Rapid gas‐liquid chromatographic determination of low levels of erucic acid in rapeseed using an internal standard

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Abstract
A method is described for rapid determination of erucic acid in low erucic rapeseed. The method is suited primarily to erucic acid levels below 1 % and so provides greater sensitivity and accuracy than other procedures adapted to this range. Oil is expressed by means of rollers and the fatty acids are routinely transmethylated before gas‐liquid chromatographic separation isothermally at 215°C. For maximum speed and accuracy the methyl ester of tricosanoic acid (C23:0) is included as internal standard. It elutes after erucic acid (C22:1) and within 15 min of injection. Satisfactory resolution of behenic (C22:0) and erucic acids is achieved, with good separation from other fatty acids and from the internal standard, on a steady baseline. Using one column repeatedly or two columns alternately, approximately 30 samples can be analysed in 1 day. With dual integrators the sample output can be doubled. Within the range below 1 % erucic acid, oils of high (0.9% m/m) and low (0.2% m/m) content returned coefficients of variation (c.v.) of ± 1.1 % and ± 2.5%, respectively. When rapeseed sample variation was included, precision fell away and c.v. changed to ± 7% and ± 12%, respectively. Sample variation is examined briefly and suggestions are made to reduce this source of error.