M.C. Mahedero

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.

Determination of binary mixtures of sulfonamides by photochemically induced fluorescence using partial least squares multivariate calibration

Binary mixtures of sulfamethazine (SMTZ), sulfamerazine (SMRZ) and sulfadiazine (SDZ) were determined by room-temperature photochemically induced fluorescence. The resolution was accomplished by partial least squares (PLS) multivariate calibration. The fluorescence intensity of these heterocyclic sulfonamides was measured after ultraviolet irradiation for 12 min. The photoproducts obtained showed analytically useful fluorescence signals when an excitation wavelength of 284 nm was used. PLS was applied with previous optimization of the calibration matrix by the PLS-1 method. The multivariate factor analysis based calibration method allowed the simultaneous determination of SMTZ–SMRZ, SMTZ–SDZ and SMRZ–SDZ mixtures.

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.

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.

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%.

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.

An Investigation of Inclusion Complexes of Cyclodextrins with Phenylurea Herbicides by Photochemically-Induced Fluorescence. Analytical Applications

The effect of β-cyclodextrin (β-CD) and hydroxypropyl-β-cyclodextrin (HP-β-CD) upon the photochemically-induced fluorescence (PIF) properties of four phenylurea herbicides, including linuron, diuron, isoproturon and neburon has been studied. Photochemical conversion of these nonfluorescent herbicides into strongly fluorescent photoproducts was shown to occur in β-CD and HP-β-CD aqueous media. The influence of pH, UV irradiation time and photoproduct stability on the fluorescence intensity was also investigated. In addition, the stoichiometry and formation constants of the complexes formed between herbicides and β-cyclodextrin (β-CD) or 2-hydroxypropyl-β-cyclodextrin (HP-β-CD) were determined. The formation constant values, ranging from 184 ± 40 to 1498 ± 245 M-1, were calculated by applying the iterative nonlinear regression (NLR) approach to the PIF data. Linear calibrations graphs were established in the interval 1–12 μg/mL, for diuron, linuron and neburon. The IUPAC limits of detection ranged between 580 and 700 ng/mL, according to the compound. Application to the analysis of phenylurea herbicides in spiked river water was also described.

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.

Fluorimetric properties of a 2-hydroxypropyl-β-cyclodextrin: 9-methyl-benzo[a]phenothiazine inclusion complex in aqueous media. Analytical usefulness1

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.

Room temperature phosphorescence of 1-naphtalenacetamide included in β-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.