AC2 ANALYSIS OF ETHANOL IN SPIRITS BY INTERNAL STANDARD GC Last Revised:
May 2015
1. PURPOSE This exercise uses the internal standard method to improve the analysis of ethanol in beverages undertaken in first year. 2. REAGENTS & EQUIPMENT 2.1 GC with polar column, TC detector 2.2 Potential internal standards: methanol, ethanol, 1‐propanol, 2‐propanol, 1‐butanol, 2‐methyl‐
1‐propanol, 2‐methyl‐2‐propanol. 2.3 Ethanol 2.4 Whisky, vodka or brandy 3. PROCEDURE 3A. Choice of internal standard 3.1 The retention times for all components under the experimental conditions will be provided. 3.2 Determine which is the best choice and conform this with your teacher. 3.3 Prepare a test solution containing about 10% of ethanol and 10% internal standard in water (eg 1 mL EtOH + 1 mL IS in 10 mL measuring cylinder). 3.4 Inject this to confirm that your choice of internal standard is satisfactory. 3B. Standard preparation 3.5 Prepare 50 mL of the following ethanol standards – 0, 5, 10 and 20%v/v – each of which contains 5 mL of your chosen internal standard. 3C. Sample preparation 3.6 Pipette 10 mL of your sample into each of three 50 mL volumetric flasks, labelled S1, S2 & RC. 3.7 Add 5 mL of the internal standard to each. 3.8 To the flask labelled RC, add 5 mL of ethanol. 3.9 Make up to the mark with water and mix well. 3D. Analysis 3.10 Inject 1 uL of each standard, ensuring that each person in the group does one injection. 3.11 Inject each sample and recovery, again ensuring that each person in the group does one injection. 3.12 Deliberately underfill the syringe and re‐inject either S1 or S2. 4. REPORT Calculations 1.
Tabulate peak area (or height) for ethanol and internal standard in all standards, samples and recovery check. Internal standard method 2.
Plot a calibration graph of peak area ratio of analyte/IS vs concentration of standard. 3.
Use this to determine the ethanol concentration in the samples (including the deliberate underfill) and recovery. 4.
Apply the dilution factor to determine the original concentration of ethanol in the duplicate samples. 5.
Calculate the average %v/v in the two correctly injected samples. 6.
Calculate the volume of ethanol in the 50 mL flasks S1, S2 and RC. 7.
Calculate the % recovery. Normal calibration graph To make a comparison of the results without the use of the internal standard: 8.
Plot a calibration graph of peak area of ethanol vs concentration of standard. 9.
Use this to determine the ethanol concentration in the samples (including the deliberate underfill) and recovery. 10. Apply the dilution factor to determine the original concentration of ethanol in the duplicate samples. 11. Calculate the average %v/v in the two correctly injected samples. 12. Calculate the volume of ethanol in the 50 mL flasks S1, S2 and RC. 13. Calculate the % recovery. Discussion 
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compare the results for the % ethanol and % recovery by internal standard and normal calibration graph compare the results for the deliberate underfill by internal standard and normal calibration discuss the reasons for your choice of the internal standard explain what the internal standard method compensates for explain why it works for the internal standard results, compare the %v/v in the sample with the expected value and comment on the recovery check result for the 10% standard, compare the peak area for the analyte and internal standard and account for any difference given the concentration of each is the same Question Gas chromatography is being replaced as a method for analysis of ethanol content in products such as spirits, wine and beer by a device known as an Aloclyzer. Read the reference article (download from website) and answer the following questions. (a) What instrumental technique does the Alcolyzer employ? (b) What are the advantages of the Alcolzyer over conventional GC analysis? (c) How is the Alcolyzer calibrated? AC2 p2