A detection method and detection device for analyzing chemical oxygen demand in water

Abstract

The present invention discloses a detection method and a detection device for analyzing chemical oxygen demand in water. The method includes: S1. Collecting a water sample, filtering it and transferring it to a reflux conical flask; S2. Sequentially adding a mercuric sulfate solution, a potassium dichromate standard solution and a mixed acid solution to the reflux conical flask, stirring and mixing evenly, then heating and refluxing, and condensing to room temperature to obtain a test solution; S3. Adding a ferroin indicator solution to the test solution, and then titrating with a ferrous ammonium sulfate standard solution until the color of the test solution changes from yellow to reddish-brown, then stopping the titration, and recording the consumed volume V1 of the ferrous ammonium sulfate standard solution; Taking distilled water with the same volume as the water sample in step S1, repeating steps S2 and S3, and recording the consumed volume V0 of the ferrous ammonium sulfate standard solution; S4. Calculating the chemical oxygen demand in water according to V1 and V0. The process design of the present invention is reasonable, reducing environmental pollution and also reducing the reagent cost, and is suitable for popularization and use.

Description

Technical Field

[0001] The present invention relates to the technical field of water quality detection and analysis, and particularly relates to a detection method and a detection device for analyzing the chemical oxygen demand in water. Background Art

[0002] Chemical oxygen demand (COD) refers to the amount of strong oxidant consumed by oxidizing reducing substances in a water sample under certain conditions, expressed in mg / L of oxygen. Generally, the level of chemical oxygen demand is used to indicate the amount of organic matter in the water body. The higher the chemical oxygen demand, the more organic matter in the water body, and the more serious the pollution degree of the water body.

[0003] Currently, the commonly used method for the national standard determination of chemical oxygen demand is the dichromate method. The determination principle of the dichromate method is as follows: A known amount of potassium dichromate solution is added to the water sample, and silver salt is used as a catalyst in a strong acid medium. After boiling and refluxing, ferroin is used as an indicator, and ammonium ferrous sulfate is used to titrate the un-reduced potassium dichromate in the water sample. The mass concentration of the consumed oxygen is calculated from the amount of potassium dichromate consumed.

[0004] However, when using the dichromate method to detect COD, in addition to consuming a large amount of concentrated sulfuric acid and expensive silver sulfate during the analysis process, and adding highly toxic mercury sulfate for masking in order to eliminate the interference of chloride ions, it also requires heating or even high-temperature digestion. Therefore, the reflux time is long, the operation process is cumbersome, the determination time is long, and secondary pollution is likely to occur. Summary of the Invention

[0005] In view of the above existing technical problems, the present invention provides a detection method and a detection device for analyzing the chemical oxygen demand in water.

[0006] The technical solution of the present invention is as follows: A detection method for analyzing the chemical oxygen demand in water includes the following steps:

[0007] S1. Water sample collection and treatment

[0008] According to the nature of the detection item and the sampling technical specification, 80 - 120 ml of water sample is collected in the detection water area, and then the water sample is filtered. Finally, 15 - 30 ml of the filtered water sample is measured and transferred to a 250 - 300 ml reflux conical flask;

[0009] S2. Mixed solution

[0010] S2-1. Add a mercury sulfate solution, a potassium dichromate standard solution, and a mixed acid solution to the reflux conical flask in step S1 in sequence; and stir and mix the mercury sulfate solution, the potassium dichromate solution, and the mixed acid solution with the water sample evenly to obtain a mixed solution;

[0011] Among them, the volume ratio of the mercury sulfate solution, potassium dichromate standard solution, mixed acid solution and water sample is (0.3 - 0.5):(2 - 6):(20 - 30):(10 - 15);

[0012] The molar concentration of the potassium dichromate standard solution is 0.25 mol / L;

[0013] The molar concentration of the mercury sulfate solution is 0.15 - 0.25 mol / L;

[0014] The mixed acid solution is prepared by mixing nitric acid with a molar concentration of 0.8 - 1.5 mol / L and sulfuric acid with a molar concentration of 1.2 - 1.7 mol / L in a volume ratio of 1:3 - 5;

[0015] S2-2. Heat and reflux the mixed solution obtained in step S2-1 at a temperature of 125 - 145 °C for 20 - 50 min, and then cool it to room temperature to obtain the test solution;

[0016] S3. Determination

[0017] S3-1. Add 2 - 5 drops of ferroin indicator solution to the test solution obtained in step S2-2, and then titrate with ammonium ferrous sulfate standard solution until the color of the test solution changes from yellow to reddish-brown, and stop titration. Record the consumption volume V of the ammonium ferrous sulfate standard solution 1 ;

[0018] Among them, the molar concentration of the ammonium ferrous sulfate standard solution is 0.1 mol / L;

[0019] S3-2. Take distilled water with the same volume as the water sample in step S1, repeat steps S2-1, S2-2 and S3-1, and record the consumption volume V of the ammonium ferrous sulfate standard solution 0 ;

[0020] S4. Calculation

[0021] According to V obtained in step S3-1 1 and V obtained in step S3-2 0 , calculate the chemical oxygen demand COD in water cr ,

[0022] In the formula, c is the molar concentration of the potassium dichromate standard solution, mol / L;

[0023] 8 is 1 / 2 of the molar mass of oxygen atom, g / mol;

[0024] V is the volume of the water sample, ml.

[0025] Further, after step S1 is completed, zeolite particles are added to the reflux conical flask; the particle size of the zeolite particles is 0.1 - 0.5 mm, and the addition amount of the zeolite particles is 7 - 11% of the total volume of the water sample;

[0026] Note: By adding zeolite particles to the reflux conical flask, the sample can boil slowly at a specific temperature, reducing the possibility of local overheating, thereby improving the accuracy of the detection results.

[0027] Further, in step S1, the sampling container is a glass container;

[0028] Note: Using a glass container to store the sample can avoid the reaction between oxides in the water sample and the container, which affects the accuracy of the detection results.

[0029] Further, after step S2-1 is completed, nitrogen gas is introduced into the mixed solution at a flow rate of 50 - 80 ml / min for 15 - 30 min at room temperature;

[0030] Note: By introducing an inert gas into the mixed solution, the chloride ions in the water sample are carried away in the form of hydrogen chloride by the inert gas, avoiding the over - high determination result value caused by the oxidation of chloride ions by potassium dichromate.

[0031] Further, after step S1 is completed, the water sample is homogenized at an ultrasonic frequency of 50 - 70 kHz for 20 - 45 min under the temperature condition of 20 - 35 °C;

[0032] Note: By performing ultrasonic homogenization treatment on the water sample, the interference of suspended substances in the water sample on the detection results can be avoided, thereby improving the representativeness of the water sample.

[0033] Further, after step S1 is completed, sulfur dioxide gas is introduced into the water sample and continuously aerated for 15 - 30 min; among them, the flow rate of the sulfur dioxide gas is 15 - 25 ml / min;

[0034] Note: By introducing sulfur dioxide gas into the water sample, the interference of residual oxidants in the water sample on the detection results can be effectively excluded, improving the accuracy of the COD value detection in the water body.

[0035] The present invention also provides a detection device for analyzing the chemical oxygen demand in water, including a sampling device for collecting water samples and a reflux condensation device for reflux - condensing the water samples. The reflux condensation device includes a base, a condenser tube fixing component, a connection component, a cooling component, and an electric heating furnace; a placement cavity is arranged inside the base, a protective cylinder is arranged at the upper end of the base, and through - chutes and transfer - chutes are vertically arranged on the side wall of the protective cylinder;

[0036] The condenser pipe fixing assembly includes a fixing plate, a limiting sleeve and a fixing clamp. Two fixing plates are provided. The two fixing plates are arranged in parallel and fixedly connected to the upper end of the protective tube. Through holes are provided at the center positions of the two fixing plates. Several sliding slots are provided on the two fixing plates and located outside the through holes. The limiting sleeve is fixedly arranged between the two fixing plates and located outside the through holes. Slots are provided at locations on the limiting sleeve corresponding to the positions of the sliding slots. Several fixing clamps are provided, and each fixing clamp is movably arranged inside each sliding slot in a one-to-one corresponding manner.

[0037] The connection assembly includes a sliding frame and a pipeline connection seat. The sliding frame is arranged inside the protective tube and is slidably engaged with the through slide groove. A toggle block is arranged on the sliding frame. The pipeline connection seat is arranged on the sliding frame and corresponds to the upper and lower positions of the placement cavity. A pipeline clamping hole is arranged on the pipeline connection seat.

[0038] The cooling assembly includes an outer protective tube and a docking turntable. Two docking turntables are provided. The two docking turntables are respectively rotatably connected to the through holes on the two fixed disks. The two docking turntables are provided with docking grooves. The docking turntable located on the upper fixed disk is provided with a hand push rod. The outer protective tube is respectively slidably connected with the two docking turntables through the docking grooves. Two first pipe joints are provided on the side wall of the outer protective tube. Two second pipe joints are provided on the top of the outer protective tube. The two first pipe joints and the two second pipe joints are connected one by one through conduits.

[0039] The electric heating furnace is movably connected to the interior of the placement cavity.

[0040] Furthermore, heat insulation cotton is provided at the connection between the electric heating furnace and the placement cavity;

[0041] Note: By setting up thermal insulation cotton, the heat preservation effect in the reflux conical flask can be improved, thereby improving the evaporation efficiency of the water sample.

[0042] Furthermore, the fixing clamp is composed of two oppositely arranged support plates, one end of the two support plates close to the fixing plate is provided with an arc groove, and a protective strip is provided inside the arc groove, one end of the two support plates close to the fixing plate is respectively hinged to the sliding slot through a spring rod, and one end of the two support plates away from the fixing plate is respectively hinged to the sliding slot;

[0043] Description: By providing an arc groove on the support clamp, the condenser tube can be accurately positioned; by providing a spring rod, the stable clamping effect of the support clamp on the condenser tube can be improved.

[0044] Furthermore, a guide slide bar is arranged inside the sliding groove, and the sliding frame is slidably engaged with the guide slide bar;

[0045] Note: Using a guide slide rod to connect the sliding frame and the protective tube is beneficial to improving the stability of the sliding frame when moving, thereby facilitating improving the accuracy of docking the condenser tube and the reflux conical flask.

[0046] The method for using the reflux condensing device of the present invention is:

[0047] When in use, the reflux conical flask is placed on the electric heating furnace through the transfer groove on the protective tube, and then the condenser is placed in a set of sliding slots corresponding to the upper and lower positions of the two fixed plates, and fixed with a fixing clamp; the evaporation tube and the reflux tube are arranged in the pipeline clamp holes of the pipeline connecting seat, and then the sliding frame is moved by the toggle block to connect the evaporation tube with the bottom end of the condenser tube, and the reflux tube with the top end of the condenser tube; the outer protective tube is pushed to move in the docking groove by the hand push rod, so that the two first pipe joints pass through the slots on the limit sleeve to dock with the condenser, and the two second pipe joints are respectively connected to the cooling assembly; finally, the electric heating furnace is turned on to carry out reflux condensation of the water sample.

[0048] Compared with the prior art, the beneficial effects of the present invention are embodied in the following aspects:

[0049] First, the method of the present invention is reasonably designed, so that the sampling volume of consumable reagents and water samples is effectively reduced, thereby reducing the use of hazardous chemicals, which not only reduces the risk of environmental pollution during the detection process, but also makes the detection data more accurate;

[0050] Second, in the process of detecting chemical oxygen demand in water, the present invention changes the catalyst to mixed acid, which greatly shortens the heating and reflux time of the sample, not only saving energy consumption, but also improving the efficiency of water quality detection;

[0051] Third, the present invention uses mercuric sulfate solution to replace the consumable reagents silver nitrate solution and bismuth nitrate solution in the prior art. Since silver nitrate is an explosive hazardous chemical, the present invention can not only reduce the use of explosive hazardous chemicals, but also the mercuric sulfate solution can better remove chlorides in water samples, eliminating the interference of chlorides on the test results;

[0052] Fourthly, the present invention also provides a detection device for analyzing chemical oxygen demand in water, wherein the reflux condensation device can realize continuous reflux condensation operation of multiple test samples, which is practical and reliable, and effectively improves the efficiency of water quality detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 is a longitudinal sectional view of the reflux condensing device of the present invention;

[0054] Figure 2 is a front view of the reflux condensing device of the present invention;

[0055] Figure 3It is a schematic diagram of the connection between the limiting sleeve and the fixing plate of the present invention;

[0056] Figure 4 It is a schematic diagram of the connection between the sliding frame and the protective tube of the present invention;

[0057] Figure 5 It is a schematic diagram of the connection between the docking turntable and the fixed disk of the present invention;

[0058] Figure 6 It is a schematic structural diagram of the outer protective tube of the present invention;

[0059] Among them, 1-base, 10-placing cavity, 11-protective cylinder, 110-through slide groove, 1100-guide slide rod, 111-transfer groove, 2-condenser fixing assembly, 20-fixed plate, 200-sliding slot, 21-limiting sleeve, 210-slot, 22-fixing clamp, 220-supporting clamp, 221-arc groove, 2210-protective strip, 222-spring rod, 3-connecting assembly, 30-sliding frame, 300-toggle block, 31-pipeline connecting seat, 310-pipeline clamp hole, 4-cooling assembly, 40-outer protective tube, 400-first pipe joint, 401-second pipe joint, 41-docking turntable, 410-docking slot, 411-hand push rod, 5-electric heating furnace. DETAILED DESCRIPTION

[0060] Example 1

[0061] A detection method for analyzing chemical oxygen demand in water, comprising the following steps:

[0062] S1. Water sample collection and processing

[0063] According to the nature of the test project and the sampling technical specifications, collect 80ml of water sample in the test water area, and then filter the water sample; finally, measure 15ml of the filtered water sample and transfer it to a 250ml reflux conical flask;

[0064] S2, mixed liquid

[0065] S2-1, sequentially add mercuric sulfate solution, potassium dichromate standard solution and mixed acid solution to the reflux conical flask in step S1; and stir and mix the mercuric sulfate solution, potassium dichromate solution and mixed acid solution with the water sample to obtain a mixed solution;

[0066] The volume ratio of mercuric sulfate solution, potassium dichromate standard solution, mixed acid solution and water sample is 0.3:2:20:10;

[0067] The molar concentration of potassium dichromate standard solution is 0.25 mol / L;

[0068] The molar concentration of mercuric sulfate solution is 0.15 mol / L;

[0069] The mixed acid solution is prepared by mixing nitric acid with a molar concentration of 0.8 mol / L and sulfuric acid with a molar concentration of 1.2 mol / L in a volume ratio of 1:3;

[0070] S2-2. Heat the mixed solution obtained in step S2-1 under reflux at 125 °C for 20 min, and then condense it to room temperature to obtain the test solution;

[0071] S3. Determination

[0072] S3-1. Add 2 drops of ferroin indicator solution to the test solution obtained in step S2-2, and then titrate with ammonium ferrous sulfate standard solution until the color of the test solution changes from yellow to reddish-brown, and then stop titration. Record the consumed volume V of the ammonium ferrous sulfate standard solution 1 ;

[0073] Among them, the molar concentration of the ammonium ferrous sulfate standard solution is 0.1 mol / L;

[0074] S3-2. Take distilled water with the same volume as the water sample in step S1, repeat steps S2-1, S2-2 and S3-1, and record the consumed volume V of the ammonium ferrous sulfate standard solution 0 ;

[0075] S4. Calculation

[0076] According to V obtained in step S3-1 1 and V obtained in step S3-2 0 , calculate the chemical oxygen demand COD in water cr ,

[0077] In the formula, c is the molar concentration of the potassium dichromate standard solution, mol / L;

[0078] 8 is 1 / 2 of the molar mass of oxygen atom, g / mol;

[0079] V is the volume of the water sample, ml.

[0080] Example 2

[0081] A detection method for analyzing the chemical oxygen demand in water, comprising the following steps:

[0082] S1. Water sample collection and treatment

[0083] According to the nature of the detection item and the sampling technical specification, collect 100 ml of water sample in the detection water area using a glass container, and then filter the water sample; finally, measure 20 ml of the filtered water sample and transfer it to a 260 ml reflux conical flask; add zeolite particles to the reflux conical flask, the particle size of the zeolite particles is 0.1 - 0.3 mm, and the addition amount of the zeolite particles is 7% of the total volume of the water sample;

[0084] S2, Mixed solution

[0085] S2-1: Sequentially add mercuric sulfate solution, potassium dichromate standard solution, and mixed acid solution to the reflux conical flask in step S1; and stir and mix the mercuric sulfate solution, potassium dichromate solution, and mixed acid solution with the water sample evenly to obtain a mixed solution;

[0086] Among them, the volume ratio of the mercuric sulfate solution, potassium dichromate standard solution, mixed acid solution, and water sample is 0.4:4:23:12;

[0087] The molar concentration of the potassium dichromate standard solution is 0.25 mol / L;

[0088] The molar concentration of the mercuric sulfate solution is 0.20 mol / L;

[0089] The mixed acid solution is prepared by mixing nitric acid with a molar concentration of 1.2 mol / L and sulfuric acid with a molar concentration of 1.5 mol / L according to a volume ratio of 1:4;

[0090] S2-2: Heat and reflux the mixed solution obtained in step S2-1 at a temperature of 135 °C for 30 min, and then condense it to room temperature to obtain a test solution;

[0091] S3, Determination

[0092] S3-1: Add 3 drops of ferroin indicator solution to the test solution obtained in step S2-2, and then titrate with ammonium ferrous sulfate standard solution until the color of the test solution changes from yellow to reddish-brown, and stop titration. Record the consumption volume V of the ammonium ferrous sulfate standard solution 1 ;

[0093] Among them, the molar concentration of the ammonium ferrous sulfate standard solution is 0.1 mol / L;

[0094] S3-2: Take distilled water with the same volume as the water sample in step S1, repeat steps S2-1, S2-2, and S3-1, and record the consumption volume V of the ammonium ferrous sulfate standard solution 0 ;

[0095] S4, Calculation

[0096] According to V obtained in step S3-1 1 and V obtained in step S3-2 0 , calculate the chemical oxygen demand COD in water cr ,

[0097] In the formula, c is the molar concentration of the potassium dichromate standard solution, mol / L;

[0098] 8 is 1 / 2 of the molar mass of oxygen atom, g / mol;

[0099] V is the volume of the water sample, ml.

[0100] Example 3

[0101] A detection method for analyzing the chemical oxygen demand in water, comprising the following steps:

[0102] S1. Water sample collection and treatment

[0103] According to the nature of the detection item and the sampling technical specification, 80 ml of water sample is collected in the detection water area, and then the water sample is filtered; finally, 15 ml of the filtered water sample is measured and transferred to a 250 ml reflux conical flask; sulfur dioxide gas is introduced into the water sample, and continuous aeration treatment is carried out for 15 min; wherein, the flow rate of the sulfur dioxide gas is 15 ml / min;

[0104] S2. Mixed solution

[0105] S2-1. Add mercuric sulfate solution, potassium dichromate standard solution and mixed acid solution to the reflux conical flask in step S1 in sequence; and stir and mix the mercuric sulfate solution, potassium dichromate solution and mixed acid solution with the water sample evenly to obtain a mixed solution; nitrogen gas is introduced into the mixed solution at a flow rate of 50 ml / min at room temperature for 15 min;

[0106] Wherein, the volume ratio of the mercuric sulfate solution, potassium dichromate standard solution, mixed acid solution and water sample is 0.3:2:20:10;

[0107] The molar concentration of the potassium dichromate standard solution is 0.25 mol / L;

[0108] The molar concentration of the mercuric sulfate solution is 0.15 mol / L;

[0109] The mixed acid solution is prepared by compounding nitric acid with a molar concentration of 0.8 mol / L and sulfuric acid with a molar concentration of 1.2 mol / L according to a volume ratio of 1:3;

[0110] S2-2. Heat and reflux the mixed solution obtained in step S2-1 at a temperature of 125 °C for 20 min, and then condense it to room temperature to obtain a test solution;

[0111] S3. Determination

[0112] S3-1. Add 2 drops of ferroin indicator solution to the test solution obtained in step S2-2, and then titrate with ammonium ferrous sulfate standard solution until the color of the test solution changes from yellow to reddish-brown, and stop titration. Record the consumed volume V of the ammonium ferrous sulfate standard solution 1 ;

[0113] Among them, the molar concentration of the ammonium ferrous sulfate standard solution is 0.1 mol / L;

[0114] S3-2: Take the same volume of distilled water as the water sample in step S1, repeat steps S2-1, S2-2, and S3-1, and record the consumed volume V of the ammonium ferrous sulfate standard solution 0 ;

[0115] S4: Calculate

[0116] According to V obtained in step S3-1 1 and V obtained in step S3-2 0 , calculate the chemical oxygen demand COD in the water cr ,

[0117] In the formula, c is the molar concentration of the potassium dichromate standard solution, mol / L;

[0118] 8 is 1 / 2 of the molar mass of the oxygen atom, g / mol;

[0119] V is the volume of the water sample, ml.

[0120] Example 4

[0121] A detection method for analyzing the chemical oxygen demand in water, comprising the following steps:

[0122] S1: Water sample collection and treatment

[0123] According to the nature of the detection item and the sampling technical specification, collect 100 ml of water sample in the detection water area, then filter the water sample; finally measure 20 ml of the filtered water sample and transfer it to a 260 ml reflux conical flask; homogenize the water sample at a temperature of 20 °C and an ultrasonic frequency of 50 kHz for 20 min;

[0124] S2: Mixed solution

[0125] S2-1: Add a mercury sulfate solution, a potassium dichromate standard solution, and a mixed acid solution to the reflux conical flask in step S1 in sequence; and stir and mix the mercury sulfate solution, the potassium dichromate solution, and the mixed acid solution with the water sample evenly to obtain a mixed solution;

[0126] Among them, the volume ratio of the mercury sulfate solution, the potassium dichromate standard solution, the mixed acid solution, and the water sample is 0.4:4:23:12;

[0127] The molar concentration of the potassium dichromate standard solution is 0.25 mol / L;

[0128] The molar concentration of the mercury sulfate solution is 0.20 mol / L;

[0129] The mixed acid solution is prepared by mixing nitric acid with a molar concentration of 1.2 mol / L and sulfuric acid with a molar concentration of 1.5 mol / L in a volume ratio of 1:4;

[0130] S2-2. Heat the mixed solution obtained in step S2-1 under reflux at 135 °C for 30 min, and then cool it to room temperature to obtain the test solution;

[0131] S3. Measurement

[0132] S3-1. Add 3 drops of ferroin indicator solution to the test solution obtained in step S2-2, and then titrate with ammonium ferrous sulfate standard solution until the color of the test solution changes from yellow to reddish-brown, and stop titration. Record the consumption volume V of the ammonium ferrous sulfate standard solution 1 ;

[0133] Among them, the molar concentration of the ammonium ferrous sulfate standard solution is 0.1 mol / L;

[0134] S3-2. Take distilled water with the same volume as the water sample in step S1, repeat steps S2-1, S2-2 and S3-1, and record the consumption volume V of the ammonium ferrous sulfate standard solution 0 ;

[0135] S4. Calculation

[0136] According to V obtained in step S3-1 1 and V obtained in step S3-2 0 , calculate the chemical oxygen demand COD in water cr ,

[0137] In the formula, c is the molar concentration of the potassium dichromate standard solution, mol / L;

[0138] 8 is 1 / 2 of the molar mass of oxygen atom, g / mol;;

[0139] V is the volume of the water sample, ml.

[0140] Example 5

[0141] A detection method for analyzing the chemical oxygen demand in water, comprising the following steps:

[0142] S1. Water sample collection and treatment

[0143] According to the nature of the detection items and the sampling technical specifications, 100 ml of water sample is collected in a glass container from the detection water area, and then the water sample is filtered; finally, 20 ml of the filtered water sample is measured and transferred to a 260 ml reflux conical flask; zeolite particles are added to the reflux conical flask; the particle size of the zeolite particles is 0.2 - 0.5 mm, and the addition amount of the zeolite particles is 11% of the total volume of the water sample; the water sample is homogenized at a temperature of 35 °C and an ultrasonic frequency of 70 kHz for 45 min; sulfur dioxide gas is introduced into the water sample, and continuous aeration treatment is carried out for 30 min; among them, the flow rate of the sulfur dioxide gas is 25 ml / min;

[0144] S2, mixed solution

[0145] S2-1. Add mercury sulfate solution, potassium dichromate standard solution and mixed acid solution to the reflux conical flask in step S1 in sequence; and stir and mix the mercury sulfate solution, potassium dichromate solution and mixed acid solution with the water sample evenly to obtain a mixed solution; nitrogen is introduced into the mixed solution at a flow rate of 80 ml / min at room temperature for 30 min;

[0146] Among them, the volume ratio of the mercury sulfate solution, potassium dichromate standard solution, mixed acid solution and water sample is 0.3:2:20:10;

[0147] The molar concentration of the potassium dichromate standard solution is 0.25 mol / L;

[0148] The molar concentration of the mercury sulfate solution is 0.20 mol / L;

[0149] The mixed acid solution is prepared by mixing nitric acid with a molar concentration of 1.2 mol / L and sulfuric acid with a molar concentration of 1.5 mol / L in a volume ratio of 1:4;

[0150] S2-2. Heat and reflux the mixed solution obtained in step S2-1 at a temperature of 130 °C for 20 min, and then condense it to room temperature to obtain a test solution;

[0151] S3. Determination

[0152] S3-1. Add 3 drops of ferroin indicator solution to the test solution obtained in step S2-2, and then titrate with ammonium ferrous sulfate standard solution until the color of the test solution changes from yellow to reddish-brown and stop titration, record the consumption volume V of the ammonium ferrous sulfate standard solution 1 ;

[0153] Among them, the molar concentration of the ammonium ferrous sulfate standard solution is 0.1 mol / L;

[0154] S3-2. Take distilled water with the same volume as the water sample in step S1, repeat steps S2-1, S2-2 and S3-1, and record the consumption volume V of the ammonium ferrous sulfate standard solution0 ;

[0155] S4. Calculate

[0156] Based on the V obtained in step S3-1 1 and the V obtained in step S3-2 0 , calculate the chemical oxygen demand COD in water cr ,

[0157] In the formula, c is the molar concentration of the potassium dichromate standard solution, mol / L;

[0158] 8 is 1 / 2 of the molar mass of oxygen atom, g / mol;

[0159] V is the volume of the water sample, ml.

[0160] Example 6

[0161] This example describes a detection device for analyzing the chemical oxygen demand in water applicable to Examples 1-5;

[0162] As Figure 1 , 2 , 4 shown, it includes a sampling device for collecting water samples and a reflux condensation device for refluxing and condensing the water samples. The reflux condensation device includes a base 1, a condenser tube fixing component 2, a connection component 3, a cooling component 4 and an electric heating furnace 5; a placement cavity 10 is arranged inside the base 1, a protective cylinder 11 is arranged at the upper end of the base, and through chutes 110 and transfer chutes 111 are vertically arranged on the side wall of the protective cylinder 11; a guiding slide bar 1100 is arranged inside the through chute 110;

[0163] As Figure 1 , 3As shown in Figures 5, the condenser fixing assembly 2 includes a fixing plate 20, a limiting sleeve 21 and a fixing clip 22. There are two fixing plates 20 which are arranged in parallel and fixedly connected to the upper end of the protective cylinder 11. Through holes are provided at the central positions of the two fixing plates 20, and 4 sliding slots 200 are provided on each of the two fixing plates 20 outside the through holes; the limiting sleeve 21 is fixedly arranged between the two fixing plates 20 and is located outside the through hole, and slots 210 are provided at positions corresponding to the sliding slots 200 on the limiting sleeve 21; there are 8 fixing clips 22, and each fixing clip 22 is respectively movably arranged inside each sliding slot 200; the fixing clip 22 is composed of two oppositely arranged support clamping plates 220. Arc-shaped grooves 221 are provided at one ends of the two support clamping plates 220 close to the fixing plate 20, and protective strips 2210 are arranged inside the arc-shaped grooves 221. One ends of the two support clamping plates 220 close to the fixing plate 20 are respectively movably hinged to the sliding slot 200 through spring rods 222, and one ends of the two support clamping plates 220 far from the fixing plate 20 are respectively movably hinged to the sliding slot 200;

[0164] As Figure 1 、 4 shown, the connecting assembly 3 includes a sliding frame 30 and a pipeline connecting seat 31. The sliding frame 30 is arranged inside the protective cylinder 11, and the sliding frame 30 is slidably clamped with the guiding slide rod 1100; a toggle block 300 is arranged on the sliding frame 30, the pipeline connecting seat 31 is arranged on the sliding frame 30 and corresponds to the placement cavity 10 in the up and down positions, and a pipeline clamping hole 310 is arranged on the pipeline connecting seat 31;

[0165] As Figure 1 、 5 shown in Figures 6, the cooling assembly 4 includes an outer protection tube 40 and a docking turntable 41. There are two docking turntables 41 which are respectively rotatably clamped inside the through holes on the two fixing plates 20. Docking grooves 410 are provided on the two docking turntables 41, and a hand push rod 411 is arranged on the docking turntable 41 on the upper fixing plate 20; the outer protection tube 40 is respectively slidably clamped with the two docking turntables 41 through the docking grooves 410. Two first pipe joints 400 are arranged on the side wall of the outer protection tube 40, two second pipe joints 401 are arranged at the top of the outer protection tube 40, and the two first pipe joints 400 and the two second pipe joints 401 are connected in one-to-one correspondence through a conduit;

[0166] As Figure 1 shown, the electric heating furnace 5 is movably clamped inside the placement cavity 10, and a heat insulation cotton is arranged at the connection between the electric heating furnace 5 and the placement cavity 10; the electric heating furnace 5 is a commercially available product and is powered by an external power supply.

[0167] Test Example

[0168] The methods of Embodiments 1-5 of the present invention were respectively used to detect the chemical oxygen demand of domestic wastewater and chemical industrial wastewater, and the detection results are shown in Table 1:

[0169] Table 1 Influence of different detection conditions on the detection results of chemical oxygen demand of wastewater;

[0170] Embodiment Domestic wastewater Chemical industrial wastewater 1 165.2 259.5 2 168.5 264.3 3 170.1 269.8 4 176.4 273.6 5 178.9 278.5

[0171] From the data in Table 1, it can be seen that compared with Embodiment 1, in Embodiment 2, by adding zeolite particles into the reflux conical flask, the sample can boil slowly at a specific temperature, reducing the possibility of local overheating, thereby improving the accuracy of the detection results; using a glass container to store the sample can avoid the reaction between oxides in the water sample and the container, which affects the accuracy of the detection results;

[0172] Compared with Embodiment 1, in Embodiment 3, by introducing an inert gas into the mixed solution, the chloride ions in the water sample are taken away in the form of hydrogen chloride by the inert gas, avoiding the over - high determination result value caused by the oxidation of chloride ions by potassium dichromate; by introducing sulfur dioxide gas into the water sample, the interference of residual oxidants in the water sample on the detection results can be effectively eliminated, improving the accuracy of the COD value detection in the water body;

[0173] Compared with Embodiment 1, in Embodiment 4, by performing ultrasonic homogenization treatment on the water sample, the interference of suspended substances in the water sample on the detection results can be avoided, improving the representativeness of the water sample, which is beneficial to improving the accuracy of the chemical oxygen demand detection results in the water;

[0174] Compared with Embodiments 1 - 4, in Embodiment 5, by comprehensively optimizing various favorable conditions, the accuracy of the detection results is improved under the premise of improving the detection efficiency.

Claims

1. A detection method for analyzing chemical oxygen demand in water, characterized in that, it includes the following steps: S1. Water sample collection and treatment According to the nature of the detection item and the sampling technical specification, 80 - 120 ml of water sample is collected in the detection water area, and then the water sample is filtered; finally, 15 - 30 ml of the filtered water sample is measured and transferred to a reflux conical flask of 250 - 300 ml; S2. Mixed solution S2-1. Add mercury sulfate solution, potassium dichromate standard solution and mixed acid solution to the reflux conical flask described in step S1 in sequence; and stir and mix the mercury sulfate solution, potassium dichromate solution and mixed acid solution with the water sample evenly to obtain a mixed solution; Among them, the volume ratio of the mercury sulfate solution, potassium dichromate standard solution, mixed acid solution and water sample is (0.3 - 0.5):(2 - 6):(20 - 30):(10 - 15); The molar concentration of the potassium dichromate standard solution is 0.25 mol / L; The molar concentration of the mercury sulfate solution is 0.15 - 0.25 mol / L; The mixed acid solution is prepared by compounding nitric acid with a molar concentration of 0.8 - 1.5 mol / L and sulfuric acid with a molar concentration of 1.2 - 1.7 mol / L according to a volume ratio of 1:3 - 5; S2-2. Heat and reflux the mixed solution obtained in step S2-1 at a temperature of 125 - 145 °C for 20 - 50 min, and then condense it to room temperature to obtain a test solution; S3. Determination S3-1. Add 2 - 5 drops of ferroin indicator solution to the test solution obtained in step S2-2, and then titrate with ammonium ferrous sulfate standard solution until the color of the test solution changes from yellow to reddish-brown, and then stop titration. Record the consumed volume V of the ammonium ferrous sulfate standard solution 1 ; Among them, the molar concentration of the ammonium ferrous sulfate standard solution is 0.1 mol / L; S3-2. Take distilled water with the same volume as the water sample in step S1, repeat steps S2-1, S2-2, and S3-1, and record the consumed volume V of the ammonium ferrous sulfate standard solution. 0 ; S4. Calculation Based on the V obtained in step S3-1 1 and the V obtained in step S3-2 0 , calculate the chemical oxygen demand COD in water cr , In the formula, c is the molar concentration of the potassium dichromate standard solution, mol / L; 8 is 1 / 2 of the molar mass of oxygen atom, g / mol; V is the volume of the water sample, ml; A device applicable to the above method includes a sampling device for collecting water samples and a reflux condensation device for refluxing and condensing water samples. The reflux condensation device includes a base (1), a condenser tube fixing component (2), a connecting component (3), a cooling component (4) and an electric heating furnace (5); a placement cavity (10) is arranged inside the base (1), a protective cylinder (11) is arranged at the upper end of the base, and a through chute (110) and a transfer chute (111) are vertically arranged on the side wall of the protective cylinder (11); The condenser tube fixing component (2) includes a fixing plate (20), a limiting sleeve (21) and a fixing clip (22). There are two fixing plates (20), the two fixing plates (20) are arranged in parallel and fixedly connected to the upper end of the protective cylinder (11). Through holes are arranged at the central positions of the two fixing plates (20), and several sliding card slots (200) are arranged on the two fixing plates (20) and outside the through holes; the limiting sleeve (21) is fixedly arranged between the two fixing plates (20) and outside the through hole, and slots (210) are arranged at positions corresponding to each sliding card slot (200) on the limiting sleeve (21); several fixing clips (22) are arranged, and each fixing clip (22) is respectively movably arranged inside each sliding card slot (200); The connecting assembly (3) comprises a sliding frame (30) and a pipeline connecting seat (31); the sliding frame (30) is arranged inside the protective tube (11) and is slidably engaged with the through slide groove (110); a toggle block (300) is arranged on the sliding frame (30); the pipeline connecting seat (31) is arranged on the sliding frame (30) and corresponds to the upper and lower positions of the placement cavity (10); and a pipeline clamping hole (310) is arranged on the pipeline connecting seat (31); The cooling assembly (4) comprises an outer protective tube (40) and a docking turntable (41), wherein two docking turntables (41) are provided, and the two docking turntables (41) are respectively rotatably engaged with the inside of through holes on the two fixed disks (20), and the two docking turntables (41) are both provided with docking grooves (410), and the docking turntable (41) located on the upper fixed disk (20) is provided with a push rod (411); the outer protective tube (40) is respectively slidably engaged with the two docking turntables (41) through the docking grooves (410), two first pipe joints (400) are provided on the side wall of the outer protective tube (40), and two second pipe joints (401) are provided on the top of the outer protective tube (40), and the two first pipe joints (400) and the two second pipe joints (401) are connected one-to-one through conduits; The electric heating furnace (5) is movably connected to the interior of the placement cavity (10); The connection between the electric heating furnace (5) and the placement cavity (10) is provided with heat insulation cotton; The fixing clamp (22) is composed of two oppositely arranged supporting plates (220), and one end of the two supporting plates (220) close to the fixing plate (20) is provided with an arc groove (221), and a protective strip (2210) is provided inside the arc groove (221), and one end of the two supporting plates (220) close to the fixing plate (20) is movably hinged to the sliding slot (200) through a spring rod (222), and one end of the two supporting plates (220) away from the fixing plate (20) is movably hinged to the sliding slot (200).

2. A detection method for analyzing chemical oxygen demand in water according to claim 1, It is characterized in that After step S1 is completed, zeolite particles are added to the reflux conical flask; the particle size of the zeolite particles is 0.1-0.5 mm, and the amount of zeolite particles added is 7-11% of the total volume of the water sample.

3. A detection method for analyzing chemical oxygen demand in water according to claim 1, It is characterized in that In step S1, the sampling container is a glass container.

4. A detection method for analyzing chemical oxygen demand in water according to claim 1, It is characterized in that After step S2-1 is completed, nitrogen is introduced into the mixed solution at a flow rate of 50 to 80 ml / min for 15 to 30 min at room temperature.

5. A detection method for analyzing chemical oxygen demand in water according to claim 1, It is characterized in that After step S1 is completed, the water sample is homogenized at a temperature of 20 to 35° C. and an ultrasonic frequency of 50 to 70 kHz for 20 to 45 minutes.

6. A detection method for analyzing chemical oxygen demand in water according to claim 1, characterized in that, after step S1 is completed, sulfur dioxide gas is introduced into the water sample, and continuous aeration treatment is carried out for 15 to 30 minutes; wherein, the flow rate of the sulfur dioxide gas is 15 to 25 ml / min.

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