The sodium salicylate method is a spectrophotometric method for determining nitrate in water, soil, and plant extracts. The method is based on the following principles: Formation of nitronium ions:

 The sodium salicylate method is a spectrophotometric method for determining nitrate in water, soil, and plant extracts. The method is based on the following principles: 

Formation of nitronium ions: In the presence of acid and heat, nitrate forms nitronium ions (NO+). 

Reaction with salicylate: In alkaline conditions, salicylate reacts with nitronium ions to form a yellow nitrobenzoic compound. 

Color measurement: The color of the nitrobenzoic compound is measured spectrophotometrically at a wavelength of 410 nm. 

The sodium salicylate method is popular because it is sensitive, low cost, and easy to use. However, it can be interfered with by ammonia, amines, chloride, chlorine, copper, iron (III), and strong oxidizing and reducing substances. 

Here are some steps for the sodium salicylate method:

Create sulfosalicylic acid by reacting sodium salicylate with sulfuric acid. 

In an anhydrous medium, react sulfosalicylic acid with nitrates to form a mixture of ortho- and para- sodium nitrosalicylate. 

Measure the color of the nitrobenzoic compound spectrophotometrically at a wavelength of 410 nm. 

Sodium salicylate is a chemical compound with the formula C7H5O3Na and a molecular weight of 160.11 g/mol. It is also known as Salsonin, Monosodium salicylate, Sodium o-hydroxybenzoate, Salicylic acid sodium salt, and Monosodium 2-hydroxybenzoate.