Soil and sediments. Determination of 36 volatile organic compounds and 35 volatile halogenated hydrocarbons. Headspace gas chromatography-mass spectrometry (1)

1.

This method is suitable for the determination of the content of volatile organic compounds in soil and sediment.

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

Second, the principle of the method

Under certain temperature conditions, the volatile components in the sample in the headspace bottle volatilize to the headspace, generating vapor pressure, and the gas-liquid-solid three-phase reaches a thermodynamic dynamic equilibrium

3.

(1) Methanol : pesticide residue level

(2) Quartz sand : 60-200 mesh, burned in a muffle furnace at 400°C for 4 hours, placed in a desiccator to cool to room temperature, and transferred to a ground glass bottle for storage

(3) Sodium chloride : pure superior grade, the processing steps are the same as those of quartz sand

(4) Phosphoric acid : pure superior grade or above

(5) Ultra-pure water: no VOCs interference, can be purchased or prepared in the laboratory

(6) Matrix modifier: Measure 500mL ultrapure water , add a few drops of premium grade phosphoric acid to adjust to pH≤2, add 180g sodium chloride , dissolve and mix

(7) Mixed standard solution of volatile organic compounds: p=1000ug/mL, and the solvent is methanol

(8) Internal standard: fluorine, 1,4-dichlorobenzene-d ₄ , chlorobenzene-d ₅ mixed standard, p=1000ug/mL, and the solvent is methanol

(9) Substitute: Toluene-d8, p-bromofluorobenzene mixed standard, p=1000g/mL, and the solvent is methanol

Other materials with similar properties can also be used

(10) p-bromo-fluorobenzene : p = 10ug / mL, the solvent is methanol

Four, instruments and equipment

(1) Reciprocating oscillator
.

(2) Headspace instrument
.

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

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

(5) Oven
.

Five, pre-treatment

(1) Sample preparation

1.
Low-content samples (samples with predicted mass concentration lower than 1000ug/kg)

After storing the sample in cold storage and returning to room temperature, weigh 2g of the sample and place it in a clean headspace bottle.
Immediately add 10mL matrix modifier, substitute and internal standard solution to the bottle.
The mass concentration of the surrogate in and the internal standard is the same), sealed quickly, and oscillated on a shaker at a frequency of 150 times/min for 10 minutes, and waited for the headspace-GC/MS detection
.

2.
High content samples (samples with predicted content higher than 1000ug/kg)

After storing the sample in refrigeration and returning to room temperature, weigh 2g of the sample and place it in a clean headspace bottle, immediately add 10 mL of methanol, seal it, and oscillate on a shaker at a frequency of 150 times/min for 10 minutes
.
After standing to settle, pipette about 1 mL of the extract into a brown glass bottle
.
After returning the extract to room temperature before analysis, add 2.
0 g of quartz sand, 10 mL of matrix modifier and 10 to 100 uL of methanol extract to the empty headspace bottle
.
Add surrogate and internal standard solution, quickly seal, oscillate on a shaker at a frequency of 150 times/min for 10 minutes, and wait for headspace-GC/MS detection
.

(2) Determination of dry matter content

Determination of Organochlorine Pesticides in Soils and Sediments Gas Chromatography (1) ——Determination of Dry Matter Content
.