Some standard content:
Coal Industry Standard of the People's Republic of China
Determination of Fluoride Ions in Coal Mine Water
1 Subject Content and Scope of Application
This standard specifies the determination of fluoride ions in water by ion selective electrodes. MT/T 360—94
This standard is applicable to the determination of fluoride ions in industrial water, domestic water, surface water and groundwater in coal mines, and its determination range is 0.05～2.5 mg/L.
2 Method Summary
Use lanthanum fluoride electrode as indicator electrode and saturated calomel electrode as reference electrode to determine the potential value at equilibrium, so as to obtain the fluoride ion content in water.
3 Reagents
3.1 Water: deionized water or water of equal purity. 3.2 Fluorine standard stock solution (1mL contains 0.1mgF): Accurately weigh 0.2210±0.0002g of high-grade pure sodium fluoride (GB1264) dried at about 120℃ for 2h, dissolve in water, transfer to a 1L volumetric flask, dilute to scale with water, and shake well. Store in a polyethylene bottle. 3.3 Fluorine standard solution (1ml contains 0.01mgF): Accurately pipette 50ml of fluorine standard stock solution (3.2), put it in a 500mL volumetric flask, dilute to scale with water, and shake well. Store in a polyethylene bottle. 3.4 Nitric acid solution: Use nitric acid (GB626) with a relative density of 1.4 to prepare a (1+1) nitric acid solution. 3.5 Total ionic strength adjustment buffer solution: weigh 60g sodium citrate dihydrate (HG3-1298) and 101g potassium nitrate (GB647), dissolve in water. Adjust to pH ~ 6.0 with (1+1) nitric acid solution (3.4), and dilute to 1L with water. 4
Instruments and equipment
4.1 Analytical balance: sensitivity 0.2mg.
4.2 Ion-F meter: digital, accuracy 0.1mV, with electrode stand, electromagnetic stirrer (continuously adjustable). 4.3 Fluoride ion selective electrode: linear range of measurement (10l ~ 10-5mol/L). 4.4 Saturated calomel electrode.
5 Determination steps
5.1 Calibrate the instrument according to the instrument manual. 5.21 Drawing the curve
5.2.1 Accurately pipette 0, 0.5, 1.0, 2.5, 10.0, 25.0 mL of the fluorine standard solution (3.3) and inject them into 100 mL volumetric flasks respectively. 5.2.2 Accurately add 20 mL of ionic strength buffer solution (3.5), dilute to the scale with water, and shake well. Transfer to a 50 mL beaker, insert the electrode into the solution, start the electromagnetic stirrer (stirring speed is medium speed), until the potential is stable (when the potential fluctuation does not exceed 1 mV within 1 minute), and record its potential.
5.2.3 On the semi-logarithmic coordinate paper, draw a curve of the potential value of the fluorine standard solution against the fluorine concentration, and mark the fluorine concentration on the logarithmic coordinate axis. 5.2.4 A working curve shall be drawn when measuring each batch of samples. Approved by the Ministry of Coal Industry of the People's Republic of China on August 31, 1994. Implemented on May 1, 1995. 5.3 Determination of samples Accurately pipette 50 mL of sample into a 100 mL volumetric flask and operate according to 5.2.2. The fluoride ion content of the sample is obtained from the working curve according to the potential value. 6 Expression of determination results The fluoride ion content is calculated according to the following formula: Where: F - fluoride ion content, mg/L; - fluoride ion content in the sample obtained from the working curve, mg; m V - sample volume, mL.
7 Precision of fluoride ion determination
When the fluoride content is not more than 1.0mg/L, the absolute allowable error of repeated determination should not exceed 0.1mg/L; when the fluoride content is greater than 1.0~～2.5mg/L, the relative allowable error of repeated determination should not exceed 10%. Additional remarks:
This standard is proposed by the National Coal Standardization Technical Committee. This standard is managed and drafted by the Sichuan Coalfield Geology Research Institute. The main drafters of this standard are Wu Fuxian, Chen Suize and Xu Ling. This standard is entrusted to the Sichuan Coalfield Geology Research Institute for interpretation. 602
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Determination of fluoride ions in coal mine water
(MT/T360-94) Preparation Instructions
(Sichuan Coalfield Geology Research Institute)
Many natural waters contain a certain amount of fluoride. According to relevant information, when the concentration of fluoride in drinking water is about 1.0 mg/L, it can prevent tooth decay and is harmless to human health. However, if the fluoride content in water exceeds a certain limit, it may cause fluoride poisoning. Therefore, it is very important to understand the fluoride content in water, especially in drinking water, and take measures to control it (add or remove it). 1. About the selection of determination methods
From the relevant standards and data documents at home and abroad, the methods for determining fluoride ions include: lanthanum-alizarin aminocarboxylic acid complex colorimetry, p-sulfonylphenylazo chromotropic acid colorimetry, zirconium oxide-alizarin (self-viewing) colorimetry, ion selective electrode method and potentiometric titration method. The concentration range of fluoride determined by colorimetry is relatively narrow, and the alkalinity of water and the presence of aluminum, chloride, iron, phosphate, sulfate, etc. in water may cause different degrees of interference to the determination of fluoride by colorimetry. The water sample is colored or turbid and cannot be directly determined. Pre-distillation is still required, which makes the analysis process complicated. The ion selective electrode method for determining fluoride is currently the most commonly used method at home and abroad. The principle of the method is based on: E = E-2. 303RTigCF
Under the condition of controlling a certain temperature and total ionic strength, E and lgCF are in a linear relationship, so fluorine can be determined. The ion selective electrode method has a wide concentration range for determining fluorine. When a specified total ionic strength buffer solution is added, it can prevent the interference of common ions in water with a certain content. In addition, the operation is relatively simple and easy to master. Therefore, the ion selective electrode method is selected as the standard for determining fluorine in coal mine water. 2 Related condition tests
2.1 Selection of the pH range of the test solutionwww.bzxz.net
Since OH- in the test solution responds to the sensitive membrane of the lanthanum fluoride electrode, H+ is easy to form a stable complex with F- that does not respond to the electrode, and a similar interfering ion exists in the test solution. Therefore, changes in the acidity of the test solution will have different degrees of influence on the measurement of the electrode potential. In this regard, the fluoride ion content of the fixed test solution was 2 mg/L, the test solution volume was 100 mL, and the test solution was measured under different pH values to determine the acidity range of the method. The test results show that when the pH value of the test solution is lower than 4 or higher than 8, the determination result of fluoride ions will increase or decrease. Therefore, it is appropriate to select the pH value of the test solution between 5.0 and 6.5. 2.2 Selection of buffer solution for adjusting ionic strength Fluoride ion is a strong complex anion, which is very easy to form stable complexes with multivalent cations such as A13+, Fe3+, etc. When considering the total ionic strength buffer solution, four buffer solutions prepared with citrate or cyclohexanediaminetetraacetic acid (CDTA) with strong release ability, and chloride or nitrate with ionic strength adjustment effect were selected. Under the condition of a total test solution volume of 100 mL, the four buffer solutions were used to conduct anti-interference ability and buffer solution addition condition tests. The test results show that when the concentration of the complexing agent in the buffer solution is high, its anti-interference ability is strong, but it is not conducive to the electrode to quickly reach the equilibrium potential; when the concentration of the complexing agent in the buffer solution is low, it is not easy to eliminate the interference. Based on the test results, the total ion strength buffer solution listed in the standard was determined.
2.3 Test on the main interfering elements
Related information, some ions contained in water (such as A13+, Fe3+, Si4+, P5+, etc.),Because of its strong complexing ability with F-, it interferes with the determination. For this reason, the amount of fluoride ion and total ionic strength buffer solution added was fixed, and different amounts of interfering components (such as Si4+: 10~50mg/L; PO-: 20~40mg/L; A13+: 1~5mg/L, etc.) were added respectively, and the determination was carried out under the condition of a total volume of 100mL of the test solution to investigate the influence of interfering components on the determination under the conditions specified in the proposed method. The experiment proved that most of the interference can be eliminated by measuring under the conditions specified in the proposed method. When the A13+ content is lower than 5mg/L, no interference is generated. When its content is higher, the amount of buffer solution can be appropriately increased to eliminate its interference. 3 Spiked recovery test
14 water samples were used, and different amounts of fluoride standard solution (the amount of fluoride standard solution added was in the range of 50~2500μg/L) were added respectively, and recovery tests were carried out. From the results of the recovery test, the recovery rates were all above 90%, and most of them were above 95%. 4 In order to investigate the precision of ion selective electrode method for determining fluorine in coal mine water, 30 water samples were repeatedly measured. After statistical calculation, the standard deviation of the repeated measurement results was 6ug/L. In combination with the specific situation of daily analysis, it is recommended that the repeatability of ion selective electrode method for determining fluorine in coal mine water be stipulated as follows: when the fluorine content in water is less than 1mg/L, the absolute allowable difference shall not exceed 0.1mg/L; when it is greater than 1mg/L, the relative allowable difference shall not exceed 10%.
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