Atanasse Coly

Fluorimetric analysis of pesticides: Methods, recent developments and applications.

The fluorimetric analysis of pesticides is reviewed with emphasis on the description of direct and indirect fluorimetric methods, including chemical derivatization, fluorogenic labelling, and photochemically-induced fluorescence. The use of fluorescence detection in TLC, HPLC and FIA as well as applications to environmental samples are discussed in detail.

Photochemically-induced fluorescence determination of sulfonylurea herbicides using micellar media

An analytical method based on the use of UV irradiation to produce fluorescent derivatives from four non-fluorescent sulfonylurea herbicides, including chlorsulfuron, metsulfuron methyl, 3-rimsulfuron and sulfometuron methyl is described. Their photochemically-induced fluorescence (PIF) properties in several solvents (water, dimethyl sulfoxide (DMSO), dimethyl formamide (DMF), acetonitrile, methanol, ethanol, propan-2-ol and their binary mixtures with water) and micellar solutions of sodium dodecyl sulfate (SDS), and cetyltrimethylammonium chloride (CTAC) are reported. Physicochemical variable influencing the sensitivity of the method have been optimized. A PIF method is developed for the determination of the four herbicides under study. Micellar media are found to provide the best analytical figures of merits. Linear dynamic ranges are established over about two orders of magnitude. The limit of detection (LOD) range from 0.2 to 6 ng ml(-1) according to the compound, with relative standard deviation (RSD) between 1.2 and 3.9%. Examples of applications to the analysis of these herbicides in spiked river water samples are given. The mean recoveries range from 80 to 104%.

Photochemical–spectrofluorimetric method for the determination of several aromatic insecticides

Ultraviolet (UV) photolysis was used to obtain fluorescent photoproducts from four naturally non-fluorescent aromatic insecticides, viz., deltamethrin, diflubenzuron, fenitrothion and fenvalerate. The photochemically-induced fluorescence properties of these insecticides in various solvents (acetonitrile, dimethyl sulfoxide, their mixtures with water, methanol, ethanol and propan-2-ol) are reported. The polarity of the solvent was shown to play an important role in the optimum UV irradiation times (8–48 min) and in the increase in the fluorescence intensity. A photochemically-induced fluorescence method was developed for the determination of the four insecticides under study. Linear dynamic ranges were established over more than two orders of magnitude. The limits of detection ranged from 0.7 to 33 ng ml–1, according to the compound, with relative standard deviations of less than 2.5%. The applicability of the method to the determination of insecticides in technical formulations was evaluated. The mean recoveries ranged from 90.8 to 100.7%, according to the compound.

Photochemical–spectrofluorimetric determination of two pyrethroid insecticides using an anionic micellar medium

The effect of sodium dodecyl sulfate (SDS) micelles on the photochemically induced fluorimetric (PIF) method was investigated in the determination of fenvalerate and deltamethrin insecticides. Physical and chemical variables affecting the sensitivity of the method were optimized. Linear calibration curves were established over more than two orders of magnitude. The limits of detection were 2.2–2.5 times lower in SDS micelles than in common organic solvents. The RSDs were between 3.7 and 5.2%. Application of the method to the analysis of commercial technical formulations and spiked water samples was evaluated. Satisfactory recoveries were found, ranging from 88.4 to 112.6%. The possible origins of the observed PIF enhancement effect in micellar solution are discussed.

Fluorimetric determination of aromatic pesticides in technical formulations. Effects of solvent and of ultraviolet photolysis

The effects of solvent and of ultraviolet (UV) photolysis on the fluorescence intensity of several aromatic pesticides including bendiocarb, chlorophacinone, coumatetralyl and pirimiphos-methyl were investigated. The type and polarity of solvent (acetonitrile, dimethylsulfoxide, methanol, ethanol and 2-propanol) were shown to play an important role in the limits of detection (LOD) of the method. UV photolysis provoked a decrease of the fluorescence signal more or less marked, depending of the structure of the pesticide. Analytical figures of merit were evaluated for the determination of pesticides under optimal conditions. The method exhibited satisfactory analytical performances. The linear dynamic ranges were obtained over more than two orders of magnitude. The LOD ranged from 0.03 to 20 ng/ml, according to the compound. The relative standard deviations were between 5.5 and 6.1%. Examples of application to the determination of pesticides in technical formulations are presented. The mean recoveries ranged from 86 to 116%. It shows the usefulness of this technique for pesticide analysis.

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.

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.

Determination of phenylurea pesticides by direct laser photo-induced fluorescence

A direct Laser Photo-Induced Fluorescence (DL-PIF) method is developed for the determination of two phenylurea pesticides, namely fenuron and diflubenzuron. The DL-PIF method uses a tunable Nd:YAG-OPO Laser to obtain the photoproduct(s) and to simultaneously analyse their fluorescence in a short acquisition time on an intensified CCD camera. Compared to classical PIF methods, the use of a tunable laser improves the selectivity (by choosing the suitable excitation wavelength), increases the sensitivity (due to the high energy of the beam) and also reduces the time of analysis. The analytical performances of this method for the determination of both pesticides are satisfactory in comparison to other classical PIF methods published for the determination of phenylurea pesticides. The calibration curves were linear over one order of magnitude and the limits of detection were in the ng mL(-1) range. Satisfactory recoveries were obtained in the analysis of both pesticides in river and sea water spiked samples.

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.

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.