Pre-treatment Method for Determination of Volatile Thio-ether Compounds in Offensive Odorous Sediment

Abstract

Method for determining volatile thio-ether compounds in offensive odorous sediment including: pre-treating a sediment sample, extracting volatile thio-ether compounds, separating and purifying the extraction supernatant in a solid phase extraction column, eluting with ethyl acetate, and finally collecting the eluent, which is then concentrated and used for determination by gas chromatography.

Claims

1. A pre-treatment method for the determination of volatile thio-ether compounds in offensive odorous sediment, comprising the following steps: (1) collecting a sample of an offensive odorous material and storing the sample away from light in a brown bottle to allow it to form a fresh sediment with a surface; (2) adding 0.1% HgCl.sub.2 to the surface of the fresh sediment for sterilization, while at the same time adding dry ice to keep the sample refrigerated and create an anaerobic environment on the surface of the fresh sediment; and finally placing the sample into a liquid nitrogen container for cold storage; (3) extracting a volatile thio ether compound from the sample in a two-step continuous extraction process, comprising a first step of alcohol/water exchange and a second step of ultrasonic extraction with a mixed extractant, wherein the first step comprises repeating three times a procedure of first weighing some sediment sample in a centrifuge tube, adding absolute methanol and NaCl, or absolute ethanol and NaCl, so that a solid-to-liquid ratio of a resulting mixture with the sample is 1:2-1:5, shaking adequately, then centrifuging and collecting supernatant after standing still, and finally combing supernatant from the three repeated procedures for further use and keeping a residual sludge of the sample for use in the second step; the second step comprises adding a mixed extraction solution of methanol/cyclohexane or ethanol/cyclohexane at a ratio of 1:0.5-1:3 to the residual sludge from the first step at a solid-to-liquid ratio of 1:2-1:3, then performing three repeats of an ultrasonic extraction in an ultrasonic cell disruption instrument, and finally combing ultrasonic extract obtained from the three repeated ultrasonic extractions; and (4) combing the combined supernatant of the first step of step (3) and the combined ultrasonic extract of the second step of step (3) to form a total extract dehydrating the total extract with absorbent cotton carrying anhydrous sodium sulfate, then applying the total extract to a solid phase extraction column at a flow rate of 3-5 mL/min; and finally eluting with an ethyl acetate solution and collecting an eluent, and concentrating the eluent on a rotary evaporator for determination.

2. The pre-treatment method according to claim 1, wherein in step (1) the sample is collected from a lake or river bed and stones, animal and plant residues are removed from the sample.

3. The pre-treatment method according to claim 1, wherein, amount of 0.1% HgCl.sub.2 used in step (2) is 5-15 mL HgCl.sub.2/kg sludge.

4. The pre-treatment method according to claim 1, wherein, extraction operation of step (3) is performed in an indoor anaerobic chamber.

5. The pre-treatment method according to claim 1, wherein, extraction temperature of volatile thio-ether compounds in step (3) is below 15, and extraction time is 10-30 min.

6. The pre-treatment method according to claim 1, wherein, concentration of NaCl added during alcohol water exchange in step (3) is 1020% (W/V).

7. The pre-treatment method according to claim 1, wherein, ratio of methanol or ethanol to cyclohexane in the mixed extraction solution in step (3) is 1:0.5-1:1.

8. The pre-treatment method according to claim 1, wherein, power of ultrasonic extraction instrument in step (3) is 900 W-1200 W.

9. (canceled)

10. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] FIG. 1 is a gas chromatogram of categories and content of volatile thio-ether compounds in sediment in Cyanobacteria area of Meiliang Bay, Taihu Lake, wherein a is hydrogen sulfide, b is methanethiol, c is dimethyl sulfide, d is dimethyl disulfide, and e is dimethyl disulfide;

[0030] FIG. 2 is a gas chromatogram of categories and content of volatile thio-ether compounds in sediment in reed wetland of Meiliang Bay, Taihu Lake, wherein a is hydrogen sulfide, b is methanethiol, c is dimethyl sulfide, d is dimethyl disulfide, and e is dimethyl disulfide;

[0031] FIG. 3 is a gas chromatogram of categories and content of volatile thio-ether compounds in sediment in river bed of Wunan River, Changzhou, wherein a is hydrogen sulfide, b is methanethiol, c is dimethyl sulfide, d is dimethyl disulfide, and e is dimethyl disulfide.

DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS OF THE INVENTION

[0032] The technical schemes of the invention will be described in detail in conjunction with Embodiments and drawings. Protection scope of the invention is not limited by the detailed embodiment, but limited by the claims.

Embodiment 1

[0033] According to the invention, the extraction method of volatile thio-ether compounds in sediment sample collected in Cyanobacteria area of Meiliang Bay, Taihu Lake is as follows:

[0034] (1) Sample collection and sealed storage away from light: collecting a cylindrical core sample of fresh sediment from a lake or river bed by a sediment corer and retaining a water column which is 20 cm long, and removing stones, animal and plant residues such as snails, corbicula fluminea and plant root system in the sludge sample; collecting 0-10 cm fresh sludge samples on the surface, rapidly filling 30 g into a 50 mL brown glass bottle after mixing adequately and retaining water of about 1 cm, and then sealing.

[0035] (2) Sample refreshing and anaerobic pre-treatment: adding 5 mL of 0.1% HgCl.sub.2 to the surface of fresh sediment for sterilization, adding 15 g of dry ice at the same time, finally placing the brown sample bottle into a liquid nitrogen container for cold storage, and transporting back to laboratory in time for determination.

[0036] (3) Volatile thio-ether compound extraction.

[0037] The first step: crude extraction: first weighing about 5 g sediment sample in a 50 mL centrifuge tube, adding absolute methanol and 10% NaCl solution at a solid-to-liquid ratio of 1:3, shaking adequately at 15 C., then centrifuging on a centrifuge at 5000 rpm at 15 C. for 10 min, collecting supernatant after standing still, repeating three times, and finally combing supernatant extracted three times above for use.

[0038] The second step: ultrasonic extraction with mixed extractant: adding 1:0.5 mixed extraction solution of methanol/cyclohexane to a residual sludge sample extracted in the first step at a solid-to-liquid ratio of 1:2, then performing ultrasonic extraction in an ultrasonic cell disruption instrument (power of ultrasonic intensity of the instrument is 900 w) at 15 C. for 15 min; then centrifuging on a centrifuge at 5000 rpm at 15 C. for 10 min, collecting supernatant after standing still, repeating three times, and finally combing supernatant extracted three times above for use.

[0039] (4) Purification of the extract: collecting and combing the extract obtained in the first step and the second step, further dehydrating with absorbent cotton carrying anhydrous sodium sulfate, and then purifying in the C18 solid phase extraction column, separating and purifying impurities in the extract at a flow rate of 5 mL/min; and finally eluting with 50 mL ethyl acetate solution, collecting the eluent at the flow rate of eluent being dropwise while eluting, and repeating three times; collecting the eluent and concentrating on a rotary evaporator to 1 mL for use and then determination.

[0040] The specific method for pre-treating C18 solid phase extraction column as well as anhydrous sodium sulfate and absorbent cotton before loading onto a chromatography column is as follows:

[0041] C18 solid phase extraction column pre-treatment: rinsing with cyclohexane in the solid phase extraction column at 5 mL/min, and repeating 3 times for use;

[0042] pre-treatment with anhydrous sodium sulfate: baking in 500 C. high-temperature furnace for 4 h, collecting in a wide-mouth glass bottle after cooling down to room temperature, sealing and storing for use; and

[0043] pre-treatment with absorbent cotton: refluxing with cyclohexane vapor for 16 h, taking out and drying in the air for use.

[0044] (5) Sample determination: determining the concentrated solution to be determined on Agilent gas chromatograph, and specific determination condition of Agilent 7890A GC-FPD: loaded gas is high-purity He, at a flow rate of 3 mL/min; hydrogen flow rate: 50 mL/min; air flow rate: 65.0 mL/min; make-up flow rate (He): 30.0 mL/min; injection port temperature: 250 C.; splitless injection; detector temperature: 250 C.; initial column temperature is 50 C., kept for 5 min, increased at 20 C./min to 250 C. and kept for 7 min.

[0045] Through determination, FIG. 1 is distribution information of volatile thio-ether compounds in sediment in Cyanobacteria area of Meiliang Bay, Taihu Lake, and provides strong technical support for scientifically evaluating diffusion flux of volatile thio-ether compounds at the sediment-water interface.

Embodiment 2

[0046] According to the invention, the extraction method of volatile thio-ether compounds in sediment sample collected in reed wetland of Meiliang Bay, Taihu Lake is as follows:

[0047] (1) Sample collection and sealed storage away from light: collecting a cylindrical core sample of fresh sediment from a lake or river bed by a sediment corer and retaining a water column which is 22 cm long, and removing stones, animal and plant residues such as snails, corbicula fluminea and plant root system in the sludge sample; collecting 0-10 cm fresh sludge samples on the surface, rapidly filling 30 g into a 50 mL brown glass bottle after mixing adequately and retaining water of about 1 cm, and then sealing.

[0048] (2) Sample refreshing and anaerobic pre-treatment: adding 10 mL of 0.1% HgCl.sub.2 to the surface of fresh sediment for sterilization, adding 15 g of dry ice at the same time, finally placing the brown sample bottle into a liquid nitrogen container for cold storage, and transporting back to laboratory in time for determination.

[0049] (3) Volatile thio-ether compound extraction.

[0050] The first step: crude extraction: first weighing about 5 g sediment sample in a 50 mL centrifuge tube, adding absolute ethanol and 20% NaCl solution at a solid-to-liquid ratio of 1:2, shaking adequately at 10 C., then centrifuging on a centrifuge at 5000 rpm at 10 C. for 10 min, collecting supernatant after standing still, repeating three times, and finally combing supernatant extracted three times above for use.

[0051] The second step: ultrasonic extraction with mixed extractant: adding 1:1 mixed extraction solution of methanol/cyclohexane to a residual sludge sample extracted in the first step at a solid-to-liquid ratio of 1:3, then performing ultrasonic extraction in an ultrasonic cell disruption instrument (power of ultrasonic intensity of the instrument is 1200 w) in 10 C. water bath for 10 min; then centrifuging on a centrifuge at 5000 rpm at 10 C. for 10 min, collecting supernatant after standing still, repeating three times, and finally combing supernatant extracted three times above for use.

[0052] (4) Purification of the extract: collecting and combing the extract obtained in the first step and the second step, further dehydrating with absorbent cotton carrying anhydrous sodium sulfate, and then purifying in the XAD-16 resin-filled solid phase extraction column, with a filling length of XAD-16 resin being 25 cm, separating and purifying impurities in the extract at a flow rate of 3 mL/min; and finally eluting with 50 mL ethyl acetate solution, collecting the eluent at the flow rate of eluent being dropwise while eluting, and repeating three times; collecting the eluent and concentrating on a rotary evaporator to 1 mL for use and then determination.

[0053] The solid phase extraction filler XAD-16 as well as anhydrous sodium sulfate and absorbent cotton are pre-treated before loading onto a chromatography column, and XAD-16 pre-treatment method is as follows:

[0054] soaking with 95% ethanol for 24 h, then rinsing with deionized water until the eluent is mixed with water without white opacity, and washing with distilled water until there is no alcohol taste; adding 4% hydrochloric acid solution to soak resin for 5 h, then washing with distilled water to be neutral; soaking the resin for additional 5 h with 5% NaOH solution, and washing with distilled water to be neutral; performing suction filtration under a vacuum pump, until no water drops, for use.

[0055] The pre-treatment method with anhydrous sodium sulfate and absorbent cotton is the same as in Embodiment 1.

[0056] (5) Sample determination: determining the concentrated solution to be determined on Agilent gas chromatograph, and specific determination condition of Agilent 7890A GC-FPD: loaded gas is high-purity He, at a flow rate of 3 mL/min; hydrogen flow rate: 50 mL/min; air flow rate: 65.0 mL/min; make-up flow rate (He): 30.0 mL/min; injection port temperature: 250 C.; splitless injection; detector temperature: 250 C.; initial column temperature is 50 C., kept for 5 min, increased at 20 C./min to 250 C. and kept for 7 min.

[0057] Through determination, FIG. 2 is distribution information of volatile thio-ether compounds in sediment in reed wetland of Meiliang Bay, Taihu Lake, and provides strong technical support for scientifically evaluating diffusion flux of volatile thio-ether compounds at the sediment-water interface.

Embodiment 3

[0058] By the technical scheme of the invention, the collected river bed sediment is subject to pre-treatment for extracting volatile thio-ether compounds:

[0059] (1) Sample collection and sealed storage away from light: collecting a cylindrical core sample of fresh sediment from a lake or river bed by a sediment corer and retaining a water column which is 25 cm long, and removing stones, animal and plant residues such as snails, corbicula fluminea and plant root system in the sludge sample; collecting 0-10 cm fresh sludge samples on the surface, rapidly filling 25 g into a 50 mL brown glass bottle after mixing adequately and retaining water of about 1 cm, and then sealing.

[0060] (2) Sample refreshing and anaerobic pre-treatment: adding 15 mL of 0.1% HgCl.sub.2 to the surface of fresh sediment for sterilization, adding 15 g of dry ice at the same time, finally placing the brown sample bottle into a liquid nitrogen container for cold storage, and transporting back to laboratory in time for determination.

[0061] (3) Volatile thio-ether compound extraction.

[0062] The first step: crude extraction: first weighing about 5 g sediment sample in a 50 mL centrifuge tube, adding absolute methanol and 15% NaCl solution at a solid-to-liquid ratio of 1:5, shaking adequately at 12 C., then centrifuging on a centrifuge at 5000 rpm at 12 C. for 10 min, collecting supernatant after standing still, repeating three times, and finally combing supernatant extracted three times above foruse.

[0063] The second step: ultrasonic extraction with mixed extractant: adding 1:3 mixed extraction solution of methanol/cyclohexane to a residual sludge sample extracted in the first step at a solid-to-liquid ratio of 1:2.5, then performing ultrasonic extraction in an ultrasonic cell disruption instrument (power of ultrasonic intensity of the instrument is 1200 w) at 12 C. for 30 min; then centrifuging on a centrifuge at 5000 rpm at 12 C. for 10 min, collecting supernatant after standing still, repeating three times, and finally combing supernatant extracted three times above for use.

[0064] (4) Purification of the extract: collecting and combing the extract obtained in the first step and the second step, further dehydrating with absorbent cotton carrying anhydrous sodium sulfate, and then purifying in the XAD-16 solid phase extraction column, with a filling length of XAD-16 resin being 25 cm, separating and purifying impurities in the extract at a flow rate of 4 mL/min; and finally eluting with 50 mL ethyl acetate solution, collecting the eluent at the flow rate of eluent being dropwise while eluting, and repeating three times; collecting the eluent and concentrating on a rotary evaporator to 1 mL for use and then determination.

[0065] The solid phase extraction filler XAD-16 as well as anhydrous sodium sulfate and absorbent cotton are pre-treated before loading onto a chromatography column, and the pre-treatment method is the same as in Embodiment 1.

[0066] (5) Sample determination: determining the concentrated solution to be determined on Agilent gas chromatograph, and specific determination condition of Agilent 7890A GC-FPD: loaded gas is high-purity He, at a flow rate of 3 mL/min; hydrogen flow rate: 50 mL/min; air flow rate: 65.0 mL/min; make-up flow rate (He): 30.0 mL/min; injection port temperature: 250 C.; splitless injection; detector temperature: 250 C.; initial column temperature is 50 C., kept for 5 min, increased at 20 C./min to 250 C. and kept for 7 min.

[0067] Through determination, FIG. 3 is distribution information of volatile thio-ether compounds in sediment in river bed of Wunan River, Changzhou, and provides strong technical support for scientifically evaluating diffusion flux of volatile thio-ether compounds at the sediment-water interface. Through determination of volatile thio-ether compounds in river bed sediment, the vertical and horizontal distribution information of volatile thio-ether compounds in the sediment can be known in time, so as to provide technical support for further implementing ecological project and eliminating black and odorous problem of the river bed.