High frequency titrations (HFT) is an analytical technique utilizing radio frequency electric fields to measure the conductivity of solutions without the use of electrodes. This method provides advantages such as eliminating polarization effects and being particularly useful for organic compounds, although it is complex and less sensitive compared to traditional methods. Various applications include acid-base, complexometric, and precipitation titrations, as well as analysis of organic compound mixtures.

1. HIGH FREQUENCY TITRATIONS
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SAGARIKA.B
M.Pharm (PA&QA)

2. INTRODUCTION
 High frequency titrimetry is closely related to conductometry .
 This method is also called as Oscillometry.
 This is an analytical technique in which a radio frequency electric field
is applied for which electric conductance of analytical substance
governs the response of detector.
 The titration vessel is kept in the field of H.F.O and changes in
conductivity of solution produce capacitance changes of the
detector circuit.
 Major advantage is elimination of electrodes .
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3. THEORY:
• The conductivity of a sol depends on the mobility of ions in an electric field.
• Use of AC to avoid electrochem. depositon still allows ion mobility which
at high frequencies can not gain their full speed here a phenomenon called
molecular polarization arises.
• Thus ionic & orientation polarization occurs .
• When a molecule is placed in a electric field,
electrons +ve electrode ; proton -ve electrode
Distortion Polarization
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4. • When dipolar molecule is placed in electric field,
+ve -ve ; -ve +ve
Orientation Polarization
• At high frequencies both & conductant current are of same magnitude
and neither can be neglected.
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5. INSTRUMENTATION :
 The technique of high frequency analysis was developed by F.W.Jensen and
A.L.Parrack.
 The cell employed for H.F.titrations is a glass or ceramic vessel which act
as conductivity cell.
 The metal electrodes are placed outside container about 2.5cm apart and
out of direct contact with the solution.
 Measurements can be made with out the danger of electrolysis and
electrode polarization and with out altering or consuming solution.
 when the vessel is placed in the field ,any changes in concentration
will be indicated in detector circuit.
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6. CELLS:
 In H.F.titrations two types of cells are used
1. Capacitative cells
2. Induction cells
 CAPACITATIVE CELLS:
• Capacitance the variable parameter is capacitance which mainly depends on
Dielectric constant and resistance of the solution in the cell .
• Two bands of copper or silver are put around the outer part of the cell and
connected to H.F.O.
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7.  INDUCTION CELLS :
 Incase of induction cell the variable parameter is the inductivity of the
Cell which is almost independent of nature and résistance of the solution .
 There are no electrodes and the cell is placed inside the induction coil
in the tuned circuit of oscillator.
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8. OSCILLATOR CIRCUIT:
o It consist of capacitance C, inductance L and
resistive component R.
o A stage called resonance is attained when the
adjustment of circuit capacitance is done .
o when the condenser is discharged through
the inductance , current will surge back
and forth from the conductor to the capacitor
at a frequency given by
F=1/2π√LC
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9. PRINCIPLE:
•Cell is filled with a solution of specific conductivity K, dielectric constant D.
•C2 denotes the capacitance into&out of cell through glass wall which is
result of capacitors in service.
• In side cell wall C1 & R1 are capacitance & resistance.
• Path length btw electrodes is d cm.
• Area A cm3
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10. • When a titration involving electrolytes change in K results in changes
of D &
• Incase of mixture of liquids changes.
• When cell is connected in parallel high frequency conductance& Cp is given by
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11. • when r2 changed both R&L change with corresponding changes in
frequency & oscillatory current of instrument.
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12.  In this resistance and inductance of primary circuit are R1 L1
Secondary circuit R2 and L2.
 Mutual conductance
k is coupling constant .
 when oscillator connected to tt response
to inductance and r is given
R =
Inductance cell:
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13. HIGH FREQUENCY TITRIMETERS
 The H.F. Titrimeter ranges from simple magic eye tube circuit of hall
To the complex oscillometer of sergent .
 The cell is put in parallel with a calibrated capacitor .
 In this method , the out put frequency of two identical oscillator circuit
is measured.
One of the circuit contains the sample cell as a part of oscillator circuit ‘f’
and other circuit serves as reference unit ‘fo’.
The output from the two units are then fed in to a mixer unit
and the difference of frequency is measured directly.
 In some titrimeters change in oscillator current from the introduction
of sample is measured.
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14. SCHEMATIC DIAGRAM OF HIGH FREQUENCY
TITRIMETER
F-fo
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15.  ACID-BASE TITRATIONS:
APPLICATIONS:
• Before carrying HFT it is necessary to determine the response of the
Instrument as the function of the electrolyte.
• During titration one of the conc. Should be higher and temp should be
kept constant.
• The acid base titrations give one or more breaks at the end points .
• The unknown sol. Can be analysed with the help of these breaks in
terms of std alkali or acid added.
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16.  COMPLEXOMETRIC TITRAITIONS:
• High frequency titrations of ions like ca, mg, cu,la give a sharp
end point with EDTA.
• The titrations of ni,cu,zn, with pyridine has been used successfully.
 PRECIPITATION TITRATIONS :
• In this the change in conductivity is small before the end point is reached .
• The exact shape point of the titration curve depends on concentration
of titrant and solution & the frequency on which the measurements
are carried out.
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17.  ANALYSIS OF MIXTURE OF ORGANIC COMPOUNDS :
• This method is based on the dielectric behavior or the mixtures .
• it can be done calibration curve are prepared and instrument readings
are converted. Into concentration ratios.
• The mixtures of P-xylenes ,hexanes ,and benzene, methanol and ethanol ,
alcohol and water are detected.
 DETERMINATION OF DIELECTRIC CONSTANT:
• Consider a non-conducting liquid placed between metal plates of a cell
behaving as two capacitors cg & cs in series.
• Cs varies from fixed co,(filled with air) to a value D depending upon
the dielectric constant of the sample.
Cs=coD
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18. ADVANTAGES :
• H.F.T reflects more complex changes occurring in the solution than
conductometric titrations.
• The method dose not require any special type of conductivity cell.
• Polarization of electrodes and chemical interaction of substances are eliminated.
• Catalytic or surface effects do not occur on platinum electrodes.
• It is particularly useful for organic compounds where low frequency method
is not helpful because of their poor conductance.
• The variation of oscillator current may be plotted against function of time if
a Potentiometric recorder is connected.
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19. DISADVANTAGES:
• The technique is complex and tuning is difficult .
• Titrimeter is less sensitive.This can be enhanced by using well designed cell.
• This method require measures at the end point.
• This method is empirical than fundamental.
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SAGARIKA