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HJ 958-2018 English PDF

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HJ 958-2018: Water quality - Determination of cobalt - Graphite furnace atomic absorption spectrometry
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Basic data

Standard ID: HJ 958-2018 (HJ958-2018)
Description (Translated English): Water quality - Determination of cobalt - Graphite furnace atomic absorption spectrometry
Sector / Industry: Environmental Protection Industry Standard
Classification of Chinese Standard: Z16
Word Count Estimation: 13,191
Date of Issue: 2018-07-29
Date of Implementation: 2019-01-01
Regulation (derived from): Ministry of Ecology and Environment Announcement No. 23 of 2018
Issuing agency(ies): Ministry of Ecology and Environment

HJ 958-2018: Water quality - Determination of cobalt - Graphite furnace atomic absorption spectrometry


---This is a DRAFT version for illustration, not a final translation. Full copy of true-PDF in English version (including equations, symbols, images, flow-chart, tables, and figures etc.) will be manually/carefully translated upon your order.
Water quality - Determination of cobalt - Graphite furnace atomic absorption spectrometry National Environmental Protection Standard of the People's Republic Determination of water quality cobalt Graphite furnace atomic absorption spectrophotometry Water quality-Determination of cobalt -Graphite furnace atomic absorption spectrometry Published on.2018-07-29 2019-01-01 Implementation Ministry of Ecology and Environment released i directory 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..2 7 instruments and equipment..2 8 samples..3 9 Analysis step 4 10 Calculation and representation of results. 5 11 Precision and Accuracy.5 12 Quality Assurance and Quality Control..6 13 Notes.6 14 Waste treatment.6 Appendix A (Normative Appendix) Matrix interference inspection method..7 Appendix B (Normative Appendix) Standard Addition Method..8 Appendix C (informative) Applicability judgment of the standard addition method..9

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, This standard is formulated to ensure human health and to regulate the determination of cobalt in water. This standard specifies the graphite furnace atomic absorption spectrophotometry for the determination of cobalt in surface water, groundwater and wastewater. Appendix A and Appendix B of this standard are normative appendices, and Appendix C is an informative appendix. This standard is the first release. This standard is formulated by the Environmental Monitoring Department of the Ministry of Ecology and Environment and the Science and Technology Standards Department. This standard was drafted. Anshan City Environmental Monitoring Center Station. This standard is verified by. Shenyang Environmental Monitoring Center Station, Dalian Environmental Monitoring Center, Harbin Environmental Monitoring Xinzhan, Liaoning Provincial Environmental Monitoring Experimental Center, Fushun Environmental Monitoring Center Station and Liaoyang Environmental Monitoring Station. This standard is approved by the Ministry of Ecology and Environment on July 29,.2018. This standard has been implemented since January 1,.2019. This standard is explained by the Ministry of Ecology and Environment. 1 Determination of cobalt in water - Graphite furnace atomic absorption spectrophotometric method Warning. Nitric acid and hydrogen peroxide are highly corrosive and strongly oxidizing. The sample preparation process should be carried out in a fume hood. Wear protective equipment as required to avoid contact with skin and clothing.

1 Scope of application

This standard specifies the graphite furnace atomic absorption spectrophotometry for the determination of cobalt in water. This standard applies to the determination of soluble cobalt and total cobalt in surface water, groundwater and wastewater. When the injection volume is 20 μl, the detection limit of soluble cobalt and total cobalt in this standard is 2 μg/L. The limit is 8 μg/L.

2 Normative references

This standard refers to the following documents or their terms. For undated references, the valid version applies to 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 cobalt soluble cobalt Refers to the cobalt measured after filtration of a non-acidified sample through a 0.45 μm filter. 3.2 Total cobalt of total quantity of cobalt Refers to the cobalt measured after acid digestion of the unfiltered sample.

4 Principle of the method

The sample is filtered or digested and injected into a graphite furnace atomizer to form a cobalt-based atom formed by drying, ashing and atomization. Vapor, selective absorption of the 240.7 nm characteristic line emitted by a cobalt hollow cathode lamp or continuous source. In a certain range The absorbance is proportional to the mass concentration of cobalt.

5 interference and elimination

5.1 Cobalt has spectral interference near the sensitive line of 240.7 nm. Selecting a narrow spectral passband for measurement can reduce interference. 25.2 Determination of cobalt by phosphoric acid and perchloric acid, 3% nitric acid and hydrogen peroxide, 0.4% sulfuric acid at a concentration of 1% or more Negative interference; hydrochloric acid with a concentration of 3% or more produces positive interference. The concentration of hydrogen peroxide in the sample after digestion is controlled below 3% Does not affect the determination of cobalt. 5.3 Ca below 500 mg/L; Mg, K, Na below.200 mg/L; Ni, Mn, Al below 4.00 mg/L Cu, Pb, Zn, Cr; Fe below 10.0 mg/L; Cl-, F-, SO42- below 100 mg/L do not interfere with the determination of cobalt. 5.4 When the sample matrix is complex and there is matrix interference, the matrix interference is checked in Appendix A; the standard addition method can be used to offset See Appendix B for the elimination of matrix interference; Appendix C for the applicability of the standard addition method.

6 reagents and materials

Unless otherwise stated, analytically pure reagents in accordance with national standards were used for the analysis, and experimental water was newly prepared deionized. Water or water of the same purity. 6.1 Nitric acid. ρ (HNO3) = 1.42 g/ml, excellent grade pure. 6.2 Hydrogen peroxide. w (H2O2) = 30%, excellent grade pure. 6.3 Nitric acid solution. 1 1. 6.4 Nitric acid solution. 1 99. 6.5 Cobalt. w≥99.99%, pure spectrum. 6.6 Magnesium nitrate [Mg(NO3)2]. 6.7 Cobalt standard stock solution. ρ (Co) = 1000 mg/L. Accurately weigh 1 g (accurate to 0.0001 g) of cobalt (6.5), dissolve in 10 ml of nitric acid solution (6.3), heat and drive off Nitrogen oxides, after cooling, transfer to a 1000 ml volumetric flask, dilute to volume with water and mix. Transfer to polyethylene bottle Medium sealed, refrigerated below 4 ° C, can be stored for 1 year. Commercially available certified standard solutions can also be used. 6.8 Cobalt standard intermediate solution. ρ (Co) = 50.0 mg/L. Accurately remove 5.00 ml of cobalt standard stock solution (6.7) in a 100 ml volumetric flask and dilute with nitric acid solution (6.4) Allow to the marking line and mix. It is sealed in a polyethylene bottle and refrigerated at 4 ° C for 30 days. 6.9 Cobalt standard use solution. ρ (Co) = 1.00 mg/L. Accurately transfer 2.00 ml of cobalt standard intermediate solution (6.8) to a 100 ml volumetric flask and dilute with nitric acid solution (6.4). Allow to the marking line and mix. Available now. 6.10 Matrix modifier. Magnesium nitrate solution. ρ [Mg (NO3) 2] = 50 g/L. Weigh 5.0 g of magnesium nitrate (6.6), dissolve it in a beaker with a small amount of water, transfer to a 100 ml volumetric flask, and dilute with water. Make up to the mark and mix. 6.11 Argon. purity ≥ 99.98%. 6.12 Membrane. Acetate or polyethylene filter with a pore size of 0.45 μm. 6.13 Quantitative filter paper.

7 Instruments and equipment

7.1 Graphite furnace atomic absorption spectrophotometer (with background correction function). 7.2 Light source. Cobalt hollow cathode lamp or continuous light source with 240.7 nm. 37.3 Pyrolytically coated graphite tubes. 7.4 Controllable temperature electric heating plate. The temperature control range is from room temperature to 300 °C, and the temperature control accuracy is ±5 °C. 7.5 Vial. 500 ml, polyethylene or equivalent. 7.6 Common instruments and equipment used in general laboratories.

8 samples

8.1 Sample collection Samples were collected according to the relevant regulations of HJ/T 91 and HJ/T 164, and samples for soluble cobalt and total cobalt should be determined. Do not collect. 8.2 Preservation of samples 8.2.1 Soluble cobalt After the sample is collected, filter it with a filter (6.12) as soon as possible, discard the initial filtrate, and collect the required volume of the filtrate in the vial (7.5). in. Add appropriate amount of nitric acid (6.1), acidify to pH ≤ 2, and measure within 14 days. 8.2.2 Total cobalt Immediately after sample collection, an appropriate amount of nitric acid (6.1) was added, acidified to pH ≤ 2, and measured within 14 days. 8.3 Preparation of samples 8.3.1 Soluble cobalt sample Take a sample of soluble cobalt (8.2.1) into the 25 ml colorimetric tube to the mark and add 0.25 ml of matrix modifier (6.10). Mix and test. 8.3.2 Total cobalt sample Measure 25.0 ml of total cobalt sample (8.2.2) in a 150 ml glass beaker, add 1 ml to 2 ml of nitric acid (6.1) and 1 ml Hydrogen peroxide (6.2) is heated and digested on a temperature-controlled electric heating plate (7.4) to ensure that the solution does not boil to about 5 ml. Add 1 ml to 2 ml of nitric acid (6.1) and continue to digest to about 1 ml. Repeated addition of nitric acid and peroxidation if necessary Hydrogen is operated until the digestion is complete. After cooling, add 5 ml of nitric acid solution (6.4) and transfer to a 25 ml colorimetric tube (eg Insoluble residue, first filtered with quantitative filter paper (6.13), and made up to the mark with nitric acid solution (6.4). Then add 0.25 ml Matrix modifier (6.10), mix and test. Note. The preparation of the total cobalt sample can also be performed by microwave digestion method according to HJ 678. 8.4 Preparation of blank samples Replace the sample with the test water, and perform the same steps as the preparation of the sample (8.3) for the soluble cobalt and total cobalt. Preparation of laboratory blank samples. 49 Analysis steps 9.1 Instrument measurement conditions Adjust the instrument to the best working condition according to the instrument operating instructions. Refer to the measurement conditions in Table 1, the graphite furnace heating program See Table 2. Table 1 Reference measurement conditions Wavelength/nm source spectral passband/nm lamp current/mA injection volume/μl 240.7 cobalt hollow cathode lamp or continuous light source 0.2 12.5 20.0 Table 2 Recommended heating procedure for graphite furnace Heating stage temperature/°C time/s Dry 80~120 30 Ashing 1300 30 Atomization (argon gas (6.11)) 2600 6 Clear 2800 4 Note. If measured using a horizontal Zeeman background subtraction instrument, the ashing, atomization, and purge temperatures can be reduced by 100 ° C to.200 ° C. 9.2 Establishment of the standard curve Transfer 0 ml, 0.25 ml, 0.50 ml, 1.00 ml, 2.00 ml, 2.50 ml, 3.00 ml of cobalt standard solution (6.9) In a 25 ml colorimetric tube, dilute to the mark with a nitric acid solution (6.4). The concentration of this standard series is 0 μg/L, 10 μg/L, 20 μg/L, 40 μg/L, 80 μg/L, 100 μg/L, 120 μg/L. Then add 0.25 ml matrix modifier (6.10), mixed uniform. The absorbance was measured in order from the low concentration to the high concentration according to the instrument measurement conditions (9.1). Mass concentration of cobalt (μg/L) For the abscissa, the standard curve is established with its corresponding absorbance as the ordinate. 9.3 Sample determination The measurement of the sample (8.3) was carried out in accordance with the same instrument measurement conditions as the establishment of the standard curve (9.2). If measured If the result is outside the range of the standard curve, the sample should be diluted with a standard series of zero concentration point solution and re-measured. 9.4 Blank test The laboratory blank sample (8.4) was measured in accordance with the same instrument measurement conditions as the sample measurement (9.3). 510 Calculation and representation of results 10.1 Calculation of results The mass concentration (μg/L) of cobalt in the sample is calculated according to formula (1). V  101 )(  (1) Where. ρ--the mass concentration of soluble cobalt or total cobalt in the sample, μg/L; 1-1-- the mass concentration of soluble cobalt or total cobalt in the sample obtained from the standard curve, μg/L; Ρ0--the mass concentration of soluble cobalt or total cobalt in the blank sample obtained from the standard curve, μg/L; V1--sample volumetric volume, ml; V--sampling volume, ml; D--sample dilution factor. 10.2 Results are expressed When the measurement result is less than 100 μg/L, it is retained to the integer position; when the measurement result is greater than or equal to 100 μg/L, it is retained. Three significant figures. 11 Precision and accuracy 11.1 Precision Six laboratories conducted a uniform sample with soluble cobalt concentrations of 20 μg/L, 60 μg/L and 100 μg/L. Repeated measures. the relative standard deviations in the laboratory ranged from 0.6% to 7.1%, 0.5% to 6.6%, and 0.8% to 4.2%, respectively; The relative standard deviations between laboratories were 7.1%, 4.3%, and 2.7%, respectively; the repeatability limits were 2 μg/L, 5 μg/L, and 7 μg/L, respectively; The reproducibility limits were 4 μg/L, 9 μg/L and 10 μg/L, respectively. Six laboratories performed six weights on a uniform sample containing total cobalt concentrations of 21 μg/L, 42 μg/L, and 63 μg/L. Complex determination. the relative standard deviations in the laboratory ranged from 1.2% to 3.7%, 0.8% to 2.9%, and 0.8% to 2.2%, respectively; The relative standard deviations between the chambers were 2.9%, 2.1%, and 2.3%, respectively; the repeatability limits were 2 μg/L, 3 μg/L, and 2 μg/L, respectively; Reproducibility limits were 2 μg/L, 3 μg/L and 4 μg/L, respectively. 11.2 Accuracy Six laboratories have certified reference materials with mass concentrations of (1.15±0.08) mg/L and (0.141±0.013) mg/L (203604 and 203605) 6 repeated measurements were performed. the relative error ranges were -2.6% to 6.1% and -3.5% to 3.6%, respectively; The relative error final values were 0.9% ± 6.1% and -0.7% ± 5.7%, respectively. Six laboratories performed six weights on a uniform sample containing total cobalt concentrations of 21 μg/L, 42 μg/L, and 63 μg/L. The standard addition analysis showed that the spiked concentrations were 20 μg/L, 30 μg/L and 40 μg/L. the recovery range of the spiked standard was 91.0%~ 108%, 97.3%~107% and 91.8%~103%; the final recoveries were 99.7%±12.0%, 102%± 6.6% and 98.3% ± 9.6%. 612 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 standard curve should be established for each sample analyzed and the correlation coefficient should be ≥0.995. 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 standard curve shall be analyzed, and the measurement result and the standard curve shall be The relative error of the point mass concentration should be within ±10%. Otherwise, the standard curve must be re-established. 12.5 Each batch of samples shall be tested for at least 10% of parallel samples. When the number of samples is less than 10, at least 1 parallel shall be determined. Double sample, the relative deviation of the measurement results should be ≤ 20%. 12.6 At least 5% of the matrix spiked samples shall be determined for each batch of samples. When the number of samples is less than 20, at least one plus shall be determined. For the standard sample, the spiked recovery rate should be controlled between 80% and 120%. Or use a certified reference material to control the accuracy of the measurement. 13 Precautions After the utensils used in the experiment are washed with detergent, they should be soaked in nitric acid solution (6.3) for more than 24 hours, and then used in sequence. Rinse the water and the test water. 14 Waste treatment The waste liquid generated in the experiment should be collected and classified, and the corresponding units should be entrusted to be processed in a centralized manner.

7 Appendix A

(normative appendix) Matrix interference check method This method is suitable for samples with a certain concentration. Take two copies of the same sample, one of which is diluted 5 times (1 4), after dilution The measured value of the sample (not less than 10 times the detection limit) multiplied by the dilution factor compared with the measured value of the undiluted sample, relative The deviation is considered to be interference-free within ±10%. Otherwise, it indicates that there is interference, which can be eliminated by dilution or standard addition. When the concentration of the sample after dilution is less than 10 times the detection limit, the slope of the standard addition method curve can be compared with the slope of the standard curve. In comparison, the relative deviation is considered to be interference-free within ±3%. Otherwise, it indicates that there is matrix interference.

8 Appendix B

(normative appendix) Standard addition method B.1 Establishment of calibration curve Four equal amounts of the same 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 standard solutions of different mass concentrations, and the mass concentrations of the four solutions are respectively Cx, Cx C0, Cx 2C0, Cx 3C0; the mass concentration of the standard solution C0 added should be approximately equal to 0.5 times the mass concentration of the sample. C0≈0.5Cx. The zero solution was adjusted to zero, and the absorbance of the four solutions was measured in sequence under the same measurement conditions. Add to the standard The mass concentration of the liquid is the abscissa, and the corresponding absorbance is plotted on the ordinate to establish a calibration curve. The intersection of the axes is the mass concentration of the sample to be tested. This method is only applicable to areas where the mass concentration and absorbance are linear. Tested The relationship between the sample mass concentration and the standard addition method standard curve is shown in Figure B.1. Figure B.1 Relationship between the concentration of the sample to be tested and the standard curve of the standard addition method B.2 Precautions B.2.1 The volume error caused by the addition of the standard solution should not exceed 0.5%. B.2.2 The standard addition method can only offset the effects of the matrix effect and cannot eliminate the influence of background absorption. B.2.3 This method is only applicable to areas where the sample concentration is linear with the absorbance.

9 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 standard curve. Add standard solution to the sample to be tested The concentration of the liquid was S, the absorbance was measured as B, and the concentration was found to be y from the standard curve. Calculated by formu......
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