Optochemical sensor for an ornidazole assay using 1-amino-4-allyloxyanthraquinone as a fluorescent indicator.

To improve the stability of optochemical sensors (optodes), the fluorescence indicator 1-amino-4-allyloxyanthraquinone (AAA), which was synthesized by reacting allyl bromide with 1-amino-4-hydroxyanthraquinone, was covalently immobilized on surface-modified glass slides. The resulting sensor was used to determine the content of ornidazole based on fluorescence quenching. It showed a linear response toward ornidazole in the concentration range of 9.0 x 10(-6) to 1.0 x 10(-3) mol L(-1) with a detection limit of 8 x 10(-6) mol L(-1) at pH 7.5. This AAA-immobilized sensor has a rapid response, high stability and good selectivity to ornidazole.     

An optical fiber sensor for berberine based on immobilized 1,4-bis(naphth[2,1-d]oxazole-2-yl)benzene in a new copolymer

A new copolymer made of 8-quinolyl methacrylate, methyl methacrylate and n-butyl acrylate(PQMB) has been used as a solid substrate for the preparation of an optical fiber berberine sensor. The sensing is based on the fluorescence of 1,4-bis(naphth[2,1-d]oxazole-2-yl)benzene(BNOB) immobilized in the copolymer quenched by berberine with the formation of 1:1 complex between them. The membrane composition was optimized using the orthogonal experimental design. Using the sensor described above, berberine in a sample solution from 4.02x10(-7) mol l(-1) to 2.82x10(-4) mol l(-1) can be detected. The sensor has satisfactory reversibility and a short response time of less than 30 s. The relative standard deviations for repeated measurements (n=15) of 8.05x10(-6) mol l(-1) and 4.02x10(-5) mol l(-1) beberine are 0.43% and 0.33%, respectively. The sensor shows good selectivity over alkali and alkali-earth metal salts and some common pharmaceutical species and can be used for the determination of berberine in pharmaceutical preparations.     

A coumarin derivative covalently immobilized on sensing membrane as a fluorescent carrier for nitrofurazone

A coumarin derivative 4-methyl-8-methylacrylamide-2H, 5H-pyrano [3, 2-C] benzpyran 2, 5-dione (MMPBD) has been synthesized as a fluorescent carrier for preparing an optical chemical sensor. The carrier is immobilized on a quartz glass plate surface treated with a silanizing agent to prevent the leakage of the dye. This MMPBD sensor can be utilized for a nitrofurazone (NF) assay based on fluorescence quenching. The sensor shows good repeatability, a long lifetime and a fast response of less then 50 s. NF can be determined in the range between 1.0x10(-6)-1.0x10(-3 )mol L(-1) with a detection limit of 8.0x10(-7) mol L(-1 )at pH 7.0.     

A selective optical chemical sensor for o-nitrophenol based on fluorescence quenching of curcumin

An optical chemical sensor has been prepared for the selective determination of o-nitrophenol in aqueous solutions based on the fluorescence quenching of curcumin in PVC membrane. The sensing mechanism of the proposed sensor for o-nitrophenol has been discussed in detail. The fluorescence changes of sensing membrane resulted from an associated complex formation between curcumin and o-nitrophenol. In pH 4.8 buffer solution, the sensor responds linearly in the measuring range from 1.0 x 10(-2) mol 1(-1) to 1.5 x 10(-4) mol 1(-1), and the experimental detection limit is evaluated to be 8.0 x 10(-5) mol 1(-1). A stable signal was obtained within less than 1.5 min. Under the optimum conditions, the sequence of selective response to the sensing membrane is o-nitrophenol > 2,4-dinitrophenol > m-nitrophenol > p-nitrophenol > 2,4,6-trinitrophenol. Phenol, aniline as well as other ions have less effect on the fluorescence of the sensor. The reproducibility for the determination of o-nitrophenol is better than 1%, and the response is reversible. The sensor can be used for the determination of o-nitrophenol in water samples.     

Fluorescence optical fiber sensor for tetracycline

A new optical fiber sensor for monitoring tetracycline has been described, based on the fluorescence quenching of 1,4-bis(5,5'-dimethylbenzoxazole-1',3'-yl-2')benzene incorporated into a thin plasticized polymer film by tetracycline extracted from aqueous phase into film phase. The sensor is fully reversible and highly reproducible. Furthermore, the sensor exhibits a linear response to tetracycline in the range 6.98x10(-7)-8.73x10(-5) mol l(-1) with a detection limit of 1.06x10(-7) mol l(-1), and with the response time <30 s. The response is also selective to tetracycline, with some common pharmaceutical species, alkali and alkali-earth metal salts being highly discriminated, suggesting that the sensor can be used to monitor tetracycline in three pharmaceutical preparations. The recovery of tetracycline from commercial formulations is 95.3-98.3%.     

Lead as own luminescent sensor for determination

In our experiments, it was observed that adding bromide to Pb2+ solution of N,N'-dimethylformamide (DMF), the highly emissive cluster Pb4Br11(3-) can be formed and the fluorescence intensity of the formed cluster is proportional to the concentration of Pb2+, based on which, a novel, simple approach that uses the emission from itself as the sensor for determination of Pb2+ is proposed. Under the optimum conditions, the linear range and detection limit is 1.0 x 10(-7) to 1.0 x 10(-5) mol l(-1) (correlation coefficient r = 0.9997) and 7.6 x 10(-9) mol l(-1), respectively. Foreign substrates effects were also investigated. The proposed method has been successfully applied to the determination of lead in the synthetic samples. The mechanism of the reaction is also studied.     

A fluorescence quenching method for the determination of nitrite with Rhodamine 110

A simple and sensitive fluorescence quenching method for the determination of trace nitrite has been developed. The method is based on the reaction of Rhodamine 110 with nitrite in acidic medium to form a new compound, which has much lower fluorescence. The optimum experimental conditions were studied. The linear range was obtained at a nitrite concentration of 1.0 x 10(-8)-3.0 x 10(-7)mol l(-1) with a detection limit of 7.0 x 10(-10) mol l(-1) (S/N=3). The proposed method has been successfully applied to the determination of nitrite in tap water and lake water without extraction.     

Potentiometric membrane electrode for salicylate based on an organotin complex with a salicylal Schiff base of amino acid.

A novel salicylate-selective electrode based on an organotin complex with a salicylal Schiff base of amino acid salicylaldehydeaminoacid-di-n-butyl-Sn(IV) [Sn(IV)-SAADB] as ionophore is described, which exhibits high selectivity for salicylate over many other common anions with an anti-Hofmeister selectivity sequence: Sal- > PhCOO- > SCN- > Cl04- > I- > NO3- > NO2- > Br- > Cl- > CH3COO-. The electrode, based on Sn(IV)-SAADB, with a 30.44 wt% PVC, a 65.45 wt% plasticizer (dioctyl phthalate, DOP), a 3.81 wt% ionophore and a 0.3 wt% anionic additive is linear in 6.0 x 10(-6) - 1.0 x 10(-1) mol l(-1) with a detection limit of 2.0 x 10(-6) mol l(-1) and a slope of 62.0 +/- 1.2 mV/decade of salicylate concentration in a phosphate buffer solution of pH 5.5 at 25 degrees C. The influence on the electrode performances by lipophilic charged additives was studied, and the possible response mechanism was investigated by UV spectra. The electrode was applied to medicine analysis and the result obtained has been satisfactory.     

A PVC plasticized sensor for Ni(II) ion based on a simple ethylenediamine derivative.

A new PVC membrane ion selective electrode which is highly selective towards Ni(II) ions was constructed using a Schiff base containing a binaphthyl moiety as the ionophore. The sensor exhibited a good Nernstian response for nickel ions over the concentration range 1.0x10(-1)-5.0x10(-6) M with a lower limit of detection of 1.3x10(-6) M. It has a fast response time and can be used for a period of 4 months with a good reproducibility. The sensor is suitable for use in aqueous solutions in a wide pH range of 3.6-7.4 and works satisfactorily in the presence of 25% (v/v) methanol or ethanol. The sensor shows high selectivity to nickel ions over a wide variety of cations. It has been successfully used as an indicator electrode in the potentiometric titration of nickel ions against EDTA and also for the direct determination of nickel content in real samples: effluent samples, chocolates and hydrogenated oils.     

Conjugated carbazole dimer as fluorescence carrier for preparation of iodine-sensitive chemical sensor

The carbazole derivative, 9-ethyl-3-carbazylidene carbazole hydrazone (ECCH) with two conjugated carbazole rings have been applied as a fluorescence carrier for preparation of an iodine sensitive optical chemical sensor. The response of the sensor is based on quenching of the fluorescence of ECCH by iodine. The conjugated carbazole dimer based sensor shows a linear response toward iodine in the concentration range 1.0 × 10⁻⁶ to 1.0 × 10⁻⁴ mol L⁻¹, with a detection limit of 8.0 × 10⁻⁷ mol L⁻¹ at pH of 7.0. The effect of composition of the sensor membrane was studied, and the experimental conditions were optimized. Most commonly coexisting ions do not interfer with the iodine assay. The sensor shows sufficient repeatability, selectivity, operational lifetime of two months and a fast response of less then 50 s. The sensor has been used for determination of iodine in water samples.     

Diffusion coefficient measurements in microfluidic devices

A glassy carbon electrode (GCE) modified with Pd/IrO(2) provides excellent electrocatalytic oxidation of hydrogen peroxide. Glucose oxidase (GOD) and xanthine oxidase (XOD) were co-immobilized on the modified electrode with a thin film Nafion coated on the enzyme layer to form a glucose (Glu)/hypoxanthine (Hx) sensor, without interference from electroactive species such as ascorbic acid (AA) and uric acid (UA). Its response was evaluated with respect to the enzyme amount on the electrode, pH and temperature of the electrolyte. The prepared bienzymic biosensor, used as the detector of HPLC gave a detection limit of 1.0x10(-6) mol l(-1) Glu and 2.0x10(-7) mol l(-1) Hx (Hx) with a linear concentration range of 5.0x10(-6)-2.5x10(-3) mol l(-1) and 1.0x10(-6)-5.0x10(-4) mol l(-1), respectively. Coupled with microdialysis, it was used to monitor the concentrations of Glu and Hx in rat brain.     

Copper (II) ion selective liquid membrane electrode based on new Schiff base carrier

Cu2+ selective PVC membrane electrode based on new Schiff base 2, 2'-[1,9 nonanediyl bis (nitriloethylidyne)]-bis-(1-naphthol) as a selective carrier was constructed. The electrode exhibited a linear potential response within the activity range of 1.0 x 10(-6) - 5.0 x 10(-3) moll(-1) with a Nernstian slope of 29 +/- 1 mV decade(-1) of Cu2+ activity and a limit of detection 8.0 x 10(-7) mol l(-1). The response time of the electrode was fast, 10 s, and stable potentials were obtained within the pH range of 3.5- 6.5. The potentiometric selectivity coefficients were evaluated using two solution method and revealed no important interferences except for Ag+ ion. The proposed electrode was applied as an indicator electrode to potentiometric titration of Cu2+ ions and determination of Cu2+ content in real samples such as black tea leaves and multivitamin capsule.     

An optode sensor for Cu2+ with high selectivity based on porphyrin derivative appended with bipyridine.

A porphyrin derivative (fluorophore) appended with bipyridine (ionophore) has been applied for preparation of a Cu2+-sensitive optical chemical sensor, which is based on fluorescence quenching of porphyrin derivative entrapped in a poly(vinyl chloride) membrane by the energy transfer process. The sensor exhibits a linear response toward Cu2+ in the concentration range 2.0 x 10(-8) - 1.0 x 10(-5) M, with a working pH range from 6.0 to 8.0 and a high selectivity. The detection limit is 5 x 10(-9) M. The response time for Cu2+ is less than 5 min with concentrations lower than 5 x 10(-6) M. The optode can be regenerated using 0.3 M EDTA (pH 9) and acetate buffer solution. The effect of the composition of the sensor membrane was studied, and the experimental conditions were optimized. The sensor has been used for direct determination of Cu2+ in water samples with satisfied results.     

Determination of ammonium in Kjeldahl digests by gas-diffusion flow-injection analysis with a bulk acoustic wave-impedance sensor

A novel flow-injection analysis (FIA) system has been developed for the rapid and direct determination of ammonium in Kjeldahl digests. The method is based on diffusion of ammonia across a PTFE gas-permeable membrane from an alkaline (NaOH/EDTA) stream into a stream of diluted boric acid. The trapped ammonium in the acceptor is determined on line by a bulk acoustic wave (BAW)-impedance sensor and the signal is proportional to the ammonium concentration present in the digests. The proposed system exhibits a favorable frequency response to 5.0 x 10(-6)-4.0 x 10(-3) mol l(-1) ammonium with a detection limit of 1.0 x 10(-6) mol l(-1), and the precision was better than 1% (RSD) for 0.025-1.0 mM ammonium at a through-put of 45-50 samples h(-1). Results obtained for nitrogen determination in amino acids and for proteins determination in blood products are in good agreement with those obtained by the conventional distillation/titration method, respectively. The effects of composition of acceptor stream, cell constant of conductivity electrode, sample volume, flow rates and potential interferents on the FIA signals were discussed in detail.     

Internal solid contact sensor for the determination of doxycycline hydrochloride in pharmaceutical formulation

The internal solid contact sensor for the determination of doxycycline hydrochloride (DC) was developed based on a conducting polypyrrole (PPy) film immobilized on a glassy carbon electrode surface casted by a plasticized polyvinyl chloride (PVC) membrane containing an ion-pair compound of DC with tetraphenylborate (TPB) and dibutylphthalate (DBP) as plasticizer. Effects of various factors for the electropolymerization of pyrrole or aniline, including monomer concentration, acidity or inorganic salt and thickness of polymer film were investigated experimentally. It was found that the slope and the linear range of SCSs changed with both the different concentration of monomer and of KCl in electrolyte solution and with the different substrate material and a marked influence of the change of solution pH on the potential response of sensor occurred when sample solution pH>3.5. Under the condition of pH 2.8, the sensor showed a near-Nernstian response over the range of DC concentration of 1.0x10(-2)-1.0x10(-5) mol l(-1) with the slope (at 25 degrees C) of 54.4 mV per decade. The detection limit obtained was 4.0x10(-6) mol l(-1).The sensor was successfully applied to determination of DC in pharmaceutical formulation.     

Bis(2-hydroxyacetophenone)ethylenediimine as a neutral carrier in a coated-wire membrane electrode for lead(II).

A coated-wire ion-selective electrode (CWISE), based on a Schiff base as a neutral carrier, was successfully developed for the detection of Pb(II) in aqueous solution. CWISE exhibited a linear response with a Nernstian slope of 29.4 +/- 0.5 mV/decade within the concentration range of 1.0 x 10(-5) - 1.0 x 10(-1) M lead ion. CWISE has shown detection limits of 5.0 x 10(-6) M. The electrode exhibited good selectivity over a number of alkali, alkaline earth, transition and heavy metal ions. This sensor yielded a steady potential within 10 to 20 s at a linear dynamic range. The electrode was suitable for use in aqueous solutions in a pH range of 2.0 to 5.0. Applications of this electrode for the determination of lead in real samples and as indicator electrode for potentiometric titration of Pb2+ ion using K2CrO4 are reported.     

Highly selective thiocyanate poly(vinyl chloride) membrane electrode based on a cadmium-Schiff's base complex

A PVC membrane electrode based on a cadmium-salen (N,N'-bis-salicylidene-1,2-ethylenediamine) complex as an anion carrier is described. The electrode has an anti-Hofmeister selectivity sequence with a preference for thiocyanate at pH 1.5-11.0. It has a linear response to thiocyanate from 1.0 x 10(-6) to 1.0 x 10(-1) mol L(-1) with a slope of 59.1 +/- 0.2 mV per decade, and a detection limit of 7 x 10(-7) mol L(-1). This electrode has high selectivity for thiocyanate relative to many common organic and inorganic anions. The proposed sensor has a fast response time of approximately 15 s. It was applied to the determination of thiocyanate in a milk sample.     

Silver(I) ion-selective membrane based on Schiff base-p-tert-butylcalix[4]arene

A PVC membrane electrode for silver(I) ion based on Schiff base-p-tert-butylcalix[4]arene is reported. The electrode works well over a wide range of concentration (1.0 x 10(-5)-1.0 x 10(-1) mol dm-3) with a Nernstian slope of 59.7 mV per decade. The electrode shows a fast response time of 20 s and operates in the pH range 1.0-5.6. The sensor can be used for more than 6 months without any divergence in the potential. The selectivity of the electrode was studied and it was found that the electrode exhibits good selectivity for silver ion over some alkali, alkaline earth and transition metal ions. The silver ion-selective electrode was used as an indicator electrode for the potentiometric titration of silver ion in solution using a standard solution of sodium chloride; a sharp potential change occurs at the end-point. The applicability of the sensor to silver(I) ion measurement in water samples spiked with silver nitrate is illustrated.     

Copper(II)-selective fluorimetric bulk optode membrane based on a 1-hydroxy-9,10-anthraquinone derivative having two propenyl arms as a neutral fluorogenic ionophore

A new optical chemical sensor has been developed for the selective determination of copper(II) ions in aqueous solutions. The reversible sensing system was prepared by incorporating 1-hydrpxy-2-(prop-2'-enyl)-4-(prop-2'-enyloxy)-9,10-anthraquinone (AQ) as a neutral Cu2+-selective fluoroionophore in the plasticized PVC membrane with potassium tetrakis(p-chlorophenyl borate) as an anionic additive. The response of the sensor is based on the fluorescence quenching of AQ by Cu2+ ions. At a pH 5.5, the proposed sensor displays a calibration response for Cu2+ over a wide concentration rang of 1.0 x 10(-2) to 1.0 x 10(-6) M, with a relatively fast response of less than 40 s. In addition to high stability and reproducibility, the sensor shows a unique selectivity towards Cu2+ ion with respect to common co-existing cations. The proposed fluorescence optode was applied successfully to the determination of copper(II) in black tea samples.     

A fluorescent probe for zinc ions based on N-methyltetraphenylporphine with high selectivity

N-methyl-alpha,beta,gamma,delta-tetraphenylporphine (NMTPPH) has been used to detect trace amount of zinc ions in ethanol-water solution by fluorescence spectroscopy. The fluorescent probe undergoes a fluorescent emission intensity enhancement upon binding to zinc ions in EtOH/H(2)O (1:1, v/v) solution. The fluorescence enhancement of NMTPPH is attributed to the 1:1 complex formation between NMTPPH and Zn(II) which has been utilized as the basis for the selective detection of Zn(II). The linear response range covers a concentration range of Zn(II) from 5.0x10(-7) to 1.0x10(-5)mol/L and the detection limit is 1.5x10(-7)mol/L. The fluorescent probe exhibits high selectivity over other common metal ions except for Cu(II).