Improvements in europium sensitized fluorimetric determination of demeclocycline and methacycline.

Demeclocycline (DM) and methacycline (MT) have been determined by europium-sensitized fluorescence, using EDTA as co-ligand and cetyltrimethylammonium chloride as surfactant. The methods have been developed in slightly alkaline solutions, with the formation of a new chelate where the lanthanide ion is bound to the beta-diketone group. Calibration graphs between 0.01 and 0.1 microg mL(-1) have been obtained for DM and MT determination. Both methods have been applied to the determination of these tetracyclines in serum samples with satisfactory recovery results.

Strategies for solving matrix effects in the analysis of sulfathiazole in honey samples using three-way photochemically induced fluorescence data.

A widely employed compound for honey treatment, sulfathiazole (ST), was determined in commercial honey samples, employing a combination of photochemically induced fluorescence excitation-emission matrices (EEMs) and chemometric processing of the recorded second-order data. Parallel Factor Analysis (PARAFAC) and Self-Weighted Alternating Trilinear Decomposition (SWATLD) methods were used for calibration. An appropriately designed calibration with a set of standards composed of 18 samples, coupled to the use of the second-order advantage offered by the applied chemometric techniques, allowed quantitation of sulfathiazole in spiked commercial honey samples. No previous separation or sample pretreatment steps were required. The results were compared with other calibration methods such as N-PLS and PLS-1 that produced good results on synthetic samples but not on the investigated commercial honey samples.

Monitoring of phenylurea and propanil herbicides in river water by solid-phase-extraction high performance liquid chromatography with photoinduced-fluorimetric detection.

The separation and determination of five herbicides, including propanil and the phenylureas diuron, isoproturon, linuron and neburon, has been performed by an HPLC method, using photochemically-induced fluorescence detection. The non-fluorescent herbicides were transformed into fluorescent compounds by post-column photochemical reaction. A 60:40 (v/v) acetonitrile-buffer solution of potassium phosphate dibasic (pH 7, 0.01 M) was used for the chromatographic elution to separate propanil, linuron and neburon. The overlapping of isoproturon and diuron peaks, in the selected conditions, was resolved by changing the initial movil phase composition to 50:50 (v/v) methanol-buffer solution of potassium phosphate dibasic (pH 7, 0.01 M). The procedure was applied with satisfactory results to the analysis of these herbicides in Guadiana river water samples (Badajoz, Spain), allowing the detection of herbicide residues in the order of mug l(-1), by using a solid-phase extraction (SPE) pre-concentration step.

Resolution of ternary mixtures of nitrofurantoin, furaltadone and furazolidone by partial least-square analysis to the spectrophotometric signals after photo-decomposition.

An UV spectroscopic method is proposed to analyze mixtures of the nitrofuran derivatives, nitrofurantoin, furaltadone and furazolidone, used in veterinary. The change of absorption spectra due to photo-decomposition is used. A 20% dimethylformamide/water, basic medium of pH 9.4 (ammonium chloride/ammonia) and a time of irradiation of 15 s are selected. Calibration graphs are established, with the percentage of decrease of absorbance as analytical signal, in the range 2-10 microg ml(-1). To analyze mixtures of the three compounds the partial least-squares (PLS) multivariate analysis method is used with the spectra obtained by subtracting the spectra after irradiation to the original spectra. Good results have been obtained in the analysis of synthetic samples and a formulation containing all these compounds.

High-performance liquid chromatographic determination of phenylureas by photochemically-induced fluorescence detection.

A HPLC method, using photochemically-induced fluorescence detection, is described for the separation and determination of four phenylurea herbicides including diuron, isoproturon, linuron and neburon. A post-column photoreactor, consisting of a reactor knitted around a 4 W xenon lamp, has been included between the column and the detector, in order to transform the non-fluorescent herbicides into fluorophors. The influence of mobile phase composition, flow-rate, pH, and buffer concentration has been studied. An acetonitrile-buffer solution of potassium phosphate dibasic of pH 7 and 0.01 M concentration (60:40, v/v), was selected as optimum. For the fluorimetric detection, optimal excitation/emission wavelengths 324/403, 301/433, 335/411 and 326/385 nm were selected for the determination of diuron, isoproturon, linuron and neburon, respectively. The detection limits ranged between 0.07 and 0.46 microg/ml, according to the compound.

Determination of sulphamethoxazole by photochemically induced fluorescence in drugs and milk.

A new first-derivative photochemically induced fluorescence (D-PF) method is proposed for the determination of sulphamethoxazole (SMXZ) in milk. A 50:50 (v/v) methanol: water medium, UV irradiation time of 2 min, and pH 5.70 were fixed. Standard addition method was used with the derivative spectra of the increase spectra as analytical signal. For determination in drugs, direct increase of fluorescence signal measure is used. In both cases the method is suitable for SMXZ concentrations comprised between 0.5 and 2.5 ppm.

Photochemical-spectrofluorimetric method for the determination of benzoylurea insecticides: applications in river water samples and in technical formulations.

Ultraviolet (UV) irradiation was used to obtain fluorescent photoproducts from four non-fluorescent benzoylurea (BU) insecticides (flufenoxuron (FLF), lufenuron (LUF), hexaflumuron (HF) and triflumuron (TRF)). The effect of solvent, pH (in aqueous solutions), organic solvent percentage and UV irradiation time on the excitation and emission wavelengths and fluorescence intensity were investigated. The largest fluorescence signals and the shortest UV irradiation time were obtained in methanol, ethanol and 2-propanol. Linear calibration graphs were established in the interval between 0.025 and 1.000 microg ml(-1) from FLF and TRF and between 0.050 and 1.000 microg ml(-1) from LUF and HF with regression coefficients larger than 0.99. A method based on the use of the first-derivative of the spectra of photoproducts was applied to the determination of BU insecticides in river water samples and in technical formulations. The mean recoveries ranged from 95.0% to 110.0% in river water samples and from 92.0% to 101.0% in technical formulations, according to the compound. A preconcentration step, using LLE, allowed to reach the concentration levels established by the EU directive for pesticides in drinking water.

Room temperature phosphorescence of 1-naphtalenacetamide included in beta-cyclodextrin in presence of 1,3-dibromopropane.

The spectral characteristics of the inclusion of 1-naphthalenacetamide in beta-cyclodextrin have been studied by luminescence methods. The addition of bromoalcohols or bromoalkanes produces a decrease of the fluorescence of the inclusion complex, giving rise to a new band corresponding to phosphorescence emission. The emission intensity is much higher in the presence of bromoalkanes than in the presence of bromoalcohols. The deoxygenation of the solutions is achieved by flowing nitrogen, by the addition of sodium sulphite and by a combination of both methods, which results in the most effective approach. The phosphorescence emission is produced in the turbid suspension formed in the presence of the bromoalkane. The formation of microcrystals seems necessary to obtain phosphorescence emission from the ternary system.

Fluorimetric properties of a 2-hydroxypropyl-beta-cyclodextrin: 9-methyl-benzo[a]phenothiazine inclusion complex in aqueous media. Analytical usefulness.

The formation of an inclusion complex between 9-methyl-12H-benzo[a]phenothiazine (MeBPHT) and 2-hydroxypropyl-beta-cyclodextrin (HP-beta-CD) was investigated in aqueous medium. A 12-fold fluorescence emission intensity enhancement was found for the complexed relative to the free analyte. MeBPHT forms a 1:1 stoichiometry complex with HP-beta-CD. A formation constant of 460 (+/-100) M(-1) was calculated using the Benesi-Hildebrand method and fluorimetric data. The limit of detection was 7 ng ml(-1) for MeBPHT in the presence of HP-beta-CD instead of 60 ng ml(-1) in the absence of HP-beta-CD.

Fluorimetric determination of tin and organotin compounds in hydroorganic and micellar media in the presence of 8-hydroxyquinoline-5-sulfonic acid.

The fluorescence of tin(IV) complexed by 8-hydroxyquinoline-5-sulfonic acid (8-HQSA) has been studied in both aqueous and hydroorganic (acetate buffer and dimethylsulfoxide) media. Several experimental parameters such as pH, DMSO/water ratio and reactant concentration have been investigated to increase the fluorescence of the tin(IV)-8-HQSA complex. A linear relationship between tin(IV) concentration and fluorescence intensity was observed between 1.7 and 20 microM). Mechanistic and quantitative studies in the presence of surfactants have been performed. Judiciously selected micellar media permitted solubilisation and quantitation of tin(IV) as well as dibutyltin compounds. A linear relationship between concentration and fluorescence intensity was found for mono-, di- and tributyltin with detection limits of 0.1 microM, 0.7 microM and 1 microM, respectively.

Analysis of sulfamethazine in the presence of sulfamerazine or sulfadiazine by first-derivative photochemically induced fluorescence.

A first-derivative photochemically-induced fluorescence method is proposed for the determination of sulfamethazine (SMTZ) in the presence of sulfamerazine (SMRZ) or sulfadiazine (SDZ). Linear calibration plots were obtained for SMTZ in SMTZ-SMRZ or SMTZ-SDZ binary mixtures with correlation coefficients larger than 0.999. For SMTZ the lower limits of detection were 7-13 ppb. Recoveries of 91-114% were obtained in the analysis of SMTZ in pharmaceutical formulations.

Fluorimetric determination of phenothiazine derivatives by photooxidation in a flow-injection system.

Flow-injection analysis (FIA) was combined with photochemically induced fluorescence (PF) detection for the determination of four phenothiazine derivatives, including unsubstituted phenothiazine, thionine, Azure A and Methylene Blue. The working analytical parameters (flow-rate, injected volume, photoreactor length) were optimized. Linear calibration graphs were obtained over about two orders of magnitude, with relative standard deviation within the range 1-2.3%. Limits of detection were between 13 and 35 ng/ml, according to the compound. The FIA-PF method was applied to the determination of phenothiazines in urine samples. Mean recoveries ranged from 94 to 117%.

Determination of sulphanilamide in milk by first-derivative and second-derivative spectrofluorimetry.

First-derivative and second-derivative spectrofluorimetric methods have been developed for the analysis of sulphanilamide (SAN) in milk, using an ethanol-water (60:40, v/v) medium. Linear calibration plots were obtained over a concentration range of 30-120 ppb, with correlation coefficients greater than 0.997. Relative standard deviations were within the range 1.6-3.6%. Limits of detection were 0.7-2.7 ppb. Recoveries of 90-102% were obtained. The derivative fluorescence methods are simple, rapid and sensitive and there is no interference from fluorescent impurities in the determination of low levels of SAN in milk.

Solvent effect on the determination of sulfamethazine by room-temperature photochemically induced fluorescence.

Room-temperature photochemically-induced fluorescence (RTPF) was applied to the determination of sulfamethazine (SMT) in methanol, ethanol and 2-propanol. Optimal ultraviolet irradiation times ranged between 2 and 6 min. Linear calibration graphs were obtained over a concentration range of more than one order of magnitude. The relative standard deviations were within the range 1.4-2.2%. Limits of detection were between 40 and 80 ng/ml. The method was evaluated for its applicability to the analysis of SMT in pharmaceutical formulations.

Spectrofluorimetric determination of sulphonamides in pharmaceutical compounds and foods.

Spectrofluorimetry and room temperature photochemically-induced fluorescence (RTPF) have been applied to the determination of sulphacetamide (SAC), sulphaguanidine (SG) and sulphamethazine (SMT) in milk and pharmaceutical formulations. The methods are suitable for determining 0.02-0.10 micrograms ml of SAC, 0.10-0.50 micrograms ml of SG, and 0.40-1.00 micrograms of SMT.