What is Analytical Chemistry ?
- Analytical chemistry deals with separating, identifying, and quantifying the
relative amounts of the components of an analyte.
- Analyte = the thing to analyzed; the component(s) of a sample that are to be
determined.
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Analytical Chemistry
analyze:
"what is it?
(qualitative
analysis)
"how much is there?“ (quantitative analysis)
2
The role of analytical chemistry: central science
The relationship between analytical chemistry and the other sciences
Chemistry :
Biological, Inorganic, Organic, Physical
Physics : Astrophysics, Astronomy, Biophysics
Biology :
Analytical
chemistry
Botany, Genetics, Microbiology, Molecular biology, Zoology
Geology : Geophysics, Geochemistry, Paleontology, Paleobiology
Environmental science : Ecology, Meteorology, Oceanography
Medicine : Clinical, Medicinal, Pharmacy, Toxicology
Material science : Metallurgy, Polymers, Solid state
Engineering : Civil, Chemical, Electronical, Mechanical
Agriculture : Agronomy, Animal, Crop, Food, Horticulture, Soil
Social Science : Archeology, Anthropology, Forensics
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Several different areas of analytical chemistry:
1. Clinical analysis - blood, urine, feces, cellular fluids, etc., for use in
diagnosis.
2. Pharmaceutical analysis - establish the physical properties, toxicity,
metabolites, quality control, etc.
3. Environmental analysis - pollutants, soil and water analysis, pesticides.
4. Forensic analysis - analysis related to criminology; DNA finger printing,
finger print detection; blood analysis.
5. Industrial quality control - required by most companies to control
product quality.
6. Bioanalytical chemistry and analysis - detection and/or analysis of
biological components (i.e., proteins, DNA, RNA, carbohydrates, metabolites,
4
etc.).
This often overlaps many areas.
Develop new tools for basic and clinical research.
History of Analytical Methods
Classical methods: early years (separation of analytes) via
precipitation, extraction or distillation
Qualitative: recognized by color, boiling point, solubility, taste
Quantitative: gravimetric or titrimetric measurements
Instrumental Methods: newer, faster, more efficient
Physical properties of analytes: conductivity, electrode
potential, light emission absorption, mass to charge ratio and
fluorescence, many more…
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Types of Analysis
Gravimetric Methods •
measure the mass of an analyte (or something chemically equivalent to the analyte)
Titrimetric (Volumetric) Methods •
measure the quantity of a reagent needed to completely react the analyte
Electroanalytical Methods •
measure the change in the electrical potential, current, resistance or charge produced by an
analyte
Spectroscopic Methods •
measure the interaction between electromagnetic radiation (light, UV, IR, etc.) and the
analyte
Chemical Separations •
separate and measure the analyte of interest by chemical means (chromatography)
Other Methods •
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Process of Analysis
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1.Define the information you need
2.Select an analysis method
3.Obtain a sample & 'clean' it up
4.Prepare the sample, solutions and standards
5.Do the analysis!
6.Account for interferences
7.Calculate results and estimate reliability
8.Convert results to information
Expressing Analysis Results
mass of analyte
mass (or volume) of sample
percent composition (% composition) - X's 100
%W/W %W/V %V/V
part per thousand (ppt) - X's 1000
parts per million (ppm) - X's 106
parts per billion (ppb) - X's 109
e.g.
22 ppm (w/v) lead
124 ppb (w/w) atrazine in soil
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Titrations
Introduction
1.) Buret Evolution

Primary tool for titration
Gay-Lussac (1824)
Blow out liquid
Mohr (1855)
Compression clip
Used for 100 years
Descroizilles (1806)
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Pour out liquid
Henry (1846)
Copper stopcock
Mohr (1855)
Glass stopcock
Principles of
Volumetric Analysis
titration
titrant
analyte
indicator
equivalence point vs. end point
titration error
blank titration
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Principles of
Volumetric Analysis
standardization
standard solution
secondary standard solution
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Principles of
Volumetric Analysis
primary standard
1. High purity
2. Stability toward air
3. Absence of hydrate water
4. Available at moderate cost
5. Soluble
6. Large F.W.
secondary standard solution
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Titrations
Introduction
Standardization

Required when a non-primary titrant is used
-
Prepare titrant with approximately the desired concentration
Use it to titrate a primary standard
Determine the concentration of the titrant
Titration
Standardization
titrant known
concentration
analyte unknown
concentration
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titrant unknown
concentration
analyte known
concentration
Standardization of
0.1 M NaOH
1-selection the PS KHP
2-wheing the PS
10*0.1=mg/204.1 213.8
3-making solution
4-addind suitable indicator
5-titration
9.1ml
6-calculation 9.1*n=213.8/204.1
n=0.115
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Titrations
Introduction
2.) Volumetric analysis

Procedures in which we measure the volume of
reagent needed to react with an analyte
3.) Titration

Increments of reagent solution (titrant) are added
to analyte until reaction is complete.
-

Calculate quantity of analyte from the amount of
titrant added.

Requires large equilibrium constant
Requires rapid reaction

-
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Usually using a buret
Titrant is rapidly consumed by analyte
Titrations
Introduction
4.) Equivalence point

Quantity of added titrant is the exact amount necessary for stoichiometric
reaction with the analyte
Ideal theoretical result
Analyte
Oxalic acid
(colorless)
Titrant
(purple)
(colorless) (colorless)
Equivalence point occurs when 2 moles of MnO4- is added to 5 moles of Oxalic acid
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Titrations
Introduction
5.) End point

What we actually measure
-
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Marked by a sudden change in the physical property of the solution
Change in color, pH, voltage, current, absorbance of light.
Titrations
Introduction
5.) End point

Occurs from the addition of a slight excess of titrant
-
Endpoint does not equal equivalence point
Analyte
Oxalic acid
(colorless)
Titrant
(purple)
(colorless) (colorless)
After equivalence point occurs, excess MnO4- turns solution purple  Endpoint
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Titrations
Introduction
5.) End point

Titration Error
-

Primary Standard
-
-
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Difference between endpoint and equivalence point
Corrected by a blank titration
i. repeat procedure without analyte
ii. Determine amount of titrant needed to observe change
iii. subtract blank volume from titration
Accuracy of titration requires knowing precisely the
quantity of titrant added.
99.9% pure or better  accurately measure concentration
Analyte
Oxalic acid
(colorless)
Titrant
(purple)
Titrations
Introduction
6.) Back Titration

Add excess of one standard reagent (known concentration)
-
Completely react all the analyte
Add enough MnO4- so all oxalic acid is converted to product
Analyte
Oxalic acid
(colorless)

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Titrant
(purple)
(colorless) (colorless)
Titrate excess standard reagent to determine how much is left
Add Fe2+ to determine the amount of MnO4- that did not react with oxalic acid
Differences is related to amount of analyte
Useful if better/easier to detect endpoint
Titrations
Titration Calculations
relate moles of titrant to moles of analyte
Calculation of ascorbic acid in Vitamin C tablet:
(i)
Starch is used as an indicator: starch + I3-  starch-I3- complex
(clear)
(deep blue)
(ii) Titrate ascorbic acid with I3-:
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1 mole ascorbic acid  1 mole I3-
Titrations
Titration Calculations
Standardization of Titrant
Standardization: Suppose 29.41 mL of I3- solution is required to react with 0.1970 g of
pure ascorbic acid, what is the molarity of the I3- solution?
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Titration Calculations
Analysis of Unknown
Analysis of Unknown: A vitamin C tablet containing ascorbic acid plus an inert binder
was ground to a powder, and 0.4242g was titrated by 31.63 mL of I3-. Find the weight
percent of ascorbic acid in the tablet.
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Volumetric
Procedures and
Calculations
relate the moles of titrant to the moles of
analyte
# moles titrant = # moles analyte
#molestitrant=(V*M)titrant
=
#molesanalyte=(V*M)analyte
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Titrations curves
Spectrophotometric Titrations
1.) Use Absorbance of Light to Follow Progress of Titration

Example:
-
Titrate a protein with Fe3+ where product (complex) has red color
Product has an absorbance maximum at 465 nm
Absorbance is proportional to the concentration of iron bound to protein
Analyte
(colorless)
titrant
(colorless)
As Fe3+ binds protein
solution turns red
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(red)
Titrations curves
Spectrophotometric Titrations
1.) Use Absorbance of Light to Follow Progress of Titration

Example:
-
As more Fe3+ is added, red color and absorbance increases,
When the protein is saturated with iron, no further color can form
End point – intersection of two lines (titrant has some absorbance at 465nm)
When all the protein is bound to Fe3+,
no further increase in absorbance.
As Fe3+ continues to bind protein
red color and absorbance increases.
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Titrations curves
Acid-base Titration Curve
1.) Graph showing how the concentration of one of the reactants varies as titrant
is added.
Sharpness determined
by titration condition
Monitor pH, voltage,
current, color,
absorbance


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Understand the chemistry that occurs during titration
Learn how experimental control can be exerted to influence the quality of
an analytical titration
-
No end point at wrong pH
Concentration of analyte and titrant and size of Ksp influence end point
Help choose indicator for acid/base and oxidation/reduction titrations
Acid-Base Indicators
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Precipitation Titration Curve
EXAMPLE: Derive a curve for the titration of
50.00 mL of 0.00500 M NaBr with 0.01000
M AgNO3.
titration curve => pAg vs. vol. AgNO3 added
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Precipitation Titration Curve
pX = - log10[X]
p-function
precipitation titration curve
four types of calculations
initial point
before equivalence point
equivalence point
after equivalence point
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Vol of titrant
pAg
5.00 9.84
25.00 6.14
25.10 4.88
Precipitation Titration
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10
pAg
8
6
4
2
0
0.00
5.00
10.00
15.00
20.00
Vol of AgNO3 added
31
25.00
30.00
2.60
2.81
3.15
3.25
3.38
3.56
3.87
4.17
Precipitation Titration
0.0025
12
0.001538
10
0.000714
0.000563
8
0.000417
0.000274
pAg
Vol of titrant
pAg
5.00
9.84
10.00
9.68
15.00
9.47
20.00
9.13
21.00
9.03
22.00
8.90
23.00
8.72
24.00
8.41
24.50
8.11
25.00
6.14
25.10
4.88
26.00
3.88
27.00
3.59
28.00
3.41
29.00
3.30
30.00
3.20
35.00
2.93
32
40.00
2.78
6
0.000135
6.71E-05
4
2
0.0001316
0.0002597
0.0003846
0.0005063
0.000625
0.0011765
0.0016667
0
0.00
10.00
20.00
30.00
Vol of AgNO3 added
40.00
50.00