Gas chromatography apparatus fitted with an electron capture detector (ECD).

Head space apparatus.

Gas chromatography column, of glass, 2 m long and 2 mm in diameter, stationary phase. OV101 10 % or equivalent, impregnating a calcined diatomaceous earth, acid washed and silanised and of a particle size of 80 to 100 mesh.

Carrier and auxiliary gas: nitrogen for gas chromatography, suitable for detection by electron capture.

Glass flasks, 10 to 15 ml, with teflon coating and aluminium stopper with fitment for entry of syringe.

Hermetically sealing clamps.

Gas syringe 0,5 to 2 ml.

Exactly weigh around 3 g of oil in a glass flask (not to be reused); hermetically seal it. Place it in a thermostat at 70 °C for one hour. Using a syringe carefully remove 0,2 to 0,5 ml of the head space. Inject this into the column of the gas chromatography apparatus regulated as follows:

• injector temperature: 150 °C,

• column temperature: 70 to 80 °C,

• detector temperature: 200 to 250 °C.

Other temperatures may also be used provided the results remain equivalent.

Reference solutions: prepare standard solutions using refined olive oil with no trace of solvents with concentrations ranging from 0,05 to 1 ppm (mg/kg) and corresponding to the presumed content of the sample. The halogenated solvents may be diluted using pentane.

Quantitative assessment: correlate the surfaces or the elevations of the peaks of the sample and of the standard solution of the concentration presumed closest. If the deviation is greater than 10 % the analysis must be repeated in comparison with another standard solution until the deviation is within 10 %. The content is determined on the basis of the average of the elementary injections.

Expression of results: in ppm (mg/kg). The detection limit for the method is 0,01 mg/kg.