Synchronous fluorescence determination of DNA based on the interaction between methylene blue and DNA

The fluorescence intensity of methylene blue (MB) quenched by DNA in the pH range of 6.5-8.0 was studied with synchronous fluorescence technology. A novel method for detecting single-stranded and double-stranded DNA was developed. The decreased fluorescence intensity at 664 nm is in proportion to the concentration of DNA in the range of 0.28-11.0 μmol L⁻¹ for ctDNA, 0.14-8.25 μmol L⁻¹ for thermally denatured ctDNA and 0.28-8.25 μmol L⁻¹ for hsDNA. The detection limits (S/N = 3) are 0.11, 0.04 and 0.04 μmol L⁻¹, respectively. The method is rapid, selective, and the reagents are lower toxic. It has been used for the determination of DNA in synthetic samples with good satisfaction. In addition, the interaction modes between MB and ctDNA and the mechanism of the fluorescence quenching were also discussed in detail. The experimental results from absorption spectra and fluorescence polarization indicate that the possible interaction modes between MB and DNA are the electrostatic binding and the intercalation binding.     

Adsorption of a protein-porphyrin complex at a liquid-liquid interface studied by total internal reflection synchronous fluorescence spectroscopy

Interfacial analysis has attracted more and more attention owing to its fundamental and biological importance. Total internal reflection fluorescence (TIRF) spectroscopy is a useful method to study interfacial properties. The synchronous scanning fluorescence technique provides a selective tool to analyze a specific component in a complex system. The interaction and adsorption of bovine serum albumin (BSA) and meso-tetrakis(4-sulfonatophenyl)porphyrin (TPPS) at toluene-water interface were studied successfully by the coupling technique of total internal reflection synchronous fluorescence (TIRSF). New methods are provided for the determination of the critical micelle concentration (cmc), apparent adsorption equilibrium constant (K_ad) and maximum amount of adsorption (f_max) at the liquid-liquid interface. The results indicated that BSA could adsorb onto the toluene-water interface as a complex of BSA-TPPS in a ratio of 1:1 ratio based on Langmuir adsorption isothermal model. The cmc, apparent K_ad and f_max for BSA at pH 3.1 were determined to be 1.0 × 10⁻⁴ mol L⁻¹, 1.15 × 10⁵ L mol⁻¹ and 1.14 × 10⁻⁹ mol cm⁻², respectively.     

Batch and flow measurement of hydrogen ions in highly acidic media using 2-(4-methoxy phenyl) 6-(4-nitrophenyl)-4-phenyl-1,3-diazabicyclo [3.1.0] hex-3-ene as an H-selective ionophore

A hydrogen ion-selective poly(vinyl chloride) (PVC) membrane electrode was developed using 2-(4-methoxy phenyl) 6-(4-nitrophenyl)-4-phenyl-1,3-diazabicyclo [3.1.0] hex-3-ene as ionophore. Effects of experimental parameters such as membrane composition, nature and amount of plasticizer, and the amount of additive on the potential response of pH sensor were investigated. This H⁺-selective membrane electrode gave a linear response over the pH range 0-4 (10⁻⁴ to 1 mol L⁻¹ HCl) with slope of 57.4 ± 0.3 mV pH⁻¹ and limit of detection 6.3 × 10⁻⁵ mol L⁻¹ at 20 °C. Also, hydrofluoric acid did not influence the surface of this electrode and thus it was maintained without showing any changes in potentials after being used in a hydrofluoric acid solution. The equilibrium water content of the electrode was determined in the presence of two different plasticizers as membrane solvent. The alkaline cation binding affinity of ionophore was very low that prove these cations do not have specific interaction with this ionophore. The electrode had fairly low electrical resistance, good potential stability and reproducibility. It has a rapid potential response to changes of pH (10 s), easily used in a single channel wall-jet flow injection system with good reproducibility (RSD% = 1.67%) and high reversibility. It was used as indicator electrode in potentiometric determination of pH in real samples.     

A rapid quantitative method for humic substances determination in natural waters

A simple and rapid method was proposed for humic substances (HS) determination at microgram levels in natural waters. This assay method is based on the binding of a dye, Toluidine Blue (TB), to HS molecules to produce a dye-HS complex, which causes a decrease in absorbance at 630 nm. This method was calibrated with HS samples with up to a concentration of 40 mg L⁻¹, which covered the range of dissolved HS concentrations present in natural waters. The detection limit was 0.8 mg L⁻¹ of HS, and the relative standard deviation of 10 replicate measurements for a 20-mg L⁻¹ standard sample was 3.5%. From the Langmuir adsorption isotherm theory, the binding equilibrium constant and total number of binding sites at neutral pH were calculated to be (8.17 ± 0.42) × 10⁵ L mol⁻¹ and N of 1.45 ± 0.04 mmol g⁻¹ HS, respectively. The determination results with five water samples from lake, river and pond were consistent with those measured with the reference methods, demonstrating that this quantification method for HS determination was rapid, sensitive and feasible.     

Rapid and sensitive determination of protein by light-scattering technique with Eriochrome Blue Black R

Based on the interaction between Eriochrome Blue Black R (EBBR) and proteins, which causes a strong light-scattering signal with the maximum scattering peak located at 398 nm, a simple, rapid, sensitive and selective method is developed for the determination of proteins by the light-scattering technique using a common spectrofluoremeter. Under proper experimental conditions, the protein determination can be performed in the range of 0.1-25, 0.1-20 and 0.25-25 μg ml⁻¹ for bovine serum albumin (BSA), human serum albumin (HSA) and human immunoglobulin G (IgG), respectively. The detection limit, calculated as 3 times the S.D. of nine blank measurements, are 33 μg l⁻¹ for BSA, 25 μg l⁻¹ for HSA and 38 μg l⁻¹ for IgG. Moreover, there is no significant difference among the scattering signals yielded by HSA, IgG and BSA, and almost no interference of many amino acids and metal ions. The method has been satisfactorily applied to the direct determination of the total protein in human serum, saliva and urine samples. The results obtained from the studies on the binding characteristics of EBBR to BSA indicated that an electrostatic force existed in the binding system, and the binding constant (K) and the number of the binding sites (n) at 25 °C are 1.69×10⁵ l mol⁻¹ and 0.946, respectively.     

Determination of proteins with Alizarin Red S by Rayleigh light scattering technique

A new protein determination method by enhanced Rayleigh light scattering (RLS) technique has been developed. In acid condition (pH=3.60), RLS of 1,2-dihydroxyanthraquinone-3-sulfonate (Alizarin Red S) can be greatly enhanced by addition of proteins, resulting in two characteristic peaks, 360 and 505 nm, respectively. The new protein assay is based on the RLS enhancement and spectrum change. The optimum condition for the reaction was investigated. The linear range is 0.20-24.9 μg ml⁻¹ for BSA and 0.20-15.5 μg ml⁻¹ for HSA. The detection limits (S/N=3) are 9.59 ng ml⁻¹ for BSA and 9.51 ng ml⁻¹ for HSA. The results of determination for human serum samples were comparable to those obtained by Bradford method. The binding stoichiometry was determined.     

Interaction of colloidal AgTiO2 nanoparticles with bovine serum albumin

The interaction between colloidal AgTiO₂ nanoparticles and bovine serum albumin (BSA) was studied by using absorption, steady state, time resolved and synchronous fluorescence spectroscopy measurements. Absorption spectroscopy proved the formation of a ground state BSA?AgTiO₂ complex. Upon excitation of BSA, colloidal AgTiO₂ nanoparticles effectively quenched the intrinsic fluorescence of BSA. The number of binding sites (n = 1.06) and apparent binding constant (K = 3.71 × 10⁵ M⁻¹) were calculated by the fluorescence quenching method. A static mechanism and conformational changes of BSA were observed.     

Influence of metal loading and humic acid functional groups on the complexation behavior of trivalent lanthanides analyzed by CE-ICP-MS

The complexation behavior of Aldrich humic acid (AHA) and a modified humic acid (AHA-PB) with blocked phenolic hydroxyl groups for trivalent lanthanides (Ln) is compared, and their influence on the mobility of Ln(III) in an aquifer is analyzed. As speciation technique, capillary electrophoresis (CE) was hyphenated with inductively coupled plasma mass spectrometry (ICP-MS). For metal loading experiments 25 mg L⁻¹ of AHA and different concentrations (c_Ln(Eu+Gd) = 100–6000 μg L⁻¹) of Eu(III) and Gd(III) in 10 mM NaClO₄ at pH 5 were applied. By CE-ICP-MS, three Ln-fractions, assumed to be uncomplexed, weakly and strongly AHA-complexed metal can be detected. For the used Ln/AHA-ratios conservative complex stability constants log β_LnAHA decrease from 6.33 (100 μg L⁻¹ Ln³⁺) to 4.31 (6000 μg L⁻¹ Ln³⁺) with growing Ln-content. In order to verify the postulated weaker and stronger humic acid binding sites for trivalent Eu and Gd, a modified AHA with blocked functional groups was used. For these experiments 500 μg L⁻¹ Eu and 25 mg L⁻¹ AHA and AHA-PB in 10 mM NaClO₄ at pH-values ranging from 3 to 10 have been applied. With AHA-PB, where 84% of the phenolic OH-groups and 40% of the COOH-groups were blocked, Eu complexation was significantly lower, especially at the strong binding sites. The log β-values decrease from 6.11 (pH 10) to 5.61 at pH 3 (AHA) and for AHA-PB from 6.01 (pH 7) to 3.94 at pH 3. As a potential consequence, particularly humic acids with a high amount of strong binding sites (e.g. phenolic OH- and COOH-groups) can be responsible for a higher metal mobility in the aquifer due to the formation of dissolved negatively charged metal-humate species.     

Electrochemical studies of the interaction of Basic Brown G with DNA and determination of DNA

A new method of electrochemical probe has been proposed for the determination of Herring Sperm DNA (DNA) based on its interaction with Basic Brown G (BBG). The electrochemical behavior of interaction of BBG with DNA was investigated on Hg electrode. In 0.1 mol L⁻¹ NH₃-NH₄Cl buffer solution (pH 8.0), BBG can be reduced on Hg electrode with a well-defined voltammetric peak at −0.67 V (versus SCE). In the presence of DNA, the reduction peak current of BBG decreases and the peak potential shifts to a more positive potential without the appearance of new peak. The study shows that a new BBG-DNA complex is formed by linear sweep voltammetry (LSV) and spectrophotometry. The decrease of the second order derivative of reductive peak current (Δi^″p) of BBG is proportional to the concentration of DNA in the range of 0.10-36 μg mL⁻¹. Limit of detection of DNA is 0.04 μg mL⁻¹. DNA of Hepatitis B Virus in serum samples was determined satisfactorily. Additionally, the binding mechanism was preliminarily discussed. The mode of interaction between BBG and DNA was found to be intercalation binding.     

Spectrometric study of the interaction between Alpinetin and bovine serum albumin using chemometrics approaches

The binding interaction of Alpinetin (APT) with bovine serum albumin (BSA) was studied by fluorescence, UV-visible and synchronous fluorescence spectroscopy (SFS) under simulated physiological conditions. The measured complex spectra were resolved by multivariate curve resolution-alternating least squares (MCR-ALS), yielding a host of data and information, which otherwise would have been impossible to obtain. The extracted profiles corresponded to the spectra of the single species in the APT/BSA mixture. In addition, the presence of the APT-BSA complex was demonstrated, and it was shown that the associated quenching of the fluorescence from the BSA protein resulted from the formation of APT-BSA complex via a static mechanism. The binding constant (K_a(ave) = 2.34 × 10⁶ L mol⁻¹) and the number of sites (n = 1) were obtained by fluorescence methods as were the thermodynamic parameters (ΔH⁰, ΔS⁰ and ΔG⁰). This work suggested that the principal binding between APT to BSA was facilitated by hydrophobic interactions. The thermodynamic parameters for APT were compared to those from the structurally similar Chrysin and Wogonin molecules. It appeared that the entropy parameters were relatively more affected by the small structural changes. SFS from the interaction of BSA and APT showed that the ligand affected the conformation of BSA. The competitive interaction of APT and site makers with BSA indicated site I as the binding area of APT in BSA.     

Synthesis of three haptens for the class-specific immunoassay of O,O-dimethyl organophosphorus pesticides and effect of hapten heterology on immunoassay sensitivity

A general and broad class-specific enzyme-linked immunosorbent assay was developed for the O,O-dimethyl organophosphorus pesticides, including malathion, dimethoate, phenthoate, phosmet, methidathion, fenitrothion, methyl parathion and fenthion. Three haptens with different spacer-arms were synthesized. The haptens were conjugated to bovine serum albumin (BSA) for immunogens and to ovalbumin (OVA) for coating antigens. Rabbits were immunized with the immunogens and six polyclonal antisera were produced and screened against each of the coating antigens using competitive indirect enzyme-linked immunosorbent assay for selecting the proper antiserum. The effect of hapten heterology on immunoassay sensitivity was also studied. The antibody-antigen combination with the most selectivity for malathion was further optimized and tested for tolerance to co-solvent, pH and ionic strength changes. The IC₅₀ values, under optimum conditions, were estimated to be 30.1 μg L⁻¹for malathion, 28.9 μg L⁻¹ for dimethoate, 88.3 μg L⁻¹ for phenthoate, 159.7 μg L⁻¹ for phosmet, 191.7 μg L⁻¹ for methidathion, 324.0 μg L⁻¹ for fenitrothion, 483.9 μg L⁻¹ for methyl parathion, and 788.9 μg L⁻¹ for fenthion. Recoveries of malathion, dimethoate, phenthoate, phosmet and methidathion from fortified Chinese cabbage samples ranged between 77.1% and 104.7%. This assay can be used in monitoring studies for the multi-residue determination of O,O-dimethyl organophosphorus pesticides.     

Determination of brominated phenols in water samples by on-line coupled isotachophoresis with capillary zone electrophoresis

A method for determination of nine brominated phenols as environmental risk compounds was developed by on-line coupled capillary isotachophoresis and capillary zone electrophoresis (ITP–CZE). For ITP step, 1 × 10⁻² mol L⁻¹ hydrochloric acid with 3 × 10⁻² mol L⁻¹ ammediol pH 9.1 was used as the leading electrolyte, and 3 × 10⁻² mol L⁻¹ β-alanine with 2 × 10⁻² mol L⁻¹ sodium hydroxide pH 10.05 was used as the terminating electrolyte. As the background electrolyte for CZE separation, 2.5 × 10⁻² mol L⁻¹ β-alanine with 2.5 × 10⁻² mol L⁻¹ lysine pH 9.6 was used. All electrolytes contained 0.05% or 0.1% (m/v) hydroxyethylcellulose to suppress the electroosmotic flow. UV detection at wavelength 220 nm was used. Detection limits in order of tens of nmol L⁻¹ were achieved. Good repeatability of migration times (less than 0.33% RSD) and good repeatability of peak areas (less than 7.19% RSD) at concentration level 5 × 10⁻⁸ mol L⁻¹ were observed. Developed ITP–CZE method was applied to determination of brominated phenols in spiked tap and river water samples.     

Linear polyamines as carriers in thiocyanate-selective membrane electrodes

The polyamines, octyl-[2-(2-octylamino-ethylamino)-ethyl]-amine (L¹) and octyl-{2-[2-(2-octylamino-ethylamino)-ethylamino]-ethyl}-amine (L²), have been used as anion ionophores in PVC-based membrane ion-selective electrodes. Different electrodes were prepared containing L¹, or L², and o-nitrophenyl octyl ether (NPOE) or bis(2-ethylhexyl)sebacate (DOS) as plasticizers. The response of the electrodes was tested in two different buffers, HEPES-KOH (pH 7) and MES-KOH (pH 5.6). Electrodes containing L¹ and L² with NPOE (E1 and E2, respectively) showed a Nernstian response for thiocyanate with a good response time. The detection limit, linear range and slope for electrode E1 were 3.8 × 10⁻⁶ mol dm⁻³, 1 × 10⁻⁵ to 1 × 10⁻¹ mol dm⁻³ and −57.2 mV decade⁻¹ at pH 5.6 and 4.47 × 10⁻⁶ mol dm⁻³, 1.95 × 10⁻⁵ to 1 × 10⁻¹ mol dm⁻³ and −58.1 mV decade⁻¹ at pH 7.0. For electrode E2 the detection limit, linear range and slope found were 2.63 × 10⁻⁶ mol dm⁻³, 7.94 × 10⁻⁶ to 1 × 10⁻¹ mol dm⁻³ and −58.5 mV decade⁻¹ at pH 5.6 and 1.23 × 10⁻⁵ mol dm⁻³, 7.95 × 10⁻⁵ to 1 × 10⁻¹ mol dm⁻³ and −46.0 mV decade⁻¹ at pH 7. In contrast, electrodes containing DOS as plasticizers gave only response at pH 5.6 (detection limit, linear range and slope at pH 5.6 were 3.16 × 10⁻⁵ mol dm⁻³, 1 × 10⁻⁴ to 1 × 10⁻¹ mol dm⁻³ and −52.6 mV decade⁻¹). Selectivity coefficients for different anions with respect to thiocyanate were calculated. The electrode E2 at pH 5.6 was also used for the determination of SCN⁻ by potentiometric titrations with Ag⁺ ions with good results. The electrode E2 was also used to determine concentrations of thiocyanate in biological samples.     

Study on the interaction between oxolinic acid aggregates and protein and its analytical application

It was found that oxolinic acid (OA) at high concentration can self-assemble into nano- to micro- meter scale OA aggregates in Tris-HCl (pH 7.48) buffer solution. The nanoparticles of OA were adopted as fluorescence probes in the quantitative analysis of proteins. Under optimum conditions, the fluorescence quenching extent of nanometer scale OA aggregates was in proportion to the concentration of albumins in the range of 3.0 × 10⁻⁸ to 3.0 × 10⁻⁵ g mL⁻¹ for bovine serum albumin (BSA) and 8.0 × 10⁻⁸ to 8.0 × 10⁻⁶ g mL⁻¹ for human serum albumin (HSA). The detection limits (S/N = 3) were 3.4 × 10⁻⁹ g mL⁻¹ for BSA, and 2.6 × 10⁻⁸ g mL⁻¹ for HSA, respectively. Samples were satisfactorily determined. The interaction mechanism of the system was studied using fluorescence, UV-vis, resonance light scattering (RLS) and transmission electron microscope (TEM) technology, etc., indicating that the nonluminescent complex was formed between serum albumin molecular and OA, to disaggregate the self-association of OA, which resulted in the dominated static fluorescence quenching in the system.     

A novel Lu fluorescent nano-chemosensor using new functionalized mesoporous structures

A new Lu³⁺ sensitive fluorescent chemosensor is designed using 8-hydroxyquinoline functionalized mesoporous silica with highly ordered structure (LUS-SPS-Q). The characterization of LUS-SPS-Q showed that the organized structure has been preserved after the post grafting procedure. The synthesized material showed a selective interaction with Lu³⁺ ion, most probably due to the presence of the fluorophore moiety at its surface. The emission intensity of the Lu³⁺-bound mesoporous material increases with an increase in concentrations of Lu³⁺ ion. Addition of other mono-, di-, trivalent ions resulted in insignificant change in the fluorescent intensity. The enhancement of fluorescence is attributed to the strong covalent binding of Lu³⁺ ion. The linear response range of Lu³⁺ chemo-sensor was from 1.6 × 10⁻⁷ to 1.0 × 10⁻⁵ mol L⁻¹. The Limit of detection obtained was 8.2 × 10⁻⁸ mol L⁻¹ and the pH range which the proposed chemo-sensor can be applied was 3.3–8.3.     

Determination of citrate in tablets and of oxytetracycline in serum using europium (III) luminescence

A direct method for the determination of citrate and oxytetracycline in samples containing complex matrices like tablets or serum has been developed using the luminescence of the ternary complex formed with Eu(III) ions. The triplet-state energy level of oxytetracycline (OxTc), the excitation maximum (412 nm) and the luminescence lifetime of Eu-OxTc (58 μs) were determined. A 17-fold luminescence enhancement at 615 nm occurs upon addition of citrate within a short 5-min incubation time at neutral pH. This is accompanied by a threefold increase of the luminescence decay time. The optimal conditions for determination of OxTc are equal concentrations of Eu (III) and citrate (C = 1 · 10^− 4 mol L^− 1) and pH 7.2. For determination of citrate, the optimal concentrations of Eu(III) and OxTc are 1 : 0.5 (C_Eu = 1 · 10^− 4 mol L^− 1, C_OxTc = 5 · 10^− 5 mol L^− 1) at pH 7.2. The linear range for determination of OxTc in serum is 0.25-250 μg mL^− 1, and for citrate in tablets from 0.5 to 10.0 μg mL^− 1 (2.3 · 10^− 6- 4 · 10^− 5 mol L^− 1). The detection limit was 0.1 μg mL^− 1 for OxTc and 0.2 μg mL^− 1 (1 · 10^-6 mol L^− 1) for citrate, respectively. A comparison of the new method with other methods for determination of citrate is given.     

Simultaneous cloud point extraction and spectrophotometric determination of carmoisine and brilliant blue FCF in food samples

A novel simultaneous cloud point extraction method for the determination of carmoisine and brilliant blue FCF by spectrophotometry has been developed. The method is based on the cloud point extraction of carmoisine and brilliant blue FCF from aqueous solution using Triton X-100, diluting the extracted surfactant rich phase with water and measuring the absorbance at 522 and 640 nm for carmoisine and brilliant blue FCF, respectively. The effects of different parameters such as pH, concentration of surfactant and temperature on the cloud point extraction of both dyes were investigated and optimum conditions were established. Linear calibration curves were obtained in the range of 0.02-3.50 μg mL⁻¹ for carmoisine and 0.05-3.50 μg mL⁻¹ for brilliant blue FCF under optimum conditions. Detection limit based on three times the standard deviation of the blank (3S_b) was 0.017 and 0.016 μg mL⁻¹ (n = 10) for carmoisine and brilliant blue FCF, respectively. The relative standard deviation (RSD) for 0.1 μg mL⁻¹ was 4.14 and 3.30% (n = 10), for carmoisine and brilliant blue FCF, respectively. The method was applied to the simultaneous determination of the dyes in different food samples.     

Voltammetric determination of sericin based on its interaction with carmine

A simple yet sensitive method is developed for the determination of sericin using voltammetry based on the interaction between sericin and carmine for the first time. In the absence of sericin, carmine has a pair of well-defined redox peaks in a pH 1.81 Britton-Robinson buffer solution. Although no new redox peaks appear upon the addition of sericin into a carmine solution, the peak currents of the old peaks reduce while the peak potentials shift positively. This observation is attributed to the decrease in the diffusion coefficient and electrode reaction rate constant of carmine in the presence of sericin. A binding mechanism is proposed and discussed, and the binding constant and binding ratio are calculated as 2.32 × 10⁶ L mol⁻¹ and 1:1, respectively. Furthermore, the decrease in the peak currents is found proportional to the sericin concentration in the range of 32.0-800.0 μg mL⁻¹ with a detection limit of 13.52 μg mL⁻¹. The method is further applied to the determination of sericin in degumming wastewater with satisfied average recoveries from 96.7 to 103.3%. The results are in good agreement with those obtained by the conventional Coomassie brilliant blue G-250 spectrophotometric method.     

A novel amperometric biosensor based on single walled carbon nanotubes with acetylcholine esterase for the detection of carbaryl pesticide in water

Amperometric biosensor is fabricated for the detection of carbaryl based on single walled carbon nanotubes (SWCNTs) and acetylcholine esterase (AchE). The dispersion of SWCNTs in positively charged polyelectrolyte, poly(diallyldimethylammonium chloride) (PDDA), possibly takes place due to weak supramolecular interaction between them, which then binds electrostatically to the negatively charged AchE at pH 7.4 using layer-by-layer (LbL) self-assembly technique. The optical intensity of UV/vis spectra increased with the number of layers, indicating the build up of a multilayer coating on the electrode. The activity of acetylcholine esterase on modified electrode of 3 mm in diameter was found to be 0.2 U. The biosensor showed good sensitivity and stability towards the monitoring of carbaryl pesticides in water with the detection limit of 10⁻¹² g L⁻¹ and recovery of 99.8 ± 2.7% to 10⁻¹⁰ g L⁻¹. This protocol can be used for the immobilization of other enzymes to fabricate a range of biosensors.     

Development and characterization of a new polyampholyte-surfactant complex applied to the solid phase extraction of bisphenol-A

This paper presents a material that has both hydrophilic and hydrophobic domains, obtained by combination of a polyampholyte with a surfactant. This material was fully characterized by different spectroscopic techniques and microscopy.Bisphenol-A (BPA) was chosen as a model molecule to study the interaction with compounds of intermediate polarity. We explored the kinetics and equilibrium of BPA on the surface of the polyampholyte-surfactant complex and found a significantly high loading capacity (2.02 mmol g⁻¹) and complete binding from solutions at concentration levels below 100 μmol L⁻¹.The complex was encapsulated in agarose gel to be used as solid phase for extraction of BPA from food simulants in contact with polycarbonate bottles under different treatments. Bisphenol was preconcentrated, extracted and analysed by liquid chromatography with an amperometric detector. The instrumental detection limit of the technique was 10 μg L⁻¹, which was lowered to 0.14 μg L⁻¹ by the preconcentration step. The BPA released from baby bottles was 2.1 ng cm⁻² (σ_n − 1: 0.1) in the first use with distilled water.