Care must be taken when interpretin

Care must be taken when interpreting computed sig
nals from integrators; they should not be assumed to
be accurate. If possible, the peak areas given should
be checked against manual calculation made by meas
uring peak height and width. For this purpose, trace
of peaks should always be produced in addition to the
printed value for peak area.
5.5 Water bath, controlled to 20°C 0.5°C.
5.6 Thermometer—accurate to 0.1°C.
5.7 Chromatography column 2 metres mm,
glass or stainless steel packed with 15% Carbowax 20M
on Chromosorb WAW DMCS, 100/100 mesh (e.g.
Phase Separations).
5.8 Filter funnels.
5.9 Filter paper—Watman No. 1.
5.10 100 ml conical flask.
5.11 Ultrasonic bath.
5.12 Pipettes—Grade bulk ml, ml, ml and
20 ml.
5.13 Volumetric flasks—Grade A, 250 ml and
100 ml.
SAMPLE PREPARATION
6.1 Adjust the temperature of the sample to 20°C
and filter 50 ml into conical flask. Discard the first
25 ml of filtrate and cover the filter funnel with clock
glass to prevent loss of ethanol.
6.2 Place the flask in the ultrasonic bath and sonic
ate to remove any remaining carbon dioxide. Seal the
flask until required for analysis.
PROCEDURE
7.1 Preparation of Standards
7.1.1
Ethanol standard 1% VYV, accurately pipette
1.0 ml of ethanol into 100 ml volumetric flask. Make
up to volume with distilled water at 20.0°C 0.1°C.
7.1.2 Ethanol standard 5% V.V, prepare as in 7.1.1
using 5.0 ml of ethanol.
7.1.3 Ethanol standard 8% V/V, accurately pipette
20.0 ml of ethanol into 250 ml volumetric flask. Make
up to volume with water at 20.0°C 0.1CC.
7.1.4 Ensure that pipettes, syringes, ethanol, water
and resulting diluted solutions are all at
20.0°C±0.1°C.
7.1.5 Check the ethanol content of the standard sol
utions by measuring the specific gravities either by
gravity bottle or meter.
7.2 Calibration
7.2.1 Attemperate the n-butanol internal standard
and the ethanol calibration standards to 20°C 0.1°C
in the water bath.
7.2.2 Prepare the gas chromatograph according to
the manufacturer's instructions.
Typical conditions:
Oven temperature 115°C
Injector temperature 150°C
Detector temperature 200°C
Carrier gas Nitrogen
Carrier gas flow rate 45 ml/min
7.2.3 Dilute ml of each ethanol standard with 20 ml
of n-butanol internal standard using an auto-diluter or
by pipetting, into clean, dry 50 ml conical flask.
Note: Ensure that both solutions are at 20°C 0.1°C
before diluting. Temperature accuracy at this stage is
critical to the accuracy of the method. Mix thoroughly.
7.2.4 Inject 0.5 or (i of the first diluted standard
ethanol solution from 7.2.3 into the gas chromato
graph.
7.2.5 Determine the areas of the ethanol and n-buta
nol internal standard peaks.
7.2.6 Repeat steps 7.2.4 and 7.2.5 for each standard
ethanol solution in duplicate.
7.3 Analysis
7.3.1 Attemperate the filtered, degassed beer sample
to 20°C 0.1°C.
7.3.2 Dilute ml of the beer sample with 20 ml of
n-butanol internal standard using the same equipment
as for the ethanol standards, into clean, dry 50 ml
conical flask. Mix thoroughly.
7.3.3 Inject 0.5 or /ul of the dilute beer from 7.3.2
into the gas chromatograph.
7.3.4 Calculate the area of the peaks due to the
ethanol and n-butanol internal standard.
CALCULATION
8.1 Plot graph of
Area of ethanol peak
Area of internal standard peak
against ethanol concentration V/V (after correcting for
purity) from the results obtained for each of the cali
bration standards. The graph should be linear and
should pass through the origin.
8.2 Fit either visually or by using linear regression,
the best straight line to the graph. Calculate the coef
ficient of correlation (r) and provided 0.99, calcu
late the gradient to give the factor F.
Ethanol concentration
Area ethanol peak/Area internal standard peak
8.3 Once the linearity of the calibration range is
established, subsequent calibrations to determine the
factor can be performed by carrying out triplicate
determinations of the standard nearest to the expected
concentration of ethanol in the sample.