🌿 Benzene in workplace air — adsorption on activated charcoal and gas chromatography (GC-FID / GC-MS)

Environment PN-Z-04016-10

Overview

Benzene (CAS 71-43-2) is a flammable, colourless or pale yellow liquid with a sweetish odour (molar mass 78.11 g/mol, boiling point 80.1 °C, vapour pressure 101 hPa at 20 °C), the vapours of which form explosive mixtures with air; in the EU it is classified as carcinogenic of category 1A and mutagenic of category 1B (H350, H340, H372, H304, H225). It is a raw material for ethylbenzene, cumene, aniline and cyclohexane, a solvent and a component of petrol. In Poland the determination of benzene in air at workplaces is governed by PN-Z-04016-10:2005: adsorption of the vapours on activated charcoal, desorption with carbon disulfide and gas chromatography; the smallest concentration determinable by this method is 0.5 mg/m³. The maximum admissible concentration (NDS) was 1.6 mg/m³ (Dz.U. 2018 poz. 1286 [Journal of Laws 2018, item 1286], the "skin" notation), and from 5 April 2026 a value of 0.66 mg/m³ (0.2 ppm) is in force. For that reason CIOP-PIB has worked out a revised method (Wasilewski, Kondej, PiMOŚP 2026, No 2(128)) with a range of 0.066–1.32 mg/m³ (1/10–2 of the new NDS), meeting PN-EN 482, with FID or MS detection, validated against a background of toluene, n-hexane, styrene, ethylbenzene and the xylenes. The validation parameters: GC-FID — LOD 0.103 µg/ml, LOQ 0.308 µg/ml, total precision 5.25 %, expanded uncertainty 23.02 %; GC-MS — LOD 0.76 ng/ml, LOQ 2.27 ng/ml, precision 5.93 %, expanded uncertainty 25.65 %. Laboratories applying PN-Z-04016-10 take the samples at a flow rate of 0.05–0.08 dm³/min up to 30 dm³ on an activated charcoal tube; samples kept in a refrigerator are stable for 7 days (according to the ŚCOP list), and in the CIOP-PIB method — for 15 days.

Method principle

The benzene contained in the air tested is retained on activated charcoal in a sorption tube (two layers: 100 mg and 50 mg, separated by glass wool), desorbed with carbon disulfide and determined chromatographically. In the CIOP-PIB method up to 9 l of air is drawn through the tube at a flow rate of not more than 1.5 l/h (the tube connected to the sampling pump from the side of the shorter layer); at concentrations even above 2 NDS the benzene does not pass to the second layer in an amount greater than 10 %. Each layer of charcoal is poured separately into a vial with a valve, 1 ml of CS₂ of a reduced benzene content is added and it is shaken for 30 min; a blank from an unused tube is prepared in an identical manner. GC-FID analysis: column HP-5 30 m × 0.32 mm × 0.25 µm, oven 60 °C (4 min) → 25 °C/min → 190 °C (9.2 min), injector 250 °C, detector 300 °C, nitrogen 25 ml/min, hydrogen 30 ml/min, air 400 ml/min, split 5:1, injection 2 µl. GC-MS analysis: column RTX-5 silMS 30 m × 0.25 mm × 0.25 µm, oven 50 °C (4 min) → 25 °C/min → 190 °C, injector and transfer line 280 °C, helium 1 ml/min, split 10:1, injection 1 µl, SIM mode m/z 51 and 78. The concentration is read from the calibration curve (0.58–12.0 µg/ml in CS₂; R ≥ 0.9999), and the result is calculated as: X = (C − Cb)·v/(V·d), where v — the volume of CS₂ [ml], V — the volume of air [l], d — the recovery factor (on average 1.01 for GC-FID, 0.95 for GC-MS). Solutions of benzene in CS₂ kept in a refrigerator are stable for 3 days; the samples on the charcoal — for 15 days.

Applications

• Control of the sanitary and hygienic conditions in refineries, in petrochemistry, in the manufacture of ethylbenzene, cumene and aniline, at filling stations and in laboratories
• Assessment of the exposure to a carcinogenic substance of category 1A over the range 1/10–2 NDS (0.066–1.32 mg/m³) in accordance with PN-EN 482
• Measurements during work with solvents, paints, resins, rubber and petrol (a parallel determination of benzene in extraction naphtha)
• Determination of benzene in the presence of toluene, n-hexane, styrene, ethylbenzene and the xylenes (BTEX)

Key parameters

Standard

Standard number

PN-Z-04016-10:2005

Title (PL)

Ochrona czystości powietrza — Badania zawartości benzenu i jego homologów z nasyconym łańcuchem bocznym — Część 10: Oznaczanie benzenu na stanowiskach pracy metodą chromatografii gazowej

Title (EN)

Air purity protection — Tests for benzene and its homologues with saturated side chain — Part 10: Determination of benzene at workplaces by gas chromatography

Step-by-step procedure

1. Sampling

   In accordance with PN-Z-04008-7 draw up to 9 l of air through the activated charcoal tube (the shorter layer on the side of the pump) at a constant flow rate of not more than 1.5 l/h; keep the samples taken in a refrigerator (stable for 15 days).

2. Standards

   Prepare by weight the intermediate (about 1 mg/ml) and the basic (about 0.1 mg/ml) solution of benzene in CS₂; into six 10 ml flasks measure out 58, 74, 150, 300, 600 and 1200 µl of the basic solution and make up with CS₂ (0.58–12.00 µg/ml); the solutions are stable for 3 days in a refrigerator.

3. Calibration curve

   Inject 2 µl (GC-FID) or 1 µl (GC-MS) of each standard twice; the difference of the results from the mean ≤ 5 %; plot the dependence of the peak area on the concentration.

4. Desorption

   Pour each layer of charcoal separately into the vials, add 1 ml portions of CS₂, close them tightly and shake them for 30 min; prepare the laboratory blank from an unused tube in an identical manner.

5. Analysis

   Analyse the solutions under the established chromatographic conditions (two measurements, the difference ≤ 5 %); read the concentration of benzene from the calibration curve; check that there is < 10 % of the benzene in the second layer.

6. Recovery and calculations

   Determine the recovery factor d on six portions of 100 mg of charcoal with 6 µl of the intermediate solution (desorption after a day) against three comparison solutions; calculate X = (C − Cb)·v/(V·d) in mg/m³ and compare it with the NDS.

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• Benzene — carcinogenic of category 1A, mutagenic of category 1B, absorbed through the skin; all operations with the standards under a fume cupboard, in gloves resistant to solvents
• Carbon disulfide — highly flammable (a very low auto-ignition temperature) and toxic; store it away from sources of heat and work under a fume cupboard
• Hydrogen for the FID — a gas installation with leak detection; the residues of CS₂ and of benzene for disposal by authorised institutions

Frequently asked questions