⛽ Hydrocarbon Oil Index in Water — Petroleum Hydrocarbons (GC-FID)

Physicochemistry PN-EN ISO 9377-2

Overview

STATUS (as of 28.10.2026). PN-EN ISO 9377-2:2003 — Polish version, published 17.10.2003, implements EN ISO 9377-2:2000 and ISO 9377-2:2000 [IDT]; it replaced PN-EN ISO 9377-2:2002 (English version). The standard is current — no withdrawal note.

SCOPE (clause 1). The method is used to determine the hydrocarbon oil index in water by gas chromatography; it is suitable for surface water, waste water and water from sewage treatment plants and allows the index to be determined at concentrations above 0.1 mg/l. It is not suitable for the quantitative determination of volatile mineral oils, but the composition of the contamination can be inferred from the appearance of the chromatogram. Mineral oil content in soil and sediments — according to ISO/TR 11046. The concentration of animal and vegetable fats in the sample should not exceed 150 mg/l, because at higher levels the capacity of the clean-up column may be insufficient; in highly polluted waste waters, especially those with large amounts of surfactants, the recovery may be low.

DEFINITION (3.1). The hydrocarbon oil index determined by GC-FID is the sum of the concentrations of compounds extractable with a hydrocarbon solvent with a boiling point of 36–69 °C, not adsorbed on Florisil and eluting with retention times between n-decane (C₁₀H₂₂) and n-tetracontane (C₄₀H₈₂). These are long-chain or branched aliphatic, alicyclic, aromatic and alkyl-substituted aromatic hydrocarbons. The result is therefore defined by the course of the method itself.

INTERFERENCES (clause 4). Compounds of low polarity (e.g. halogenated hydrocarbons) and high concentrations of polar substances interfere; surfactants interfere with the extraction.

CALIBRATION AND STANDARDS (clause 6). The external standard is a mixture of equal amounts of two mineral oils without additives: type A — with distinct peaks, e.g. diesel fuel, and type B — with a higher boiling range and an unresolved signal, e.g. a lubricating oil with a boiling range of 325–460 °C; together approx. 10 mg/ml. At least five calibration solutions, e.g. 0; 0.2; 0.4; 0.6; 0.8 and 1.0 mg/ml, stable for up to six months at 4–8 °C. The extraction solvent contains n-decane and n-tetracontane as markers of the limits of the retention window. A mixture of n-alkanes (C₂₀, C₄₀ and at least three others) is used to check the chromatographic system, and a stearyl stearate solution to check the Florisil.

CONTROL REQUIREMENTS (clause 9). A blank in every series; recovery from water spiked with the control standard, preferably in every series, within 80–110 %; suitability of every new batch of Florisil — stearyl stearate must be retained and the recovery of mineral oil through the column must be at least 80 %; the n-alkane peaks resolved to the baseline, and the response of n-tetracontane relative to n-eicosane at least 0.8 (otherwise the injector discriminates against heavy hydrocarbons).

WHAT WE DO NOT GIVE HERE. The chromatographic conditions (an example in Annex B), details of the calibration, the calculation formulas and the precision data (9.7.2 onwards) — we only know their titles.

Method principle

The water sample (acidified to pH 2) is extracted in the bottle in which it was collected with a hydrocarbon solvent with a boiling point of 36–69 °C containing n-decane and n-tetracontane, stirring for 30 minutes with a magnetic stirrer; magnesium sulfate prevents emulsion. Polar substances are removed from the extract on a column of 2 g of Florisil under 2 g of anhydrous sodium sulfate, the extract is concentrated to 1 ml and analysed by capillary gas chromatography on a non-polar column with a flame ionisation detector.

The total peak area between n-decane and n-tetracontane is measured and the hydrocarbon oil index is calculated against an external standard of two specified mineral oils. The mass of the sample is determined by weighing the bottle before extraction and after emptying it.

Applications

• Surface waters — hydrocarbon oil index above 0.1 mg/l
• Waste waters and water from sewage treatment plants — with a limit for animal and vegetable fats (up to 150 mg/l) and a risk of low recovery with large amounts of surfactants
• Groundwaters — with field preservation, unless a high content of humic substances rules out acidification
• Qualitative assessment of the composition of mineral oil contamination from the appearance of the chromatogram

Key parameters

Standard

Standard number

PN-EN ISO 9377-2:2003

Title (PL)

Jakość wody — Oznaczanie indeksu oleju mineralnego — Część 2: Metoda z zastosowaniem ekstrakcji rozpuszczalnikiem i chromatografii gazowej

Title (EN)

Water quality — Determination of hydrocarbon oil index — Part 2: Method using solvent extraction and gas chromatography

Step-by-step procedure

1. Sampling and storage

   According to ISO 5667-3. Fill a glass bottle to approx. 90 %, close it and weigh it (m1). Store at approx. 4 °C and extract as soon as possible, at the latest within 4 days. If necessary, preserve in the field with acid to pH 2 — recommended for surface waters and groundwaters, but not with a high content of humic substances (yellow-brown colour). If an emulsion or fats above 150 mg/l are expected, additionally take a smaller sample in a 250 ml bottle (clause 8).

   🌡 Temperature: approx. 4 °C

2. Blank and recovery

   A blank with every series, with all reagents and glassware. Recovery — preferably in every series: 900 ml of water with 1.0 ml of control standard, the entire procedure; recovery 80–110 % (9.1–9.2).

3. Extraction

   If necessary, cool the sample to approx. 10 °C, acidify to pH 2 (if not done in the field), add approx. 80 g of magnesium sulfate per 900 ml (not needed if the sample does not form an emulsion), 50 ml of extraction solvent with the standards and a stirring bar; stir vigorously for 30 min. Collect the solvent layer with a microseparator, avoiding transfer of water; break strong emulsions by centrifugation. Extraction by shaking is permitted after its efficiency has been checked (9.3).

4. Clean-up on Florisil

   Pass the extract through a column of 2 g of Florisil under 2 g of sodium sulfate, then an additional 10 ml of solvent; rinse the column with approx. 10 ml. Shaking the whole extract with 2 g of Florisil for 30 min is permitted if the results are equivalent (9.4).

5. Concentration

   Concentrate to approx. 6 ml in a Kuderna-Danish apparatus or an evaporator, then with a gentle stream of nitrogen to slightly below 1 ml and make up to 1.0 ml (or determine the volume by weighing). With a high expected index or injection of large volumes, concentration may be omitted. Dry the empty bottle for 5 min and weigh it (m2) to the nearest 1 g (9.5).

6. Checking the Florisil

   Periodically and with every new batch: stearyl stearate must be retained and the recovery of mineral oil through the column must be at least 80 %; otherwise wash and reactivate the Florisil or use another batch (9.6).

7. Gas chromatography

   Choose the conditions so that the peaks of the n-alkane mixture are resolved to the baseline and the response of n-tetracontane relative to n-eicosane is at least 0.8 — otherwise improve or replace the injection system (9.7.1). Calibration, integration of the area between C₁₀ and C₄₀ and calculation of the index — according to the further clauses of the standard.

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• The extraction solvent (boiling point 36–69 °C) is extremely flammable — work in a fume hood, away from ignition sources
• Concentrated hydrochloric acid (12 mol/l) is corrosive — follow the safety data sheet
• Hydrogen for the flame ionisation detector — check the tightness of the chromatograph gas installation
• The test requires suitably qualified staff (clause 5)

Frequently asked questions