HJ 957-2018Water quality - Determination of cobalt - Flame atomic absorption spectrometry (English PDF)

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 flame 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 - Flame atomic absorption spectrophotometric method

Warning. Nitric acid and perchloric acid are highly corrosive and 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 flame atomic absorption spectrophotometric method 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.

The detection limit of soluble cobalt in this standard is 0.05 mg/L, the lower limit of determination is 0.20 mg/L; the method of total cobalt is detected.

The limit is 0.06 mg/L and the lower limit of determination is 0.24 mg/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.

Soluble cobalt soluble cobalt Refers to the cobalt measured after filtration of a non-acidified sample through a 0.45 µm filter.

Total cobalt of total quantity of cobalt Refers to the cobalt measured after acid digestion of the unfiltered sample.

4 Principle of the method

After filtering or digesting, the sample is sprayed into a lean-burning air-acetylene flame, and the cobalt-based atom formed in the high-temperature flame is cobalt.

The 240.7 nm characteristic line emitted by a hollow cathode lamp or continuous source produces selective absorption. Absorbance within a certain range it 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 Hydrochloric acid, phosphoric acid and perchloric acid with a concentration greater than or equal to 5% produce positive interference with the determination of cobalt; concentrations greater than or equal to 5% Sulfuric acid produces a negative interference. The concentration of perchloric acid in the sample after digestion is controlled below 2% without affecting the determination of cobalt.

5.3 Determination of cobalt when Ca concentration is greater than.200 mg/L, Ni concentration is greater than 40 mg/L, and Si concentration is greater than 100 mg/L Negative interference is generated. See Appendix A for inspection of matrix interference; matrix interference can be offset by standard addition method, see Appendix B; Standard the applicability judgment of the joining method is given in Appendix C.

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. rho (HNO3) = 1.42 g/ml, excellent grade pure.

6.2 Perchloric acid. rho (HClO4) = 1.67 g/ml, 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 Lanthanum nitrate [La(NO3)3] or cerium nitrate [Sr(NO3)2].

6.7 Cobalt standard stock solution. rho (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 use solution. rho (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 Matrix modifier. cerium nitrate solution, rho (La) = 20 g/L; or cerium nitrate solution, rho (Sr) = 20 g/L.

Weigh 4.7 g of cerium nitrate (6.6) or 4.9 g of cerium nitrate (6.6), dissolve it in a beaker with a small amount of water and transfer to 100 ml.

In a volumetric flask, dilute to volume with water and mix.

6.10 Gas. Acetylene, purity >= 99.6%.

6.11 Gas-assisted gas. Air, water, oil and other impurities should be removed before entering the burner.

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 Flame atomic absorption spectrophotometer.

7.2 Light source. Cobalt hollow cathode lamp or continuous light source with 240.7 nm.

7.3 Controllable temperature electric heating plate. The temperature control range is from room temperature to 300 °C, and the temperature control accuracy is ±5 °C.

7.4 Vial. 500 ml, polyethylene or equivalent.

7.5 Common instruments and equipment used in general laboratories.

38 Samples

8.1 Sample collection Sample collection was performed in accordance with the relevant regulations of HJ/T 91 and HJ/T 164. Determination of soluble cobalt and total cobalt should be divided into samples 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 (7.4).

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 soluble cobalt sample (8.2.1) into the 50 ml colorimetric tube to the mark and add 0.60 ml of matrix modifier (6.9).

Mix and test.

8.3.2 Total cobalt sample Measure 50.0 ml of total cobalt sample (8.2.2) in a 250 ml glass beaker and add 2.5 ml of nitric acid (6.1).

Heat and digest on a warm electric heating plate (7.3) to ensure that the solution does not boil, to about 5 ml. Add 2.5 ml of nitric acid (6.1) Continue digestion with 1 ml of perchloric acid (6.2) to approximately 1 ml. Repeat the process of adding nitric acid and perchloric acid if necessary, straight to dissolve completely. After cooling, add 10 ml of nitric acid solution (6.4) and transfer to a 50 ml colorimetric tube (if there is insoluble residue, First, filter with a quantitative filter paper (6.13), dilute to the mark with a nitric acid solution (6.4), and then add 0.60 ml of matrix modifier.

(6.9), mix and test.

Note 1. The preparation of the total cobalt sample can also be carried out by microwave digestion method according to HJ 678.

Note 2. Other digestion systems such as HNO3-H2O2 can also be used for the preparation of total cobalt samples.

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.

9 Analysis steps

9.1 Instrument measurement conditions Adjust the instrument to the best working condition according to the instrument operating instructions. Refer to Table 1 for reference measurement conditions.

4 Table 1 Reference measurement conditions Wavelength/nm source flame type spectrum passband/nm lamp current/mA 240.7 Cobalt hollow cathode lamp or even Continuous light source Air-acetylene (lean burn) Acetylene flow 1.5 L/min, empty Air flow 15 L/min, the combustion ratio is 10.1.

0.2 12.5

9.2 Establishment of the standard curve Transfer 0 ml, 0.20 ml, 1.00 ml, 2.00 ml, 3.00 ml, 4.00 ml, 5.00 ml of cobalt standard solution (6.8) in a 50 ml colorimetric tube, dilute to the mark with a nitric acid solution (6.4). The concentration of this standard series is 0 mg/L, 0.20 mg/L, 1.00 mg/L, 2.00 mg/L, 3.00 mg/L, 4.00 mg/L, 5.00 mg/L. Then add 0.60 ml of matrix modifier (6.9), Mix well. 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 (mg/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).

10 Calculation and representation of results

10.1 Calculation of results the mass concentration of cobalt in the sample (mg/L) is calculated according to formula (1).

V xx-= 101 )( (1)

Where. rho--the mass concentration of soluble cobalt or total cobalt in the sample, mg/L;

1-1-- the mass concentration of soluble cobalt or total cobalt in the sample obtained from the standard curve, mg/L;

rho0--the mass concentration of soluble cobalt or total cobalt in the blank sample obtained from the standard curve, mg/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 1 mg/L, the two decimal places are retained; when the measurement result is greater than or equal to 1 mg/L, the retention is retained.

Three significant figures.

511 precision and accuracy

11.1 Precision

Six laboratories for uniform samples containing soluble cobalt concentrations of 0.30 mg/L, 2.50 mg/L, and 4.50 mg/L Six replicate measurements were performed. the relative standard deviations in the laboratory ranged from 0.4% to 2.9%, 0.5% to 4.1%, and 0.3%, respectively.

1.6%; the relative standard deviations between laboratories were 2.6%, 1.1%, and 2.4%, respectively; the repeatability limits were 0.02 mg/L, respectively.

0.13 mg/L and 0.15 mg/L; reproducibility limits were 0.03 mg/L, 0.14 mg/L and 0.33 mg/L, respectively.

Six laboratories conducted uniform samples with total cobalt concentrations of 1.03 mg/L, 2.08 mg/L, and 3.15 mg/L.

6 repeated measurements. the relative standard deviations in the laboratory ranged from 0% to 2.3%, 0.4% to 1.2%, and 0.3% to 1.6%, respectively;

The relative standard deviations between laboratories were 1.2%, 2.9%, and 2.7%, respectively; the repeatability limits were 0.04 mg/L and 0.05 mg/L, respectively.

And 0.07 mg/L; the reproducibility limits were 0.05 mg/L, 0.17 mg/L and 0.24 mg/L, respectively.

11.2 Accuracy

Six laboratories performed 6 weights on certified reference material (203604) with a mass concentration of (1.15±0.08) mg/L.

Complex determination. the relative error range is -0.9% to 4.4%; the relative error is 0.8% ± 4.0%.

Six laboratories conducted uniform samples with total cobalt concentrations of 1.03 mg/L, 2.08 mg/L, and 3.15 mg/L.

Six times of repeated spike analysis, the spiked concentrations were 1.00 mg/L, 1.00 mg/L and 1.50 mg/L. spiked recovery rate the circumference is 95.6%~110%, 93.0%~108% and 95.3%~103% respectively; the final value of the spiked recovery rate is 103%± 12.0%, 101% ± 10.6% and 99.8% ± 5.8%.

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 standard curve should be established for each sample analysis, and the correlation coefficient should be >=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 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 85% and 115%. 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.

614 Waste treatment

The waste liquid generated in the experiment should be collected and classified, and the corresponding units should be properly identified and entrusted to qualified units for centralized treatment.

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 formula (C.1) Test sample content c.

c x-= )( (C.1)

When there is no matrix effect, S/(yx) should be 1, ie c=x, at which point the standard solution calibration curve method can be used. 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.