Nitrate level in vegetables by ion chromatography.

High nitrate concentrations in salads and vegetables have attracted increased attention. It is well know that nitrate can cause serious health problems to humans such as methemoglobinemia of infants 111. Under certain conditions, specially in the human body carcinogenic nitrosamines can be formed [2]. However, nitrate content of different types of vegetables fluctuates substantially with variety, season, time of day in which harvesting took place, and fertilizers used (31. In the case of leafy vegetables such as spinach it is also a common practice to apply addition of nitrogen (N) as sidedressing several weeks before harvest [4].Nevertheless, the level of nitrate in vegetables is not only influenced by the amount and frequency of the addition of nitrogenous fertilizers, but also by the types of the nitrogenous compounds as by well as the presence of other macro and micronutrients in the soil (5). But N follows a complex cycle of transformations in soil [6], because soil microbial biomass appears to play a key role acting both as a mediator of transformations and as a reservoir of mobile N 17). This biomass has been determined using the urease test (81, where urease activity reflects the amount of ammonium ion liberated by urea hidrolysis in 100 g of soil. At the same time the pH values of the soils under study were determined using the method of Peech [9]. A simple and precise ion chromatographic (IC) method for determination of NO-, in soil was used [lo]. Water samples were injected directly and in order to analize vegetable samples a method previously described [11,12] was used. The vegetable samples, F1 variety (tardy cycle hybrid) oleracea,L., a high yielding crop for summer and autumn, and with stout, smooth, dark green leaves, recommended for processing, were obtained from Industrias Prieto S.A. (Murcia, Spain) in April 1991. Leaves were harvested and immediately sent in truckloads to the processing plant. They were passed through shakers to remove any debris.