Determination of dioxins in soil and sediments. Isotope dilution high resolution gas chromatography-high resolution mass spectrometry (1)

1.

This method is suitable for dioxin analysis in soil background, farmland soil environment, soil environmental assessment of construction projects, soil pollution accidents, and environmental investigations of rivers, lakes and marine sediments

Second, the principle of the method

This method uses isotope dilution high-resolution gas chromatography-high-resolution mass spectrometry to determine dioxins in soil and sediment towels.

3.

(1) 100/200ng/mLEPA-1613LCS

(2) 200ng/mLEPA-1613ISS

(3) Calibration curve standard: 0.

(4) Toluene : pesticide residue level

(5) Acetone : pesticide residue level

(6) Dichloromethane : pesticide residue level

(7) N-hexane : pesticide residue level

(8) Methanol : pesticide residue level

(9) Cyclohexane : pesticide residue level

(10) Nonane : 99% chromatographic standard

(11) Concentrated sulfuric acid : pure superior grade

(12) Anhydrous sodium sulfate : pure superior grade, burned at 450°C for 4 hours, and used after natural cooling to room temperature

(13) Neutral silica gel: Ultra-pure neutral silica gel with 120-200 mesh, extracted with pesticide residue dichloromethane for 24 hours before use , sealed in a clean glass bottle for use after vacuum drying
.

(14) Acidic activated alumina : imported acidic alumina , activated in an oven at 170°C for 24h before use, and used after natural cooling to room temperature
.

(15) CarbopackC activated carbon: 120～400μm imported graphite carbon
.

(16) Celite545 diatomaceous earth: imported diatomaceous earth, baked at 450℃ for 5h before use, and placed in a clean glass bottle for later use after cooling
.

Four, instruments and equipment

(1) Soxhlet extractor
.

(2) Rotary evaporator
.

(3) Nitrogen blowing instrument
.

(4) Glass packed column
.

(5) High resolution gas chromatography-high resolution mass spectrometer
.

(6) Oven
.

Five, pre-treatment

(1) Air-drying and screening of samples

The air-drying and screening of soil and sediment samples are performed in accordance with the relevant parts of HJ/T166 and GB17378.
5.
When collecting samples, air-drying and screening should avoid sunlight and cross-contamination between samples; samples can also be freeze-dried for moisture Remove
.

(2) Determination of moisture content

Weigh more than 5g of soil and sediment samples, bake them at 105-110°C for 4 hours, cool them to room temperature in a desiccator, and weigh them
.
Use the following formula to calculate the moisture content (wH2o, %)
.

WH ₂ o=(sample weight before drying-sample weight after drying)/sample weight before drying×100% (1)

(3) Sample extraction

1.
Environmental conditions and special equipment in the pretreatment room

The sample extraction and pre-treatment are carried out in the dioxin superclean laboratory
.

Special equipment: heating jacket, rotary evaporator, oven, ultrasonic cleaner, nitrogen blowing instrument, reagent cabinet
.
Supporting facilities: special container for ultra-pure water, bottle washing lye tank, full set of pre-treatment glassware, dryer, bottle drying rack, injection needle
.

2.
Sample extraction

Weigh a certain amount of sample (such as 10g) into a Soxhlet extractor, add 20uL 100/200ng/mL EPA-1613LCS to extract the internal standard, and extract with toluene for more than 18 hours
.
It should be noted that a certain amount of copper flakes or copper powder treated with dilute hydrochloric acid (copper flakes are recommended to facilitate the transfer of subsequent samples) to be used for desulfurization in the flask
.

(4) Sample purification

1.
Concentrate

After the extract has dropped to near room temperature (otherwise it is easy to suck), it is concentrated to near dryness with a rotary evaporator, and the concentrated bottle is rinsed several times with 16 mL of dichloromethane and transferred to a sample bottle, and dried with a nitrogen blower
.

2.
Concentrated sulfuric acid purification

Add 7 mL of n-hexane to the above sample bottle, ultrasonically shake, then add 8 mL of concentrated sulfuric acid to mix, shake, centrifuge, and take the supernatant
.
(Note: If the upper layer liquid is darker, it can be pickled multiple times)
.

3.
Silica gel alumina column purification

Packing: Both the acidic silica gel column and the acidic alumina column use dry packing (filling weight is 3.
5g and 4.
5g), the silica gel column and the alumina column are connected in series, and the silica gel column is on top
.

Wash the column: Wet and clean the column with 15-20 mL of n-hexane
.

Passing the column: Add the upper layer purified by concentrated sulfuric acid to the silica gel column, and then wash the concentrated acid layer twice with 7mL n-hexane.
The upper cleaning solution is also applied to the column, and the silica gel wall is washed 3 times with 2mL n-hexane, and the silica gel is removed.
For the column, clean the alumina column several times with 8 mL of dichloromethane -n-hexane solvent with a volume ratio of 6:94 , and the above eluents can be collected as waste liquid
.
Then use 16 mL of dichloromethane-n-hexane (60/40) (V/V) solvent with a volume ratio of 6:4 to clean the alumina column several times, and collect the eluent into a sample bottle.
The eluent is nitrogen Blow dry
.

4.
Carbon column purification

Wash the column: first wash the charcoal column with 10mL of toluene (filled with 2g), then wash with 6mL of n-hexane , and then turn the column upside down
.

Passing the column: Rinse the above sample bottles several times with 6mL cyclohexane- dichloromethane equal volume solvent, apply the cleaning solution to the column, and clean the column wall with 2mL 50/50(V/V) cyclohexane/dichloromethane solvent Then use 2 mL of a dichloromethane-methanol-toluene mixed solvent with a volume ratio of 75:20:5 to wash the column (the eluent is a waste liquid)
.
The column was inverted, eluted with 30 mL of toluene solvent, and collected the eluate with a 100 mL flat-bottomed flask
.

5.
Concentrate

The eluate is concentrated to near dryness with a rotary evaporator, and the concentration bottle is rinsed several times with 16 mL-methyl chloride.
The rinse is transferred to another sample bottle and dried with a nitrogen blower
.
Rinse the sample bottle several times with 1.
2mL dichloromethane, transfer the rinse solution to a 1.
5mL sharp-bottomed bottle, let the sample dry naturally, use a 25uL injection needle to transfer 20uL 100ng/mL EPA-1613ISS internal sample injection standard (Dilute 200ng/mL EPA-1613ISS twice with kane) into a sharp-bottomed sample bottle and analyze on the machine
.

Related Links: Determination of 60 Semi-volatile Organic Compounds in Soil and Sediment Gas Chromatography-Mass Spectrometry (3)