Determination of Cypermethrin Insecticide Residues In Senegal Waters

Determination of α-Cypermethrin Insecticide Residues In Senegal Waters By A Flow Injection Analysis - Photochemically Induced Fluorescence (FIA-PIF) Method Jean-Jacques Aaron 1, Moussa Mbaye 1, 2, Mame Diabou Gaye Seye 1, 2 1 Laboratoire Géomatériaux et Environnement (LGE), Université Paris-Est Marne-la-Vallée, France 2 Laboratoire de Photochimie et d'Analyse, Faculté des Sciences et Techniques, Université Cheikh Anta Diop, Dakar, Sénégal

INTRODUCTION Ø α-cypermethrin: the most widely used pyrethroid insecticide in Sénégal Ø As a consequence, serious problems of contamination of natural waters by α- cypermethrin Ø Chromatographic methods applied to the identification and determination of α-cypermethrin and other pesticide residues in natural waters, but several drawbacks (expensive equipment & chemicals; time-consuming optimization and derivation procedures) Ø Recent development of a sensitive and simple photochemically-induced fluorescence (PIF) method in stationary solution to transform by UV irradiation nonfluorescent α-cypermethrin into strongly fluorescent photoproduct(s)

GOALS OF THE WORK ✓ Development and optimisation of a PIF method combined with flow injection analysis (FIA-PIF method) for determination of α-cypermethrin, using organic solutions and cyclodextrin (CD) media ✓ Evaluation of the analytical performances of the FIAPIF method for α-cypermethrin ✓ Application of the FIA-PIF method to the quantitative analysis of α-cypermethrin in natural waters collected in Sénégal

α- CYPERMETHRIN STRUCTURES

EXPERIMENTAL ✓ On-line FIA-PIF system: peristaltic pump + injection loop + Knauer photoreactor (low pressure UV lamp) + Kontron SFM-25 spectrofluorimeter + PC ✓ [ -cypermethrin] = 40 -4170 ng m. L-1 in all media under study ✓ CD concentrations: [ -CD] = 8 x 10 -3 M; [HP- -CD] = 10 -2 M ✓ PIF excitation and emission λ = 285 and 333 nm in acetonitrile ; 288 and 318 nm in CD media ✓ Injected volumes: 100 -280 L; Flow rate : 0. 3 -1. 8 m. L min-1; Reactor length: 100 -240 cm; FIA mobile phase: de-ionized water ✓ Analytical applications performed by the direct spiking procedure : tap water and natural water samples collected in Sénégal (Niayes agricultural area) & fortified with 41 -416 ng m. L-1 of -cypermethrin

RESULTS Ø Optimization of the FIA parameters Flow rate effect on the FIA-PIF signals ✓ Smaller optimal flow rates (maximum PIF-FIA signals) in CD media (0. 7 & 0. 3 m. L min-1 in -CD & HP- CD, respectively) than in acetonitrile, indicating : Ø Longer exposure time of -cypermethrin in the photoreactor, so that the photoreaction can take place with a larger photoconversion yield in CD media

Flow rate effect on the FIA-PIF signal of -cypermethrin Conditions: 10 -5 M α-cypermethrin in 10 -2 M HP-β-CD solution, after online UV irradiation. Injected volume = 140 µL; photoreactor length = 200 cm

Reactor length effect on the FIA-gram Conditions: 10 -5 M αcypermethrin in 10 -2 M HP-β-CD solution, after on-line UV irradiation. Injected volume = 140 µL; flow rate = 0. 7 m. L min-1 üWell-resolved FIA-PIF peaks üHigher FIA-PIF signal for a reactor length of 200 cm in all media under study

Injection volume effect on the FIA-PIF signal of -cypermethrin Conditions: 10 -5 M αcypermethrin in 8 x 10 -3 M β-CD solution, after on-line UV irradiation. Flow rate = 0. 7 m. L min-1; photoreactor length = 200 cm üWeak variation of the FIA-PIF intensity with the injection volume in CD media ✓Optimal injection volumes = 140 L in β-CD medium and 196 L in acetonitrile and in HP-β-CD

Optimum analytical parameters for the FIA-PIF determination of α-cypermethrin 10 -5 M in various media Analytical parameters Studied range Acetonitrile HP-β-CD 10 -2 M β-CD 8 x 10 -3 M λex (nm) - 284 282 λem (nm) - 333 318 316 Flow rate (m. L min-1) 0. 3 - 1. 8 1. 5 0. 3 0. 7 Volume injected ( L) 102 – 283 196 140 Reactor length (cm) 50 – 250 200 200 Sampling frequency - 51 14 32 Residence time (min) 0. 25 – 1. 50 0. 66 3. 33 1. 43 1 - 10 5 5 5 Factor

FIA-PIF analytical performances of α-cypermethrin in different media Medium LDR (ng/m. L) r LOD (ng/m. L) LOQ (ng/m. L) RSD (%) Acetonitrile HP-β-CD 10 -2 M β-CD 8 x 10 -3 M 42 – 833 0. 995 68 227 3. 8 130 -4163 0. 999 41 138 1. 2 416 -4163 0. 998 126 420 1. 4 ✓ Good precision of the calibration curves : “r” close to unity ✓ Good sensitivity of the method FIA-PIF: low LOD values ✓ Rather wide concentration LDR: 1 to 2 orders of magnitude ✓ Satisfactory reproducibility : small RSD values

Analytical applications in natural waters Water Sample α-cypermethrin (ng/m. L) Recovery (%) ± RSD(%) Added Found 41. 6 83. 3 208. 15 416. 3 36. 4 ± 2. 0 70. 0 ± 5. 3 191. 4 ± 8. 2 388 ± 18. 2 87. 5 ± 7. 2 84. 0 ± 8. 3 92. 0 ± 12. 1 93. 2 ± 10. 5 41. 6 83. 3 208. 15 416. 3 44. 7 ± 1. 8 86. 5 ± 5. 2 232. 8 ± 8. 7 437. 6 ± 16. 2 107. 4 ± 5. 6 103. 8 ± 4. 7 111. 8 ± 8. 1 105. 1 ± 6. 4 41. 6 Underground 83. 3 (depth ~ 1. 5 -3 m) 208. 15 416. 3 44. 7 ± 1. 7 86. 5 ± 4. 6 224. 4 ± 6. 1 446. 0 ± 19. 2 107. 4 ± 4. 8 103. 8 ± 4. 2 107. 8 ± 7. 5 107. 1 ± 7. 3 Surface Underground (depth~1. 5 m) ✓ Satisfactory recovery values for natural water samples ✓ No significant interference from the background resulting from inorganic and/or organic compounds probably present in the natural water samples under study

C O N C L U S I O NS ✓ Simplicity and low cost of the FIA-PIF method ✓ Enhancement of the sensitivity of the FIA-PIF method in HP-β-CD ✓ Higher frequency of samples/hour with the FIA-PIF method than with stationary PIF ✓ Detection of -cypermethrin residues at the ng m. L-1 level in spiked tap water and natural waters, using HP-βCD media ✓ Possible use of FIA-PIF as a routine method for determination of -cypermethrin in polluted surface waters and ground waters.