CHEM 455
The class describes the principles and applications of modern
analytical instruments. Emphasis is placed upon the theoretical
basis of each type of instrument, its optimal area of application, its
sensitivity, its precision, and its limitations. Elementary integrated
circuitry and treatment of analytical data are introduced.
• Outcomes

Understanding the fundamental chemical and physical
properties that are used in instrumentation

Ability to evaluate and utilize data from instruments

Limitation of experimental instrumentation
Investigation of modern topics in analytical chemistry
1-1
Chap. 1 (Introduction), Chap. 2
(Components and Circuits)
• Methods of Analytical Chemistry
 Classical methods
 Separation of components
* Precipitation, extraction, distillation
 Identification by properties
 Color, melting point, solubilities
 Amount determined by mass or titration
 Instrumental methods
 interaction with electrons or photons
* Electronic or nuclear properties are identified
 Some properties based on bulk properties
* Thermal analysis
1-2
Methods
1-3
Instruments
• Converts information in
the sample to
information expressed in
an instrument
 Results are given in
differing data
domains
 Electrical and
non-electrical
1-4
Components
1-5
Interdomain Conversions
1-6
Electrical Domains
• Analog domains
 Magnitude of electrical quantity
 Voltage, currant, power, charge
* Correlation of two signals
 NMR, IR, DTA
* Susceptible to noise
1-7
Electrical domains
• Time domains
 Time component of
signals
 Duration of signal
above a threshold
* HI above and LO
below
 Frequency
and period
1-8
Electrical Domains
• Digital Domain
 2 level scheme
On, off; high, low
* Each selection is a bit
 Bit is termed count digital data
 Numbers can be represented in binary
1 or 0
* 101 = 1x22+0x21+1x20= 5
1-9
Detectors, Transducers, and Sensors
• Terms often interchanged
• Detector
 Device that identifies, records, or indicates
change in variable
Pressure, temperature, concentration,
charge, radiation
 Chemical, mechanical, or electrical device
• Transducer
 Converts information from non-electrical to
electrical domain
Photomultipliers, photodiodes
1-10
Sensor
• Sensors monitor a specific chemical species
 Ion sensitive electrode
 Piezoelectric crystal
 Functionalization of surface
 Crystal oscillates at constant frequency in an
electric circuit
 Change in mass can be detected
CF 2 M
F 
A
 C is a constant, F is frequency, M is mass, and A is
surface area
* Also works in spectroscopy (photoacoustic)
1-11
Selection of Method
•
•
•
•
•
•
Accuracy
Sample size
Concentration range
Interference
Matrix
Number of samples
1-12
Criteria
• Precision

Degree of mutual
agreement

Can be quantified
• Bias

Difference in true
sample
measurement

Bias=m-xt

m is mean, xt is true
measurement
1-13
Criteria
• Sensitivity
 Ability to distinguish analyte differences
 Based on linear calibration curve
* S=mc+Sbl
 S = signal, m = slope, c= concentration,
Sbl=blank signal
 Slope is calibration sensitivity
 Analytical senstivity
 g=m/ss, ss =standard deviation
• Detection limit
 Minimum analyte concentration that can be
detected
 Approaches blank signal
 Generally blank plus 3 times blank standard
deviation
1-14
Criteria
cm 
S m  S bl
m
• Detection limit
 Equation used to convert Sm to detection limit (cm)
• Dynamic range
1-15
Criteria
• Selectivity
 Impact of matrix on sample measurement
 Saturation of detector by matrix
 Similar chemical behavior
* Group chemistry
 Physical properties
* Mass similarity
 Can be defined by selectivity coefficient
 0 and above
* Can be greater than unity
1-16
Calibration
• Calibration curve
 Standard are
measured and
response
recorded
 Need to
consider matrix
 Can be nonlinear
1-17
Calibration
• Standard Addition
 Addition of standard directly to sample
 Multiple samples used to determine unknown
concentration
ScV
cx 
1 s
s
( S 2  S1 )Vx
 cx=unknown concentration, S is response for
sample (1) and sample plus standard (2), cs is
concentration of added standard, Vx is volume of
unknown, Vs is volume of added sample
• Internal Standard
 Standard added to all samples, blanks, and
calibration
1-18
Chap 2 Electric components and circuits
• Instruments rely upon measurements in a
circuit
 Based on electricity laws
Ohms law
* V=IR (V= potential difference in
volts, R is resistance in ohms, and I is
current in amperes
Kirchhoff’s law
* Sum of current around a point is 0
Power Law
* P=IV (P in watts)
1-19
Current Circuits
• Series Circuit
 R and V related
based on
fundamental laws
 Vx=V(Rx/R)
• Apply Kirchhoff’s law
and Ohm’s law to find
voltage at any point
1-20
Voltage divider
• In many circuits, it is necessary to obtain a voltage not
available from the main power source
 can derive other voltages from the main power
source
 voltage is less than the voltage from the main
source
 use resistors in an appropriate configuration to
reduce the voltage from the power source
• Potentiometers
1-21
Parallel Circuit
• A collection of series
circuits
 Kirchhoff’s and
Ohm’s law still
apply
 More electrons flow
through resistor
with lower
resistance
• Voltage for each section
 V=IxRx
1
1

 It=V/Rt
Rt
x
Rx
1-22
Measurements
• Voltmeter
 Integrated circuit
 Power supply
 Display
 Uses analog to digital converter
1-23
AC circuits
• Current or potential fluctuates with time
 F=1/t (Hz)
 Cycles per second
 Waves can differ
 Sinusoidal, square wave, ramp, sawtooth
• Equations can describe fundamental properties
 Angular velocity
  2f
1-24
Capacitors and Capacitance
• Conductors separated by dielectric
substance
• Can store an electrical charge
 Capacitor accepts electrons and
stores the charge
 Releases electrons
Equipment can have charge
when unplugged
v
c
r
1-25
Band Gap and Semiconductor
• Distinguish between conductor and insulators based on
band gap
• Thermal and photoexcitation
 Thermal promotes electron and creates hole
• Chemical excitation
 Inject impurities
Dopants
* i.e., P for Si, extra electron goes into conductive
band
Can apply Bohr model to describe single electron
Replace eo with e (dielectric constant) and me with
effective mass
m e4
E  k 
e
8e 0 h 2
1-26
Chemical doping
• Dieletric constant for Si = 11.7, effective mass is 0.2 me
 = 0.02 eV, measurement is 0.045 eV
• Calculate Bohr radius
 r1=ae/m= 30 A
Greater orbit
 Donor electron promoted to conduction band by
thermal energy
Ionized electron goes into conduction band
* Level below conduction band is donor level
 Most electrons from P
Electrons in band from P and governed by P
1-27
Dopants
The value of semiconductors for solid state device fabrication lies in the fact that
the number and type of conducting electric charge carriers [electrons are n-type
(negative), holes are p-type (positive)] can be controlled through incorporation of
appropriate dopant elements. Thus the substitutional incorporation of Group V
elements (Sb, As, P) provides for shallow donor levels in the band gap at about
0.01 eV from the conduction band. The substitutional incorporation of Group III
elements (B, Al) generates acceptor levels in the band gap at about 0.01 eV
from the valence band. The two types of impurities are almost completely
ionized at room temperature and give rise to extrinsic n-type and p-type
conductivity – the basis for the formation of junction devices such as diodes and
transistors (fig. 8).
Of increasing importance are compound III–V ( adamantine) semiconductors,
such as GaAs, InSb, InP and GaP (compounds of Group III and Group V
elements). Together these compounds provide eight valence electrons and, by
sp 3 hybridization, are able to form a diamond-like, covalent crystal structure
with semiconductor properties. These compounds (GaAs, for example) exhibit
electron mobilities which are higher than those of silicon and, therefore, are of
1-28
considerable interest for advanced device technology.
1-29
Doping
• N-type (negative)
 Electron extrinsic semiconductor (extra e-)
• Dope with subvalent impurity
 B in Si
Removes electron from valance band
* Creates hole that is mobile
Apply Bohr model is hole
Energy level are slightly about
valence band
Acceptor level (0.01 eV about
valence band)
1-30
* P- type
Semiconductor
• Make a p-n junction
1-31
1-32
Solids
• Ordered solids
 crystalline
• Irregular solids
 No long range order
Amorphous (glass)
• Band gaps > 3 eV are transparent
• Shapes are based on packing
1-33
1-34
1-35
Digital Electronics and Microcomputers
• Analog and digital signals
 Use of binary numbers
• ADC and DAC
 Transducers to data
• Controlled by computer
1-36
Lecture Extra
Bohr Atom
• Models of atoms
 Plum pudding
 Bohr atom
Inclusion of quantum states
Based on Rutherford atom
• Bohr atom for 1 electron system
 Etotal =1/2mev2+q1q2/4eor
q2=-e
* Include proton and electron
 1/2mev2-Ze2/4eor
1-37
Bohr Atom
• Net force on the electron is zero
 0=Fdynamic+Fcoulombic
 1/2mev2/r+q1q2/4eor2
Force is 1/r2E   Fdr
Energy 1/r
 1/2mev2/r-Ze2/4eor2
Z is charge on nucleus
• Quantize energy through angular momentum
 mvr=nh/2, n=1,2,3….
Can solve for r, E, v
1-38
Bohr radius
• R=(eoh2/mee2)(n2/Z)
 Radius is quantized and goes at n2
 R=0.529 Å for Z=1, n=1
Ao (Bohr radius)
1-39
Atomic Spectra
• Quantum numbers
 n=1,2,3,4
 r=aon2/Z for gases with 1 electron
• Energy
 E=-(mee4/8eo2h2)Z2/n2
 For ground state H
E=2.18E-18 J/atom=k
* Can determine J/mole 1312 kJ/mole
Energy goes as –k/n2
* System converges to limit
1-40
Energy
• n=infinity, r=infinity , E=0, unbound e• Ionization energy
 k is ionization energy
• Velocity
 v=nh/2mer
• Ionization energy
 Minimum energy required to remove
electron from atom in gas phase
Multiple ionization energies
1-41
Balmer states
• Gas H in tube
 Four lines in visible region
 Fit lines
• 1/l=(1/22-1/n2)R, R=1.1E-7 m-1
 1/ln (wavenumber)
 E=1/2mev2=eV (V=Volts)
At 1 V = 1.6E-19 J =eV
K=13.6 eV
1-42
Matter energy interaction
• Eincident=1/2mv2=qV
• Escattered
 E =Eincident-Escattered
 E=kZ2(1/n2final-1/n2in)=hn=hc/l
 De-excitation of electron results in photon
emission
Corresponds to line emission
1-43