Determination of Polycyclic Aromatic Hydrocarbons in Soils and Sediments Gas Chromatography-Mass Spectrometry (1)

1.

This method is suitable for the determination of 17 kinds of polycyclic aromatic hydrocarbons in ten soils and sediments.

After the applicability of other PAH compounds has been verified, this method can also be used for analysis

Second, the principle of the method

The polycyclic aromatic hydrocarbons in the soil or sediment are extracted by pressurized fluid extraction, and the appropriate purification method (copper powder desulfurization, silica gel alumina chromatography column, etc.

3.

Unless otherwise stated, the analysis is performed with superior grade pure chemical reagents that meet the national standards, and the experimental water is newly prepared ultrapure water

(1) N-hexane : pesticide residue level

(2) Dichloromethane : pesticide residue level

(3) Acetone : pesticide residue level

(4) Standard solution of polycyclic aromatic hydrocarbons , p=1000ug/mL, solvent is n-hexane

(5) Substitute: pyrene-du, p=1000ug/mL, solvent is n-hexane

(6) Internal standard: mixed standard solution of naphthalene-d8, acenaphthene-d10, qi-d, perylene-d12, phenanthrene-d10, p=1000ug/mL, solvent is n-hexane

(7) decafluoro triphenylphosphonium : p = 10ug / mL, the solvent is n-hexane

(8) Diatomite: 60 mesh

(9) Quartz sand: 40-100 mesh, burn it in a muffle furnace at 450℃ for 4h before use

(10) Anhydrous sodium carbonate : burn it in a muffle furnace at 450°C for 4 hours before use

(11) Copper sheet: Use dilute hydrochloric acid solution to remove the oxides on the surface of the copper powder before use, rinse with experimental water to remove the acid, and rinse with acetone , then dry it with nitrogen until it is used.
Treat each time before use to keep the surface of the copper sheet Bright
.

(12) Ultra-pure silica gel (for column chromatography): 70-230 mesh
.

Pre-treatment method: extraction (n-hexane-dichloromethane equal volume mixed solvent) → take out and dry in a fume hood → bake at 170°C for at least 24 hours → cool in the fume hood → add 3% (mass ratio) ultra pure Water deactivation → Shake fully (1 shake in half a day, 30 minutes each time, 3 times in total) → Add n-hexane to soak and store (equilibrium)
.

(13) Alumina: chromatographically pure
.

Pre-treatment method: burn at 250℃ for 4h → let cool in a fume hood → add 3% (mass ratio) ultrapure water to deactivate → fully shake (1 shake in half a day, 30 minutes each time, 3 times in total) → add Zhengji Soak and preserve in alkane (equilibrium)
.

(14) Absorbent cotton: medical absorbent cotton, washed with a mixed solvent of equal volume of n-hexane-dichloromethane for many times, after washing, take it out and place it in a fume hood to dry and seal for later use
.

Four, instruments and equipment

(1) EI source single quadrupole gas chromatography mass spectrometer
.

(2) Chromatographic column: HP-5MS UI, 30m×0.
25mm×0.
25um
.

(3) Pressurized fluid extraction device
.

(4) Rotary evaporator
.

(5) Balance: the accuracy is 0.
01g
.

(6) Oven
.

Five, pre-treatment

(1) Sample preparation

" Determination of Organochlorine Pesticides in Soils and Sediments by Gas Chromatography (1) "

(2) Pressurized fluid extraction

Weigh 10g fresh/freeze-dried sample, add a certain amount of substitute (the recommended mass concentration on the machine is the same as the substitute mass concentration in the standard series) and mix well, then add 8-10g diatomaceous earth, mix well, and place in the extraction tank In the process, continue adding diatomaceous earth until the extraction tank is filled, and then perform pressurized fluid extraction
.
The operating conditions are as follows: Extraction agent: equal volume mixed solvent of n-hexane and acetone, extraction tank temperature 100℃, extraction pressure 1500psi, static extraction time 10min, rinsing is 60% of the tank volume, nitrogen blowing time is 60s, extraction cycle number is 2 Second, collect the extract
.

(3) Sample desulfurization,

" Determination of Organochlorine Pesticides in Soils and Sediments by Gas Chromatography (1) "

(4) Purification

According to the degree of contamination of the sample, sample purification can be selectively performed.
This method provides silica gel alumina chromatography column purification method, as follows:

(1) Dry/wet column packing: The inner diameter of the glass column is 1cm, and the packing is a small amount of absorbent cotton, silica gel 12cm, alumina 6cm, and anhydrous sodium sulfate 1cm from bottom to top
.

(2) Sample loading: transfer the enriched sample solution (solvent is n-hexane, about 1 mL) to separation and purification, rinse with 10 mL n-hexane, and discard the eluent
.

(3) Elution: Elute with 80mL of dichloromethane-n-hexane mixed solvent with a volume ratio of 3:7, collect the eluate in a pear-shaped bottle, and concentrate to about 0.
5mL by rotary evaporation in a water bath at 35°C, and transfer to a cell bottle In the medium, use n-hexane to make the volume to 1.
0 mL, and add a certain amount of internal standard liquid (the mass concentration of the internal standard is recommended to be consistent with the internal standard mass concentration in the standard series), and wait for the machine to analyze
.

(5) Determination of dry matter content

" Determination of Organochlorine Pesticides in Soils and Sediments by Gas Chromatography (1) "