Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:13:p4
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 13 (pt 4/9)
Character Range: 858653–861668

≤6°C with minimum headspace and away from all possible sources of contamination.

Note: If a different fraction split is requested, the relevant compounds shall be represented in the calibration standard solution.

While it may be possible to store and use the stock solutions for longer than 12 months after preparation, the laboratory should assure itself of the stability of the solution by carrying out regular checks of the concentration of the analyte. The laboratory should retain records to confirm the stability of the solutions.

Calibration verification standard solution
Calibration performance should be assessed against ethanol-free petrol or any other suitable product with predominant hydrocarbons in the nC6nC10 range used to check validity of the calibration curve.

The product should be well characterised, such that the quantitative composition of the relevant fractions is known. This allows the assignment of a portion of a known quantity of this product to a particular fraction.

Calibration standards

Initial calibration

This involves analysis of at least five different concentrations covering the working range of the instrument used. Extrapolation of the response curve above the highest calibration level is not recommended. Initial calibration is run at the beginning of each analytical sequence.

13.2.5.3     Procedure
    1. Open the sample jar quickly, scrape off the top 1 cm of sample and discard. Remove all extraneous material (grass, pebbles, etc.) from the sample. Obtain the subsample by driving an inert coring device (PTFE or stainless steel spatula) into the sample and rapidly transfer a minimum of 5 g into a tared extraction vessel. Record the weight.
    2. Add methanol (at a minimum ratio of 1:2 sample:solvent) and an appropriate amount of surrogate standard solution in order to produce a final surrogate concentration at about the midpoint of the calibration range, taking further dilutions into consideration.
    3. Shake extract for about 30 minutes using end-over-end tumbler, orbital shaker or ultrasonic bath. Allow to settle. Clay samples should be completely disintegrated before an aliquot is taken for analysis. Samples should be maintained in a cool environment to ensure they do not overheat.
    4. Analyse an aliquot of methanol extract using an appropriate instrument for hydrocarbon analysis. If an internal standard is used, it should be included with the methanol extract transfer. Alternatively, the internal standard may be added automatically by instruments having this capability.

    13.2.6     GC Analysis

13.2.6.1     Calibration
At least five calibration standards should be prepared from the relevant calibration standard solution.
    * The calibration curve should have a linear regression of >0.99
    * At a minimum, run a daily check of the lowest calibration standard and the midpoint calibration standard to confirm stability of the calibration curve. Rerun the calibration curve if the low standard deviates by more than