DETERMINATION OF NITRATE IN UNFILTERED EXTRACTS OF MUSKMELON TISSUE BY ION-SELECTIVE ELECTRODES

Nitrate (NO3-N) determination with ion-selective electrodes (ISE) on m uskmelon (Cucumis melo L.) leaf petiole tissue was equivalent to the c admium (Cd) reduction method provided that the aluminum sulfate [Al2(S O4)3] buffer solution was >0.04M to eliminate ionic strength effects f rom varying NO3 and chloride (Cl) concentrations. Recovery of added NO 3 was better with the HACH ISE, 98.8%, as compared with Orion ISE, 93. 6%. The addition of silver sulfate (Ag2SO4) did not significantly impr ove NO3 recovery with either ISE. The addition of carbon depressed the detected NO3 concentration by 9.7%. The HACH ISE offers the advantage of a inexpensive, easy-to-use, single body electrode with a durable m embrane allowing the filtration step to be eliminated.