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HJ 904-2017 English PDF

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HJ 904-2017: Ambient air. Determination of polychlorinated biphenyl mixtures. Gas chromatography
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Standard ID	Contents [version]	USD	STEP2	[PDF] delivered in	Standard Title (Description)	Status	PDF
HJ 904-2017	English	419	Add to Cart	4 days [Need to translate]	Ambient air. Determination of polychlorinated biphenyl mixtures. Gas chromatography	Valid	HJ 904-2017

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Basic data

Standard ID	HJ 904-2017 (HJ904-2017)
Description (Translated English)	Ambient air. Determination of polychlorinated biphenyl mixtures. Gas chromatography
Sector / Industry	Environmental Protection Industry Standard
Classification of Chinese Standard	Z15
Classification of International Standard	13.040.20
Word Count Estimation	18,146
Date of Issue	2017-12-14
Date of Implementation	2018-03-01
Quoted Standard	HJ 194; HJ 691
Regulation (derived from)	Ministry of Environmental Protection Bulletin 2017 No. 71
Issuing agency(ies)	Ministry of Ecology and Environment
Summary	This standard specifies gas chromatography for the determination of industrial mixtures of polychlorinated biphenyls in ambient air. This standard is applicable to the determination of seven kinds of polychlorinated biphenyl industrial products such as PCB 1221, PCB 1232, PCB 1242, PCB 1248, PCB 1254, PCB 1016 and PCB 1260 in the ambient air phase and particulate matter. See Appendix B for details. When the sampling volume is 350 m^(3) (standard state) and the volume of concentrated constant volume is 1.0 ml, the detection limit of the seven PCBs determined by this method is 0.02 to 0.09 ng/m^(3). The lower limit is 0.08 to 0.36 ng/m^(3). See Appendix A for details.

HJ 904-2017: Ambient air. Determination of polychlorinated biphenyl mixtures. Gas chromatography

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(Ambient air - Determination of PCB mixtures - Gas chromatography) People's Republic of China national environmental protection standards Ambient air - Determination of PCB mixtures Gas chromatography Ambient air-Determination of polychlorinated biphenyl mixtures -Gas chromatography 2017-12-14 Published 2018-03-01 implementation Ministry of Environmental Protection released Directory Preface ... i 1 Scope ... 1 2 Normative references ... 1 3 method principle ... 1 4 Interference and elimination ... 1 5 Reagents and materials ... 1 6 Instruments and Equipment ... 3 7 samples ... 4 8 Analysis step ... 6 9 Calculation and Expression of Results ... 6 10 Precision and accuracy ... 7 11 Quality Assurance and Quality Control ...8 12 Waste treatment ... 8 Appendix A (Normative) Detection limit and lower limit of the method ... 10 Appendix B (Informative) Compound List ... 11 Appendix C (informative) Characteristic peaks and standard spectra of PCB industrial products ... 12 Appendix D (informative) method of precision and accuracy ... 16 i Foreword In order to implement the Law of the People's Republic of China on Environmental Protection and the Law of the People's Republic of China on Prevention and Control of Atmospheric Pollution, Habitat to protect human health, standardize the ambient air Determination of PCB mixtures, the development of this standard. This standard specifies the determination of ambient air polychlorinated biphenyl industrial mixtures by gas chromatography. Appendix A of this standard is a normative appendix, Appendix B ~ Appendix D is an informative annex. This standard is released for the first time. This standard by the Environmental Protection Department of Environmental Monitoring Division and Science and Technology Standards Division to develop. This standard was drafted. Shenyang Environmental Monitoring Center Station. This standard verification unit. Jiangsu Province Environmental Monitoring Center, Henan Province Environmental Monitoring Center, Liaoning Province, environmental monitoring experiments Heart, Dalian Environmental Monitoring Center, Anshan Environmental Monitoring Center Station and Shenyang Environmental Protection Bureau Tiexi Branch Environmental Monitoring Station. This standard MEP approved on December 14,.2017. This standard since March 1,.2018 into effect. This standard is interpreted by the MEP. 1 Ambient air - Determination of polychlorinated biphenyls - Gas chromatography Warning. The solvents and reagents used in this method are toxic and experimental procedures should be performed in a fume cupboard Always wear protective equipment to avoid contact with skin and clothing.

1 scope of application

This standard specifies the determination of ambient air polychlorinated biphenyl industrial mixtures by gas chromatography. This standard applies to ambient air and particulate matter in the PCB 1221, PCB 1232, PCB 1242, PCB 1248, PCB 1254, PCB 1016 and PCB 1260 a total of seven kinds of industrial PCB determination. See Appendix B for details. When the sampling volume is 350 m3 (standard state) and the volume of concentrated volume is 1.0 ml, the method determines that more than 7 The detection limit of PCBs ranged from 0.02 ng/m3 to 0.09 ng/m3, and the lower limit of determination ranged from 0.08 ng/m3 to 0.36 ng/m3. See appendix A.

2 Normative references

This standard references the following documents in the terms. For undated references, the effective version applies This standard. HJ 194 Manual Air Quality Monitoring Technical Specifications HJ 691 Environmental airborne semi-volatile organic compounds sampling techniques

3 method principle

Use large flow or medium flow sampler to collect the PCBs and polyurethanes from ambient air and particulate matter Foam (PUF), with ether - n-hexane mixed solvent extraction, the extract was concentrated, purified, gas chromatographic separation, Electronic capture detector detection, according to the peak peak and standard peak shape and retention time to compare qualitative, select 3 to 5 A characteristic peak, using internal standard method or external standard method to take the average value of quantitative.

4 Interference and elimination

Other organic matter in the sample may interfere with the determination, the choice of sulfuric acid, magnesium silicate chromatography column or a composite silica gel column Methods to remove interference, see 7.3.3.

5 Reagents and materials

Unless otherwise specified, analytical grade analytical reagents used in accordance with national standards were used. Experimental water is freshly prepared Pure water. 5.1 acetone (C3H6O). pesticide grade. 5.2 n-hexane (C6H14). pesticide residues. 5.3 ether (C4H10O). Chromatography. 5.4 Dichloromethane (CH2Cl2). pesticide grade. 25.5 Anhydrous sodium sulfate (Na2SO4). Bake in a muffle furnace at 400 ° C for 4 h before use, cool, Sealed and saved 5.6 Sodium chloride (NaCl). Bake in a muffle furnace at 400 ° C for 4 h before use, then cool and seal in a ground-glass jar Save. 5.7 sulfuric acid (H2SO4). ρ = 1.84 g/cm3, excellent grade pure. 5.8 ether - n-hexane mixed solvent. 1 9, Pro use now. 5.9 Diethyl ether - n-hexane mixed solvent. 6 94, Pro use now. 5.10 Sodium chloride solution. ρ = 50 g/L. Weigh 50.0 g of sodium chloride (5.6), dissolved in a beaker of water and set to 1000 ml, mix, Pro with the current. 5.11 Substitute stock solution. ρ = 500 μg/ml. Direct purchase of a certified commercial standard solution containing 2,4,5,6-tetrachloro-m-xylene (TCX) and decabllylene (DCBP) mixed Liquid together. Other suitable alternatives may also be used. 5.12 Substitute intermediate solution. ρ = 50.0 μg/ml. Pipette 1.00 ml of stock solution (5.11) into a 10 ml volumetric flask, dilute with n-hexane (5.2) and mix well. 5.13 Alternative solution. ρ = 1.00 μg/ml. Pipette 1.00 ml of intermediate stock solution (5.12) into a 50 ml volumetric flask and dilute to volume with n-hexane (5.2) and mix well. 5.14 Internal standard stock solution. ρ = 1000 μg/ml. Direct purchase of a certified commercial standard solution containing 1-bromo-2-nitrobenzene (BNB). 5.15 Internal standard intermediate solution. ρ = 100 μg/ml. Pipette 1.00 ml internal standard stock solution (5.14) in 10 ml volumetric flask, with n-hexane (5.2) volume, mix. 5.16 Internal standard solution. ρ = 10.0 μg/ml. Pipette 1.00 ml internal standard solution (5.15) in 10 ml volumetric flask, with n-hexane (5.2) volume, mix. 5.17 standard stock solution. ρ = 1000 μg/ml. Buy a commercially available Certified Standard Solution directly, PCB 1221, PCB 1232, PCB 1242, PCB 1248, PCB 1254 Single standard and PCB 1016 and PCB 1260 mixed standard, sealed at 4 ℃ the following preservation, or reference standard solution certificate storage conditions. 5.18 standard intermediate solution. ρ = 100 μg/ml. Pipette 1.00 ml standard stock solution (5.17) in 10 ml volumetric flask, with n-hexane (5.2) constant volume, mix well, with PCB 1221, PCB 1232, PCB 1242, PCB 1248, PCB 1254 single standard intermediate solution and PCB 1016 and PCB 1260 mixed standard solution. 5.19 standard solution. ρ = 10.0 μg/ml. Pipette 1.00 ml standard intermediate solution (5.18) and.200 μl intermediate solution (5.12) in 10 ml volumetric flask, With n-hexane (5.2) constant volume, mixing, preparation of PCB 1221, PCB 1232, PCB 1242, PCB 1248, PCB 1254 Single standard solution and PCB 1016 and PCB 1260 mixed standard solution. Note. The concentration of surrogate in standard use solution (5.19) is 1.00 μg/ml. All solutions (5.11-5.19) were transferred to polytetrafluoroethylene Ethylene liner screw glass, 4 ℃ the following refrigeration, sealed dark to save. 5.20 composite silica gel column The bottom of the column filled with glass wool (5.25), from the bottom were filled with anhydrous sodium sulfate 4 g, silica gel 0.9 g, 2% KOH 3 Silica gel 3 g, Silica gel 0.9 g, 44% Silica gel 4.5 g, 22% Silica gel 6 g, Silica gel 0.9 g, 10% silver nitrate silica gel 3 g, The top is anhydrous sodium sulfate 6 g. Can be purchased directly composite silica column commodity column. 5.21 Magnesium silicate. 150 μm to 250 μm (100 mesh to 60 mesh), activated at 130 ° C for 18 h before use and placed After cooling in the desiccator, transfer to a glass bottle and seal it for preservation. 5.22 Quartz/glass fiber filter. According to the sampling head to select the appropriate size of the filter. Cut the filter to 0.3 μm standard particles Stay efficiency of not less than 99%. Before use in the muffle furnace 400 ℃ heating 5 h above, after cooling, stored in the filter box, to ensure The filters are not contaminated before and after sampling and are in a flat state before sampling. 5.23 Polyurethane Foam (PUF). polyether type, with a density of 22 mg/cm3 ~ 25 mg/cm3, cut to grow 70 mm, straight Cylindrical diameter of 45 mm to 65 mm (length, diameter as determined by the specifications of the glass sampling cartridge). Use hot water before use Scald, and then repeatedly rub into warm water, drained, rinsed with acetone (5.1) three times and placed in a Soxhlet extractor (6.4) Followed by acetone (5.1), ether - n-hexane mixed solvent (5.8) reflux extraction 16 h, replace 2 times to 3 times fresh B Ether - n-hexane mixed solvent (5.8) reflux extraction, removed after the nitrogen (5.24) stream drying (also can be true at room temperature Empty dry 2 h ~ 3 h). Place glass sampling cartridge (6.3.2) in a suitable container and seal it. 5.24 Nitrogen. Purity ≥99.999%. 5.25 glass wool. before use dichloromethane (5.4) reflux extraction 2 h ~ 4 h, dried and sealed.

6 instruments and equipment

6.1 Gas Chromatograph. with split/splitless inlet, temperature programmed function, and electron capture detector. 6.2 Column. Quartz capillary column, 30 m (length) × 0.25 mm (ID) × 0.25 μm (film thickness), two The column has different polarities of the stationary phase. It is recommended that Column 1 has a 5% phenyl 95% dimethylpolysiloxane or other phase The column, column 2 stationary phase is 14% cyanopropylphenyl 86% dimethylpolysiloxane or other equivalent column. 6.3 Sampling device 6.3.1 Sampler. to meet the HJ 691 requirements, with automatic accumulation of sample size, the standard conversion volume automatically convert the volume of the function, And automatic timer, power off function and automatically compensate for voltage fluctuations, changes in resistance caused by changes in flow function. In loading With filters and sorbents, the sampler load flow should be 125 L/min for medium flow sampling For the point of 100 L/min; for large flow sampling, the sampler load flow should be able to reach 250 L/min, the working point Flow rate of 225 L/min; for large flow sampling, the sampler load flow should be able to reach 900 L/min, the working point flow The amount is 800 L/min. 6.3.2 Sampling head. to meet the HJ 691 requirements, by the filter holder and the sampling sleeve sleeve of two parts, as shown in Figure 1. Sampling head The material selection of PTFE or stainless steel and other non-adsorption of organic materials. Filter clip includes filter ring, filter and filter Film stent. Sampling tube Sleeve equipped with a glass sampling cylinder, the bottom of the sampling cylinder supported by a stainless steel mesh, the adsorption cartridge The material is PUF (5.23). Sampling tube sealed with a silicone rubber seal between the filter holder and the suction pump. Soxhlet extractor. 500 ml or 1000 ml. Other performance extraction devices may also be used. 6.5 Glass Column. 350 mm long, 20 mm id, glass column with Teflon piston on the bottom. 6.6 Concentration device. Rotary evaporator, nitrogen blowing concentrator and other performance-equivalent equipment. 6.7 solid phase extraction device. 6.8 separatory funnel. 60 ml. 46.9 Common Laboratory Equipment. 1-gas flow inlet; 2-filter holder; 3- sampling sleeve Barrel; 4-gas outlet; 5-filter ring; 6- Silicone rubber ring; 7-filter; 8- stainless steel mesh; 9-filter holder; 10-glass sampling cartridge. Figure 1 sampling head schematic

7 samples

7.1 Sample Collection 7.1.1 Ambient air samples According to HJ 194 and HJ 691, sampling points should be laid for the determination of meteorological parameters and sample collection. In situ sampling followed by the installation of membrane clamps, sampling tube sleeve, connected to the sampler, adjusting the sampling flow, began sampling. Mining After the sample is removed, the filter is removed and the sample dust is folded inwards. The glass sampling cylinder is removed, wrapped in aluminum foil, and placed in a box Save sealed. 7.1.2 Site blank samples Will seal the preservation of the blank glass sampling cartridge and filter to the sampling site, installed in the sampling head without sampling, after Remove the cartridge and filter, store it in the same way as the sample, and ship it back to the lab with the sample. 57.2 Sample Storage Samples were stored at room temperature protected from light and extracted within 24 h; otherwise, the samples were stored in the dark at 4 ° C and extracted within 7 days. The sample extract is refrigerated at below 4 ° C and analyzed within 40 days. 7.3 Sample Preparation 7.3.1 Sample Extraction Filter and glass sampling cartridges were transferred to a Soxhlet extractor (6.4),.200 μL of replacement fluid (5.13) was added to the PUF, Add 300 ml ~ 500 ml ether - n-hexane mixed solvent (5.8) reflux extraction 16 h or more, refluxed three times per hour ~ 4 Times. After the extraction is completed and cooled to room temperature, the bottom bottle is taken out, the extraction cup interface is washed, and the cleaning liquid is transferred to the bottom bottle together. Add nothing Sodium sulphate (5.5) to sodium sulphate granules are free-flowing and are allowed to dry for 30 min. Note. If using automatic Soxhlet extraction, with ether - n-hexane mixed solvent (5.8) reflux extraction of not less than 40 cycles. As long as you can achieve this Standards require quality control requirements, but also other sample extraction methods. 7.3.2 Sample concentration The sample extract was transferred to a concentration apparatus, concentrated at below 45 ℃, the solvent was replaced by n-hexane, concentrated to 1 ml about. If using sulfuric acid purification (7.3.3.1), concentrated to about 10 ml. 7.3.3 Sample Purification 7.3.3.1 sulfuric acid purification The sample extract concentrate (7.3.2) was transferred to a separatory funnel (6.8), add 5 ml sulfuric acid (5.7), gently Shake and deflate, shaking 1 min, after standing layered layer of sulfuric acid removed. Repeat the above procedure until the sulfuric acid layer is colorless. Add 5 ml of organic phase Sodium chloride solution (5.10), mix well, leave the aqueous layer after standing stratification, add anhydrous sodium sulfate (5.5) in the organic phase off Water, according to 7.3.2 concentrated below 1 ml, to be purified. If no further purification is required, dilute to 1.0 ml if internal standard is used The amount of law, adding 10.0 μl of internal standard solution (5.16), transferred to the vial to be analyzed. 7.3.3.2 Magnesium silicate column purification The bottom of the glass column (6.5) is filled with glass wool (5.25), wetted with 20 g of magnesium silicate (5.21) with n-hexane (5.2) Exhaust air bubbles, add 1 cm ~ 2 cm anhydrous sodium sulfate (5.5) on the top. Pre-rinse with 60 ml of n-hexane (5.2) and keep Liquid level slightly higher than the bed, the extract concentrated (7.3.2) or concentrated sulfuric acid (7.3.3.1) was transferred to the column, The sample vial was washed twice with 1 ml of n-hexane and transferred to the column. The eluate was discarded. The column was eluted with.200 ml of ether-n-hexane mixed solvent (5.9) at an elution rate of 2 ml/min to 5 ml/min Receive eluate. Eluate according to 7.3.2 concentrated to 1.0 ml or less, constant volume to 1.0 ml, if using internal standard method, adding 10.0 μl internal standard solution (5.16), transfer to the vial for analysis. 7.3.3.3 Compound silica gel column purification Take compound silica gel column (5.20), pre-rinse with 100 ml of n-hexane (5.2), keep the liquid level slightly higher than the bed, The extract concentrate (7.3.2) was transferred to the column and the vial was washed twice with 1 ml of n-hexane (5.2) and transferred to the column together. Discard the effluent. Add.200 ml of n-hexane (5.2) for elution, control the flow rate of 2.5 ml/min or so and collect the eluent. Eluent according to 7.3.2 Concentrate to 1.0 ml or less and dilute to 1.0 ml. If using internal standard method, add 10.0 μl internal standard solution (5.16) 6 Transfer to vial for analysis. Note. by the column size, the amount of adsorbent and other effects, the amount of eluent may be different, the laboratory before the need to carry out the conditions of the real Inspection; as long as the quality control requirements of this standard can be achieved, you can also use other sample purification methods. 7.4 Preparation of blank samples 7.4.1 Site blank On-site blank samples (7.1.2) In-situ blank samples were prepared according to the same procedure as Preparation of samples (7.3). 7.4.2 Laboratory blank The same batch of sampling cartridges and filters in accordance with the sample preparation of the same procedure (7.3) Preparation of laboratory blank samples.

8 Analysis steps

8.1 Instrument reference conditions Use (6.2) in the two different polarity of the column, one for the analytical column, one for the verification column. Inlet. 250 ° C; splitless injection, shunt at 0.75 min, split ratio 60.1; injection volume. 2.0 μl; column temperature. 50 ℃ for 1 min, with 25 ℃/min heating to 180 ℃, holding 2 min, 5 ℃/min heating to 280 ℃, Hold for 5 min; Carrier gas. Nitrogen (5.24); Flow rate. 1.0 ml/min; Electron capture detector (ECD). 300 ° C. 8.2 standard curve drawing Pipette a certain amount of PCB 1016 and PCB 1260 standard solution (5.19), diluted with n-hexane (5.2) Preparation standards Series, the standard solution concentrations were followed by 50.0 μg/L, 100 μg/L, 500 μg/L, 1000 μg/L, 2500 μg/L The concentrations were 5.0 μg/L, 10.0 μg/L, 50.0 μg/L, 100 μg/L and 250 μg/L respectively. If using internal standard method, Add 10.0 μl of internal standard solution (5.16) per 1.0 ml standard solution. Analyze according to instrument reference conditions (8.1). each Select 3 kinds of industrial products 5 characteristic peaks, record the retention time, peak area (or peak height). Each characteristic peak is targeted The compound concentration (or the ratio to the internal standard concentration) is the abscissa and the peak area or peak height of the characteristic peak of the target compound Standard peak area or peak height ratio) for the vertical axis, using the least squares method to draw the standard curve. The other five PCBs only formulated 500 μg/L standard solution, according to the instrument reference conditions (8.1) for analysis, record Characteristic peak retention time, peak area (or peak height). The characteristic peaks and standard chromatograms of polychlorinated biphenyls industrial products are given in Appendix C. 8.3 Determination of the sample The sample was measured according to the same instrument conditions (8.1) as the standard curve, the characteristic peak retention time and peak Area (or peak height). 8.4 Blank test The blank sample (7.4) was measured according to the same instrument conditions as the sample.

9 results calculated and expressed

9.1 Qualitative method 7 According to the chromatographic peaks and different polychlorinated biphenyls industrial products peak shape and retention time for qualitative comparison. Retention time change Does not exceed ± 0.05 min, when the sample peak and PCB industrial peak height ratio and retention time of a Time, it is confirmed that the corresponding polychlorinated biphenyls industrial products. When the sample peak characteristics of the peak is not significant, you must verify the analysis of a different polarity of the column. 9.2 Quantitative method Each polychlorinated biphenyl industrial choice of 3 to 5 characteristic peaks, the peak height of at least 25% of the peak. Polychlorinated biphenyls The characteristic peak of the product is shown in Appendix C. After the identification of PCBs, the peak area (or peak height) of the characteristic peak is quantified by the internal standard method or the external standard method, The mass concentration of polychlorinated biphenyls in the sample is the average value of the mass concentration of 3 to 5 characteristic peaks. PCB 1016 and PCB 1260 meets the linearity requirements, quantified using a standard curve, and the other five PCBs make use of single-point quantitation. Quantitative results of polychlorinated biphenyls in industrial samples are reported in the analytical column. 9.3 Results Calculation The mass concentration of PCBs in ambient air () is calculated according to equation (1). 1 n VF     (1) Where. ρ - ambient air concentration of PCBs industrial concentration, ng/m3; n - the number of selected industrial polychlorinated biphenyls characteristic peaks; ρi - from the standard curve or single quantitative determination of industrial polychlorinated biphenyls characteristic peak mass concentration, μg/L; V-- sample volume constant volume, ml; F - sample dilution multiple; Vs - Sampling volume at standard conditions (101.325 kPa, 273 K), m3. 9.4 results indicated When the concentration of PCBs in ambient air is greater than or equal to 1.00 ng/m3, the result retains three significant digits; less than At 1.00 ng/m3, the result is retained until the second decimal place. 10 precision and accuracy 10.1 Precision Six laboratories were repeated determination (n = 6) of the low concentration of spiked samples (standard addition of 30.0 ng ~ 100 ng, phase At 0.09 ng/m3 ~ 0.29 ng/m3), and the relative standard deviations in the laboratory ranged from 3.6% to 14%. The relative standard deviation The difference ranged from 3.1% to 8.5%. The reproducibility ranged from 0.02 ng/m3 to 0.06 ng/m3. The reproducibility ranged from 0.02 ng/m3 to 0.07 ng/m3. Blank spiked samples of PCB 1016 and PCB 1260 with scans of 500 ng and.2000 ng (equivalent to air samples 1.43 ng/m3 and 5.71 ng/m3 respectively). The relative standard deviations in the laboratory ranged from 2.8% to 12%, 3.0% to 10% and 1.7% 11% and 2.0% ~ 11% respectively. The relative standard deviations (RSDs) in laboratory were 6.9%, 5.4%, 3.8% and 3.1% Not 0.17 ng/m3, 0.76 ng/m3 and 0.19 ng/m3, 0.74 ng/m3 respectively; the reproducibility limits were 0.25 ng/m3 and 0.97 ng/m3 8 and 0.22 ng/m3, 0.82 ng/m3. Six laboratories repeated the determinations (n = 6) of uniform real samples containing 7.37 ng/m3 PCB 1242, respectively, in the laboratory The relative standard deviations were 2.2% -4.1%, the relative standard deviations (RSDs) were 4.9%, the repeatability was 0.65 ng/m3, Reproducibility limit is 1.17 ng/m3. See Table D.1 for details. 10.2 Accuracy Six laboratories repeated the spiking (n = 6) blank spiked samples with scans of 500 ng and.2000 ng (equivalent to null Gas sample 1.43 ng/m3 and 5.71 ng/m3) PCB 1016 and PCB 1260 respectively, the recoveries of spiked samples were 64.6% -84.9% And 83.6% ~ 96.2% respectively. The final recoveries were 70.3% ± 9.8%, 78.4% ± 8.6% and 88.7% ± 6.8%, respectively. 92.9% ± 5.6%. Six laboratories, respectively, repeated determination (n = 6) containing PCB 1242 ambient air samples, the standard addition of 1000 ng (phase When the air sample was 2.86 ng/m3), the spiked recoveries ranged from 69.2% to 96.5%. The final spiked recoveries were 80.2% ± 23.4%. See Table D.2 for details. 11 Quality Assurance and Quality Control 11.1 blank At least 1 field blank and 1 lab blank are determined for each batch of samples, and the blank value must not exceed the method detection limit. 11.2 Calibration 11.2.1 Initial calibration The correlation coefficient of the standard curve is ≥0.995, otherwise, a new standard curve is drawn. 11.2.2 Continuous calibration The standard solution of the midpoint concentration of the curve is measured at least once every 24 h during the measurement of the sample, and the measur...

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