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HJ 757-2015 English PDF

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HJ 757-2015: Water quality. Determination of chromium. Flame atomic absorption spectrometry
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Basic data

Standard ID HJ 757-2015 (HJ757-2015)
Description (Translated English) Water quality. Determination of chromium. Flame atomic absorption spectrometry
Sector / Industry Environmental Protection Industry Standard
Word Count Estimation 13,149
Date of Issue 2015-10-22
Date of Implementation 2015-12-01
Quoted Standard HJ 678; HJ/T 91; HJ/T 164
Regulation (derived from) Ministry of Environment Announcement 2015 No.62
Issuing agency(ies) Ministry of Ecology and Environment
Summary This standard specifies the determination of chromium in water by flame atomic absorption spectrophotometry. This standard applies to the determination of high concentrations of water-soluble chromium and total chromium and wastewater. When the volume of the sample volume and the volume of sample preparation is the same, this standard assay detection limit of chromium 0.03mg/L, detection limit of 0.12mg/L.

HJ 757-2015: Water quality. Determination of chromium. Flame atomic absorption spectrometry

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Water quality.Determination of chromium.Flame atomic absorption spectrometry National Environmental Protection Standard of the People's Republic Determination of chromium in water Flame atomic absorption spectrophotometry Water quality - Determination of chromium -Flame atomic absorption spectrometry Published on.2015-10-22 2015-12-01 Implementation release Ministry of Environmental Protection

Content

Foreword.ii 1 Scope.1 2 Normative references.1 3 Terms and Definitions 1 4 principle of the method.1 5 interference and elimination 1 6 Reagents and materials 1 7 Instruments and equipment 2 8 sample 2 9 Analysis steps.3 10 Calculation and representation of results. 4 11 precision and accuracy. 4 12 Quality Assurance and Quality Control..5 13 Waste treatment.5 14 Notes.5 Appendix A (Normative Appendix) Matrix Interference Inspection Method.6 Appendix B (normative appendix) standard addition method.7 Applicability judgment of Appendix C (normative appendix) standard addition method.8

Foreword

To implement the Environmental Protection Law of the People's Republic of China and the Law of the People's Republic of China on Water Pollution Prevention and Control, to protect the environment, To ensure human health, standardize the determination method of chromium in water, and develop this standard. This standard specifies flame atomic absorption spectrophotometry for the determination of high concentrations of soluble chromium and total chromium in water and wastewater. This standard is the first release. Appendix A and B of this standard are normative appendices, and Appendix C is an informative appendix. This standard was formulated by the Science and Technology Standards Department of the Ministry of Environmental Protection. This standard is mainly drafted by. Liaoning Provincial Environmental Monitoring Experimental Center. This standard is verified by. Jilin Province Environmental Monitoring Center Station, Anshan Environmental Monitoring Center Station, Dandong City Environmental Monitoring Xinzhan, Fushun Environmental Monitoring Center Station, Jinzhou Environmental Monitoring Center Station and Tieling Environmental Monitoring Center Station. This standard was approved by the Ministry of Environmental Protection on October 22,.2015. This standard has been implemented since December 1,.2015. This standard is explained by the Ministry of Environmental Protection. 1 Determination of chromium in water - Flame atomic absorption spectrophotometric method Warning. Hydrochloric acid is highly corrosive and highly volatile. Nitric acid and hydrogen peroxide are highly corrosive and strong oxidizing. Wear protective equipment as required to avoid contact with skin and clothing. Pretreatment of all samples should be carried out in a fume hood.

1 Scope of application

This standard specifies the flame atomic absorption spectrophotometry for the determination of chromium in water. This standard applies to the determination of high concentrations of soluble chromium and total chromium in water and wastewater. When the sampling volume is the same as the volume of the sample after preparation, the detection limit of chromium in this method is 0.03 mg/L. The limit is 0.12 mg/L.

2 Normative references

The contents of this standard refer to the following documents or their terms. For undated references, the valid version is appropriate. Used in this standard. HJ 678 Water quality metal total digestion microwave digestion method HJ/T 91 Surface Water and Wastewater Monitoring Technical Specifications HJ/T 164 Technical Specifications for Groundwater Environmental Monitoring

3 Terms and definitions

The following terms and definitions apply to this standard. 3.1 soluble chromium soluble chromium Refers to chromium that has not been acidified and filtered through a 0.45 μm filter. 3.2 total chromium total quantity of chromium Refers to chromium that has been determined after digestion of the unfiltered sample.

4 Principle of the method

After the sample is filtered or digested, it is sprayed into a rich air-acetylene flame, and the chromium ground state atom formed in the high temperature flame is chrome-free. The 357.9 nm characteristic line emitted by a cardiac cathode lamp or a continuous light source produces selective absorption, and under certain conditions, its absorbance value It is proportional to the mass concentration of chromium.

5 interference and elimination

5.1 1 mg/L Fe and Ni, 2 mg/L Co, 5 mg/L Mg, 20 mg/L Al, 100 mg/L Ca to chromium The measurement has negative interference; the addition of ammonium chloride can eliminate the interference of the above metal ions; 20 mg/L of Cu and Zn, 500 mg/L Na and K did not interfere with the determination of chromium, and the addition of ammonium chloride had no effect on the determination of the above metal ions. 5.2 When the existing matrix interference cannot be eliminated by the above method, the standard addition method can be used to eliminate the interference, see Appendix B. See Appendix A for the inspection of matrix interference and Appendix C for the applicability of the standard addition method.

6 reagents and materials

Analytically pure reagents that meet national standards are used for analysis, unless otherwise stated. The experimental water is deionized water or equivalent. Purity of water. 26.1 Hydrochloric acid. ρ (HCl) = 1.19 g/ml, excellent grade pure. 6.2 Hydrochloric acid solution. 1 1, prepared with hydrochloric acid (6.1). 6.3 Nitric acid. ρ (HNO3) = 1.42 g/ml, excellent grade pure. 6.4 Nitric acid. ρ (HNO3) = 1.42 g/ml. 6.5 Nitric acid solution. 19. Prepared with nitric acid (6.4). 6.6 Hydrogen peroxide. ω (H2O2) = 30%. 6.7 Ammonium chloride [NH4Cl]. 6.8 Ammonium chloride solution. ρ(NH4Cl) = 100 g/L. Accurately weigh 10 g of ammonium chloride (6.7), dissolve it in a small amount of water and transfer it to a 100 ml volumetric flask. Mark the line and shake it. 6.9 Potassium dichromate [K2Cr2O7]. Reference reagent. 6.10 chromium standard stock solution. ρ (Cr) = 1000 mg/L. Accurately weigh 0.2829 g of potassium dichromate (6.9) which was pre-dried at 120 °C ± 2 °C for 2 h and constant weight, dissolved in a small amount of water. Transfer the whole amount to a 100 ml volumetric flask, add 0.5 ml of nitric acid (6.3), dilute to the mark with water, and shake well. Dark room temperature protection Store in a polyethylene bottle or borosilicate glass bottle and keep the pH between 1 and 2 for 1 year. Or purchase a commercially available certified standard substance. 6.11 Chromium standard use solution. ρ (Cr) = 50.0 mg/L. Pipette 5.00 ml of chromium standard stock solution (6.10) into a 100 ml volumetric flask, add 0.1 ml of nitric acid (6.3), dilute with water To the marking line. Can be stored for 1 month. 6.12 Gas. Acetylene, purity ≥ 99.6%. 6.13 Gas-assisted gas. Air should be properly filtered to remove water, oil and other impurities before entering the burner. 6.14 Membrane. Acetate or polyethylene filter with a pore size of 0.45 μm.

7 Instruments and equipment

7.1 Flame atomic absorption spectrophotometer and corresponding auxiliary equipment. 7.2 Light source. chrome hollow cathode lamp or continuous light source with 357.9 nm. 7.3 Microwave digestion instrument. microwave power is 600 W~1500 W; temperature control accuracy can reach ±2.5 °C; equipped with microwave digestion tank. 7.4 Temperature-controlled electric heating plate. The temperature control range is from room temperature to.200 °C. 7.5 Vials. 500 ml, polyethylene or hard glass bottles. 7.6 Commonly used laboratory instruments and equipment.

8 samples

8.1 Sample collection Sample collection is performed in accordance with the relevant regulations of HJ/T 91 and HJ/T 164, and samples of soluble chromium and total chromium should be collected separately. 8.2 Preservation of samples 8.2.1 Soluble chromium sample After the sample was collected, it was filtered through a 0.45 μm filter (6.14) as soon as possible, and the initial filtrate was discarded. Collect the required volume of filtrate In the sample vial. 1 ml of nitric acid (6.3) was added to each 100 ml of filtrate and determined within 14 days. 38.2.2 Total chromium sample After sample collection, acid (6.3) was added to acidify to pH ≤ 2, measured within 14 days. 8.3 Preparation of samples 8.3.1 Soluble chromium sample Measure a volume of water in a 50 ml volumetric flask, add 5 ml of ammonium chloride solution (6.8) and 3 ml of hydrochloric acid solution (6.2). Dilute to the mark with water. 8.3.2 Total chromium sample (1) Electric heating plate digestion method Measure 50.0 ml of the mixed water sample in a 150 ml beaker or Erlenmeyer flask, add 5 ml of nitric acid (6.3), and place it in temperature control. On the electric heating plate (7.4), cover the surface dish or small funnel, keep the temperature of the hot plate at 180 °C, and heat it for 30 minutes without boiling. Remove the watch glass and evaporate until the solution is about 5 ml to stop heating. After cooling, add 5 ml of nitric acid (6.3) and cover. The watch glass is heated to reflux. If brown smoke is generated, repeat this step (add 5ml of nitric acid each time) until Then brown smoke is formed and the solution is evaporated to about 5 ml. After the solution is cooled, slowly add 3 ml of hydrogen peroxide (6.6). Continue to cover the watch glass, and keep the temperature of the hot plate at 95 °C, heating until no more bubbles are generated. Wait for the solution to cool and continue. Add hydrogen peroxide (6.6), 1 ml each time, until only the fine bubbles or the general appearance does not change, remove the watch glass, Heating is continued until the solution volume evaporates to about 5 ml. After the solution is cooled, rinse the inner wall with an appropriate amount of water at least 3 times and transfer to In a 50 ml volumetric flask, add 5 ml of ammonium chloride solution (6.8) and 3 ml of hydrochloric acid solution (6.2) to dilute to the mark with water. (2) Microwave digestion Sample digestion was performed according to the relevant method of HJ 678, the digested solution was transferred to a 50 ml volumetric flask, and 5 ml of ammonium chloride was added. The solution (6.8) and 1 ml of hydrochloric acid solution (6.2) were diluted with water to the mark. Low concentration samples can also be heated and concentrated by hot plates. Transfer to a 25 ml volumetric flask, add 2.5 ml of ammonium chloride solution (6.8) and 0.5 ml of hydrochloric acid solution (6.2) to dilute with water. To the marking line. Note 1. The high concentration sample should be diluted and determined according to the method of Appendix A to determine whether there is matrix interference. 8.4 Preparation of blank samples A soluble chromium blank sample, replaced with water, was prepared according to the procedure of 8.3.1. The total chromium blank sample, replacing the sample with water, was prepared according to the procedure of 8.3.2.

9 Analysis steps

9.1 Instrument Commissioning Adjust the instrument to the best working condition according to the instrument operating instructions. Refer to Table 1 for the measurement conditions. Table 1 Reference measurement conditions Measuring wavelength, nm 357.9 Passband width, nm 0.2 Burner height, mm 10 Flame type air-acetylene flame, rich combustion type Note 2. After igniting the air-acetylene flame, the burner temperature should be brought to thermal equilibrium before measurement. Note 3. Flame type and burner height have a great influence on the sensitivity of chromium determination. Therefore, the ratio of acetylene to air should be strictly controlled and adjusted. Burner height. 49.2 Establishment of the standard curve Remove 0.00, 0.50, 1.00, 2.00, 3.00, 4.00, 5.00 ml of chromium standard solution (6.11) in 50 ml capacity Add 5 ml of ammonium chloride solution (6.8) and 3 ml of hydrochloric acid solution (6.2) to the measuring flask, and dilute to the mark with water and shake well. The standard series mass concentrations are 0, 0.50, 1.00, 2.00, 3.00, 4.00 and 5.00 mg/L, respectively. In accordance with the conditions of (9.1), The absorbance of the standard series of solutions is measured sequentially from low to high concentration. The mass concentration of chromium (mg/L) is taken as the abscissa, and the corresponding absorbance after subtracting the zero concentration is plotted on the ordinate. standard curve line. 9.3 Sample determination The absorbance of the sample was measured in the same manner as the standard curve. 9.4 Blank test The absorbance of the blank sample was measured in the same manner as in the sample measurement (9.3). 10 Calculation and representation of results 10.1 Calculation of results The mass concentration ρ of chromium in the sample is calculated according to the formula (1).   fV  101  (1) Where.  - the concentration of soluble chromium or total chromium in the sample, mg/L; 1 - mass concentration of soluble chromium or total chromium in the sample obtained from the standard curve, mg/L; 0 - mass concentration of soluble chromium or total chromium in the blank sample obtained from the standard curve, mg/L; 1V - the volume of the sample after preparation, ml; V - sampling volume, ml; f - dilution factor. 10.2 Results Representation When the measurement result is less than 1 mg/L, two digits after the decimal point are retained. When the measurement result is greater than or equal to 1 mg/L, the remaining three are retained. Effective figures. 11 Precision and accuracy 11.1 precision Six laboratories conducted a standard solution of chromium concentrations of 0.20 mg/L, 2.50 mg/L and 4.50 mg/L, respectively. Six replicate determinations of soluble chromium, the relative standard deviations in the laboratory were 1.7% to 6.2%, 0.1% to 2.0%, and 0.1% to 2.7%. The relative standard deviations between laboratories were 9.4%, 1.0%, and 0.9%; the repeatability limits r were 0.02 mg/L, 0.10 mg/L, and 0.17 mg/L; The reproducibility limits R were 0.06 mg/L, 0.11 mg/L, and 0.19 mg/L. Surface water and domestic pollution of total chromium concentrations of 0.19 mg/L, 1.53 mg/L and 2.08 mg/L in six laboratories The water and industrial wastewater were repeatedly determined by electrothermal plate digestion method. The relative standard deviations in the laboratory were 2.4%~6.6%, 0.8%~2.7%, 0.3%~6.8%; the relative standard deviation between laboratories was 3.3%, 3.2% and 9.0%; the repeatability limit r was 0.02 mg/L, 0.06 mg/L and 0.16 mg/L; reproducibility limits R were 0.03 mg/L, 0.15 mg/L and 0.55 mg/L, respectively. Surface water and domestic pollution of total chromium concentrations of 0.19 mg/L, 1.53 mg/L and 2.08 mg/L in six laboratories 5 water and industrial wastewater were repeatedly determined by microwave digestion method, and the relative standard deviations in the laboratory were 2.7%~6.3%, 0.7%~3.0%, 0.6%~5.5%, the relative standard deviation between laboratories was 4.6%, 6.2% and 7.3%; the repeatability limit r was 0.02 mg/L, 0.08 mg/L and 0.13 mg/L; reproducibility limits R were 0.03 mg/L, 0.28 mg/L and 0.43 mg/L. 11.2 Accuracy Surface water and domestic pollution of total chromium concentrations of 0.19 mg/L, 1.53 mg/L and 2.08 mg/L in six laboratories Water and industrial wastewater were measured by electrothermal plate digestion method for 6 times, and the spiked concentrations were 0.20 mg/L and 1.50 mg/L, respectively. 2.00 mg/L, the standard recovery rate was 95.1% ~ 107%, 89.2% ~ 103%, 99.0% ~ 104%; The final values were 97.6% ± 11.2%, 98.4% ± 10.6%, and 101% ± 3.8%, respectively. Surface water and domestic pollution of total chromium concentrations of 0.19 mg/L, 1.53 mg/L and 2.08 mg/L in six laboratories Water and industrial wastewater were determined by microwave digestion method for 6 times, and the spiked concentrations were 0.20 mg/L, 1.50 mg/L and 2.00, respectively. The recoveries of mg/L and spiked were 91.2%-107%, 90.7%-106%, 97.0%-107%, respectively. 96.0% ± 11.6%, 97.6% ± 11.2%, 101% ± 7.0%. 12 Quality Assurance and Quality Control 12.1 At least one laboratory blank should be made for each batch of samples, and the results should be lower than the method detection limit. 12.2 A calibration curve should be drawn for each sample analyzed, and the correlation coefficient should be greater than or equal to 0.999. 12.3 An instrument zero calibration should be performed for every 10 samples analyzed. 12.4 For every 10 samples, a standard solution of the intermediate point concentration of a calibration curve shall be analyzed, and the measurement result and the calibration curve are qualitative. The relative deviation of the concentration should be less than 10%. Otherwise, the calibration curve needs to be redrawn. 12.5 Each batch of samples shall be tested with at least 10% of parallel samples. When the number of samples is less than 10, at least one parallel sample shall be determined. The relative deviation of the measurement results is less than 20%. 12.6 At least 10% of the matrix spiked samples shall be determined for each batch of samples. When the number of samples is less than 10, at least one standard sample shall be determined. The recovery rate of the product should be between 85% and 115%. 13 Waste treatment The waste liquid produced in this experiment shall be kept in a safe place and shall not be discarded at will, and collected and sent to a qualified unit for disposal. 14 Precautions Glassware, polyethylene containers, etc. used in the experiment shall not be washed with potassium dichromate washing solution, and must be washed first with detergent. Soak it in a nitric acid solution (6.5) for more than 24 hours, and then wash it with tap water and experimental water before use.

6 Appendix A

(normative appendix) Matrix interference check method This method is suitable for samples with a certain concentration. Take two identical water samples, one of which is diluted 5 times (1 4), diluted The measured value of the sample (not less than 10 times the detection limit) multiplied by the dilution factor and the undiluted sample measured value, phase The deviation is considered to be interference-free within ±10%. Otherwise, indicating that there is chemical or physical interference, you can take dilution or standard The quasi-addition method is eliminated. When the sample concentration is lower than the above requirements, the slope of the standard addition method curve can be compared with the slope of the standard curve. The difference is considered to be interference-free within ±5%. Otherwise, it indicates that there is matrix interference.

7 Appendix B

(normative appendix) Standard addition method B.1 Drawing of the calibration curve Four equal amounts of the sample to be tested were separately weighed to prepare four solutions of the same total volume. The first part does not add a standard solution, The second, third, and fourth portions are respectively added with different concentrations of the standard solution, and the concentrations of the four solutions are. CX, CX C0, CX 2C0, CX 3C0; The concentration of the standard solution C0 added should be approximately equal to 0.5 times the concentration of the sample, ie C0 ≈ 0.5 CX. use The blank solution was zeroed and the absorbance of the four solutions was measured sequentially under the same measurement conditions. Add absorbance as the ordinate The concentration of the standard solution is plotted on the abscissa, and a calibration curve is drawn. The intersection of the curve's reverse extension and the concentration axis is the sample to be tested. concentration. The relationship between the concentration of the sample to be tested and the corresponding absorbance is shown in Figure B.1. Figure B.1 Relationship between sample concentration and corresponding absorbance B.2 Precautions B.2.1 This method is only applicable to the area where the concentration of the sample to be tested is linear with the absorbance. B.2.2 The volume error caused by the addition of the standard solution should not exceed 0.5%. B.2.3 This method can only eliminate the effects of matrix effects and cannot eliminate the effects of background absorption. B.2.4 The interference effect shall not change with the change of the ratio of the concentration of the element to be tested to the matrix. Standards and elements to be tested The same analytical response should be available under the selected measurement conditions. Concentration (mg/L) 3C02C0C0Cx 0

8 Appendix C

(informative appendix) Judging the applicability of the standard addition method The absorbance of the sample to be tested was determined to be A, and the concentration was found to be x from the calibration curve. Add the standard to the sample to be tested The concentration of the solution was s, the absorbance was determined to be B, and the concentration was found to be y from the calibration curve. According to formula (C.1) Calculate the content of the sample to be tested c. Xy Sc  )( (C.1) When there is no matrix effect, s/(yx) should be 1, ie c=x, at which point the calibration method can be calibrated using standard solutions. When there is For the matrix effect, s/(yx) is between 0.5 and 1.5, and the standard addition method can be used. When s/(yx) is outside this range, the standard addition method is used. Not applicable, the substrate must be separated before measurement.

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