Experiments for the determination of nitrate-nitrogen content in plants
Experiments for the determination of nitrate-nitrogen content in plants
Nitrate nitrogen is the most important source of nitrogen in plants, and the nitrate nitrogen content in plants can reflect the nitrogen supply of the soil, so it is often used as a fertilizer indicator. Vegetable leaves and root vegetables often contain a lot of nitrate, in the cooking and pickling process can be converted to nitrite and jeopardize human health, therefore, the nitrate content has become an important indicator of the quality of identification of vegetables and their processed products. The purpose of this experiment is to master the principle and method of determining nitrate nitrogen content.
Operation method
Experiments for the determination of nitrate-nitrogen content in plants
Principle
NO3- reacts with salicylic acid under strong acid conditions to produce nitrosalicylic acid. Generated nitrosalicylic acid in alkaline conditions (pH>12) is yellow, in a certain range, the color of the shade is proportional to the content, can be directly measured by spectrophotometer. Move I. Material Instrumentation and Reagents For more product details, please visit Aladdin Scientific website.
1. Material: leaves of plants such as wheat or rice;
2. Instrumentation: spectrophotometer; electronic analytical balance; 10 ml, 20 ml graduated test tubes; pipettes; 25 ml volumetric flasks; small funnels (ф5 cm); glass rods; earwash balls; electric stove; aluminum pot; glass bubbles; a number of 13.7 cm quantitative filter paper.
3. Reagents and preparation
Preparation of 10μg-ml-1 NO3--N standard master batch: accurately weigh 30.1444g of KNO baked to constant weight, dissolve it in distilled water, and then volume it to 200ml (i.e. 100μg-ml-1 NO3--N solution). Then 10ml of the solution was sucked and diluted to 100ml with distilled water, i.e. 10μg-ml-1 NO3--N standard solution.
5% salicylic acid - sulfuric acid solution preparation: weigh 5g of salicylic acid first add a small amount of concentrated sulfuric acid (density of 1.84) dissolved, then add concentrated sulfuric acid to 100ml, shake well, stored in a brown bottle, placed in the refrigerator to save a week effective.
8% sodium hydroxide solution preparation: weigh 20g sodium hydroxide dissolved in 250ml distilled water.
Experimental steps
1. Production of NO3--N standard curve
(1) Take six 10 ml graduated test tubes, number them, and prepare NO3--N standard solution with the content of 0-10 μg in each tube according to the table below. Add the reagents in the table and shake well. After 20 min at room temperature, add 8.6 ml of 8% NaOH solution to each tube, shake well, so that the total volume of the color solution is 10 ml. Then use tube 0 as a blank control, and measure the absorbance (A) at 410 nm. 
(2) Standard curve
The NO3--N content of tubes No. 1 to 5 was taken as the horizontal coordinate, and the absorbance value was taken as the vertical coordinate to draw the standard curve.
2. Determination of nitrate in samples
(1) Preparation of sample solution
Take a certain amount of plant leaves cut and mixed, weigh 2-3g (three copies), respectively, into three 20ml graduated test tubes, add 10ml distilled water, sealed with a glass bubble, placed in a boiling water bath extraction for 30min. to the time to take out, cooled with tap water, will be filtered into 25ml volumetric flasks, and distilled water repeatedly rinse the residue, and finally fixed to the scale.
(2) Determination of sample solution
Take three 10 ml graduated test tubes, add 0.1 ml of sample solution, 0.9 ml of distilled water, 0.4 ml of 5% salicylic acid - sulfuric acid solution, mix well and set at room temperature for 20 min, then slowly add 8.6 ml of 8% NaOH solution, shaking well, so that the total volume of the color development of 10 ml, to be cooled to room temperature, with the standard curve No. 0 tubes as a blank control, at 410 m wavelength to determine the absorbance (A) value. The absorbance (A) value was measured at 410m.
Calculation of results
According to the absorbance (A) value measured in the sample solution, find out the NO3--N content from the standard curve, and calculate the NO3--N content in the sample according to the following formula. 