Rapid detection method for total nitrogen and total phosphorus in seawater

Abstract

The invention discloses a method for rapidly detecting total nitrogen and total phosphorus in seawater. The method comprises the following steps: collecting a seawater sample to be detected; adding an alkaline persulfate solution into the seawater sample for digestion; screening out an inorganic nitrogen kit and an orthophosphate kit suitable for seawater quality detection from common nitrogen and phosphorus rapid detection kits in the market; and determining total nitrogen and total phosphorus in the digested seawater sample by using the screened inorganic nitrogen kit and orthophosphate kit, and the like. The method has the remarkable effects that the operation is rapid and convenient, the accuracy is reliable, the total nitrogen and the total phosphorus can be measured at the same time, secondary digestion is not needed, the application scene is not limited, the method is suitable for on-site monitoring of the total nitrogen and the total phosphorus in a sewage treatment plant and a fishery breeding plant, the detection time and the detection cost are greatly reduced, and the detection efficiency is improved.

Description

Technical Field

[0001] The invention relates to the technical field of water quality detection, and in particular to a method for rapid detection of total nitrogen and total phosphorus in seawater. Background Art

[0002] Total nitrogen includes inorganic nitrogen such as nitrate, nitrite and ammonium salt, and organic nitrogen such as protein, amino acid, RNA, enzyme and organic amine. The total nitrogen content is one of the important indicators to measure the quality of fishery water. It is often used to indicate the degree of water pollution by nutrients and is one of the main items for the detection of fishery tail water. The total phosphorus includes elemental phosphorus, orthophosphate, condensed sulfate, pyrophosphate, metaphosphate and phosphate combined with organic groups. Excessive phosphorus will cause the water to be dirty and smelly, resulting in eutrophication of the water and the appearance of red tide in the receiving bay. Therefore, it is very necessary to detect the total nitrogen and total phosphorus in the water quality.

[0003] At present, the laboratory analysis method of total nitrogen in seawater often uses alkaline potassium persulfate digestion-ultraviolet spectrophotometry, and the experimental laboratory analysis method of total phosphorus in seawater often uses potassium persulfate digestion-ammonium molybdate spectrophotometry. The existing seawater detection methods and the determination methods of total nitrogen and total phosphorus in water quality are relatively cumbersome in pre-treatment, and the manual work is long, and there is also a certain pollution to the reagents and tools used for determination, which brings inconvenience to the analysis work. In addition, the analysis process is carried out separately for the detection of the two parameters of total nitrogen and total phosphorus, and the digestion time is 30 minutes. Therefore, if the total nitrogen and total phosphorus content in seawater is to be detected, the two independent digestion processes from heating to sample cooling to room temperature will take about 5 hours, which greatly reduces the detection efficiency. The seawater samples after digestion are determined by spectrophotometry. The detection technology has high requirements on equipment, the operation steps are cumbersome, and the experimental process can only be carried out in the laboratory, and on-site monitoring cannot be achieved. Summary of the invention

[0004] In view of the deficiencies in the prior art, the purpose of the present invention is to provide a method for rapid detection of total nitrogen and total phosphorus in seawater, which can detect total nitrogen and total phosphorus in seawater in a simple, intuitive, rapid, sensitive, accurate, low-cost and easy-to-carry manner.

[0005] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] A rapid detection method for total nitrogen and total phosphorus in seawater, the key of which is: comprising the following steps:

[0007] Step 1, water sample collection: collect the seawater sample to be tested;

[0008] Step 2, sample digestion: adding alkaline persulfate solution to the seawater sample for digestion;

[0009] Step 3, kit screening: select inorganic nitrogen kit and orthophosphate kit suitable for seawater quality testing from the common nitrogen and phosphorus rapid test kits on the market;

[0010] Step 4, sample testing: Use the screened inorganic nitrogen kit and orthophosphate kit to determine the total nitrogen and total phosphorus in the digested seawater sample.

[0011] Furthermore, the alkaline persulfate solution in step 2 is an alkaline sodium persulfate solution or an alkaline potassium persulfate solution.

[0012] Furthermore, the preparation method of the alkaline sodium persulfate solution is: weighing sodium hydroxide and potassium persulfate in a mass ratio of 3:10, respectively, dissolving them with pure water and fixing the volume;

[0013] The preparation method of the alkaline potassium persulfate solution is: weigh sodium hydroxide and potassium persulfate in a mass ratio of 3:10, respectively, and dissolve and fix the volume with pure water.

[0014] Furthermore, in step 2, if alkaline sodium persulfate solution is used for sample digestion, the digestion temperature is 150° C. and the digestion time is 5 min; if alkaline potassium persulfate solution is used for sample digestion, the digestion temperature is 150° C. and the digestion time is 10 min.

[0015] Furthermore, in step 2, after adding the alkaline persulfate solution to the seawater sample, the pH value of the mixed solution is 6.5 to 7.5.

[0016] Further, the specific steps of performing sample digestion in step 2 are:

[0017] Step 2.1, placing the digestion container in the portable digestion device, and injecting the seawater sample into the digestion container;

[0018] Step 2.2, adding alkaline persulfate solution into the digestion container;

[0019] Step 2.3, shake and mix, heat, and digest at 150°C for 5 to 10 minutes;

[0020] Step 2.4: After digestion is completed, take out the digestion container and cool it naturally to room temperature.

[0021] Furthermore, the screening steps of the inorganic nitrogen kit in step 3 are:

[0022] A1. Through market research, select several alternative inorganic nitrogen test kits that are currently highly recognized in the market;

[0023] A2. Prepare artificial seawater and total nitrogen standard solution, and test the influence of seawater matrix effect on several selected inorganic nitrogen test kits;

[0024] A3. Based on the test results, select the alternative inorganic nitrogen test kit that is least affected by the seawater matrix as the required inorganic nitrogen test kit.

[0025] Further, the screening steps of the orthophosphate kit in step 3 are:

[0026] B1. Through market research, select several alternative orthophosphate test kits that are currently highly recognized in the market;

[0027] B2. Prepare artificial seawater and total phosphorus standard solution, and test the influence of seawater matrix effect on several selected orthophosphate test kits;

[0028] B3. Based on the test results, select the alternative orthophosphate kit that is least affected by the seawater matrix as the required orthophosphate kit.

[0029] Furthermore, the specific steps of using the screened inorganic nitrogen kit to determine the total nitrogen in the digested seawater sample in step 4 are:

[0030] Step C1, taking a certain amount of digested seawater sample and adding it into a total nitrogen determination container;

[0031] Step C2, adding K-1 reagent for total nitrogen determination into the total nitrogen determination container;

[0032] Step C3, adding K-2 reagent for total nitrogen determination into the total nitrogen determination container;

[0033] Step C4, covering the total nitrogen determination container with a lid and shaking for a first time period;

[0034] Step C5, removing the lid of the total nitrogen determination container and leaving it to stand for a second period of time;

[0035] Step C6, pulling out the wire at the top of the total nitrogen determination tube;

[0036] Step C7, place the water absorption hole of the total nitrogen determination tube upward, pinch the lower part of the total nitrogen determination tube with your fingers, and squeeze out the air in the total nitrogen determination tube;

[0037] Step C8, place the water absorption hole of the total nitrogen determination tube in the seawater sample, release your fingers, wait for the seawater sample to be completely absorbed into the total nitrogen determination tube, and shake to mix;

[0038] Step C9: After the third time period, place the total nitrogen determination tube on the white background of the standard card for colorimetry to obtain the total nitrogen measurement value of the seawater sample.

[0039] Furthermore, the specific steps of using the screened orthophosphate kit in step 4 to determine the total phosphorus in the digested seawater sample are:

[0040] Step D1, taking a certain amount of digested seawater sample and adding it into a total phosphorus determination container;

[0041] Step D2, adding K-1 reagent for total phosphorus determination into the total phosphorus determination container;

[0042] Step D3, cover the total phosphorus determination container with a lid and shake for a fourth period of time;

[0043] Step D4, pulling out the wire at the top of the total phosphorus determination tube;

[0044] Step D5, with the water absorption hole of the total phosphorus determination tube facing upward, pinch the lower part of the total phosphorus determination tube with your fingers to squeeze out the air in the total phosphorus determination tube;

[0045] Step D6, place the water absorption hole of the total phosphorus determination tube directly into the test water, place it in the seawater sample, release your fingers, and shake to mix;

[0046] Step D7: After the fifth period of time, place the total phosphorus determination tube on the white background of the standard card for colorimetry to obtain the total phosphorus measurement value of the seawater sample.

[0047] The remarkable effects of the present invention are:

[0048] (1) The method of the present invention is fast, convenient, and accurate, and can simultaneously measure total nitrogen and total phosphorus without the need for secondary digestion. The method is not limited in application scenarios and is suitable for on-site monitoring of total nitrogen and total phosphorus in sewage treatment plants and fishery farms, which greatly reduces the detection time and cost and improves the detection efficiency.

[0049] (2) The use of a portable digestion device avoids the drawbacks of slow total nitrogen and total phosphorus analysis caused by high temperature and high pressure conditions. The digestion temperature does not need to be too high, which helps to shorten the detection time and improve the detection efficiency.

[0050] (3) The present invention can simultaneously digest total nitrogen and total phosphorus in seawater without the need to digest the water sample twice. The digestion time is only 10 minutes, which further speeds up the detection time and improves the detection efficiency.

[0051] (4) The present invention adds alkaline persulfate before digestion, adjusts the water sample to a specific alkaline condition, neutralizes the sulfuric acid produced after the persulfate oxidatively decomposes the total nitrogen solution, and the pH of the water sample after digestion is close to neutral, and can be directly measured using a total nitrogen and total phosphorus rapid test kit;

[0052] (5) The method of the present invention is a conventional rapid semi-quantitative detection method, which is to screen seawater samples on site under non-laboratory conditions, does not require large equipment and highly skilled personnel, avoids waste of manpower and material resources, can greatly simplify the operation process, shorten the detection time, and can complete on-site sample detection within 30 minutes;

[0053] (6) The total nitrogen and total phosphorus rapid test kit screened by the present invention is not affected by the seawater matrix and can eliminate the interference of matrix effects such as seawater salinity and hardness on the measurement results. The measurement results are accurate and suitable for the determination of total nitrogen and total phosphorus in seawater of different salinities and hardnesses. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 is a flow chart of the method of the present invention;

[0055] Figure 2 It is a schematic diagram of the structure of a water sample collection device;

[0056] Figure 3 yes Figure 2 A is a partial enlarged schematic diagram;

[0057] Figure 4 It is a schematic diagram of the structure of a portable digestion device;

[0058] Figure 5 It is the piping structure diagram of the portable digestion device;

[0059] Figure 6 It is the control principle block diagram of the portable digestion device;

[0060] Figure 7 It is the usage status diagram of the digestion container.

[0061] Explanation of the reference numerals: 100, water sample collection device; 11, shell; 11a, sealing groove; 12, counterweight chamber; 13, partition; 14, sampling chamber; 15, first sealing assembly; 16, first inlet; 17, battery pack; 18, hatch; 19, second sealing assembly; 191, sealing drive motor; 192, drive rod; 193, sealing plate; 110, second inlet; 111, pressure sensor; 112, first controller; 113, liquid level sensor; 114, sealing plug; 115, lifting ring; 116, first sealing member; 117, second sealing member; 200, portable digestion device; 21, first flow meter; 22, second flow meter ; 23. Thermometer; 24. Operation button; 25. Interface module; 26. Power module; 27. Second controller; 28. First control valve; 29. ​​First infusion pump; 210. Second control valve; 211. Second infusion pump; 212. Heating assembly; 213. Oscillation assembly; 2131. Installation cavity; 2132. First oscillation motor; 2133. Second oscillation motor; 2134. Third oscillation motor; 2135. Support plate; 214. Display module; 215. First liquid storage cavity; 216. Second liquid storage cavity; 217. First infusion tube; 218. Second infusion tube; 219. Digestion container; 220 Housing; 221. Protective cover. DETAILED DESCRIPTION

[0062] The specific implementation manner and working principle of the present invention are further described in detail below with reference to the accompanying drawings.

[0063] Embodiment 1:

[0064] like Figure 1 As shown, this embodiment proposes a rapid detection method for total nitrogen and total phosphorus in seawater, and the specific steps are as follows:

[0065] Step 1, water sample collection: using the water sample collection device 100 to collect the seawater sample to be tested;

[0066] In this embodiment, the structure of the water sample collection device 100 is as follows: Figure 2 As shown, it includes a hollow and sealed shell 11, in which a counterweight chamber 12 and a sampling chamber 14 are divided by a partition 13. A first inlet 16 connected to the counterweight chamber 12 is opened at the upper part of the shell 11, and a first sealing component 15 for on-off control of the first inlet 16 is arranged in the shell 11. A second inlet 110 connected to the sampling chamber 14 is opened at the lower part of the shell 11, and a second sealing component 19 for on-off control of the second inlet 110 is arranged in the shell 11. A liquid outlet is opened at the bottom of the sampling chamber 14, and a sealing plug 114 is threadedly connected to the liquid outlet.

[0067] Based on the above structure, the weight of the water sample collection device 100 can be adjusted by controlling the weight of the seawater in the counterweight chamber 12, so that the water sample collection device 100 can sink to different depths to achieve seawater sampling at different depths. When the required depth is reached, the second sealing component 19 is controlled to open, and seawater enters the sampling chamber 14 through the second inlet 110. After the sampling is completed, the second sealing component 19 is controlled to close, and the sampling of the seawater sample can be achieved. After the water sample collection device 100 is recovered, the seawater sample in the sampling chamber 14 can be poured out by opening the sealing plug 114 at the bottom.

[0068] from Figure 2 It can also be seen that a first controller 112 is arranged in the partition 13, a liquid level sensor 113 is arranged on the lower surface of the partition 13, and a pressure sensor 111 is arranged on the outer wall of the shell 11. The output ends of the pressure sensor 111 and the liquid level sensor 113 are connected to the input end of the first controller 112, and the output end of the first controller 112 is connected to the control end of the first sealing component 15 and the second sealing component 19.

[0069] By detecting the pressure at the location of the water sample collection device 100 through the pressure sensor 111, the depth of the location of the water sample collection device 100 can be calculated based on the knowledge of physics, combined with the density of seawater and the acceleration of gravity, so that the first controller 112 can control the first sealing component 15 to control the amount of seawater in the counterweight chamber 12, thereby adjusting the deadweight of the water sample collection device 100. When the water sample collection device 100 reaches the specified depth and the pressure sensor 111 detects that the pressure value is stable, the first controller 112 sends a control signal to control the second sealing component 19 to open, and seawater enters the sampling chamber 14 through the second inlet 110. After the sampling is completed, the second sealing component 19 is controlled to close. During the sampling process, the liquid level of the sampled seawater sample can be detected through the detection signal of the liquid level sensor 113, so that the first controller 112 can control the state of the second sealing component 19 to control the volume of the sampled seawater sample.

[0070] from Figure 2 It can also be seen that a battery pack 17 for powering the first controller 112 is installed in the partition 13 , and a hatch 18 is arranged on the shell 11 , and the battery pack 17 can be replaced by opening and closing the hatch 18 .

[0071] A hanging ring 115 is fixed on the top of the housing 11 , and the hanging ring 115 can be connected to a pull rope, so as to facilitate the lowering and recovery of the water sample collection device 100 .

[0072] In this embodiment, the structures of the first sealing component 15 and the second sealing component 19 are consistent. In this embodiment, the second sealing component 19 is taken as an example for description. Figure 3 The second sealing assembly 19 includes a sealing drive motor 191, a drive rod 192, and a sealing plate 193. The sealing drive motor 191 is embedded in the shell 11 above the second inlet 110. A sealing groove 11a is opened on the shell 11 around the second inlet 110. The sealing plate 193 is slidably arranged in the sealing groove 11a. The upper end of the sealing plate 193 is fixedly connected to the output shaft of the sealing drive motor 191 through the drive rod 192. The sealing drive motor 191 can drive the sealing plate 193 to move up and down through the drive rod 192. A first sealing member 116 and a second sealing member 117 are fixed in the sealing groove 11a, wherein the first sealing member 116 is located above the sealing plate 193, and the second sealing member 117 is located below the sealing plate 193.

[0073] The output shaft of the sealing drive motor 191 can make corresponding actions according to the control signal of the first controller 112, so that the sealing plate 193 can be driven to move up and down through the driving rod 192 to realize the opening and closing control of the second inlet 110, and then control the start and end of the sampling process. And through the arrangement of the first sealing member 116 and the second sealing member 117, the sealing plate 193 can be sealed, so that the sampling chamber 14 is sealed, thereby preventing seawater from other depths from entering the sampling chamber 14 to contaminate the collected seawater samples, making the final detection data more reliable.

[0074] In a specific implementation process, the first controller 112 can also communicate with a host computer through a communication module, so as to facilitate monitoring and control of the entire seawater sample sampling process.

[0075] When collecting seawater samples, firstly, the collection depth of the water sample collection device 100 is set according to the determined needs, and then the water sample collection device 100 is placed in the seawater to let it sink naturally. At the same time, the pressure sensor 111 detects the depth position of the water sample collection device 100. When the water sample collection device 100 stops sinking, the pressure signal is calculated. If the collection depth is less than the preset collection depth, the first controller 112 sends a control signal, the first sealing component 15 opens the first inlet 16, and seawater enters the counterweight chamber 12, changing the deadweight of the water sample collection device 100, so that the water sample collection device 100 continues to sink until the set depth is reached. The first controller 112 sends a control signal to control the first sealing component 15 to close the first inlet 16; after the signal value detected by the pressure sensor 111 is stable, that is, after the depth position of the water sample collection device 100 is stable, the first controller 112 sends a control signal to control the second sealing component 19 to open the second inlet 110 to collect seawater samples. Compared with directly starting the seawater sample collection, the final detection data can be made more reliable and less affected by accidental factors. During the sampling process, the liquid level of the seawater sample in the sampling chamber 14 is monitored in real time by the liquid level sensor 113. When the required liquid level is reached, the first controller 112 sends a control signal to the second sealing component 19 to close the second inlet 110 and stop collecting seawater samples. At this time, the water sample collection device 100 can be taken out of the seawater to complete the entire seawater sample collection process.

[0076] Step 2, sample digestion: inject the seawater sample into a digestion container, add alkaline potassium persulfate solution to the seawater sample for digestion, place the digestion container in a portable digestion device for digestion, and after the digestion, the total nitrogen in the water sample is completely oxidized to nitrate nitrogen, and the total phosphorus is completely oxidized to orthophosphate;

[0077] In this example, the potassium persulfate concentration in the alkaline potassium persulfate solution is close to saturation, which is 50 g / L, ensuring that the total nitrogen and total phosphorus in the water sample can be fully digested. The sodium hydroxide concentration is 15 g / L, ensuring that the pH of the seawater sample after digestion is close to neutral, ensuring that the detection process of the total nitrogen and total phosphorus test kit is not interfered by the pH of the water sample, and the seawater sample can be directly tested for total nitrogen and total phosphorus.

[0078] like Figure 4-Figure 7 As shown, the portable digestion device 200 includes a housing 220, in which a first liquid storage chamber 215, a second liquid storage chamber 216, a second controller 27, a first control valve 28, a first infusion pump 29, a second control valve 210, a second infusion pump 211, a heating component 212, an oscillating component 213, a first infusion tube 217, a second infusion tube 218, and a digestion container 219 are arranged. The outlet of the first liquid storage chamber 215 is connected to the inlet of the first infusion tube 217, and the first control valve 28 and the first infusion pump 29 are arranged on the first infusion tube 217 in sequence. The second liquid storage chamber 210, the second infusion pump 211, the heating component 212, the oscillating component 213, the first infusion tube 217, the second infusion tube 218, and the digestion container 219 are arranged. 6 is connected to the inlet of the second infusion tube 218, and the second control valve 210 and the second infusion pump 211 are sequentially arranged on the second infusion tube 218. The outlet of the first infusion tube 217 and the outlet of the second infusion tube 218 both extend into the digestion container 219. The digestion container 219 is placed on the oscillation component 213, and a heating component 212 is circumferentially arranged around the digestion container 219. The outer shell 220 above the digestion container 219 is connected to a protective cover through a driving component. When the protective cover covers the digestion container 219 and its upper surface is flush with the upper surface of the outer shell 220.

[0079] When sample digestion is required, the seawater sample and the alkaline persulfate solution are respectively loaded into the first liquid storage chamber 215 and the second liquid storage chamber 216, then the lid of the digestion container 219 is opened, the first control valve 28 and the first infusion pump 29 are opened (the first control valve 28, the first infusion pump 29, the second control valve 210 and the second infusion pump 211 are all in a closed state initially), a certain amount of seawater sample is added into the digestion container 219, and then the first control valve 28 and the first infusion pump 29 are closed; then, the second control valve 210 and the second infusion pump 211 are opened, a certain amount of alkaline persulfate solution is injected into the digestion container 219, and then the second control valve 210 and the second infusion pump 211 are closed; then, the lid of the digestion container 219 is closed, the oscillation component 213 is controlled to work to oscillate and mix the mixed solution in the digestion container 219, and at the same time, the heating component 212 is controlled to heat the mixed solution in the digestion container 219 to the required digestion temperature and then keep it warm until the digestion is completed. After the digestion is completed, open the protective cover, take out the digestion container 219 and cool it naturally to room temperature to complete the entire digestion process. This device avoids the defects of slow analysis of total nitrogen and total phosphorus due to high temperature and high pressure conditions by oscillating, mixing and heating during the digestion process. The digestion temperature does not need to be too high, which helps to shorten the detection time and improve the detection efficiency; it can digest the total nitrogen and total phosphorus of seawater at the same time, without the need to digest the water sample twice, and the digestion time is only 10 minutes, which further speeds up the detection time and improves the detection efficiency; this device can be used for digestion anytime and anywhere, without being restricted by the application scenario, and does not require large equipment and highly skilled personnel, avoiding the waste of manpower and material resources, and can greatly simplify the operation process.

[0080] from Figure 4 It can also be seen that the shell 220 is stepped, an operation button 24 is arranged on the front side of the shell 220, an interface module 25 is arranged on the right side wall of the shell 220, a display module 214 is arranged on the upper surface of the first step, and the pipeline part of the device is arranged in the second step.

[0081] The digestion process can be controlled and the digestion parameters can be set by operating the buttons 24. The temperature, time and other data of the digestion process can be displayed in real time by the display module 214, so that the detection personnel can grasp the digestion progress. The data export of the device or the input of the control program can be realized by the interface module 25.

[0082] The structure of the pipeline part of this device is as follows Figure 5 As shown, the first infusion tube 217 and the second infusion tube 218 are respectively provided with a first flow meter 21 and a second flow meter 22. The first flow meter 21 and the second flow meter 22 can accurately control the flow of the solution in the first infusion tube 217 and the second infusion tube 218.

[0083] A second controller 27, a thermometer 23, and a power module 26 are also provided in the housing 220. Specifically, the principle block diagram of the portable digestion device 200 of this embodiment is as follows: Figure 6 As shown, the input end group of the second controller 27 is connected to the output ends of the first flowmeter 21, the second flowmeter 22, the thermometer 23, and the operation button 24, the output end group of the second controller 27 is connected to the control ends of the first control valve 28, the first infusion pump 29, the second control valve 210, the second infusion pump 211, the heating component 212, and the oscillation component 213, the second controller 27 also exchanges data with the interface module 25, the second controller 27 is also connected to the input end of the display module 214, and the power module 26 is used to provide working power for the above-mentioned modules, thereby realizing the mobile digestion of the portable digestion device 200.

[0084] The second control module can detect the flow of the solution in the first infusion tube 217 and the second infusion tube 218 through the setting of the first flowmeter 21 and the second flowmeter 22, detect the temperature of the solution in the digestion container 219 through the thermometer 23, and obtain the input instructions of the detection personnel through the operation button 24. The second control module controls the working states of the first control valve 28, the first infusion pump 29, the second control valve 210, the second infusion pump 211, the heating component 212, and the oscillation component 213 according to the signals obtained by the detection and the input instructions, thereby realizing fully automatic digestion of seawater samples.

[0085] See attached Figure 7 In this example, the matching structure of the shell 220, the oscillation component 213, the digestion container 219 and the heating component 212 is shown in the figure. The oscillation component 213 is arranged in the shell 220, the digestion container 219 is placed on the oscillation component 213, the heating component 212 is arranged around the side of the digestion container 219, and the protective cover is arranged on the top of the digestion container 219 during digestion. Specifically, the oscillation component 213 includes an installation cavity 2131 opened in the shell 220, and a first oscillation motor 2132, a second oscillation motor 2133, a third oscillation motor 2134 and a support plate 2135 are arranged in the installation cavity 2131. The first oscillation motor 2132, the second oscillation motor 2133, and the third oscillation motor 2134 are distributed in an equilateral triangle, and the output shafts of the first oscillation motor 2132, the second oscillation motor 2133, and the third oscillation motor 2134 are all connected to the lower surface of the support plate 2135. The digestion container 219 is placed on the upper surface of the support plate 2135, and a fixing part 222 for fixing the digestion container 219 is formed on the upper surface of the support plate 2135.

[0086] Based on the above structure, by controlling the movement sequence and direction of the output shafts of the first oscillation motor 2132, the second oscillation motor 2133, and the third oscillation motor 2134, the inclination angle and inclination direction of the support plate 2135 can be changed, thereby realizing the oscillation of the digestion container 219 to mix the solution in the digestion container 219, thereby speeding up the digestion time and improving the digestion efficiency.

[0087] Based on the portable digestion device 200 of the above structure, the specific steps of sample digestion in this step are:

[0088] Step 2.1, prepare 10mL alkaline potassium persulfate solution, including 0.5g potassium persulfate and 0.15g sodium hydroxide;

[0089] Step 2.2, placing the digestion container 219 in the portable digestion device 200, opening the lid of the digestion container 219, and opening the first control valve 28 and the first infusion pump 29, and accurately injecting 5 mL of seawater sample into the digestion container 219 by measuring through the first flowmeter 21; then opening the second control valve 210 and the second infusion pump 211, and accurately adding 0.5 mL of the alkaline potassium persulfate solution prepared in step 2.1 into the digestion container 219 by measuring through the second flowmeter 22;

[0090] Step 2.3, after closing the lid of the digestion container 219, the second controller 27 controls the driving member to close the protective cover 221, and then controls the oscillating component 213 to oscillate and mix the mixed solution in the digestion container 219, and then controls the heating component 212 to heat and digest at 150°C for 10 minutes;

[0091] Step 2.4: After the digestion is completed, the second controller 27 first controls the driving member to open the protective cover 221, takes out the digestion container 219, and allows the seawater sample to cool naturally to room temperature.

[0092] Step 3, kit screening: From the common nitrogen and phosphorus rapid test kits on the market, select inorganic nitrogen kits and orthophosphate kits with high sensitivity, convenient operation, accurate test results and suitable for seawater quality testing;

[0093] Specifically, the total nitrogen and total phosphorus in the seawater samples are converted into nitrate nitrogen and orthophosphate respectively after digestion. Therefore, the total nitrogen can be tested using the total inorganic nitrogen rapid test kit or the nitrate nitrogen rapid test kit, and the total phosphorus can be tested using the orthophosphate rapid test kit.

[0094] In this example, the screening steps of the inorganic nitrogen kit are:

[0095] A1. Through market research, four alternative inorganic nitrogen test kits were selected, including the inorganic nitrogen test kit of Japan Kyoritsu Instrument Co., Ltd., the inorganic nitrogen test kit of Shenzhen Fink Instrument Co., Ltd., the inorganic nitrogen test kit of Zhejiang Luheng Environmental Technology Co., Ltd., and the nitric acid nitrogen test kit of Japan Kyoritsu Instrument Co., Ltd.;

[0096] A2. Prepare artificial seawater and total nitrogen standard solution, and test the influence of seawater matrix effect on several selected inorganic nitrogen test kits through experiments; the test process is as follows:

[0097] Preparation of artificial seawater: Weigh 31.0 g of sodium chloride, 10.0 g of magnesium sulfate and 0.5 g of sodium bicarbonate, dissolve in water, dilute to 1 L, and obtain seawater with a salinity of 35.

[0098] Screening test of candidate total nitrogen test kits: potassium nitrate nitrogen (in terms of N) was used as the total nitrogen standard, 0.5 mL of the standard solution with a total nitrogen concentration of 100 mg / L was measured, diluted to 10 mL with artificial seawater, and mixed to obtain a total nitrogen standard solution with a concentration of 5 mg / L, which was determined using 4 test kits. The test results are shown in Table 1. The results show that the inorganic nitrogen test kits of Shenzhen Fink Instrument Co., Ltd. and Zhejiang Luheng Environmental Technology Co., Ltd. have a determination concentration of 1 and 0.5 mg / L, respectively, and the nitrate nitrogen test kit of Japan Kyoritsu Instrument Co., Ltd. has a determination concentration of 2 mg / L. The test results are all lower than the actual values, indicating that the seawater matrix has a greater interference with the determination of the above three test kits. Only the inorganic nitrogen test kit of Japan Kyoritsu Instrument Co., Ltd. has a determination result of 5 mg / L, indicating that the test kit is not interfered by the seawater matrix and can be used as a rapid test kit for total nitrogen in seawater.

[0099] Table 1 Effect of seawater matrix on the test results

[0100]

[0101] A3. According to the test results, the alternative inorganic nitrogen test kit that is least affected by the seawater matrix is ​​selected, that is, the inorganic nitrogen test kit of Kyoritsu Instruments Co., Ltd. of Japan as the required inorganic nitrogen test kit.

[0102] In this example, the screening steps of the orthophosphate kit are:

[0103] B1. Through market research, four alternative orthophosphate test kits were selected, including the orthophosphate test kits of Japan Kyoritsu Instruments Co., Ltd., Shenzhen Fink Instrument Co., Ltd., Zhejiang Luheng Environmental Technology Co., Ltd., and Guangdong Zhongke Gongchuang Technology Co., Ltd., which have high market recognition.

[0104] B2. Prepare artificial seawater and total phosphorus standard solution, and test the influence of seawater matrix effect on several selected orthophosphate test kits through experiments; the test process is as follows:

[0105] Preparation of artificial seawater: Weigh 31.0 g of sodium chloride, 10.0 g of magnesium sulfate and 0.5 g of sodium bicarbonate, dissolve in water, dilute to 1 L, and obtain seawater with a salinity of 35.

[0106] Screening test of candidate total phosphorus test kits: potassium dihydrogen phosphate (in terms of P) was used as the total phosphorus standard, and 10 mL of 1 mg / L total phosphorus standard solution was prepared with artificial seawater, and the test was performed with 5 test kits. The test results are shown in Table 2. The orthophosphate test kits of Zhejiang Luheng Environmental Technology Co., Ltd. and Guangdong Zhongke Gongchuang Technology Co., Ltd. were 2 mg / L and 5 mg / L, respectively, which were high; only the orthophosphate test kit (high concentration) of Japan Kyoritsu Instrument Co., Ltd. and the orthophosphate test kit of Shenzhen Fink Instrument Co., Ltd. had a test result of 1 mg / L, which was not interfered by the seawater matrix and could be used as seawater total phosphorus detection kits.

[0107] Table 2 Results of seawater matrix effect determination

[0108]

[0109] Based on the seawater matrix effect, the orthophosphate test kit of Kyoritsu Instruments Co., Ltd. of Japan and the orthophosphate test kit of Shenzhen Fink Instruments Co., Ltd. were screened out, and the sensitivity, detection range and color development time of the two test kits were further compared.

[0110] The test results are shown in Table 3. The detection range of the two kits is 0-5 mg / L, but the orthophosphate kit of Japan Kyoritsu Instruments Co., Ltd. has a higher sensitivity of 0.1 mg / L and a shorter color development time of only 1 minute. Therefore, the orthophosphate kit of Japan Kyoritsu Instruments Co., Ltd. is more suitable for the rapid detection of total phosphorus in seawater.

[0111] Table 3 Comparison results of two orthophosphate kits

[0112]

[0113] B3. Based on the test results, select the alternative orthophosphate test kit that is least affected by the seawater matrix, that is, the orthophosphate test kit of Kyoritsu Instruments Co., Ltd. of Japan as the required orthophosphate test kit.

[0114] The total nitrogen and total phosphorus rapid test kit screened out in this embodiment is not affected by the seawater matrix, can eliminate the interference of matrix effects such as seawater salinity and hardness on the measurement results, and the measurement results are accurate, and is suitable for the determination of total nitrogen and total phosphorus in seawater of different salinities and hardnesses.

[0115] Step 4, sample testing: Use the screened inorganic nitrogen kit and orthophosphate kit to determine the total nitrogen and total phosphorus in the digested seawater sample.

[0116] In this example, the specific steps for determining the total nitrogen in the digested seawater sample using the screened inorganic nitrogen kit are as follows:

[0117] Step C1, taking 0.3 mL of the digested seawater sample and adding it into a total nitrogen determination container;

[0118] Step C2, adding 1.5 mL of K-1 reagent for total nitrogen determination into the total nitrogen determination container;

[0119] Step C3, cut off the K-2 reagent (in a small bag) and add it to the total nitrogen determination container;

[0120] Step C4, cover the total nitrogen determination container with a lid and shake for 30 seconds;

[0121] Step C5, remove the lid of the total nitrogen determination container and let it stand for 15 minutes;

[0122] Step C6, pulling out the wire at the top of the total nitrogen determination tube;

[0123] Step C7, place the water absorption hole of the total nitrogen determination tube upward, pinch the lower part of the total nitrogen determination tube with your fingers, and squeeze out the air in the total nitrogen determination tube;

[0124] Step C8, place the water absorption hole of the total nitrogen determination tube in the seawater sample, release your fingers, wait for the seawater sample to be completely absorbed into the total nitrogen determination tube, shake and mix for about 10 times, and be careful not to let the liquid leak out;

[0125] Step C9: After 5 minutes, place the total nitrogen determination tube on the white background of the standard card for colorimetry. The closest standard color value is the measured value of the test water, and the total nitrogen measurement value of the seawater sample is obtained.

[0126] In this example, the specific steps for determining the total phosphorus in the digested seawater sample using the screened orthophosphate kit are as follows:

[0127] Step D1, taking 1.5 mL of the digested seawater sample and adding it into a total phosphorus determination container;

[0128] Step D2, adding 4 drops of K-1 reagent for total phosphorus determination into the total phosphorus determination container;

[0129] Step D3, cover the total phosphorus determination container with a lid and shake it 2 to 3 times;

[0130] Step D4, pulling out the wire at the top of the total phosphorus determination tube;

[0131] Step D5, with the water absorption hole of the total phosphorus determination tube facing upward, pinch the lower part of the total phosphorus determination tube with your fingers to squeeze out the air in the total phosphorus determination tube;

[0132] Step D6, place the water absorption hole of the total phosphorus determination tube directly into the test water, place it in the seawater sample, release your fingers, shake and mix for about 5 to 6 times, and be careful not to let the liquid leak;

[0133] Step D7: After 1 minute, place the total phosphorus determination tube on the white background of the standard card for colorimetry to obtain the total phosphorus measurement value of the seawater sample.

[0134] This embodiment also optimizes the sodium hydroxide concentration in the digestion reagent to control the pH of the water sample after digestion, so that the water sample after digestion can be directly used for the test kit determination, without having to adjust the pH of the water sample after digestion according to the pH applicable range of the total nitrogen and total phosphorus test kits.

[0135] Take 5 sample digestion containers 219, add 10 mg / L total nitrogen and 2 mg / L total phosphorus standards in sequence, then add 0.5 mL of alkaline potassium persulfate solution with sodium hydroxide concentrations of 0, 10, 12, 15 and 20 g / L, dilute to 5 mL with artificial seawater, and screw on the lid to mix. Put 5 test tubes into the portable digestion device 200, digest at 150 ° C for 10 minutes, stop heating, take out the digestion container 219, and cool naturally to room temperature. Determine with the total inorganic nitrogen kit and orthophosphate kit of Japan Kyoritsu Instrument Co., Ltd. respectively. The results show that when the sodium hydroxide concentration is too high or too low, it has a greater impact on the measurement results. When the sodium hydroxide concentration is 15 mg / L, the solution is close to neutral, and the pH is 7.1. At this time, the total nitrogen and total phosphorus have the highest recovery rates, both of which are 100%.

[0136] Table 4 Effect of sodium hydroxide concentration

[0137]

[0138]

[0139] This embodiment also optimizes the volume of alkaline potassium persulfate during the digestion process, so that on the one hand, the total nitrogen and total phosphorus in the water sample are completely digested, and on the other hand, the pH of the water sample after digestion can be adjusted so that the water sample after digestion can be directly used for the test kit determination.

[0140] Take 4 sample digestion containers 219, add 10 mg / L total nitrogen and 2 mg / L total phosphorus standards in sequence, then add 0, 0.1, 0.3 and 0.5 mL of alkaline potassium persulfate solution with a sodium hydroxide concentration of 15 g / L, dilute to 5 mL with artificial seawater, and screw on the cap to mix. Put the 4 digestion containers 219 into the portable digestion device 200, digest at 150°C for 10 min, stop heating, take out the digestion container 219, and cool naturally to room temperature. Use the total inorganic nitrogen kit and orthophosphate kit of Kyoritsu Instrument Co., Ltd. of Japan for determination respectively. The results show that when the volume of alkaline potassium persulfate is 0.5 mL, the spiked recoveries of total nitrogen and total phosphorus are both 100%.

[0141] Table 5 Effect of alkaline potassium persulfate volume results

[0142]

[0143] Embodiment 2:

[0144] The difference between this embodiment and embodiment 1 is that alkaline sodium persulfate is used as a digestion reagent in step 2, and the digestion time of the seawater sample can be reduced from the original 10 minutes to 5 minutes.

[0145] This example also verifies the influence of alkaline potassium persulfate and alkaline sodium persulfate as digestion reagents on the determination results of total nitrogen and total phosphorus in seawater through experiments. The specific experimental process is:

[0146] Alkaline sodium persulfate: Take a digestion container 219, add 10 mg / L total nitrogen and 2 mg / L total phosphorus standards, dilute to 5 mL with artificial seawater, then add 80 mg sodium persulfate powder and 40 uL 600 g / L sodium hydroxide solution, respectively; place the digestion container 219 in the portable digestion device 200, digest at 150°C for 5 min, stop heating, take out the digestion container 219, and cool naturally to room temperature. Determine total nitrogen and total phosphorus using the total inorganic nitrogen kit and orthophosphate kit of Kyoritsu Instruments Co., Ltd.

[0147] Alkaline potassium persulfate: Take a digestion container 219, add a total nitrogen standard sample with a concentration of 10 mg / L and a total phosphorus standard sample with a concentration of 2 mg / L, dilute to 5 mL with artificial seawater, then add 0.5 mL of an alkaline potassium persulfate solution with a sodium hydroxide concentration of 15 g / L and a potassium persulfate concentration of 50 g / L, dilute to 5 mL with artificial seawater, then place the digestion container 219 in the portable digestion device 200, digest at 150°C for 10 min, stop heating, take out the digestion container 219, and cool naturally to room temperature. Determine total nitrogen and total phosphorus using the total inorganic nitrogen kit and orthophosphate kit of Kyoritsu Instruments Co., Ltd.

[0148] The results of total nitrogen and total phosphorus determination using the two digestion reagents are shown in Table 6.

[0149] Table 6 Comparison of the results of the two digestion reagents

[0150]

[0151] As can be seen from Table 6, the spiked recoveries of total nitrogen and total phosphorus were both 100%, indicating that both alkaline sodium persulfate and alkaline potassium persulfate digestion reagents are feasible, and the alkaline sodium persulfate digestion time is shorter.

[0152] Embodiment 3:

[0153] In this embodiment, actual samples were collected, and the total nitrogen and total phosphorus determination results of Example 1 of the present invention were compared with the determination results of the standard method. Marine aquaculture water bodies of 7 white shrimp farms in Putian City were collected, and the total nitrogen was determined by the standard method for determination of total nitrogen in "Determination of Total Nitrogen in Water Quality Flow Injection-Naphthylethylenediamine Hydrochloride Spectrophotometry" (HJ 668-2013) and the rapid detection method for total nitrogen in seawater, and the total phosphorus was determined by the standard method for determination of total phosphorus in "Determination of Total Phosphorus in Water Quality Flow Injection-Ammonium Molybdate Spectrophotometry" (HJ 671-2013) and the rapid detection method for total phosphorus in seawater, and the determination results of the two methods were compared.

[0154] When the total phosphorus and total nitrogen concentrations of the samples are low, the concentration errors of the two methods are small, but the relative errors are large. In order to objectively reflect the comparability of the two methods: when the total nitrogen concentration is less than or equal to 3 mg / L, or the total phosphorus concentration is less than or equal to 1 mg / L, the measurement results of the two methods are expressed in absolute errors; when the total nitrogen concentration is greater than 3 mg / L or the total phosphorus concentration is greater than 1 mg / L, the measurement results of the two methods are expressed in relative errors. The results are detailed in Tables 7 and 8.

[0155] Table 7 Comparison results of total nitrogen detection methods in aquaculture tail water

[0156]

[0157] Table 8 Comparison results of total phosphorus detection methods in aquaculture tail water

[0158]

[0159] It can be seen from Table 7 and Table 8 that when the total nitrogen concentration of seawater samples is between 0 and 3 mg / L, the absolute values ​​of the absolute errors of the two methods are less than 0.5 mg / L; when the total nitrogen concentration of seawater samples is between 3 and 10 mg / L, the relative errors of the two methods are between -29.97% and 7.18%. When the total phosphorus concentration of seawater samples is between 0 and 1 mg / L, the absolute values ​​of the absolute errors of the two methods are less than 0.1 mg / L; when the concentration of seawater samples is between 1 and 5 mg / L, the relative errors are between -25.09% and 21.21%. Therefore, compared with the standard method, when the total nitrogen and total phosphorus concentrations of water samples are low, the absolute error of this method is lower, and when the total nitrogen and total phosphorus concentrations of water samples are high, the relative error of this method is lower, indicating that the results of this method are accurate and reliable, the operation is simple and standardized, and it has good promotion.

[0160] In summary, the method of the present invention adds alkaline persulfate before digestion, adjusts the water sample to a specific alkaline condition, neutralizes the sulfuric acid produced after the persulfate oxidative decomposition of the total nitrogen solution, and the pH of the water sample after digestion is close to neutral, and can be directly measured using the total nitrogen and total phosphorus quick test kit; at the same time, the portable digestion device 200 is used to avoid the defect of slow analysis speed of total nitrogen and total phosphorus caused by high temperature and high pressure conditions, and the digestion temperature does not need to be too high, which helps to shorten the detection time and improve the detection efficiency; in addition, the total nitrogen and total phosphorus of seawater can be digested at the same time, without the need to digest the water sample twice, and the digestion time is only 10min, which further speeds up the detection time and improves the detection efficiency; it is suitable for on-site monitoring of total nitrogen and total phosphorus in sewage treatment plants and fishery breeding plants, greatly reducing the detection time and detection cost, and improving the detection efficiency. In addition, the present invention is a conventional rapid semi-quantitative detection, which is to screen seawater samples on site under non-laboratory conditions, does not require large-scale equipment and high-tech personnel, avoids the waste of manpower and material resources, can greatly simplify the operation process, shorten the detection time, and can complete the on-site sample detection within 30 minutes.

[0161] The technical solution provided by the present invention is described in detail above. Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea. It should be pointed out that for ordinary technicians in this technical field, without departing from the principle of the present invention, the present invention can also be improved and modified in a number of ways, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims

1. A rapid detection method for total nitrogen and total phosphorus in seawater, characterized in that: The steps include: Step 1, water sample collection: collect the seawater sample to be tested; Step 2, sample digestion: adding alkaline persulfate solution to the seawater sample for digestion; Step 3, kit screening: select inorganic nitrogen kit and orthophosphate kit suitable for seawater quality testing from the common nitrogen and phosphorus rapid test kits on the market; Step 4, sample testing: Use the screened inorganic nitrogen kit and orthophosphate kit to determine the total nitrogen and total phosphorus in the digested seawater sample.

2. The rapid detection method for total nitrogen and total phosphorus in seawater according to claim 1, characterized in that: The alkaline persulfate solution in step 2 is an alkaline sodium persulfate solution or an alkaline potassium persulfate solution.

3. The rapid detection method for total nitrogen and total phosphorus in seawater according to claim 2, characterized in that: The preparation method of the alkaline sodium persulfate solution is as follows: sodium hydroxide and potassium persulfate are weighed in a mass ratio of 3:10, and dissolved and fixed to volume with pure water; The preparation method of the alkaline potassium persulfate solution is: weigh sodium hydroxide and potassium persulfate in a mass ratio of 3:10, respectively, and dissolve and fix the volume with pure water.

4. The rapid detection method for total nitrogen and total phosphorus in seawater according to claim 2, characterized in that: In step 2, if alkaline sodium persulfate solution is used for sample digestion, the digestion temperature is 150° C. and the digestion time is 5 min; if alkaline potassium persulfate solution is used for sample digestion, the digestion temperature is 150° C. and the digestion time is 10 min.

5. The rapid detection method for total nitrogen and total phosphorus in seawater according to claim 1, characterized in that: In step 2, after adding the alkaline persulfate solution to the seawater sample, the pH value of the mixed solution is 6.5-7.

5.

6. The rapid detection method for total nitrogen and total phosphorus in seawater according to any one of claims 1 to 5, characterized in that: The specific steps for sample digestion in step 2 are: Step 2.1, placing the digestion container in the portable digestion device, and injecting the seawater sample into the digestion container; Step 2.2, adding alkaline persulfate solution into the digestion container; Step 2.3, shake and mix, heat, and digest at 150°C for 5 to 10 minutes; Step 2.4: After digestion is completed, take out the digestion container and cool it naturally to room temperature.

7. The rapid detection method for total nitrogen and total phosphorus in seawater according to claim 1, characterized in that: The screening steps of the inorganic nitrogen kit in step 3 are: A1. Through market research, select several alternative inorganic nitrogen test kits that are currently highly recognized in the market; A2. Prepare artificial seawater and total nitrogen standard solution, and test the influence of seawater matrix effect on several selected inorganic nitrogen test kits; A3. Based on the test results, select the alternative inorganic nitrogen test kit that is least affected by the seawater matrix as the required inorganic nitrogen test kit.

8. The rapid detection method for total nitrogen and total phosphorus in seawater according to claim 1, characterized in that: The screening steps of the orthophosphate kit described in step 3 are: B1. Through market research, select several alternative orthophosphate test kits that are currently highly recognized in the market; B2. Prepare artificial seawater and total phosphorus standard solution, and test the influence of seawater matrix effect on several selected orthophosphate test kits; B3. Based on the test results, select the alternative orthophosphate kit that is least affected by the seawater matrix as the required orthophosphate kit.

9. The rapid detection method for total nitrogen and total phosphorus in seawater according to claim 1, characterized in that: The specific steps of using the screened inorganic nitrogen kit to determine the total nitrogen in the digested seawater sample in step 4 are: Step C1, taking a certain amount of digested seawater sample and adding it into a total nitrogen determination container; Step C2, adding K-1 reagent for total nitrogen determination into the total nitrogen determination container; Step C3, adding K-2 reagent for total nitrogen determination into the total nitrogen determination container; Step C4, covering the total nitrogen determination container with a lid and shaking for a first time period; Step C5, removing the lid of the total nitrogen determination container and leaving it to stand for a second period of time; Step C6, pulling out the wire at the top of the total nitrogen determination tube; Step C7, place the water absorption hole of the total nitrogen determination tube upward, pinch the lower part of the total nitrogen determination tube with your fingers, and squeeze out the air in the total nitrogen determination tube; Step C8, place the water absorption hole of the total nitrogen determination tube in the seawater sample, release your fingers, wait for the seawater sample to be completely absorbed into the total nitrogen determination tube, and shake to mix; Step C9: After the third time period, place the total nitrogen determination tube on the white background of the standard card for colorimetry to obtain the total nitrogen measurement value of the seawater sample.

10. The rapid detection method for total nitrogen and total phosphorus in seawater according to claim 1, characterized in that: The specific steps of using the screened orthophosphate kit to determine the total phosphorus in the digested seawater sample in step 4 are: Step D1, taking a certain amount of digested seawater sample and adding it into a total phosphorus determination container; Step D2, adding K-1 reagent for total phosphorus determination into the total phosphorus determination container; Step D3, cover the total phosphorus determination container with a lid and shake for a fourth period of time; Step D4, pulling out the wire at the top of the total phosphorus determination tube; Step D5, with the water absorption hole of the total phosphorus determination tube facing upward, pinch the lower part of the total phosphorus determination tube with your fingers to squeeze out the air in the total phosphorus determination tube; Step D6, place the water absorption hole of the total phosphorus determination tube directly into the test water, place it in the seawater sample, release your fingers, and shake to mix; Step D7: After the fifth period of time, place the total phosphorus determination tube on the white background of the standard card for colorimetry to obtain the total phosphorus measurement value of the seawater sample.

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