Cyclodextrin-enhanced photo-induced fluorescence of tau-fluvalinate, molecular modelling of inclusion complexes and determination in natural waters.

The effect of adding organized supramolecular systems such as ß-cyclodextrin (ß-CD) and hydroxypropyl-ß-cyclodextrin (HP-ß-CD) on the photochemically-induced fluorescence (PIF) spectral properties of tau-fluvalinate (TFV) in aqueous solutions was examined. The influence of pH, UV irradiation time and photoproduct stability on the cyclodextrin-enhanced photochemically-induced fluorescence intensity was also investigated. The spectral changes associated with the inclusion process yielded values for the formation constants of TFV inclusion complexes between 450 and 640 M-1, which were calculated using the nonlinear iterative regression approach least squares. In addition, host-guest interaction was clearly determined by PIF enhancement and a 1 : 1 stoichiometry was found for the ß-CD and HP-ß-CD complexes formed with TFV. The negative free energy (ΔG°) value indicated that the reaction of TFV with cyclodextrins was thermodynamically favorable. Furthermore, the structures of inclusion complexes of TFV with cyclodextrins were elucidated by 3-21G ab initio calculations. The limits of detection and quantification obtained ranged between 1.3 and 4.0 ng mL-1 and from 4.4 to 13.0 ng mL-1 in ß-CD and HP-ß-CD media, respectively. The analytical application in tap and river water samples yielded satisfactory mean recoveries ranging from 98.12 to 102.97%. Due to its sensitivity and ease of use, this method can be reliably applied to routine analysis.

Direct Spectrofluorimetric Method for the Analysis of Carbofuran and Fluometuron in Senegalese Natural Waters.

In this work, analytical study of carbofuran (CAF) and fluometuron (FLM) pesticides was carried out using direct spectrofluorimetric method in various solvents. Results showed that CAF and FLM are naturally fluorescent in all solvents under study including organic (MeOH, MeCN, DMF) and aqueous micellar one (CTAC, SDS, Brij-700). For the analysis of FLM, CTAC give the best fluorescence signal enhancement. Analytical performances, such as limit of detection (LOD) and quantification (LOQ) was evaluated after solvent optimization and were found to vary, respectively, between 0.1 and 11 ng mL- 1 and between 0.3 and 36.6 ng mL- 1. Analytical application in various environmental aqueous samples matrices (sea, tap, runoff and well waters) give satisfactory recovery rates in the limits of 73.7-113.7% for both pesticides. This method is described for its simplicity for routine analysis.

Analysis of non-native fluorescent pesticides by thermo-induced and photo-induced fluorescence, a comparative study.

This paper compares the performance of three analytical methods for the determination of pesticides in natural waters. As many pesticides are non-fluorescent, they are transformed into highly fluorescent by-products in two ways: elevated temperature in an alkaline medium (thermo-induced fluorescence - TIF); or UV irradiation in water (photo-induced fluorescence - PIF). The first method studied uses TIF, the second one uses PIF and the third one uses an automatic sampling and analysing PIF system. Analytical applications were carried out using the three methods for the determination of deltamethrin and cyhalothrin, pesticides widely used in Senegal. In both cases, the calibration curves obtained are linear without matrix effects, and the detection limits are good in the ng mL-1 range. It appears that the analytical performances of the automatic PIF method are better than the two others. The advantages and disadvantages of the three methods are then compared and discussed in term of analytical performance and usability.

High sensitivity on-site early warning system monitoring of pesticides by photo-induced fluorescence.

This paper describes the prototype of an on-site High Sensitivity Early Warning Monitoring System, using Photo-Induced Fluorescence, for pesticide monitoring in natural waters (HSEWPIF). To obtain a high sensitivity, the prototype was designed with four main features. Four UV LEDs are used to excite the photoproducts at different wavelengths and select the most efficient one. Two UV LEDs are used simultaneously at each wavelength to increase the excitation power and then the fluorescence emission of the photoproducts. High-pass filters are used to avoid the saturation of the spectrophotometer and to increase the signal-to-noise ratio. The HSEWPIF prototype also employs UV absorption to detect any occasional increase of suspended and dissolved organic matter, which could disrupt the fluorescence measurement. The conception of this new experimental set-up is explained and described, then analytical applications are carried out online for the determination of fipronil and monolinuron. We obtained a linear calibration range from 0 to 3 µg mL-1 with limits of detection of 1.24 ng mL-1 for fipronil and 0.32 ng mL-1 for monolinuron. A mean recovery of 99.2% for fipronil and 100.9% for monolinuron show that the method is accurate, moreover a standard deviation of 1.96% for fipronil and 2.49% for monolinuron show that the method is repeatable. Compared to other methods for the determination of pesticides by photo-induced fluorescence, the HSEWPIF prototype has good sensitivity with better limits of detection, and good analytical performances. These results show that HSEWPIF can be used for monitoring pesticide in natural waters to protect industrial facilities against accidental contamination.

Micellar enhanced photo-induced fluorescence and absorbance for the development of an on-site early warning water quality monitoring system for pesticides.

This paper describes two prototypes of an on-site Early Warning Water Quality Monitoring System (EWWQMS) for pesticide quantification in natural waters. As many pesticides are non-fluorescent, the EWWQMS setup uses UV photoconversion to form highly fluorescent photoproducts. To enhance sensitivity, the two prototypes use micellar-enhanced fluorescence with surfactant (cetyl trimethyl ammonium chloride) in aqueous solution. To improve specificity, four UV LEDs at different wavelengths then excite the fluorescent photoproducts. The EWWQMS prototypes also employ UV absorption for quantification of non-photosensitive pesticides. The first prototype detects the pesticides via a diode array spectrometer. The second system is developed with higher resolution spectrometer and an intensified CCD camera detection to improve the sensitivity of the method. These experimental set-ups are described, explained and tested. Analytical applications were carried out online in CTAC aqueous solution, for the determination of isoproturon, flufenoxuron and profenofos. The calibration curves obtained are linear over one order of magnitude, and the detection limits are in the ng mL-1 range. The analytical performances of these new methods are good compared with other published classical micellar enhanced photo-induced fluorescence methods for the determination of pesticides in aqueous solutions. Our results show that these EWWQMS prototypes can be used as a warning system to protect against pesticide contamination exceeding the threshold of treatment capabilities at industrial facilities using natural waters.

Development of an on-site early warning water quality monitoring system for pesticide detection by absorption and photo-induced fluorescence.

This paper describes prototypes of an on-site early warning water quality monitoring system (EWWQMS) for pesticide quantification in natural waters by fluorescence and absorbance. As many pesticides are not naturally fluorescent, this EWWQMS uses UV irradiation to transform these compounds into highly fluorescent photoproducts and obtain sufficient sensitivity. To obtain a better specificity, the system uses four UV LEDs at different wavelengths to excite the fluorescent photoproducts. For pesticides that are not sensitive to photoconversion, the EWWQMS prototypes also use UV absorption for their quantification, thus offering a wider application range. A first system uses a diode array spectrometer for detection. A second system uses a higher resolution spectrometer and an intensified CCD camera detection to increase sensitivity. Analytical applications were conducted for the determination of fipronil, acetamipride, cyprodinil, trifluraline and pendimethaline in water using both the EWWQMS prototypes. The analytical performances of these new systems are good compared with other photo-induced fluorescence methods already published. Limits of detection without pre-concentration are in the range of 0.2 to 3 ng mL-1 and the recovery values range from 95 to 108%. These results show that the EWWQMS prototypes can be used as an alert system to protect industrial plants from pesticide contaminations that exceed the capabilities of their cleaning processes.

Analysis of Oxadiazon Herbicide in Natural Water Samples by a Micellar-enhanced Photo-induced Fluorescence.

A micellar-enhanced photo-induced fluorescence (ME-PIF) method was developed to analyze, for the first time, oxadiazole herbicide (namely oxadiazon) in natural water samples. Photo-conversion under UV irradiation of the herbicide into strongly fluorescent photoproducts was performed in aqueous solution and in the presence of two surfactants, cetyltrimethylammonium chloride (CTAC) or Tween 20, at micellar concentrations. The ME-PIF parameters were optimized. The ME-PIF method gave very good results with satisfactory analytical performance for the determination of a selected pesticide with concentration linear dynamic ranges of over one to two orders of magnitude. It yielded good reproducibility (RSD values of between 3.6 and 9.6%) in tap, river and sea water spiked samples, and the limits of detection were in the ng mL-1 range.

Inclusion Complex of O-phthalaldehyde-Buprofezin with Dimethyl-ß-Cyclodextrin Using Thermochemically-Induced Fluorescence Derivatization (TIFD) Method and its Analytical Application in Waters.

Improvement of the TIFD method to determine buprofezin (BUP) founded on the O-phthalaldehyde (OPA)-thermoproduct complex of buprofezin (OPA-BUP) with dimethyl-ß-cyclodextrin (DMßCD) was investigated at 25 °C. The TIFD method developed in DMßCD medium, was optimized with respect to the reaction time, DMßCD concentration and pH. Based on the inclusion reaction, the OPA-BUP: DMßCD inclusion complex was developed in two aqueous media pH 7 and pH 13. A 1:1 stoichiometric ratio of OPA-BUP: DMßCD complex was obtained. The binding constants (K) and Gibbs energy (ΔG°) values increasing and decreasing with pH, respectively, show the spontaneous and thermodynamically favorable at 25 °C of the inclusion complexes formation. Normalized TIFD spectra were measured at 425 nm for emission and at 345 nm for excitation. Limits of detection (LOD) and quantification (LOQ) obtained, according to the pH, were in the ranges 0.05-0.1 ng mL ̶ 1 and 0.2-0.4 ng mL ̶ 1, respectively. Relative standard deviation (RSD) values, less than 1.3% corroborated TIFD method repeatability in DMßCD medium. Solid phase extraction (SPE) procedure which was used for quantitative analysis of natural water samples collected from Niayes area, led to satisfactory recovery rates values 99.5-117.3%.

Combination of photoinduced fluorescence and GC-MS for elucidating the photodegradation mechanisms of diflubenzuron and fenuron pesticides.

Diflubenzuron (DFB) and fenuron (FEN) are benzoylurea and phenylurea pesticides, widely used in Senegal, that do not exhibit any natural fluorescence, but can be determined by means of photoinduced fluorescence (PIF) methods. Photodegradation of DFB and FEN yielded a number of fluorescent and non-fluorescent photoproducts. For both pesticides, at least 10 photoproducts were detected and identified by gas chromatography-mass spectrometry (GC/MS). To identify the formed fluorescent DFB and FEN photoproducts, their fluorescence spectra were compared with those of standard compounds, including phenol and p-hydroxyaniline.

Spectrofluorometric Determination of Putrescine: Optimization of the Putrescine-Orthophthaldehyde Complex Using Spectrofluorometry.

In alkaline medium, the complex formed between putrescine and orthophthalaldehyde was studied using spectrofluorescence. The derivative is kinetically stable 24 h after complexation. The stoichiometry of the complex is 1:1 at maximum fluorescence intensity, also 24 h after complexation.

New method for the determination of metolachlor and buprofezin in natural water using orthophthalaldehyde by thermochemically-induced fluorescence derivatization (TIFD).

Herbicide metolachlor (MET) and insecticide buprofezin (BUP) were determined in natural waters by means of a newly-developed, simple and sensitive thermochemically-induced fluorescence derivatization (TIFD) method. The TIFD approach is based on the thermolysis transformation of naturally non-fluorescent pesticides into fluorescent complex O-phthalaldehyde-thermoproduct(s) in water at 70°C for MET and at 80°C for BUP. The TIFD method was optimized with respect to the temperature, pH, complex formation kinetic and pesticides concentrations. The limit of detection (LOD=0.8ngmL(-1) for MET and 3.0ngmL(-1) for BUP) and quantification (LOQ=2.6ngmL(-1) for MET and 9.5 ngmL(-1) for BUP) values were low, and the relative standard deviation (RSD) values were small (between 1.2% and 1.8%), which indicates a good analytical sensitivity and a great repeatability of TIFD method. Recovery studies were performed on spiked well, sea and draining waters samples collected in the Niayes area by using the solid phase extraction (SPE) procedure. Satisfactory recovery results (84-118%) were obtained for the determination of MET and BUP in these natural waters.

Spectrofluorometric Determination of Putrescine Using Orthophthaldehyde as a Fluorophore: A Novel Method.

This paper concerns spectrofluorometric analysis of putrescine using orthophthaladehyde as a fluorophore in aqueous alkaline medium. Wavelengths of excitation and emission in acid, neutral, and alkaline media were different. There is a maximum intensity of fluorescence in alkaline medium 24 h after complexation compared with other media. Putrescine and orthophthaladehyde are used at an equimolar ratio, and the product is kinetically stable in alkaline medium. Calibration curves obtained gave limits of detection and quantification of 39 and 65 ng/mL, respectively. The correlation coefficient obtained in alkaline medium was 0.992 at pH 12. Results obtained largely showed a good reproducibility of our method.

Photochemically-induced fluorescence dosage of non-fluorescent pyrethroid (Etofenprox) in natural water using a cationic micellar medium.

An analytical method based on the use of UV-irradiation to produce fluorescent derivatives from Etofenprox a non-fluorescent pyrethroid insecticide is described. The impact of cetyltrimethylammonium chloride (CTAC) micellar medium on the Etofenprox photochemically-induced fluorescence (PIF) is reported. Parameters influencing the sensitivity and repeatability of the PIF method have been optimized. The alkaline medium (NaOH 6 × 10(-2) M) + CTAC surfactant molecules (3.84 mg/ml) in acetonitrile is found to be very suitable for this pyrethroid insecticide analysis in environment matrices. Linear dynamic range is established over more than two orders of magnitude. The limit of detection is lower than 5 ng/ml. The method seems to be suitable for environmental matrices quality control. Application to the analysis of spiked natural waters gave recoveries rate ranged from 94 to 104% and 107 to 115% respectively for river and pound water.

Usefulness of cyclodextrin media for the determination of alpha-cypermethrin by photochemically induced fluorescence: analytical applications to natural waters.

The photochemically induced fluorescence (PIF) spectral properties of alpha-cypermethrin in organic solvents (hexane, dichloromethane, acetonitrile, ethanol) and in cyclodextrin aqueous solutions (beta-CD and 2-hydroxypropyl-beta-CD, 2-HP-beta-CD) were investigated. The photolysis kinetics of alpha-cypermethrin were evaluated in the various media. The PIF signal was found to be significantly enhanced in the CD media relative to the organic solvents. The stoichiometry and the formation constants of the alpha-cypermethrin inclusion complexes formed with the CDs were determined. The analytical performances of the PIF method were improved in the presence of HP-beta-CD relative to the other media, and a CD-enhanced PIF analytical method was developed. The limits of detection and limits of quantification ranged, respectively, between 6 and 98 ng/mL and between 24 and 343 ng/mL, depending on the medium. Application to the analysis of tap water and Senegal natural water samples collected close to agricultural areas and spiked with alpha-cypermethrin yielded satisfactory recoveries going from about 77% to 98%. An interference study of foreign species, including pesticides and inorganic ions likely to be present in natural waters, was also carried out.

Fluorimetric determination of histamine in fish using micellar media and fluorescamine as labelling reagent.

An analytical method based on the use of fluorescamine to produce a fluorescent derivative with histamine and combined with micellar-enhanced fluorescence detection of the formed complex is developed for the sensitive and rapid determination of histamine in fishes. The fluorescence properties of the obtained complex in water and micellar solutions of sodium dodecyl sulfate (SDS), cetyltrimethylammonium chloride (CTAC) and brij-700 are reported. Physicochemical variables influencing the sensitivity of the method (pH, micellar, fluorescamine and NaCl relative concentrations) have been optimized. The stability of the formed complex, as shown by kinetic study, depends on the pH of the solution. Linear calibration curves allowing an effective histamine determination were established with large linear dynamic range (LDR), and low limits of detection (LOD) between 0.5 and 33 ng mL-1, according to the solvent. Application to the analysis of fish samples (sardines) yielded satisfactory results. The method seems to be suitable for environmental fish quality control.

Photodegradation kinetics of some indolecarboxylic acids and their regulation effects on plant growth (groundnut and haricot bean).

Indolecarboxylic acids belong to the auxins group. They constitute a class of phytohormones, which play an important role in plant growth. This paper deals with the kinetics of six indolecarboxylic acids and their regulation effects on the growth of groundnut (Arachis hypogea) and haricot bean (Phaseolus vulgaris). The results obtained enabled us to establish a relationship between photodegradation rate constants and their regulation properties on the growth of these two plants. The paper shows that the compounds yielding the highest photodegradation rates were efficient growth regulators. In this regard, a few explanations are provided.

Contributions to the determination of histamine rate by measuring out the histamine-orthophthalaldehyde complex in the absorption and fluorescence.

Histamine is an important compound from a physiological point of view, but it is toxic since the absorption of low amounts of histamine can cause abdominal pains accompanied with vomiting. Why we have developed a new method for histamine analysis in order to improve Lerke and Bell method. From the absorption spectra, we showed that the stoichiometry of the complex histamine-orthophthalaldehyde (OPA) is 1:1. From the emission spectra, it was observed that the complex fluorescence is inhibited in acidic medium. In alkaline medium, an exaltation of fluorescence was observed, but the complex histamine-OPA was unstable. Nevertheless, kinetic study showed that good linear correlations between the fluorescence maxima of the formed complex and the histamine concentration could be obtained in this alkaline medium.