Thin layer chromatography for analysis of chlorinated pesticides in food samples

1. THIN LAYER CHROMATOGRAPHY FOR
IDENTIFICATION OF CHLORINATED PESTICIDES
IN FOOD PRODUCTS
(Chemical Analysis)
Submitted by:-
Nidhi Maheshwari
M.Sc. (Applied Chemistry)

2. CONTENTS
• Introduction
• What are chlorinated
pesticides?
• TLC for analysis of
chlorinated pesticides
• Merits and Demerits of
TLC analysis

3. Pesticides are chemicals used in agriculture to
destroy or control weeds, insects, fungi and
other pests.
Pesticides are organic compounds and degrade
very slowly.
They remain in food products as residues; thus
posing health risks to the consumers.
Important chromatographic methods employed
for pesticide analysis include GLC, HPLC and
TLC.
Introduction

4.  Chemically, chlorinated hydrocarbon
pesticide.
 Nerve agents used for killing noxious pests.
 Properties:-
 Water insoluble
 Very persistent in soils (half life vary from 2
to 16 years)
 Bioaccumulates in fat
 Biomagnifies in food chain

5.  Some other examples are:

6. • Examples of food stuff which may
contain chlorinates pesticide residues:
 Leafy and root vegetables
 Fruits
 Diary products
 Meat
 Fish

7. TLC for analysis of Chlorinated
Pesticides
• TLC is an important qualitative and semi -
quantitative technique for analysis of
chlorinated pesticide residues in food
products.
• Standard AOAC method recommendations:-
 Stationary Phase : Silica Gel G
 Developer : n - hexane
 Visualizing Agent : 0.1% AgNO3 followed by
exposure to UV light

8. • Steps involved in
analysis are:-
1. Sample extract
preparation
2. Application of Spot
on TLC plate and
development of plate
3. Detection
4. Identification
5. Semi - quantitative
analysis

9.  PREPARATION OF PESTICIDE
WORKING STANDARDS, i.e.,
preparation of reference:
Standard solution is prepared in n-
hexane.
1. Stock Solution - 1 mg/mL
2. Intermediate - 10 μg/mL
3. Working standards - 0.1 μg/mL,
0.2 μg/mL, 0.5 μg/mL, etc.

10. 1. Sample Extract Preparation
Chop, blend and homogenize food sample
Extraction of residue by acetonitrile
Fat and other co-extractive removal using
petroleum ether, followed by water
Final clean up using acetonitrile
Extraction of pesticide residue in n-hexane

11. 2. Application of sample spot on TLC plate and
development of the plate
• Silica Gel G
• Activated by heating in oven at
110° C
Preparation of TLC
plate (Stationary
Phase)
• By standard syringe with flattened
needle by solvent flush technique
• Almost 2 cm from bottom of plate
Application of
sample and
reference
• Developer: n-hexane
• Tightly close tank saturated with
solvent vapours
Development of
Chromatogram

12. 3. Detection
Take out
developed
chromatogram
Dry
Spray 0.1%
AgNO3
solution
Expose to UV
light or
sunlight for 10
minutes

13. 4. Identification
• By calculation and then comparison of the
sample Rf value with the reference
• Permissible error: about 2 mm difference in
migration distances of sample and standard.

14. 
Rf value range of some chlorinated
pesticides (n-hexane solvent system)
PESTICIDE Rf VALUE RANGE
Aldrin 0.78 – 0.81
DDT 0.59 – 0.62
Perthane 0.48 – 0.50
BHC (Lindane) 0.39 – 0.41
Dieldrin 0.17 – 0.19
Methoxychlor 0.10 – 0.12

15. 5. Semi - Quantitative Analysis
 Accuracy: ± 20%
 By comparing spot intensity of sample
with standard
 By comparing spot area of sample with
standard
 By comparing both, intensity and area, of
the sample spot with the standard
 Formula:-

16. Merits and Demerits of TLC
Analysis
 Merits:-
 Can be performed anywhere
 No sophisticated instrument
required
 Inexpensive
 Easy
 Less time consuming
 Demerit:-
 Low degree of accuracy

17. THANK YOU