Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:13:p8
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 13 (pt 8/9)
Character Range: 869588–872586

of sample extract into a suitable solvent for clean-up. For example, a 1:1 DCM:acetone extract should be exchanged into a solvent other than acetone, to allow for removal of polar substances.
    * To the solvent-exchanged extract add an appropriate weight of silica gel. If an empirical determination of bulk density has been made, the weight may be replaced with an appropriate volume.
    * Mix the extract and silica gel thoroughly (e.g. witha  vortex mixer) and allow the sorbent to settle before removing a portion of the extract for analysis.
US EPA 3630C silica clean-up method gives information about clean-up of PAHs, PCBs, OCs and phenols but not specifically for hydrocarbons. On the other hand, US EPA Method 1664 gives silica gel clean-up information specifically for hydrocarbons.
Limitations
    1. Silica gel has a capacity to adsorb polar compounds, at approximately 30 mg per gram of material. Silica may become overloaded if too much polar material is present beyond the capacity of silica gel used. In such cases, multiple clean-up steps may be required.
    2. Waste sludges containing paint can give anomalous results due to clean-up procedures being unable to remove all such unwanted material. Such non-polar polymeric materials remaining in a solvent extract can then degrade in the high temperature GC injector, producing smaller hydrocarbon molecules recorded as petroleum hydrocarbons. In such situations, alternate clean-up procedures should be investigated, for example, gel permeation chromatography (GPC).
    3. Soils high in organic matter may also give false positive results.

    13.3.6     GC analysis
The sample should be analysed using a gas chromatograph fitted with an FID.

13.3.6.1     GC conditions
The exact conditions used will vary from laboratory to laboratory.

Injector: a split/splitless injector at >250°C is recommended. The injection liner should be checked and replaced regularly.

Oven: the oven ramp should be a single linear ramp. The final temperature of the oven program should be as high as possible to ensure maximum removal of the higher molecular weight hydrocarbons from the column prior to the next analysis.

Column: the capillary column should be a non-polar to semipolar phase—such as a bonded phase of polydimethylsiloxane containing up to 5% phenyl polydimethylsiloxane.

13.3.6.2     Chromatographic integration
The sample sequence should have adequate solvent blanks run to monitor baseline drift. Samples are integrated by taking a horizontal line from a baseline point after the elution of nC10. The fraction areas are calculated by the software and concentrations determined according to the 'Calculations' section below.

13.3.6.3     GC calibration
Perform calibration and retention time marking for the nC10 to nC40 hydrocarbons using approximately equal weights of nC10, nC16, nC34 and nC40 hydrocarbons dissolved in hexane (toluene can be added to assist dissolution).
    * At a minimum, run a 5-point calibration