Avaliaçäo de métodos para determinaçäo de fumonisinas B1 e B2 em milho / Evaluation of analytical methods and optimization of conditions for the determination of fumonisins B1 and B2 in corn

RESUMO

Sistemas de extraçäo e limpeza foram avaliados para determinaçäo de fumonisimas em milho. O método descrito por Sydenham et alii (1992) apresentou a melhor limpeza. A recuperaçäo encontrada, no entanto, estava abaixo de 50 (por cento) para fumonisinas B1 e B2 (FB1 e FB2). O método foi modificado e a extraçäo com metanol/água (3+1) foi mantida, os volumes de solventes no condicionamento e lavagem da coluna de troca aniônica forte foram aumentados para 10 mL e o volume e composiçäo do solvente de eluiçäo alterado para 20 mL metanol/ácido acético (95+5). Após estas modificaçöes a recuperaçäo elevou-se para a faixa de 93 a 96 (por cento) para FB1 e 69 a 85 (por cento) para FB2. O solvente de eluiçäo por CLAE com detecçäo por fluorescência foi modificado para acetonitrila/água/ácido acético glacial (50+50+0,5) durante os primeiros 15 minutos com troca para acetonitrila pura até o final da corrida. As condiçöes de derivaçäo das FB1 e FB2 com o o-ftaldialdeído (OPA) foram também otimizadas empregando 100 L de extrato com 200 L do reagente OPA entre 5 - 15oC por 60 segundos. As novas condiçöes melhoram os limites de detecçäo para 20 e 40 ng/g FB1 E FB2, respectivamente, e o desvio padräo relativo entre duplicatas para 0,6(por cento) para FB1 e 2,2(por cento) para FB2. (AU)

ABSTRACT

Extraction and clean up systems were evaluated for the determination of fumonisins in com. The best clean up was found in the method described by Sydenham et alii (1992). Recovery, nonetheless, was found to be bellow 50% for fumonisins B I and B2 (FB 1 and FB2). The method was modified and methanol/water (3+ I) was kept as the extraction solvent, the volumes of the anionic Exchange column conditioning and washing solventes were increased to 10 mL and both the volume and the composition of the eluting solvente were altered to 20 mL methanol/acetic acid (95+5). After these modifications were introduced the method recovery was 95 to 96% for FB 1 and 69 to 72% for FB2. The eIution solvente for the HPLC with fIourescence detection step was also modified to acetonitri- le/water/acetic acid (50+50+0,5) during the first 15 minutes followed by purê acetonitrile for the rest of the run. The conditions employed during the derivatization reaction of fumonsins with o-phtaldialdehy- de (OPA) were also optimized to utilize 100 L sample extract and 200 L OPA solution at 5 - 15 T during60 seconds.The newconditions improved the detection limits to 20 and 40 ng/g for FB 1 and FB2, respectively, and to an average standard deviation between duplicates of 0,6% for FB I and for FB2. (AU) .