Strong enhancement of the chemiluminescence of the cerium(IV)-thiosulfate reaction by carbon dots,and its application to the sensitive determination of dopamine

We show that the very weak chemiluminescence (CL) of the Ce(IV)-thiosulfate system is enhanced by a factor of ~150 in the presence of fluorescent carbon dots (C-dots). The C-dots were prepared by a solvothermal method and characterized by fluorescence spectra and transmission electron microscopy. Possible mechanisms that lead to the effect were elucidated by recording fluorescence and CL spectra. It is found that dopamine at even nanomolar levels exerts a diminishing effect on the enhancement of CL. This was exploited to design a method for the determination of dopamine in the concentration range from 2.5 nM to 20 μM, with a limit of detection (at 3 s) of 1.0 nM. Dopamine was determined by this method in spiked human plasma samples with satisfactory results.

Determination of Vitamin A in Infant Milk-Based Formulas and Pharmaceutical Formulations Using Flow Injection with Ce(IV)–Na2SO3 Chemiluminescence Detection

A rapid and simple flow injection (FI) method is reported for the determination of vitamin A (retinol) based on its strong enhancing effect on the Ce(IV)–Na₂SO₃ chemiluminescence (CL) reaction in an acidic solution. The effect of key chemical and physical parameters (i.e., reagent concentrations, flow rate, and sample volume) was optimized and potential interferences examined. Under the selected experimental conditions, a linear calibration was obtained between the CL intensity and vitamin A concentration in the range 0.1–8.0 µg mL^?1 (r ²  = 0.9986, n = 8). The limit of detection (3 s x blank) was 0.01 µg mL^?1 retinol (n = 6) and the relative standard deviation (RSD) for 0.25 µg mL^?1 retinol was 2.3% (n = 10) with a sampling rate of 180 h^?1. The method was successfully applied to infant milk-based formulas and pharmaceutical formulations and the results were not significantly different at 95% confidence interval with those obtained by using a spectrophotometric reference method. The possible CL mechanism is also discussed briefly supporting with UV-visible, fluorescence, and CL spectra.     

Evaluation of a cloud point extraction method for the preconcentration and quantification of silver nanoparticles in water samples by ETAAS

ABSTRACT

A simple and reliable analytical method using instrumentation available in most of the laboratories has been developed for the separation and determination of silver nanoparticles in water samples. Cloud point extraction (CPE) was used for the separation of silver nanoparticles (AgNPs) from the sample and these nanoparticles were then determined by electrothermal atomic absorption spectrometry (ETAAS). Parameters related to the cloud point extraction procedure (Triton X-114 concentration, type of complexing agent (EDTA or Na₂S₂O₃), pH, incubation temperature, incubation and centrifugation time) were selected using a multivariate approach (designs of experiments); 8.6% (v/v) Triton X-114, 750 µL saturated EDTA and pH 7 were selected as the optimum conditions. Calibration standards in a concentration range from 0 to 10 µg L^?1 of AgNPs were subjected to the CPE procedure to obtain quantitative recoveries. The LOD and LOQ were 0.04 and 0.13 µg L^?1, respectively. The method is selective for the extraction of AgNPs, and ionic Ag remains in the aqueous phase. Single particle inductively coupled plasma mass spectrometry (SP-ICP-MS) was used to evaluate the effect of the CPE procedure in particle size, and no changes were observed. Finally, the procedure was applied to wastewater samples spiked with nanoparticles with quantitative recoveries.     

Chemiluminescence immunoassay for cardiac troponin T by using silver nanoparticles functionalized with hemin/G-quadruplex DNAzyme on a glass chip array

The authors describe an array for chemiluminescence (CL) based determination of cardiac troponin T (cTnT), an important cardiovascular disease marker. The tracing tag consists of silver nanoparticles (AgNPs) loaded with guanine-rich DNA sequences and detection antibody in a high numerical ratio. The loaded AgNPs were then reacted with hemin to form a hemin/G-quadruplex DNAzyme. A disposable immunosensor array was fabricated by immobilizing capture antibody on corresponding sensing sites on a glass chip. Once a sandwich immunocomplex is formed on the array, the tracing tag catalyzes the CL reaction of the luminol-p-iodophenol and H₂O₂ system to produce a CL signal, which is collected by a CCD camera. An intuitive CL image is obtained containing all of the spots on the array. Under optimal conditions, the method shows a wide linear range over 4 orders of magnitude (from 0.003 to 270 ng·L^?1), a detection limit down to 84 fg·L^?1, and a throughput as high as 44 tests·h^?1. The results obtained with serum samples are in acceptable agreement with reference values. The AgNP-based tracing tag as well as the immunoassay method shows a promising potential for point-of-care testing for the early clinical diagnosis of cardiovascular disease.

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Graphical abstract Schematic presentation of silver nanoparticles (AgNPs) functionalized with hemin/G-quadruplex DNAzyme for highly sensitive chemiluminescence (CL) immunoassay of cardiac troponin T (cTnT) on a glass chip array.

     

Detection and characterization of silver nanoparticles in chicken meat by asymmetric flow field flow fractionation with detection by conventional or single particle ICP-MS

A method of analysis of silver nanoparticles (AgNPs) in chicken meat was developed. The homogenized chicken meat sample, which was spiked with AgNPs, was subjected to enzymolysis by Proteinase K for 40 min at 37 °C. Transmission electron microscopy and inductively coupled plasma mass spectrometry (ICP-MS) in single particle mode were used to characterize the number-based size distribution of AgNPs in the meat digestate. Because similar size distributions were found in the meat digestate and in the aqueous suspension of AgNPs used for spiking the meat, it was shown that no detectable dissolution of the AgNPs took place during the sample preparation stage. The digestate was injected into the asymmetric flow field flow fractionation (AF⁴) -ICP-MS system, which enabled fractionation of nanoparticles from the remaining meat matrix, and resulted in one large peak in the fractograms as well as two smaller peaks eluting close to the void volume. The recovery of silver contained in the large AgNP peak was around 80 %. Size determination of AgNPs in the meat matrix, based on external size calibration of the AF⁴ channel, was hampered by non-ideal (early elution) behavior of the AgNPs. Single particle ICP-MS was applied for determination of the number-based particle size distribution of AgNPs in collected fractions. The presented work describes for the first time the coupling of AF⁴ and ICP-MS for AgNP separation in a food matrix.     

A simple non-enzymatic strategy for adenosine triphosphate electrochemical aptasensor using silver nanoparticle-decorated graphene oxide

In this work, a sensitive electrochemical aptasensor for the detection of adenosine triphosphate (ATP) has been introduced. A simple and non-enzymatic signal amplification strategy is utilized using silver nanoparticle-decorated graphene oxide (AgNPs–GO) as a redox probe. The modified electrode surface was characterized by scanning electron microscopy, FTIR and UV–Vis spectroscopy, and electrochemical impedance spectroscopy. GO provides an excellent substrate for the presence of the large number of AgNPs, so the monitored oxidation signal of AgNPs has been amplified. ATP-specific DNA aptamer is split into two fragments (F₁ & F₂) in order to design a sandwich-type assay. For the construction of the sensor, the surface of a graphite screen-printed electrode is modified with electrodeposited gold nanoparticles followed by self-assembling a monolayer of 3-mercaptopropionic acid on the electrode surface. The first amino-labeled fragment, F₁, is immobilized on the modified electrode via carbodiimide chemistry. The synthesized AgNPs–GO interacts with F₁ via \(\pi{-}\pi\) stacking. In the presence of ATP, the second fragment of the aptamer, F₂, forms an associated complex with the immobilized F₁ and causes AgNPs–GO to leave the surface. Consequently, a remarkable decrease in the oxidation signal of the AgNPs is observed. The percentage of this decrease has been monitored as an analytical signal, which is proportional to ATP concentration, and delivers a linear response over the range of 10.0 (±0.6) to 850 (±5) nM with a detection limit of 5.0 (±0.2) nM.     

Effect of silver nanoparticles concentration on the metal enhancement and quenching of ciprofloxacin fluorescence intensity

Concentration effect of silver nanoparticles (AgNPs) on the photophysical properties of ciprofloxacin (Cip) have been investigated using optical absorption and fluorescence techniques. When performed AgNPs solution was added to the Cip solution, metal-enhanced fluorescence intensity and a blue-shift of 20 nm in the maximum emission spectra of Cip has been observed. The enhanced intensity of this system is strongly dependent on the AgNPs concentration and largest at the 6.0 × 10^?6 mol L^?1. With increase of AgNPs concentration, quenching of fluorescence is observed. Stern–Volmer quenching constants have been calculated at four temperatures. The results show the quenching constants are directly correlated with temperature. It indicates the quenching mechanism is the dynamic quenching in nature rather than static quenching. From which we determined the activation energy for the quenching of Cip-AgNPs to be about 31.1 kJ mol^?1. In addition, in the presence of optimum AgNPs concentration, a sensitive fluorimetric method for the determination of ciprofloxacin at the range 5.0 × 10^?7–3.0 × 10^?5 mol L^?1 and the detection limit of 2 × 10^?8 mol L^?1 in solution is proposed.     

The determination of copper ions based on sensitized chemiluminescence of silver nanoclusters

We report on the first application of novel, water-soluble and fluorescent silver nanoclusters (Ag NCs) in a chemiluminescent (CL) detection system. A method has been developed for the determination of copper(II) ion that is based on the fact that the weak CL resulting from the redox reaction between Ce(IV) ion and sulfite ion is strongly enhanced by the Ag NCs and that the main CL signals now originate from Ag NCs. UV-visible spectra, CL spectra and fluorescent (FL) spectra were acquired to investigate the enhanced CL mechanism. It is proposed that the electronic energy of the excited state intermediate SO₂* that originates from the CL reaction is transferred to Ag NCs to form an electronically excited NC whose emission is observed. In addition, it is found that copper(II) is capable of inhibiting the CL of the nanoclusters system, but not if other common metal ions are present. The detection of copper(II) is achieved indirectly by measuring the CL intensity of Ag NCs. Under the optimized experimental conditions, a linear relationship does exist between the intensity of CL and the concentrations of copper(II) in the range of 0.2?nM to 0.1?m??. The detection limit is 0.12?nM. The method is applied to the determination of copper(II) ion in tap water with satisfactory results.

Simple and rapid surface-enhanced Raman Spectroscopy assay for safranine T and its application in highly sensitive determination of mercury (Ⅱ)

A simple and sensitive surface-enhanced Raman spectroscopy (SERS) method for the detection of safranine T (ST) and Hg²⁺ using silver nanoparticles (AgNPs) as substrate was developed. ST can absorb on the surface of AgNPs through electrostatic interaction, the electromagnetic effect combined with chemical adsorption effect give a notable Raman enhancement for ST. The presence of Hg²⁺ well decreased the absorbed ST molecules on AgNPs, leading to a significant decrease of SERS signals thus enabling to detect Hg²⁺. The determination conditions for SERS, including the amount of AgNPs, the concentration of NaCl, the concentration of HCl, the concentration of ST and the reaction time, were optimised. Under the optimised experimental conditions, good linear responses were obtained for ST and Hg²⁺ in the concentration ranges of 0.01–4.0 μmol L^?1 (3.5–1403.4 ng mL^?1) and 0.01–2.0 μmol L^?1 (2.0–401.2 ng mL^?1), the limit of detection were 3.0 nmol L^?1 (1.1 ng mL^?1) and 2.0 nmol L^?1 (0.4 ng mL^?1), respectively. The present method was subsequently applied to the determination of ST in tomato sauces and Hg²⁺ in environmental waters, the recoveries of ST and Hg²⁺ in spiked samples are 95.5–107.8% and 91.4–110.8 %, respectively.     

A New Flow‐Injection Chemiluminescence Method for the Determination of Acyclovir and Gancyclovir

Abstract

A rapid and sensitive flow‐injection chemiluminescence (FI‐CL) method, which is based on the CL intensity that generated from the redox reaction of Ce(IV)‐rhodamine B in H₂SO₄ medium, for the determination of acyclovir and gancyclovir is described. For acyclovir, the determination range is 3×10^?8 g mL^?1–7×10^?5 g mL^?1, with 1.56×10^?8 g mL^?1 as its determination limit. During 11 repeated measurements for 1×10^?6 g mL^?1 acyclovir, the relative standard deviation was 2.08%. For gancyclovir, the determination range was 5×10^?8 g mL^?1–7×10^?5 g mL^?1, with 2.35×10^?8 g mL^?1 as its determination limit. The relative standard deviation is 2.83% with 11 repeated measurements of 1×10^?6 g mL^?1 gancyclovir. This method can be successfully used to determine the content of acyclovir and gancyclovir in injections, acyclovir in eye drops, and, maybe, also for other ciclovirs.     

Surface Plasmon Resonance (SPR) Based Optimization of Biosynthesis of Silver Nanoparticles from Rhizome Extract of <Emphasis Type="Italic">Curculigo orchioides</Emphasis> Gaertn. and Its Antioxidant Potential

The present study for the first time explores the use of Central composite design (CCD) of RSM to optimize the process parameters of biosynthesis of AgNPs from rhizome extract of Curculigo orchioides based on the absorbance of surface plasmon resonance (SPR) band at 430 nm that corresponds to the synthesis of mono-disperse, spherical AgNPs. A polynomial model was established as a functional relationship between the synthesis of AgNPs and four independent variables such as concentration of AgNO₃, % rhizome extract, pH and temperature. The optimum conditions for maximum AgNPs synthesis were 2 mM concentration of AgNO₃, 20 % rhizome extract, pH 8, and temperature of 60 °C. A significant correlation (R ² = 0.8947) was observed between the experimental data and the predicted values indicating the adequacy of the model. Transmission electron microscopy (TEM) revealed spherical particles with size range of 5–28 nm. Selected area electron diffraction pattern and X-ray diffraction analysis confirmed the face-centered cubic structure of metallic silver. The plausible mechanism for the reduction of AgNO₃ to AgNPs was proposed following the identification of functional groups by FTIR. The antioxidative activity of AgNPs was demonstrated with scavenging of hydrogen peroxide (H₂O₂), 1,1-Diphenyl-2-picrylhydrazyl (DPPH) and superoxide radicals.     

Flow injection chemiluminescence determination of isoniazid using luminol and silver nanoparticles

The effect of silver colloidal nanoparticles (AgNPs) on the luminol–isoniazid system was investigated. It was found that AgNPs could act as a nanocatalyst on the luminol–isoniazid system to generate chemiluminescence (CL). The CL emission spectrum of the luminol–isoniazid–AgNPs system showed a peak with a maximum at 425 nm. It was suggested that the luminophor species was the excited state 3-aminophthalate. The reduction of dissolved O₂ to H₂O₂ by isoniazid and decomposition of H₂O₂ to the oxygen-related radicals were attributed to the catalytic effect of AgNPs. Under optimized conditions, the CL signal intensity was linear with the isoniazid concentration in the range of 10–1000 ng mL^{− 1}, with the correlation coefficient of 0.9996. The limit of detection was 2.7 ng mL^{− 1} isoniazid. The relative standard deviations for seven repeated measurements of 60 and 200 ng mL^{− 1} isoniazid were 1.4 and 2.4%, respectively. The effect of potent interfering compounds on the CL signal intensity of the proposed luminol–isoniazid–AgNPs system was investigated. The proposed method was successfully applied to the determination of isoniazid in a pharmaceutical sample.     

Redox Behavior of Zearalenone in Various Solvents

The redox equilibriums involving zearalenone were studied by cyclic and differential pulse voltammetry on a glassy carbon electrode. The cyclic voltammograms of zearalenone in DMSO at a glassy carbon electrode in the potential range from ?600 to 1400 mV vs. the Ag/AgCl have two oxidation peaks and a reduction one. Zaralenone concentration may be determined by DPV at +1050 mV. The method was applied to the determination of zearalenone concentration in corn, barley, and maize. Studies performed in aqueous solution or in mixed solvents water-acetonitrile containing 1 M H₂SO₄ showed that the oxidation of ZEN with an aqueous solution of Ce(IV) at room temperature, in the dark, occurs with the destruction of ZEN molecule. Studies performed in aqueous solution or in mixed solvents water-acetonitrile containing 1 M H₂SO₄ showed that the oxidation of ZEN with an aqueous solution of Ce(IV) at room temperature, in the dark, occurs with the destruction of ZEN molecule.     

Antibacterial effect of silver nanoparticles prepared in bipolymers at moderate temperature

The purpose of this study was to investigate the antibacterial effect of silver nanoparticles in chitosan–poly(ethylene glycol) suspension. The silver nanoparticles (AgNPs) were prepared by use of an environmentally benign method from chitosan (Cts) and poly(ethylene glycol) (PEG) at moderate temperature and with stirring for different times. Silver nitrate (AgNO₃) was used as the metal precursor and Cts and PEG were used as solid support and polymeric stabilizer, respectively. The antibacterial activity of silver–chitosan–poly(ethylene glycol) nanocomposites (Ag–Cts–PEG NCs) against Staphylococcus aureus, Micrococcus luteum, Pseudomonas aeruginosa, and Escherichia coli was tested by use of the Mueller–Hinton agar disk-diffusion method. Formation of AgNPs was determined by UV–visible spectroscopy; surface plasmon absorption maxima were observed at 415–430 nm in the UV–visible spectrum. The peaks in the XRD pattern confirmed that the AgNPs had a face-centered cubic structure; peaks of contaminated crystalline phases were not observed. Transmission electron microscopy (TEM) revealed that the AgNPs synthesized were spherical. The optimum stirring time for synthesis of the smallest particle size (mean diameter 5.50 nm) was 12 h. The AgNPs in Cts–PEG were effective against all the bacteria tested. Higher antibacterial activity was observed for AgNPs with smaller size. These results suggest that AgNPs can be used as an effective inhibitor of bacteria and can be used in medical applications. These results also suggest that AgNPs were successfully synthesized in Cts–PEG suspension at moderate temperature with different stirring times.     

Silver nanoparticle-initiated chemiluminescence reaction of luminol-AgNO3 and its analytical application

Ag⁺ has been regarded as an inert chemiluminescent oxidant. In this work, it was found that in the presence of silver nanoparticles (AgNPs), AgNO₃ could react with luminol to produce strong chemiluminescence (CL). The AgNPs with smaller size could initiate stronger CL emission. To investigate the CL mechanism of the AgNPs–luminol–AgNO₃ system, the UV–visible spectra and the CL spectrum of the CL system were obtained. The CL reaction mechanism involving catalysis was proposed. Compared with the reported nanoparticles–luminol–H₂O₂ CL system, the AgNPs–luminol–AgNO₃ CL system has the advantages of low background and good stability. Moreover, the new CL system was used in immunoassay for IgG.     

The Determination of Perphenazine by a New Simple Flow‐Injection Chemiluminescence Method

Abstract

A rapid and simple flow‐injection chemiluminescence (CL) method is described for the determination of perphenazine, which is based on the CL intensity that generated from the redox reaction of Ce (IV)-perphenazine in HNO₃ medium is proportional to the perphenazine concentration without any sensitizers. The proposed method allows the determination range within 1.0×10^?7–7.0 ×10^?5 g mL^?1 with a detection limit of 8.0×10^?8 g mL^?1, and it has been successfully applied to the determination of the perphenazine in pharmaceutical tablet compared well with the official method.     

A sensitive chemiluminescence method for the determination of cysteine based on silver nanoclusters

We have developed a sensitive chemiluminescent (CL) assay for cysteine. It is based on the use of water-soluble and fluorescent silver nanoclusters (Ag NCs) which are found to be able to strongly enhance the weak CL signal resulting from the redox reaction between Ce(IV) ion and sulfite ion. This enhancement is inhibited by cysteine under appropriate conditions. Taking advantage of this specific CL inhibition, a novel CL method for the sensitive and selective detection of cysteine was developed. This effect is interpreted in terms of an electronic energy transfer from excited state intermediate sulfur dioxide (originating from the CL reaction between Ce(IV) and sulfite ions) to the Ag-NCs. The latter become electronically excited and thus can act as a new source of emission. The method was applied to the determination of cysteine in the range from 5.0?nM to 1.0?μM, with a detection limit at 2.5?nM (S/N?=?3).

Synthesis of differently sized silver nanoparticles on a screen-printed electrode sensitized with a nanocomposites consisting of reduced graphene oxide and cerium(IV) oxide for nonenzymatic sensing of hydrogen peroxide

The authors describe a screen-printed and disposable electrode for the nonenzymatic determination of hydrogen peroxide (H₂O₂). It is based on the controllable synthesis and deposition of silver nanoparticles (AgNPs) of different sizes on a nanocomposite consisting of reduced graphene oxide and cerium (IV) oxide (rGO@CeO₂) that was placed on a screen-printed electrode (SPE). X-ray powder diffractometry and Fourier transform infrared spectroscopy were used to characterize the composition of the hybrid nanomaterials. Electrochemical impedance spectroscopy and scanning electron microscopy were employed to study the interfacial properties and morphologies of different electrodes. The sensor was investigated by cyclic voltammetry and chronoamperometry (i-t plots). After optimization, the modified SPE showed a good performance towards the electrocatalytic reduction of H₂O₂, best at a working potential of ?0.3 V (vs. Ag/AgCl). Features of merit include a broad linear analytical range extending from 0.5 μM to 12 mM, and a limit of detection as low as 0.21 μM (at an S/N ratio of 3). The sensor is simple, quick, stable and reliable. It was applied to the determination of H₂O₂ in (spiked) contact lens care solutions with good accuracy and recovery.

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Graphical abstract An enhanced sensing platform for nonenzymatic hydrogen peroxide (H₂O₂) based on controllable synthesis of differently sized silver nanoparticles (AgNPs) loaded on reduced graphene oxide and cerium(IV) oxide (rGO@CeO₂) nanocomposites to sensitize screen-printed electrode (SPE) was fabricated.

     

Investigation on sensitized chemiluminescence systems and their mechanism for five fluoroquinolones

The novel chemiluminescence (CL) reaction systems were established for lomefloxacin (LMFX), ofloxacin(OFLX), norfloxacin (NFLX), gatifloxacin (GAFX) and enoxacin (ENX). The sensitized CL emission mechanism was investigated for the five systems by comparing the fluorescence emission with CL spectra. For LMFX-Ce(IV)-S₂O₃²⁻-H₂SO₄ and OFLX-Ce(IV)-S₂O₄²⁻-H₂SO₄ systems, the CL intensity is enhanced through intermolecular energy transfer from the excited SO₂^* to LMFX and OFLX. For NFLX-Ce(IV)-S₂O₄²⁻-HNO₃ system, the sensitized CL is based on intermolecular energy transfer from the excited SO₂^* to NFLX oxide. For Eu³⁺-GAFX-Ce(IV)-S₂O₄²⁻-HCl and Dy³⁺-ENX-Ce(IV)-S₂O₃²⁻-H₂SO₄ systems, the CL spectra are from the narrow characteristic emission at 590, 619 and 649 nm of Eu^3+* (⁵D₀ → ⁷F₁, ⁵D₀ → ⁷F₂, ⁵D₀ → ⁷F₃) and at 482 and 578 nm of Dy³⁺ (⁴F₉ → ⁶H_15/2, ⁴F₉ → ⁶H_13/2) through intermolecular energy transfer from the excited SO₂^* to GAFX and ENX, followed by intramolecular energy transfer from GAFX^* to Eu³⁺ and ENX^* to Dy³⁺. The conditions of CL emission were investigated and optimized. The proposed five enhanced CL systems have good linearity, higher sensitivity, precision and potential capability for residue analysis of studied analytes in foods and biological samples.     

Determination of Three Nonsteroidal Anti-Inflammatory Drugs in Human Plasma by LC Coupled with Chemiluminescence Detection

A simple and sensitive method was developed for the determination of three nonsteroidal anti-inflammatory drugs (NSAIDs)—ibuprofen, naproxen and fenbufen in human plasma. The method involved in column liquid chromatographic separation and chemilumenescence (CL) detection based on the CL reaction of NSAIDs, potassium permanganate (KMnO₄) and sodium sulfite (Na₂SO₃) in sulfuric acid (H₂SO₄) medium. The chromatographic separation was carried out using a reversed-phase C₁₈ column, which allowed the selective determination of the three medicines in the complicated samples. The special features of the CL detector provided lower LOD for determination than that of existing chromatographic alternatives. The results indicated that the linear ranges were 0.01–10.0 μg mL^?1 for ibuprofen, 0.001–1.0 μg mL^?1 for naproxen, and 0.01–10.0 μg mL^?1 for fenbufen. The limits of detection were 0.5 ng mL^?1 for ibuprofen, 0.05 ng mL^?1 for naproxen and 0.5 ng mL^?1 for fenbufen (S/N = 3). All average recoveries were in the range of 90.0–102.3%. Finally, the method had been satisfactorily applied for the determination of ibuprofen, naproxen and fenbufen in human plasma samples.