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Experiment - Fatty Acid Determination Using Gas Chromatography

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Fatty Acid Determination using Gas Chromatography

Dayangku Siti Nurfariza Binti Awang Ahmad Safri

Faculty Of Applied Science

UiTM Sarawak

OBJECTIVE

To determine the the components present in fatty acids based on the tR by using Gas Chromatography (GC).

ABSTRACT

The purpose of this experiment is to determine the components present in fatty acids based on the retention time,tR by using Gas Chromatography. The fatty acid methyl ester samples are obtained via esterification and reflux of fat samples. Only the organic layer is injected into the GC as water can ruin the GC column.  The retention time,tR of the components present in fatty acids in the experiment is compare with the standard mixture under the same condition of analysis.

INTRODUCTION

Fatty acids are not sufficiently volatile for GC analysis. IN addition, acids are reactive compounds and are too polar to be well separated by GC. Direct GC analysis of acids tends to cause peak tailing due to the adsorption and non-specific interaction with the column. Derivatization is the process of chemically modifying a compound to produce a new compound which has properties that are suitable for GC analysis. This experiment introduces a derivatization procedure routinely used for fat analysis in which nonvolatile fatty acids are chemically converted to the corresponding volatile methyl esters (FAME). The resulting volatile mixture can be analyzed by GC.

Gas chromatography (GC) is one of the most versatile and ubiquitous analytical techniques in the laboratory. It is widely used for the determination of organic compounds. Very complex mixtures can be separated by this technique. When coupled with mass spectrometry as a detection system, virtually positive identification of the eluted compounds is possible at very high sensitivity, creating a very powerful analytical system.

In chromatographic analysis, the eluted compounds are characterized by retention times, tR. Qualitative analysis involves determination of tR of analytes and comparing them with tR of standards. Quantitative analysis is accomplished by comparing the areas of the analyte peaks with those of standards.

METHODOLOGY

  1. Sample preparation

2 g of oil or fat was weighed out approximately and the exact weight was recorded. The sample wa transferred into a 50 mL flask equipped with air condenser. 5 mL of 0.5 M methanolic solution was added and refluxed for 3 – 4 minutes. 15 mL of esterification reagent was added and refluxed for 3 minutes. The mixture was transferred into a separatory flask. 50 mL saturated NaCl and 25mL diethyl ether was added. The mixture was shake vigorously for 2 minutes and the aqueous layer was discarded. The organic layer was transfer into a screw cap vial. Only the organic layer was injected into the GC as water can ruin the GC column.

  1. Sampling handling

The syringe was rinse before filling it with the fatty acid methyl ester sample. The volume of the sample may be more than the required volume. Make sure there are no air bubbles in the syringe. The syringe was tap gently to remove air bubbles. The syringe was held vertically, needle up, and the plunger was push to the required volume at eye level. The excess sample was removed by using tissues.

  1. Operation og Gas Chromatography (GC)

The instrument was switch on. The GC was set using the following conditions; Injection port : Split (40:1), Injection port temperature : 250ᵒC, Column temperature : 100ᵒC to 290ᵒC at 40ᵒC min-1, Carrier gas flow rate : 30 mL s-1, Detector temperature : 250ᵒC. Then, the component fatty acid sample was injected and the retention time of each component was determined individually. The standard mixture was injected and each component present was identified by comparing the retention time of each component with the retention time of each single component determined previously. The result was recorded. The instrument was switching off after completed get the result. The temperature of the GC reduces to 50ᵒC before switch off.

RESULTS AND DISCUSSION

Result of fatty acid

Number chemical components

Retention time,tR (min)

Remarks

1

9.742

C12:0

2

11.957

C14:0

3

12.418

C16:0

4

14.336

C18:0

5

14.420

C18:2

6

14.570

7

14.675

8

14.747

9

14.829

10

14.913

11

15.142

12

15.318

13

15.480

14

15.509

15

15.658

16

16.327

17

17.316

18

18.063

19

18.506

20

19.836

21

20.275

22

20.414

23

21.938

24

23.477

Table 1

Result of standard mixture

Retention time,tR (min)

Chemical no.

Name of chemical

Constituents

1

8.944

1

methyl laurate

C12:0

2

9.401

2

methyl myristate

C14:0

3

9.845

3

methyl palmitate

C16:0

4

10.317

4

methyl stearate

C18:0

5

10.373

5

methyl lioleate

C18:2

Table 2

...

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