Optical ascorbic acid sensor based on the fluorescence quenching of silver nanoparticles.

A sensitive and selective fluorimetric sensor for the assay of ascorbic acid (AA) using silver nanoparticles as emission reagent was investigated. In this study, silver nanoparticles were prepared based on aqueous-gaseous phase reaction of silver nitrate solution and ammonia gas. The nanoparticles were water-soluble, stable and had a narrow emission band. They were used as a fluorescence probe for the assay of ascorbic acid on its quenching effect on the emission of silver nanoparticles. The principal reason for quenching is likely to be a complexation between ascorbic acid and silver nanoparticles. The quenching mechanism was established by Stern-Volmer law. Under the optimum conditions, the quenched fluorescence intensity was linear with the concentration of ascorbic acid in the range of 4.1 x 10(-6) to 1.0 x 10(-4) m (r = 0.9985) with a detection limit of 1.0 x 10(-7) m. The RSD for repeatability of the sensor for the assay of ascorbic acid concentration of 3.0 x 10(-5) and 4.0 x 10(-6) m was found to be 1.5 and 1.3%, respectively. The proposed method was applied to the determination of ascorbic acid in vegetables and vitamin C tablets.

Application of a lanthanide composite nanoparticle-sensitized luminescence method for the determination of salicylic acid in pharmaceutical formulations and human plasma.

Terbium-acetylacetone (Tb-acac) composite nanoparticles were synthesized using the ultrasonic method. The nanoparticles are water-soluble, stable and have extremely narrow emission bands and high internal quantum efficiencies. They were used as fluorimetric probes in the determination of salicylic acid (SA), based on the fluorescence enhancement of nanoparticles through fluorescence resonance energy transfer (FRET). The influence of buffer solution was investigated. Under the optimum conditions, a linear calibration graph was obtained over the SA concentration range 5 x 10(-7)-1 x 10(-4) mol/L. The limit of detection was found to be 2.5 x 10(-8) mol/L. The relative standard deviation (RSD) for six repeated measurements of 1 x 10(-4) mol/LSA was 1.75%. The method was applied to the determination of SA in pharmaceutical formulations and human plasma. We believe that the proposed approach has great potential for clinical purposes.

Simultaneous determination of levodopa and carbidopa by synchronous fluorescence spectrometry using double scans.

A synchronous fluorescence spectrometric method is described for the simultaneous determination of binary mixtures of levodopa and carbidopa in pharmaceutical formulation and urine sample, without prior separation steps, using two scans. At Delta lambda = 30 nm, only carbidopa yields a detectable signal that is independent of the presence of levodopa. Similarly, at Delta lambda = 65 nm the signal of levodopa is not influenced by the presence of carbidopa. Signals at two wavelengths, 288 nm (Delta lambda = 30 nm) and 281 nm (Delta lambda = 65 nm), vary linearly with carbidopa and levodopa concentrations over the range 0.019-1.971 microg mL(-1) (for levodopa) and 0.022-2.262 microg mL(-1) (for carbidopa), respectively. The correlation coefficients for the standard calibration graphs were 0.9962 and 0.9951 (n=10) for carbidopa and levodopa, respectively. The limits of detection (LOD estimated as per IUPAC recommendations) were 0.01 and 0.006 microg mL(-1) for carbidopa and levodopa, respectively. The method was successfully applied to the determination of levodopa and carbidopa in pharmaceutical formulation and urine sample. The recovery results were satisfactory.

Development of a sensitive flow-injection-chemiluminescence detection method for the determination of levodopa.

A simple chemiluminometric method using flow injection has been developed for the determination of levodopa, based on its sensitizing effect on the weak chemiluminescence (CL) reaction between Na(2)SO(3) and acidic KMnO4. Under optimum experimental conditions, the CL intensity was linearly related to the concentration of levodopa from 3.4 x 10(-8) to 2.4 x 10(-5) mol/L and the detection limit was 1.1 x 10(-8) mol/L (s:n = 3). The relative standard deviation (RSD) of the proposed method calculated from 20 replicate injection of 3 x 10(-7) mol/L levodopa was 3.3%. The correlation coefficient was 0.997. The method was successfully applied to the determination of levodopa in commercial pharmaceutical formulations and spiked urine samples.

Determination of enoxacin using Tb composite nanoparticles sensitized luminescence method.

In our study, terbium-acetylacetone (Tb-acac) composite nanoparticles have been prepared under vigorous ultrasonic irradiation. The nanoparticles are water soluble, stable and have extremely narrow emission bands and high internal quantum efficiencies. They were used as fluorescence probes in the determination of enoxacin (Enox) based on the fluorescence enhancement of nanoparticles through fluorescence resonance energy transfer (FRET). The influence of buffer solution on the fluorescence intensity was investigated. Under the optimum conditions, the fluorescence intensity of the Tb-acac-Enox system is linearly proportional to the Enox concentration in the Enox concentration range of 2 x 10(-7)-1 x 10(-4) M. The correlation coefficient for the calibration curve was 0.9976. The limit of detection as defined by IUPAC, C (LOD) = 3S (b)/m (where S (b) is the standard deviation of the blank signals and m is the slope of the calibration graph) was found to be 3 x 10(-8) M. The relative standard deviation (RSD) for six repeated measurements of 1 x 10(-4) M Enox was 1.35%. The method was applied to the determination of Enox in pharmaceutical formulation and recovery results were obtained from urine samples.

Optical flow-through sensor for the determination of norfloxacin based on emission of KMnO(4)-Na (2)SO (3)-Tb (3+) system.

A simple and selective method to determine norfloxacin using an optical flow-through sensor has been developed. The present sensor was prepared by packing anionic ion exchange resin in a glass tube, followed by introducing KMnO(4) solution to the glass tube for immobilization on resin. The optical sensor is based on the emission intensity from the Tb(III) solution sensitized by norfloxacin. The excitation of norfloxacin occurred by the chemiluminescence from the reaction of KMnO(4) and Na(2)SO(4) solutions. The effects of pH, concentration of Tb(III) ion, KMnO(4) and Na(2)SO(4) solutions and flow rate of the norfloxacin solution on the chemiluminescence intensity were studied to find the optimum experimental conditions. The emission intensity increased linearly with increasing norfloxacin concentration from 1.0 x 10(-3) to 1.0 x 10(-8) M and the detection limit (3sigma) was 8.7 x 10(-9). The applicability of the present method was demonstrated by determination of norfloxacin in various pharmaceutical preparations and serum sample.

Selective fluorimetric recognition of cesium ion by 15-crown-5-anthracene.

A selective fluorescent cesium optode on a chromoionophore consisting of anthracene covalently linked through an imine bond to a 15-crown-5 derivative has been reported. In the present system, 15-crown-5 derivative including anthracene was used a fluoroionophore. The fluorescence response mechanism is based on the photo-induced electron transfer (PET) from the lone pair of electrons of the nitrogen to the anthracene group and inhibition of PET system by cesium binding while increasing the fluorescence intensity. Emission intensity 15-crown-5 anthracene was measured at 500 nm with absorbance at 400 nm in CH(3)CN-H(2)O (1:1) media. The method shows a very good selectivity and sensitivity for cesium with respect to other cations such as K(+), Na(+) and Li(+) with linear range and detection limit of 5.0 x 10(-5) to 5.0 x 10(-1)M and 3.0 x 10(-6)M respectively.

Quantitative determination of bilirubin by inhibition of chemiluminescence from lucigenin.

Bilirubin is a metabolic breakdown product of blood haem, of great biological and diagnostic importance. A new chemiluminescence (CL) method has been developed for the quantification of bilirubin. The method is combined with the flow injection analysis (FIA) technique and based on the inhibition effect of bilirubin on the CL from the lucigenin-hydrogen peroxide system in an alkaline medium. Under the optimum conditions, the decreased CL intensity was proportional to the concentration of bilirubin, in the range 0.0585-58.47 microg/mL. The detection limit estimated from the calibration graph was about 7.8826 ng/mL. The relative standard deviation (RSD) of 10 parallel measurements (1 x 10(-4) mol/L bilirubin) was 2.5%. Recoveries of bilirubin were found to fall in the range 94-97.5% using control sera. The method is interference-free, fast and easy to carry out.

Spectrofluorimetric estimation of norepinephrine using ethylenediamine condensation method.

A simple and sensitive method for the determination of norepinephrine is described. Norepinephrine (NE) was oxidized by mercury (II) nitrate and the oxidation product was condensed with ethylenediamine (EDA) to form a strong fluorescent compound. The addition of acetone enhances the light intensity. The measurement was carried out at 507 nm with excitation at 420 nm. A linear relationship was obtained between the fluorescence intensity and norepinephrine concentration in the range of 0.01 microM-0.014 mM; the correlation coefficient and the detection limit are 0.99813 and 2.5 nM, respectively. The interference from dopamine (DA) can be eliminated by first derivative synchronous fluorimetric method using peak to zero technique. The recovery efficiency was performed using known amounts of norepinephrine in urine sample and the results indicate a 95-98.62% recovery. The proposed method was also applied to the determination of norepinephrine in injections solution. The reaction mechanism was also described.

Simultaneous determination of acetylsalicylic acid and caffeine in pharmaceutical formulation by first derivative synchronous fluorimetric method.

A sensitive, rapid, and specific assay has been developed for the simultaneous determination of acetylsalicylic acid and caffeine in commercial tablets based on their natural fluorescence. The mixture of these drugs was resolved by first derivative synchronous fluorimetric technique using two scans. At Deltalambda=106 nm, using first derivative synchronous scanning, only acetylsalicylic acid yields a detectable signal at 316 nm (peak to zero method) which is unaffected by caffeine. At Deltalambda=30 nm, the signal of caffeine at 288 nm (peak to zero method) is not affected by acetylsalicylic acid. The range of application is between 0.021 and 41.62 microg ml(-1) (correlation coefficient, R=0.9995) for acetylsalicylic acid and between 0.4486 and 44.86 microg ml(-1) (correlation coefficient, R=0.99786) for caffeine. The recovery range of 98.40-102% for acetylsalicylic acid and 90-100.5% for caffeine from their synthetic mixture was reported. Overall recovery of both compounds about 97-99% for acetylsalicylic acid and 97-98% for caffeine was obtained from real sample analysis. The detection limits are 0.0013 microg ml(-1) and 0.0306 microg ml(-1) for acetylsalicylic acid and caffeine, respectively. The relative standard deviation (n=10) for 20 microg ml(-1) of acetylsalicylic acid is 2.75% and for 2.2 microg ml(-1)of caffeine is 1.7%.

A batch chemiluminescence determination of enoxacin using a tris-(1,10-phenanthroline)ruthenium(II)-cerium(IV) system.

A batch type chemiluminescence (CL) determination of enoxacin is described. In this work, it was observed that enoxacin could enhance the chemiluminescence (CL) emission Ru(phen)3(2+)-Ce(IV) system and this enhancement effect was dependent on the concentration of enoxacin, based on which, CL system was established for the determination of enoxacin. Under the optimum experimental conditions, the linear range and detection limit are 0.6406-64.06 microg/ml and 0.0210 microg/ml, respectively. The R.S.D. is 1.75%. (n = 10). The proposed method has been applied to detect the content of enoxacin in pharmaceutical formulation and human serum with satisfactory results. The possible mechanism of the CL reaction was discussed.

Fluorimetric determination of cerium(IV) with ascorbic acid.

A simple, sensitive, and selective method for the determination of cerium(IV), based on the oxidative reaction between cerium(IV) and ascorbic acid, has been described. The fluorescence comes from Ce(III) at lambda(excitation) 298 nm and lambda(emission) 358 nm, which, in turn, is obtained from the oxidation of ascorbic acid by Ce(IV) in the presence of sulfuric acid. The optimum conditions such as concentrations of ascorbic acid, sulfuric acid media and pH of the buffer solution were investigated. The fluorescent intensity of the system is linear over the range 0.0531 microg/ml to 0.3322 mg/ml Ce(IV) and detection limit and correlation coefficient are 0.0145 microg/ml and R=0.99987, respectively.

Treatment of colored effluent of the textile industry in Bangladesh using zinc chloride treated indigenous activated carbons.

The adsorption of colored compounds from the textile dyeing effluents of Bangladesh on granulated activated carbons produced from indigenous vegetable sources by chemical activation with zinc chloride was studied. The most important parameters in chemical activation were found be the chemical ratio of ZnCl2 to feed (3:1), carbonization temperature (450-465 degrees C) and activation time (80 min). The adsorbances at 511 nm (red effluent) and 615 nm (blue effluent) were used for color estimation. It is established that at optimum temperature (50 degrees C), time of contact (30-40 min) and adsorbent loading (2 g l(-1)), activated carbons developed from Segun saw-dust and water hyacinth showed substantial capability to remove coloring materials from the effluents. It is observed that adsorption of reactive dyes by all sorts of activated carbons is higher than disperse dyes. It is explained that activated carbon, because of its acidic nature, can better adsorb reactive dye particles containing large number of nitrogen sites and -SO3Na group in their structure. The use of carbons would be economical, as saw-dust and water hyacinth are waste products and abundant in Bangladesh.

Analysis of salicylic acid based on the fluorescence enhancement of the As(III)-salicylic acid system.

A new, simple and sensitive spectrofluorimetric method for the determination of salicylic acid (lambda(ex)=315 nm, lambda(em) = 408 nm) using As(III) as a sensitizing reagent has been investigated by measuring the increase of fluorescence intensity of salicylic acid due to the complexation of As(III)-salicylic acid in presence of sodium dodecyl sulfate (SDS) 10(-3) M. Under optimum conditions, a significant relationship was obtained between the fluorescence intensity and salicylic acid concentration. A linear calibration curve was obtained in the range 13.8-13812 microg l(-1) with product-moment correlation coefficient (R) 0.99985 and detection limit 4.2 microg l(-1). The R.S.D. is 2.35% (n=5). The method was applied successfully to the determination of salicylic acid in human serum.

Determination of catechin in aqueous solution by chemiluminescence method.

A method to determine catechin in aqueous solution by measuring chemiluminescence intensities using a stopped flow system has been studied. The lucigenin-hydrogen peroxide chemiluminescence reaction was chosen for the determination of catechin. Fe(II) ion was added to the chemiluminescence system to increase the sensitivity. The chemiluminescence intensity from the lucigenin system was increased by the addition of catechin. Effects of flow rates of reagent and sample and concentrations of lucigenin, hydrogen peroxide, Fe(II) ion and KOH were investigated. The calibration curve for catechin was linear over the range from 1.0x10(-6) to 1.0x10(-3) M and the detection limit was 3.0x10(-7) M under the optimal experimental conditions.