Electroanalysis, zyxwvu 6( zyxwvut 1994) 694-702 zyxwv Polarographic Study of the Herbicide Metamitron Carlos Olmedo, Luis Deban,' Dolores Vazqueq Rafael Pardo, and Susana Palme?*o Departni?iento de Qziiimca Aiznli'tzca Facultad de Cieiiczm zyxwv 1 mi er-szdud de Vnlladolid C/Prndo de In .llagahleizn s/17 zyxwvutsrqpo 47005 Vnlladol~~ Spm? Kecezi ed Iune -33 1992 ABSTRACT The electrochemical characteristics of the herbicide metamitron have been studied in the pH range 1 to 9 b! . applying several polarographic techniques. name]!- DCP. TAST. and DPP. adsorptil-e stripping voltammetn. and cyclic voltammetn with HMDE. The reduction of this molecule evolves in four processes in pHt; lower than 3. and in tn-o steps between pH 3 and 9. All processes involve two electrons. are irreversible. and imply the reduction of the functions C=N and N-NH, that are present in the molecule. Also. an adsorption phenomenon was observed in several processes. The quantitative determination of metamitron can be carried out in an acetate medium (pH 4.6). by applying DPP. with a detection limit of 50 pg/L and using adsorptive stripping voltanmiern-. reaching a detection limit of 0.5 pg/L. Assays of commercial samples are illustrated. KEY WORDS: Metamitron. Polarography. Llechanism. INTRODUCTION It is necessan.. in the areas where beetroots are grown, to apply treatments with triazinic herbicides. in presom- ing as nell as in pre- or postemergency times, because of the selective character and usefulness of these pesti- cides on this ype of cultivation. Such compounds act b!. interfering in the photosyn- thesis of the plants and causing their death by stan-ation. $.nimals. not possessing this function. should not be af- fected directly by these products despite their persis- renq. as the!- are cataloged of low tosicin. for mammals. Yet, some studies carried out by Ehrlich and Ehrlich zyxwvu [l] lead to the suspicion that triazines have mutagenic ef- fects. Moreover. the degradation of these herbicides is rather slow (some persisting for several !-ears) and as such could sometimes have an effect upon subsequent cultivations. Several articles [ 1-61 used electrochemical tech- niques to study and determine triazinic compounds; others, though not studying specifically these com- pounds. have been v e n helpful for the interpretation of processes and mechanisms l7.81. The objective of this research was to elucidate the electrochemical behavior of the herbicide meramitron with the help of several polarographic techniques. Regarding this herbicide, its determination by dif- ferential pulse polarography has been published [ 91. Kevertheless. in our srudy we have serious questions with 694 10~0-039-/9i/OfiOS-O69i~j 00 T 2i/0 respect to it. mainly regarding the interpretation of the reduction process. EXPERIMENTAL. Reagents Anal!-tical-reagent grade materials were used. Metami- tron 70% (n./n-). obtained from Bayer Hispania Com- mercial S.A.. was used after purification by cq-stallization from CI 12Clz up to 99.S%. The follon-ing starting reagents were used: concentrated H,SO,: concentrated AcH. NaH,PO,. H20. and SaOH: all of anal>.tical qualiy. Apparatus DC, TAST: and DP polarographies have been performed with the help of a METROHM HERISAU E-506 polaro- graph. using a reference electrode Ag/AgCl/KCI and a platinum ausilian electrode. The cyclic and adsorptive stripping voltammetries have been performed mith an EGBG PAR Model 273 potentiostat with working HMDE METROHM EA 290. calomel reference electrode. and platinum ausilian electrode. The measurements of pH have been carried out with a METROH,\.I 654 pH meter. The coulometries have been carried out with a COULOSTAT hIETROHb1 E 524 with an integrator METROH31 E 52.5. 'To whom correspondence should be addressed. C; 1994 VCH Vcrk~gs~~sellscliaf~ mbH. D-69469 Weinheim