Abstract
A method of residual analysis of a new herbicide, naproanilide, α-(2-naphthoxy) propionanilide, and its degradation product, naphthoxypropionic acid (NPA) was established. Both compounds in rice grain or rice straw were extracted with acetone and the solvent was distilled off under vacuum. The residues were dissolvent in n-hexane and extracted with acetonitrile. The solution was diluted with basic water and propanilide was extracted with ether. NPA was extracted with dichloromethane after the aqueous solution was acidified with hydrochloric acid. Then the residues were cleaned up by column chromatography as follows. Compound naproanilide was applied to a Florisil column and eluted with n-hexane containing 30% of ether. NPA was applied to a silica gel column and eluted with a mixture of n-hexane, ether and acetic acid (100:100:0.5). When rice straw was used as the sample, further cleanup process by column chromatography using silica gel as adsorbent was required. The determinations of both compounds were performed on a high speed liquid chromatograph fitted with a glass column (3mm×50cm) packed with Hitachi-gel #3010. Methanol and methanol containing 0.25% of acetic acid were used as eluting solvents for naproanilide and NPA, respectively, at a flow rate of 1.5ml/min. A fluorophotometer with a flow cell (2×20mm) was used as the detector. Wave length for excitation was 280nm and that for emission was 340nm. Any interfering peak was not found in chromatograms obtained in analyses of rice grain and rice straw. The lower limits of detection of each compound were 0.004ppm (grain) and 0.008ppm (straw), so this method was as sensitive as ECD-gaschromatography. The recovery ranged between 74 and 99%.
