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Study Notes: Quantitative GC

The technique of GC can be used for qualitative analysis (identifying the presence or absence of certain analytes in a sample) and quantitative analysis (determining the concentration of analytes).

In quantitative GC, the area under a peak or peak height is indicative of the concentration of the component represented by the peak. At SimuLab, the chart recorder on the virtual GC has an integrator that electronically determines and displays peak areas (which are reported as a unitless number). The bigger the peak area, the greater the concentration.

A chromatogram and associated integrator report displaying areas for the 3 respective peaks.

Let us consider the quantitation of ethyl acetate in beer. This compound is important as it is very flavour-active and contributes to the overall character of a beer-type.

The Beer Standard chromatogram prepared for the detection of can lacquer contamination also shows a peak for ethyl acetate – the analytical and instrumental conditions selected for measurement of the contaminants are also suitable for ethyl acetate. SimuLab also uses this procedure is analysis of ethyl acetate in beer.

The Beer Standard chromatogram with peak 3 highlighted - this peak corresponds to ethyl acetate.

SimuLab quantitates ethyl acetate in beer by preparing a standard curve of concentration versus peak area for a range of ethyl acetate standard solutions. The standards are analysed under the same GC conditions as used for the samples – their concentration range spans that anticipated for the samples.

A standard curve used to determine ethyl acetate concentration in beer over the range 0 to 30 mg/L. The line goes through 0 and the point (40, 20.0), where Peak area (x1000) is on the horizontal axis and ethyl acetate concentration (mg/L) is on the vertical axis.

The standard curve shows that an ethyl acetate peak area of 40 000 equates to a concentration of 20.0 mg/L in the beer sample.

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