Determination of nitrate in agricultural products
Determination of nitrate in agricultural products
The experiment for the determination of nitrate in agricultural products can be used for: (1) detecting the content of nitrate and nitrite in food; (2) as one of the measurement standards for food quality and hazards to human health.
Operation method
Determination of nitrate in agricultural products
Principle
Nitrate Determination: After the sample is precipitated protein and fat is removed, the solution is passed through cadmium column or cadmium powder is added to reduce the nitrate ion into nitrite ion, under weak acidic condition, nitrite and p-aminobenzene sulfonic acid are diazotized, and then coupled with N-1 naphthalene ethylenediamine to form a red dye, the total amount of nitrite is measured, and the total amount of nitrite minus the amount of nitrite content is obtained. Nitrate content was subtracted from the total nitrite content to obtain the total nitrite content.
Materials and Instruments
Sample Move I. Preparation reagents Caveat Vegetables and pickles contain high levels of nitrate. The sample solution can be diluted to the appropriate concentration according to the actual level of nitrate in the sample. Common Problems Nitrate levels in edible vegetables do not exceed standard allowances and are generally below 432 PPm. For more product details, please visit Aladdin Scientific website.
Ammonium chloride buffer solution Cadmium sulfate solution Cadmium sulfate Hydrochloric acid Sodium nitrate
Cadmium column
2 Cadmium sulfate solution (0.14mol/L): weigh 37g of cadmium sulfate (CdSO4·8H2O), dissolve with water, and then volume it to 1L.
3 Hydrochloric acid solution (0.1mol/L): take 8.4mL of hydrochloric acid, and then dilute it to 1L with water.
4 Standard solution of sodium nitrate: Accurately weigh 500.0mg in 110 ~ 120 ℃ dry constant weight of sodium nitrate, add water to dissolve, transfer to a 500mL volumetric flask, add 50mL ammonium chloride buffer, dilute with water to the scale, mix, and store in a refrigerator at 4 ℃ away from light. Each milliliter of this solution is equivalent to 1mg of sodium nitrate.
5 Sodium nitrate standard use solution: 1.0mL of sodium nitrate standard solution was sucked up and placed in a 100mL volumetric flask, diluted with water to the scale, mixed well, and then dispensed at the time of use. Each milliliter of this solution is equivalent to 10μg sodium nitrate.
6 sodium nitrite standard use of the same 3.8.
7 cadmium column (cadmium powder).
7.1 Preparation of sponge cadmium powder: in 500mL of cadmium sulphate solution, put enough zinc rods by 3 ~ 4h, when all of the cadmium is replaced by zinc, gently scrape down with a glass rod, remove the remnants of zinc rods, cadmium sinking to the bottom, pour off the upper layer of the clear liquid to water with a Tilt method for several times, and then moved to the crusher, add 500mL of water, pounding about 2s, water will be washed to the standard sieve of fine metal particles, take 20 ~ 40 mesh between the part of the reagent bottles, water capping preservation, standby.
7.2 Cadmium column reduction efficiency determination: take 25mL acid burette several, to the bottom of the column pressed into the 1cm-high glass wool as a cushion, a small funnel on the top, will be the newly formulated cadmium Cadmium powder with water to join the column, gently knocking the column while loading, to exclude the air inside the column, add cadmium powder to 8 ~ 10cm high, covered with 1cm high glass wool on top, on top of a storage funnel.
When the cadmium column is filled, the first 25mL hydrochloric acid (0.1 mol / L) wash, and then wash with water twice, each time 25mL, adjust the column flow rate to 3 ~ 5mL / min. Cadmium column is not used to cover with water, at any time to maintain the level of cadmium layer above the level of cadmium layer shall not make the cadmium layer of air bubbles.
After each use of the cadmium column, it should be washed with 25mL of hydrochloric acid (0.1mol/L), then washed with water twice, 25mL each time, and finally covered with water.
Column first add 25mL ammonium chloride buffer, until the liquid level is close to the sponge cadmium, suck 2.0mL sodium nitrate standard use solution (10μ g/mL), through the column reduction, control the flow rate of 3-5mL/min, with 50mL volumetric flasks to receive. Add 5mL ammonium chloride buffer solution, the liquid level is close to the cadmium sponge, add 15mL of water to wash the column, the reduction solution and the wash solution flow into the 50mL volumetric flask together.
Add 5mL 60% acetic acid, 10mL color developer, dilute with water to the scale, mix well, placed in the dark for 25min. 1cm colorimetric cup, adjust the zero point with the standard zero tube, measure the absorbance at a wavelength of 550nm, according to the standard curve of nitrite to calculate the reduction efficiency (such as cadmium column reduction rate of less than 95%, it should be activated by hydrochloric acid soaking).
7.3 Determination of the reduction efficiency of cadmium powder: cadmium powder before use, activated by hydrochloric acid soaking. Before use, the cadmium powder should be activated by hydrochloric acid immersion, then washed twice with water and submerged in water for use. Add the cadmium powder into a 25mL graduated test tube with stopper to 5mL scale with a horn spoon; seal with a small amount of water. Pipette 2.0mL of Sodium Nitrate Standard Use Solution and add 5mL of Ammonium Chloride Buffer. Cover the test tube with a stopper, shake for 2 min, let it rest for 5 min, filter with a small funnel stuffed with a small amount of cotton wool in the neck of the funnel, collect the filtrate quantitatively in a 50mL volumetric flask, and wash the cadmium powder with 15mL of water a small amount of times, and the washings and filtrates were combined. Add 5mL acetic acid (60%), immediately add 10mL colorant, dilute with water to the scale, mix, dark disposal for 25min. 1cm colorimetric cup, adjust the zero point with the standard zero tube, measure the absorbance at 550nm, and calculate the reduction efficiency according to the nitrite standard curve. 
(B) experimental methods and procedures
1 sample treatment
2 determination (with cadmium column method or cadmium powder method to reduce nitrate to nitrite)
2.1 A method (cadmium column method): the activation of cadmium column first add 25mL ammonium chloride buffer, to the liquid surface close to the sponge cadmium, accurately suck 5.1 of the sample filtrate 10.0mL, add the cadmium column reduction. The following according to 9.7.2 since & ldquo; control flow rate of 3 ~ 5mL/min & rdquo; from the operation according to law.
2.2 B method (cadmium powder method): accurately sucked up the sample filtrate of 5.1 10.0mL, placed in a height of 5mL cadmium powder in a 25mL corked graduated test tube. Since & ldquo; add 5mL ammonium chloride buffer…” according to 9.7.3 according to the law.
Note: Vegetables, pickles in food with high nitrate content, according to the actual content of nitrate in the sample, the sample solution can be diluted to the appropriate concentration.
(iii) Calculation of results 