Instrument and method for simultaneously testing molecular weight distribution and organic nitrogen level of water sample

Abstract

An instrument and a method for simultaneously testing a molecular weight distribution and an organic nitrogen level of a water sample are provided. The instrument comprises: a tail-end injection valve, a chromatographic column, a pressure relief valve, an acid-adding injection valve, an oxygen-adding injection valve, a helical tube for an acid-oxygen reaction, a CO.sub.2 remover, a UV digester, a second gas-water separator membrane, a buffer solution injection valve, a helical tube for a buffer solution reaction, a cadmium column, a chromogenic agent injection valve, a helical tube for a chromogenic agent reaction, and a UV detector, sequentially connected via a pipeline. The tail-end injection valve is for receiving a fluid phase and a sample. The second gas-water separator membrane is connected to an electrical conductivity-based CO2 detector. The UV detector and the electrical conductivity-based CO.sub.2 detector are connected to a data processing computer.

Claims

1. An instrument for simultaneously testing a molecular weight distribution and an organic nitrogen of water samples, comprising a tail-end injection valve, a chromatographic column, a pressure relief valve, an acid-adding injection valve, an oxygen-adding injection valve, an helical tube for an acid-oxygen reaction, a carbon dioxide (CO.sub.2) remover, a ultraviolet digester, a second gas-water separation membrane, a buffer solution injection valve, a helical tube for a buffer solution reaction, a cadmium column, a chromogenic agent injection valve, a helical tube for a chromogenic agent reaction and a ultraviolet detector, sequentially connected via a pipeline, the tail-end injection valve is configured to receive a fluid phase and a sample, the second gas-water separation membrane is connected to an electrical conductivity-based CO.sub.2 detector, the ultraviolet detector and the electrical conductivity-based CO.sub.2 detector are both connected to a data processing computer.

2. The instrument for simultaneously testing the molecular weight distribution and the organic nitrogen of the water samples according to claim 1, wherein the tail-end injection valve is connected with a sampling pump and a sample bottle, and the tail-end injection valve is further connected with a fluid phase infusion pump and a fluid phase reagent bottle, the acid-adding injection valve is connected with an acid injection pump and an acid bottle, the oxygen-adding injection valve is connected with an oxygen liquid injection pump and an oxygen liquid bottle, the buffer solution injection valve is connected with a buffer solution injection pump and a buffer solution reagent bottle, the chromogenic agent injection valve is connected with a chromogenic agent injection pump and a chromogenic agent reagent bottle.

3. The instrument for simultaneously testing the molecular weight distribution and the organic nitrogen of the water samples according to claim 1, wherein the CO.sub.2 remover comprises a first gas-water separation membrane, a gas collecting coil, a purge pump and a diaphragm, the first gas-water separation membrane, the gas collecting coil and the diaphragm are connected in sequence, and the first gas-water separation membrane is connected to an acid-oxygen reaction spiral pipe through a pipeline, the diaphragm is connected with the ultraviolet digester (16) through a pipeline, the blow-off pump is connected to the gas collecting coil.

4. The instrument for simultaneously testing the molecular weight distribution and the organic nitrogen of the water samples according to claim 3, wherein the ultraviolet digester comprises a heating wire, a transparent quartz spiral tube and an ultraviolet lamp, the transparent quartz spiral tube is connected between the diaphragm and the second gas-water separation membrane through a pipeline, the ultraviolet lamp is located above the transparent quartz spiral tube (30), the heating wire is located under the transparent quartz spiral tube.

5. The instrument for simultaneously testing the molecular weight distribution and the organic nitrogen of the water samples according to claim 1, wherein the electrical conductivity-based CO.sub.2 detector comprises an ultra-pure water tank and an ultra-pure water pump and a conductivity cell, which are connected in sequence, the sample oxidized by the ultraviolet digester passes through a gas-water separation membrane, the CO.sub.2 separates and dissolves in ultra-pure water driven by the ultra-pure water pump and purifies by ion purification resin, then passes into the conductivity cell, the amount of CO.sub.2 is measured by detecting the change of liquid conductivity in the conductivity cell, and a specific conversion relationship characterizes a concentration of TOC.

6. A method of using the instrument for simultaneously testing the molecular weight distribution and the organic nitrogen of the water samples according to claim 1, comprising the following steps: a sample is collected into a pipeline, mixed with a fluid phase, and then separated by a chromatographic column, components of the sample flow out in sequence according to a different molecular weight, and then a pressure is reduced by a pressure relief valve, the different molecular weight of the components of the separated sample pass through an acid-adding injection valve and an oxygen-adding injection valve, injecting an acid liquor into the acid-adding injection valve, injecting an oxygen liquor into the oxygen-adding injection valve, and fully reacting the components to be detected, the fluid phase, the acid liquor and the oxygen liquor in an acid-oxygen reaction spiral tube; inorganic carbon in the components to be detected is acidified by the acid liquor to produce CO.sub.2, which is blown off into the air through the back remover of CO.sub.2; the components to be detected removed from inorganic carbon reach in a ultraviolet digester through a pipeline, TOC of the components is oxidized to CO.sub.2 and DON is oxidized to nitrate nitrogen, the oxidized sample passes through a gas-liquid separation membrane to separate the generated CO.sub.2 into an electrical conductivity-based CO.sub.2 detector, the electrical conductivity-based CO2 detector detects an amount of CO.sub.2, and a specific conversion relationship characterizes a concentration of TOC, after that, the remaining components without TOC are added to a buffer solution through a buffer solution injection valve, then after a reduction of a cadmium column, nitrate nitrogen is reduced to nitrite nitrogen, then a reagent is added through a chromogenic agent injection valve, and a mixing reaction is carried out in a helical tube for a chromogenic agent reaction, finally as an amount of nitrate-nitrogen is detected at 540 nm in a UV detector and a specific conversion relationship characterizes a concentration of DON.

7. The method according to claim 6, wherein the fluid phase is selected as phosphate buffer solution, a ionic strength is 0.1-0.4 M, a pH value is 6.8±0.2, a flow rate of a fluid phase infusion pump is selected to be 0.4-1.0 mL/min, a pressure of the fluid phase infusion pump is selected to be 1.8±0.2 MPa, a maintaining temperature of a chromatographic column is 30-60° C., a pressure is 1.8±0.2 MPa before the chromatographic column, a pressure after the chromatographic column passes through a pressure relief valve is 1 bar, a flow state is free flow, in the ultraviolet digester, a wavelength of a UV lamp is 190 nm, and a heating temperature is set to be 95±2° C.

8. The method according to claim 6, wherein the sampling pump adopts a microinjection pump, a pump's working pressure is higher than 1500 psi, and a highest precision is less than 0.1%, a sampling volume is 50-500 μL, an acid injection pump and an oxygen liquid injection pump adopt the microinjection pump, a working pressure is higher than 1500 psi, a highest precision is less than 0.1% and pulse-free transportation, a flow rate of the acid oxygen injection pump and the oxygen liquid injection pump is 1.0-4.0 μL/min, and a flow rate of a chromogenic agent injection pump is 1.0-4.0 μL/min.

9. The method according to claim 6, wherein a tail-end injection valve, the acid-adding injection valve, the oxygen-adding injection valve, the buffer solution injection valve, and the chromogenic agent injection valve are all stable to add one liquid to another liquid slowly and stably for mixing without having a back suction.

10. The method according to claim 6, wherein the acid-oxygen reaction spiral tube, a helical tube for a buffer solution reaction and a chromogenic agent reaction spiral tube are all made of stainless steel PEEK tubes in a spiral manner, and the stainless steel PEEK tubes are selected as the sample pipelines in the instrument.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic diagram of the instrument structure;

(2) FIG. 2 is a schematic diagram of the structure of a CO.sub.2 remover;

(3) FIG. 3 is a schematic diagram of the structure of an ultraviolet digester.

(4) Reference numerals in the figure: 1—fluid phase reagent bottle; 2—fluid phase infusion pump; 3—tail—end injection valve; 4—sampling pump; 5—sample bottle; 6—chromatographic column; 7—column thermostat; 8—pressure relief valve; 9—acid—adding injection valve; 10—acid injection pump; 11—acid bottle; 12—oxygen—adding injection valve; 13—oxygen injection pump; 14—oxygen bottle; 15—helical tube for an acid—oxygen reaction; 16—UV digester; 17—buffer solution syringe pump; 18—buffer solution reagent bottle; 19—buffer solution injection valve; 20—helical tube for a buffer solution reaction; 21—cadmium column; 22—color reagent injection Valve; 23—chromogenic reagent injection pump; 24—chromogenic reagent bottle; 25—chromogenic reagent reaction spiral tube; 26—UV detector; 27—Waste liquid barrel; 28—computer; 29—heating wire; 30—transparent quartz spiral tube; 31—UV lamp; 32—CO.sub.2 remover; 33—second gas—water separation membrane; 34—electrical conductivity—based CO.sub.2 detector; 35—ultra pure water tank; 36—ultra pure water pump; 37—conductivity cell; 38—first gas—water separation membrane; 39—gas collecting coil; 40—purge pump; 41—diaphragm; 42—outlet vent pipe; 43—ultraviolet detector data line; 44—electrical conductivity—based CO.sub.2 detector data line.

DETAILED DESCRIPTION

(5) As shown in FIG. 1, an instrument for simultaneously testing the molecular weight distribution and organic nitrogen of water samples, including tail-end injection valve 3, chromatographic column 6, pressure relief valve 8, acid-adding injection valve 9, oxygen-adding injection valve 12, helical tube for an acid-oxygen reaction 15, carbon dioxide (CO.sub.2) remover 32, ultraviolet digester 16, the second gas-water separation membrane 33, the buffer solution injection valve 19, the helical tube for a buffer solution reaction 20, the cadmium column 21, the chromogenic agent injection valve 22, the helical tube for a chromogenic agent reaction 25 and the ultraviolet detector 26; all these devices are connected in sequence by pipelines. The tail-end injection valve 3 is used to receive the fluid phase and the sample. The second gas-water separation membrane 33 is connected to an electrical conductivity-based CO.sub.2 detector 34. The ultraviolet detector 26 and the electrical conductivity-based CO.sub.2 detector 34 are both connected to a computer 28 for data processing.

(6) The tail-end injection valve 3 is connected with a sampling pump 4 and a sample bottle 5, and it is also connected with a fluid phase infusion pump 2 and a fluid phase reagent bottle 1. The acid-adding injection valve 9 is connected with an acid injection pump 10 and an acid bottle 11. The oxygen-adding injection valve 12 is connected with an oxygen liquid injection pump 13 and an oxygen liquid bottle 14. The buffer solution injection valve 19 is connected with the buffer solution injection pump 17 and the buffer solution reagent bottle 18. The chromogenic agent injection valve 22 is connected with the chromogenic agent injection pump 23 and the chromogenic agent reagent bottle 24. The chromatographic column 6 is located in a chromatographic column temperature box 7. The UV detector 26 is connected with the waste liquid bucket 27. The UV detector 26 is connected to a computer 28 for data processing through a UV detector data line 43. The Electrical conductivity-based CO.sub.2 detector 34 is connected to a computer 28 for data processing through a Electrical conductivity-based CO.sub.2 detector data line 44.

(7) As shown in FIG. 2, the CO.sub.2 remover 32 includes a first gas-water separation membrane 38, a gas collecting coil 39, a purge pump 40 and a diaphragm 41. The first gas-water separation membrane 38, the gas collecting coil 39 and the diaphragm 41 are connected in sequence. The first gas-water separation membrane 38 is connected to the acid-oxygen reaction spiral pipe 15 through a pipeline. The diaphragm 41 is connected with the transparent quartz spiral tube 30 through the outlet vent pipe 42 and pipeline. The blow-off pump 40 is connected to the gas collecting coil 39. The first gas-water separation membrane 38 function is to separate the CO.sub.2 produced by inorganic carbonation from the liquid components and then enter the gas collecting coil. The first gas-water separation membrane 38 is preferably a polydimethylsiloxane membrane, an oxygen-rich membrane with a stable structure and a good separation effect on CO.sub.2. The diaphragm 41 purpose is to isolate the air's CO.sub.2 and prevent it from entering the tested components. The blow-off pump's 40 function is to provide blow-off power and blow out the gas collecting coil's CO.sub.2. The blow-off pump 40 is a micro pneumatic diaphragm pump, which is small in size, can effectively provide blowing power and is cheap.

(8) As shown in FIG. 3, the ultraviolet digester 16 includes a heating wire 29, a transparent quartz spiral tube 30 and an ultraviolet lamp 31. The transparent quartz spiral tube 30 is connected between the diaphragm 41 and the second gas-water separation membrane 33 through a pipeline. The ultraviolet lamp 31 is located above the transparent quartz spiral tube 30. The heating wire 29 is located under the transparent quartz spiral tube.

(9) The second water-gas separation membrane 33 is connected between the UV digestion apparatus 16 and buffer solution injection valve 19. The second gas-water separation membrane 33 connected with electrical conductivity-based CO.sub.2 detector 34, which is used for separating CO.sub.2 produced in UV digestion apparatus 16. The rest of the sample enter into the buffer solution injection valve 19, and then enter the UV detector. The second gas water separation membrane 33 optimization is polydimethylsiloxane membrane, belongs to the oxygen-enriched membrane. It has a good separation effect on CO.sub.2 and has a stable structure.

(10) The electrical conductivity-based CO.sub.2 detector 34 comprises an ultra-pure water tank 35 and an ultra-pure water pump 36 connected sequentially. The sample oxidized by a UV digestion device 16 pass through a gas-water separation membrane 19. The CO.sub.2 was separated and dissolved in ultra-pure water driven by an ultra-pure water pump 36 and purified by ion purification resin. Then, it was passed into the conductivity cell. The amount of CO.sub.2 was measured by detecting the change of liquid conductivity in the conductivity cell, and a specific conversion relationship characterized the concentration of TOC.

(11) As the best choice, the ultra-pure water is made by Milli-Q ultra-pure water instrument, the resistance is 18.2 mΩ.Math.cm, the ultra-pure water pump 36 is micro-infusion pump, and the conductivity electrode flow cell with measuring range of 0.01 μs/cm-300 μs/cm, resolution of 0.01 μs/cm is selected.

(12) The technical route of the invention is shown in FIG. 1:

(13) The samples 5 are transmitted by the sampling pump 4, reached the pipeline, and injected into the fluid phase pipeline by the tail-end injection valve 3. The fluid phase in the fluid phase reagent bottle 1 is transmitted to the main flow path under the action of the fluid phase infusion pump 2 and mixed with the sample after reaching the tail-end injection valve 3. The fluid phase carries the sample and is separated by a chromatographic column 6 in a temperature box 7. After separation by chromatographic column 6, the sample to be measured flows out according to its components' molecular weight in turn. The pressure is reduced to atmospheric pressure, and the flow pattern is the free outflow through the pressure reduction valve 8. The components to be tested then arrive at the acid-adding injection valve 9 and the oxygen-adding injection valve 12 in the mainstream road, mixed with the acid and oxygen transferred by the liquid injection pump 10 and the oxygen injection pump 13 and further reached the spiral tube of the acid-oxygen reaction. In the fluid phase, the components to be measured, the acid solution and the oxygen solution, are thoroughly mixed in the acid-oxygen reaction's spiral 15.

(14) In the spiral of acid-oxygen reaction spiral 15, inorganic carbon is completely acidified to CO.sub.2 (reaction 1).
2H.sup.++CO.sub.3.sup.2−.fwdarw.CO.sub.2+H.sub.2O  (1)

(15) The inorganic carbon (IC) in the component to be tested is acidified by acid solution. The resulting CO.sub.2 is mixed in the pipeline, entered into the CO.sub.2 remover 16, and then separated from the liquid phase and discharged into the air. The structure of the CO.sub.2 remover 16 is as mentioned above: the resulting CO.sub.2 is immediately separated from the liquid phase by the first gas-water separation membrane 38, enters the gas collecting coil 39, transmits through the blow-off pump 40, and blows the CO.sub.2 into the air after blowing through the diaphragm 41. The CO.sub.2 in the air is blocked by the diaphragm 41 and does not enter the liquid phase.

(16) The remaining components to be tested and the fluid phase of inorganic carbon were removed and entered the UV digester 16. The UV digester 16 structure is described as above: the transparent quartz reaction spiral tube provides the reaction space in which the components to be tested. In the fluid phase, the oxygen solution and the acid are filled with a mixed spiral advance. Under the UV lamp's 31 irradiation and the heating condition of electric heating wire 29, the TOC is oxidized to CO.sub.2. The DON is oxidized to nitrate ion (reaction 2, 3).

(17) ##STR00003##

(18) At this time, CO.sub.2 produced by TOC oxidation enters into the second gas-water separation membrane 33, separated from the liquid phase and enters into the electrical conductivity-based CO.sub.2 detector 34. The structure of the electrical conductivity-based CO.sub.2 detector is shown in the dashed box of FIG. 1. The separated CO.sub.2 enters the electrical conductivity-based CO.sub.2 detector from another flow path and is dissolved in the ultrapure water pipeline. The ultrapure water is driven by an ultrapure water pump and drawn from the ultrapure water tank. After dissolving CO.sub.2, it enters into the conductive cell. The change of conductance detects the CO.sub.2 content and then shows the TOC concentration.

(19) The organic carbon-removed components reach the buffer solution injection valve 19 and are mixed with the buffer solution injection pump's 17 buffer solution. The mixed solution enters the helical tube for a buffer solution reaction 20 for further mixing and then enters the cadmium column 21 to reduce the nitrate-nitrogen produced by oxidation to nitrite nitrogen. Subsequently, the liquid stream is mixed with the chromogenic agent delivered by the chromogenic agent injection pump 23 at the chromogenic agent injection valve 22 and further reacts in the chromogenic agent reaction spiral tube 25. In the presence of an acidic medium, nitrite nitrogen undergoes a diazotization reaction with sulfonamides and then couples with naphthalene ethylenediamine hydrochloride to produce a purple-red substance.

(20) ##STR00004##

(21) Finally, the reaction solution enters the ultraviolet detector 26, and the nitrite nitrogen is used to generate absorption under ultraviolet light with a wavelength of 540 nm. The absorption amount conforms to Beer's law. After the photoelectric sensor obtains the signal, the amount of nitrite nitrogen is obtained after processing, which further characterizes DON concentration.

(22) The wastewater at the outlet of the conductivity cell 37 and the wastewater at the ultraviolet detector 26 outlet are combined and collected into a waste liquid bucket 27. The data of the conductivity cell 23 and the UV detector 33 are respectively sent to the computer 28 through the data transmission line 35 and 34 for further storage and processing.

(23) The outlet wastewater is collected into a waste liquid bucket 27 after confluence. The ultraviolet detector 26 is connected to the computer 28 for data processing through the ultraviolet detector data line 43. The conductivity detector 34 is connected to the computer 28 for data processing through the conductance detector data line 44. The computer 28 performs further storage and processing.

(24) The present invention will be described in detail regarding the drawings and specific embodiments.

Embodiment

(25) Preparation:

(26) Turn on the instrument and computer 28. The fluid phase is subjected to ultrasonic degassing treatment for 20 minutes to eliminate bubbles in the fluid phase. This operation can avoid interference with the test results. Pass the sample through a 0.45 μm PTFE membrane to remove particulate impurities and avoid clogging of the instrument. Set the temperature of the column oven. In the ultraviolet digester 16, the ultraviolet lamp's wavelength is set to 190 nm, and the heating temperature is set to 95° C. Turn on the ultraviolet detector 26, and set the detection wavelength to 540 nm. The ultrapure water pump 36 is turned on, and the ultrapure water in the CO.sub.2 detector starts to flow. Empty the waste container 27.

(27) Operation Steps:

(28) After the preparation work is finished, turn on the fluid phase infusion pump 2, and set the flow rate and pressure. After the baseline is stable (1 to 2 hours), set the sampling volume of the sampling pump, the acid oxygen injection pump's flow rate, the buffer solution injection pump, and the chromogenic agent injection pump. Turn on the sampling pump 4, acid injection pump 10, oxygen injection pump 13, buffer solution injection pump 17, and chromogenic agent injection pump 23. Inject the sample into the fluid phase through the tail-end injection valve 3, inject the acid and oxygen into the fluid phase, and then wait for the test result.

(29) The main chromatographic condition intervals of this embodiment are as follows:

(30) TABLE-US-00001 Flow rate of fluid Flow rate Flow rate phase Flow rate of of buffer of color infusion Volume of Temperature acid/oxidant solution reagent pump water of column injection injection injection SEC column (mL/min) sample thermostat pump pump Valve TSkgel 0.4~1.0 50~100 40~60 2.0~4.0 2.0~4.0 2.0~4.0 G5000PW.sub.XL and TSkgel G2500PW.sub.XL columns series

(31) The residence time of different molecular weight standard samples obtained from TOC chromatographic peaks is as follows:

(32) TABLE-US-00002 MW 210 4300 6800 10000 17000 32000 77000 150000 2600000 Concentration 0.5 0.5 1.0 1.0 2.0 2.0 4.0 10.0 40.0 of TOC (ppm) Actual 0.493 0.498 0.991 0.997 1.999 1.998 4.000 10.000 40.000 concentration after deducting the baseline (ppm) Retention 41.52 23.69 23.33 23.01 22.81 22.28 21.41 20.55 16.45 time (min)

(33) Using bovine serum albumin as the DON concentration test sample, the results are as follows:

(34) Detection of the concentration of organic carbon: the detection range of the concentration of organic carbon provided by the present invention is 0.03 μg/L to 50 mg/L;

(35) Detection of organic nitrogen concentration: when the optical detection path of the ultraviolet detector is 10 mm, the present invention's method measures the organic nitrogen concentration in a range of 0.12 mg/L to 10 mg/L.

(36) The above description of the embodiments is to facilitate ordinary skill in the technical field to understand and use the invention. Those skilled in the art can easily modify these embodiments and apply the general principles described here to other embodiments without creative work. Therefore, the present invention is not limited to the embodiments mentioned above. The improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the present invention's scope should fall within the protection scope of the present invention.