ANA INS-POST LAB 4- denisse tan (1) (1)
docx
keyboard_arrow_up
School
Centennial College *
*We aren’t endorsed by this school
Course
207
Subject
Aerospace Engineering
Date
Dec 6, 2023
Type
docx
Pages
5
Uploaded by MegaFalcon2779
DENISSE MAE TAN 301235992
October 9, 2023
Experiment 4:
Determination of Percentage Ethanol in Beverages by Gas
Chromatography
Observations:
The unknown sample is light brown in color and has a strong, sweet alcohol smell
The known sample has a very light brown or pale brown in color and has a strong, sweet alcohol smell.
The cuvettes/containers used to read the samples are very minute in size.
The order of analysis in the GC machine is as follows: the standard sample is run first, followed by the known sample, and finally, the unidentified sample.
Results:
Table 1: Gas Chromatography results showing Alcohol Peak, N Propanol Peak and its Average Results
Area peak
Average
sample
Alcohol
peak
1 propanol
peak
Alcohol
average
N propanol average
Standard 1
0.0218
0.1060
0.0216
0.1074
Standard 2
0.0214
0.1088
Known 1
0.0742
0.1358
0.0757
0.1566
Known 2
0.0772
0.1774
Unknown 1
0.1082
0.3119
0.0844
0.2141
Unknown 2
0.0606
0.1163
*Samples were run in duplicate and average was taken and was used for calculations
DENISSE MAE TAN 301235992
October 9, 2023
Actual results from lab manual:
DENISSE MAE TAN 301235992
October 9, 2023
POST-LAB QUESTIONS: 1. Calculate the percentage ethanol content of your known samples separately for both GCs (Show all calculations). Compare the calculated ethanol content of your known sample to the value given on its bottle. Which GC analysis gave better results? Percent Ethanol
=
0.0757
0.1566
0.0216
0.1074
x
4.75%
%
Ethanol
=
11.42%
*N propanol was used instead of acetic acid
2. Calculate the percentage ethanol content of your unknown sample separately for both GCs (Show all calculations). Are the two values similar to each other? Percent Ethanol
=
0.0844
0.2141
0.0216
0.1074
x
4.75%
%
Ethanol
=
9.31%
*N propanol was used instead of acetic acid
3. Explain why the accuracy of the internal standard method does not depend on the accuracy of the volume of sample injected into the GC?
The accuracy of the internal standard method in gas chromatography (GC) isn't tied to the exact sample injection volume. GC relies on relative ratios, comparing the area under the peaks of the compound of interest to an internal standard. Even with slight injection volume variations, both the compound and the
Your preview ends here
Eager to read complete document? Join bartleby learn and gain access to the full version
- Access to all documents
- Unlimited textbook solutions
- 24/7 expert homework help
DENISSE MAE TAN 301235992
October 9, 2023
internal standard are affected equally, keeping the ratio consistent and the method accurate. GC prioritizes precision over absolute accuracy, and the internal standard helps correct for variations, ensuring reliable results. While controlling injection volume is important, it's the consistent ratio that matters most for accurate GC analysis (Analysis Results of GC, n.d.)
4. What result would increasing the length of the column have on the observed chromatogram (assuming no other changes)? Separation is generally improved by longer columns. Because of increased longitudinal diffusion inside the column, the retention time increases proportionally to column length and a significant peak broadening is also observed (n.d.)
5. The Varian GC uses a packed column while the Thermo Scientific GC uses a capillary column. How are capillary columns different from packed columns?
Capillary columns and packed columns in gas chromatography (GC) differ in design and function. Packed columns contain a finely divided, inert, solid support material coated with a liquid stationary phase. They typically have an internal diameter of 2 - 4mm and a length of 1.5 - 10m. In contrast, capillary columns, with an internal diameter of a few tenths of a millimeter, offer superior separation and efficiency for complex mixtures. Packed columns are mainly used for simpler samples, while capillary columns are better suited for smaller sample volumes and exhibit inertness due to coatings. Capillary columns have become the modern standard in GC, widely applicable in various fields like chemistry and pharmaceuticals, while packed columns have limited applications in niche cases. (Gas Chromatography, n.d.).
DISCUSSION
Comparing these results, it's evident that the known sample's calculated ethanol percentage is higher than that of the unknown sample. This difference may be attributed to various factors, these errors could arise from variations in sample preparation, including inaccuracies in adding n-propanol or distilled water and inconsistencies in mixing techniques. The condition of the GC column, such as contamination, aging, or damage, could also have impacted the accuracy of the results. Furthermore, sample or injection system contamination with impurities or residues from previous analyses might have introduced errors.
DENISSE MAE TAN 301235992
October 9, 2023
Reference: Analysis results of GC. (n.d.). https://www.shimadzu.com/an/service-
support/technical-support/analysis-basics/fundamentals/results.html
Gas Chromatography
. (n.d.). Retrieved November 6, 2022, from https://teaching.shu.ac.uk/hwb/chemistry/tutorials/chrom/gaschrm.htm
How does column length affect HPLC? – Shabupc.com. https://www.shabupc.com/how-does-column-length-affect-hplc/#:~:text=A
%20longer%20column%20generally%20im
proves%20the%20separation.
%20The,because%20of%20increased%20longitudinal%20diffusion%20inside
%20the%20column.