4.20  Determination of polycyclic aromatic hydrocarbons (PAHs) in air

4.20.1  Introduction

Sampling is performed using a high volume sampler. Particle bound polycyclic aromatic hydrocarbons (PAHs) are collected on a glass fibre filter, and more volatile PAHs are adsorbed to plugs of polyurethane foam (PUF) placed behind the filter. The filter and the plugs are soxhlet extracted with cyclohexane after sampling. The pre-concentrated extracts are cleaned using liquid/liquid extraction and HPLC before analysis using high resolution gas chromatography combined with mass spectrometry (GC/MS).


4.20.2  Equipment and instruments

4.20.2.1  Gas chromatography/mass spectrometry (GC/MS)

Autosampler                             Hewlett-Packard 7673 or similar
Detector                                   : Hewlett-Packard 5970 Mass Selective Detector (MSD), 5973 MSD or similar
Gas chromatography                 : Hewlett-Packard 5890 or similar with splitless injector
GC-column : Capillary column, 25-30 m x 0.25 cm, CP-Sil 8CB, SE 52 or similar, 0.1 µm film thickness
Integrator system  Hewlett-Packard Pascal 3.2 ChemStation or similar

4.20.2.2  Liquid chromatograph

Injector                                     : Rheodyne 7125 with 2 ml sample loop
Column                                     Lichrosorb Si-60-5, 5 mm, 4.6 mm x 25 cm
Pump                                        : LDC Constametric model III
Syringe                                     : 1000 ml, Hamilton no. 1001
UV-detector LDC UVIII monitor model 1203
Valve for switching solvent : Hamilton no. 86414

4.20.2.3  Soxhlet equipment

Extractors                                 : 60 ml, male glass joint 24/29 and female glass joint 34/35
500 ml, male glass joint 24/29 and female glass joint 60/48
2000 ml, male glass joint 34/35 with flat lid, size 34/35
Extraction thimbles : 28 x 80 mm, cellulose, Schleicher & Schuell
53 x 145 mm, cellulose, Schleicher & Schuell
60 x 180 mm, cellulose, Schleicher & Schuell
Coolers                                     : double surface, 345 mm long with male glass joint 34/35
cooler, 260 mm long with male glass joint 34/35
cooler, 330 mm long with male glass joint 24/29
Connector                                 : female glass joint 34/35 to male glass joint 60/48

4.20.2.4  Glass equipment

Desiccator                                internal diam. 30 cm, lid with vacuum connection
Micro pipettes                           10, 20, 25, 50, 100 ml, < +0.25%, Brand or similar
Graduated cylinders                   : 100, 200 and 500 ml
Pasteur pipettes : 150 and 230 mm long
Sample vials  : 1.5 ml (Brown cat.no. 150900) with screw cap, Teflon lined (Brown cat.no. 150930)
Round bottomed flasks 250, 500 and 1000 ml, ground glass joint 24/29
3000 ml, ground glass joint 34/35
Centrifuge tube : 15 ml, conical with ground glass plug 14/15, graded to 10 ml

   
4.20.2.5  Other equipment

Analytical balance, 0-160 g, precision ± 0.02 mg
Gloves, thin polyethylene, KEBO
Gloves, solvent resistant of PE/EVOH/PE
Membrane vacuum pumps with Teflon membrane (solvent resistant), 2.4 m3/h
Metal cartridges (metal cylinders), for active carbon/ molecular sieve filter
Micro balance, capacity 3000 mg, precision + 1 mg
Millipore, MilliQ plus, water purifier
Pressure valve GA 2 (L'Air Liquide) with needle valve ALG 2B (L'Air Liquide)
Porcelain dish
TurboVap 500 pre-concentrator, Zymark
Tissue paper Kimwipes, Kimberly-Clark
Ultrasonic bath
Heater mantles for round bottomed flasks for 500, 1000 and 3000 ml flasks
Oven, 50–500°C


4.20.3  Chemicals and gases

Helium, 4.6                     99.996%,   Hydro
Nitrogen Hydro Ultra, 5.0   99.999%,   Hydro

Active carbon, 1.5 mm diam., Merck no. 2514
Chrompack Gas Clean moisture filter, no. 7971
Chrompack Gas Clean oxygen/charcoal filter, no. 7972
Molecular sieve, 0.5-2 mm diam., Merck no. 5707

Acetone, Merck no. 12
Acetonitrile, Ratburn no. RH1016
Diethylether, Ratburn no. RG2013
2,2-Dimethoxypropane, Merck no. 802936
Dimethylformamide, Rathburn no. RG2014
Acetic acid, Merck no. 62
Hexane, Merck no. 4371
Chloroform, Merck no. 2445
Methanol, Merck no. 6011
Sodium sulphate, Merck no. 6649
PAH-standards, see 6.1
RBS 25, lab detergent
Cyclohexane, Merck no. 2817
Toluene, Merck no. 8389


4.20.4  Cleaning of equipment and chemicals

4.20.4.1  Glass equipment

All glass equipment must be decontaminated before use. Leave the equipment in 2.5% RBS in water for 16 hours. Flush well with hot tap water followed by MilliQ water. Leave to dry on a clean surface.

4.20.4.2  Glass fibre filter

Put ca 50 filters (Gelman-Type A/E, 142 mm) on an Al-foil and heat to 450°C for 8 hours. After cooling to room temperature wrap each filter in Al-foil.

4.20.4.3  Extraction thimbles

Extract thimbles for 8 hours ("1 day") with cyclohexane in a 600 ml soxhlet extractor. Dry in a desiccator connected to a vacuum pump (capacity 2.4 m3/h, and 80 kPa (0.8 bar) at 100°C. Connect pump outlet to a cooler to condense solvent. Wrap dry thimbles in Al-foil.

4.20.4.4  Sampler

Dismantle the sampler. Wash glass, metal parts and gaskets with warm detergent (2.5% RBS 25 in water). Flush all parts except the gaskets, with warm water, distilled water and acetone. Flush the gaskets with warm water, distilled water, not acetone.

4.20.4.5  Sodium sulphate

Heat ca. 100 g sodium sulphate in a porcelain dish at 600°C for ca. 20 hours. Store in a 250 ml Pyrex bottle with tight screw cap. Label the bottle with date for cleaning. Max. storage time is 1 month.

4.20.4.6  PUF-plugs

Toluene
Clean new PUF-plugs with toluene (Merck no. 8389) in a 2000 ml soxhlet extractor. The extractor can take up to 8 plugs simultaneously. Use a 3000 ml round bottomed flask and fill toluene into the extractor until it empties the content into the round-bottomed flask. Add ca. 500 ml toluene and mount the lid and cooler. Turn on the heater and the cooling water. Extract the plugs for 24 hours.

Acetone, cyclohexane
Squeeze toluene out of the plugs (solvent resistant gloves!) and transfer the plugs to another 2000 ml soxhlet extractor. Acetone is added as prescribed for toluene and the plugs are extracted for 8 hours.

Finally, extract with cyclohexane (new extractor) for 8 hours.

Observe! Used plugs (which previously have passed trough the whole cleaning procedure, toluene included) can be cleaned as follows:

               1) Soxhlet extraction with acetone for 8 h
               2) Soxhlet extraction with cyclohexane for 8 h

4.20.4.7  Drying

After final extraction squeeze the cyclohexane out of the plugs. Place the plugs in a desiccator. Put the desiccator in an oven at 60°C, and connect desiccator to a vacuum pump. Dry for 16 hrs and wrap the plugs in Al-foil individually. Store pairs of plugs and a filter in zip-shut plastic bags.

4.20.4.8  XAD-2

Fill XAD-2 in a thimble and put it in a soxhlet extractor. Extract for 8 h with each of the following solvents: Methanol, acetonitrile and diethyl ether. Leave the wet adsorbent on an Al-foil in a fume hood until it appears dry. Dry in an oven at 35°C overnight.


4.20.5  Gas cleaning

4.20.5.1  Gas bottle exchange

  1. Gas bottles must be replaced when the pressure approach 20 bar. The bottle pressure should never be lower than 15 bar.
  2. Before exchanging GC-carrier gas bottles, set GC-oven temperature below 50°C.
  3. Bottle exchange should be performed rapidly. Collect the new bottle before disconnecting the old one.
  4. If only one spare bottle is in the storage room, order a new batch.
  5. Flush the bottle valve on the new bottle twice (ear protection) before connecting the pressure reduction valve.
  6. Connect pressure reduction valve firmly and open it.
  7. Check for leaks with leak detector (Ion Sciences: Gas Check B4 or Supelco: Snoop leak detector).
  8. Mount valve protection cap on the empty bottle and transport the bottle to the storage room.

4.20.5.2  Special procedures

Helium GC carrier gas cleaning:

  1. Chrompack Gas Clean Oxygen Filter (with charcoal) and Chrompack Gas Clean Moisture Filter are connected in series after the pressure reduction valve. Exchange the units after exchanging 5 bottles or once a year.
  2. Two metal cartridges are mounted in series on the gas line before each GC inlet. The first is filled with active carbon, the second is filled with molecular sieves. Exchange adsorbents each 3 years and after irregularities (empty gas bottle).

Nitrogen used for final sample blow-down/pre-concentration is cleaned using a metal cartridge filled with active carbon. Exchange adsorbent when exchanging the gas bottle.


4.20.6  Treatment of adsorbents

Chrompack filters are discarded after use.

Re-activation of molecular sieves: Fill molecular sieves in a metal cartridge and activate at 300°C (3 h) in an oven, flushing the cartridge with 20 ml/min. pre-filtered helium.

Active carbon is discarded after use.


4.20.7  Analysis

Sampling, extraction, pre-concentration and weighing is described in chapters 3.14.4 - 3.14.7.

4.20.7.1  Adding internal standards

Depending of sample type the internal standard is added in an amount similar to the expected concentration level of the sample.

4.20.7.2  Clean-up

The extract is cleaned using liquid/liquid distribution between cyclohexane and dimethylformamide (DMF). Mix DMF and water in the ratio 9:1 (DMF:water), e.g. 180 ml DMF and 20 ml de-ionised water (MilliQ-plus).

  1. The extract (4 ml) from 5.2 is transferred to a 15 ml centrifuge tube (graded to 10 ml). 3.2±0.1 ml DMF/water (9:1) is added with a pipette. Plug the tube and shake.
  2. Centrifuge for 5 min. at ca 2500 rpm. Transfer the cyclohexane phase, using a Pasteur pipette, to a new tube and add 1.2±0.1 ml DMF/water (9:1). Shake well, centrifuge and add the DMF/water phase to the DMF/water from point 1. If no emulsion is formed after shaking the centrifuge step may be omitted. Discard the cyclohexane.
  3. Add 5.2±0.2 ml (10 ml pipette) water and 3.2±0.1 ml cyclohexane to the DMF/water phase (totally 12.8 ml in the centrifuge tube). Shake well, centrifuge and remove (but keep) the cyclohexane phase. The DMF/water phase is extracted again with 1.0±0.1 ml cyclohexane and the two cyclo­hexane phases are combined. Discard the DMF/water.
  4. Add 2 ml water to "wash" the cyclohexane phase. Transfer the cyclohexane extract to a new glass and dry by adding 1/2 teaspoon of water free sodium sulphate. The extract is transferred to a new tube and pre-concentrated to 0.5 ml.

Often samples may be ready for GC/MS at this stage. Dirty samples may require an additional HPLC-clean-up step.

4.20.7.3  Sample clean-up using HPLC

Cleaned cyclohexane extracts, except low level samples from background areas, are cleaned using a silica-column (Lichrosorb SI-60-7, 250 x 4.6 mm). More polar compounds than unsubstituted PAHs will adsorb to the column, whereas the PAH-fraction elutes rapidly to be collected. The UV-detector is operated at 254 mm. The column is flushed with chloroform after each sample.

Between the pump and the eluent reservoirs a solvent switch makes it easy to change from one eluent to another. Cyclohexane, which is saturated with water, and chloroform are used as eluents. Water saturated cyclohexane is made by adding a few millilitres of water (MilliQ plus) to a bottle of cyclohexane. Sonicate the bottle for 30 min. Leave to separate overnight and decant the cyclohexane phase into another bottle the next day.

Start up:

  1. Turn on the detector. Set sensitivity to 2.048 absorbance units.
  2. Start the pump and set the flow to 1 ml/min. Check that there is no air in the tubes.

If there is, disconnect column, vent the air from the system and connect the column again.

  1. Flush the column with cyclohexane for a few minutes. Turn on the recorder and check that the baseline is stable. The recorder settings are 10 mV and 30 cm/h.
  2. Inject ca 1 ml (1000 µl syringe) of a naphthalene and coronene standard mix and mark the injection point on the recorder paper. Elute the compounds. Measure the distance from the injection point to the naphthalene peak start and from the injection point to the coronene peak end.
    Use 90% of the distance to the naphthalene start and 125% of the distance to the coronene end, as measure for collecting the PAH fraction.

Sample clean-up:

  1. Start the pump (1 ml/min) and the recorder and inject the sample with a clean syringe. Mark the injection point on the recorder paper.
  2. Collect the PAH-fraction in a 15 ml centrifuge tube after the measures described in the previous section.
  3. Switch to the chloroform eluent reservoir and increase the flow to 2 ml/min.
  4. After flushing most of the adsorbed compounds from the column (about 5 min), switch back to cyclohexane. When the baseline reaches the same level as before, the system is ready for the next injection.
  5. After cleaning 10 samples, perform a new standard injection as described in 5.3.1.1.
  6. Pre-concentrate the collected fraction, first using TurboVap and finally using a gentle nitrogen gas flow. Avoid evaporation of the sample to dryness.

4.20.7.4  Cleaning of the column

With time the columns separating performance will decrease and a cleaning is necessary. Make mixes of methanol/water 1:1 (50% vol. water) and methanol/ water 19:1 (5% water) and hexane/acetic acid/dimethoxypropane 44:5:1 (88% vol. hexane, 10% vol. acetic acid, 2% vol. dimethoxypropane). Use the following solvents at a flow of 2 ml/min.:

  1. Chloroform for ca 5 min.
  2. Methanol for ca 5 min.
  3. 1:1 Methanol/water for ca 30 min.
  4. Methanol for ca 5 min.
  5. Chloroform for ca 5 min.
  6. Hexane/acetic acid/dimethoxypropane 44:5:1 for ca 20 min.
  7. Chloroform for ca 5 min.
  8. Methanol with 5% water for ca 5 min.
  9. Chloroform for ca 5 min.
  10. Cyclohexane saturated with water until the baseline is stable


4.20.8  Calibration and quantification

4.20.8.1  PAH-standards

The standards should have the highest possible purity and, if available, be certified.

 

Certified standards from Community Bureau of Reference (BCR): Purity  (%)
Fluoranthene
Pyrene
Benzo[ghi]fluoranthene
Benz[a]anthracene
Chrysene
Triphenylene
Benzo[a]fluoranthene
Benzo[b]fluoranthene
Benzo[j]fluoranthene
Benzo[e]pyrene
Benzo[a]pyrene
Indeno[1,2,3-cd]pyrene
Dibenz[a,c]anthracene
Dibenz[a,h]anthracene
Benzo[ghi]perylene
Coronene
99.49
99.75
99.4
99.78
99.20
99.77
99.5
99.5
99.5
99.0
99.3
99.8
99.5
99.8
99.0
99.83

 

Standards from Tokyo Kasei Kogyo, Ltd., Japan: Purity (%)
Biphenyl 
Acenaphthene
Phenanthrene
Anthracene
Fluorene
>99
>99
Zone Refined, 30 passes
Zone Refined, 70 passes
Zone Refined, 70 passes

 

Standard from Dr. Ehrensdorfer GmbH, Germany: Purity (%)
Dibenzothiophene 99.7

 

Standards from Promochem GmbH, Wesel, Germany: Purity (%)
Naphtalene
1-Methylnaphtalene
2-Methylnaphtalene
Acenaphtylene 
3-Methylphenanthrene
2-Metyhlphenanthrene
2-Metyhlanthracene 
9-Methylphenanthrene
Benzo[b]fluorene
Cyclopenta[cd]pyrene
Anthanthrene
Perylene
Dibenzo[a,e]pyrene
Dibenzo[a,i]pyrene 
Dibenzo[a,h]pyrene
99.8
97
98
99.8
99.8
99
>99
99.9
99.5
99
>99
99.6
99.8
99.9
99.8

 

Certified standards from Chem Service, Inc., West Chester, USA: Purity (%)
1-Methylphenanthrene
Dibenzofuran
Benzo[a]fluorene
Retene
Benzo[k]fluoranthene 
99.5
98
99
85
99.0

 

Labelled standards from C/D/N Isotopes Inc., Canada: Purity (%)
2-Methylnaphtalene-D10 
Acenaphthene-D10
Anthracene-D10
Fluoranthene-D10
Pyrene-D10
Benz[a]anthracene-D10
Benzo[e]pyrene-D12
Benzo[ghi]perylene-D12
99.3
99.7
99.3
98.8
99.9
99.1
99.6
99.1

 

4.20.8.2   Main standard

The following compounds may be included in the main standard:

Naphtalene
2-Methylnaphtalene
1-Methylnaphtalene
Biphenyl 
Acenaphthylene
Acenaphthene
Dibenzofuran
Fluorene 
Dibenzothiophene
Phenanthrene
Anthracene
3-Methylphenanthrene
2-Methylphenanthrene
2-Methylanthracene
9-Methylphenanthrene
1-Methylphenanthrene
Fluoranthene
Pyrene 
Benzo[a]fluoren
Retene 
Benzo[b]fluoren
Benzo[ghi]fluoranthene
Syklopenta[cd]pyrene
Benz[a]anthracene
Chrysene
Triphenylene
Benzo[b]fluoranthene
Benzo[j]fluoranthene
Benzo[k]fluoranthene
Benzo[a]fluoranthene
Benzo[e]pyrene
Benzo[a]pyrene
Perylene
Indeno[1,2,3-cd]pyrene
Dibenz[a,c]anthracene
Dibenz[a,h]anthracene
Benzo[ghi]perylene
Anthranthene
Coronene
Dibenzo[ae]pyrene
Dibenzo[ai]pyrene
Dibenzo[ah]pyrene

 

Perform the weighing using the micro balance. Use gloves and a dust mask. Spatulas and other equipment should be rinsed with toluene before use. When all compounds are weighed, transfer them to a 25 ml volumetric flask using a Pasteur pipette and toluene. Fill the flask to the mark and sonicate until all PAH is dissolved. Compute the exact concentration for each compound (ng/ml). The individual concentration should be in the range 15±10 ng/ml. This corresponds to 300±100 mg of each single compound. Transfer mix to well labelled vial with Teflon lined screw cap. Weigh the vial and store it in a freezer.

4.20.8.3  Internal standards

The internal standard includes the following compounds: 2-methylnaphtalene-D10 (ISTD I), acenaphthene-D10 (ISTD II), anthracene-D10 (ISTD III), pyrene-D10 (ISTD IV), benz[a]anthracene-D12 (ISTD V), benzo[e]pyrene-D12 (ISTD VI), benzo[ghi]perylene-D112 (ISTD VII).

Ca. 1 mg of ISTD I, II, III, IV and ca 0.5 mg of ISTD V, VI, VII are weighed as described under 6.1.1 and transferred to a 25 ml volumetric flask filled to the mark with cyclohexane. The concentration range is ca 20-40 ng/µl. Transfer mix to a well-labelled vial with Teflon lined screw cap. Weigh the vial and store it in a freezer.

Transfer ca. 1 ml to a sample vial. Label the vial and use as working standard. Weighing is not necessary. Store in a refrigerator.

4.20.8.4  Recovery standard

As recovery standard fluoranthene-D10 may be used. Weigh in ca 1 mg, transfer to a 25 ml volumetric flask and fill to the mark with cyclohexane as described in 6.1.1. Transfer mix to well labelled vial with Teflon lined screw cap. Weigh the vial and store it in a freezer.

Transfer ca 1 ml to a sample vial. Mark the vial and use as working standard. Weighing is not necessary. Store in a refrigerator.

4.20.8.5  Quantification standard

Remove the flasks with main standard, internal standard and recovery standard from the freezer and leave to melt at room temperature. Use aluminium foil to protect the flasks against sunlight. Remove the foil and sonicate flasks for 5 minutes. Check that all PAH is dissolved. If crystals are visible, repeat sonication. Check the flasks for weight loss and compensate an eventual loss with solvent. 2 ml main standard is transferred to a 50 ml volumetric flask using a 2 ml pipette. To the same flask further 1 ml internal standard and 2 ml recovery standard are transferred. Fill the flask to the mark with cyclohexane. Transfer mix a well labelled vial with Teflon lined screw cap. Weigh the vial and store it in a freezer.

Transfer ca. 1 ml to a sample vial. Label the vial and use as working standard. Weighing is not necessary. Store in a refrigerator.

4.20.8.6  Control standard

This standard is used to check the GC/MS quantification performance (chapter 6.2.4). The standard may contain the following compounds:

          Biphenyl
          Phenanthrene
          Fluoranthene
          Benzo[a]anthracene
          Benzo[e]pyrene
          Benzo[ghi]perylene

First a mother standard is made as described under 6.1.1. 300±100 mg of each compound is weighed and dissolved in cyclohexane in a 10 ml volumetric flask. Label the flask, weigh and store in a freezer.

Working solution is made as described under 6.1.2. 1 ml. The mother standard is diluted to 50 ml with cyclohexane in a 50 ml volumetric flask. Store the flask in a freezer.

Transfer ca. 1 ml to a 2 ml sample vial. Label the vial and use as working standard. Weighing is not necessary. Store in a refrigerator.

4.20.8.7  Retention standard, HPLC

This standard is used to check retention times before HPLC clean-up.

Ca. 5 mg naphthalene and ca. 10 mg coronene is dissolved in 100 ml cyclohexane. The concentrations are ca. 50 mg naphthalene and ca. 100 mg coronene pr. ml. Store in a refrigerator.


4.20.9  Separation and quantification

The cleaned sample extracts are analysed using gas chromatography combined with mass spectrometry (GC/MS). The compounds are identified according to their retention time and molecular weight and quantified using internal standards.

4.20.9.1  GC separation

GC conditions:
- Column : CP-Sil 8CB, 25 m x 0.25 mm x 0.12 µm film thickness or similar.
- Injector temperature 300°C
- Temperature program : 50-100°C with 20°C/min., 100-300°C with 10°C/min., 300°C for 5-10 min.
- Carrier, helium : 85 kPa
- Split gasflow 40 +10 ml/min.
- Sample volume 1 ml splitless, (Autosampler or “hot-needle” injection)
Autosampler conditions:
- Solvent A : toluene
- Solvent B cyclohexane
- Sample wash  : 0
- Sample pumps 6
- Sample volume 1 µl
- Solvent A, washes 6
- Solvent B, washes : 6

Solvent A and B for syringe cleaning must be exchanged each day.

4.20.9.2  Mass spectrometry (MS)

Electron impact ionisation (EI) is used. Inject the quantification standard before each sample series and after each 10 samples.

MS conditions for EI (MSD 5970 and MSD 5973):
- GC/MS-interface 290°C
- Electron energy 70 eV
- Calibration compound : Perfluorotributylamine (PFTBA)


Automatic tuning (“Autotune”), or manual optimisation of mass scale and transmission of the mass filter (quadrupole) with PFTBA using mass fragments m/z 69.0, 219.0 and 502.0. Mass resolution, signal width at half height: 0.55±0.03. Calibration of mass scale at ±0.05 amu.

The following SIM-program may be used for quantification:

SIM-function

Compound group

Mass

1

 

 

 

 

Naphtalene

128.1

2-Methylnaphtalene

142.1

1-Methylnaphtalene

142.1

d10 z-Methylnaphtalene

152.1

Biphenyl

154.1

2

 

 

 

 

Acenaphthylene

152.1

Acenaphthene

154.1

d10 Acenaphthene

164.1

Dibenzofuran

168.1

Fluorene

166.1

3

 

 

 

 

 

 

 

 

Dibenzothiophene

184.1

Phenanthrene

178.1

Anthracene

178.1

d10 Anthracene

188.1

3-Metylphenanthrene

192.1

2-Methylphenanthrene

192.1

2-Methylanthracene

192.1

9-Methylphenanthrene

192.1

1-Methylphenanthrene

192.1

4

 

 

 

 

 

 

Fluoranthene

202.1

d10 Fluoranthene

212.1

Pyrene

202.1

d10Pyrene

212.1

Benzo[a]fluorene

216.1

Retene

234.1

Benzo[b]fluorene

216.1

5

 

 

 

 

Benzo[ghi]fluoranthene

226.1

Cyclopenta[cd]pyrene

226.1

Benz[a]anthracene

228.1

d12 Benz[a]anthracene

240.1

Chrysene/triphenylene

228.1

6

 

 

 

 

 

Benzo[b/j/k]fluoranthenes

252.1

Benzo[a]fluoranthene

252.1

Benzo[e]pyrene

252.1

d10 Benzo[e]pyrene

264.1

Benzo[a]pyrene

252.1

Perylene

252.1

7

 

 

 

 

 

 

 

 

Inden[1,2,3-cd]pyrene

276.1

Dibenz[a,c/a,h]anthracenes

278.1

Benzo[ghi]perylene

276.1

d10 Benzo[ghi]perylene

288.1

Anthanthrene

276.1

Coronene

300.1

Dibenzo[a,e]pyrene

302.1

Dibenzo[a,i]pyrene

302.1

Dibenzo[a,h]pyrene

302.1

 

If compounds occur at concentrations which saturate the detector these compounds may be quantified using the signal from the 13C-isotope in the compound, detected at a mass one amu higher than the number indicated in the table.

4.20.9.3  Quantification

1.    Relative response factors, RRFi, are computed for the single compounds relative to the internal standard (ISTD) after analysing the quantification standard with known concentrations.

               

            RRFi       : Relative response factor of compound i
            Amt.ISTD
 : Amount of internal standard injected
            Amt.i      : Amount of compound i injected
            Areai      : Peak area of compound i
            AreaISTD
  : Peak area of internal standard

2.    Quantification of samples is based on relative response factor, added amount internal standard and the peak area of each compound i.

               

            Amt.i      : Amount of compound i in the sample
            Amt.ISTD : Amount of internal standard added
            Areai      : Peak area of compound i
            RRFi
       : Relative response factor for compound i
            AreaISTD
 : Peak area of internal standard

Check the chromatogram for eventual interference and correct retention times before quantification.

3.    Recovery of internal standard (added before sample clean-up) is computed relative to amount of recovery standard added before the quantification. Relative response factors based on the recovery standard (RRFg) is calculated for each ISTD-compound from the quantification standard analysis.

         

          

            Amt.ISTD  : Amount internal standard added before extraction
            Amt.GSTD : Amount of recovery standard added before quantification
   
         AreaISTD   : Peak area of internal standard
   
         AreaGSTD  : Peak area of recovery standard

4.20.9.4  GC/MS-analysis

  1. Before each sample series the quantification standard is injected twice. The first injection is used to deactivate the injector and is not used for quantification.
  2. Inject the quantification standard not later than each 10 samples.
  3. The last injection should be a quantification standard.

4.20.9.5  Detection limit

The detection limit is defined as 3 times the noise level (compound signal/noise = 3:1) as shown in the following figure.

For outdoor air the detection limit is normally reported in the unit pg/m3. The detection limit varies according to the concentration level in the sample, the sample volume, the purity of the sample extract, sample loss during clean-up and the pre-concentration factor.


4.20.10  Quality assurance

4.20.10.1  Reception and storage of samples

Incoming samples must be registered in a sample journal with date, a sample number and an analysis form which follows the sample during the whole analysis.

A cleaned sample extract ready for GC/MS may be stored up to 6 months in a freezer before analysis.

4.20.10.2  Standard mixtures

PAHs dissolved in cyclohexane and stored in a freezer (dark) are stable for years. The main standard, quantification standard, internal standard, control standard and recovery standard must be stored in a freezer (<18°C). Control of weight and corrections for weight loss must be recorded. Max. storage time is 5 years.

The working solutions are stored in a refrigerator (4-6°C) and weight loss control is not necessary. Max. storage time is 6 months.

All new standards must be checked against the old standard and concentration deviations should be within ±10%.

4.20.10.3  Control standard

To check the GC/MS quantification a control standard must be analysed. The standard covers the whole volatility range of the PAHs to be quantified.

The standard must be analysed after every 20th sample or every 14th day when less then 20 samples are analysed. For long periods without any activity (months), the standard must be analysed once a month.

Plots showing the single results for each compound and an average of the last 10 analyses must be available.

4.20.10.4  Recovery of internal standard

Before GC/MS-analysis a recovery standard is added to the sample in an amount according to the amount of internal standard added.

The recovery of the internal standards should be within the following limits:

          ISTD      II              >10 to 100%
          ISTD      III, IV        >20 to 100%
          ISTD      V, IV, VII   >30 to 120%

Since the results for bicyclic PAHs is uncertain and the interest for these compounds is low, no limit is given for ISTD I.

If recovery is outside limits a note about this must be given in the analysis report. Low recovery is caused by losses during clean-up and pre-concentration. The result will be less reliable than with normal recovery.

Too high recovery may be caused by interference on the ISTD-signal. In such cases the quantification should be based on another ISTD with normal recovery.

4.20.10.5  Blanks

Blank tests must be performed on clean filters and PUF plugs using the complete method. 2 unexposed plugs and 1 unexposed filter are extracted and analysed as if it was a normal sample. This must be done after each 20th sample.

4.20.10.6  Control of results

The following criteria must be fulfilled for a satisfactory identification and quantifica­tion:


Last revision: November 2001