Article Quanification of nitrate

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A derivative spectrophotometric method was developed to determine NO₃⁻–N in plant tissues. The method is based on the measurement of the first-derivative spectrum of nitrosalicylic acid in basic solution. The nitrosalicylic acid was obtained by the reaction of samples with salicylic acid in concentrated sulfuric acid and was used by Cataldo et al. in nonderivative spectrophotometry. The main strength of this technique is the lack of matrix background interference, typical of plant extracts in traditional spectrophotometric methods. This method is fast, inexpensive, easy to apply, and highly selective. The calibration graph was linear in the range of 0.1 and 1.0 mg/L N as NO₃⁻. The average recovery in real matrices (lettuce and spinach) was 102.6%; the average standard deviation was 3.3. This method has been applied to leaves of four types of lettuce