Division 5.2.2 Choice of operating conditions for waxes and methyl and ethyl esters (Note 6).F1

The operating conditions are generally as follows:

— Column temperature

20 °C/min 5 °C/min

80 °C at first (1′) 140 °C 335 °C (20)

— Detector temperature

350 °C.

— Amount injected

1 μl of n-heptane solution (2-4 ml).

— Carrier gas

helium or hydrogen at the optimal linear speed for the gas chosen (see Appendix A).

— Instrument sensitivity

suitable for fulfilling the above conditions.

These conditions may be modified to suit the characteristics of the column and the gas chromatograph in order to separate all the waxes and fatty acid methyl and ethyl esters and to obtain satisfactory peak separation (see Figures 2, 3 and 4) and a retention time of 18 ± 3 minutes for the lauryl arachidate internal standard. The most representative peak of the waxes must be over 60 % of the full-scale value while the methyl heptadecanoate internal standard for the methyl and ethyl esters must reach the full-scale value.

The peak integration parameters should be determined in such a way as to obtain a correct evaluation of the peak areas considered.