Physical methods of analysis
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Transcript Physical methods of analysis
Physical methods of analysis:
classification and
metrological characteristics
Assistant of the
pharmaceutical chemistry department
Burmas Nataliya Ivanivna
e-mail: [email protected]
Plan
1. Classification the methods of analysis,
advantages and lacks of the physical
methods of analysis (PMA).
2. Metrological characteristics of PMA and
physical and chemical methods of
analysis (PCMA).
3. Refractometry.
4. Polarimetry.
1. Classification the methods of analysis, advantages
and lacks of the physical methods of analysis (PMA)
Methods of analysis are divided into:
1.Chemical methods:
3. Physical methods:
- gravimetry
- spectral
- titrimetry
- kernel-physical
2. Physical and
- mas-spectroscopic
chemical methods:
- thermal
- electrochemical
4. biological methods
- photometric
- kinetic
- chromatographic
Physical and physical- chemical methods
of analysis
are based on the using of the
relationship between
measurable physical properties
of substances and qualitative
and quantitative composition.
Physical methods of analysis
based on measuring the effect caused by
the interaction of substance with a
radiation – the stream of quantum or
particles.
physical methods of analysis are such
methods in which identification of the
element based on the properties of its
atoms and and nucleus.
Physical properties of materials
measured by different instruments
(tools), so physical and physicalchemical methods are called
instrumental.
Advantage of PMA
1. High sensitivity - low limit of detection
(10-9 mkg) and the definition.
2. The high selectivity.
3. The expressity.
4. The possibility of automation and
computerization.
5. The possibility of analysis on the
distance.
6. The possibility of analysis without
destroying the sample.
7. The possibility of local analysis.
Lacks of PМА
1. Error of determination near
5% (in special case to 20%), then
0,01-0,005 % for gravimetry and
0,1-0,05 % for titrimetry.
2. Reproducibility of results in the
individual methods is lower than
in classical methods of analysis.
Lacks of PМА
3.The complexity of the equipment
used, its high cost and also high
value of standard substances.
4.The need for standards and standard
solutions, calibration equipment and
construction of calibration graphs.
2. Metrological characteristics of PMA and
physical and chemical methods of analysis
(PCMA)
The sensitivity of method is determined by factors:
a) intensity of measured physical properties
b) sensitiveness of detectors
The little-intensity properties : refraction of light,
rotation of the plane polarization of light –
refractometry and polarimetry has a low sensitivity.
The hight-intensity properties : absorption of light
(from nature), fluorescence, radio-activity, emission
– are the sensitivity of such methods from 10-6 to 1015 g.
Sensitivity of some instrumental methods of analysis
Method
Limit of exposure
Photometry (PMA)
110-6
Fluorimetry (PMA and PCMA)
110-10
Polarography (PCMA)
110-8
Emission spectral analysis (PMA)
110-10
Atomno-absorbcition analysis (PCMA)
110-10
Gas chromatography (PCMA)
110-11
Radioisotope analysis (PMA)
110-15
Mas-spectroscopic (PMA)
110-12
Coulometry (PCMA)
110-10
Kinetic analysis (PMA and PCMA)
110-11
The selectivity of method is the selectivity
determination of this substance in presence other
without of previous separation
High selectivity is inherent the methods,
which are based on characteristic properties
of molecules, functional groups, atoms,
which in same queue own emission and
absorbcition properties, radio-activity, ability
to electrochemical oxidization or reduction.
Low selectivity is characteristic, for
example, refractometry is used for the
analysis of individual substances or mixtures
with 2-3 substances.
The regularity of method is closeness the got
result to the truth value of content of the
determined substance in the experimental object
Depends on how measured physical property
is adequately reflects the structure and
connected with it is strictly defined by laws.
Exactness of calibration of analytical equipment
will influence on the regularity of method.
The standard specimen is a substance which
has constant composition and properties.
The reproducility of method
characterized by variation of results at the
parallel measurings.
On the producibility influences:
the exactness of measuring;
the exactness of weighing;
the exactness to use of dishes;
stability work of the analytical appliance
(apply the special methods of
measurings).
3. Refractometry
Refractometry is a set of methods of the
research of physical and chemical
properties substance are on the basis of
measuring their indexes of refraction by
light.
Refractometry is a method of qualitative
and quantitative analysis, which is based
on the measuring the index of refraction
by the liquid or crystals.
Index of refraction
n=sin1/sin 2
Absolute index of refraction (N) is the
relation of speed widening of light in the
vacuum to its speed in the present medium :
N C0 C
Relative index of refraction (n) is the
relation of speed widening of light in the
air to its speed in the present medium:
n Cair C
Connection between the absolute
and relative indexes of refraction
is described by a formula:
N 1,00027 n
The index of refraction is the
difficult function which depends
from the influence of many factors:
a) the nature of refractive medium;
b) light is refracted (D =589,3
nm);
c) temperature (200,3 С);
d) the concentration of solution;
e) from direction falling on the crystal
of light.
In these conditions measuring the
refractive index has a value between
1,3-1,7.
Exactness of measuring on
refraction‘s Abbe arrives from
0,0001 to 0,0003.
In practice, refractometry is used to
determine the concentration of
solution is below 3%.
1. Scale
2. Amici‘s prism (scray of
dispersion)
3. Prizmenity block
4. Lighting prism
5. Layer of examinee
liquid
6. Measuring prism
7. Crossing for adjusting
of light and shade in an
eyepiece
Qualitative analysis
Every clean, optically transparent
substance
(liquid,
crystal)
is
characterized by the defined numerical
value the index of refraction, that used
in the qualitative analysis (metanol –
1,3286; ethanol – 1,3613; acetone –
1,3591; chloroform – 1,4456; water –
1,3330).
Quantitative analysis
It is based on used of dependence
between the index of refraction by
trial solution and content X of
determined substance.
n n0
X
F
n2 n1
F
X 2 X1
Basic methods of quantitative analysis:
1. The method of calibration chart
n f (X )
2. Calculation
n n0
X
F
3. By special of refractometric tables
Advantages of the method: simplicity of
apparatus design, the speed of execution.
Lacks of the method: a low exactness and
a low sensitivity (the area determined of
contents) X 1%
The absolute error doesn't must exceed
0,0002 - 0,005 (for medical means
0,0002)
Application: for control quality of
substances, solvents and solutions.
4. Polarimetry
the method of analysis, which is based on
measuring of angle rotation by space
polarization of the monochromatic
light at passing its through the optically
active substance– an individual substance
or a solution.
has «+» for right-rotation
substance
has «-» for left-rotation substance
The angle rotation of space polarization
depends from:
a) light
b) the thickness of layer
c) the nature of a solvent
d) the density of optically active medium
e) the concentration of optically active
substance
f) a temperature
20
[ ]D
Specific rotation
- is the angle
rotation of space
polarization of
monochromatic radiation at thickness of
the layer 1 dm and the content of
optically active substance 1 g/ml.
Specific rotation by the individual
substances :
[ ]
l
for solutions of optically active substances:
100
[ ]
C l
Qualitative analysis
it is based on measuring of the angle
rotation of space polarization by
examinee substance or its solution
and calculation of specific rotation.
100
[ ]
C l
Quantitative analysis
calculation method
100
C
[ ] l
Advantages of method: the simplicity of
apparatus design.
Lacks of method: a low exactness and a low
sensitivity (area of determined contents).
Application:
a) to control the purity of substances of optically
active compounds (carbohydrates, amino acids);
b) for conformation of identity and authenticity by
the size of specific rotation (ascorbic acid,
camphor, levomicetin, morphine);
c) for the quantitative determination of sugars
(saccharides).