LEAD/SULFATE
HI 4012
HI 4112
LEAD/SULFATE
COMBINATION
Instruction Manual
HI 4012HI 4012
HI 4012
HI 4012HI 4012
HI 4112HI 4112
HI 4112
HI 4112HI 4112
Half-cell
Combination
Lead Ion
Selective Electrode
1
HI 4012 Lead Half-cellHI 4012 Lead Half-cell
HI 4012 Lead Half-cell
HI 4012 Lead Half-cellHI 4012 Lead Half-cell
HI 4112 Lead Combination ElectrodeHI 4112 Lead Combination Electrode
HI 4112 Lead Combination Electrode
HI 4112 Lead Combination ElectrodeHI 4112 Lead Combination Electrode
I. I.
Introduction:Introduction:
I.
Introduction:
I. I.
Introduction:Introduction:
The Hanna HI 4012 and HI 4112 are ion selective electrodes designed for the measurement of Lead ions in
aqueous solutions. The HI 4012 is a solid state half-cell
sensor that requires a separate reference. The HI 4112 is a
combination ion selective electrode.
IIII
SpecificationsSpecifications
II.
Specifications
IIII
SpecificationsSpecifications
Type: Solid State electrode with
a lead sulfide pellet.
+2 +2
+2
Ion(s) measured: Lead (Pb
+2 +2
)
Measurement range: 0.1 M to 1X 10
-6
M
20700 to 0.21 ppm
Interfering ions: Silver, Copper, Cadmium
Iron (2+ 3+) and Mercury must be absent. Any ion that
forms a more insoluble sulfide than lead sulfide will interfere
with the electrode response. Long term exposure in this ion
will poison the lead surface. Oxidation of the lead surface
will also poison the electrode.
Operating Temperature: 0-80°C
Operating pH: 4 to 7 pH
(recommended)
Dimensions: 12 mm (OD) X 120 mm
nominal insertion
(0.47” X 4.72”)
Connection: BNC
2
III. III.
Theory of OperationTheory of Operation
III.
Theory of Operation
III. III.
Theory of OperationTheory of Operation
::
:
::
The HI 4012 or HI 4112 lead electrodes are potentiometric
devices used for the rapid determination of free lead ions in
plating baths and as a detector for the titration of sulfate or
thorium with lead perchlorate
. Lead sensors are “elec-
trodes of the third kind” because they detect cations which
also form low-solubility salts with sulfide anions and forms
low-solubility salts with silver.
The electrode functions as a sensor or ionic conductor. The
HI 4012 requires a separate reference electrode to complete
its electrolytic circuit. The HI 4112 incorporates a reference
electrode. The mixed lead sulfide/ silver sulfide membrane
produces a potential change due to changes in the sample’s
lead ion activity. When the ionic strength of the sample is
fixed by the addition of ISA, the voltage is proportional to
the concentration of Lead ions in solution and the electrode
follows the Nernst equation.
E= Ea +2.3 RT/nF log A
ion
E= observed potential
Ea= Reference and fixed internal voltages
R= gas constant (8.314 volt coulomb/K Mole)
n= Charge on ion (2+)
A i=ion activity in sample
T= absolute temperature in K
F= Faraday constant (9.648 x 104 coulombs/mole)
3
IV. IV.
Design elements of the HI 4012 and HI 4112Design elements of the HI 4012 and HI 4112
IV.
Design elements of the HI 4012 and HI 4112
IV. IV.
Design elements of the HI 4012 and HI 4112Design elements of the HI 4012 and HI 4112
electrodeselectrodes
electrodes
electrodeselectrodes
Cap
Sensor Body
Sensing
Membrane
Upper Cap
Upper
Threads
HI 4012
LEAD/SULFATE
Spring
O-Ring
Ceramic Junction
on Inner Stem
Liquid junction
Fill Hole
O-Ring and
Plug
Outer Sleeve
Sensing
Membrane
4
V. V.
Equipment required:Equipment required:
V.
Equipment required:
V. V.
Equipment required:Equipment required:
• Hanna HI 5315 Double Junction Reference Electrode
with HI 7072 Fill Solution for HI 4012.
• 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 (ion) meter is not available).
• Hanna HI 180 Magnetic Stirrer or equivalent with TFE
coated stirring bars (HI 731320). Note: isolate beakers from stirrer motor heat by placing insulating
material such as foam or cork between them.
• Hanna HI 76404 Electrode Holder or equivalent.
• Plastic beakers (HI 740036P) or other suitable mea-
surement vessel.
VI. VI.
Solutions RequiredSolutions Required
VI.
Solutions Required
VI. VI.
Solutions RequiredSolutions Required
For Lead Measurements
0.1 M lead standard, (500 mL) HI 4012-01
ISA, (5 X 100 mL) HI 4012-00
For Sulfate Titrations
(used to standardize lead perchlorate solutions)
0.1 M sulfate standard, (500 mL) HI 4012-21
See Section XII ; Titrations
User supplied solutions:
A user supplied Methanol/Formalin solution is required to
decrease pellet solubility and oxidative effects. To prepare,
add 200 µL 37 wt. % formalin in H
O to 500 mL of
2
reagent grade methanol. Stir and store in tightly closed
glass bottle. This solution is used at a dose of 50 parts of
the Methanol/Formalin solution to 50 parts standard or
sample.
For Direct lead measurements- Using volumetric pipettes
and glassware, make dilutions of HI 4012-01 to bracket
the concentration of the samples. Note: 0.1M lead standard is equivalent to 20,720 ppm. Standards with concentrations < 10
-3
M (207ppm) should be prepared daily.
Store in tightly closed plastic bottle. To 50 parts standard or
sample add 50 parts Methanol/Formalin solution plus 2
mL of ISA.
5
VIIVII
General GuidelinesGeneral Guidelines
VII.
General Guidelines
VIIVII
General GuidelinesGeneral Guidelines
• Use of a hood and protective clothings is advised
when handling lead solutions.
• Concentrated samples (>0.10 M) should be diluted
before measurement. Multiply the final result by the
corresponding dilution factor.
• Calibration standards and sample solutions should
have the same ionic strength. ISA and Methanol/
Formalin should be added to both samples and standards in the same ratio. 2 parts ISA to 50 parts standard (or sample)/50 parts Methanol/Formalin is the
normal dosing. Note: no correction for dilution factor is
required for this because standards and samples are
treated in the same way.
• For high ionic strength samples, use standard addi-
tion or titration methods.
• Calibration standards and sample solutions should
be at same temperature.
• The magnetic stirrer may generate heat. Thermally
insulate beaker containing standard or sample from
magnetic stirrer by placing cork or other insulative
sheet between beaker and stirrer plate.
• Calibration standards and sample solutions should
be stirred at the same rate using identical sized TFE
coated stir bars.
• Rinse electrode pair with distilled or deionized water
between samples and gently dab dry with soft disposable absorbent toweling. Do not rub electrodes.
• Presoaking lead sensor in a dilute standard will opti-
mize response. Use concentrations approximately
-3
10
M or less with Methanol/Formalim and ISA added.
• A scratched, pitted, or oxidized pellet surface can cause
drift, a loss of low level response, or poor repeatability.
Optimum response can be restored by removing the
damaged surface with the microabrasive strip HI 4000-
70. Use gloves to protect skin.
• Avoid large changes in temperature (thermal shock)
as it may damage the sensor.
6
• Gas bubbles may form from solution out-gassing due
to temperature change. Gently tap body of sensor to
dislodge them from sensing membrane.
HI 4012
• Remove protective cover from sensor tip.
HI 4112
• Remove the protective plastic wrap that covers the
ceramic junction before assembling sensor for the first
time.
• HI 7072 reference fill solution should be added daily
to electrolyte reservoir before electrode use.
• During measurement always operate electrode with
the fill hole open.
• During normal use, fill solution will slowly drain out
of the tapered cone junction at the lower portion of the
electrode. Excessive loss (>4 cm drop within 24 hours)
is not normal. If this occurs verify cap is tightened and
the interface between the internal cone and outer
body is free of debris.
• Add fill solution daily to maintain a good head pres-
sure. For optimum response, this level should be maintained and not be allowed to drop more than 2-3 cm
(1-inch) below fill hole. Fill solution must cover the
ceramic found on the inner stem.
• If an erratic measurement occurs, check to see if for-
eign matter is seen trapped near the internal cone.
Drain, wipe off outer cone while depressing cap, release cap and refill with fresh fill solution.
7
VIII. VIII.
Electrode PreparationElectrode Preparation
VIII.
Electrode Preparation
VIII. VIII.
Electrode PreparationElectrode Preparation
HI 4012
1. Remove protective cover from sensor tip.
2. Prepare reference electrode by filling outer electrolyte
reservoir with HI 7072.
3. Place sensor and reference electrodes into electrode
holder and connect cable connectors to meter.
HI 4112
1. Unwrap plastic film seal found over ceramic junction
on inner stem and discard. This is only used for shipping and long term storage.
2. Rinse inner stem with deionized water making certain
to wet the o-ring found on the inner stem.
Remove
Water
Deionized
3. Reassemble electrode by gently pushing the inner
assembly into the outer body, sliding spring down
cable, and screwing cap into place.
4. Remove fill hole cover and o-ring on fill hole spout.
5. Using the dropper pipette provided, add a few drops
HI 7072 fill solution to the electrode, wetting the oring and rinsing out the fill solution chamber.
8
Parafilm
6. Holding the body of the electrode gently press upper
cap with your thumb. This permits the fill solution to
drain out of the body. Release cap and verify electrode returns to its original position. (You may need to
gently assist for this to occur).
COMBINATION
LEAD/SULFATE
HI 4112
7. Tighten the electrode cap onto the body and fill electrode body until fill solution volume is just below fill
hole.
8. Position electrode in a Hanna HI 76404 electrode
holder (or equivalent) and connect plug to meter.
9
IX. IX.
Quick Check of Electrode SlopeQuick Check of Electrode Slope
IX.
Quick Check of Electrode Slope
IX. IX.
Quick Check of Electrode SlopeQuick Check of Electrode Slope
Use of a hood and protective clothing is strongly advised.
• Connect sensors to pH/mV/ISE meter
• Place meter in mV mode.
• Place 50 mL of deionized water into a beaker with stir
bar and 2 mL of HI 4012-00 ISA. Add 50 mL of the
methanol/Formalin mixture. Add stir bar and place
on magnetic stirrer.
• Place electrodes into prepared sample.
• Add 1 mL of the stock standard HI 4012-01 (or .01 M
or .001 M standard by dilution) to the beaker.
Record the mV value when reading has stabilized.
• Add an additional 10 mL of standard HI 4012-01 (or
same dilute standard) to the solution. Record the mV
when reading has stabilized. This value should be
more positive than the previous noted.
• Determine the difference between the two mV values.
An acceptable value for this slope is +27 ± 4 mV.
X. X.
Corrective actionCorrective action
X.
Corrective action
X. X.
Corrective actionCorrective action
• Verify protective cap has been removed (HI 4012).
• Verify plastic film has been removed from inner stem
(HI 4112).
• Verify electrodes are connected properly to meter and
meter is powered.
• Verify standard has been properly stored. Remake
standards if appropriate.
• If the sensor slope just misses the suggested slope
window, soaking the sensor in a dilute standard with
the methanol/formalin added may solve the problem. (<10
-3
M standard).
• A scratched, pitted or oxidized sensing surface can be
polished with HI 4000-70 polishing strip. Cut off
approximately 1 inch of the micro-abrasive strip. Wear
protectice gloves. Wet the frosted side with deionized
water and place against damaged membrane of the
electrode. Place your gloved thumb against the shiny
backing and slowly rotate back and forth while
10
applying gentle pressure. Continue polishing until
you are satisfied with the surface. If dark deposits
appear on polishing strip move the paper slightly
and continue polishing.
• If the membrane is damaged, the response becomes
extremely sluggish, or the slope of the electrode has
decreased significantly, and procedures above have
not helped, the sensor should be replaced.
XI. XI.
Direct Calibration and MeasurementDirect Calibration and Measurement
XI.
Direct Calibration and Measurement
XI. XI.
Direct Calibration and MeasurementDirect Calibration and Measurement
This method is a simple procedure for measuring many
samples. Use of protective clothing is advised when handling lead samples and standards. A direct reading ISE
meter (HI 4222 or equivalent) determines concentration of
the unknown by a direct reading after calibrating the meter
with the standards. The meter is calibrated with two or
more freshly made standards that are in the linear measurement range of the unknowns. Two mL of ISA (HI 4001-
12) is added to each 50 mL volume of standard or sample.
Fifty milliliters of the methanol/formalin mixture is also
added to each sample or standard. More calibration standards are required in non-linear regions. Unknowns are
read directly.
Samples with concentration greater than 0.1 M should be
diluted to be within the working range of the electrodes.
The final result must be multiplied by the corresponding
dilution factor to determine the actual concentration.
A pH/mV meter in mV mode with semi-log graph paper
may also be used. Two or more freshly prepared standards
that are in the measurement range of the unknowns are
measured in mV mode on the meter.
These values are plotted on the semi-log paper and the
points are connected to form a straight-line curve. When
samples are measured, their mV values are converted to
concentration by following the mV to the concentration axis
on the semi-log plot.
11
Procedure
V
1) Follow sections VIII and IX to prepare sensors for
measurement.
2) Follow section VI to prepare standards / solution.
Standards should bracket and fall within the range of
interest.
Two mL HI 4012-00 ISA is added to 50 mL of both
samples and standards. Fifty milliliters of the methanol/formalin mixture is also added to each sample or
standard. Add stir bar and mix before taking measurements.
3) Follow section VII; General Guidelines to optimize test
set-up.
4) During calibration it is best to start with lower concentration samples first. Wait for a stable measurement
before recording values. Slightly longer equilibrations are required at lower concentrations .
5) To prevent carry over and contamination of samples,
rinse sensors with deionized and dab dry with
absorbant laboratory tissue between samples.
Typical Line arity for HI 4012 and HI 4112 Lead Electrodes
-75
-100
-125
-150
m
-175
-200
-225
-250
1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6
XII. XII.
Other Measurement TOther Measurement T
XII.
Other Measurement T
XII. XII.
Other Measurement TOther Measurement T
- Log of the Conc
echniquesechniques
echniques
echniquesechniques
Known Addition (for Pb2+)
An unknown concentration can be determined by adding a
known amount (volume and concentration) of measured
ion to a known volume of the sample. A mV value is taken
before and after the addition of standard, and using the
equation provided, the unknown concentration is found.
12
This technique is called Known Addition. The method can
use an ideal sensor slope, but actual determined slopes at
the temperature of measurement should be used if known.
The volume and concentration of the added standard must
cause a mV change of at least 8 mV. This method is
preprogrammed in the Hanna HI 4222 pH/ISE/mV meter,
which simplifies the method greatly. The method works
well for samples with high ionic strengths.
Example: Lead ion determination in samples with concentrations less than 1 X 10
-3
M using known addition.
1. A 25 mL sample of unknown concentration (Vsample)
is placed in a clean plastic beaker with a lead sensor
with 1 mL of HI 4012-00 ISA (V
ISA=1 mL
) and 25 mL
of the methanol/formalin solution. The stable mV
value (mV 1) is recorded after the sample is mixed.
2. 5mL (Vstd) of 10-1M standard (Cstd) is added to the
beaker and the mV value increases as does the con-
centration. ∆E is calculated as mV2-mV1. The un-
known lead concentration in the original sample
(Csample) can then be determined by the following
equation. Note: The methanol/formalin volume is
included into the volume calculations.
C
C
=
sample
(V
sample+Vstandard+VISA +VMeOH-Form
(V
sampl e+VISA +VMeOH-Form
standardVstandard
(V
)10
T
∆E/S
- (VS’)
)= V
V
V
)= V
S’
S’
sample
T
3. The procedure can be repeated with a second standard addition to verify slope and operation of the
method.
Titration of Sulfate
A Lead electrode may be used as an indicator to follow
the progress and detect the endpoint of a precipitation
titration of sulfate (with concentration >50 ppm) with
lead perchlorate standard. During the titration the sensor
follows the lead concentration while small additions of
lead perchlorate titrant are added. The lead reacts with
13
the sulfate ions forming a precipitate.
Pb2+ + SO
2-
<—> PbSO
4.
4
(insoluble)
At the stoichiometric end point, a change in mV occurs.
Measurements may be automated by use of the Hanna
Titrator HI 901 or titrated manually.
Plot generated on Hanna HI 901 Titrator duringPlot generated on Hanna HI 901 Titrator during
Plot generated on Hanna HI 901 Titrator during
Plot generated on Hanna HI 901 Titrator duringPlot generated on Hanna HI 901 Titrator during
automated sulfate titration using HI 4112automated sulfate titration using HI 4112
automated sulfate titration using HI 4112
automated sulfate titration using HI 4112automated sulfate titration using HI 4112
electrode.electrode.
electrode.
electrode.electrode.
Notes:
• Use of the methanol/formalin antioxidant is
advised to increase sensitivity.
• Addition of ISA is suggested (2mL/50mL sample).
• pH adjustment of the sample to 4-6 range is advised.
If required, use perchloric acid or sodium hydroxide.
• The lead titrant should be 10X more concentrated
than the expected sulfate and should be standardized
against a standard sulfate solution.
Titration of Lead
A Lead electrode may be used as an indicator to follow the
progress and detect the endpoint of a chelometric titration
of lead with disodium EDTA. During the titration the sensor
follows the decreasing lead concentration as small additions
of disodium EDTA titrant are added. The EDTA reacts with
the lead forming a complex. The EDTA also can react with
a host of other metals so optimizing pH of the Pb-EDTA
complex and masking possible interferents should be
considered. Consult a comprehensive Analytical Chemistry
Treatise for techniques concerning your particular interferent.
At the end point, a larger change in mV occurs. The Hanna
Titrator, HI 901 may be used to automate this procedure.
14
Plot generated on Hanna HI 901 Titrator duringPlot generated on Hanna HI 901 Titrator during
Plot generated on Hanna HI 901 Titrator during
Plot generated on Hanna HI 901 Titrator duringPlot generated on Hanna HI 901 Titrator during
automated lead titration using HI 4112 electrode.automated lead titration using HI 4112 electrode.
automated lead titration using HI 4112 electrode.
automated lead titration using HI 4112 electrode.automated lead titration using HI 4112 electrode.
Notes:
• Use of the methanol/formalin antioxidant is
advised to increase sensitivity.
• pH adjustment of the sample to 4-7 pH is advised to
favor the Pb-EDTA formation constant.
XIII.XIII.
pHpH
XIII.
pH
XIII.XIII.
pHpH
HI 4112 and HI 4012 electrodes may be used in solutions
with pH values between 4 and 6. Samples that fall beyond
this range should be adjusted with perchloric acid or sodium
hydroxide.
XIV. SXIV. S
torage and Care of the HI 4012 andtorage and Care of the HI 4012 and
XIV. S
torage and Care of the HI 4012 and
XIV. SXIV. S
torage and Care of the HI 4012 andtorage and Care of the HI 4012 and
HI 4112 sensors HI 4112 sensors
HI 4112 sensors
HI 4112 sensors HI 4112 sensors
The HI 4012 and HI 4112 sensor can be stored in very
dilute standards (<10-3M) for short periods of time.
The HI4012 should be stored dry with it’s protective cap
on for longer periods. For longer term storage of the
model HI 4112 combination electrode ;Drain and wash
of salts with distilled or deionized water. Unscrew the
upper cap and move outer sleeve up cable. Wrap the
ceramic junction on the inner stem with Parafilm® or
other sealing wrap. Place the protective cap provided
over the dried membrane and store in original storage
box provided with electrode.
2+2+
2+
XVXV
. .
Conversion TConversion T
XV
.
Conversion T
XVXV
. .
Conversion TConversion T
ables For Pbables For Pb
ables For Pb
ables For Pbables For Pb
2+2+
MultiplyMultiply
Multiply
MultiplyMultiply
Moles/L (M) to ppm (mg/L) 2.072 x 10
ppm (mg/L) to M (moles/L) 4.826 x 10
15
5
-6
MAN4112 01/07
WARRANTY WARRANTY
WARRANTY
WARRANTY WARRANTY
Hanna Instruments Ion Selective Electrodes are warranted
to be free of defects in material and workmanship for 6
months from date of purchase when used for their intended
purpose and maintained according to instructions. If they
fail to work when first used contact your dealer immediately.
Damage due to accidents, misuse, misapplication, tampering
or lack of prescribed maintenance is not covered.
Hanna Instruments reserves the right to modify the design,
construction or appearance of its products without advance
notice.
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