Fluorimetric determination of aminocaproic acid in pharmaceutical formulations using a sequential injection analysis system

A sequential injection analysis (SIA) methodology for the fluorimetric determination of aminocaproic acid in pharmaceutical formulations is proposed. The developed analytical procedure is based on the derivatisation reaction of the aminocaproic primary amine with o-phthalaldehyde (OPA) and N-acetylcysteine (NAC) and fluorimetric detection of the formed product (λ_ex = 350 nm; λ_em = 450 nm). The implementation of a SIA flow system allowed for the development of a simple, fast and versatile automated methodology, which exhibits evident advantages regarding the US Pharmacopoeia 24 (USP 24) reference procedure. By combining the SIA time-based sample insertion with a subsequent zone sampling approach, which permitted to select for detection of a well-defined sample zone, it was possible to implement an on-line dilution strategy that enabled the expansion of the analytical working range of the methodology, and thus its application in dissolution studies, without manifold re-configuration.Linear calibration plots were obtained for aminocaproic acid concentrations up to 6 × 10⁻⁵ mol l⁻¹. The developed methodology exhibit a good precision, with a R.S.D. < 2.0% (n = 15) and the detection limit was 2.5 × 10⁻⁷ mol l⁻¹. The obtained results complied with those furnished by the reference procedure with a relative deviation lower than 1.2%. No interference was found.     

Sensitive sequential injection determination of naproxen based on interaction with beta-cyclodextrin

A sensitive sequential injection analysis (SIA) methodology for the fluorimetric determination of naproxen is proposed. The developed automatic analytical procedure is based on the complexation of naproxen with β-cyclodextrin (β-CD) yielding an enhanced fluorimetric signal (λ_ex = 280 nm, λ_em = 356 nm).Linear calibration plots were obtained for naproxen concentrations up to 1 × 10⁻⁵ mol l⁻¹. The developed methodology exhibited a good precision, with a R.S.D. < 2.1% (n = 15). The detection limit of the determination was 1.9 × 10⁻⁷ mol l⁻¹ with a sampling rate of about 70 h⁻¹. The automatic method was applied to the determination of naproxen in pharmaceutical formulations. The obtained results were compared with those furnished by the reference procedure and the relative deviations were lower than 3.6%. No interference was found from the excipients usually used in solid pharmaceutical formulations.     

Ultrasensitive determination of silver ion based on synchronous fluorescence spectroscopy with nanoparticles

Based on the characteristics of synchronous fluorescence spectroscopy (SFS), a new method with high sensitivity and selectivity was developed for rapid determination of silver ion with functional cadmium sulphide (CdS) nanoparticles as a fluorescence probe. When Δλ (λ_em − λ_ex) = 215 nm, maximum synchronous fluorescence is produced at 304 nm. Under optimal conditions, functional cadmium sulphide displayed a calibration response for silver ion over a wide concentration range from 0.8 × 10⁻¹⁰ to 1.5 × 10⁻⁸ mol L⁻¹. The limit of detection was 0.4 × 10⁻¹⁰ mol L⁻¹ and the relative standard deviation of seven replicate measurements for the lowest concentration (0.8 × 10⁻¹⁰ mol L⁻¹) was 2.8%. Compared with several fluorescence methods, the proposed method had a wider linear range and improved the sensitivity. Furthermore, the concentration dependence of the synchronous fluorescence intensity is effectively described by a Langmuir-type binding isotherm.     

Electroanalytical determination of estriol hormone using a boron-doped diamond electrode

A boron-doped diamond (BDD) electrode was used for the electroanalytical determination of estriol hormone in a pharmaceutical product and a urine sample taken during pregnancy by square-wave voltammetry. The optimized experimental conditions were: (1) a supporting electrolyte solution of NaOH at a pH of 12.0, and (2) a frequency of 20 Hz, a pulse height of 30 mV and a scan increment of 2 mV (for the square-wave parameters). The analytical curve was linear in the concentration range of 2.0 × 10⁻⁷ to 2.0 × 10⁻⁵ mol L⁻¹ (r = 0.9994), with a detection limit of 1.7 × 10⁻⁷ mol L⁻¹ and quantification limit of 8.5 × 10⁻⁷ mol L⁻¹. Recoveries of estriol were in the range of 98.6-101.0%, for the pharmaceutical sample, and 100.2-103.4% for the urine sample, indicating no significant matrix interference effects on the analytical results. The accuracy of the electroanalytical methodology proposed was compared to that of the radioimmunoassay method. The values for the relative error between the proposed and standard methods were −7.29% for the determination of estriol in the commercial product and −4.98% in a urine sample taken during pregnancy. The results obtained suggest a reliable and interesting alternative method for electroanalytical determination of estriol in pharmaceutical products and urine samples taken during pregnancy using a boron-doped diamond electrode.     

Electronic micropipettor: a versatile fluid propulsion and injection device for micro-flow analysis

The shortage of ready to use small sized liquid propulsion and switching devices for microfluidic cells (μ-cell) is a bottleneck in the dissemination of micro-flow analysis (μ-FA), now that microfluidic electrochemical cells can be designed and assembled in any laboratory by thermal transfer of laser printed masks and CD-Rs. Microprocessor-controlled electronic pipettors, commercially available with minimum capacity of 10 μL, represent a compromise solution between oversized peristaltic pumps and tiny “on a chip” micropumps and valves. The versatility of the electronic pipette coupled with the μ-cell (13-μm deep longitudinal channel) was demonstrated in three operation modes: SIA like, FIA like and direct injection analysis (DIA). Injections of 100 nL K₄Fe(CN)₆ (0.1 mol L⁻¹ KCl) define a linear analytical curve (r = 0.999) in the range of 5 × 10⁻⁷ to 1.0 × 10⁻³ mol L⁻¹ for flow amperometry at a gold electrode potentiostated at 0.4 V versus Ag/AgCl. Methods for the amperometric μ-flow determination of promethazine (FIA like), dipyrone (SIA like) and chlorpromazine (DIA) in pharmaceutical formulations were developed and applied to real samples. Excellent linearity of analytical curves and high repeatability (R.S.D. < 3.0%) at the low picomole range was obtained and all results for real samples were in agreement with reference methods. The results reflect the stability and the reliability of the setups envisioned for the electronic pipette coupled with amperometric μ-cell and the validity of the μ-FA methods.     

Flow-injection determination of hydrogen peroxide based on fluorescence quenching of chromotropic acid catalyzed with Fe(II)

Flow-injection analysis system (FIA system), which was based on Fe(II)-catalyzed oxidation of chromotropic acid with hydrogen peroxide, was developed for the determination of hydrogen peroxide. The chromotropic acid has a fluorescence measured at λ_em = 440 nm (emission wavelength) with λ_ex = 235 nm (excitation wavelength), and the fluorescence intensity at λ_em = 440 nm quietly decreased in the presence of hydrogen peroxide and Fe(II), which was caused by Fe(II)-catalyzed oxidation of chromotropic acid with hydrogen peroxide. By measuring the difference of fluorescence intensity, hydrogen peroxide (1.0 × 10⁻⁸-1.0 × 10⁻³ mol L⁻¹) could be determined by the proposed FIA system, whose analytical throughput was 40 samples h⁻¹. The relative standard deviation (RSD) was 1.03% (n = 10) for 4.0 × 10⁻⁸ mol L⁻¹ hydrogen peroxide. The proposed FIA technique could be applied to the determination of hydrogen peroxide in rain water samples.     

Enzymatic chemiluminescent assay of glucose by sequential-injection analysis with soluble enzyme and on-line sample dilution

This work reports a sequential-injection analysis (SIA) method for the enzymatic assay of glucose with soluble glucose oxidase (GOD) and on-line sample dilution with chemiluminescence (CL) detection. A zone of sample was aspirated in the holding coil of the SIA manifold and, if necessary, was diluted on-line by means of an auxiliary dilution conduit. Then, a zone of GOD was aspirated adjacent to the sample zone and a stopped-flow period was applied to allow the enzymatic reaction to proceed with production of hydrogen peroxide. Then, zones of a catalyst (Co(II) solution) and alkaline luminol were aspirated into the holding coil. Finally, the flow was reversed and the stacked zones were sent to a flow-cell located in front of a photomultiplier tube (PMT) that monitored the CL intensity. The linear dynamic range was 1 × 10⁻⁵-1 × 10⁻³ mol L⁻¹ glucose, the coefficient of variation at 8 × 10⁻⁵ mol L⁻¹ of glucose was s_r = 3.1% (n = 8), the limit of detection at the 3σ level was c_L = 1 × 10⁻⁶ mol L⁻¹ and the sampling frequency was 28 h⁻¹. With on-line dilution by a factor of 1/200, the linear range could be extended up to 0.2 mol L⁻¹ glucose. The advantages of the proposed method are the simple manifold and instrumentation used, the scope for automated on-line dilution, the low consumption of sample and reagents and the elimination of enzyme immobilisation procedures. The method was applied to the analysis of commercial drinks and honey with percent relative errors in glucose determination in the range 100 ± 6.1%.     

Selective determination of bisphenol A (BPA) in water by a reversible fluorescence sensor using pyrene/dimethyl β-cyclodextrin complex

A bifurcated optical fiber chemical sensor for continuous monitoring of bisphenol A (BPA) has been proposed based on the fluorescence quenching (λ_ex/λ_em = 286/390 nm) of pyrene/dimethyl β-cyclodextrin (HDM-β-CD) supramolecular complex immobilized in a plasticized poly(vinyl chloride) (PVC) membrane, in which pyrene served as a sensitive fluorescence indicator probe. The decrease of the fluorescence intensity of pyrene/HDM-β-CD complex upon the addition of BPA was attributed to the displacement of pyrene by BPA, which has been utilized as the basis of the fabrication of a BPA-sensitive fluorescence sensor. The response mechanism of the sensor was discussed in detail. The sensor exhibited a dynamic detection range from 7.90 × 10⁻⁸ to 1.66 × 10⁻⁵ mol L⁻¹ with a detection limit of 7.00 × 10⁻⁸ mol L⁻¹, and showed excellent reproducibility, reversibility, selectivity, and lifetime. The proposed sensor was successfully used for the determination of BPA in water samples and landfill leachate.     

Rapid simultaneous analysis of 1-hydroxypyrene, 2-hydroxyfluorene, 9-hydroxyphenanthrene, 1- and 2-naphthol in urine by first derivative synchronous fluorescence spectrometry using Tween-20 as a sensitizer

A novel method of first derivative synchronous fluorescence was developed for the rapid simultaneous analysis of trace 1-hydroxypyrene (1-OHP), 1-naphthol (1-NAP), 2-naphthol (2-NAP), 9-hydroxyphenanthrene (9-OHPe) and 2-hydroxyfluorene (2-OHFlu) in human urine. Only one single scan was needed for quantitative determination of five compounds simultaneously when Δλ = 10 nm was chosen. In the optimal experimental conditions, there was a linear relationship between the fluorescence intensity and the concentration of 1-OHP, 1-NAP, 2-NAP, 9-OHPe and 2-OHFlu in the range of 1.75 × 10⁻⁹ to 4.50 × 10⁻⁶ mol L⁻¹, 3.64 × 10⁻⁸ to 2.20 × 10⁻⁴ mol L⁻¹, 8.18 × 10⁻⁹ to 1.20 × 10⁻⁴ mol L⁻¹, 3.26 × 10⁻⁹ to 8.50 × 10⁻⁵ mol L⁻¹ and 4.88 × 10⁻⁹ to 5.50 × 10⁻⁶ mol L⁻¹, respectively. The limits of detection (LOD) were found to be 5.25 × 10⁻¹⁰ mol L⁻¹ for 1-OHP, 1.10 × 10⁻⁸ mol L⁻¹ for 1-NAP, 2.46 × 10⁻⁹ mol L⁻¹ for 2-NAP, 9.77 × 10⁻¹⁰ mol L⁻¹ for 9-OHPe and 1.46 × 10⁻⁹ mol L⁻¹ for 2-OHFlu. The proposed method is reliable, selective and sensitive, and has been used successfully in the determination of traces of 1-OHP, 1-NAP, 2-NAP, 9-OHPe and 2-OHFlu in human urine samples, whose results were in good agreement with those gained by the HPLC method.     

Catalytic-adsorptive stripping voltammetric determination of ultra-trace iridium(III). Application to fresh- and sea-water

An extremely sensitive stripping voltammetric procedure for ultra-trace determination of iridium(III) is reported. The method is based on the interfacial accumulation of the iridium(III)-CTAB complex onto the glassy carbon electrode, followed by the catalytic reduction of the adsorbed complex in the presence of bromate. 0.3 mol L⁻¹ acetate buffer pH 4.7 + 6.9 × 10⁻² mol L⁻¹ NaBrO₃ + 2.7 × 10⁻⁵ mol L⁻¹ cetyltrimethylammonium bromide (CTAB) + 0.2 mol L⁻¹ KCl was employed as the supporting electrolyte.The analytical procedure was verified by the analysis of the standard reference materials: Sea Water BCR-CRM 403 and Fresh Water NIST-SRM 1643d.The accuracy, expressed as relative error e%, was satisfactory, being lower than 6%, while precision as repeatability, expressed as relative standard deviation s_r%, was generally lower than 5%. The limit of detection was of the order of 2-3 ng L⁻¹.Once set up on the standard reference materials, the analytical procedure was transferred and applied to superficial water sampled in proximity to superhighway and in the Po river mouth area.     

Sensing hydrogen peroxide involving intramolecular charge transfer pathway: A boronate-functioned styryl dye as a highly selective and sensitive naked-eye sensor

The synthesis, properties and applications of a novel boronate-functioned styryl dye, BSD, as a colorimetric sensor for hydrogen peroxide is presented. The dye displayed remarkable color change from colorless (λ_max = 391 nm) to deep red (λ_max = 522 nm) in the presence of H₂O₂ and the behavior could be rationalized by the chemoselective H₂O₂-mediated transformation of arylboronate to phenolate, resulting in the release of the merocyanine dye which featured with strong intramolecular charge transfer (ICT) absorption band. The absorption increment of merocyanine at λ_max = 522 nm (? = 87000 L mol⁻¹ cm⁻¹) is linear with the concentration of H₂O₂ in the range of 1.0 × 10⁻⁷-2.5 × 10⁻⁵ mol L⁻¹ with the detection limit of 6.8 × 10⁻⁸ mol L⁻¹ under optimum conditions. There is almost no interference by other species that commonly exist due to the specific deprotection of H₂O₂ towards arylboronate group on BSD. The chromogenic sensor has been applied to the detection of trace amounts of hydrogen peroxide in rain water.     

Flow injection determination of thyroxine in pharmaceutical preparations using tris(2,2′-bipyridyl)ruthenium(III)-NADH chemiluminescence detection

A flow injection (FI) method is reported for the determination of thyroxine based on its enhancement of chemiluminescence (CL) from the Ru(bpy)₃³⁺-NADH system. The calibration graph was linear over the range 2.0-10 × 10⁻⁸ mol L⁻¹ (r² = 0.9989) with relative standard deviations (R.S.D.) in the range 2.0-4.5% (n = 4). The limit of detection (3σ blank) was 1.0 × 10⁻⁹ mol L⁻¹ with sample throughput of 120 h⁻¹. The effect of some organic compounds, anions and cations were studied for l-thyroxine determination. The method was applied to pharmaceutical preparations and the results obtained were in reasonable agreement with the amount labeled. The method was statistically compared with the results obtained by RIA; no significant disagreement at 95% confidence limit was observed. A calibration graph of NADH over the range 1.3 × 10⁻⁸-1.3 × 10⁻⁶ mol L⁻¹ was also established (r² = 0.9992) with R.S.D. in the range1.0-3.5% (n = 4). The limit of detection (3σ) was 1.0 × 10⁻¹⁰ mol L⁻¹ NADH.     

An emphatic orthogonal signal correction-support vector machine method for the classification of tissue sections of endometrial carcinoma by near infrared spectroscopy

A sequential injection analysis (SIA) spectrophotometric method for determining tetracycline (TC), chlortetracycline (CTC) and oxytetracycline (OTC) in different sample matrices were described. The method was based on the reaction between tetracyclines and yttrium (III) in weak basic micellar medium, yielding the light yellow complexes, which were monitored at 390, 392 and 395 nm, respectively. A cationic surfactant, cetyltrimethylammonium bromide (CTAB) was used to obtain the micellar system. The linear ranges of calibration graphs were between 1.0 × 10⁻⁵ and 4 × 10⁻⁴ mol L⁻¹, respectively. The molar absorptivities were 5.24 × 10⁵, 4.98 × 10⁴ and 4.78 × 10⁴ L mol⁻¹ cm⁻¹. The detection limits (3σ) were between 4.9 × 10⁻⁶ and 7.8 × 10⁻⁶ mol L⁻¹ whereas the limit of quantitations (10σ) were between 1.63 × 10⁻⁵ and 2.60 × 10⁻⁵ mol L⁻¹ the interday and intraday precisions within a weak revealed as the relative standard deviations (R.S.D., n = 11) were less than 4%. The method was rapid with a sampling rate of over 60 samples h⁻¹ for the three drugs. The proposed method has been satisfactorily applied for the determination of tetracycline and its derivatives in pharmaceutical preparations together with their residues in milk and honey samples collected in Chiang Mai Province. The accuracy was found to be high as the Student's t-values were found to be less than the theoretical ones. The results were compared favorably with those obtained by the conventional spectrophotometric method.     

Determination of melamine in different milk batches using a novel chemosensor based on the luminescence quenching of Ru(II) carbonyl complex

A novel, simple, sensitive and precise spectrofluorimetric method was developed for measuring the melamine concentration in different milk batch samples. The method was based upon measuring the quenching of the luminescence intensity of the produced yellow colored ruthenium^(II) carbonyl complex of the general formula [Ru(CO)₂(L)] (where L = anion of tetradentate Schiff base). The Ru^(II) complex exhibited characteristic luminescence band in the visible region. The remarkable quenching of the luminescence intensity of [Ru(CO)₂(L)] complex by various concentrations of melamine was successfully used as a chemosensor for the assessment of melamine in different milk samples at λ_ex = 400 nm and pH 7.4 in DMSO with a linear dynamic range 1.0 × 10⁻⁶ to 3.0 × 10⁻⁹ mol L⁻¹ and lower detection limit (LOD) and quantification detection limit (QOD) of 3.3 × 10⁻¹⁰ and 1.0 × 10⁻⁹ mol L⁻¹, respectively.     

Determination of diclofenac in pharmaceutical preparations by diffuse reflectance photometry

A quantitative analytical method for the determination of diclofenac in pharmaceutical preparations by diffuse reflectance in the visible region of the spectrum is presented. The color reaction is done directly in the measuring cell immediately after mixing, using small volumes of the analyte solution, of the reagent and of the buffer solutions. All reflectance measurements were carried out in a home made reflectometer equipped with a red LED as light source and a LDR as detector. The calibration curves were constructed from 1.0 to 18 mg mL⁻¹ (about 3.0 × 10⁻³ to 5.5 × 10⁻² mol L⁻¹) of sodium diclofenac or of potassium diclofenac in the analytical solution, with typical correlation coefficients equal to 0.999. The detection limit was estimated to be about 0.7 mg mL⁻¹ (2 × 10⁻³ mol L⁻¹). The method was applied to determine diclofenac in solid and liquid pharmaceutical preparations. The R.S.D. varied from 2% to 4% depending of the sample. The results were compared with those obtained with the HPLC procedure recommended by the United States Pharmacopoeia using the statistical Student's t-test procedure.     

Highly sensitive and selective spectrofluorimetric determination of tolnaftate through the formation of ternary inclusion complex of beta-naphthol/beta-cyclodextrin/anionic surfactant system

An indirect spectrofluorimetric method with high sensitivity and selectivity was developed for the determination of antifungal drug: tolnaftate (TNF), depending on the supramolecualr multirecognition interaction among the anionic surfactant sodium laurylsulfate (SLS), β-cyclodextrin (β-CD) and β-naphthol (ROH). The mechanism of the inclusion was studied and discussed by means of fluorescence spectrum, infra-red spectrograms and ¹HNMR spectroscopy. Results showed that the naphthalene ring of ROH and the hydrophobic hydrocarbon chain of SLS were included into the β-CD's cavity to form a ROH:SLS:β-CD ternary inclusion complex with stoichiometry of 1:1:1 at room temperature, which provided effective protection for the excited state of ROH. At λ_ex/λ_em = 273/360 nm, the fluorescence intensity was linear over a tolnaftate concentration range of 2.46 × 10⁻⁹ to 2.10 × 10⁻⁶ mol L⁻¹. The detection limit and relative standard deviation was 7.50 × 10⁻¹⁰ mol L⁻¹ and 1.4%, respectively. The interference of 31 foreign substances was slight. The proposed method had been successfully applied to the determination of tolnaftate in artificial mixed samples with almost quantitative recovery.     

Electrochemiluminescent behaviors of alkaloids and tris(2,2'-bipyridine) ruthenium in organically modified silicate film

Electrogenerated chemiluminescences (ECLs) of alkaloids, such as berberine, trigonelline, allantoin and betaine, were studied in an aqueous alkaline buffer solution (pH 9.5), based on tris(2,2′-bipyridine)ruthenium(II) [Ru(bpy)₃²⁺] immobilized in organically modified silicates (ORMOSILs) film on a glassy carbon electrode (GCE). The immobilized Ru(bpy)₃²⁺ showed good electrochemical and photochemical activities. In a flow system, the eluted alkaloids were oxidized on the modified GCE, and reacted with immobilized Ru(bpy)₃²⁺ at the potential of +1.50 V (versus Ag/AgCl). The luminescence with λ_max 610 nm was caused by a reaction of electrolytically formed Ru(bpy)₃³⁺ with an oxidized amine group to generate Ru(bpy)₃^2+*. The determination limit was 5 × 10⁻⁶ mol L⁻¹, 8 × 10⁻⁶ mol L⁻¹, 2.0 × 10⁻⁵ mol L⁻¹ and 5.0 × 10⁻⁵ mol L⁻¹ for berberine, trigonelline, allantoin and betaine at S/N 3, respectively. In addition, the factors affecting the determination of the four alkaloids were also studied.     

A potential visual fluorescence probe for ultratrace arsenic (III) detection by using glutathione-capped CdTe quantum dots

The interaction between mercaptoacetic acid (MA)-capped CdTe QDs, MA-capped CdTe/ZnS QDs or glutathione (GSH)-capped CdTe QDs with As(III) was studied using fluorescence spectrometry. As (III) has a high-affinity to reduced-GSH to form As(SG)₃, and the emission of the GSH-capped CdTe QDs (λ_em. = 612 nm) is quenched effectively. Thus, a novel fluorescence spectrometric method was developed for As (III) determination by using GSH-CdTe QDs. Under optimal conditions, the quenched fluorescence intensity (F₀/F) increased linearly with the concentration of As (III) ranging from 5.0 × 10⁻⁶ to 25 × 10⁻⁵ mol L⁻¹. The limit of detection (3σ) for As (III) was found to be 2 × 10⁻⁸ mol L⁻¹. This method is potentially useful in visual detection of As (III) under irradiation of the ultraviolet light.     

Determination of epinephrine based on its enhancement for electrochemiluminescence of lucigenin

Epinephrine was found to be able to strongly enhance the electrochemiluminescence (ECL) of lucigenin system by using the anodic potential sweep. Based on which, a novel ECL method for the determination of epinephrine was developed. Under the optimum condition, the enhanced ECL intensity was linear with the epinephrine concentration in the range of 4.0 × 10⁻⁸ to 2.0 × 10⁻⁷ mol L⁻¹. The detection limit (defined as S/N = 3) was 2.4 × 10⁻⁸ mol L⁻¹, and the relative standard deviation was 2.7% for 1.0 × 10⁻⁷ mol L⁻¹ epinephrine (n = 11). The method was successfully applied to the determination of epinephrine in pharmaceutical samples with satisfactory results. In addition, the possible mechanism for the lucigenin ECL system in the presence of epinephrine has also been discussed.