Fatty acid analysed

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Introduction

In this essay, I am going to choose write about fatty acid analysed through the method of HPLC (High Performance Chromatography) and Gas chromatography.

Fatty acids are found in the lipids, plants, waxes, fats and essential oils (different types of oils) and used for cooking, food engineering and in the production of soaps, cosmetics and detergents.

All the fatty acids are building blocks for lipids and phospholipids. Fatty acids have three benefits:

  • They make skin to be healthy
  • They help the arteries by preventing the excess of cholesterol in the circulatory system
  • They help the brain system to function properly

The fatty acids are also organic acids (well known as carboxylic acids) which contain long hydrocarbon chains (long tails). This shows that fatty acids can be either saturated or unsaturated fat. This is because the fatty acids have the number of the carbon atoms in which they made up by acetate.

There are two types of fatty acid are:

  • Saturated fat
  • Unsaturated fat

The table below shows the different types of unsaturated and saturated fats:

Examples of unsaturated and saturated fats

SATURATED

Lauric

CH3(CH2)10COOH

+44

Graphic

Chime

Palmitic

CH3(CH2)14COOH

+63

.

Chime

Stearic

CH3(CH2)16COOH

+70

Graphic

Chime

UNSATURATED

Oleic

CH3(CH2)7CH=CH(CH2)7COOH

+16

Graphic

Chime

Linoleic

CH3(CH2)4(CH=CHCH2)2(CH2)6COOH

-5

Graphic

Chime

Linolenic

CH3CH2(CH=CHCH2)3(CH2)6COOH

-11

Chime

Arachi-
donic

CH3(CH2)4(CH=CHCH2)4(CH2)2COOH

-50

Graphic

Chime

These tables shows that fatty acids (including unsaturated and saturated fats) have the different numbers of carbon atoms, and it makes up to 30 carbon atoms. We are able to see that saturated fats (such as Lauric, Palmitic and Stearic)contain no double bond in between carbon atoms, because they are single bonds. With respect to unsaturated fats (including: Oleic, Linoleic, Linolenic and Arachidonic) all have double and triple bonds in the between carbon atoms.

We can say the bonds in unsaturated fats are stronger compared to the ones in saturated fats, because their bonds are double.

Method analysis

We can analyse on the separation of fatty acids by using gas chromatography, a type of chromatography technique in which is use for identifying components in the column. It only works when a lipid sample is injected into the column it converts to gas as it passes through the column.

A sample injector can only work by injecting sample of fatty acids, so that it can pass towards the column. Imagine if a fatty acid sample is activated by sample injector, it will stick in between sample injector and column. This means a large fatty acid sample cannot flow to the column.

There are two types of sample injector:

  • Split injection
  • Splitless injection

As can be seen from this diagram, it shows that split injection allows small sample to be vaporised, so one gas flows towards column and other one flows to the ‘'atmosphere''. We can also able to see that a thick line (is a WCOT column) in which it removes excess of fatty acid from the column.

Splitless injection allows high boiling point and (small sample of fatty acid) to be injected into the chamber as the fatty acid converts to mixture of carrier gas.

As we have come across with those two different types of injectors (i.e. spit and spitless injections), they have ability to inject a small sample so they can vaporise to carrier gas before they entering to the column. This is how they work during the injection process.

Once a carrier gas flows out from the column, it goes to the detector. The technique (detector) is used to measure the readings of a small fatty acid sample to identify their organic compounds in the wavelength.

There are number of ways in which the detectors can be used to find the peak areas of each lipid samples. These are:

  • Flame ionisation detectors
  • Electron-capture detectors
  • Mass spectroscopy

According to this diagram shows flame ionisation detector is used to identify the organic compounds (of fatty acid sample) in the column. A flame burns fatty acid sample so that it produces ions to conduct electricity.

Electron-capture detector is use to knock beta particles as the carrier gas is passing through the chamber. The beta particles are making thousands of electrons in which they are affected by voltage. This typical of gives a very good response for detecting on molecules containing halogen atoms.

Mass spectroscopy detects the ions of the organic molecules in which the ions passed through electrostatic field and then it arrives in the column to separate its components. This technique removes electrons to form positively charge and then positive ions will divide into smaller entities before they flow to electrostatic field (in which it causes the smaller ions to separate the components).

At high resolution, the peaks will have accurate readings to find the peak areas of each solution, whereas at low resolution, the peak will have lower readings of peak areas for each solution.

Gas chromatography works when a lipid sample is injected into the column, so that it will flows to liquid phase to separate the components. The detectors (including mass spectroscopy, electron ionisation and flame ionisation detectors) checks the readings of lipid sample to see how fast they separated during the retention time.

According to Christie (2007), he claimed that the major advantages gas chromatography:

  1. It is a useful technique for the separation of lipid samples to provide good mixture of components.
  2. It volatiles the lipid sample to form gas.
  3. It also provides accurate results in the detectors (especially in temperature programmed analysis) so it will be easier to identify their organic compounds in the peak areas.

The major disadvantages of gas chromatography are:

  1. There could be errors in the peak area of lipid samples.
  2. It can very difficult to identify the organic compounds in the peak areas
  3. And it is very expensive

We can also analyse the separation of fatty acid by using HPLC, a powerful technique which provides good mixture of components. This technique allows injecting small lipid sample into the column, so it can pass through the stationary phase (liquid) to give better separation of fatty acids (lipid sample).

HPLC can be used as UV detector to identify organic compounds of fatty acid separation. The UV detector measures the reading of how much lipid sample is absorbed the UV light in the column to find their peak areas.

This diagram below, it shows that these peak areas (in the wavelength) are separation of fatty acids in which has been detected by the UV light (reversed HPLC). We can also able to see that first double bond reduces by 2 carbons, for example 18:1 removes fatty acids just after 16:0.

HPLC technique works by injecting a lipid sample into the column (HPLC technique), so it can start to separate the components. UV detector measures the reading of how fast lipid sample is separated during retention time.

The major advantages of HPLC are:

  1. It provides better separation of fatty acid, so that it will be easier to find their components in the column.
  2. It also produces accurate readings of fatty acid separation in HPLC detector, so it will also be easier to identify organic compounds in the peak areas.

The disadvantages of HPLC are:

  1. It doesn't volatile fatty acid sample.
  2. It reduces the selectively of fatty acid separation

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