Some standard content:
National Standard of the People's Republic of China
Health standard for fluorides in the air of workplace
Health standard for fluorides in the air of workplace Subject content and scope of applicationbZxz.net
This standard specifies the maximum allowable concentration of fluorides in the air of workplace and its monitoring and inspection methods. This standard applies to all types of enterprises that produce and use fluorides. 2 Hygiene requirements
The maximum allowable concentration of fluorides (excluding hydrogen fluoride) in workplace air is 1.0 mg/m (measured in fluorine). 3 Monitoring and inspection methods
The monitoring and inspection methods of this standard adopt the ion selective electrode method, see Appendix A (supplement). GB 16228-1996 approved by the State Administration of Technical Supervision on April 3, 1996
Implementation on September 1, 1996
A1 Principle
GB 16228-1996
Appendix A
Ion Selective Electrode Method
(Supplement)
Gaseous fluorine and fluorine-containing smoke in the air are collected and absorbed by the filter material soaked in alkaline, and dissolved in hydrochloric acid to prepare the sample solution. The ion selective electrode made of fluoride single crystal has a linear relationship between the electrode potential and the logarithm of the fluoride ion activity in the solution. The fluoride ion content in the sample solution is obtained from the measured potential value through the standard series method. A2 Instrument
A2.1 Sampling clamp.
A2.2 Filter material: ultrafine glass fiber filter paper. A2.3 Vacuum pump.
A2.4 Flow meter: 0～20L/min.
A2.5 Ion activity meter, electrode potentiometer or precision pH meter. A2.6 Fluoride ion selective electrode.
A2.7 Magnetic stirrer.
A2.8 Plastic beaker: 50mL.
A3 Reagents
The experimental water is distilled water.
A3.1 Soaking solution: 8g sodium hydroxide (super pure) is dissolved in water, 20mL propylene glycol is added, and diluted to 1L with water. Used to soak ultrafine glass fiber filter paper.
A3.2 Hydrochloric acid solution: c(HCI)=0.5mol/L. A3.3 Ammonium hydroxide solution: c(NH,OH)=6mol/L. A3.4 Bromocresol green indicator: 0.1g bromocresol green and 3mL c(NaOH)-0.05mol/L sodium hydroxide solution are ground together and diluted with water to 250mL.
A3.5 Total ionic strength buffer: Weigh 59g sodium citrate (Na:CH.O, 2H2O) and 11.6g sodium chloride, dissolve in appropriate amount of water, add 2mL bromocresol green indicator and 11.4ml. glacial acetic acid, neutralize with c(NaOH)=6mol/L sodium hydroxide until the indicator just turns blue, then add 1-2 drops of hydrochloric acid solution (A3.2) to make the indicator blue-green (pH value is about 5.8 at this time), dilute with water to 1L. A3.6 Standard solution: Weigh 0.2210g sodium fluoride dried at 110℃ for 2h, dissolve in a small amount of water, transfer to a 1L volumetric flask, and add water to the scale. This solution is 1mL = 100μg fluorine, stored in a polyethylene bottle, and diluted with water before use to a standard solution of 1mL = 10μg fluorine. A4 Sampling
A4.1 Soaking filter paper: Cut the ultrafine glass fiber filter paper into small discs with a diameter of 40mm, clamp it with tweezers, and soak it in 3 cups of soaking solution (A3.1) in sequence, 2 to 3 seconds each time, take it out and drain it slightly, then put it on a large filter paper and dry it at 60 to 80℃ (be careful not to burn it, otherwise it will affect the fluorine blank value of the filter paper). A4.2 Sampling: Clamp two soaked filter papers in the sampling clamp, and extract 75L of air at a speed of 15L/min. A5 Analysis steps
A5.1 Control test: Analyze the filter paper that was taken to the site on the sampling clamp but was not sampled (the number is 1/10 of the total number of samples, and 1 piece is used when the total number of samples is less than 520
10) in the same way as the sample. GB16228—1996
A5.2 Sample treatment: Place the two filter papers before and after sampling in two plastic beakers, add 16mL hydrochloric acid solution (A3.2) and 2mL water to each, crush the filter paper with a glass rod, put in an iron core plastic sleeve stirrer, and stir on a magnetic stirrer for 3-5 minutes; at this time, the filter paper has been beaten into pulp.
A5.3 Drawing of standard curve: Take 8 beakers, add 1 piece of soaked filter paper to each, and prepare the standard series according to Table A1. Then stir in the same way as the sample. Add 1.3mL ammonium hydroxide solution (A3.3) and 2-3 drops of bromocresol green indicator (A3.4) to each cup, and continue to use hydrochloric acid solution (A3.2) and ammonium hydroxide solution (A3.3) to adjust the pH value of the solution until the indicator turns blue-green while stirring. Table A1: Preparation of fluoride standard tubes
Standard solution (10 μg/mL), mL
Standard solution (100 μg/ml.), ml
Water, mL
Fluoride content, g
Add 5 mL of total ionic strength buffer (A3.5), insert the fluoride electrode and saturated calomel electrode, continue stirring for 4~~5 minutes, stop and measure the potential (mV) of the solution. Stir for another 1~2 minutes, stop, and read the potential value again until the reading remains unchanged. Use semi-logarithmic coordinate paper to represent mV with equidistant coordinates and fluoride ion content with logarithmic coordinates, and draw a standard curve (or use logarithmic curve regression method to obtain the regression equation).
A5.4 Add ammonium hydroxide to the treated sample pulp suspension in the same way as the standard series, neutralize and adjust the pH value; then add the total ionic strength buffer, insert the electrode, and measure its potential (mV) value. According to the potential value of the sample solution, the fluoride ion content in the solution is obtained from the curve (or regression equation).
A6 Calculation
Where: X
The concentration of total fluoride (converted into fluorine) in the air, mg/m; C, C2——the fluorine content on the front and back two filter papers, μg; V.——The sample volume under standard conditions, L. A7 Description
-(A1)
A7.1 The detection limit of fluoride ion in solution determined by this method is 1μg/25mL. When the sampling volume is 150L, 25mL solution is made, and the minimum detection concentration for air is 0.0067mg/m. The upper detection limit in the solution is 3 to 4 orders of magnitude higher than the lower limit. When the concentration of fluoride ion (F-) in the solution is 5.0mg/L, the coefficient of variation of this method is 4.56%. A7.2 Overlap two filter papers for sampling, and the total sampling efficiency is 96%. A7.3 There is no significant difference in the analysis results within 1 week after the sample is collected. When the fluorine in the air is mainly in the form of dust particles, the sampling surface of the filter paper should be folded inward into a fan shape after sampling, and then placed in a paper bag and carried back to the laboratory. A7.4 When soaking the filter paper, use a 250mL beaker to hold 200mL of dipping solution, a total of 3 cups; after soaking each sheet, touch the edge of the cup and hold for a few seconds to drain slightly, and then do the same in the second and third cups. After soaking 200 filter papers, the first cup of dipping solution should be discarded even if it has not been used up (because it already contains a certain amount of fluoride ions), and the second and third cups should be replaced with the first and second cups in order, and another 200mL of clean dipping solution should be taken as the third cup to continue soaking. Only by handling according to the above method can the blank value of each filter paper be guaranteed not to exceed a certain limit. The impregnated filter paper should be properly sealed in a plastic or cowhide paper bag and taken out before use. After each batch of filter paper is impregnated, 6 to 8 sheets should be randomly taken out to determine their blank values. The blank value limit of each sheet should be within 0.2 ± 0.05 g fluorine; otherwise, excessive fluctuations will affect the accuracy of the measurement results. A7.5 The fluorine electrode responds quickly and effectively at high concentrations; but the response time is extended at low concentrations. Generally, when the fluoride ion concentration is 0.1 to 0.2 mg/L, the response time is 3 to 5 minutes; when it is above 0.5 mg/L, it is 1 to 3 minutes. According to this situation, master the stirring time; after measuring a reading, stir for 1 to 2 minutes and read the result again. A7.6 If the pH value of the measured solution exceeds the range of 5 to 8, it may cause a large error; in the test of a large number of samples, it is important to pay attention to adjusting the pH value.
A7.7Temperature also affects the electrode potential value; in actual work, if there is a large difference between the sample solution and the solution temperature when drawing the standard curve, the standard curve should be redone.
A7.8 Most anions do not interfere with the determination; only cations such as iron and aluminum interfere with the determination of fluoride. Citrate is a good masking agent for iron and aluminum.
Additional Notes:
This standard is proposed by the Ministry of Health of the People's Republic of China. This standard was drafted by the Hunan Provincial Institute of Labor Hygiene and Occupational Disease Prevention and Control, the Xinyang Municipal Health and Epidemic Prevention Station of Henan Province, and the Guangxi District Health and Epidemic Prevention Station.
The main drafter of this standard is Wang Jie.
This standard is interpreted by the Institute of Labor Hygiene and Occupational Diseases of the Chinese Academy of Preventive Medicine, the technical unit entrusted by the Ministry of Health. 522
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