Residues of free and bound maleic hydrazide in potato tubers

The method of Vadukul (1991) for determining maleic hydrazide (MH) was modi fied and gave recoveries of free MH of 89% +/- 4%. The values recorded on i ndividual tubers ranged from 2-14 mg kg(-1). Maleic hydrazide was evenly di stributed throughout the tuber (peel, outer and inner flesh) but concentrat ion increased slightly as tuber size increased. The concentration of Gee MH decreased from 7 to 3 mg kg(-1) over the storage period of 5 1/2 months. A cid hydrolysis released substantial amounts of MH particularly from older p otatoes (13 mg kg(-1)) compared with 6 mg kg(-1) from new potatoes, implyin g that free MH is gradually converted to a bound form with time after treat ment. No evidence was found for the presence of a beta-glucoside of MH.