Gas Liquid Chromatography for the Determination of Ethanol Percentage in Beer

Abstract

The method of using gas liquid chromatography for the determination of percent of ethanol in beer has been applied in many breweries. Ethanol percentage in beer is determined by liquid gas chromatography because it is thermally stable and is also volatile as the operating temperatures of gas liquid chromatography. The report details the gas liquid chromatography used in determining the percent of alcohol in a beer. Stella Artois beer was degassed by pouring into two beakers. 400 µl (0.4 cm3) of Propane-1-ol was added in all ethanol concentrations from 0 to 6% v/v then made to the mark with distilled water. The beer sample was prepared by pouring 400 µl of Propane-1-ol into a 10 cm3 volumetric flask and made to the mark with degassed beer. Then the volumetric flasks, which were labeled from 0 to 6 and the one-labeled beer, were taken to the GLC machine where 2 µl were injected each time and twice for each solution on to Gas liquid chromatographs. Finally, the results were printed by chromatograms. The results indicated that the percent ethanol concentration in a beer solution being (4.7%, 4.9%) and (5.5% and 5.4%). This was approximately in the range of alcohol percentage allowed in the beer of 4.8%- 5.2%. The error could have been through human error during the injection, air bubbles in the syringe, or may be the syringe was not cleaned properly.

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1. 0 Introduction

Traditional methods of ethanol analysis that involves mass determinations and/or distillations are known to have small inaccuracies because of the presence of other beer components and interfering volatiles (Buckee and Mundy 1993). Similarly, the current recommended reference method for determining alcohol in beers majorly relies on distillation then by a specific distillate gravity measurement. However, the procedure cannot be automated, is labour intensive and requires the operator to possess analytical skills. Moreover, the method of distillation is not specific to ethanol unlike gas chromatography, since it is subject to interference from different materials. Therefore, many laboratories has shifted to other alternative methods which has the capability of automation and are rapid such as gas-liquid chromatography. Chromatograph is a technique of separation where component molecules in a mixture of sample are transported over a stationery phase by a mobile phase. The mobile phase may be a liquid or a gas (solvent system) (Buckee and Mundy 1993). Gas liquid chromatography, with column packing that is appropriately chosen is inherently specific and separates volatile compounds on the basis partitioning properties specific to compounds between gas phase and liquid phase. The volatile constituents’ contribution is approximately in the region of 0.02%V/V (Buckee and Mundy 1993). Further advantages of gas chromatography method is its ability to be amenable to the traceability to National Standards.

The aim of the report is to determine, accurately, the ethanol content of a can of beer by gas liquid chromatography using external standardization, with an internal standard. The work is very important because in determining the content of ethanol in beer, the manufacturer must declare the content of alcohol to the consumer and also to pay the customs duty. Ethanol can be determined by GLC since it is volatile and thermally stable at the operating temperature of GLC

2.0 Method

2.1 Principle

• The sample of beer was de-gassed by pouring into two beakers
• As an internal standard, the sample was then diluted with a known Propan-1-ol quantity before going for injection.
• The diluted liquid sample was injected into a gas chromatography column, which was calibrated previously using standard solutions of ethanol
• A can of propan-1-ol and ethanol has been used in the experiment. The GLC detector response that uses the integrator which was already set to operate for ethanol analysis included packed carbon wax 20mpolar phase column and 80⁰C, nitrogen carrier gas and ionization detector at 150⁰C in order to carry out the experiment.
• The ethanol v/v percentage in the sample was calculated from the ethanol peak areas and Propan-1-ol peaks, using a calibration factor previously calculated

2.2 Reagents

The experiment used only recognised reagents of the analytical grade and the distilled water

• Ethanol
• Internal standard, Propan-1-ol
• Distilled water

2.3 Instruments

• Gas chromatograph that was fitted with a detector for flame ionization and an oven that was capable of isothermally operate at 115⁰C.
• 10 µl gas-tight positive displacement syringe/ gas chromatograph auto sampler- for injecting 1µ or 0.5 of liquid sample
• Automatic pipettes
• Chart recorder and integrator. Care was observed when interpreting the signals from the integrators. The given peak areas was checked against a made manual calculation my measuring the width and height of peak. For this reason, a trace of peaks was produced in addition to the value of peak area printed
• Accurate thermometers to ± 0.1⁰C
• Chromatography columns, 100/100 mesh packed stainless steel or glass with 20M on 15% Chromosorb WAW DMCS
• Pipettes- Grade A bulk 20ml, 5ml, 3ml, 1 ml
• Seven Volumetric flasks- (10cm3)
• Beakers

2.4 Sample preparation

1. The beer was degassed by pouring it between two beakers
2. 400 µl (0.4 cm3) of Propane-1-ol was added in all concentrations from 0 to 6% v/v then made to the mark with distilled water
3. Beer: 400 µl of propane-1-ol + degased beer to the mark (in volumetric flask marked at 10cm3). See table 1 below

1. The group took the solutions to M block, second floor where Gas Liquid Chromatograms were placed
2. Only 2 µl were injected each time and twice for each solution
3. The results were printed by chromatograms

2.5.2 Calibration

1. The gas chromatograph was prepared according to the instructions of the manufacturer. The provided conditions from the manufacturer was as follows

• Injector temperature 150⁰C
• Oven temperature 115⁰C
• Detector temperature 150⁰C
• Flow rate of Carrier gas 45ml/min
• Carrier gas Nitrogen

1. Only 2 µl were injected each time and twice for each solution
2. Determination of the areas of Propan-1-ol and ethanol internal standard peaks was done
3. The experiment repeated step 2 and step 3 in duplicate for each of the standard solution

2.5.3 Analysis

1. The degassed beer sample by pouring between two beakers was thoroughly mixed
2. Only 2 µl were injected each time and twice for each solution in gas chromatographs
3. The area of the peaks due to the Propan-1-ol internal standard and ethanol was then calculated

2.6 calculation

Percentage of ethanol is the ethanol’s peak height divided by the peak height of Propan-1-ol and the quantity s divided by the gradient/slope of the line gotten from the calibration curve.

%EtOH =

The percentage of ethanol was calculated from the slope/gradient of the line equation gotten from the calibration curve

Solve for X

Y=mx+b

3.0 Results

The results of the experiments are shown in table 2 below:

Ethanol calibration graph

1. Graph of variation in peak area of ethanol verses ethanol concentration

Table 3

Herman Bailey

With a student-centered approach, I create engaging and informative blog posts that tackle relevant topics for students. My content aims to equip students with the knowledge and tools they need to succeed academically and beyond.