🧪 Petroleum Ether-Extractable Substances
Gravimetric determination of organic substances extractable with petroleum ether from wastewater and water — fats, oils, petroleum substances. Classic Polish standard used in industrial wastewater monitoring.
Overview
Petroleum ether-extractable substances (PEES) include group of organic compounds extractable from water and wastewater using petroleum ether (extraction gasoline, fraction 40–60°C). This group includes: petroleum substances (hydrocarbons, mineral oils), animal and vegetable fats, waxes, resins, fatty acids, and other non-polar compounds. PEES parameter is summary indicator of organic contamination of wastewater.
Polish standard PN-C-04559 describes gravimetric method — water sample is acidified and extracted with petroleum ether, extract is evaporated, and dry residue weighed on analytical balance. Method is simple, does not require expensive apparatus, but is time-consuming and less selective — does not distinguish petroleum substances from fats.
Difference between indicators: PEES includes ALL non-polar substances (petroleum + biogenic), while hydrocarbon oil index (PN-EN ISO 9377-2, GC-FID) includes ONLY C10–C40 hydrocarbons after polar substance removal. In practice: PEES > HOI, because PEES contains fats, esters, etc.
PEES parameter is required in water permits, municipal and industrial wastewater control (meat plants, dairies, refineries, auto workshops), and fat and oil separator effectiveness assessment.
Method principle
Wastewater sample (0.5–1 L) is acidified with hydrochloric or sulfuric acid to pH < 2, ensuring transfer of fatty acids and soaps to free (non-ionic) form, extractable with ether. Acidified sample is extracted three times with petroleum ether (fraction 40–60°C) in separatory funnel or by continuous extraction in Soxhlet apparatus. Combined ether extracts are dried with anhydrous sodium sulfate, evaporated on rotary evaporator or in water bath (under fume hood), and dry residue is dried at 105°C (30 min) and weighed on analytical balance with accuracy ±0.1 mg. Result expressed in mg/L.
Applications
- Municipal and industrial wastewater quality control (water permit)
- Wastewater from food plants monitoring (dairies, meat plants, slaughterhouses)
- Wastewater from refineries, fuel stations, auto workshops control
- Fat and oil separator effectiveness assessment
- Landfill leachate testing
- Surface water monitoring — fat and oil contamination
Key parameters
| Parameter | Value |
|---|---|
| Measurement range | 0.5–10,000 mg/L (with dilution) |
| Limit of quantification (LOQ) | 0.5 mg/L (extraction of 1 L sample) |
| Solvent | Petroleum ether (extraction gasoline) fr. 40–60°C |
| Weighing accuracy | ±0.1 mg (analytical balance) |
| Precision (CV) | 10–20% (gravimetric method — lower precision) |
| Analysis time | 4–8 hours (extraction + evaporation + drying) |
Standard
- Standard number
- PN-C-04559:1982
- Title (PL)
- Woda i ścieki — Badania zawartości substancji ekstrahujących się eterem naftowym
- Title (EN)
- Water and wastewater — Determination of petroleum ether-extractable substances
Step-by-step procedure
1. Glassware preparation
Wash 250 mL round-bottom flasks with acetone and petroleum ether. Dry at 105°C (30 min). Cool in desiccator. Weigh with accuracy 0.1 mg (mass m₀).
2. Sample acidification
Measure 1 L wastewater sample. Acidify with HCl to pH < 2 (check with indicator paper). Mix 5 min.
3. Extraction I
Transfer acidified sample to 2 L separatory funnel. Add 50 mL petroleum ether. Shake vigorously 3 min (carefully — vent). Let phases separate (15 min).
4. Extraction II and III
Drain aqueous phase. Repeat extraction twice with 50 mL petroleum ether each. Combine all organic phases.
5. Extract drying
Pass combined ether extracts through funnel with 20 g anhydrous Na₂SO₄. Collect in pre-weighed round-bottom flask.
6. Solvent evaporation
Evaporate petroleum ether on rotary evaporator (water bath 40°C, vacuum). Or evaporate under fume hood in water bath. Do not overheat — volatile substances may be lost.
7. Residue drying
Place flask with residue in oven at 105°C for 30 minutes. Cool in desiccator to room temperature (30 min).
8. Weighing
Weigh flask with residue (mass m₁) with accuracy 0.1 mg. Repeat drying and weighing to constant mass (difference < 0.5 mg).
9. Calculations
PEES [mg/L] = (m₁ - m₀) × 1000 / V_sample [L], where m₁ — flask mass with residue, m₀ — empty flask mass, V — sample volume.
10. Quality control
Blank (clean water through entire procedure) < 0.5 mg/L. Duplicate: RPD < 25%. Spike with mineral oil — recovery 70–120%.
Required equipment and apparatus
| Equipment | Example | Indicative price |
|---|---|---|
| Analytical balance | Mettler Toledo XPR205, Sartorius Quintix 224, accuracy 0.1 mg | 8,000–25,000 PLN |
| Glass separatory funnels 1–2 L | DURAN, Simax, borosilicate with PTFE stopcock | 100–300 PLN/pc |
| Rotary evaporator (rotavapor) | Heidolph Hei-VAP, IKA RV 10, Buchi Rotavapor R-300 | 15,000–50,000 PLN |
| Laboratory oven (105°C) | Binder ED 56, Memmert UN 30, POL-EKO SLW 32 | 5,000–15,000 PLN |
| Water bath (for evaporation under fume hood) | Memmert WNB 7, Julabo TW 8 | 3,000–8,000 PLN |
| Beakers, flasks, pipettes | DURAN borosilicate glassware, round-bottom flasks 250 mL | 20–100 PLN/pc |
Reagents, media and consumables
| Reagent | CAS | Details |
|---|---|---|
| Petroleum ether (extraction gasoline) fr. 40–60°C | 8032-32-4 | Analytical grade, fraction 40–60°C, extraction solvent, 150–200 mL per determination |
| Diluted hydrochloric acid (HCl) | 7647-01-0 | For sample acidification to pH < 2 before extraction |
| Anhydrous sodium sulfate (Na₂SO₄) | 7757-82-6 | Analytical grade, drying agent, calcined 400°C/4 h |
| Acetone (for glassware cleaning) | 67-64-1 | Analytical grade, for rinsing glassware before and after analysis |
Health and safety (OHS)
- Petroleum ether — highly flammable (flash point < -20°C), vapors heavier than air — EXCLUSIVELY in fume hood!
- Petroleum ether vapors — narcotic at high concentrations, irritant to respiratory tract
- Hydrochloric acid — corrosive, irritant vapors, eye and hand protection
- Wastewater samples — potentially infectious, nitrile gloves and face protection
- Rotavapor with water bath — do not exceed 40°C when evaporating ether
- Collect ether waste in sealed flammable organic waste container