Matrix effect of spinach on agricultural chemical residue analysis by a commercially available ELISA kit

The matrix effect of spinach on residue analysis by commercially available ELISA kits was significant and different by every kit used. In particular, a serious influence was observed with the kit for imidacloprid and fenitrothion measurement. The substances that caused the matrix effect were removed with ultrafiltration (UF10000). It was conjectured that these substances is hydrophobic particles in the suspension.