This standard specifies the technical requirements, determination methods and calculation methods for the observation of seawater chemical elements. This standard applies to the observation of seawater chemical elements in the investigation of basic elements of the marine environment. GB/T 12763.4-1991 Marine Survey Specification for Seawater Chemical Element Observation GB/T12763.4-1991 Standard Download Decompression Password: www.bzxz.net
This standard specifies the technical requirements, determination methods and calculation methods for the observation of seawater chemical elements. This standard applies to the observation of seawater chemical elements in the investigation of basic elements of the marine environment.

National Standard of the People's Republic of China
Specification for oceanographic survey
Observation of chemical parameters in sea waterWww.bzxZ.net
The specification for oceanographic survey observationsof chemical parametersg in sea water1Subject content and scope of application
GB 12763. 4—91
This standard specifies the technical requirements, determination methods and calculation methods of determination data for observation of chemical parameters in sea water. This standard applies to observation of chemical parameters in sea water in the survey of basic elements of the marine environment. 2 Reference standards
GB 12763. 1
GB 12763. 2
GB 12763. 7
3 Technical design
Marine hydrographic observation
Marine survey data processing
Part I General provisions
Technical design must be carried out before the start of the survey work, and its contents should include: the purpose and tasks of the survey;
The location, time and number of surveys;
Observation items, methods and technical requirements,
Determination methods and quality control:
Required equipment, reagents, forms, etc.:
Submitted materials and results;
Personnel and funds:
Certain special conditions must be guaranteed.
Observation items and requirements
Observation items, determination methods and main instruments are shown in Table 1. Other determination methods that have been confirmed to meet the technical indicators specified in this standard through mutual calibration may also be used.
5 Quality control of the determination process
5.1 Verification and calibration of weighing and volumetric instruments: Approved by the State Administration of Technical Supervision on 1991-03-22, implemented on January 1, 1992
GB 12763.491
5.1.1 Analytical balances must be verified and deemed qualified by the national verification agency and used within the verification period. The base code is a third-class magnetic code that has been verified and qualified.
5.1.2 Burettes, pipettes, single-line bottles (referred to as volumetric bottles) and other measuring containers shall all use nationally certified matching products and be used within the verification period.
Table 1 Observation items, methods and instruments
Observation items
Dissolved fluoride
Total alkalinity
Active silicate
Active iodate
Nitrite
Nitrate
Ammonia (including some amino acids)
Fluoride and chlorine
Determination method
Austenometric titration
PH meter electrical measurement method
PH measurement method
Silica blue method (Metol reduction method)
Phosphorus blue method (ascorbic acid-tartrate oxygen
Potassium antimony)
Diazonazo method
Zinc-cadmium reduction method
Sodium hypobromate oxidation method
Argentometric titration
Note: 1) Oxygen content is measured only when there is a special requirement. Dissolved fluorine burette
Main instruments
Digital pH meter; resolution 0. 01 pH; with gradient compensation. Reproducibility ≤ 0. 02 pH
The instrument must be shockproof and moisture-proof
Digital spectrophotometer: instrument noise is not more than 0.2%; zero drift is not more than 1×10-2h-. Wavelength range 300~900nm
Borne tube, seawater straw
5.2 The standard solution used uniformly in the marine survey must be a product certified by the state. When the standard solution used uniformly is insufficient, it can be prepared by yourself, but 5 parallel samples of the self-prepared standard solution must be taken and calibrated with the above standard solution: to obtain its average concentration.
5.3 Before each survey task begins, the investigators must conduct a comparative test. If there is more than one ship participating in the survey, the laboratories of each ship should conduct a comparative test.
5.4 When measuring samples, standard solutions of known concentration must be used for comparison at regular intervals as a quality control during measurement, and inserted in order and recorded in the water sample measurement record sheet. 5.5 The chemical reagents used in this standard are all secondary reagents unless otherwise indicated. All dilution steps, except for those with specified droppers, refer to dilution with distilled water or deionized water. Unless otherwise specified, hot distilled water and deionized water can be used equally. 5.6 The silicon-free, "ammonia-free" (meaning no inorganic combined nitrogen), ammonia-free seawater, and distilled water mentioned in this standard refer to seawater and distilled steel water whose concentration cannot be measured using the methods specified in this standard. 6 Preparation before going out to sea
6:1 Sufficient equipment and materials should be prepared according to the survey plan. A list should be made for inspection. 6.2 Water sample bottles should be numbered and arranged in order. Dissolved oxygen water sample bottles must be prepared according to 11.3 and 12.3. 6.3 The performance of various instruments must be normal. And check and register according to the general rules of marine survey in GB12763.1 standard. 6.4 Before going out to sea, a comprehensive inspection of the preparation work should be carried out, and a trial survey should be carried out if necessary. 7 Collection, pretreatment and storage of water samples
7.1 According to the needs of the observation project, appropriate water sampling equipment should be selected and cleaned. 7.2 In order to avoid the disturbance of the water body by the ship, sampling should be carried out after the ship stops steadily at the station. 7.3 The water sampling level should avoid the sewage outlet on the ship (or the survey ship must stop sewage discharge after arriving at the predetermined station) to prevent water samples and underwater instruments from being contaminated.
7.4 See Table 2 for the standard level.
Water depth standard
GB 12763. 491
Table 2 Observation standard layer
Standard layer
Surface layer, 5, 10, 20, 30, Bottom layer
Table, 10, 20, 30.50, 75, 100, 150, 200.300, 400, 500, 600, 800, 1000, 1200, 1500, 200, 2 500, 3 000, add one layer for every kilometer below, bottom layer Note: ①Surface layer refers to the water layer about 1 meter below sea level. (②Bottom layer position and wire rope inclination correction according to CB 12763. 2 Haixiang Survey Specifications Haixiang Hydrological Observation regulations shall be implemented. 7.5 Before sampling, the water sample registration form (Appendix C1) should be filled in and the bottle number should be checked. After water is collected, the samples should be separated immediately. 7.6 The order of sampling: dissolved oxygen (take two bottles), pH, total alkalinity (if measuring chlorine, the water sample can be combined into one bottle) and five nutrient salts (combined bottle)
7.7 Loading, pretreatment and storage of various daily water samples. 7.7.1 Dissolved oxygen
7.7.1.1 The water sample bottle is a brown ground-mouth hard glass bottle with a volume of about 120cm (the volume has been accurately measured to 0.1.cm in advance), and its R value has been calculated. The bottle stopper should have an inclined flat bottom,
7.7.1.2 Each layer of water sample is loaded Take two bottles.
7.7.1.3 Loading and Removing Method
Connect one end of the latex tube to the glass tube, and put the other end on the water outlet of the water sampler. Release a small amount of water sample to clean the water sample bottle twice. Insert the glass tube to the bottom of the sample bottle, slowly inject the water sample, and when the water sample is full and overflows about half of the bottle volume, slowly withdraw the glass tube, and immediately use an automatic liquid adder (the tip of the tube is close to the liquid surface) to inject 1.0cm2 of manganese fluoride solution and 1.0cm2 of alkaline potassium iodide solution in sequence (the preparation of the two solutions is shown in 11.2.1 and 11.2.2), plug the bottle tightly and hold the bottle stopper and the bottom of the bottle with your hand, slowly turn the bottle upside down 20 times, soak it in water, and allow it to be stored for 24 hours.
7.7.2.1 The water sample bottle is a double-layer polyethylene bottle with a volume of 50cm. 7.7.2.2 Filling and Removing Method
Wash the water sample bottle twice with a small amount of water sample, slowly fill the bottle, immediately cover the bottle stopper, place it indoors, and measure when the water sample temperature is close to room temperature. If 1 drop of chlorination solution (p(HgC12)=25.0g/dm is added, cover the bottle cap, mix evenly, and allow to store for 24 hours. 7.7.3 Total Alkalinity, Oxygen Content
7.7.3.1 The water sample bottle is a hard glass bottle with a volume of 250cm2, a stopper and a flat bottom. Before the first use, soak it in 1.0% (V/V) hydrochloric acid solution or natural seawater for 24 hours, and then rinse it clean. 7.7.3.2 Filling and Removing Method
Wash the water sample bottle twice with a small amount of water sample, then fill it with about 100cm of water sample (if fluoride needs to be measured, 100cm of water sample should be added) and immediately cover the bottle stopper. It should be within 24 hours The determination is completed. 7.7.4 Five nutrient salts
7.7.4.t The water sample bottle is a high-density polyethylene bottle with a volume of 500cm*, double-layer cover. Before the first use, it must be soaked in 1.0% (V/V) hydrochloric acid or natural seawater for 24 hours and then rinsed clean
7.7.4.2 Filter membrane treatment
The pore size is 0.Before using the 45μm mixed cellulose ester microporous filter membrane, first use 1.0% (V/W) hydrochloric acid to permeate for 12 hours, then wash with distilled water until neutral and soak. Before using each batch of filter membrane, a blank test must be carried out. 7.7.4.3 Loading and Removing Method
GB12763.4-91
Wash the water sample bottle twice with a small amount of water sample, then take 500cm of water sample and immediately filter it with a treated microporous filter membrane with a pore size of 0.45um. If it needs to be stored, add trichloromethane accounting for two-tenths of the sample volume, cover the bottle stopper, shake vigorously for about 1 minute, and store it in a refrigerator or ice bucket at a low temperature of 4-6℃. The water sample is allowed to be stored for 24 hours. 7.7.5 Sample Separation At the end, carefully check whether the samples are complete and the records are complete. 8 General requirements for observation data record arrangement
8.1 Data recording and arrangement shall be carried out in accordance with the provisions of GB12763.1 standard, and the filling of observation reports shall be carried out in accordance with the provisions of GB12763.7 standard.
8.2 After the entire investigation is completed, the investigation report must be prepared in accordance with the requirements of the contract task book and the relevant provisions of GB12763.1 standard. 8.3. Data archiving shall be carried out in accordance with the provisions of GB12763.1 and GB12763.7 standards. Part II Dissolved Oxygen Determination (Iodine Titration Method) 9 Terminology
Dissolved oxygen refers to the oxygen dissolved in seawater. Use the symbol DO Indicates. It is converted to μ mol/dm oxygen atom. Oxygen concentration refers to the percentage of the measured bath oxygen concentration to the theoretical saturation concentration under the conditions of on-site water temperature and salinity when the atmospheric pressure is 1013.25hpa.
The volume correction coefficient f of sodium thiosulfate solution indicates that the volume of sodium thiosulfate solution with a concentration of o(NaS.O·5H20)=0.01000mol/dm is equivalent to 1cm of sodium thiosulfate solution used for titration! (cm*). 10 Technical indicators
10.1 Determination range; 5.3μmal/dms-~1.0×10μmol/dm*10. 2 Detection limit; 5.3 μ mol/dm
10.3 Precision: When the oxygen content is less than 160μmal/dm, the standard deviation is ±2.8×10-μmol/dm; when the oxygen content is ≥550umol/dm, the standard deviation is ±1.0Lmol/dm: 11 Determination method
11.1 Principle of the method
In a quantitative water sample, after adding suitable manganese chloride and alkaline potassium iodide reagents, the generated manganese hydroxide is oxidized by the dissolved oxygen in the water to form a brown precipitate, mainly MnO(OH). After sulfation, the precipitate dissolves: in the presence of iodide, the oxidized manganese is reduced to a divalent state, and iodine molecules with the same molar number as the dissolved oxygen atoms are precipitated. The precipitated iodine is titrated with sodium thiosulfate solution, and starch indicates the end point. 11.2 Reagents and their preparation
11.2. 1 Manganese hydroxide solution (c: (Mn21) = 2. 1 mol/dm\］Dissolve 480g MnCl2·4H2O in distilled water and dilute to 1000cm11-2.2 Alkaline potassium iodide solution [c(Naol[)=6. 4 nol/dm,c(K1)=1. 8 mol/dm\. Dissolve 256g sodium hydroxide in 300cm2 distilled water, dissolve 300g potassium iodide in 300cm2 distilled water, then mix the above two solutions and dilute to 1 000cm.
11.2.3 Starch-glycerol (glycerol) indicator Add 3.0g soluble starch (CIf0) to 100cm2 glycerol rCH(OH)s, heat to 190℃ until the starch is completely dissolved: This solution can be stored for years at room temperature, and the appearance of turbidity does not affect the effectiveness of the indicator. 11.2. 41:3 (V/W) Sulfuric acid
With stirring and cooling in a water bath, slowly add one volume of concentrated sulfuric acid (=1.81g/cm\) to three volumes of Yan Zeng water towel. GB 12763. 4-91
11.2.5 Sodium thiosulfate solution (c(Na,S,0,)=0.01mol/dm) Weigh 25.0g sodium thiosulfate (NazS:0:·5Hz0), dissolve it with a small amount of distilled water, dilute to 1000cm*, add 1.0g anhydrous sodium carbonate (Na.CO.). Mix well. Store in a brown reagent bottle. The concentration of this solution is 0.1mol/dm. After 15 days, dilute it with distilled water that has just been boiled and cooled to a solution of 0.01mal/dm. 11.2.6 Potassium iodate standard solution Cc(1/6KI0)=1.000×10°μmal/dm: Potassium iodate standard solution (national secondary standard material) b. Prepare potassium iodate standard solution by yourself and calibrate it regularly with the above potassium iodate standard solution (11.2.6.a) according to the provisions of 5.2. Preparation method: Take a small amount of potassium iodate and bake it at 120℃ for 2h, cool it in a desiccator, accurately weigh 3.567g and dissolve it in steamed stuffing water that has just been boiled and cooled to room temperature, transfer it to a 1000cm volumetric flask, dilute to the mark, mix, store in a brown reagent bottle, and store at 56℃. The validity period is 3 months. Dilute it to 10 times when using, and you will get c(1/6KI0g)=1. 000×10\μmol/um3 potassium iodate standard solution. 11.3 Main instruments
. Water sample bottle: Brown ground glass bottle with a volume of about 120cm, the bottle stopper is conical or oblique flat bottom, the ground mouth should be tight, each water sample bottle is accurately measured according to 12.3 to 0.1cm and the R value table is compiled: b. Dissolved oxygen burette: 25cm2 leather head, sub-scale value is 0.05cm;, electromagnetic stirrer;
d, 15.00cm seawater pipette;
e. 1.0cm, 5.0cm adjustable quantitative liquid adding device. 11. 4 Determination steps
11.4.1 Calibration of sodium thiosulfate solution
Use a straw pipette to absorb 15.00cm potassium iodate standard solution (see 11.26, double), inject it into the iodine volume bottle along the wall, rinse the bottle wall with a small amount of distilled water, and add 0.6 potassium iodide. Mix well and add 1.0cm1:3 (V/V) sulfuric acid, mix again, cover the bottle stopper, and leave for 2 minutes. Wash 110cm of distilled water along the wall and put in the magnetic rotor. Immediately start stirring and titrate with sodium thiosulfate solution. When the test solution turns light yellow, add 3~4 drops of starch indicator and continue to drip until the blue color of the solution just disappears. Repeat the calibration until the difference between the two burette readings does not exceed 0.03cm\. Record the burette reading in the dissolved oxygen determination record sheet (Appendix C2) and calibrate once every 24 hours.
11.4.2 Water sample determination:
After the water sample is fixed, wait for the precipitate to drop to the bottom of the bottle, and then titrate. a. Open the water sample bottle stopper, pour part of the upper clear liquid into the conical flask, and immediately add 1.0cm21:3 (V/V) vegetable acid to the precipitate; plug the bottle stopper tightly and shake the water sample bottle until the precipitate is completely dissolved. b. Open the water sample bottle, pour the solution in the bottle into the conical flask along the wall, and immediately start stirring and titrating. When the test solution turns light yellow, add 3 to 4 drops of starch indicator and continue to titrate until it turns light blue. c. Pour out part of the test solution in the conical flask and rinse it in the original water sample bottle, then pour it back into the conical flask and continue titrating until it is colorless. After 20 seconds, if the test solution is not light blue, it is the end point. Record the volume of sodium thiosulfate solution consumed in the titration in the dissolved oxygen determination record sheet Appendix c2).
11.4.3 Determination of reagent blank (m)
Put 1.00cm2c (1/6K10s) = 1.000×10μmol/dm potassium iodate standard solution into an iodine volumetric flask, add 120cm2 distilled water, 1.0cm2 1:3 (V/V) sulfuric acid, 1.0cm alkaline potassium iodide solution and 1.0cm2 manganese chloride solution in sequence (mix each reagent thoroughly), then immediately titrate with calibrated sodium thiosulfate solution to the full point. The volume of sodium thiosulfate solution consumed is Vat.
Add 1.00cm2 potassium iodate standard solution to the above solution, mix thoroughly, and immediately re-titrate with sodium thiosulfate solution to the end point. The volume of sodium thiosulfate solution consumed is Vz, then Bam=Vl-V.2. When the Bamp value is greater than 9.0μmol/dm, the reagent must be replaced.
12 Calculation of measurement data
GB127 63. 4-91
12. Calculation of volume correction factor of sodium thiosulfate solution: f
Where: V,——the volume of 1.000×10\umol/dm potassium iodate solution used during calibration, cm*V---the volume of sodium thiosulfate solution consumed during calibration, cm\. The f value must be between 0.9 and 1.1, otherwise the concentration of sodium thiosulfate solution must be adjusted. 12.2 The concentration of sodium thiosulfate solution reduced by dissolution is calculated according to formula (2): c(Sr0-) = f × 1.0 × 10*μ mol/dm* = f × 10t u mol/dm12.3 Water sample bottle volume measurement
Fill the water sample bottle with distilled water, cool it down, wipe it dry and weigh it, subtract the weight of the dry empty bottle. Divide it by the specific gravity of the distilled water at that water temperature (see Appendix B10). Compile the R value table based on the measurement results. 12.4 The dissolved oxygen concentration in seawater is calculated by the following formula: r(0) =
V. Xfx ci
(- V) X 2
The volume of sodium thiosulfate solution consumed during titration, cm; "volumetric correction coefficient of sodium thiosulfate solution; concentration of potassium iodate standard solution 1,000×10umal/dmV.-
volume of water sample bottle, cm2;
total volume of two fixatives (MnCly, KI-NaOH), cm\Ci
{V3—V)X2
Then formula (3) can be expressed as c(O) V × f × R. For a water sample bottle, the ratio is a constant, called the oxygen saturation of the water sample bottle. 12.5 Calculation of oxygen saturation (0)
Where: r(o) is the measured oxygen concentration of the water sample, H mol/dm*;cor-
-The saturated concentration of oxygen in the air in the seawater under the conditions of water temperature, salinity and pressure at the site, μmol/dm (obtained from Appendix B1).
12.6 The saturated concentration of oxygen in seawater of different humidities and salinities can be calculated according to the UNESCO value (see Appendix B1). That is: Inc(Or)=A+A(100/T)+An(T/100)+A(T/100)+$[B,+ B2(T/100) + B;(T/100)*3
Where: e(or)—
The saturated concentration of oxygen in seawater. That is, when the total atmospheric pressure is 1 013.25 hPa, the solubility of oxygen in seawater in the atmosphere containing 20.95% oxygen by volume and saturated with water vapor. T-thermodynamic temperature, K;
8-salinity:
A, R---constant. Its value is 1
A,= -173. 429 2:
Az249.6339;
4g=143.3483
Af = —21. 849 2;
B =-0. 033 096 :
Bg —0. 014 259 ;
Bs=-0.001700 0
GB 12763. 4
Note: The saturation concentration calculated by formula (5) and the above parameters is measured in cm/m. If it is converted to /mol/dm oxygen atoms, the calculated result should be multiplied by the conversion factor 89, 23.
Part III pH determination (pH meter electrical measurement method)
13 Terminology
pH is a scale that represents the activity of hydrogen ions in a solution (l), and is defined as: pH represents the negative logarithm of the activity of hydrogen ions. That is, pH-lg[a]
14 Technical indicators
14. 1 Precision: ±0. 01 pHl.
14. 2 Accuracy: 0. 02 pH,
15 Determination method
15.1 Principle of the method
The pH value of seawater is determined by measuring the relationship between the pH of the glass electrode and the electromotive force of the battery, which is defined as: the electromotive force of the calomel electrode pair. Because the pH of seawater sample and standard solution is pH,=pH,+(E,-Er)/(RT/^). In10When the glass-calomel electrode pair is inserted into the standard buffer solution, let:
A = pH,
pH = A
In10RT/F
In10 RT/E
At the same temperature, the electromotive force of the same electrode pair in the standard buffer solution and water is measured respectively, then the pH value of the water sample is: pH,- pH, +
E, —
In10 H7/F
Where: pHL-pH value of water sample
pH-—pH of standard buffer solution Value,
E—Electromotive force of glass-calomel electrode inserted into water sample, mV; 5 Electromotive force of glass-calomel electrode inserted into standard buffer solution, VR—Gas constant,
F—Faraday constant,
(6)
(8)
T—Thermodynamic temperature, K.
15.2 Reagents and their preparation
15.2. 1 pH buffer in bags (see Appendix B2) GB 12763.4—91
a. Potassium o-benzoate (25℃, pH=4.003) b. Mixed phosphate (25℃, pH=6.864); c. Sodium tetraborate decahydrate (borax, 25℃+PH=9.182). 15.2.2 pH standard buffer solution can also be prepared as follows 15.2.2.1 Pretreatment of standard substances t
Potassium hydrogen phthalate (COOHCH,COOE). Bake at 115℃±5℃ for 2h and cool in a desiccator; b. Sodium hydrogen phosphate (Na2HPO4) and potassium dihydrogen phosphate (KH2PO4) are pre-bake at 115±5℃ for 2h and cool in a desiccator; c. Sodium tetraborate decahydrate (NaB2O4·10H2O4) is placed in a desiccator containing saturated sucrose solution for 48h and then kept in the desiccator; d. Distilled water: The conductivity should be less than 2×10:S/em (s is Siemens). To prepare sodium tetraborate standard solution, the distilled water used should be boiled for 10 min, and then prepared immediately after cooling; 15.2.2.2 Preparation method: Preparation of 0.050 mol/dm potassium hydrogen phthalate buffer solution: Dissolve 10.12 g potassium hydrogen phthalate in a small amount of distilled water, dilute to 1 000 cm, add 11.0 cm2 chloroform, mix well and store in a polyethylene bottle, which can be stable for 3 months. b. Preparation of 0.025 mol/dm potassium dihydrogen phosphate and 0.025 mol/dm dihydrogen phosphate mixed standard buffer solution: Dissolve 3.388 g potassium dihydrogen phosphate and 4.428 g disodium hydrogen phosphate in a small amount of distilled water, dilute to 1 000 cm, add 1.0 cm2 chloroform, mix well and store in a polyethylene bottle, which can be stable for 3 months. c. Preparation of 0.0100mol/dm sodium tetraborate buffer solution: Weigh 3.800g sodium tetraborate decahydrate and dissolve it in a small amount of fresh distilled water, dilute to 1000cm, mix, and store in butyl polyethylene bottles. Seal the bottles with wax. It can be stable for 3 months. When preparing, add 1.0 cm\ chloroform per liter as a preservative. After opening the bottle, the usage period shall not exceed one week.
The pH value of the standard buffer solution changes with temperature. The pH value at 0~45°C is listed in Appendix B2. 15.2.3 Saturated potassium chloride (KCl) solution
Weigh 40% potassium fluoride and dissolve it in 100cm hot distilled water (this solution should coexist with solid potassium chloride). 15.2.4 Mercuric chloride (HgCl2) solution (pH=25.0 g/dm\), dissolved in a brown reagent bottle 15.3 Main instruments
Digital H meter (must have temperature compensation and two-point positioning function). 15.4 Determination steps
15.4.1 If it is not a composite electrode, it must be carefully matched. 15.4.2 Avoid double-standard positioning of the H meter.
15.4.3 Water sample determination
After positioning, lift the electrode pair, remove the standard buffer solution, rinse the electrode with distilled water, absorb the water with a filter paper, and then immerse it in the water sample bottle. After the reading is stable, record the temperature and pH reading of the water sample and fill in the pH determination record sheet (Appendix C3): 16 Determination data calculation
16.1 Convert the experimental data into on-site pH, and perform temperature and pressure correction according to the public (9). pH.=pHm + attmt)βd
Wherein: pHpH is the pH at the scene and at the time of measurement, respectively; (9
GB 12763. 4-91
is the water temperature at the scene and at the time of measurement, respectively, and d is the depth of the water sample, m;
is the temperature and pressure correction coefficient, respectively, (tmt) and d are obtained from Appendix B3 and Appendix B4. ,8
If the water depth is within 500m, no pressure correction is made, and formula (9) is simplified to formula (10): pH = pHn + a(tm t)
Part 4 Determination of Total Alkalinity (pH Method)
17 Terminology
The total alkalinity of seawater is the amount of ammonium ions neutralized by weak acid anions in seawater divided by the volume of seawater. The total alkalinity of seawater is represented by the symbol A and the unit is mmal/dm. It can be expressed by the following formula:.10)
A—(HCO;）+2(CO-）+[B(OH)+(OH-）—(H)+c(residue) The last term in the formula is the residual alkalinity, which refers to the sum of the concentrations of all weak acid anions other than carbonate, boric acid and hydroxide. Its content is much lower than other terms and can be ignored under normal circumstances.
18 Technical indicators
18.1 Accuracy: When the total alkalinity is 1.5mmol/dm, the relative error is ±3.5%: When the total alkalinity is 2.2mmol/dm2, the relative error is ±2.5%.
18.2 Precision: Relative standard deviation: ±1.5%. 19 Determination method
19.1 Principle of the method
Add excess hydrochloric acid standard solution to the water sample, use a pH meter to determine the pH value of the mixed solution, and calculate the total alkalinity of the water sample according to the formula. 19.2 Reagents and their preparation
19.2.10.05tol/dtm3 Phthalate nitrogen potassium standard buffer solution, same as 15.2.2.2. 19.2.20.00600mol/dm hydrochloric acid standard solution (national third-level standard material), or prepare as follows: a. Measure 8.4 cma first-grade concentrated hydrochloric acid (n=1.18 g/cm2) in a 1000 cm* volumetric flask, and dilute to the mark with distilled water that has been boiled for 15 minutes and cooled to room temperature
b. Measure 60cm of the above hydrochloric acid (a) and dilute to 1000cm. This is a dilute hydrochloric acid solution with a concentration of about 0.006mol/dm. 19.2.3 Sodium carbonate solution [c(
-Nagcog)=0. 010 00 mol/dm
Weigh 0.5300 g of anhydrous sodium carbonate (a primary reagent, kept at 220°C for 2 h and cooled to room temperature in a desiccator), quench it with a small amount of distilled water, and dilute to 1 000 cm.
19.2.4 Methyl red [(CH.)NCH.NNC.HCOOH]--methylene blue mixed indicator Weigh 0.032g methyl red and dissolve it in 80cm95% ethanol, add 6.0cm methylene blue ethanol solution (0.01g methylene blue dissolved in 100cm*95% ethanol), mix and add 1.2cm sodium hydroxide solution (pNcm=40.0g/dm, dissolve into dark color, stick" brown bottle.
19.2.5 Determination and concentration calculation of hydrochloric acid standard solution Pipette 15.00cm sodium carbonate standard solution into a conical flask, add 6 drops of methyl red-methylene blue mixed indicator, and titrate with dilute hydrochloric acid solution. When the solution changes from orange-yellow to stable light purple-red, it is the end point. Calculate the concentration of hydrochloric acid standard solution according to formula (11): Where: r(HCI)-
GB 12763. 4—91
Concentration of hydrochloric acid standard solution, mol/dm
-NazcO,)—Concentration of sodium carbonate standard solution, mol/dmVCI
Volume of hydrochloric acid standard solution, cm,
19.3 Main instruments
Volume of sodium carbonate standard solution, cm.
a. Digital pH meter
50cm Polyethylene wide-mouth bottle with inner stopper, b.
Burette with stopper.
19.4 Determination steps
XVna,to
19.4.1 pH meter positioning: Use 0.05mol/dm2 phthalic acid hydrogen rheological standard buffer solution for positioning - (11)
19.4.2 Take 25.0cm2 water sample and put it in a 50cm polyethylene wide-mouth bottle with a stopper. Take two copies of each bottle of water sample in parallel. Use a pipette to take 10.00cm hydrochloric acid standard solution and add it to the water sample. Cover and tighten it, and shake it thoroughly. 19.4.3 The pH value of the acidified water sample should be within the range of 3.40~3.90. If it is greater than 3.90, remove the electrode pair and add 1.00cm standard acid. If it is less than 3.40, add 5.0cm water sample and record the volume (cm) of hydrochloric acid standard solution or seawater added in the total alkalinity determination record sheet (Appendix C4). 20 Calculation of measurement data
The total alkalinity of seawater is calculated according to formula (12):
1 000 X at+ × (V+ Vua) -
X VHel X e(HCI)
V. X+
Wherein: Vw-
The volume of water sample, cm\
The concentration of hydrochloric acid standard solution, mal/dm: c(HCI)-
21Terminology
The volume of hydrochloric acid standard solution, cm;
The activity coefficient of hydrogen ions in the mixed solution (can be found in Appendix B5); The activity coefficient of hydrogen ions in the mixed solution (can be found in Appendix B6). Chapter 5 Determination of Active Silicate (Silicon Molybdenum Blue Method) ←12)
Active silicate refers to the dissolved silicate that can produce a yellow reaction with ammonium molybdate reagent, measured by the silicon atom in its silicate radical, represented by the symbol Siog-Si, and the unit is μmol/dm. Salt effect refers to the phenomenon that the difference in sample salinity causes the error in the measurement result. 22 Technical Indicators
22.1 Detection limit: 0.05 μ mol/dm22.2 Accuracy: When the silicate concentration is 4.5μmol/dm*, the relative error is ±5.0%. When the concentration is 45μmol/dm*, the relative error is ±3.0%.
22.3 Precision: When the silicate concentration is 4.5umol/dm, the relative standard deviation is ±4.0%. When the concentration is 45mol/dm, the relative standard deviation is: ±3.0% =
23 Determination method
23.1 Method principle
GB 12763.4-91
The active silicate in the water sample reacts with ammonium molybdate-hydrochloric acid to generate silica yellow heteropoly acid, which is then reduced to silica blue by metol-sodium sulfite and photometrically determined at a wavelength of 12 nm. 23.2 Reagents and their preparation
23.2.1 The water used for the preparation of reagents in this article is silicon-free distilled water or fresh deionized water. It should be stored in a polyethylene bottle, and the reagent blank absorbance value is about 0.05.
Silicon-free distilled water: Sub-boiling distilled water can be used: or steamed water (or rice water) can be passed through two series-connected ion exchange water purifiers. 23.2.2 Acidic ammonium molybdate solution: Weigh 8.0 g of ammonium molybdate [(NIIa)Mo;Oz+4Hz0], dissolve in 600 cm3 of distilled water, add 24.0 cm3 of concentrated acid (p-1.18 g/cm2) to dilute to 1 000 cm2, place in a polyethylene bottle. 23.2.3 Oxalic acid solution (pmc = 100 g/dm2): Weigh 10 g of oxalic acid (H2O2C)0*2H2O, dissolve in a small amount of distilled water, dilute to 100 cm2, place in a reagent bottle. 23.2.41 3 (V/V) sulfuric acid: Slowly add 100 cm2 of concentrated sulfuric acid (PuSO, 1.84 g/cm2) to 300 cm2 of distilled water while stirring and cooling in a water bath. 23.2.5 Methionin: Sodium sulfite reducing agent: Weigh 5.0 g of sodium sulfite reducing agent. $Metol [(HOC, H, NHCHa), H2SO] is dissolved in 240 cm2 of distilled water, and 3.0 g of anhydrous sodium sulfite (Na2SO4) is added. After dissolution, dilute to 250 cm2, filter with a filter membrane, and store in a brown bottle. 23.2.6 Mixed reagents
Mix 100 cm2 of metol-sodium sulfite solution and 60 cm2 of oxalic acid solution, add 120 cm2 of 1:3 (V/V) sulfuric acid, cool, dilute to 300 cm2 with distilled water, and store in a polyethylene bottle. The shelf life is two weeks. 23.2.7 Shanghai water (must be prepared with first-class reagents): Salinity 28: Weigh 25.0 g of sodium chloride (NaCl) and 8.0 g of magnesium sulfate (MgSO·7H2O) and dissolve them in distilled water without silicon, dilute to 1000 cm\, store in a polyethylene bottle; b. Salinity 35, weigh 31.0g sodium chloride and 10.0g magnesium sulfate, dissolve in a small amount of uncontaminated water and dilute to 1000cm*, store in a polyethylene bottle, artificial swimming water of other salinities can be prepared according to the above proportions. 23.2.8 Silicate series standard solution (national first-class standard material). 23.2.9 Prepare your own silicate standard solution (must be calibrated with the solution in 23.2.8 according to the provisions of 5.2). The preparation method is as follows: 23.2.9.1 Use sodium fluoride (Na2SiF.) to prepare silicate standard stock bath solution: Dry the graded sodium silicate at 105℃ for 1h, cool to room temperature in a desiccator, weigh 4.7020 ml into a polyethylene beaker, add about 300cm2 of silicon-free distilled water, stir until completely dissolved, transfer to a 1000cm2 volumetric flask, and dilute to the mark: 1.00cm of this solution contains 25. U μ mol SiO.-Si. Add 1.0 cm of monochloromethane to the polyethylene bottle.Valid for one year. 23.2.9.2 Use silicon dioxide (SiO2) to prepare silicate standard solution: weigh 0.750g silicon dioxide (first dried at 120℃ for 1h, cooled in a desiccator), add 1ε anhydrous sodium carbonate and mix well, place in a platinum solution, melt at 960~1000℃ for 1h, cool, and dissolve in hot, silicon-free water. Add 2 grains (about 0.5g) of sodium hydroxide, transfer to a 500cm volumetric flask, and dilute to the mark. This solution contains 25.0μmolSiOs-Si per 1.00cm. Place in a polyethylene bottle and add 1.0cm chloroform. Valid for 1 year
23.2.9.3 Preparation of silicate standard solution: Add 10 cm artificial seawater to a 100 cm2 bottle. Add 5 drops of 1:4 (V/V) sulfuric acid to acidify (if sodium fluorosilicate standard solution is used, acidification is not necessary). Then transfer 2.00 cm silicate standard stock solution (23.2.9.1 or 23.2.9.2) and dilute to the mark with silicon-free distilled water. This drop contains 0.500 μmol SiO.Si in 1.00 cm of the solution in a polyethylene bottle. Valid for 24 h. 23.3 Main instruments
Digital spectrophotometer;
b. 60 cm2 polyethylene bottle.
23. 4 Determination steps
GB 12763. 491
23.4.1 Establish a standard curve (0~~25.0μmol/dm): 8. Take 6 100cm2 volumetric flasks, transfer 0, 1.00, 2.00, 3.00, 1.00, 5.00cm2 of silicate standard solution into them respectively, dilute to the mark with artificial seawater with salinity close to that of the water sample. Mix and you will get a series of silicate standard solutions. b. Add 10.0cm2 of ammonium hydroxide solution into each of 12 50cm2 polyethylene bottles, and add 25.0cm of the above (a) silicon standard solution (two portions of each containing base), mix immediately, let stand for 10min (absolutely not more than 30min), add 15.0cm of mixed reagent and mix:
After 3h, use 1.0cm or 2.0cm measuring cell to compare with artificial seawater, measure the absorbance of each solution at 812nm wavelength on the spectrophotometer (the absorbance value of the small reagent plus artificial seawater is A), and record it in the standard curve data recording table (Appendix C5). The color can be stable for 12h;
d, use the least squares method to find the regression line equation of the standard curve Aa+bXr
Where: c—, the concentration of the standard solution.μmol/dtn; A—the absorbance value of the solution when it is referenced to artificial seawater—slope, that is, the regression coefficient;
a intercept, that is, the blank absorbance value of the falling liquid. -(13)
When formulating the standard curve, different numbers of concentration series are used. The requirements for the critical value of the correlation coefficient are shown in Table 3. If the values ​​in the table are not met, the standard curve must be redone. Table 3 Requirements for the correlation coefficient of different numbers of standard series Standard Melt concentration series number (m)
Correlation coefficient (↑)
23.4.2 Water sample determination
Add 10.0 cm of acidic ammonium nitrate solution to a 50 cm* polyethylene bottle, then transfer 25.0 cm2 of water sample (take two portions of each bottle of water sample), mix for 10 minutes (absolutely not more than 30 minutes), add 15.0 cm of mixed reagent, mix for 3 hours: on the spectrophotometer, use an appropriate measuring cell to compare with artificial seawater, and measure the absorbance of the water sample at 3-812 nm, and at the same time measure the blank absorbance of the reagent plus artificial seawater A, (A is determined as follows: transfer artificial seawater to two 100 cm polyethylene bottles respectively) 25.0cm, then add the reagent according to the above amount to one bottle. Determine its absorbance A; add the reagent in an effective amount of twice the amount to another bottle, determine the absorbance A, then 3
o2—A> is recorded in the active silicate determination record table (Appendix C6). If the silicate concentration is too high, it can be measured after dilution with artificial seawater. If the silicate liquid concentration in the entire surveyed sea area is high, it can be measured by the silica yellow method (Appendix A). However, water samples from different levels of the same station shall not be measured by two different methods. 24 Calculation of measurement data
24.1 The absorbance value A of active silicate in the water sample is calculated according to formula (14): Average absorbance value of water sample:
Where: Aw
Double reagent blank absorbance value;
A, - w
Ana+ An
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