All chemical reagents used were of analytical grade. HPLC-grade acetonitrile and methanol were both from Carlo-Erba (Rodano, Italy), and formic acid was from Interchim (Montluc¸ on, France). All of them were used without any further purification
All chemical reagents used wereof analytical grade. HPLC-grade acetonitrile and methanol wereboth from Carlo-Erba (Rodano, Italy), and formic acid was fromInterchim (Montluc¸ on, France). All of them were used without anyfurther purification