CHAPTER 1: INTRODUCTION TO
CHEMICAL ANALYSIS
SALAMIAH BINTI ZAKARIA
FSG, UiTM PERLIS
What is analytical chemistry?
Analytical
chemistry
is
a
measurement science consisting
of a set of powerful ideas and
methods that are useful in all
fields of science and medicine.
©Gary Christian, Analytical Chemistry,
6th Ed. (Wiley)
How is it important and relevant to you?
Chemical analysis provides the methods and tools
needed for insight into our material world for
answering four basic questions about a material
sample.
• What?
• Where?
• How much
• What arrangement, structure or form?
Background of chemical analysis
A.) CHEMICAL ANALYSIS: The Science of Chemical Measurements.
B.) ANALYTE: The compound or chemical species to be measured, separated or studied
C.) TYPES of ANALYTICAL METHODS:
1.) Classical Methods (Earliest Techniques)
a.) Separations: precipitation, extraction, distillation
b.) Qualitative: boiling points, melting points, refractive index, color,
odor, solubilities
c.) Quantitative: titrations, gravimetric analysis
2.) Instrumental Methods (~post-1930’s)
a.) separations: chromatography, electrophoresis, etc.
b.) Qualitative or Quantitative: spectroscopy, electrochemical methods,
mass spectrometry, NMR,
radiochemical methods, etc.
CHOOSING AN ANALYTICAL METHOD
What Factors to Consider:
What type of information does the method provide?
What are the advantages or disadvantages of the technique versus other methods?
How reproducible and accurate is the technique?
How much or how little sample is required?
How much or how little analyte can be detected?
What types of samples can the method be used with?
Will other components of the sample cause interference?
Other factors: speed, convenience, cost, availability, skill required.
Areas of Chemical Analysis and
Question They Answer
QUALITATIVE
Analysis conducted to identify what are the constituents present
in the sample (identification of the sample component)
QUANTITATIVE
Analysis to determine how much of each
present in the sample.
constituent
SEPARATION
-How can the species of interest be separated from the
sample matrix for better quantitative and qualitative
analysis.
SAMPLING AND EVALUATION OF
EXPERIMENTAL DATA
 Population
- The group of things, items or
units under investigation
 Sample
- Obtained by collecting
information only about some members of
a "population“
– Act of collecting sample to
produce meaningful
information.
 Sampling
What is the purpose of sampling?
• The purpose of SAMPLING is to obtain a
REPRESENTATIVE SAMPLES of the whole
sample that can be taken to the laboratory
for chemical analysis and the results
obtain will be ACCURATE.
In a chemical analysis :
A
chemical analysis is usually performed
on only small portion of the material
collected to be characterized.
 If
the amount of material is very small and it
is not needed for further use, then the
entire samples may be used for analysis.
WHAT ARE THE MATERIALS THAT CAN
BE SAMPLED?????????
Sampling
Air Sampling
Solid Sampling
Liquid Sampling
Air Sampling
Grab sampling
•
An actual sample of air is taken
in a flask, bottle, bag or other in
suitable container.
•
Done over a period of few
seconds or up to 1-2 minutes.
ANALYSIS
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Continuous or integrated sampling
• Gases or vapours are removed from the air
over a measured time-period and concentrated
by passage through a solid or liquid sorbent.
•A sample is collected
by opening a tube,
connecting it to a
sample pump, and
pulling air through
the tube with the
pump.
•Airborne chemicals
are trapped onto the
surface of the
sorbent.
Liquid sampling
•
•
•
•
Liquid sample tend to be homogeneous and are more
easier to sample.
Liquids mix by diffusion only very slowly and must
be shaken to obtain a homogeneous mixture.
If water sample is taken from the river, then the water
samples is collected at the SURFACE, MIDDLE and at
the BOTTOM of the river bed.
If the liquid is in a large container, then the liquid
should be stirred first before the samples are taken
at the top, middle and at the bottom of the container
Solid sampling

Inhomogeneity of the solid sample, variation in sample size and
variation
 within the particle size make sampling of solids more difficult then
other material.
 The easiest but usually the most unreliable way to sample a solid
material is by the grab sample, which is one sample taken at random
and assume to be representative.
 Solid samples usually need further treatment.
 Example if ores are being sampled, first crush the ore to a smaller
size and then sieve and use the QUARTERING TECHNIQUE to get
the right sample size to the laboratory.
 Solid samples may need drying
SOLID SAMPLING: QUARTERING TECHNIQUE
•Quartering is a method used by analytical
chemists to reduce the sample size of a powder
without creating a systematic bias .
•This technique involves placing the sample on
a flat surface in the form of a conical heap. The
heap is then spread out and fattened into a
circular cake, which is then divided into
approximately equal quarters.
• One pair of opposite quarters is removed,
combined and formed into a new cone for the
process to be repeated (with the other two
quarters discarded).
•The process is repeated as many times as is
necessary to obtain a sample of the required
size
Can be send for analysis
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Purpose of drying solid samples :
To ensure that the exact weight is obtained during the
QUANTITATIVE chemical analysis.
How it is done :
Solid samples dried in oven at 105 – 110oC for 1- 2
hours. Plant and tissue samples dried by heating
16
Problems associated with drying of
samples :
1. Samples might decompose at high
temperature.
2. Some samples are sensitive to heat,
therefore drying can be carried out in a
desiccators.
17
SAMPLE STORAGE
Samples storage purposes:
 There is a time gap between when the sample is taken and the actual
analysis is being carried out.

For liquids samples, make sure that it is kept in bottles with
stoppers.

Acidic liquid samples can be stored in glass container whereas
basic liquid samples in plastic container.

Solid samples is easier to keep and have less chance to be
adulterated by foreign matters.
 Sometimes it can also get absorbed or adsorbed to the wall of the
container.
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What are the problems encounter during storage of samples?
19
The sample can be adulterated / contaminated by foreign matter .
- The sample should not react with the wall of the container or get
adulterated.
1.
2. During storage of samples eg liquid samples, sometimes there is a lost of analyte
if it is volatile .Hence, the container should be closed tightly.
3. Decomposition of sample.
Side reactions can occur. Example in the air pollution studies the content of SO2 in
air is not stable due to the following reaction
2SO2 + O2  2SO3
To avoid the above reaction the sample is cooled to 4oC
Replicate Samples
Most
chemical analyses are performed on
replicate samples whose weights or volumes
have
been
determined
by
careful
measurements with an analytical balance or
with a precise volumetric device.
Obtaining replicate data on samples improves
the quality of the results and provides a
measure of their reliability.
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Sample Preparation
using solution
Most analyses are performed on solution of the
sample. Ideally, the solvent should dissolve the
entire sample rapidly.
using solid
-ashing - in analytical chemistry is defined as the heating
of a substance to leave only noncombustible ash, which is
analyzed
for
it's
elemental
composition
WET ASHING, DRY
ASHING,
MICROWAVE, FUSIONS.
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Advantages of Ashing





The ability to decompose large sample sizes.
Little or no reagents is required.
The technique is relatively safe.
The ability to prepare samples containing
volatile combustion elements such as sulfur,
fluorine and chlorine (the Schöniger oxygen
flask combustion technique is very popular in
this case).
The technique lends itself to mass production.
Schöniger oxidation :
combustion of a sample in pure oxygen, followed
by the absorption of the combustion products by
a solution of NaOH
22
Disadvantages of Ashing







Losses due to retention to the ashing container.
Losses due to volatilization.
Contamination from the ashing container.
Contamination from the muffle furnace.
Physical loss of 'low density' ashes when the
muffle door is opened (air currents).
Difficulty in dissolving certain metal oxides.
Formation of toxic gases in poorly ventilated
areas. (Note that all charring should take place in a
hood and the muffle furnace must have a hood
canopy for proper ventilation).
23
Wet Ashing
•
•
•
•
•
To treat solid sample by acid digestion, producing clear
solution with no loss of the element to be determine.
Strong mineral acids are good solvents for many
inorganics.
Hydrochloric acid, nitric acid or aqua regia (3:1 HCl:
HNO3) dissolve many inorganic substances.
HF acid decompose silicates.
Perchloric acid is used to break up organic complexes.
24
DRY ASHING (GRAVIMETRIC)
•Performed by weighed sample in crucible, heated in muffle
furnace then the residue is dissolve in suitable acid.
•Typical ashing temperatures are 450 to 550 °C. Magnesium
nitrate is commonly used as an ashing aid.
•Charring the sample prior to muffling is preferred. Charring
is accomplished using an open flame.
•Care must be taken to ensure that non of the volatile
elements (Hg, Arsenic, Pb) from escaping during ashing.
•Dry ashing often used to remove organic substances from
interfering with the analyte
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MICROWAVE

In some cases the dissolution of sample can be done by
using microwave oven to accelerate the dissolution
process (at microwaves T=100 – 250oC).
 The sample is sealed in specially designed micromave
digestion vessel with a mixture of appropriate acids.
 Microwave ovens can be used for rapid and efficient
drying and acid decomposition of samples.
 Advantages of microwave digestions include reduction in
times from hours to minutes and low blank levels due to
reduced amounts of reagents required.
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FUSION

A weighed sample is mixed with a flux (sodium
peroxide) in a metal (zirconium) or graphite crucible.
The mixture is heated over a flame, or in furnace and
the resulting fused material is leached with either water
or appropriate acid (dilute mineral acid) or alkali.
 These techniques are required for sample types that are
inorganic in nature and unreactive toward acid
decomposition
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Fusions for Trace Analysts
Fusions are considered to be more of a 'last
resort' by trace analysts because:
1. They are expensive and often not available (high purity
fluxes).
2. They yield high solids solutions that can salt out in the
nebulizer.
3. Large dilutions of the sample are a necessity.
4. They often require expensive equipment.
5. Spectral interferences from the flux and/or crucible
construction material must be considered.
6. Contamination of the sample with the crucible
construction element and impurities must be considered
7. They are labor intensive.
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