Use of a graphite–polyurethane composite electrode for electroanalytical determination of indole-3-acetic acid in soil samples

A new electroanalytical methodology was developed for the quantification of the phytohormone indole-3-acetic acid (IAA), using a graphite–polyurethane composite electrode (GPU) and the square wave voltammetry (SWV), in 0.1 mol L^− 1 phosphoric acid solution (pH 1.6). Analytical curves were constructed under optimized conditions (f = 100 s^− 1, a = 50 mV, E_i = 5 mV) and the reached detection and quantification limits were 26 μg L^− 1 and 0.2 mg L^− 1, respectively. The developed methodology is simple and accurate for the routine determination of IAA. In order to verify the application of the electroanalytical methodology in fortified soil samples without previous treatment, an IAA assay was performed without serious interferences of the soil constituents.     

Determination of zinc and copper in human hair by slurry sampling employing sequential multi-element flame atomic absorption spectrometry

The present work proposes a direct method based on slurry sampling for the determination of zinc and copper in human hair samples by multi-element sequential flame atomic absorption spectrometry. The slurries were prepared by cryogenic grinding and sonication of the samples. The optimization step was performed using univariate methodology and the factors studied were: nature and concentration of the acid solution, amount sample/slurry volume, sonication time, and particle size. The established experimental conditions are the use of a sample mass of 50 mg, 2 mol L^− 1 nitric acid solution, sonication time of 20 min and slurry volume of 10 mL. Adopting the optimized conditions, this method allows the determination of zinc and copper with detection limits of 88.3 and 53.3 ng g^− 1, respectively, and precision expressed as relative standard deviation (RSD) of 1.7% and 1.6% (both, n = 10) for contents of zinc and copper of 100.0 and 33.3 μg g^− 1, respectively. The accuracy was checked and confirmed by analysis of two certified reference materials of human hair. The procedure was applied for the determination of zinc and copper in two human hair samples. The zinc and copper contents varied from 100.0 to 175.6 and from 3.2 to 32.8 μg g^− 1, respectively. These samples were also analyzed after complete digestion in a closed system and determination by FAAS. The statistical comparison by t-test (95% confidence level) showed no significant difference between these results.     

Assay of femtogram level nitrite in human urine using luminol–myoglobin chemiluminescence

In this paper, a sensitive flow injection chemiluminescence system luminol–myoglobin was described for determining femtogram nitrite. Nitrite bound myoglobin producing the ferric heme nitrite complexes, which catalyzed the electron transfer of luminol to myoglobin leading to fast chemiluminescence. The chemiluminescence intensity in the presence of nitrite was remarkably enhanced compared with that in the absence of it. Under the optimum reaction conditions the chemiluminescence increment produced was proportional to the concentration of nitrite in the range of 0.05 pg ml^− 1–1.0 ng ml^− 1 (R² = 0.9991), with a detection limit (3σ) of 20.0 fg ml^− 1. At the flow rate of 2.0 ml min^− 1, the whole process including sampling and washing could be completed in 0.5 min offering the sampling efficiency of 120 h^− 1 accordingly, and the relative standard deviation (RSD) was less than 2.60% (n = 5). It was satisfactory for the application to determine nitrite in human urine samples, and the possible mechanism was proposed.     

Determination of 4-methylbenzilidene camphor in sunscreen by square wave voltammetry in media of cationic surfactant

The voltammetric behavior of 4-methylbenzelidene camphor (MBC) was studied by square wave voltammetry (SWV) using mercury electrode. The experimental condition that provided the highest peak current with the best reduction signal definition of MBC was found in Britton-Robinson buffer and cationic surfactants, cetyltrimethylammoniun bromide (CTABr). A single peak of MBC reduction was observed at − 1.21 V versus Ag/AgCl. The developed methodology was applied for determination of MBC in commercial sunscreen SPF 15, 20 and 30 and for the simultaneous determination when other protection agents were associated, such as benzophenone-3 (BENZO) and octyl methoxycinammate (OMC). Both methodologies had shown good determination values for the analyzed samples. The calculated detection limit was 2.99 × 10^− 9 mol L^− 1 and the quantification limit was 9.98 × 10^− 9 mol L^− 1.     

Headspace solid-phase micro-extraction and gas chromatography-ion trap tandem mass spectrometry method for butyltin analysis in sediments: Optimization and validation

In this work, headspace solid-phase micro-extraction (SPME) combined with gas chromatography-mass spectrometry (GC-MS) method for analysis of butyltin compounds in sediment samples was upgraded by the introduction of tandem mass spectrometry (MS/MS). Optimization and validation of this method based on an one step procedure, tetraethylborate in situ ethylation with simultaneous extraction by headspace SPME, combined with tandem mass spectrometry is described. A simple leaching/extraction step of mono-(M), di-(D) and tri-(T) butyltin (BT) compounds from the sediment is required as sample pre-treatment. The combination of the two techniques headspace SPME and MS/MS, led to very little matrix interference which permitted to attain limits of detection three or more orders of magnitude lower than those attained in previous methods: 0.3 pg g^− 1 for MBT, 1 pg g^− 1 for DBT and 0.4 pg g^− 1 for TBT. Linear response range was from 0.02–1260 ng g^− 1 for MBT, 0.07–1568 ng g^− 1 for DBT and 0.04–2146 ng g^− 1 for TBT and RSD < 15% was also obtained. The method was efficiently applied to a real sample sediment from Sado River estuary in Portugal, revealing the existence of BTs pollution, as the TBT level of 189 ± 15 ng g^− 1 was much higher than the maximum established as provisional ecotoxicological assessment criteria.     

Coupling on-line preconcentration by ion-exchange with microwave plasma torch-atomic emission spectrometry for the determination of cobalt and nickel

In the present work, a simple and sensitive preconcentration-microwave plasma torch-atomic emission spectrometric procedure was carried out for the determination of cobalt and nickel. The method was based upon a flow-injection system with on-line preconcentration of the metal ions on a minicolumn of a strong acid cation-exchange resin. The operation parameters including sample acidity, flow rate, loading time, and eluent concentration, flow rate were studied and optimized. Under the optimal experimental conditions the enrichment factors were calculated as 13.58 and 17.65 for cobalt and nickel, respectively. The relative standard deviations, 3.73% for cobalt and 4.23% for nickel (n = 7), and a sample throughput of 40 h^− 1 were obtained. Furthermore, the limits of detection were shown to be 1.28 and 1.80 μg·L^− 1 for cobalt and nickel, respectively. The method was applied to the determination of cobalt and nickel in tea samples and the accuracy was assessed through recovery experiments.     

On-line molecularly imprinted solid phase extraction for the selective spectrophotometric determination of catechol

A molecularly imprinted polymer has been synthesized for a selective on-line catechol extraction, followed by its spectrophotometric determination in guarana powder, mate tea and tap water samples. A clean-up column, containing a methacrylic polymer + C₁₈ solid phase, was also used in order to enhance selectivity. The imprinted polymer was prepared by bulk polymerization using catechol as template and 4-vinylpyridine as the functional monomer. Permanganate solution was used as spectrophotometric reagent, where Mn(VII) was reduced to Mn(II) by catechol in an acid medium, causing color loss, which was monitored at 528 nm. Physical (extraction flow rate, elution flow rate, coil length) and chemical (nature and concentration of the eluent, potassium permanganate concentration) variables were optimized, and the selectivity was appraised using three molecules (4-chloro-2-methylphenol, 2-cresol, 2-methoxyphenol) similar to catechol. These molecules did not present interference in 1:8, 1:10 and 1:10 (catechol/concomitant) proportions, respectively. The analytical calibration curve ranged from 3.0 up to 100 μmol L^− 1 (r > 0.999; seven concentrations levels, n = 3) and the limits of detection (LOD) and quantification (LOQ) were 0.8 and 2.7 μmol L^− 1, respectively. Precision, expressed as RSD, was of 3.0% (20 μmol L^− 1, n = 10), and the analytical frequency was 15 h^− 1. Accuracy was checked by the HPLC technique and the results did not present significant difference at 95% confidence levels according to the t test.     

Development and critical comparison of greener flow procedures for nitrite determination in natural waters

Two greener procedures for flow-injection spectrophotometric determination of nitrite in natural waters were developed and critically compared. Replacement of toxic reagents, waste minimization and treatment were exploited to attend the standards of clean chemistry. The flow system was designed with solenoid micro-pumps in order to minimize reagent consumption and waste generation. The first procedure is based on the Griess diazo-coupling reaction with sulfanilamide and N-(1-naphthyl)ethylenediamine (NED) yielding an azo dye, followed by photodegradation of the low amount of waste generated based on the photo-Fenton reaction. The second procedure is based on the formation of iodine from nitrite and iodide in acid medium in order to avoid the use of toxic reagents. For Griess method, linear response was achieved up to 1.0 mg L^− 1, described by the equation A = − 0.007 + 0.460C (mg L^− 1), r = 0.999. The detection limit was estimated as 8 μg L^− 1 at the 99.7% confidence level and the coefficient of variation was 0.8% (n = 20). The sampling rate was estimated as 108 determinations per hour. The consumption of the most toxic reagent (NED) is reduced 55-fold and 20-fold in comparison to batch method and flow injection with continuous reagent addition, respectively. A colorless residue was obtained by in-line photodegradation with reduction of 87% of the total organic carbon content. The results obtained for natural water samples were in agreement with those achieved by the reference method at the 95% confidence level. For the nitrite–iodide method, linear response was observed up to 2.0 mg L^− 1, described by the equation A = − 0.024 + 0.148C (mg L^− 1), r = 0.999. The detection limit was estimated as 25 μg L^− 1 at the 99.7% confidence level and the coefficient of variation was 0.6% (n = 20). The sampling rate was estimated as 44 determinations per hour. Despite avoiding the use of toxic reagents, the nitrite–iodide method presented worst performance in terms of selectivity and sensitivity.     

Combined use of Pd and HF as chemical modifiers for the determination of total chromium in produced waters from petroleum exploration by ET AAS

This work reports the evaluation of the combined use of Pd and HF as chemical modifiers for the direct determination of total chromium in waters derived from petroleum exploration employing electrothermal atomic absorption spectrometry (ET AAS). Such waters, usually called as produced waters, have complex composition presenting a number of organic and inorganic substances. When obtained from offshore operations they also present high salinity. In order establish conditions for chromium measurement pyrolysis and atomization curves were built up in different media and employing Pd and HF as chemical modifiers. Also, a detailed study about calibration strategy was performed. At best conditions, pyrolysis and atomization temperatures were 1200 °C and 2600 °C, respectively, and 10 μL of a 500 mg L^− 1 Pd solution was added together with 10 μL of a 50% (v/v) HF solution on 20 μL of sample. Obtained results indicate that, in this kind of sample, chromium can be determined by standard addition method or employing external calibration with standard solutions prepared in 0.8 mol L^− 1 NaCl medium. In order to evaluate the accuracy of the procedure, a recovery test was performed with seven spiked samples of produced waters. The detection limit, quantification limit and the relative standard deviation in 0.8 mol L^− 1 NaCl were also calculated and the values found were 0.45 μg L^− 1, 1.5 μg L^− 1 and 6.0% (at 2.5 μg L^− 1 level), respectively.     

Tyrosinase/laccase bienzyme biosensor for amperometric determination of phenolic compounds

Tyrosinase/laccase bienzyme biosensor for amperometric determination of phenolic compounds was constructed. Enzymes were immobilized in titania gel matrix. The obtained biosensor was successfully used for determination of 2,6-dimethoxyphenol, 4-tertbutylcatechol, 4-methylcatechol, 3-chlorophenol and catechol. The highest sensitivity and the widest linear range were noticed for catechol, 234 mA L mol^− 1 and 2.0 × 10^− 7–3.2 × 10^− 5 mol/L, respectively. Detection limit for catechol, at signal-to-noise ratio of 3 was 1.3 × 10^− 7 mol/L.     

Kinetic determination of organosulphur ligands by inhibition: Trace determination of cysteine and maleonitriledithiolate (MNDT)

Some organosulphur ligands have been found to inhibit the mercury(II) catalyzed substitution of cyanide in hexacyanoferrate(II) by N-methylpyrazinium ion (Mpz⁺). The inhibitory effect is due to the binding tendency of catalyst Hg²⁺ with these inhibitors. This effect has been used as a basis to develop a kinetic method for the determination of trace amounts of two organosulphur ligands viz. cysteine and MNDT. The reaction was followed spectrophotometrically at 655 nm by measuring the decrease in absorbance of the product [Fe(CN)₅Mpz]²⁻. The influence of the reaction variables has also been studied. A general mechanistic scheme of the indicator reaction system including the role of inhibitor has been proposed and applied to determine the organosulphur ligands. Under the selected experimental conditions cysteine and MNDT have been determined in the range of 2–20 × 10^− 7 M and 5 × 10^− 8 M to 12 × 10^− 7 M respectively in various aqueous samples. The analytical concentration range depends upon the amount of Hg²⁺ present in the indicator reaction and also on the stability of the Hg²⁺-inhibitor complex in question. Under specified conditions, the detection limit for cysteine and MNDT are 2 × 10^− 7 M and 5 × 10^− 8 M respectively. The influences of possible interference by major amino acids, on the determination of cysteine and their limits have been investigated.     

Flow injection determination of ketotifen fumarate using PVC membrane selective electrodes

In this study a PVC membrane electrode for determination of ketotifen fumarate is reported, where ketotifen tetraphenylborate (Keto-TPB) was used as ion exchanger. The electrode has linear range of 5.6 × 10^− 6–1.0 × 10^− 2 and 1.0 × 10^− 5–1.0 × 10^− 2 mol/L, with detection limits 2.37 × 10^− 6and 4.60 × 10^− 6 mol/L in batch and flow injection analysis (FIA), respectively. The electrodes show a Nernstian slope value (58.40 and 61.50 mV/decade in batch and FIA, respectively), and the response time is very short (≤ 10 s). The potential is nearly stable over the pH range 2.0–8.0. Selectivity coefficient values towards different inorganic cations, sugars and amino acids reflect high selectivity of the prepared electrodes. These are used for determination of Ketotifen using potentiometric titration and standard addition methods in pure samples and its pharmaceutical preparations (Zaditen tablets and syrup). The average recovery values are 99.5 and 99.2% with RSD 1.4 and 1.2% for potentiometric titrations and standard addition methods, respectively. The electrode response at different temperatures was also studied.     

Occurrence of ochratoxin A in Turkish wines

A total of 95 wine samples including 34 white, 10 rosé and 51 red wines originating from four different Turkish areas were analysed for ochratoxin A (OTA). An analytical method based on immunoaffinity column (IAC) for clean-up and high performance liquid chromatography with fluorescence detection (HPLC-FD) was used to determine OTA in wines. The limit of detection (LOD) was estimated as 0.006 ng ml^− 1 for white wine and 0.010 ng ml^− 1 for rosé and red wines. The limit of quantification (LOQ) was estimated as 0.020 ng ml^− 1 in white wine and 0.030 ng ml^− 1 in rosé and red wines. Recovery experiments were carried out with spiked samples in the range 0.1–1 ng ml^− 1 of OTA. The average OTA recoveries from spiked white wine samples varied from 79.43% to 85.07%; while the mean recoveries for rosé and red wine samples were in the range of 77.48–83.96% and 76.61–83.55%, respectively. OTA was detected in 82 (86%) wine samples at levels of < 0.006–0.815 ng ml^− 1, which were below the maximum allowable limit established by the European Community. The mean OTA concentration in red wines was slightly higher than in white and rosé wines. Furthermore, our data indicate that the geographic region of origin has strong influence on OTA level for white, rosé and red wines: wines originating from Thrace (n = 44, mean = 0.158 ng ml^− 1) and Aegean (n = 28, mean = 0.060 ng ml^− 1) regions of Turkey were more contaminated with OTA compared with wines originating from central (n = 15, mean = 0.027 ng ml⁻¹) and east Anatolia (n = 8, mean = 0.027 ng ml^− 1) areas. This study showed that the occurrence of OTA in Turkish wines is high, but at levels that probably leads to a non-significant human exposure to OTA by consumption of wines.     

Homogeneous liquid-liquid extraction combined with gas chromatography-electron capture detector for the determination of three pesticide residues in soils

In this study, a new method was developed for analyzing malathion, cypermethrin and lambda-cyhalothrin from soil samples by using homogeneous liquid–liquid extraction (HLLE) and gas chromatography with electron capture detector (GC–ECD). Acetone was used as extraction solvent for the extraction of target pesticides from soil samples. When the extraction process was finished, the target analytes in the extraction solvent were rapidly transferred from the acetone extract to carbon tetrachloride, using HLLE. Under the optimum conditions, linearity was obtained in the range of 0.05–40 μg kg⁻¹ for malathion, 0.04–10 μg kg⁻¹ for lambda-cyhalothrin and 0.05–50 μg kg⁻¹ for cypermethrin, respectively. Coefficients of correlation (r²) ranged from 0.9993 to 0.9998. The repeatability was carried out by spiking soil samples at concentration levels of 2.5 μg kg⁻¹ for lambda-cyhalothrin, and 10 μg kg⁻¹ for malathion and cypermethrin, respectively. The relative standard deviations (RSDs) varied between 2.3 and 9.6% (n = 3). The limits of detection (LODs), based on signal-to-noise ratio (S/N) of 3, varied between 0.01 and 0.04 μg kg⁻¹. The relative recoveries of three pesticides from soil A1, A2 and A3 at spiking levels of 2.5, 5 and 10 μg kg⁻¹ were in the range of 82.20–91.60%, 88.90–110.5% and 77.10–98.50%, respectively. In conclusion, the proposed method can be successfully applied for the determination of target pesticide residues in real soil samples.     

Use of high resolution continuum source atomic absorption spectrometry as a detector for chemically generated noble and transition metal vapors

Vapor generation and atomization conditions in a heated quartz tube to detect Ag, Cd, Co, Cu, Ni and Zn using High Resolution Continuum Source AAS (HRCSAAS), were optimized. Vapors were generated after mixing acidified solutions containing 8-hydroxiquinoline (oxine) with sodium tetrahydroborate. Afterwards, they were swept to the heated quartz cell by an argon flow.Reaction loop size and temperature of the quartz cell were optimized for each element. A temperature of 960 °C was selected as a compromise value to detect most of the metals. Afterwards, a Plackett–Burmann design was proposed to select which parameters were most important. Type of acid and its concentration were the most statistical significant variables. Optimum conditions for sequential detection of Cd, Cu, Ni and Zn were: 1 mg L^− 1 Co as catalyst, 250 mg L^− 1 oxine, 0.6 M nitric acid, 1.75% (w/w) sodium tetrahydroborate (prepared in 0.4 (w/v)% NaOH), a reaction loop of 250 µL, and a 25 L h^− 1 carrier Ar flow. Ag and Co were each detected in their own optimized conditions. Analytical performance of the system was evaluated in connection with a selected pixel number, and spectral correction was used to eliminate NO absorption bands interference in Zn detection. Detection limits were in the range of 1.5–18 μg L^− 1 for Ag, Cu, Cd and Zn, whereas sensitivity was worst for Co (169 μg L^− 1) and Ni (586 μg L^− 1). Atomization in a quartz cell of Co and Ni volatile species, generated by an addition of sodium tetrahydroborate to an acidified solution of the analytes, was reported for the first time in this paper. Precision expressed as RSD(%) had values lower than 10% except for Ni.     

A novel on-line preconcentration method for trace molybdenum determination by USN–ICP OES with biosorption on immobilized yeasts

A new system for on-line preconcentration of molybdenum by sorption on a minicolumn associated to inductively coupled plasma — optical emission spectrometry with ultrasonic nebulization was studied. It is based on the sorption of molybdenum on a column packed with immobilized baker's yeasts on controlled pore glass without further complexing reagent. The molybdenum preconcentrated by biosorption was subsequently eluted with hydrochloric acid. Considering a sample flow rate of 5.0 mL min^− 1, 10 mL of sample was preconcentrated in 2 min achieving a sensitive total enhancement factor of 480-fold, and the detection limit (3 s) obtained was 21 ng L^− 1. Additionally, the calculated precisions expressed as percent relative standard deviation (RSD%) was 1.9%.Satisfactory results were obtained for the determination of molybdenum in standard reference material NIST 1643e Trace Elements in Water and real water samples.     

Determination of linuron in water samples by high performance liquid chromatography after preconcentration with octadecyl silanized magnetite

A sensitive and selective batch adsorption method is proposed for the preconcentration and determination of linuron. Linuron was preconcentrated on octadecyl silanized (ODS) magnetite as an adsorbent and then determined by high performance liquid chromatography (HPLC). Several parameters on the recovery of the analyte were investigated. The experimental results showed that it was possible to obtain sufficient preconcentration efficiency when the solution pH was 6 using 100 mL of sample solution containing 1.0 μg of linuron and 3 mL of ethanol as a desorption solution. Recovery of linuron was 50.7 ± 1.9% with a relative standard deviation for five determinations of 3.0% under optimum conditions. The calibration curve of linuron was linear up to 200 ng mL^− 1 with a correlation coefficient of 0.998 and the detection limit (3S/N) was 1.0 ng mL^− 1. The capacity of the adsorbent was also examined and found to be 0.15 mg g^− 1 for linuron. ODS-magnetite is suitable for repeated use without decreasing recovery at least 4 adsorption–desorption cycles. The proposed method was successfully applied to the determination of linuron in river water with high precision and accuracy.     

Electrochemistry of the interaction of furazolidone and bovine serum albumin

The electrochemical behavior of the interaction of furazolidone (Fu) with bovine serum albumin (BSA) was investigated by cyclic voltammetry and differential pulse voltammetry at a glassy carbon electrode. Fu shows an irreversible reduction at − 0.34 V in pH 4.0 Britton–Robinson buffer (B–R) buffer–10% DMF solution. After the addition of BSA into the Fu solution, the reductive peak currents decreased without any significant shift of the peak potential and the appearance of new peaks. The electrochemical parameters of the interaction system were calculated in the absence and presence of BSA. This electrochemical method was further applied to the determination of BSA samples and the results were in good agreement with the traditional cellulose acetate electrophoresis. The linear dynamic range was between 10.0 and 80.0 mg l^− 1. The detection limit was 7.6 mg l^− 1 and the recoveries were obtained from 97.0% to 104.0%.     

Determination of highly polar catecholamine with liquid chromatography–tandem mass spectrometry using weak cation-exchange stationary phase to increase retention time

This paper reports method development and validation work to determine highly polar bases, catecholamine compounds, using weak cation-exchange liquid chromatography of low ionic strength mobile phase with electrospray tandem mass spectrometry. Catecholamine compounds, such as epinephrine and norepinephrine, well-known biomarkers to diagnose hypertension disease, spiked in saline solutions are purified with solid phase extraction (SPE) using alumina powders. The extracts are loaded into a weak cation-exchange liquid chromatographic column via an injection loop and analyzed with electrospray-mass spectrometer. The de-salted extracts contain only small amounts of electrolytes to avoid saturating weak cation-exchange sites in the stationary phase with sodium ions. Using carefully selected mobile-phase solvents with optimized compositions (acetonitrile and water 10:90 v/v) and with dilute acid additives (acetic acid 0.1% v/v), we are able to elute catecholamine at sufficient retention times to avoid co-elution of saline matrix residues while maintaining adequate electrospray ionization efficiency of these compounds. Using epinephrine and norepinephrine standards, these methods are validated at the range of 5 to 500 ng mL^− 1. The measurement accuracy and precision of using epinephrine standards are within 12% and 5.3% respectively, whereas the accuracy and precision are within 6.0% and 4.2% respectively using epinephrine standards.The detection limits of epinephrine and norepinephrine are 0.10 ng mL^− 1 and 0.45 ng mL^− 1 respectively. The recovery percentages of our solid phase extraction methods using alumina powders are higher than 74%. When the validated calibration curves are used to determine epinephrine and norepinephrine in rat blood dialysates, the determination errors of accuracy and precision are both within 4%, while the determination errors are within 3% in rat blood plasma samples.     

Voltammetric determination of quercetin at a multi-walled carbon nanotubes paste electrode

Quercetin can effectively accumulate at multi-walled carbon nanotubes-paraffin oil paste electrodes (CNTPE) and cause a sensitive anodic peak at around 0.32 V (vs. SCE) in a 0.10 M phosphate buffer solution (pH = 4.0). Under optimized conditions, the anodic peak current is linear to quercetin concentration in the ranges of 2.0 × 10^− 9−1.0 × 10^− 7 M and 1.0 × 10^− 7−2.0 × 10^− 5 M, and the regression equations are i_p (μA) = 0.0017 + 0.928c (μM, r = 0.999) and i_p (μA) = 0.183 + 0.0731c (μM, r = 0.995), respectively. This paste electrode can be regenerated by repetitively cycling in a blank solution for about 2 min. A 1.0 × 10^− 6 M quercetin solution is measured for 10 times using the same electrode regenerated after every determination, and the relative standard deviation of the peak current is 1.7%. The method has been applied to the determination of quercetin in hydrolysate product of rutin and the recovery is 99.2–102.6%. In comparison with graphite paste electrode, carbon nanotubes-nujol paste electrode and carbon nanotubes casting film modified glassy carbon electrode, the CNTPE gives higher ratio of signal to background current and better defined voltammetric peak.