Anti-salinity interference vanadium (III) reduced seawater nitrate analysis device

Abstract

The utility model discloses an anti-salinity interference vanadium (III) reduced seawater nitrate analysis device, and relates to the field of analytical chemistry detection. Comprising an automatic sample injection module, a flow analysis module, a mixing-constant temperature module and a light splitting detection module, the flow analysis module comprises an injection pump, an injector and a multi-position selection valve; the multi-position selection valve is respectively connected with the automatic sample injection module, the pure water storage bottle, the sulfanilamide solution storage bottle, the N-(1-naphthyl) ethylenediamine hydrochloride solution storage bottle, the vanadium (III) solution storage bottle, the mixing-constant temperature module and the light splitting detection module through pipelines; the injector is connected with the multi-position selection valve, and the liquid amount is controlled through the injection pump.

Description

Technical Field

[0001] This utility model relates to the field of analytical chemistry detection, and in particular to a vanadium(III)-reduced seawater nitrate analysis device resistant to salinity interference. Background Technology

[0002] Nitrate, as one of the main forms of nitrogen in water bodies, has attracted much attention for its environmental behavior and ecological effects. In natural water bodies, nitrate is not only a key nitrogen source for primary producers such as algae and phytoplankton to synthesize proteins, nucleic acids, and chlorophyll, but also a core factor driving primary productivity and regulating the biogeochemical processes of the nitrogen cycle. However, with the rapid development of industry and agriculture and the acceleration of urbanization, excessive nitrate is introduced into nearshore waters through various pathways, including agricultural non-point source pollution, industrial wastewater discharge, and urban surface runoff, leading to regional nutrient imbalances. This imbalance results in seasonal hypoxia and harmful algal blooms in nearshore waters, causing ecological disasters such as the decline of fishery resources and biodiversity, posing a severe challenge to marine ecosystem services and the sustainable development of the blue economy.

[0003] The determination of nitrates in seawater typically employs the copper-cadmium reduction method or the zinc-cadmium reduction method, first reducing nitrates to nitrites, and then measuring them using diazo-azo spectrophotometry. This method is characterized by good reproducibility and high sensitivity, and is widely used in marine monitoring, serving as the standard method for nitrate analysis in seawater. However, this method has several drawbacks: ① Cadmium is a highly toxic substance, and long-term exposure may pose health risks to laboratory personnel, and improper waste disposal can easily lead to secondary pollution; ② As a solid reducing agent, the activation, loading, and maintenance processes of the copper-cadmium reduction column, as well as the preparation process of the zinc coil, are relatively cumbersome; ③ The reduction efficiency of the reduction column may decrease after long-term use, requiring frequent calibration or replacement to maintain detection accuracy. Therefore, it is necessary to develop safer and more efficient alternative methods to reduce dependence on highly toxic reagents and improve analytical efficiency. Summary of the Invention

[0004] The purpose of this invention is to solve the aforementioned problems in the prior art and provide a vanadium(III)-reduced seawater nitrate analysis device resistant to salinity interference. Using a flow sequence batch analyzer as the carrier, vanadium(III) solution is used to reduce nitrate to nitrite, followed by determination of seawater nitrate using the diazo-azo method. This method eliminates the need for nitrate concentration correction based on sample salinity and offers advantages such as simplicity, speed, and sensitivity.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A vanadium(III)-reduced seawater nitrate analysis device resistant to salinity interference includes an automatic sample injection module, a flow analysis module, a mixing-isothermal module, and a spectrophotometric detection module. The flow analysis module includes a syringe pump, a syringe, and a multi-position selector valve. The multi-position selector valve is connected via pipelines to the automatic sample injection module, a pure water storage bottle, a sulfonamide solution storage bottle, a naphthylethylenediamine hydrochloride solution storage bottle, a vanadium(III) solution storage bottle, the mixing-isothermal module, and the spectrophotometric detection module. The syringe is connected to the multi-position selector valve and the liquid volume is controlled by the syringe pump.

[0007] This utility model also includes a control module, which uses a computer host computer to control the operation of the injection pump of the flow analysis module, the temperature regulation of the mixing-constant temperature module, and to collect the absorbance data of the spectrophotometer and perform signal processing.

[0008] This utility model also includes a waste liquid bottle, which is connected to the outlet of the spectrophotometer and a multi-position selector valve via a pipeline.

[0009] The automatic sample introduction module includes a multi-channel selection valve for switching the sample to be tested.

[0010] The multi-channel selection valve of the automatic sample injection module is a sixteen-channel selection valve, a twenty-four-channel selection valve, or a selection valve with more than one channel.

[0011] The mixing-constant temperature module includes a mixing coil and a constant temperature heating rod, which is used to control the reaction temperature of the mixing coil. The constant temperature heating rod can be made of aluminum or other thermally conductive metal, and the temperature control range is 25–120°C.

[0012] The hybrid coil is a corrosion-resistant material tube with an inner diameter of 0.5 to 3.0 mm and a length of 10 to 1000 cm, such as a polytetrafluoroethylene tube.

[0013] The syringe for the flow analysis module has a capacity of 0.5 to 5.0 mL.

[0014] The selection valve in the flow analysis module can be a nine-position selection valve, a twelve-position selection valve, or a selection valve with more than one position.

[0015] The determination method of the vanadium(III)-reduced seawater nitrate analyzer based on salinity interference resistance includes the following steps:

[0016] 1) The syringe pump repeatedly draws in and discharges pure water to clean the syringe, mixing coil, and flow cell of the spectrophotometer detection module;

[0017] 2) The syringe pump draws in and discharges the sample to be tested, and rinses the sample inlet tubing;

[0018] 3) The syringe pump draws in the sample to be tested, and then sequentially draws in sulfonamide solution, naphthylethylenediamine hydrochloride solution and vanadium(III) solution. The resulting mixed solution is mixed by repeatedly pumping in and out of the mixing coil and then remains in the mixing coil for a constant temperature reaction.

[0019] 4) The syringe pump pumps the mixed solution after the isothermal reaction into the spectrophotometer detection module and records the change in absorbance.

[0020] 5) Repeat steps 1) to 4) until all samples have been tested.

[0021] Compared with the prior art, the beneficial effects achieved by the technical solution of this utility model are:

[0022] 1) This device uses a liquid reducing agent to reduce nitrates, avoiding the use of the highly toxic reagent cadmium;

[0023] 2) The device uses a syringe pump, which allows for precise dilution of the sample directly using a syringe, avoiding the influence of the sample substrate (such as salinity) on the measurement; the device does not require frequent replacement of the pump tubing, improving the stability and accuracy of long-term measurements.

[0024] 3) The device is equipped with a mixing-temperature control module, which, in conjunction with the reciprocating motion of the syringe, can make the mixing more thorough and improve the reaction rate. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the structure and flow path of this utility model;

[0026] Figure 2 The standard working curves for nitrates are provided for pure water and seawater substrates.

[0027] Figure labels: 1. Automatic sample injection module, 2. Sample, 3. Pure water, 4. Sulfonamide solution storage bottle, 5. Naphthylethylenediamine hydrochloride solution storage bottle, 6. Vanadium(III) solution storage bottle, 7. Flow analysis module, 8. Syringe, 9. Multi-position selector valve, 10. Mixing-thermal module, 11. Mixing coil, 12. Thermostatic heating rod, 13. Spectrophotometer detection module, 14. Waste liquid bottle. Detailed Implementation

[0028] To make the technical problems, technical solutions and beneficial effects of this utility model clearer and more understandable, the present utility model will be further described in detail below with reference to the accompanying drawings and embodiments.

[0029] Example 1

[0030] This invention relates to a vanadium(III)-reduced seawater nitrate analysis device resistant to salinity interference, such as... Figure 1As shown, it mainly includes an automatic sample injection module 1, a flow analysis module 7, a mixing-isothermal module 10, a spectrophotometric detection module 13, a control module, and a waste liquid bottle 14;

[0031] The flow analysis module includes a syringe pump, a syringe 8, and a multi-position selector valve 9. The multi-position selector valve 9 is connected to the automatic sample injection module 1, a pure water storage bottle 3, a sulfanilamide solution storage bottle 4, a naphthylethylenediamine hydrochloride solution storage bottle 5, a vanadium(III) solution storage bottle 6, a mixing-isothermal module 10, and a spectrophotometric detection module via tubing. The syringe 8 is connected to the multi-position selector valve 9 and controls the liquid volume via the syringe pump. Specifically, valve position a of the multi-position selector valve 9 is connected to the automatic sample injection module 1 via tubing, valve position b is connected to the pure water storage bottle 3 via tubing, valve position c is connected to the sulfanilamide solution storage bottle 4 via tubing, valve position d is connected to the naphthylethylenediamine hydrochloride solution storage bottle 5 via tubing, valve position e is connected to the vanadium(III) solution storage bottle 6 via tubing, and valve position i is connected to the waste liquid bottle 14.

[0032] The control module uses a computer to control the operation of the injection pump of the flow analysis module 4, the temperature regulation of the mixing-temperature control module 10, and to collect the absorbance data of the spectrophotometer detection module 13 and perform signal processing.

[0033] The automatic sample injection module 1 includes a multi-channel selection valve for switching between different samples 2; the multi-channel selection valve of the automatic sample injection module is a sixteen-channel selection valve, a twenty-four-channel selection valve, or a selection valve with more than one channel.

[0034] The mixing-thermal module 10 includes a mixing coil 11 and a thermostatic heating rod 12. The thermostatic heating rod 12 is used to control the reaction temperature of the mixing coil. The inlet end of the mixing coil 11 is connected to the valve position g of the multi-position selector valve 9, and the outlet end is connected to the air.

[0035] The inlet of the spectrophotometer detection module 13 is connected to the valve position h of the multi-position selector valve 9, and the outlet is connected to the waste liquid bottle 14.

[0036] Application Example 1: Determination of nitrate standard curves under different salinity bases

[0037] This embodiment is based on the vanadium(III) reduction-diazoazo spectrophotometric method. The reagents used include sulfanilamide solution, naphthylethylenediamine hydrochloride solution, and vanadium(III) solution. The mass-volume concentration of the sulfanilamide solution is 10 g / L, the mass-volume concentration of the naphthylethylenediamine hydrochloride solution is 1 g / L, and the mass-volume concentration of the vanadium(III) solution is 20 g / L. The absorption ratio of the sulfanilamide solution, naphthylethylenediamine hydrochloride solution, and vanadium(III) solution is 1.25:1:2. The automatic sample injection module of this invention uses a sixteen-channel selector valve 1, the flow analysis module 7 uses a 1 mL syringe 8 and a nine-position selector valve 9, and the mixing-thermostatic module 10 uses a PTFE tube 11 with an inner diameter of 1 mm and a length of 250 cm and a 90°C thermostatic heating rod 12. The thermostatic heating rod 12 is made of aluminum.

[0038] Before the experiment, two sets of nitrate standard solutions with concentrations of 0, 10, 20, 40, and 60 μM were prepared using pure water (salinity 0) and oligotrophic ocean seawater (salinity 35), respectively. The determination was carried out according to the following steps:

[0039] 1) The syringe draws in 1mL of pure water through valve position b of the nine-position selector valve, pumps it repeatedly into and out of the mixing coil through valve position g, and then pumps it into the spectrophotometer detection module through valve position h, and discharges it into the waste bottle. Repeat this process 4 times to clean the syringe, mixing coil and spectrophotometer detection module.

[0040] 2) The syringe draws in 100 μL of pure water-based nitrate sample placed in the sixteen-channel selector valve through valve position a of the nine-position selector valve, and draws in 675 μL of pure water through valve position b to complete the automatic dilution of the sample.

[0041] 3) The syringe sequentially draws in 25 μL of sulfanilamide solution, 20 μL of naphthylethylenediamine hydrochloride solution and 40 μL of vanadium(III) solution through valve positions c, d and e of the nine-position selector valve. The mixture is then mixed with 775 μL of diluted sample. The resulting mixture is repeatedly pumped into and out of the mixing coil through valve position g to complete the mixing process, and then reacted on a constant temperature heating rod for 90 s.

[0042] 4) After the reaction time is reached, the syringe pumps the mixed solution after the isothermal reaction into the spectrophotometer detection module through the valve position h of the nine-position selector valve, and records the change in absorbance value.

[0043] 5) Switch the sixteen-channel selector valve to the next concentration of nitrate sample, and repeat steps 1) to 4) until the determination of the two sets of nitrate standard working solutions with different substrates is completed.

[0044] 6) Based on the concentration and the obtained absorbance values, plot the standard working curves for nitrate on pure water and seawater substrates.

[0045] The measurement results are as follows Figure 2(Salinity in ‰), the standard working curve for nitrates on a pure water base is A1 = (0.0129 ± 0.0003)C1 + (0.0784 ± 0.0099) (R 2 =0.9984, n=5), the standard working curve for nitrates on seawater substrates is A2=(0.0126±0.0003)C2+(0.0784±0.0091)(R 2 =0.9986, n=5).

[0046] Application Example 2: Spiking recovery rate of nitrate concentration in seawater substrate samples with different salinities

[0047] The present invention was used to test the recovery rate of seawater substrate samples with different salinities. The determination procedure was performed according to Application Example 1, and the results are shown in Table 1.

[0048] Table 1

[0049]

[0050] In summary, this invention provides a safe, efficient, and salinity-resistant seawater nitrate analysis device. Compared to the traditional copper-cadmium reduction method, its core advantages lie not only in avoiding the use of highly toxic reagents, but also in the precise volume control via an injection pump and the enhanced reaction kinetics through a mixing-isothermal module, enabling direct determination of nitrates under complex salinity conditions and significantly reducing the complexity of sample pretreatment.

Claims

1. A vanadium(III)-reduced seawater nitrate analysis device resistant to salinity interference, characterized in that: It includes an automatic sample injection module, a flow analysis module, a mixing-isothermal module, and a spectrophotometric detection module; the flow analysis module includes a syringe pump, a syringe, and a multi-position selector valve, which is connected to the automatic sample injection module, a pure water storage bottle, a sulfonamide solution storage bottle, a naphthylethylenediamine hydrochloride solution storage bottle, a vanadium(III) solution storage bottle, the mixing-isothermal module, and the spectrophotometric detection module via tubing; the syringe is connected to the multi-position selector valve and the liquid volume is controlled by the syringe pump.

2. The vanadium(III)-reduced seawater nitrate analysis device resistant to salinity interference as described in claim 1, characterized in that: It also includes a control module, which uses a computer host computer to control the operation of the injection pump of the flow analysis module, the temperature regulation of the mixing-thermostatic module, and to collect absorbance data from the spectrophotometer and perform signal processing.

3. The vanadium(III)-reduced seawater nitrate analysis device resistant to salinity interference as described in claim 1, characterized in that: It also includes a waste liquid bottle, which is connected to the outlet of the spectrophotometer and a multi-position selector valve via a pipeline.

4. The vanadium(III)-reduced seawater nitrate analysis device resistant to salinity interference as described in claim 1, characterized in that: The automatic sample introduction module includes a multi-channel selection valve for switching the sample to be tested.

5. The vanadium(III)-reduced seawater nitrate analysis device resistant to salinity interference as described in claim 4, characterized in that: The multi-channel selection valve of the automatic sample injection module is a sixteen-channel selection valve, a twenty-four-channel selection valve, or a selection valve with more than one channel.

6. The vanadium(III)-reduced seawater nitrate analysis device resistant to salinity interference as described in claim 1, characterized in that: The mixing-thermal module includes a mixing coil and a thermostatic heating rod, the thermostatic heating rod being used to control the reaction temperature of the mixing coil.

7. The vanadium(III)-reduced seawater nitrate analysis apparatus resistant to salinity interference as described in claim 6, characterized in that: The hybrid coil is a corrosion-resistant material tube with an inner diameter of 0.5–3.0 mm and a length of 10–1000 cm.

8. The vanadium(III)-reduced seawater nitrate analysis apparatus resistant to salinity interference as described in claim 1, characterized in that: The syringe for the flow analysis module has a capacity of 0.5 to 5.0 mL.

Images