🌿 PAH in soil (GC-MS)
Determination of 16 EPA polycyclic aromatic hydrocarbons (PAH) in soil by gas chromatography-mass spectrometry. Key test for soil contamination assessment.
Overview
Polycyclic aromatic hydrocarbons (PAH) are a group of over 100 organic compounds formed during incomplete combustion of organic matter. 16 PAHs from the EPA list (naphthalene, acenaphthylene, acenaphthene, fluorene, phenanthrene, anthracene, fluoranthene, pyrene, benzo[a]anthracene, chrysene, benzo[b]fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene, dibenzo[a,h]anthracene, benzo[g,h,i]perylene, indeno[1,2,3-cd]pyrene) constitute an environmental contamination indicator.
PAHs in soil originate from industry (coke plants, gasworks, refineries), transport, waste incineration, and natural processes. Benzo[a]pyrene is an IARC Group 1 carcinogenicity marker. The 2016 Polish regulation establishes permissible PAH concentrations in soil: 1 mg/kg for Group I soils (residential areas) and 20 mg/kg for Group IV (industrial areas).
The ISO 18287 method involves solvent extraction (Soxhlet, ASE, or ultrasound), extract cleanup on SPE columns (silica gel, florisil), and GC-MS analysis in SIM mode. It provides identification and quantification of individual PAHs with detection limits of 0.01–0.1 mg/kg dry mass.
Method principle
The dried and homogenized soil sample is extracted with organic solvent (dichloromethane, acetone/hexane, or toluene). The extract is purified on an SPE column with silica gel to remove interfering substances (fats, humic substances). The purified extract is analyzed by gas chromatography with mass spectrometric detection (GC-MS) in selected ion monitoring (SIM) mode. PAH identification is based on retention times and mass spectra, and quantification uses the internal standard method (deuterated PAHs).
Applications
- Assessment of soil contamination on post-industrial sites
- Soil testing for real estate transactions (due diligence)
- Environmental monitoring around coke plants, steel mills, and refineries
- Soil remediation — cleanup progress control
- Agricultural soil quality assessment (2016 Polish regulation)
- Soil testing for construction projects
Key parameters
| Parameter | Value |
|---|---|
| Number of analytes | 16 EPA PAHs |
| Detection limit | 0.01–0.1 mg/kg d.m. |
| Measurement range | 0.01–1000 mg/kg |
| B[a]P limit (Group I) | 1 mg/kg d.m. |
| Precision (CV) | 10–20% |
Standard
- Standard number
- PN-EN ISO 18287:2008
- Title (PL)
- Jakość gleby — Oznaczanie wielopierścieniowych węglowodorów aromatycznych (WWA) — Metoda chromatografii gazowej z detekcją spektrometryczną (GC-MS)
- Title (EN)
- Soil quality — Determination of polycyclic aromatic hydrocarbons (PAH) — Gas chromatographic method with mass spectrometric detection (GC-MS)
Step-by-step procedure
1. Sample preparation
Dry soil sample at room temperature (not >40°C). Sieve through 2 mm sieve. Homogenize. Weigh 10–20 g into ASE cell or Soxhlet thimble.
2. Internal standard addition
Add deuterated PAHs (spike) to sample before extraction. Concentration 100–500 µg/kg.
3. Extraction
ASE: acetone/hexane 1:1, 100°C, 100 bar, 3 cycles × 5 min. Soxhlet: DCM, 6–8 h (min. 20 cycles).
4. Extract concentration
Evaporate solvent on rotary evaporator to ~2 mL. Do not evaporate to dryness!
5. SPE cleanup
Pass extract through SPE column with silica gel. Elute with 20 mL DCM/hexane 1:1. Collect eluate.
6. Final concentration
Evaporate to ~1 mL under nitrogen stream. Add 100 µL chromatographic standard.
7. GC-MS analysis
Temperature program: 60°C (2 min) → 8°C/min → 300°C (10 min). Column: HP-5ms 30 m. SIM mode — qualifier ions for each PAH.
8. Calculations and reporting
Calculate concentrations using internal standard method. Convert to dry mass. Check internal standard recovery (40–120%).
Required equipment and apparatus
| Equipment | Example | Indicative price |
|---|---|---|
| Gas chromatograph GC-MS | Agilent 7890B/5977B, Shimadzu GCMS-QP2020 NX, Thermo ISQ 7610 | 400,000–800,000 PLN |
| ASE system (accelerated solvent extraction) | Thermo Dionex ASE 350, Büchi E-916 | 150,000–250,000 PLN |
| Soxhlet apparatus | BÜCHI E-812/E-816, VELP SER 148/6 | 20,000–50,000 PLN |
| SPE columns (silica gel/florisil) | Supelco LC-Si, Macherey-Nagel Chromabond | 20–50 PLN/pc. |
| Analytical balance | Mettler Toledo ME204, 0.1 mg accuracy | 5,000–15,000 PLN |
| Rotary evaporator | Büchi R-300, Heidolph Hei-VAP | 15,000–35,000 PLN |
Reagents, media and consumables
| Reagent | CAS | Details |
|---|---|---|
| Dichloromethane (DCM) | 75-09-2 | Pesticide analysis grade, extraction solvent |
| Acetone | 67-64-1 | Pesticide analysis grade, for extraction mixtures |
| n-Hexane | 110-54-3 | Pesticide analysis grade, solvent for cleanup |
| 16 EPA PAH standard | mix | 200 µg/mL solution in dichloromethane, certified CRM (Supelco EPA 610) |
| Internal standard (deuterated PAHs) | — | Naphthalene-d8, acenaphthene-d10, phenanthrene-d10, chrysene-d12, perylene-d12 |
| Activated silica gel | 112926-00-8 | For SPE columns, activation 400°C/4h |
Health and safety (OHS)
- Dichloromethane — suspected carcinogen (cat. 2), work in fume hood
- n-Hexane — neurotoxic with chronic exposure, vapor flammable
- Soil samples may contain toxic substances — nitrile gloves mandatory
- GC-MS — helium under pressure, do not damage lines
- Collect solvent waste in hazardous waste containers