Analytical Chemistry 2001
chrupn@lsu.edu
Dr Kresimir Rupnik, Ph.D.
LSU, Fall 2015
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: Moodle
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• News updates, schedule/exams calendar
• Lecture notes/supplements (print important pages
!!!!!!, 4 or 6 on one page). You can fill in what is
needed during the lecture!!!
• HW, pre- Exams
• Check for updates and notes!!!!
• E-mail if you have questions, e-mail to report
interesting of difficult parts from reading a night
before the class
If you want to do more-and get
some credit for it…
• Read additional material from the textbook
• Read articles in Analytical Chemistry
(Science, Nature , JACS.. also may have
relevant research). Check websites
Introduction to The Analytical
Process: Analytical Chemistry in
application
• Chapter 0 (read it !)
Chapter 0 contains IMPORTANT take home messages
about the Analytical Chemistry: What, why, how
Most answers are given in this “representative” example which deals
with the analysis of chocolate.
Q; What are we analyzing for?
A: Analytes: caffeine and theobromine.
Q: Why are we analyzing?
A: We have a well defined goal related to some application such as
are quality, CSI , etc……The questions asked here could be: How
does the amount of caffeine compare with the quality of chocolate, say
which is better white or dark chocolate? Or : Are the two chocolate
samples from the same origin, say the one that a crime suspect is
eating and the one that was found at the crime scene – and both have
similar packing?
…and last but not least important question:
Q : How can we (or a CSI lab) find the caffeine
and its quantity in chocolate?
A: Find or make the procedure. In chemical
analysis that is a process that can be
described in terms of 7 important steps
• The real life analytical chemists knows the procedure,
that is knows general steps in a Chemical Analysis
0-2 IMPORTANT THM: 7 General Steps in
Chemical Analysis
•
•
•
•
•
•
•
Formulating the question
Selecting analytical procedures
Sampling
Sample preparation
Analysis (Chemical or Physical)
Reporting and interpretation
Drawing conclusions
Clicker!!
STEP 1:
Formulating
the question:
I need to
know what I
am looking
for!
Only then I
can select an
analytical
procedure
STEP 1:
Formulating
the question:
I need to
know what I
am looking
for!
Only then I
can select an
analytical
procedure
STEP 2 , selecting
analytical
procedure
Choices of
methods, more on
methods
throughout the
textbook.
Signal analysis ,
more in the first 5
chapters
Caffeine again: HPLC p. 4
High Performance (Pressure) Liquid Chromatography
Instrument, more on HPLC we will learn in “Separations”,
Chapter 23 and on
STEP 3: SAMPLING
• Sampling: how many chocolate bars, which
chocolates?
• Constructing a representative sample (Box 0-1,
p.7): random, homogeneous, inhomogeneous,
segregated material, composite sample
• STEP 4: SAMPLE PREPARATION,
• Sample preparation (for chemical analysis):
transforming a sample into a state that is
suitable for analyis.
• More in chapter 28
STEP 3, STEP 4: terminology
SAMPLES: Analytical chemist takes SAMPLES (small parts) of the materials for
analysis.
ALIQUOT: A small portion of the sample . Aliquotes masses are measured before
analysis!
ANALYTE: The compound you want to measure.
SAMPLE is ANALYZED for a compound or analyte.
Elements, ions, molecules, compounds are identified in sample (example: penicillin in
antibiotic). A sample is ANALYZED for elements, ions, molecules, compounds
(example: for penicillin). If the amount of elements, ions, molecules, compounds in the
sample is found, we use the word quantitation (amount of penicillin in the sample is
found).
An ASSAY for a compound or analyte
If we intend to determine what fraction of a sample is some named material, we use the
word determination or ASSAY. The named material is called the ANALYTE. We can
run an assay for that material.
NOTE : Analytical chemistry has its own language-learn it (see the
“Terms to Understand at the end of the chapter). You can more about
these concepts in chapters 0, 5, 28
PROCEDURES, PROTOCOLS, TECHNIQUES:
A protocol is a fixed sequence of actions (events) to be carried out (example: by US
EPA). These methods commonly define:
-sample handling requirements
-analytical TECHNIQUES
VALIDATION:
We need a validation of a new method by showing that its results agree with those
obtained using older (other), accepted procedures. When validated, we know that
the procedure measures what the analyst says it measures on a specific type of
sample. .
INTERFERENTS: They are “the enemy”. Interference occurs when a species
(other compounds than analyte) contribute the instrument signal intensity or
amplitude , by increasing it or decreasing it. So it looks like if there is more or less
of the analyte then the real concentration. Interfering species determine what is the
best method and protocol. We can MASK them by other chemicals so they do not
interfere.
STEP 5: Chemical (or Physical) Analysis
• Qualitative analysis: which substance
• Quantitative analysis: how much of it
Note: Analytical Chemistry is a Science that helps
improve methods of analysis. Novel directions in
analysis usually also include smaller, faster,
simpler cheaper methods.
Our choice was HPLC –how it
works?
Column
~25cm
long
where the
separation
takes place
HPLC Chromatography, p. 4 Fig 0-4, the column
Results of the Caffeine Analysis: Chromatogram, it shows
time on the x-axis and detector response or intensity of the
signal on the y-axis. Note the three analytes in this
example arrive at different (retention) times!!!
CHAPTER 00: Unnumbered Figure 0-3
CHAPTER 00: Unnumbered Figure 0-4
CHAPTER 00: Figure 0-7
CHAPTER 00: Figure 0-9
CHAPTER 00: Figure 0-10
HANDOUTS
Textbook p 5 and6
Figures 0-5,0-6
and 0-7
Can you tell what is
going on here?
CHAPTER 00: Figure 0-11
CHAPTER 00: Figure 0-12
CHAPTER 00: Figure 0-13
Analytical “two-step”
• 1st step: Calibration with
known standards. Use
standards, pure
compound same as
analyte with known
concentrations and
record the reading on the
instrument. Form a new
diagram (Figure 0-7) to
get the calibration curve –
you can use Excel fitting.
• 2nd step:
Measurement of
analyte and
quantitative
analysis from that
known calibration
curve.
STEP 6: Data Analysis and Reporting
• This is what we will do in chapters 3, 4 and 5. We will
discuss the so called statistical analysis which will give
us uncertainty (error) limits to our data presentation and
interpretation of our results. It will provide us with the
limits of confidence and consequently the limits for
possible answers to our question.
• An example: After such analysis was done we can
answer the question about caffeine in our chocolate:
Table 0-2.
STEP 6: terminology
SIGNALS
Total analysis technique & Concentration techniques
SA(signal due to analyte) =k CA (concentration of analyte)
CALIBRATIONS
-Accuracy, precision, sensitivity, selectivity, detection limits,
noise
-Robust and rugged method
-Scale of operation (analytes classification )
Calibration curve shows the response of the instruments signal to different
concentrations (quantities) of the analyte. It is done by the measurement of
standards before the measurement of analyte!! Standards are prepared
carefully, not from sample!!
There are methods how to calculate the
best fit: linear regression of straight-line
calibration curves
STEP 6:Reporting and STEP 7: Interpreting results
• Analysis of dark and light chocolate, grams of
analyte per 100g of chocolate
Analyte
Dark
chocolate
White chocolate
Theobro
mine
0.392+-0.002
0.010+-0.007
Caffeine
0.050+-0.003
0.0009+-0.0014
**
uncertainties
=standard
deviation
CHAPTER 00: Table 0-1
CHAPTER 00: Table 0-2
STEP 7 : Conclusion
Note on the methods
• Not all instruments are “ BIG” lab
equipment. Read about biosensors, p 1
of your textbook.
Note on analytical Chemistry Applications
• Industry (almost all need QC and analysis- food,
materials, …)
• Bio-Medicine (the basis of diagnosis, individual
susceptibilities, changes..)
• Environment (QC, monitoring, regulations)
• Law (CSI, ..)
• Others
SEE ALSO: Analytical Chemistry Division at ACS and
NSF. Check the pending changes in classifications! For
new instrumentation see also DOE. For new protocols
and standards NIST. For medical applications see NIH.
1. Measurements-Basic Tools
-qualitative aspects
(chemistry, physics)
-quantitative aspects
(numbers, units, uncertainty)
A SHORT REVIEW
Reading: Chapter 1
CHAPTER 01: Opener A
CHAPTER 01: Opener B
CHAPTER 01: Opener C
1-1Units of Measurement
IMPORTANT
SI Units (from 1960) = Metric system
• There are two types of units for measured
physical quantities (=number and unit): (1) 7
fundamental (or base) units:
and (2)(many) derived units obtained from base units
(example velocity).
Mole = unit for the number of
objects
• 6.02 10 ^23 objects is in a mole.
• 6.02 10 ^23 of oranges is one mole of
oranges.
• 6.02 10 ^23 = Avogadro’s number = 1
mole of objects
Q: Who found or measured Avogadros’ number
first?
Units of Measurement: SI Units
IMPORTANT
Powers of ten and exponential (scientific) notation are used for
convenience with smaller or larger units in the SI system.
There is more….
SI Units of Measurement
IMPORTANT
Length and Mass: meter (m) kilogram (kg).
(1 kg
= 2.2046 lb.)
Temperature: Kelvin Scale
Lowest temperature possible (absolute zero) is zero Kelvin.
Celsius Scale has the same temperature increment (ok.
in science, but be careful !)
Absolute zero: 0 K = -273.15oC.
Water freezes at 0oC and boils at 100oC.
To convert: K = oC + 273.15.
Examples: (1) Using two or more conversion
factors:
# m -------- # in.
# m * 100cm/m * 1in./2.4cm = # in.
(2) Conversions involving volume and density
# g of 2.00in.3 of gold if density = 19.3g/cm3
2.54cm=1.in. and 1cm3 = 19.3g gold
2.00in.3 *( 2.54cm/1.in. )3 * 19.3g/ 1cm3 =633g
Dimensional Analysis
IMPORTANT
Solving problems in chemistry requires careful manipulation of
numbers and their associated units, a method known as
dimensional analysis.
Given units can be multiplied and divided to give the
desired units.
•Use known conversion factors in the form:(Desired
unit / Given unit )
•Desired unit = Given unit(Desired unit / Given unit)
•Example: 8.50 inches in cm?
•Number cm = 8.50in x
(2.54cm/1 in) = 21.6cm
CHEM2001-2 Review: Moles, concentrations
etc.
# moles for element “E" = # grams of “E" /atomic mass of “E"
# moles for molecule “MO" = # grams of “MO"/molecular weight of
MO
# moles for compound “COm" = # grams of “COm"/formula weight of
“COm"
*YOU CAN USE CORRECT NOTATION: MOLAR MASS (MM)
Example: How many moles are present in 60.0 g H2SO4 ?
# moles of H2SO4 = 60.0 g H2SO4 * (1 mole H2SO4/98.0 g
H2SO4)
= 0.612 moles
Check the numbers!!
1 Molecule
23
6.02*10
..
Molecules
The Mole
IMPORTANT
Interconverting Masses, Moles, and Numbers of
Particles
6.02*1023
Molecules
(g/mol)
Number
Of molecules
Concentrations of solutions
• CONCENTRATION: the amount of solute in
the dissolved in a given quantity (volume or
mass) of solvent or solution.
Molarity = Moles of solute / Liters of solution
Molarity = (n / V) molL-1
What if not molecular compounds?
M and F (textbook)
Formality or Formal Concentration:
F
The molarity of strong electrolites is called formal concentration.
Formula mass (FM)
The molecular mass of strong electrolyte is called FM.
Note that the concept of “formal” indicates that the
compound is not the compound as written, it has been
dissociated or we do not know what it is exactly, that is
how many are in a unit or how many ions etc.
M== F ,
MM== FM (FW)
same units moles/L
same units g/mole
* We will not use amu unit here.
When one mole NaCl is dissolved in H2O, Na+ & Cl- ions are present and no
intact NaCl molecules! Term from freshman chemistry "formula weight" ( salts of
strong acids and strong bases should dissolve completely).
WHEN one mole CH3COOH acetic acid is placed into water not only does it
dissociates into CH3COO- & H+3O ions, but also some CH3COOH remains not
dissociated. Thus; all three are present in the aqueous solution. Formality again can be
used to describe the solution.
However, one mole of sucrose in one liter of water would be a one molar
solution and not a formal one.
Note: Chemists sometimes use formality to describe the initial concentrations of
substances that ionize in solution, whereas their equilibrium concentrations are
described in terms of molarity.
Molarity describes both the initial and equilibrium concentrations of non-ionic
substances.
Molarity: Moles of solute per liter of solution: How to
do it??
.250L of 1.00M solution of CuSO4
39.9g of CuSO4 (FW= 159.6amu)
Important:
Example: molarity of a solution
23.4 g Na2SO4 * (1 mol/142gNa2SO4 ) = .165 mol
Na2SO4
V=125mL solution (In H2O)= 0.125L
Molarity = .165 mol Na2SO4/ 0.125L = 1.32M
Molarity: Expressing the concentration of electrolytes
What are the molar concentrations of each of the ions
present in a dissolved electrolyte?
Example: given: 0.025M of calcium nitrate
Ca(NO3)2  0.025M in Ca 2+
what is ion concentration of (NO3)- ( 2 per molecule !!)
2*0.025M = 0.050M in (NO3)-
Molarity: Interconverting Molarity , Moles
and Volume
M = n/V
n= V*M = .400 mol = 2.0 L * 0.200M
V=n/M
Molarity (.200M of HNO3 for example ) is a conversion
factor between volume of solution (2.L, for example) and
moles of solute (0.400mol HNO3, for example).
Molarity: Dilution, from initial concentration to
the final with the SAME number of molecules
(moles) only the volume changes
n(initial)
=
n(final)
Example:
M initial (= 3.0M H2SO4) * Vinitial( ? )
= Mfinal (=0.10M H2SO4) * Vfinal (=0.450L H2SO4)
More Ways of Expressing Concentration
•All methods involve quantifying amount of solute per amount of
solvent (or solution).
•Generally amounts are measures are masses, moles or liters.
•Qualitatively solutions are dilute or concentrated.
•Definitions:
mass of component in soln
Mass % of component 
 100
total mass of soln
mass of component in soln
ppm of component 
 106
total mass of soln
Ways of Expressing Concentration
• Parts per million (ppm) can be expressed as
1 mg of solute per kilogram of solution.
– If the density of the solution is 1g/mL, then 1 ppm
= 1 mg solute per liter of solution.
• Parts per billion (ppb) are 1 g of solute per
kilogram of solution.
More Ways of Expressing Concentration
Mole Fraction
Recall mass can be converted to moles using
the molar mass.
moles of component
Mole fraction of component 
total moles of all components
l
Molality
Molality = (moles of solute / kilograms of solvent)
molkg-1
»Converting between molarity (M) and molality (m) requires density.
Ways of Expressing Concentration
Mole Fraction, Molarity, and Molality
FYI: Normality (old unit) = (# equivalents / Liters of solution)= " N "
An equivalent =“the amount of one chemical species reacting stoichiometrically with
other chemical species DEPENDS ON CHEMICAL REACTION!!!
An equivalent = (# g compound /MW compound) * (# H+ions, if acid)
(# OH-ions, if base)
(# e- lost or gained if
oxidized or reduced species)
So that : EW = FW/n
So that: N= n x M
Examples:
a 1M HCl soln. would be ---> 1N HCl soln.
and
a 1M H2SO4 would be ---> 2N H2SO4
1M FeCl3 soln where iron is +3, would be ----> 3N Fe+3 soln
pH=-log[H+],
What is pCl- ?
1-4 Real chemical reaction: the chemical change is a
transformation where atoms (physical objects) are conserved: mass,
charge, protons, atoms, electrons
Chemical Equations: Description of
Chemical Reactions in terms of
Atoms and their quantities
• Reactants
and
products:
2H2 + O2 
2H2O
• Stoichiometric coefficients in front of
chemical formulas give the number of
reactants and number of products.
IMPORTANT
Quantitative Information from
Balanced Equations (AB)
Titration (textbook example)
The Equilibrium Constant (Review)
For the reaction aA + bB cC + dD, the equilibrium constant, K, is
K=
[C]c[D]d
[A]a[B]b
Reaction is favored whenever K > 1
Evaluating the equilibrium constant
1) The concentration of solutes should be expressed as moles per liter
2) The concentration of gases should be expressed in atmospheres
3) The concentrations of pure solids, pure liquids and solvents are omitted because they are unity
Manipulating Equilibrium Constants
HA  H+ + A–
K1 =
[H+][A–]
[HA]
K1' =
[HA]
1
=
[H+][A–] K1
Reverse Reaction,
H+ + A–  HA
Add Two Reactions
HA  H+ + A–
H+ + C  CH+
K1
K2
HW and practice
Complete Problem Set 1 , HW 1 and preexam.