full report for tlc

8/7/2019 Full Report for TLC

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GENERAL ANALYTICAL CHEMISTRY

LABORATORY EXPERIMENTS

SSC 1891

EXPERIMENT 4:

SEPARATION OF ORGANIC DYES USING THIN

LAYER CHROMATOGRAPHY

INSTRUCTOR: PROF.MADYA HJ JAMIL YUSOF

&

ASSOC.PROF.JAFARIAH JAAFAR

Prepared by:

LAU TIAN FWU

ANG YEW SEE 33.33%

CHIU SIEW LING 33.33%


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Introduction

Chromatography is method of separating

mixtures of two or more compounds

Distribute mixture between stationaryphase and mobile phase

Different compounds have different

solubility and adsorption to the two phase


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Introduction

Thin layer chromatography (TLC) is a

solid-liquid technique

Using two phase : stationary phase (solid)and mobile phase (liquid)

Solid are silica gel (SiO2.xH2O) and

alumina (Al2O3.H2O)

Alumina more polar compare with silica

gel


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Introduction

TLC is a sensitive, fast, simple and

inexpensive analytical technique

TLC is micro technique As little as 10-9 g of material can be

detected


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Introduction

Retention is using to measure the speed

at which a substance moves

In TLC, retention is measured as retentionfactor,Rf

Retention compound due to variations of

eluent, stationary phase, temperature and

setup


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How It Work

TLC involves spotting sample to be

analyed near one of aluminium plate

It is coated with thin layer of adsorbent The plate placed on the end in a covered

jar containing a shallow layer of solvent

Solvent rises by capillary action upthrough the adsorbent


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How It Work

Differential partitioning occurs between the

components of the mixture dissolved in the

solvent More strongly given component of a

mixture is adsorbed onto the stationary

phase

Less time will spend in mobile phase, the

more slowly it will migrate up the plate


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Purpose

Determine composition of some organic

dyes

Determine the identity of organic dye inthe sample


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Apparatus

Aluminum plate layered with silica gel Jar

Capillary tubes

ReagentsOrganic dyes (Rhodamine B,

Flourescein and Bromo cresol green)

Sample (mixture of organic dyes)

Diethyl ether

Acetone

Petroleum spirit


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Procedure

Three aluminium plates were prepared A line 10mm from the base was drawn

Four dots are etched into the absorbent withequal distance in the line

The capillary tube was dipped into the first dyewith a small quantity

The first dot on each of the three plates istouched

The spotting is repeated 2 or 3 times after it dry

A different capillary tube is used to spot thesecond dye on the second spot


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Procedure

The spotting is repeated 3 times The spotting for the other dyes and sample is

repeated

A jar containing solvent 5mm deep is prepared

Mixtures 1, 2, and 3 is placed into the jars 1, 2,and 3 respectively and properly closed with a lid

A plate with the spots is placed at the bottom ineach of the jars

The solvent is let to move until about 0.5cm fromthe end of the plate

The solvent front is marked and Rf value foreach spots are calculated


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Table 1 : Mixture of solvents for the

mobile phaseSolution Diethyl

ether

Acetone Petroleum

spirit

Mixture 1 1 mL 4 mL 2 mL




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Result & Discussion

Mixture 1 Mixture 2 Mixture 3

dA dB dC dA dB dC dA dB dC

Rhodamine B 3.70 2.95 4.9

Flourescein 4.40 2.40 5.1 2.9

Bromo cresol

green4.50 0 0.2

Sample A 3.70 4.50 0 2.95 0.2 4.9

Sample B 4.40 4.50 0 2.40 0.2 5.1 2.9


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Mixture 1 Mixture 2 Mixture 3

Rf Rf Rf

Rhodamine

B

0.67 0.54 0.89

Flourescein 0.80 0.44 0.93 0.53

Bromo

cresol green

0.81 0 0.04

Sample A 0.67 0.81 0 0.54 0.04 0.89

Sample B 0.80 0.81 0 0.44 0.04 0.93 0.53


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Calculation:

Rf = distance solute moves

Distance solvent front movesMixture 1: Rhodamine B ( first data )

Rf =3.7

5.5

= 0.67

Starting point

Solvent front

Spots

a

Mixture 1 : a = 5.5 cm




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Discussion

Non-polar compounds would be forced to

the top of the plate by non-polar solvent as the

compounds dissolved well & did not interactwith polar stationary phase.

The solvents (mixture 1-3---mobile phase)

moved the components of the samples atvarious rate (different degree of interaction

with matrix by capillarity---stationary phase)


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Retardation factor (Rf) depends on:

Solvent system

Absorbent Amount of material spotted

Temperature


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Thin layer plate (silica gel or alumina) with

thickness 0.2-0.3mm used

Thinner layer give rise to erratic Rfvalue

Presence ofimpurities effect Rf

Optimum amount of sample required to

produce detectable spots with minimum

spreading

Samples larger than 50g was overloaded

In TLC, small increase in Rfobserved even

with 20C rise


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Polarity of solvents:

Petroleum spirit


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Suggestions & Recommendations

Avoid from dropping others organic compounds onplate prevent random spots

Use pencil rather than ink pen prevent blur of bluespots

Small amount of dyes spotted avoid formation ofseparated spot

Jar must be closed properly create saturated vaporenvironment

Solvent used to dissolved samples should be volatile for easily diffused

Avoid using same capillary tube for spotting reagents may affect Rfobtained


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Conclusions

TLC can be used in identifying compounds ina sample

Third mixtures (2mL diethyl ether, 4mL

acetone, 4mL petroleum spirits) gave betterresolution to the mixture)

Compounds existed in each sample:

Sample A - Rhodamine B & Bromo cresolgreen

Sample B - Flourescein & Bromo cresolgreen


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References

F.W.Fifield andD.Kealey, PRINCIPLES AND

PRACTICE OF ANALYTICAL CHEMISTRY, 4th

Edition, Blackie Academic Professional, an imprint

of Chapman & Hall,1995, pg148-149 Mohrig, 16/09/2006, Thin Layer Chromatography,

http://www.wellesley.edu/Chemistry/chem211lab/Orgo_L

ab_Manual/Appendix/Techniques/TLC/thin_layer_chrom.

html


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References

Wikipedia, 16/09/2006, Thin Layer

Chromatography,http://en.wikipedia.org/wiki/Thin_layer_chromatography

Bernard Fried and Joseph Sherman, THIN

LAYER CHROMATOGRAPHY, Marcel Dekker,

2nd edition,1986, pg213-223

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