (A680/A530) has a linear proportionality with cysteine concentration in the range of 0.04-1.20 µmol L-1 with a limit of detection of 0.009 µmol L-1. The fabrication of the reported nanosensor is simple, fast, and is capable of efficient quantification of ultra traces of cysteine in human serum and urine real samples.

Carbon dots doped by nitrogen and sulfur for dual-mode colorimetric and fluorometric determination of Fe3+ and histidine and intracellular imaging of Fe3+ in living cells.

The first dual-modality highly intensive fluorescent and colorimetric nanoprobe for Fe3+ ions and histidine is reported. The carbon dots doped by nitrogen and sulfur (N,S-CDs) prepared by the one-pot hydrothermal method have an excitation/emission wavelength of 320/420 nm with 56% quantum yield. N,S-CDs exhibit strong visible fluorescence with high stability at pH ~ 7.0. The fluorescence intensity of the N,S-CDs is quenched in the presence of Fe3+ ions which are recovered upon the addition of histidine. The addition of Fe3+ ions also induces a color change from yellow to red. Using colorimetric determination, Fe3+ and histidine exhibited linearity in the range 75-675 and 100-375 µmol L-1, respectively, while with fluorometric determinations the dynamic range was 0.1-275 and 0.1-3 µmol L-1 for Fe3+ and histidine, respectively. The limits of detection were 19 nmol L-1 and 0.03 µmol L-1 using fluorometry and 20 µmol L-1 and 24.2 µmol L-1 using colorimetry, for Fe3+ and histidine respectively. The relative standard deviations (n = 5) for Fe3+ (10 µmol L-1) and histidine (1 µmol L-1) using fluorometry were 4.6 and 7.3% and using colorimetry at 100 µmol L-1 of Fe3+ and 150 µmol L-1 of histidine were 3.2 and 5.6%, respectively. The developed fluorometric method was applied for the determination of Fe3+ and histidine in various foods and biological fluid samples as well as intracellular imaging of iron. The accuracy of the method for iron determination was confirmed by the analysis of certified reference materials (wheat flour, tomato leaves, and whole milk powder) and quality control materials (whole milk powder, serum, and urine), whereas for histidine, the accuracy was determined by recovery experiment and independent analysis. Good recovery values in ranges of 92-96% and 94-98% were achieved for Fe3+ and histidine, respectively. Graphical abstract.

Selective fluorometric determination of sulfadiazine based on the growth of silver nanoparticles on graphene quantum dots.

A sensitive fluorometric assay is described for the direct determination of the antibiotic sulfadiazine. Silver nanoparticles placed on graphene quantum dots (Ag NP-GQDs) were synthesized by reduction of AgNO3 with sodium borohydride in the presence of GQDs. The growth of Ag NPs on the surface of the GQDs causes quenching of the blue fluorescence of the GQDs with an emission maximum at 470 nm by surface-enhanced energy transfer. If sulfadiazine is added, it interacts with Ag NPs and fluorescence is restored. Under optimal conditions, the fluorescence increases linearly in the sulfadiazine concentration range of 0.04-22.0 µM. The detection limit is 10 nM with relative standard deviations of 2.3 and 4.2 (at 10 µM of sulfadiazine; for n = 6) for intra- and inter-day assays. Graphical abstractSchematic representation of sulfadiazine determination using Ag NP-GQDs as a fluorescent nanoprobe.

Surface molecularly imprinted polymer on magnetic multi-walled carbon nanotubes for selective recognition and preconcentration of metformin in biological fluids prior to its sensitive chemiluminescence determination: Central composite design optimization.

Novel molecularly imprinted polymer (MIP) for metformin was synthesized on the surface of magnetic multi-walled carbon nanotubes (MMWCNTs) as the support. Metformin was used as the template, methacrylic acid (MAA) as the functional monomer, ethylene glycol dimethacrylate (EGDMA) as the cross-linker and 2,2'-azoisobutyronitrile (AIBN) as the initiator. The synthesized composite was characterized by field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), vibrating sample magnetometer (VSM), and Fourier transform infrared spectroscopy (FTIR). The surface molecularly imprinted composite was used for magnetic solid phase microextraction (MSPME) of metformin before its chemiluminescence (CL) determination and its capability was compared with non-imprinted polymer (NIP). The central composite design was used for optimization as well as consideration of possible interaction of effective variables on extraction. Under the optimized conditions, the developed method exhibited the linear dynamic range of 0.5-50.0 µg L-1 with a detection limit of 0.13 µg L-1 and enhancement factor of 195.3 for the preconcentration of 100 mL of the sample and 500 µL of an eluent. The intra- and inter-day relative standard deviations (RSD%) at 5.0 µg L-1 level of metformin (n = 6) were 3.7 and 4.9%, respectively. The maximum adsorption capacity of the sorbent was found to be 80.0 mg g-1, the adsorption of metformin was endothermic and spontaneous and followed the Langmuir isotherm model. The adsorption kinetic was also found to be best fitted with the pseudo-second-order model. The designed method was successfully applied to the extraction and determination of metformin in biological fluids and water samples.

Non-enzymatic sensing of dopamine by localized surface plasmon resonance using carbon dots-functionalized gold nanoparticles.

A highly selective, sensitive, and rapid colorimetric sensor for the determination of dopamine (DA) was developed using the color change of S-doped carbon dots functionalized gold nanoparticles (S-CDs@Au NPs). The base of the method is the formation of a complex between the amine groups of dopamine with carboxylic groups of S-CDs@Au NPs followed by their aggregation with Fe3+ ions which acts as the linkers causing a red shift from 520 to 670 nm in the localized surface plasmon peak of S-CDs@Au NPs. The ratio of absorbance intensity at 670 nm to 520 nm was monitored as the analytical signal for determination of dopamine. The parameters affecting the analytical signal including reaction time, solution pH, the concentration of Au NPs and concentration of Fe3+ were optimized. At optimized conditions, the calibration curve was linear in the concentration range of 0.81-16.80 µM of dopamine. The detection and quantification limits were 0.23 µM and 0.77 µM, respectively. The intra-day and inter-day relative standard deviation (RSDs) at 5.0 µM of DA were 3.9% and 5.6%, respectively (n = 5). The applicability of the method for determination of DA in dopamine ampoule, urine and serum human samples was investigated.

Modified dispersive liquid-phase microextraction based on sequential injection solidified floating organic drop combined with HPLC for the determination of phenobarbital and phenytoin.

A modified dispersive liquid phase microextraction based on sequential injection solidified floating organic drop was developed for simultaneous separation/preconcentration of trace amounts of phenobarbital and phenytoin. The important factors affecting on the extraction recovery including pH, the volume of extraction solvent, ionic strength, and the number of injections were investigated and optimized by Box-Behnken design and desirability function. Under the optimum experimental conditions, the calibration graph was linear in the concentration range of 1.0-300.0 µg/L (r2  = 0.997) for phenobarbital and 2.0-400.0 µg/L (r2  = 0.996) for phenytoin. The limit of detection and limit of quantification were 0.35 and 1.2 µg/L for phenobarbital and 0.65 and 2.2 µg/L for phenytoin, respectively. The relative standard deviation for six replicate determinations at 10 µg/L was 3.3 and 4.1% for phenobarbital and phenytoin, respectively. The developed method was successfully applied to the determination of phenobarbital and phenytoin in urine and plasma samples.

Synthesis, characterization, and application of a Zn (II)-imprinted polymer grafted on graphene oxide/magnetic chitosan nanocomposite for selective extraction of zinc ions from different food samples.

A novel Zn(II) imprinted polymer was synthesized via a co-precipitation method using graphene oxide/magnetic chitosan nanocomposite as supporting material. The synthesized imprinted polymer was characterized by Fourier transform infrared spectrometry (FTIR) and scanning electron microscopy (SEM) and applied as a sorbent for selective magnetic solid phase extraction of zinc followed by its determination by flame atomic absorption spectrometry. The kinetic and isothermal adsorption experiments were carried out and all parameters affecting the extraction process was optimized. Under the optimal experimental conditions, the developed procedure exhibits a linear dynamic range of 0.5-5.0µgL-1 with a detection limit of 0.09µgL-1 and quantification limit of 0.3µgL-1. The maximum sorption capacity of the sorbent was found to be 71.4mgg-1. The developed procedure was successfully applied to the selective extraction and determination of zinc in various samples including well water, drinking water, black tea, rice, and milk.

Indirect spectrophotometric determination of sulfadiazine based on localized surface plasmon resonance peak of silver nanoparticles after cloud point extraction.

A novel, efficient, easy to use, environmentally friendly and cost-effective methodology is developed for the indirect spectrophotometric determination of sulfadiazine in different samples. The method is based on the micelle-mediated extraction of silver sulfadiazine and converting the silver content of the resultant surfactant-rich phase to the silver nanoparticles via generation of [Ag(NH3)2]+ followed by its chemical reduction using ascorbic acid. The changes in the amplitude of localized surface plasmon resonance peak of silver nanoparticles as a function of sulfadiazine concentration in the sample solution was monitored using fiber optic linear array spectrophotometry at 457nm. The experimental conditions were thoroughly investigated and optimized. Under the optimized condition, the developed procedure showed dynamic linear calibration within the range of 10.0-800.0µgL-1 with a detection limit of 2.8µgL-1 for sulfadiazine. The relative standard deviation of the method for six replicate measurements at 150.0µgL-1 of sulfadiazine was 4.7%. The developed method was successfully applied to the determination of sulfadiazine in different samples including well water, human urine, milk and pharmaceutical formulation.

Preparation of magnetic mesoporous silica composite for the solid-phase microextraction of diazinon and malathion before their determination by high-performance liquid chromatography.

A novel magnetic mesoporous silica material was synthesized and used as the sorbent for the magnetic solid-phase microextraction of diazinon and malathion before their quantification by high-performance liquid chromatography with UV detection. The sorbent was synthesized by a surfactant-templated one-pot sol-gel procedure using SiO2 -coated Fe3 O4 as the magnetic support, cetyltrimethylammonium bromide as the template and tetraethyl orthosilicate as the silicon source. The characteristics of the prepared sorbent were investigated using Fourier transform infrared spectroscopy, scanning electron microscopy, and X-ray diffraction. The sorbent exhibited a high maximum adsorption capacity of 19.2 and 9.4 mg/g for diazinon and malathion, respectively. The parameters affecting the microextraction were optimized by the MultiSimplex method. Under the optimized conditions, the calibration graphs were linear in the concentration ranges of 0.3-50.0 and 0.5-50 µg/L with the limits of detection of 0.09 and 0.14 µg/L for diazinon and malathion, respectively. The relative standard deviations (n = 5) at a concentration level of 10.0 µg/L of analytes were less than 2.5 and 4% for intra and interday, respectively. The developed method was successfully used for the determination of diazinon and malathion in apple, tomato, cucumber, tap water, and well water samples.

Application of graphene oxide-silica composite reinforced hollow fibers as a novel device for pseudo-stir bar solid phase microextraction of sulfadiazine in different matrices prior to its spectrophotometric determination.

This study presents a novel, simple and efficient pseudo-stir bar solid phase microextraction method for separation and preconcentration of sulfadiazine. To develop the method, a graphene oxide-silica composite reinforced hollow fiber was prepared via sol-gel technology and used as a novel device to extract sulfadiazine. The retained sulfadiazine was eluted using 180µL of methanol/acetic acid (6:4) and quantified by fiber optic linear array spectrophotometry based on the formation of its azo dye with thenoyltrifluoroacetone. Under optimized conditions, the method exhibited a linear dynamic range of 5-150µgL-1 with a detection limit of 1.5µgL-1 and an enrichment factor of 100. The relative standard deviations of 2.9% and 5.8% (n=6) were obtained at 60µgL-1 level of sulfadiazine for intra- and inter-day analysis respectively. The method was successfully applied to determine sulfadiazine in honey, milk, human urine and environmental water samples.

Simultaneous extraction and determination of albendazole and triclabendazole by a novel syringe to syringe dispersive liquid phase microextraction-solidified floating organic drop combined with high performance liquid chromatography.

A syringe to syringe dispersive liquid phase microextraction-solidified floating organic drop was introduced and used for the simultaneous extraction of trace amounts of albendazole and triclabendazole from different matrices. The extracted analytes were determined by high performance liquid chromatography along with fluorescence detection. The analytical parameters affecting the microextraction efficiency including the nature and volume of the extraction solvent, sample volume, sample pH, ionic strength and the cycles of extraction were optimized. The calibration curves were linear in the range of 0.1-30.0 µg L(-1) and 0.2-30.0 µg L(-1) with determination coefficients of 0.9999 and 0.9998 for albendazole and triclabendazole respectively. The detection limits defined as three folds of the signal to noise ratio were found to be 0.02 µg L(-1) for albendazole and 0.06 µg L(-1) for triclabendazole. The inter-day and intra-day precision (RSD%) for both analytes at three concentration levels (0.5, 2.0 and 10.0 µg L(-1)) were in the range of 6.3-10.1% and 5.0-7.5% respectively. The developed method was successfully applied to determine albendazole and triclabendazole in water, cow milk, honey, and urine samples.

Simultaneous extraction and quantification of albendazole and triclabendazole using vortex-assisted hollow-fiber liquid-phase microextraction combined with high-performance liquid chromatography.

A novel, simple, and rapid vortex-assisted hollow-fiber liquid-phase microextraction method was developed for the simultaneous extraction of albendazole and triclabendazole from various matrices before their determination by high-performance liquid chromatography with fluorescence detection. Several factors influencing the microextraction efficiency including sample pH, nature and volume of extraction solvent, ionic strength, vortex time, and sample volume were investigated and optimized. Under the optimal conditions, the limits of detection were 0.08 and 0.12 µg/L for albendazole and triclabendazole, respectively. The calibration curves were linear in the concentration ranges of 0.3-50.0 and 0.4-50.0 µg/L with the coefficients of determination of 0.9999 and 0.9995 for albendazole and triclabendazole, respectively. The interday and intraday relative standard deviations for albendazole and triclabendazole at three concentration levels (1.0, 10.0, and 30.0 µg/L) were in the range of 6.0-11.0 and 5.0-7.9%, respectively. The developed method was successfully applied to determine albendazole and triclabendazole in water, milk, honey, and urine samples.

Synthesis and application of a nanoporous ion-imprinted polymer for the separation and preconcentration of trace amounts of vanadium from food samples before determination by electrothermal atomic absorption spectrometry.

A vanadium ion-imprinted polymer was synthesized in the presence of V(V) and N-benzoyl-N-phenyl hydroxyl amine using 4-vinyl pyridine as the monomer, ethylene glycol dimethacrylate as the cross linker and 2,2'-azobis(isobutyronitrile) as the initiator. The imprinted V(V) ions were completely removed by leaching the polymer with 5 mol/L nitric acid, and the polymer structure was characterized by Fourier transform infrared spectroscopy and scanning electron microscopy. The ion-imprinted polymer was used as the sorbent in the development of the solid-phase extraction method for V(V) prior to its determination by electrothermal atomic absorption spectrometry. The maximum sorption capacity for V(V) ions was 26.7 mg/g at pH 4.0. Under the optimum conditions, for a sample volume of 150.0 mL, an enrichment factor of 289.0 and a detection limit of 6.4 ng/L were obtained. The developed method was successfully applied to the determination of vanadium in parsley, zucchini, black tea, rice, and water samples.