Abstract
Disclosed is an organic carbon detector that can be used with a liquid chromatography equipment such as a size exclusion chromatography. The organic carbon detector contains a carbon oxidization subsystem and a stripping and CO.sub.2 detection subsystem arranged and detachably connected with each other in said order. The carbon oxidization subsystem contains a microfluidic agent injection module (1), an inorganic carbon removal module (2), a microfluidic ultraviolet oxidation module (3) and a vacuum pumping system (4), configured to remove inorganic carbons and oxidize organic carbons. The stripping and CO.sub.2 detection subsystem contains a stripping module (7) and a CO.sub.2 detector (12), using a carrier gas to transfer the organic carbon converted gas to the CO.sub.2 detector (12). Also disclosed is a method of using the organic carbon detector in water quality monitoring.
Claims
1. An organic carbon detector that can be used with a liquid chromatography equipment, comprising a carbon oxidization subsystem, and a stripping and CO.sub.2 detection subsystem, wherein the carbon oxidization subsystem and the stripping and CO.sub.2 detection subsystem are detachably connected and arranged in said order, the carbon oxidization subsystem contains a microfluidic ultraviolet oxidation module (3), the microfluidic ultraviolet oxidation module (3) contains an ultraviolet lamp (301) and a micro-channel (303), and the micro-channel (303) is composed of a capillary wound into a helix structure.
2. The organic carbon detector according to claim 1, wherein the microfluidic ultraviolet oxidation module (3) is configured to oxidize organic carbons contained in a liquid sample flowing into the microfluidic ultraviolet oxidation module (3).
3. The organic carbon detector according to claim 1, wherein the ultraviolet lamp (301) is arranged at the center of the helix structure of the capillary.
4. The organic carbon detector according to claim 1, wherein the micro-channel (303) is a microfluidic quartz chip etched with a spiral shaped micro-channel.
5. The organic carbon detector according to claim 4, wherein the ultraviolet lamp (301) is arranged on the surface of the microfluidic quartz chip.
6. The organic carbon detector according to claim 2, wherein the carbon oxidization subsystem further contains a microfluidic agent injection module (1) configured to inject an oxidant to the liquid sample.
7. The organic carbon detector according to claim 6, wherein the microfluidic agent injection module (1) contains an oxidant injection pump (103), an oxidant storing tank (104) and a microfluidic tubing.
8. The organic carbon detector according to claim 2, wherein the carbon oxidization subsystem further contains an inorganic carbon removal module (2) arranged upstream of the microfluidic ultraviolet oxidation module (3) and configured to remove inorganic carbons contained in the liquid sample.
9. The organic carbon detector according to claim 8, wherein the carbon oxidization subsystem further contains a microfluidic agent injection module (1) and a vacuum pumping system (4), wherein the inorganic carbon removal module (2) contains a tube coil (201) and an inorganic carbon removal module casing (202), wherein the tube coil (201) is an air permeable but waterproof capillary wound in a spiral of rings, wherein the microfluidic agent injection module (1) is configured to inject an acidic agent to the liquid sample, and the vacuum pumping system (4) is configured to vacuumize the inorganic carbon removal module casing (202).
10. The organic carbon detector according to claim 9, wherein the microfluidic agent injection module (1) contains an acidic agent injection pump (101), an acidic agent storing tank (102), and a microfluidic tubing.
11. The organic carbon detector according to claim 9, wherein the vacuum pumping system (4) contains a micro vacuum pump (401), a speed control circuit (402), a vacuum sensor (403), a one-way valve (404), and connecting pipes.
12. The organic carbon detector according to claim 2, wherein the carbon oxidization subsystem further contains a vacuum pumping system (4) configured to vacuumize the microfluidic ultraviolet oxidation module (3).
13. The organic carbon detector according to 1, wherein the stripping and CO.sub.2 detection subsystem contains a stripping module (7) and a CO.sub.2 detector (12).
14. The organic carbon detector according to 13, wherein a carrier gas is introduced to the stripping module (7) to carry organic carbon converted gas to the CO.sub.2 detector (12).
15. The organic carbon detector according to 13, wherein the CO.sub.2 detection subsystem contains a carrier gas source (5), a pressure and speed adjustment module (6), a condensation and dehumidification module (8), a halogen removal module (9), a gas filter (10), and an electronic gas flowmeter (11).
16. A method for determining organic carbons in a liquid sample using an organic carbon detector comprising a carbon oxidization subsystem and a stripping and CO.sub.2 detection subsystem, comprising: flowing a liquid sample to the carbon oxidization subsystem, injecting, by a microfluidic agent injection module (1) in the carbon oxidization subsystem, an oxidant to the liquid sample, oxidizing, by a microfluidic ultraviolet oxidation module (3) in the carbon oxidization subsystem, organic carbons contained in the liquid sample, and flowing the liquid sample to the stripping and CO.sub.2 detection subsystem.
17. The method according to claim 16, wherein the liquid sample is subject to liquid chromatography before treated in the organic carbon detector.
18. The method according to claim 16, further comprising: removing, by an inorganic carbon removal module (2) arranged upstream of the microfluidic ultraviolet oxidation module (3) in the carbon oxidization subsystem, inorganic carbons contained in the liquid sample.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) FIG. 1 is a block diagram showing module functions in an organic carbon detector for liquid chromatography of the present disclosure.
(2) FIG. 2 is a schematic diagram of structure of an organic carbon detector for liquid chromatography of Example 1.
(3) FIG. 3 shows the molecular weight distribution of carbon-containing organic molecules in water collected from Wastewater treatment plant 1 as tested by an organic carbon detector for liquid chromatography of Example 1.
(4) FIG. 4 is a schematic diagram of structure of an organic carbon detector for liquid chromatography of Example 2.
(5) FIG. 5 shows the molecular weight distribution of carbon-containing organic molecules in water collected from Wastewater treatment plant 2 as tested by an organic carbon detector for liquid chromatography of Example 2.
(6) FIG. 6 is a schematic diagram of structure of an organic carbon detector for liquid chromatography of Example 3.
(7) FIG. 7 shows the carbon/nitrogen-containing organic molecules' molecular weight distribution curves, particularly the molecular weight distribution curve of carbon-containing organic molecules as tested in Example 4(a), and the molecular weight distribution curve of nitrogen-containing organic molecules as tested in Example 4(b).
REFERENCE NUMERALS
(8) 1—microfluidic agent injection module; 2—inorganic carbon removal module; 3—microfluidic ultraviolet oxidization module; 4—vacuum pumping system; 5—nitrogen carrier gas source; 6—pressure and speed adjustment module; 7—stripping module; 8—condensation and dehumidification module; 9—halogen removal module; 10—gas filter; 11—electronic gas flowmeter module; 12—CO.sub.2 detector; 101—acidic agent injection pump; 102—acidic agent storing tank; 103—oxidant injection pump; 104—oxidant storing tank; 201—tube coil; 202—inorganic carbon removal module casing; 301—ultraviolet lamp; 302—ultraviolet lamp power supply; 303—micro-channel; 304—microfluidic ultraviolet oxidization module casing; 401—micro vacuum pump; 402—speed control circuit; 403—vacuum sensor; 404—one-way valve; 601—electromagnetic valve; 602—pressure control valve; 603—pressure gauge; 604—gas flow rate control valve; 701—casing; 702—liquid inlet; 703—liquid outlet; 704—gas inlet; 705—gas outlet; 706—sieve plate; 707—heating mantle; 708—liquid seal drum A; 709—liquid seal drum B.
DETAILED DESCRIPTION OF THE INVENTION
(9) The present disclosure will be further described with reference to the Examples.
EXAMPLE 1
(10) The present Example provides an organic carbon detector for liquid chromatography, as shown in FIG. 1, containing a microfluidic agent injection module 1, an inorganic carbon removal module 2, a microfluidic ultraviolet oxidation module 3, a vacuum pumping system 4, a carrier gas source 5, a pressure and speed adjustment module 6, a stripping module 7, a stripping gas treatment unit, and a CO.sub.2 detector 12. The stripping gas treatment unit contains a condensation and dehumidification module 8, a halogen removal module 9, a gas filter 10 and an electronic gas flowmeter module 11.
(11) As shown in FIG. 2, the microfluidic agent injection module 1 contains an acidic agent injection pump 101, an acidic agent storing tank 102 and a microfluidic tubing. The acidic agent injection pump precisely drives a screw rod by a stepper motor to pull a 500 μL micro syringe to take in the acidic agent from the acidic agent storing tank, and then pushes the syringe to sustainably expel the acidic agent to the pipeline where a liquid sample such as a liquid chromatography mobile phase flows. The acidic agent is 30.0 vol % phosphorus acid, and the acidic agent is injected at a flow rate of 2.0 μl/min.
(12) As shown in FIG. 2, the microfluidic agent injection module 1 further contains an oxidant injection pump 103, an oxidant storing tank 104 and a microfluidic tubing. The oxidant injection pump precisely drives a screw rod by a stepper motor to pull a 500 μL micro syringe to take in the oxidant from the oxidant storing tank, and then pushes the syringe to sustainably expel the oxidant to the pipeline where the liquid sample flows. The oxidant is a solution containing 5.0 mass % of potassium persulfate, and the oxidant is injected at a flow rate of 2.0 μl/min.
(13) As shown in FIG. 2, the inorganic carbon removal module 2 mainly contains a tube coil 201 and a casing 202, wherein the tube coil 201 is an air permeable but waterproof capillary wound in a spiral of rings, and the capillary is made of ethylene tetrafluoroethylene (Teflon® ETFE) and has an inner diameter of 0.5 mm, an outer diameter of 1/16 inch and a length of 5.0 m. When the liquid sample passes through the coil in the vacuumized inorganic carbon removal module 2, the gases dissolved in the liquid sample such as O.sub.2 and CO.sub.2 diffuse to the casing 202 outside the capillary and then removed by the vacuum pumping system 4.
(14) As shown in FIG. 2, the vacuum pumping system 4 contains a micro vacuum pump 401, a speed control circuit 402, a vacuum sensor 403, a one-way valve 404 and connecting pipelines. The vacuum pumping system 4 provide a vacuum required by the inorganic carbon removal module 2. The micro vacuum pump 401 is connected to the casing 202 of the inorganic carbon removal module via a one-way valve for vacuumizing the inorganic carbon removal module. The vacuum sensor 403 is arranged between the one-way valve 404 and the vacuumized casing 202 via a three-way valve, and transmits the pressure data monitored real-timely to the speed control circuit 402. The speed control circuit 402 controls the micro vacuum pump 401 by pulse width modulation according to the difference between the real-time pressure value and a preset target, so as to keep the inorganic carbon removal module 2 at a pressure lower than the atmospheric pressure by at least 90 kPa.
(15) As shown in FIG. 2, the microfluidic ultraviolet oxidation module 3 contains an ultraviolet lamp 301, an ultraviolet lamp power supply 302, a micro-channel 303 and a casing 304, wherein the lamp pipe of the ultraviolet lamp 301 and the micro-channel 303 are inside the casing 304. A pen-shaped low voltage mercury lamp is used as the ultraviolet lamp 301, and the lamp pipe is 7.0 cm in length and has an outer diameter of 6.5 mm. The ultraviolet lamp power supply 302 provides a high voltage for lighting the low voltage mercury lamp. The micro-channel 303 is composed of a JGS2 quartz capillary having an inner diameter of 0.8 mm, an outer diameter of 2.0 mm and a length of 124.0 cm, wherein the quartz capillary is wound into a helix having a helix inner diameter of 10.0 mm. The ultraviolet lamp tube is positioned at the center of the helix structure. The quartz capillary made micro-channel 303 is connected to a pipe of poly-ether-ether-ketone (PEEK) outside the casing 304 using a custom-made two-way valve also made of PEEK.
(16) As shown in FIG. 2, the pressure and speed adjustment module 6 contains an electromagnetic valve 601, a pressure control valve 602, a pressure gauge 603 and a gas flow rate control valve 604. The electromagnetic valve 601 controls the on-off of the carrier gas flow, and the pressure control valve 602 may adjust the pressure of the carrier gas entering the detector and display the pressure on the pressure gauge 603. The gas flow rate control valve 604 controls the flow rate of the carrier gas, and flow rate is monitored by the electronic gas flowmeter 11.
(17) As shown in FIG. 2, the stripping module 7, a place where the liquid sample flow meets the gas flow, contains a casing 701, a liquid inlet 702, a liquid outlet 703, a gas inlet 704, a gas outlet 705, a sieve plate 706, a heating mantle 707, a liquid seal drum A 708 and a liquid seal drum B 709. The liquid sample flows continuously into the stripping module from the liquid inlet 702. The carrier nitrogen gas enters the stripping module upwards from the gas inlet 704, passes through the sieve plate 706 to continuously form bubbles in the flowing liquid sample containing H.sub.2CO.sub.3/CO.sub.2 so as to move the H.sub.2CO.sub.3/CO.sub.2 as CO.sub.2 to the carrier nitrogen gas, and then enters the downstream gas pipeline from the gas outlet 705. The liquid sample with CO.sub.2 removed is discharged from the liquid outlet 703. To prevent the carrier gas from leaking out of the stripping module from the liquid outlet 703, the liquid outlet 703 is linked to the liquid seal drum A 708, the liquid in which is sufficient to provide a pressure higher than the maximal pressure difference between the stripping module and the outlet of the CO.sub.2 detector. The heating mantle 707 is used to heat the stripping module 7, keeping the temperature at 35° C., which helps to reduce CO.sub.2 solubility in water and promote nitrogen gas stripping.
(18) As shown in FIG. 2, the condensation and dehumidification module 8 is arranged between the stripping module 7 and the halogen removal module 9, and contains a condensing tube and an electronic condenser. The condensing tube is arranged between the liquid outlet of the liquid seal drum A 708 and the liquid inlet of the liquid seal drum B 709 by a three-way valve. The liquid seal drum A 708 and liquid seal drum B 709 may avoid gas leak from the condensing tube, and the condensate may be introduced continuously to the liquid seal drum A 708 and liquid seal drum B 709 to keep a constant liquid level in these two liquid seal drums.
(19) As shown in FIG. 2, the halogen removal module 9 contains copper granules in the interior. When a liquid sample contains a relatively high level of chloride and/or bromide ions, these ions react with the hydroxyl radicals, reactive oxygen species or the like during ultraviolet oxidation and turn into hypochlorous acid and/or hypobromous acid, which will join the carrier gas as Cl.sub.2 and/or Br.sub.2 in the stripping module. The Cl.sub.2 and Br.sub.2 are both oxidizing agents, and may react with the reducing copper ions, the products of which may be removed readily. The gas filter 10 uses an air-permeable hydrophobic film made of PTFE to trap particulate matters in the gas, so as to avoid any damage to the CO.sub.2 detector.
(20) As shown in FIG. 2, the electronic gas flowmeter 11 contains a sensor chip adopting the thermal mass flow measuring principle with no temperature calibration needed. The electronic gas flowmeter may measure the flow rate in the range of 0-2 L/min, and records the flow rate Q of the gas entering the CO.sub.2 detector.
(21) As shown in FIG. 2, the CO.sub.2 detector 12 is a non-dispersive infrared spectroscopy based gas sensor. Specifically, Lark-1 non-dispersive infrared spectroscopy based CO.sub.2 sensor (Suzhou PromiSense Electronic Technology Co., Ltd) capable of measuring gases at the 1.0-100.0 ppm level is used in the present example to determine the CO.sub.2 concentration in the carrier gas.
(22) As shown in FIG. 1 and FIG. 2, a liquid sample to be analyzed enters the organic carbon detector. An acidic agent 102, or a combination of an acidic agent 102 and and/or an oxidant 104 are injected to the liquid sample via the injection pump 101/103. Under an acidic condition with a pH lower than 3, H.sub.2CO.sub.3/CO.sub.2 generated with inorganic carbons in the liquid sample is removed in the inorganic carbon removal module 2, wherein the vacuum pumping system 4 works to form a vacuum in the inorganic carbon removal module 2. When the liquid sample flows through the microfluidic ultraviolet oxidation module 3, the persulfate radicals contained in the liquid sample are converted to sulfate radicals, hydroxyl radicals and the like, which radicals are strong oxidizing agents that convert the organic carbons in the liquid sample to H.sub.2CO.sub.3/CO.sub.2 under an acidic condition. Then the liquid sample enters the stripping module 7. The carrier source 5 supplies highly pure nitrogen as the carrier gas, which is treated in the pressure and speed adjustment module 6 and then enters the stripping module 7 at a certain speed where the H.sub.2CO.sub.3/CO.sub.2 in the liquid sample is moved to the carrier nitrogen gas. The steam and CO.sub.2 containing carrier gas passes through the condensation and dehumidification module 8 to reduce the moisture in the carrier gas, removes chlorine and/or bromine at a trace amount in the halogen removal module 9, leaves particulate matters in the gas filter 10, has its gas flow rate determined in the electronic flowmeter 11, and finally enters the non-dispersive infrared spectroscopy based CO.sub.2 detector to test the CO.sub.2 concentration in the carrier gas. An electronic circuit system in the CO.sub.2 detector processes and transmit the generated signals to a master computer.
(23) The organic carbon detector in the present example was used with a size exclusion chromatography system. The size exclusion liquid chromatography system was LC100 liquid chromatography system (Shanghai Wufeng Scientific Instruments Co., Ltd) containing a binary pump, an automatic injector, a column oven, and a size exclusion liquid chromatography column (DOC-PW30S, Nanjing Tongkai Environmental Technologies Co., Ltd). A phosphate buffer solution containing 2.5 g/L KH.sub.2PO.sub.4 and 1.5 g/L Na.sub.2HPO.sub.4.2H.sub.2O was used as the chromatography mobile phase, and 500 μL wastewater that was collected from a sedimentation tank of wastewater treatment plant 1 and had passed through a 0.45 μm membrane filter was injected to the detection system for analysis. The test results were shown in FIG. 3, wherein the organic substances having a peak at 18-22 min were defined as macromolecular proteins, and those having a peak at 30-40 min were humic acids and fulvic acids. In addition, the organic matters having peaks at 40-49 min were defined as block buildings, and the matters having peaks at 50 min or later were deemed as small molecules.
EXAMPLE 2
(24) The organic carbon detector in the present example differs from the one in Example 1 in the following aspects.
(25) As shown in FIG. 4, the microfluidic agent injection module 1 contains only the acidic agent injection pump 101, the acidic agent storing tank 102, and a microfluidic tubing. No oxidant is injected to the liquid sample in this example, and the organic matters are mainly oxidized by the strong oxidizing agents such as hydroxyl radicals generated in the micro-channel 303 with ultraviolet radiation.
(26) As shown in FIG. 4, a PTFE capillary having an inner diameter of 0.25 mm, an outer diameter of 1.20 mm and a length of 10.0 m is used in the inorganic carbon removal module 2.
(27) As shown in FIG. 4, a microfluidic chip of JGS1 quartz is used as the micro-channel 303 in the microfluidic ultraviolet oxidation module 3, wherein the micro groove on the chip has a width of 0.40 mm, a height of 0.20 mm and a total length of 4.0 m. The micro groove is arranged featuring the shape of letter “S” and the whole arrangement covers a 8.0 cm×4.0 cm area. The ultraviolet lamp 301 is arranged 2.0 mm below the micro-channel 303 (i.e., the quartz microfluidic chip). In addition to the inorganic carbon removal module 2, the vacuum pumping system 4 also vacuumizes the microfluidic ultraviolet oxidation module 3, to reduce or eliminate absorbance of the ultraviolet lamp 301 emitted 185 nm light by O.sub.2 and H.sub.2O, such that the organic carbon oxidation may be improved.
(28) The organic carbon detector in the present example was used with a size exclusion chromatography system. The size exclusion liquid chromatography system was LC100 liquid chromatography system (Shanghai Wufeng Scientific Instruments Co., Ltd) containing a binary pump, an automatic injector, a column oven, a size exclusion liquid chromatography column (DOC-PW30S, Nanjing Tongkai Environmental Technologies Co., Ltd) and a ultraviolet absorbance detector. A phosphate buffer solution containing 2.5 g/L KH.sub.2PO.sub.4 and 1.5 g/L Na.sub.2HPO.sub.4.2H.sub.2O was used as the chromatography mobile phase, and 500 μL wastewater that was collected from a sedimentation tank of wastewater treatment plant 2 and had passed through a 0.45 μm membrane filter was injected to the detection system for analysis. The test results were shown in FIG. 5.
EXAMPLE 3
(29) The organic carbon detector in the present example differs from the one in Example 1 in the following aspects.
(30) As shown in FIG. 6, a microfluidic chip of JGS1 quartz is used as the micro-channel 303 in the microfluidic ultraviolet oxidation module 3, wherein the micro groove on the chip has a width of 0.40 mm, a height of 0.20 mm, and a length of 4.0 m. The micro groove is arranged featuring the shape of letter “S” and the whole arrangement covers a 8.0 cm×4.0 cm area. The ultraviolet lamp 301 is arranged 2.0 mm below the micro-channel 303 (i.e., the quartz microfluidic chip).
(31) As shown in FIG. 6, the carrier gas source 5 supplies highly pure nitrogen as the carrier gas. After treated in the pressure and speed adjustment module 6, the carrier gas passes at a certain flow rate through the casing 304 of the microfluidic ultraviolet oxidation module 3, and then enters the stripping module 7 to form bubbles in the oxidized liquid sample. As nitrogen gas does not absorb the 185 nm ultraviolet light, it is used to remove air within the casing 304 to avoid the attenuation of 185 nm ultraviolet light emitted by the ultraviolet lamp 301.
(32) The organic carbon detector was used with the size exclusion liquid chromatography system of Example 1, and 500 μL wastewater that was collected from a sedimentation tank of wastewater treatment plant 2 and had passed through a 0.45 μm membrane filter was injected to the detection system for analysis. A molecular weight distribution curve of soluble organic carbon containing molecules was obtained, which was similar to that as shown in FIG. 7(a).
EXAMPLE 4
(33) The organic carbon detector in the present example differs from the one in Example 3 in the following aspects.
(34) The liquid outlet of the microfluidic ultraviolet oxidation module 3 is connected with the inlet of the ultraviolet absorbance detector of the LC100 liquid chromatography system of Example 2, and the outlet of the ultraviolet absorbance detector is connected to the liquid inlet of the stripping module 7. The organic nitrogen can be sufficiently oxidized and converted to NO.sub.3.sup.− in the microfluidic ultraviolet oxidation module 3. As NO.sub.3.sup.− absorbs 220 nm ultraviolet lights while no other inorganic salts containing elements at the highest oxidation states absorb 220 nm ultraviolet lights, the test wavelength is set at 220 nm for the ultraviolet absorbance detector. In this respect, the soluble organic nitrogen and carbon containing organic substances can be tested in series.
(35) The organic carbon detector was used with the size exclusion liquid chromatography system of Example 3, and 500 μL wastewater that was collected from a sedimentation tank of wastewater treatment plant 2 and had passed through a 0.45 μm membrane filter was injected to the detection system for analysis. The molecular weight distribution curve of soluble nitrogen containing organic molecules was shown in FIG. 7(b) and the molecular weight distribution curve of soluble carbon containing organic molecules was shown in FIG. 7(a). In the molecular weight distribution curve of soluble nitrogen containing organic molecules, the peaks at 15-45 min showed the molecular weight and concentration of nitrogen containing organic matters, and the peak at 45-59 min reflected the concentration of NO.sub.3.sup.− originally present in the water sample.
