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HJ 1050-2019: Water quality - Determination of chlorate, chlorite, bromate, dichloracetic acid and trichloracetic acid - Ion chromatography
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Basic data

Standard ID HJ 1050-2019 (HJ1050-2019)
Description (Translated English) Water quality - Determination of chlorate, chlorite, bromate, dichloracetic acid and trichloracetic acid - Ion chromatography
Sector / Industry Environmental Protection Industry Standard
Classification of Chinese Standard Z16
Classification of International Standard 13.060
Word Count Estimation 19,131
Date of Issue 2019
Date of Implementation 2020-04-24
Issuing agency(ies) Ministry of Ecology and Environment

HJ 1050-2019: Water quality - Determination of chlorate, chlorite, bromate, dichloracetic acid and trichloracetic acid - Ion chromatography


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(Water quality-Determination of chlorate, chlorite, bromate, dichloroacetic acid and trichloroacetic acid-Ion chromatography) National Environmental Protection Standard of the People's Republic of China Water quality chlorate, chlorite, bromate, di Determination of chloroacetic acid and trichloroacetic acid. Ion chromatography Water quality-Determination of chlorate, chlorite, bromate, dichloracetic acid and trichloracetic acid-Ion chromatography 2019-10-24 released 2020-04-24 Implementation Ministry of Ecology and Environment

Contents

Foreword ... ii 1 Scope ... 1 2 Normative references ... 1 3 Methodology ... 1 4 Interference and cancellation ... 1 5 Reagents and materials ... 2 6 Instruments and equipment ... 4 7 Sample ... 4 8 Analysis steps ... 5 9 Calculation and Representation of Results ... 6 10 Precision and accuracy ... 7 11 Quality Assurance and Quality Control ... 7 12 Waste disposal ... 8 13 Notes ... 8 Appendix A (Normative Appendix) Calibration method for chlorite stock solution ... 9 Appendix B (informative) Reference chromatograms of target compounds ... 11 Appendix C (informative) Method precision and accuracy ... 13

Foreword

In order 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 Control", protect the ecology Environment, protect human health, standardize the determination methods of chlorate, chlorite, bromate, dichloroacetic acid and trichloroacetic acid Law to formulate this standard. This standard specifies the determination of chlorate, chlorite, bromate, and chlorite in surface water, groundwater, domestic sewage and industrial wastewater. Ion chromatography of dichloroacetic acid and trichloroacetic acid. Appendix A of this standard is a normative appendix, and Appendix B and Appendix C are informative appendixes. This standard is issued for the first time. This standard is formulated by the Department of Eco-Environmental Monitoring, Laws and Standards Department of the Ministry of Ecology and Environment. This standard was drafted. China Environmental Monitoring Station. Verification units of this standard. Liaoning Provincial Ecological Environment Monitoring Center, Inner Mongolia Environmental Monitoring Center Station, Shanxi Original Ecological Environment Monitoring Center, Yangzhou Environmental Monitoring Center of Jiangsu Province, Environmental Protection Monitoring Station of Zhanjiang City, Qingdao Ecology of Shandong Province Environmental Monitoring Center and Handan Environmental Monitoring Center. This standard was approved by the Ministry of Ecology and Environment on October 24,.2019. This standard will be implemented from April 24, 2020. This standard is explained by the Ministry of Ecology and Environment. Water quality chlorate, chlorite, bromate, dichloroacetic acid and trichloroacetic acid Determination of ion chromatography Warning. The acetonitrile, acetic acid, and formic acid used in the experiment are volatile, and the sulfuric acid and sodium hydroxide are strongly corrosive. Reagent preparation should be performed in a fume hood; protective equipment should be worn as required during operation to avoid breathing into the respiratory tract or touching the skin and Clothing.

1 Scope

This standard specifies ion chromatography for the determination of chlorate, chlorite, bromate, dichloroacetic acid and trichloroacetic acid in water. This standard applies to chlorate, chlorite, bromate, and chlorite in surface water, groundwater, domestic sewage and industrial wastewater. Determination of chloroacetic acid and trichloroacetic acid. When the injection volume is.200 l, the chlorate (as ClO3 -Meter), chlorite (as ClO2 -Calculated), bromate (as BrO3 Method), the detection limits of the methods of dichloroacetic acid (DCAA) and trichloroacetic acid (TCAA) are 0.005 mg/L, 0.002 mg/L, 0.002 mg/L, 0.005 mg/L, and 0.01 mg/L, and the lower detection limits are 0.020 mg/L, 0.008 mg/L, 0.008 mg/L, 0.020 mg/L, and 0.04 mg/L.

2 Normative references

This standard refers to the following documents or clauses therein. For undated references, the valid version applies to this standard. HJ/T 91 Technical specifications for surface water and sewage monitoring HJ/T 164 Technical Specifications for Groundwater Environmental Monitoring

3 Method principle

The target compound in the sample is separated into the ion chromatography separation column with the eluent, and detected by a conductivity detector. Qualitative in time, quantitative in height or area.

4 Interference and cancellation

4.1 Chloride may interfere with the determination of bromate or dichloroacetic acid. Available if sample peaks overlap Ag/Na columns remove interference. 4.2 Sulfate ion may interfere with the determination of trichloroacetic acid. If chromatographic peaks overlap, the Ba column can be used for sample pretreatment. Eliminate interference, or achieve effective separation by reducing eluent concentration. 4.3 Nitrite may interfere with the determination of dichloroacetic acid. If chromatographic peaks overlap, you can reduce the eluent concentration and adjust Column temperature or the amount of acetonitrile added to achieve effective separation. 4.4 The reducing ions in the sample will make the chlorite measurement result low, which can be masked by adding thiourea. 4.5 The presence of high concentrations of chlorine dioxide in the sample affects the analysis. Interference can be eliminated by blowing nitrogen and adding thiourea.

5 Reagents and materials

Unless otherwise stated, analytical reagents that meet national standards are used in the analysis. The experimental water is free of target compounds. Deionized water with resistivity ≥18.2 Mcm (25 ° C). 5.1 Acetonitrile (CH3CN). chromatographically pure. 5.2 Sodium hydroxide (NaOH). excellent grade, granular. 5.3 Thiourea (CH4N2S). 5.4 Sodium carbonate (Na2CO3). excellent grade pure. Bake at 105 ° C ± 5 ° C for 2 h before use and store in a desiccator. 5.5 Sodium bicarbonate (NaHCO3). excellent grade pure. Equilibrate in a desiccator for 24 h before use. 5.6 Sodium chlorate. w (NaClO3) ≥99%. 5.7 Sodium chlorite. w (NaClO2) ≥80%. 5.8 Sodium bromate. w (NaBrO3) ≥99%. 5.9 Dichloroacetic acid. ρ (Cl2C2H2O2) = 1.56 g/ml. 5.10 Trichloroacetic acid. w (Cl3C2HO2) ≥99%. 5.11 Stock solution of sodium hydroxide eluent. ρ (NaOH) = 1.53 g/ml. Accurately weigh 100.0 g of sodium hydroxide (5.2), add 100 ml of water, stir until completely dissolved, and let it stand in a polyethylene bottle. Leave it for 24 hours and keep it sealed for 3 months. Commercial solutions can also be purchased. 5.12 Sodium hydroxide solution. ρ (NaOH) = 4 g/L. Weigh 1 g of sodium hydroxide (5.2) and dissolve in 250 ml of water. 5.13 Sodium hydroxide solution. ρ (NaOH) = 0.004 g/L. Measure 1.0 ml of sodium hydroxide solution (5.12) and dilute to 1 L with water. 5.14 Standard chlorate stock solution. ρ (ClO3 -) = 1000 mg/L. Accurately weigh 0.1290 g of sodium chlorate (5.6), dissolve it with a small amount of water, and transfer it into a 100 ml volumetric flask. Mark the line, mix well, transfer it to the reagent bottle, and store it under 4 ° C under cold storage for 4 months. Commercially Available Certified Standards Also Available Solution. 5.15 Chlorite standard stock solution. ρ (ClO2 -) ≈1000 mg/L. Accurately weigh 0.1680 g of sodium chlorite (5.7), dissolve it with a small amount of sodium hydroxide solution (5.13), and transfer to a 100 ml volume Measuring bottle, dilute with sodium hydroxide solution (5.13) to the mark, mix well, transfer to the reagent bottle, refrigerate below 4 ° C to avoid It can be stored for 4 months under light storage. Calibration is required before use. For details, see Appendix A. Commercially Available Certified Standards Also Available Solution. 5.16 Standard bromide stock solution. ρ (BrO3 -) = 1000 mg/L. Accurately weigh 0.1170 g of sodium bromide (5.8), dissolve it in a small amount of water, and transfer it into a 100 ml volumetric flask. Mark the line, mix well, transfer to the reagent bottle, and store it under 4 ° C under cold storage for 4 months. Commercially available certified standard solvent liquid. 5.17 Dichloroacetic acid standard stock solution. ρ (DCAA) = 1000 mg/L. Accurately measure 0.641 ml of dichloroacetic acid (5.9), dilute it with a small amount of water and transfer it to a 1000 ml volumetric flask. Fill to mark line, mix well, transfer to reagent bottle, refrigerate and store below 4 ℃, it can be stored for 4 months. Can also be purchased with a commercial license standard solution. 5.18 Trichloroacetic acid standard stock solution. ρ (TCAA) = 1000 mg/L. Accurately weigh 0.1010 g of trichloroacetic acid (5.10), dissolve it with a small amount of water, and transfer it into a 100 ml volumetric flask. Fill to mark line, mix well, transfer to reagent bottle, refrigerate and store below 4 ℃, it can be stored for 4 months. Can also be purchased with a commercial license standard solution. 5.19 Mix standard intermediate solution. Accurately measure 5.00 ml of chlorate standard stock solution (5.14), and appropriate amount (about 2.00 ml) of chlorite standard after calibration Quasi stock solution (5.15), 2.00 ml bromate standard stock solution (5.16), 5.00 ml dichloroacetic acid standard stock solution (5.17) And 10.0 ml trichloroacetic acid standard stock solution (5.18) in a 100 ml volumetric flask, make up to volume with sodium hydroxide solution (5.13) Graticule, mix well, where ClO3 -, ClO2 -, BrO3 -, DCAA and TCAA concentrations are 50.0 mg/L, 20.0 mg/L, 20.0 mg/L, 50.0 mg/L, and 100 mg/L, transferred to a reagent bottle, refrigerated and protected from light below 4 ° C for 14 days. 5.20 Mix standard use solution. Accurately measure 10.0 ml of standard material mixed intermediate solution (5.19) into a 100 ml volumetric flask, and use sodium hydroxide solution (5.13) Dilute to the mark, mix well, where ClO3 -, ClO2 -, BrO3 -, DCAA and TCAA concentrations are 5.00 mg/L, 2.00 mg/L, 2.00 mg/L, 5.00 mg/L, and 10.0 mg/L, transfer to a reagent bottle, and store in a cool and dark place below 4 ℃. Save for 7 days. 5.21 Eluent. 5.21.1 Carbonate eluent I. c (Na2CO3) = 0.6 mmol/L, c (NaHCO3) = 0.6 mmol/L. Accurately weigh 0.127 g of sodium carbonate (5.4) and 0.101 g of sodium bicarbonate (5.5), dissolve in appropriate amount of water and transfer to.2000 ml Volumetric flask, dilute with water to the mark and mix. Note. The eluent concentration can also be adjusted according to the performance of the column or the use conditions in the instructions. 5.21.2 Carbonate eluent II. c (Na2CO3) = 4.0 mmol/L, c (NaHCO3) = 0.6 mmol/L, 9% acetonitrile. Accurately weigh 0.848 g of sodium carbonate (5.4) and 0.336 g of sodium bicarbonate (5.5), transfer to.2000 ml after dissolving in an appropriate amount of water Volumetric flask, add 180 ml of acetonitrile (5.1), dilute with water to the mark, and mix. Note. The eluent concentration can also be adjusted according to the performance of the column or the use conditions in the instructions. 5.21.3 Hydroxide eluent. 5.21.3.1 Hydroxide eluent I. The required concentration is automatically generated by the eluent on-line generator. 5.21.3.2 Hydroxide eluent II. c (OH-) = 50 mmol/L. Accurately measure 5.20 ml of sodium hydroxide eluent stock solution (5.11) into a.2000 ml volumetric flask, and dilute with water to the standard volume. Line, transfer to the eluent bottle immediately after mixing, and protect it with nitrogen (5.22) to relieve the alkaline eluent from absorbing air Of CO2. The gradient pump automatically dilutes to the required concentration. 5.22 Nitrogen. Purity ≥99.999%. 5.23 Microporous membrane. pore size ≤0.45 m, made of acetate fiber or polyethylene.

6 Instruments and equipment

6.1 Ion chromatograph. with conductivity detector and suppressor. If you use hydroxide eluent, you need to equip it with eluent Or a binary or higher gradient pump. 6.2 Column. 6.2.1 Anion separation column Ⅰ. the packing is polystyrene/divinylbenzene, polyvinyl alcohol and other polymer matrix, alkyl quaternary ammonium Functional groups such as quaternary ammonium alkoxide and corresponding anion protection columns are suitable for carbonate eluent. Or other equivalent anion chromatography column. 6.2.2 Anion separation column Ⅱ. The packing is polystyrene/divinylbenzene, alkanol quaternary ammonium, etc. Secondary guard column, suitable for hydroxide eluent. Or other equivalent anion columns. 6.3 Suction filter device. equipped with a microporous filter membrane (5.23). 6.4 Sample bottles. polyethylene and other plastic materials. When measuring chlorite, use tin foil to protect it from light. 6.5 Needle-type microporous membrane filter. 0.22 μm pore size, hydrophilic material. 6.6 Syringe. 1 ml to 10 ml. 6.7 Anion purification column. Na type, Ag type and Ba type, size 1 g. 6.8 Organic purification column. C18 or similar purification column, specification 1 g or 2.5 g. 6.9 Instruments and equipment commonly used in general laboratories.

7 samples

7.1 Sample collection and storage Collect samples in accordance with the relevant regulations of HJ/T 91 and HJ/T 164. Collect at least 250 ml samples. The storage conditions and time are shown in Table 1. Table 1 Sample storage conditions and time Ion name preservation conditions ClO3 Acidic samples require pH adjustment To around 7, below 4 ℃ Keep refrigerated and sealed. / 7 d ClO2 0.5 g thiourea per 250 ml sample (5.3) Keep away from light. 24 h, 6 h for domestic and industrial wastewater Determined as soon as possible. BrO3 -/ 7 d DCAA/2 d TCAA/2 d 7.2 Preparation of test specimens The sample can be directly measured after being filtered through a needle-type microporous membrane filter (6.5). If chloride and sulfate ions interfere with the determination of the target, it can be removed with an anion purification column (6.7). With injection The device (6.6) draws 10 ml of experimental water, slowly passes through the column at 2 ml/min ～ 4 ml/min, and leaves it for 30 minutes before using it. Take an appropriate amount of sample and run it through the column at the same speed. Discard 3 times the volume of the initial filtrate and directly measure it. Hydrophobic organics can affect the lifetime of an ion chromatography column. If the sample contains high levels of hydrophobic organics, use The organic substance purification column (6.8) was directly measured after filtering. Before using the organic purification column, use chromatography in accordance with the instructions. Pure methanol and experimental water were activated. 7.3 Preparation of blank samples Use experimental water to replace the sample, and follow the same steps as in sample preparation (7.2) to prepare a laboratory blank sample.

8 Analysis steps

8.1 Instrument Reference Conditions 8.1.1 Reference condition 1 Anion separation column I (6.2.1), suppressor, conductivity detector, injection volume..200 μl. Carbonate eluent I (5.21.1), flow rate. 1.3 ml/min, column temperature. 25 ° C; Or carbonate eluent II (5.21.2), flow rate. 1.0 ml/min, column temperature. 45 ° C. See Figure B.1 and Figure B.2. Of Appendix B for anion standard solution chromatograms under this reference condition. 8.1.2 Reference condition 2 Anion separation column II (6.2.2), flow rate. 1.0 ml/min, conductivity cell temperature 30 ° C, column temperature 25 ° C, injection volume. 200 μl. Hydrogen leaching system gradient leaching conditions. c (OH-) is 5 mmol/L at 0 min ～ 18 min, 18 min ～ 30 min C (OH-) increased from 5 mmol/L to 45 mmol/L at 3 h, and c (OH-) was 5 mmol/L at 30.1 min to 35 min. If there is an eluent on-line generating device, it can automatically generate hydroxide eluent Ⅰ (5.21.3.1); if it is diluted by a gradient pump automatically The mobile phase A is the experimental water and the mobile phase B is the hydroxide eluent II (5.21.3.2). See Table 2 for the analysis conditions. The chromatogram of the anion standard solution under this reference condition is shown in Figure B.3 in Appendix B. Table 2 Analysis conditions of hydroxide eluent gradient program Time/min AB 0 90% 10% 18 90% 10% 30 10% 90% 30.1 90% 10% 40 90% 10% Note. When using a gradient pump, in order to ensure a stable baseline between adjacent samples, the analysis time is extended to 40 min after 35 min. 8.2 Establishment of standard curve Accurately remove 0 ml, 0.25 ml, 0.50 ml, 1.00 ml, 5.00 ml, and 20.00 ml of mixed standard use solution (5.20) In a set of 100 ml volumetric flasks, dilute to volume with sodium hydroxide solution (5.13) to the mark and mix. Reference series Degrees are shown in Table 3. According to the instrument reference conditions (8.1), determine the concentration in order from low to high. By the mass of each ion The concentration (mg/L) is the abscissa, and the peak height or area is the ordinate. A standard curve is established. Note. The appropriate standard series concentration range can be determined according to the concentration level of the target ion in the measured sample. Table 3 Reference mass concentration of standard series Unit. mg/L Target compound name 1 2 3 4 5 6 ClO3 -0 0.025 0.050 0.100 0.250 1.00 ClO2 -0 0.010 0.020 0.040 0.100 0.400 BrO3 -0 0.010 0.020 0.040 0.100 0.400 DCAA 0 0.025 0.050 0.100 0.250 1.00 TCAA 0 0.05 0.10 0.20 0.50 2.00 8.3 Sample determination The measurement of the sample (7.2) should be carried out under the same conditions and procedures as those used to establish the standard curve (8.2). If the sample concentration If the concentration is higher than the highest point of the standard curve, it can also be determined by diluting the sample with sodium hydroxide solution (5.13). D. 8.4 Blank test The blank sample (7.3) was measured under the same conditions and procedures as the sample measurement (8.3).

9 Calculation and representation of results

9.1 Qualitative analysis Characterized by the retention time of the target compound in the sample. 9.2 Result calculation Masses of five target compounds (chlorate, chlorite, bromate, dichloroacetic acid, and trichloroacetic acid) in the sample Concentration (mg/L), calculated according to formula (1). ρi = ρis × D (1) Where. ρ -The mass concentration of the i-th target compound in the sample, mg/L; ρis--mass concentration of the ith target compound obtained from the standard curve, mg/L; D--Dilution multiple. 9.3 Representation of results The number of digits after the decimal point in the measurement result is the same as the detection limit of the method. A maximum of three significant digits are retained. 10 Precision and accuracy 10.1 Precision The concentration of chlorate and dichloroacetic acid in 7 laboratories were 0.025 mg/L, 0.100 mg/L and 1.00 mg/L, respectively. And bromate concentrations were 0.010 mg/L, 0.040 mg/L, and 0.400 mg/L, respectively, and trichloroacetic acid concentrations were Three replicates of three standard solutions of 0.05 mg/L, 0.20 mg/L, and 2.00 mg/L were used for 6 replicate determinations in the laboratory. Relative standard deviation is 0.1% to 16%, relative standard deviation between laboratories is 0.0% to 8.2%, and repeatability limit is 0.002 mg/L ～ 0.027 mg/L, and the reproducibility limit is 0.003 mg/L ～ 0.12 mg/L. Seven laboratories performed 6 repeated determinations of surface water, groundwater, domestic sewage and industrial wastewater at different spiked concentrations. The relative standard deviation in the laboratory is 0.0% ～ 24%, the relative standard deviation in the laboratory is 4.4% ～ 16%, and the repeatability limit is 0.003 mg/L ～ 0.019 mg/L, the reproducibility limit is 0.005 mg/L ～ 0.064 mg/L. Refer to Table C.1 and Table C.2 in Appendix C for the method precision test results. 10.2 Accuracy The concentration of chlorate, chlorite, bromate, dichloroacetic acid and trichloroacetic acid in 7 laboratories is ND ～ 0.104 mg/L Surface water, groundwater, domestic sewage, and industrial wastewater were repeatedly spiked for 6 times, and the spiked concentrations of 5 target substances 0.020 mg/L ~ 0.25 mg/L. The spiked recovery is 66.8% ~ 128%. The results of the method accuracy tests are shown in Table C.3 in Appendix C. 11 Quality Assurance and Quality Control 11.1 A blank test should be performed before analyzing the sample. Every 10 or each batch (≤10/batch) samples should be made at least 1 Analysis of blank samples. The target compound content in the blank sample should be lower than the corresponding method detection limit. 11.2 Use at least 6 concentrations (including zero concentration points) to establish a standard curve, and the correlation coefficient should be ≥0.999. Every 20 or each Batch (≤20/batch) samples should be analyzed with a standard solution at the middle point of the standard curve. The relative error between the concentrations at the point of the line should be within ± 15%. 11.3 At least one parallel double sample shall be determined for every 20 samples or batches (≤20 samples/batch). Parallel double sample measurement results The relative deviation should be ≤35%. 11.4 Every 20 samples or batches (≤20 samples/batch) should be tested for at least 1 standard recovery test or certified reference material. set. Among them, the spiked recovery rate should be controlled between 65% and 130%, and the measured value of the reference material should be within the uncertainty range given by it. Within. 12 Waste treatment The waste liquid generated in the experiment should be collected centrally, classified and stored, and properly labeled, and entrusted to a qualified unit for processing Management. 13 Notes 13.1 After adding acetonitrile to the eluent, it is easy to generate air bubbles, which needs to be removed with a suction filtration device (6.3). 13.2 Pre-treatment purification columns (6.7 and 6.8) can be filtered with a small volume syringe of 1 ml to 2 ml to reduce Resistance to control filtration flow rate. 13.3 If an electrochemical continuous regeneration suppressor is used, the addition of organic solvents to the eluent may affect baseline stability. In this case, it is best to use deionized water for the regeneration solution of the suppressor.

Appendix A

(Normative appendix) Calibration method of chlorite stock solution A.1 Principle Under acidic conditions, chlorite can oxidize iodine ions to iodine simple substance, and titration of iodide ions by iodometric method can indirectly obtain Concentration of chlorate stock solution. A.2 Reagent Unless otherwise specified, analytical reagents that comply with national standards are used in the analysis. The experimental water is double distilled water or Water prepared by pure water equipment, resistivity ≥18 Mcm (25 ° C). A.2.1 Hydrochloric acid. ρ (HCl) = 1.19 g/ml. A.2.2 Potassium iodide (KI). A.2.3 Potassium iodate (KClO3). Excellent grade pure. Use after drying at 110 ℃ for 2 h. A.2.4 Sodium thiosulfate (Na2S2O3 · 5H2O). A.2.5 Sodium carbonate (Na2CO3). A.2.6 Soluble starch. A.2.7 Hydrochloric acid solution. c (HCl) = 2.5 mol/L. Dilute 20 ml of hydrochloric acid (A.2.1) with water to 100 ml. A.2.8 Standard solution of potassium iodate. ρ (1/6KIO3) = 3.0 mg/L Weigh 1.5 g of potassium iodate (A.2.3), accurate to 0.0001 g, and accurately dilute to 500 ml after dissolving in water and transfer to The reagent bottle is refrigerated below 4 ° C and can be stored for half a year. A.2.9 Starch solution. ρ = 5.0 g/L. Weigh 0.50 g of soluble starch (A.2.6), add a little water to make a paste, slowly pour into 100 ml boiling water and continue cooking Boil until the solution is clear, and store in a narrow-mouth bottle after cooling. A.2.10 Sodium thiosulfate solution. c (Na2S2O3) = 0.1 mol/L. Weigh 25 g of sodium thiosulfate (A.2.4) in 1000 ml of freshly boiled and cooled water and add 0.20 g of sodium carbonate (A.2.5), stored in a brown narrow-necked bottle, and allowed to stand for one week to calibrate its concentration. If the solution appears cloudy, it should be filtered. Refrigerated below 4 ℃, can be stored for half a year, and calibrated before use. Calibration method. Pipette 25.00 ml of potassium iodate standard solution (A.2.8), put it in a 250 ml iodine volumetric flask, add 70 ml Freshly boiled and cooled water, add 1.0 g potassium iodide (A.2.2), shake until completely dissolved, then add 2.00 ml hydrochloric acid to dissolve Liquid (A.2.7), immediately cap the stopper and mix well. After 5 minutes in the dark, drop it with sodium thios...

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