Study of the relative response factors of various gas chromatograph-flame ionisation detector systems for measurement of C2-C9 hydrocarbons in air.

The assumption of an instrument response that is linear with carbon number is frequently used to quantify atmospheric non-methane hydrocarbons (NMHCs) when using gas chromatography (GC) and detection by flame ionisation detector (FID). In order to assess the validity of this widely used method the results of intercomparison measurements by 14 laboratories across Europe were evaluated. The intercomparison measurements were made on synthetic, gravimetrically-prepared, gas mixtures containing 30 hydrocarbons (C2-C9) in the low ppbv range, using various different GC-FID systems. The response per carbon atom of GC-FID systems to individual NMHCs, relative to that of butane, were found to differ by more than 25% across different systems. The differences were mostly caused by analytical errors within particular GC-FID systems and to a more minor degree by systematic deviations related to the molecular structure. (Correction factors due to the molecular structure would lessen the differences, e.g. by about 5% for olefin compounds.) The differences were larger than 10% even after elimination of obvious outliers. Thus, calibration of GC-FID systems with multicomponent NMHC mixtures is found to be essential whenever the accuracy of NMHC measurements is required to be better than about 10%. If calibration by multicomponent gas mixtures is not possible and effective carbon atom response factors are used to quantify the individual NMHC compounds then the particular analytical system should be carefully characterised and its responses to individual compounds be verified.

[Concentration profiles of putrescine and cadaverine in inoculated vacuum packed beef]. / Konzentrationsprofile von Putrescin und Cadaverin in beimpftem vakuumverpacktem Rindfleisch.

The potential of some Lactobacillus, Staphylococcus and Streptococcus strains for producing putrescine and cadavering during growth in vacuum packed beef was studied. Throughout the six weeks storage at 4 degrees C the samples were sensorily assessed at regular intervals, and their pH values and diamine contents were determined. The amines were quantified by means of capillary gas chromatography. The putrescine and cadaverine contents remained within the range of the initial values until overt spoilage at the end of the sixth week (at about 0.08 mg amine/100 g).

Determination of biogenic amines in meat by combined ion-exchange and capillary gas chromatography.

A procedure is described for the determination of putrescine, cadaverine and histamine in meat. Crude perchloric acid extracts were pre-separated on a weakly acidic cation exchanger and the amines quantified by capillary gas chromatography. The diamines were analysed as trifluoroacetyl derivatives and histamine was converted into N alpha-trifluoroacetyl-N tau-ethoxycarbonylhistamine. The accuracy of the determination of diamines was examined by a precipitation pre-separation method and by mass fragmentometric quantification. The proposed procedure allows the sensitive, sufficiently precise and highly specific determination of putrescine and cadaverine in meat.