Hanna Instruments HI 4105 User Manual

H

I 4105

DIOXIDE

CARBON

Instruction Manual

HI 4105HI 4105

HI 4105

HI 4105HI 4105

Carbon Dioxide

Ion

Selective Electrode

1

HI 4105 Carbon Dioxide ElectrodeHI 4105 Carbon Dioxide Electrode

HI 4105 Carbon Dioxide Electrode

HI 4105 Carbon Dioxide ElectrodeHI 4105 Carbon Dioxide Electrode

I. I.

Introduction:Introduction:

I.

Introduction:

I. I.

Introduction:Introduction:
The Hanna HI 4105 Carbon Dioxide gas sensing electrode
is a combination electrode designed for the measurement
of Carbon Dioxide in aqueous solutions such as water, soft
drinks or wine, samples. Carbonate and Bicarbonate ions
are also measured by conversion to Carbon Dioxide gas
upon ISA addition.

II.II.

SpecificationsSpecifications

II.

Specifications

II.II.

SpecificationsSpecifications

Type: CO2 gas sensing

electrode with glass pH
internal, Ag/ AgCl
reference and gas
permeable membrane.

2-

Species detected: CO

-

,HCO

, CO

3

3

2

CO2 Measurement Range: 0.02 M to 4 x 10-4M

880 to 17.6 ppm

2-

Interfering ions: SO2/SO

3

, H2S/S

2-

Operating Temperature: 0 to 40°C

Operating pH: 4-5 pH

Dimensions: 12 mm (OD) X 120

mm (insertion)

0.47”x 4.72”

Wetted materials: Delrin®, body and cap

with PTFE membrane

Connection: BNC

2

3

III.III.

Theory of OperationTheory of Operation

III.

Theory of Operation

III.III.

Theory of OperationTheory of Operation

::

:

::
The Carbon Dioxide electrode is a complete potentiometric
cell that contains both a silver/silver chloride (Ag/AgCl)
reference and a pH measurement element. These elements
are housed within a thermoplastic body in a chloride ion­containing electrolyte, and are isolated from the sample by
a PTFE membrane.
ISA addition changes the pH of the sample to approxi­mately 4.7 pH and Bicarbonate (HCO

2-

(CO

) ions in the sample are converted to carbon dioxide

3

-

) and carbonate

3

(CO2). The CO2 in the sample solution diffuses through the
PTFE membrane where it dissolves into the thin film of fill
solution found between the membrane and the internal pH
membrane. Here it converts back into bicarbonate and
hydrogen ions. The pH changes proportionally with the
concentration of dissolved gas in the sample solution. Dif­fusion of CO2 continues until the partial pressures of the gas
in the sample and thin film are equal.
The Nernst expression for an Carbon Dioxide sensor is ex­pressed in the equation below. Note that the potential is a
function of the Carbon Dioxide gas, which in turn is related
to the hydrogen ion concentration. The glass internal,
Ag/AgCl reference, equilibrium constant and Henry’s law
constant are rolled into the E’ and Eo terms. The Nernst
equation for the sensor becomes the equation noted below:

E = E’+2.3RT/nF log [CO2]= E

E = observed potential

E’ = Reference and fixed internal voltages

o

+0.059 log [H

+

]

IV.IV.

Design ElementsDesign Elements

IV.

Design Elements

IV.IV.

Design ElementsDesign Elements
The Hanna HI 4105 Carbon Dioxide gas sensor has 3 main
parts. These are the membrane/membrane cap, outer probe
body with antirotation key and the pH/reference assembly
which includes the outer electrode cap, spring, inner cap
and pH/reference electrode assembly.

pH/reference electrode assembly

cable

outer electrode
cap

spring

antirotation key inner cap

Outer probe body

Reference
electrode

R = gas constant (8.314 J/K Mol)

n= Charge on ion (equivalents/mol)

T = absolute temperature in K

4

F = Faraday constant (9.648 x 10

C/equivalent)

The mV should increase in a Nernstian manner as the
carbon dioxide partial pressure increases in the sample.

4

O-ring

pH

sensitive

membrane

Membrane/membrane cap

5

V.V.

Equipment Required:Equipment Required:

V.

Equipment Required:

V.V.

Equipment Required:Equipment Required:

• Hanna HI 4222 pH/ISE/mV meter or other suitable

ion or pH/mV meter. (Note: log/linear graph paper is
useful if an ISE meter is not available).

• Hanna HI 180 magnetic stirrer or equivalent with

stirring bars. (Note: Isolate beakers from stirrer motor
heat by placing insulating material such as foam or
cork between them).

• Hanna HI 4000-71 gas sensor test vessel or

Hanna HI 76404 electrode holder or equivalent with
Beakers or other suitable measurement vessel with
plastic sealing film or wrap.

VI. VI.

Solutions Required for Calibration:Solutions Required for Calibration:

VI.

Solutions Required for Calibration:

VI. VI.

Solutions Required for Calibration:Solutions Required for Calibration:
Ionic Strength Adjuster (ISA), 500 mL: HI 4005-00
Hanna 0.1 M standard, 500 mL: HI 4005-01
Hanna 1000 ppm CO2 standard, 500 mL: HI 4005-03*
*Please Note: This calibration standards is ppm as CaCO

See Section XVII for additional solutions and accessories
used for maintenance.

Using volumetric pipettes and glassware prepare serial
dilutions of the standard. Select concentrations that will
approximately bracket the concentration of the samples to
be measured. Standards with concentrations less than
10-3M should be prepared fresh daily. Store solution in a
tightly sealed bottle without ISA added. 10 mL of HI 4005­00 ISA should be added to each 100 mL sample of stan­dard and samples just prior to measurement. ISA adjusts
the pH of the sample or standard to about pH 4.7 thus
converting carbonate and bicarbonate ion to carbon diox­ide. It also provides samples and standards a constant
ionic strength background that stabilizes the solutions ac­tivity coefficient and permits concentration to be measured
directly.

VIIVII

General GuidelinesGeneral Guidelines

VII.

General Guidelines

VIIVII

General GuidelinesGeneral Guidelines

• Calibration standards and sample solutions should

have the same ionic strength. ISA should be added to
both samples and standards immediately before tak­ing measurements.

• Calibration standards and sample solutions should be

stirred at the same rate using identical sized stir bars.
Stir thoroughly and continuously.

• Calibration standards and sample solutions should be

at the same temperature. Thermally insulate solution
vessel from magnetic stirrer with cork or other insulat­ing medium.

• Wait until sensor value has stabilized before taking

reading (at least 5 minutes when going from more
dilute to more concentrated samples, longer when the
order is reversed).

• Surface coating on the PTFE membrane will effect the

3

response. Inspect sensor before using. Wash off with a
jet of deionized water or mild detergent to remove
film.

• Replace PTFE membrane if damage is evident or a

droplet of internal electrolyte is seen.

• Rinse electrode with distilled or deionized water be-

tween samples and dab dry with lab wipe or other soft
disposable absorbent toweling.

• Check calibration every 1-2 hours. Recalibrate if nec-

essary.

• Position sensors at an angle of approximately 20° to
30° from verticle to reduce possibility of trapping gas

bubbles on on the membrane cap. Gas bubbles also
form from solution out-gassing due to temperature
change. Gently tap body of sensor to dislodge them.

• Close container with plastic wrap or use HI 4000-71

gas sensor test vessel to prevent gas from leaving.

• If electrode was left out in air for a prolonged period,

gently pulling cable will permit an exchange of fill
solution at the membrane surface. Re-Calibration is
required.

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