Fluoride Detection in Agricultural Products by Ashing Experiment

Summary

Fluorine is an essential nutrient for the human body and a toxic pollutant. Fluorine in nature mainly exists in natural minerals such as fluorspar and apatite. Fluorine is mainly discharged from the industry as fluorine gas, liquid and waste residue, as well as the application of phosphate fertilizers and fluorine pesticides such as sodium fluoride, sodium fluorosilicate, etc. into the soil and plant system, and then through the food chain into the animal and human body. Long-term intake of excessive fluoride by the human body can cause fluorosis, which can result in enameled teeth in mild cases and bone fluorosis in severe cases.

Operation method

Fluoride Detection in Agricultural Products by Ashing Experiment

Principle

Lanthanum fluoride single crystal has a selective logarithmic response to fluoride ions, and a primary cell is formed by immersing the fluoride ion-selective electrode and the external reference electrode into the fluoride-containing leaching solution after ashing. The electric potential of the primary cell is linearly related to the logarithm of fluoride ion activity, so the fluoride ion concentration in the solution to be measured can be calculated by measuring the electric potential of the primary cell composed of the electrode and the solution with known fluoride ion concentration and the electric potential of the electrode and the solution with fluoride ion concentration to be measured.

Materials and Instruments

Fluorine Electrode Acidity Meter Magnetic Stirrer Type 232 Glycine Mercury Electrode Polyethylene Beaker Muffle Furnace Porcelain Crucible

Move

I. Experimental apparatus, equipment and reagents

1、Instruments, equipment

(1) Fluorine electrode: CSB-F-l type or other models

(2) Acidity meter: pHS-2 type or potentiostat.

(3) Magnetic stirrer

(4) Glycine Mercury Electrode Type 232 or Silver-Silver Chloride Electrode

(5) Polyethylene beaker 100 ml

(6) Muffle furnace

(7) Porcelain crucible

2. Reagents

1. Magnesium nitrate solution: take Mg (N03)2-6H2O 950g dissolved in water and diluted to 1000ml.

2. Fluoride standard reserve solution: weigh 0.22log benchmark sodium fluoride (pre-drying at 105-110 ℃ for 2 hours) dissolved in water and transferred to 1000 ml volumetric flasks, diluted to the scale, shaking, stored in polyethylene bottles, this solution contains fluoride ions lOOug per milliliter.

3. Fluoride standard solution: absorb 10ml of fluoride standard reserve solution diluted in 100ml volumetric flask, dilute to the scale, shake well, this solution contains 10ug of fluoride ions per milliliter.

4. 0.5mol / L sodium hydroxide solution

5. Ion intensity mediation buffer solution (TISAB): weigh 58.8g of sodium citrate dihydrate and 85g of sodium nitrate in a beaker, add water to dissolve, hydrochloric acid to adjust the pH to 5-6 transferred to 1000ml volumetric flasks, dilute to scale.

(ii) Measurement steps

1. Weigh the sample l 2g in a porcelain crucible, add Mg (NO3) 2 solution 1ml, placed in a boiling water bath, a few minutes, carefully add a few drops of concentrated hydrochloric acid, pay attention to avoid the sample overflowing crucible, continue to add concentrated hydrochloric acid 2-3 times, a few drops each time, until the sample is nearly dry. If the contents are viscous, they must be dried with a hot plate and then charred. Cover the crucible with a lid and place in a cold muffle furnace, heat and burn at 500-550°C for 6 hours until the ash separates into a light gray color, remove and allow to cool. The contents of the crucible a hydrochloric acid (1:4) into a l00ml beaker, add 5ml of concentrated hydrochloric acid, placed in a water bath and evaporated.

Wet the beaker with 2 ml of concentrated hydrochloric acid, then add 50 mL of water, heat on the water bath for several minutes, remove and cool, transfer to a volumetric flask of l00 ml, fixed volume. Filtration, discard the beginning to consider the liquid spare.

2. Drawing of standard curve: Pipette l0ug.ml-1F-standard solution 0.5, 1.0, 2.0, 4.0, 6.0, 8.0, 10.0 ml were put into seven 50ml volumetric flasks, add l0ml of total ionic strength adjusting buffer solution, dilute it to the scale with water, and shake well.

That is, the standard series containing F-0.2, 0.4, 0.8, 1.6, 2.4, 3.2, 4.0ug.ml-l, respectively, were transferred to 150ml beaker into the rotor, according to the concentration of the order from low to high sequentially inserted into the electrode, and then stirred to determine the number of mv records. And do mv-logCF curve.

3. Determination of the liquid to be measured: Aspirate 20-50 ml of the liquid to be measured into a 50 ml volumetric flask, adjust the liquid to be measured with 0.5 ml.L-1NaOH to make it nearly neutral, add 10 ml of total ionic strength adjusting buffer, dilute it with water to the scale, and shake it well. Transfer it to 150ml beaker, put it into the rotor, insert the electrode and read the mv value after the potential stabilizes under stirring.

4. Blank: Replace with distilled water and measure according to the sample.

5. Calculation of results:

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