TRƯỜNG ĐẠI HỌC KHOA HỌC VÀ CÔNG NGHỆ HÀ NỘI

UNIVERSITY OF SCIENCE AND TECHNOLOGY OF HANOI

UNIVERSITÉ DES SCIENCES ET DES TECHNOLOGIES DE HANOI

DEPARTMENT OF FUNDAMENTAL AND APPLIED SCIENCE

INSTRUMENTAL ANALYSIS

Dr. TO Hai Tung

TEXTBOOK
 CHAPTER 1
INTRODUCTION
 Introduction to Analytical Chemistry
ANALYTICAL CHEMISTRY: The Science of Chemical Measurements
Analytical chemistry is not a separate branch of chemistry, but simply the application of chemical knowledge
 TYPES of ANALYTICAL METHODS:
1.) Classical Methods (Earliest Techniques)
a.) Separations: Precipitation, Extraction, Distillation, Sublimation
b.) Qualitative: Boiling points, Melting points, Refractive index, Color,
Odor, Solubility
c.) Quantitative: Titrations, Gravimetric analysis

2.) Instrumental Methods (~post-1930’s)

a.) Separations: Chromatography, electrophoresis, etc.
b.) Qualitative or Quantitative: Spectrometric methods, Electrochemical
methods, Mass spectrometry, NMR ....
 Comparison of Different analytical methods
Approx. Approx. Selectivity Speed Cost Principle uses
Method range precision
( mol/L) (%)

Gravimetry 10-1-10-2 0.1 Poor-Moderate Slow Low Inorg.

Titrimetry 10-1-10-4 0.1-1 Poor-Moderate Moderate Low Inorg., Org.
Potentionmetry 10-1-10-6 2 Good Fast Moderate Inorg.
Electrogravimetry, 10-1-10-4 0.01-2 Moderate Slow-Moderate Moderate Inorg., Org.
coulometry
Voltammetry 10-3-10-10 2-5 Good Moderate Moderate Inorg., Org.

Spectrophotometry 10-3-10-6 2 Moderate-Good Moderate-Fast Low- Inorg., Org.

Moderate
Fluorometry 10-6-10-9 2-5 Moderate Moderate Moderate Org.
Atomic spectrometry 10-3-10-9 2-10 Good Fast Moderate- Inorg- Multielement
High
Chromatography 10-3-10-9 2-5 Good Moderate-Fast Moderate- Org. Multicomponent
High
Kinetic methods 10-3-10-10 2-10 Moderate-Good Moderate-Fast Moderate Inorg.,Org, Enzyme
 Overall process of an instrumental measurement

Instrument Energy Source Analytical

(stimulus) Information
Photometer Tungsten lamp Attenuated light beam
Coulometer Direct-current source Charge required to reduce or
oxidize analyte
Mass spectrometer Ion source Mass-to-charge ratio
 Nonelectrical
domain
Encoding
Analytical Data
Information domain
- Analog
Electrical
- Time
domain
- Digital
 2. Selecting
1. Defining the
analytical 3. Sampling
problem
method

ANALYTICAL
7. Data processing PROCESS
and 4. Sample
Report Results preparation

5. Chemical
6. Analysis Separation and
Enrichment
 Defining the problem

1. What accuracy is required? most important

2. How much sample is available? determine how sensitive the

3. What is the concentration range of the analyte? method must be

4. What components of the sample might cause interference?

determine the selectivity required of the method
5. What are the physical and chemical properties of the sample matrix?
compatibility of analyte with method

6. How many samples are to be analyzed? economic standpoint

 Selecting analytical method
Performance Characteristics of Instruments
 Precision
Illustrating the difference between “accuracy” and “precision”

Low accuracy, low precision Low accuracy, high precision

High accuracy, low precision High accuracy, high precision

 All Methods, except counting, contain
errors – don’t know “true” value

Accuracy: The degree to which an experimental result approaches the true or accepted answer
Error: An experimental measure of accuracy. The difference between the result obtained by
a method and the true or accepted value.
There are two ways to represent the error in the experiment
Absolute Error = (X – µ)
Relative Error (%) = 100(X – µ)/µ
X = The experimental result ; µ = The true result
Precision: Describes the range of spread of the individual measurements from the average
value for the series: deviation; variation; variance
- Describes the reproducibility of the measurement

Reproducibility and Repeatability

 Bias

Error: An experimental measure of accuracy. The difference between the

result obtained by a method and the true or accepted value.

Bias: The difference between the mean (average value) (of a large
number of repeated measurement results) and the true or accepted value.

Represent Bias via Error

 Random Systematic
Error Error

(indeterminate error) (determinate error)

• Cannot be determined (no control over) • Known cause: Operator; Calibration of

• A result of fluctuations (+ and -) in glassware, sensor, or instrument
random variables • A result of a bias in one direction
• Multiple trials help to minimize (+ or -)
• Random errors can be reduced by: • When determined can be corrected
- Better experiments (equipment, • May be of a constant or proportional
methodology, training of analyst) nature
- Large number of replicate samples
 Systematic
Error

Constant Proportional
Determinate Determinate
Error Error

Does not depend on the Be proportional to the

sample size (more or less analyzed sample size
sample size)
Use Standard
Run a blank
Reference
sample
Materials

Detect
a systematic
error

Use different Participate in

analytical “round robin”
methods experiments
 Sensitivity
The sensitivity of an instrument or a method is a measure of its ability to
discriminate between small differences in analyte concentration
0.18

0.16

0.14

Calibration Calibration 0.12

Y =A +B* X
0.10
sensitivity curve 0.08
Parameter Value Error
------------------------------------------------------------

Abs
A 2.31211E-4 0.00124
0.06
B 0.00413 5.89054E-5
0.04 ------------------------------------------------------------

S = mc + Sbl 0.02

0.00
R SD N P
------------------------------------------------------------

S: measured signal -0.02

0.99939 0.00232 8 <0.0001

0 10 20 30 40
c: concentration of the analyte CAs.10 M
7

Sbl: instrumental signal for a blank

m: slope of the straight line For two methods with equal
precision, the one with the steeper
Calibration sensitivity = m calibration curve is more sensitive
 Analytical
Sensitivity

(Defined by Mandel and Stiehler )

γ = m/Ss 0.18

0.16

Ss: standard deviation 0.14

m: slope of the straight line 0.12

Y =A +B* X
0.10
Parameter Value Error
0.08 ------------------------------------------------------------

Abs
A 2.31211E-4 0.00124
0.06
B 0.00413 5.89054E-5
0.04 ------------------------------------------------------------

0.02 R SD N P
two methods have calibration curves 0.00
------------------------------------------------------------
0.99939 0.00232 8 <0.0001
with equal slopes, the one with -0.02
0 10 20 30 40

higher precision is more sensitive CAs.10 M

7
determine LOD: Limit of Detection (Cm)
LOQ: Limit of Quantitation
LOL: Limit of Linearity
 Detection limit - LOD
the minimum concentration or mass of analyte that can be detected at a
known confidence level
Analytical signal must be statistically greater than the random noise of the blank

2- 3 times = peak noise

S/N (Signal-to-noise) = 3.1/1/7 = 1.8

 Calculation of LOD
• The minimal detectable analytical signal (Sm) is given by:
Sm = Sbl + k.SDbl

Sbl : Mean blank signal (obtain by 20/30-time blank measurements

k :3
SDbl: Standard deviation of blank signals

• Detection limit or LOD (Cm)

Cm = (Sm-Sbl)/m = 3SDbl/m

m: slope of calibration curve

Dynamic Range – LOQ and LOL

• LOQ (limit of quantitation):

[lowest] at which
quantitative measurements
can reliably be made.
LOQ = 10SDbl/m
• LOL (limit of linearity):
point where signal is no longer
proportional to concentration.

• Dynamic Range: from LOQ

to LOL
 Selectivity
Degree to which the method is free from interference by other species
contained in the sample matrix

No analytical method is totally free from interference from other species

Minimize the effects of these interferences

Sample containing an analyte A and potential interfering species B and C

The total instrument signal

S = maca + mbcb + mccc + Sbl
70

60 Selectivity coefficient (k):

50
influence of interferences on analyte
40 Positive
30
Species b
Negative kInt/Ana = mInt/mAna
20
Species c
Zero
10

0
0 2 4 6 8 10 12
S = ma(ca + kb/acc + kc/acc) + Sbl
Concentration (mM)
1 . Calculate the calibration sensitivity

2. Find the analytical sensitivity at each analyte concentration

3. What is the detection limit for the method?

 S = mc + Sbl

y = 0.067x + 0,031
Calibration sensitivity m = 0.067

Sm = Sbl + k.SDbl = 0.031 + 3x0.0079 = 0.0547

Cm = (Sm-Sbl)/m = (0.0547-0.031)/0.067 = 0.35 ppm

Introduction of Spectroscopic Methods
 Spectroscopic
Spectroscopy
Methods

The interaction of radiation and matter

Atoms
Atomic spectrometric
Matter methods
Molecular spectrometric
Molecules
methods

Electromagnetic Other sources

Radiation radiation (waves) (ions, electrons)
 Electromagnetic radiation

1. Gamma rays
2. X-rays
3. Light (Ultraviolet, Visible, Infrared)
4. Microwaves
5. Radio waves

Planck’s Law relates frequency (or wavelength) of an The wavenumber ν, which is defined as the reciprocal of
electromagnetic wave to the energy of the photon the wavelength in centimeters, is yet another way of
describing electromagnetic radiation
Planck’s law
E = h ν = 1/ λ (cm-1)
E = h(c/λ)
E is the energy.
: the frequency. λ: the wavelength
Spectroscopic Methods Based on Electromagnetic Radiation
Emission Interactions Absorption
of of Radiation of
Radiation and Matter Radiation
 Emission of Radiation

How to excite ???

(1) Bombardment with electrons or other elementary particles, which generally leads to the
emission of X-radiation
(2) Exposure to an electric current, an ac spark, or an intense heat source (flame, dc arc, or
furnace), producing ultraviolet, visible, or infrared radiation
(3) Irradiation with a beam of electromagnetic radiation, which produces fluorescence
radiation
(4) An exothermic chemical reaction that produces chemiluminescence
 Absorption of Radiation

For absorption of radiation to occur, the energy of the exciting photon

must exactly match the energy difference between the ground state and
one of the excited states of the absorbing species

Energy differences are unique

Molecular Atomic
Qualitative analysis
absorption absorption
Fluorescence Photoluminescence Phosphorescence
Time of relaxation Time of relaxation
process: 10-5 s process: > 10-5 s
Emission + Absorption

Energy release in 2 ways:

radiative and nonradiactive
processes
 Absorbance
the logarithm of the ratio of incident to transmitted radiant power through a sample
(excluding the effects on cell walls)
 Molecular
absorption

Eelectronic > Evibrational > Erotational

Line spectrum λelectronic < λvibrational < λrotational

UV-Vis Infrared Microwave

Band spectrum Band spectrum

 Quantitative Aspects
Establishment of Calibration curve

plot the data as signal vs. concentration