Determination of heavy metals in soil

by atomic absorption spectrometry

(AAS)

• Aleksandar Bojić

______________________________________________________________________________________________________
This project has been funded with support from the European Commission. This publication reflects the views only of the authors,
and the Commission cannot be held responsible for any use which may be made of the information contained therein.
 NETCHEM Remote Access Laboratory Guide
Determination of heavy metals in soil by atomic
absorption spectrometry (AAS)

In this exercise, you will:

• Measure.
• Perform chemical analysis.
• Calculate the concentration.
• Gain experience in atomic absorption spectrometry usage

______________________________________________________________________________________________________
This project has been funded with support from the European Commission. This publication reflects the views only of the authors,
and the Commission cannot be held responsible for any use which may be made of the information contained therein.
 Background

Heavy metals are considered to be one of the main sources of pollution in the environment,
because of their significant effect on the ecological quality. The main sources of heavy metal
pollution in the environment are man-made effects, including combustion of fossil fuels, mining
activities, wastewater discharges of manufacturing industries, and waste disposal. High levels of
heavy metals in the sediments and soils may pass to the aquatic environment, groundwater, and
plants through the transfer processes and reach to the animals and humans. Therefore, the use of
simple and accurate methods for monitoring heavy metals has a great importance among the
environmental studies.

This method for determination of heavy metals in soil has been written to provide digestion
procedures for the preparation of sediments, sludges, and soil samples for analysis by flame atomic
absorption spectrometry (AAS)

______________________________________________________________________________________________________
This project has been funded with support from the European Commission. This publication reflects the views only of the authors,
and the Commission cannot be held responsible for any use which may be made of the information contained therein.
 Aparatus
• Digestion Vessels – 250 mL.
• Vapor recovery device (appropriate refluxing device).
• Drying ovens - able to maintain 30°C + 4°C.
• Temperature measurement device capable of measuring to at least 125°C with suitable
precision and accuracy (e.g., thermometer, IR sensor, thermocouple, etc.)
• Filter paper - Whatman No. 41 or equivalent.
• Centrifuge and centrifuge tubes.
• Analytical balance - capable of accurate weighing's to 0.01 g.
• Heating source - Adjustable and able to maintain a temperature of 90-95°C. (e.g., hot plate,
block digestor, microwave, etc.)
• Funnel or equivalent.
• Graduated cylinder or equivalent volume measuring device.
• Volumetric Flasks – 50 mL.

______________________________________________________________________________________________________
This project has been funded with support from the European Commission. This publication reflects the views only of the authors,
and the Commission cannot be held responsible for any use which may be made of the information contained therein.
 Reagents
• Nitric acid (69%), HNO3

• Hydrogen peroxide (30%), H2O2.

Sample collection, preservation, and

handling
• The soil samples were collected from topsoil at the depths of 0–20 cm using soil auger, after
manual removal of leaves, roots and stones. At site for sampling, five sub-sites were taken
for the purpose of random sampling and five soil samples were randomly collected from each
of the five sub-sites and pooled together to obtain a composite sample. Soils were sieved
through a 2 mm sieve in order to eliminate stones and other materials extraneous to
soil. Finally, sample were transferred in to polyethylene bag or plastic and glass containers
and transported to the laboratory.
• Dry samples should be refrigerated upon receipt and analyzed as soon as possible.
• It can be difficult to obtain a representative sample with wet or damp materials. Wet samples
may be dried at 90 °C.
______________________________________________________________________________________________________
This project has been funded with support from the European Commission. This publication reflects the views only of the authors,
and the Commission cannot be held responsible for any use which may be made of the information contained therein.
 Procedure:
 Mix the sample thoroughly to achieve homogeneity and sieve, if necessary. For each digestion
procedure, weigh to the nearest 0.01 g and transfer a 1-2 g sample (wet weight) or 1 g sample (dry
weight) to a digestion vessel. For samples with high liquid content, a larger sample size may be used
as long as digestion is completed.
 NOTE: All steps requiring the use of acids should be conducted under a fume hood by properly trained personnel using
appropriate laboratory safety equipment. The use of an acid vapor scrubber system for waste minimization is encouraged

 For the digestion of samples for analysis by AAS, add 10 mL of 1:1 HNO3, mix the slurry, and cover
with a watch glass or vapor recovery device. Heat the sample to 95°C ± 5°C and reflux for 10 to 15
minutes without boiling. Allow the sample to cool, add 5 mL of concentrated HNO3, replace the cover,
and reflux for 30 minutes. If brown fumes are generated, indicating oxidation of the sample by HNO3,
repeat this step (addition of 5 mL of conc. HNO3) over and over until no brown fumes are given off by
the sample indicating the complete reaction with HNO3. Use a ribbed watch glass or vapor recovery
system, either allow the solution to evaporate to approximately 5 mL without boiling or heat at 95°C ±
5°C without boiling for two hours. Maintain a covering of solution over the bottom of the vessel at all
times.
 After the previous step has been completed and the sample has cooled, add 2 mL of water and 3 mL
of 30% H2O2. Cover the vessel with a watch glass or vapor recovery device and return the covered
vessel to the heat source for warming and to start the peroxide reaction. Care must be taken to ensure
that losses do not occur due to excessively vigorous effervescence. Heat until effervescence subsides
and cool the vessel.

______________________________________________________________________________________________________
This project has been funded with support from the European Commission. This publication reflects the views only of the authors,
and the Commission cannot be held responsible for any use which may be made of the information contained therein.
 Procedure:
 Continue to add 30% H2O2 in 1 mL aliquots with warming until the effervescence is minimal or until the
general sample appearance is unchanged.
 NOTE: Do not add more than a total of 10 mL 30% H2O2.

 Cover the sample with a ribbed watch glass or vapor recovery device and continue heating the acid-
peroxide digestate until the volume has been reduced to approximately 5 mL or heat at 95°C ± 5°C
without boiling for two hours. Maintain a covering of solution over the bottom of the vessel at all times.
 After cooling, dilute to 50 mL with water. Particulates in the digestate should then be removed by
filtration, by centrifugation, or by allowing the sample to settle. The sample is now ready for analysis by
AAS.
 Filtration - Filter through Whatman No. 41 filter paper (or equivalent).
 Centrifugation -Centrifugation at 2,000-3,000 rpm for 10 minutes is usually sufficient to clear the supernatant.
 The diluted digestate solution contains approximately 5% (v/v) HNO3. For analysis, withdraw aliquots of
appropriate volume and add any required reagent or matrix modifier.
 The concentrations determined are to be reported on the basis of the actual weight of the sample. If a
dry weight analysis is desired, then the percent solids of the sample must also be provided.
 If percent solids is desired, a separate determination of percent solids must be performed on a
homogeneous aliquot of the sample.

______________________________________________________________________________________________________
This project has been funded with support from the European Commission. This publication reflects the views only of the authors,
and the Commission cannot be held responsible for any use which may be made of the information contained therein.
 DESCRIPTION OF THE EDUCATIONAL ELEMENT
Determination of heavy metals in soil by atomic
Educational element title
absorption spectrometry (AAS)
Educational field Chemistry
Level of study PhD studies
Title of course in which Educational element Remediation Technologies
is implemented (lecture or lab exercise)
Analysis of the types and distribution of pollutants
Title of teaching unit
in remediation technologies
Teacher PhD Aleksandar Bojić, full professor
Target group (study program, year of study) PhD Study Program - Chemistry, 2nd year
Educational objectives of educational The demonstrator shows how to perform the
element determination of metals in soil
Basic knowledge of chemistry and experimental
Required preliminary knowledge and skills
procedures and methods
Material available at Moodle platform for the
educational element:
- Type (.mp4/.avi/.ppt/.pdf/.doc/.jpeg Video clip (.mp4)
…): 33 MB
- Size (MB): English
- Used language in the material:
Remote access classroom-laboratory No

______________________________________________________________________________________________________
This project has been funded with support from the European Commission. This publication reflects the views only of the authors,
and the Commission cannot be held responsible for any use which may be made of the information contained therein.
 DESCRIPTION OF REMOTE ACCESS
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internet interactions (in real time and not in real time) between participants via
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______________________________________________________________________________________________________
This project has been funded with support from the European Commission. This publication reflects the views only of the authors,
and the Commission cannot be held responsible for any use which may be made of the information contained therein.
 Author, Editor and Referee References
This remote access laboratory was created thanks to work done primarily at University of Niš.

Contributors to this material were: PhD Aleksandar Bojić, full professor

Refereeing of this material was done by: _____________________

Editing into NETCHEM Format and onto NETCHEM platform was completed by: ______________

______________________________________________________________________________________________________
This project has been funded with support from the European Commission. This publication reflects the views only of the authors,
and the Commission cannot be held responsible for any use which may be made of the information contained therein.
 References and Supplemental Material
The NETCHEM platform was established at the University of Nis in 2016-2019 through the Erasmus
Programme.

Please contact a NETCHEM representatives at your institution or visit our website for an expanded
contact list.

The work included had been led by the NETCHEM staff at your institution.

______________________________________________________________________________________________________
This project has been funded with support from the European Commission. This publication reflects the views only of the authors,
and the Commission cannot be held responsible for any use which may be made of the information contained therein.