1. Intellical Red-ROD technology
High performance pH probes for HQd-series

2. IntelliCal pH Red-Rod sensors portfolio
PHC705
PHC705A
PHC725
PHC735
Diaphragm Types & Flow rates
Porous
pin
Annular
ring
Sleeve
Porous pin,
A = Alkaline
Annular Ring,
PHC735 = High Flow
50 µL/h
120 µL/h
1 mL/h
~10 µL/h
PHC729
PHC745
flat, surface
ring diaphragm
Sleeve junction with
Adjustable high flow

3. IntelliCal Red-Rod Applications
Common features:
Glass Body
Red Rod Saturated KCl reference
Refillable reference element
Temperature range: From -10°C to 100°C
pH Range: from 0 to 14 pH
Model Type
Applications
Junction Types
PHC705
General Purposes
Porous Pin
PHC705A
High-alkalinity media
PHC725
General Purposes & Low Ionic Strength media
Annular Ring
PHC735
Dirty Samples (eg. Untreated Surface Waters)
Annular Ring (High Flow)
PHC745
Challenging Samples (eg. Wastewater influent, Emulsions)
Reverse Sleeve (High Flow, Fast cleaning)
PHC729
Surface Measurements
Flat Annular Ring

4. comparison of “Standard” vs. “Red-Rod”

5. Red-rod vs Light influence
Red tubes inside the probe
Looking at a Red-Rod pH probe, the first visible difference from
“standard” pH probes is the two inner red glass tubes.
What is their purpose? The standard reference system comprises a combination of silver wire (Ag) and silver chloride (AgCl) in equilibrium:
AgCl  Ag+ + Cl-,
The status of the equilibrium depends on AgCl, Silver and Chloride
ions. If one side of the reaction changes, the equilibrium changes as
well. Therefore the reference element is no longer stable, identified
by a changing reference potential and a shorter lifetime.
Ambient light, especially the daylight, reacts continuously with AgCl
and reduces traces of silver ion to silver metal. This reduces the
lifetime of the probe.
AgCl + [UV or blue light]  2 Ag + Cl2 
Red colored glass tubes protect the reference system eliminating the effect of UV or blue light thus ensuring the reference systems remains stable over a long period of time.

6. Red-rod vs Temperature variations
The filling solution of standard pH probes is non saturated 3 molar KCl, it does not provide any indication to the operator of possible variations in refill electrolyte solution impacting reference element mV response due to of dilution or clogging crystallization.
Red-Rod Saturated KCl filling solution allows visual control of suspended crystals giving a clear indicator to operators that solution remains saturated, ensure stable saturated KCl concentration and a stable reference potential with temperature increase.
Red-Rod pH sensors contain additional KCl crystals in pH bulb and in reference element “buffering” KCl solubility changes with temperature to ensure reference filling electrolytes stability through temperature variations up to 100°C!
Special KCl crystals for Red Rod prevent (re)crystallization clogging of the junction ensuring KCl crystals keep moving freely.
Red Rod saturated KCl ensures visual control at glance and reference systems mV reading stability over temperature variations.

7. Red-rod vs Reading stability
Symmetrical Reference System
Usually a combined pH probe reference system consists in a Ag/AgCl/KCl system in both elements, Reference & Indicating. Standard pH probes are usually mounted with a basic Ag wire coated with AgCl immersed directly in the KCl electrolyte solution. Such “wire” design cannot ensure both Ag/AgCl reference elements match equally from the start and over the electrode usage period, thus creating an asymmetric geometry causing an Asymmetry Potential difference from an ideal zero mV.
Red-Rod technology design assembly ensures a perfect symmetry in construction offering a quasi-perfect potential reading which is stable over time.
Red-Rod
Standard
Red Rod Symmetrical System ensures stability of reference systems mV reading over time.
Coated silver
wire only

8. Red-rod: Reading stability
mV measured
in buffer 4.01
mV difference
after one year
mV measured
in buffer 7.00
mV difference
after one year
mV measured
in buffer 10.01
Red-Rod pH probes demonstrate perfect mV reading stability

9. Red-rod : Response Time
Red-Rod pH probes symmetric reference design ensures faster stabilization time and more accurate reading, especially in cold buffers.
15 vs. 90 sec.
response time

10. Red-rod benefits
Red Rod encapsulated reference and indicating elements prevent silver ion diffusion. 
Dramatically reduce the risk of contamination and junction reference clogging. 
Ensure mV reading accuracy and extended probe lifetime
Red tubes protect from UV light degradation over time. 
Symmetrical Red Rod reference elements reduce asymmetry potential
Ensure mV reading stability over time. 
Saturated KCl solution with
KCl crystals
Determine electrolyte status at a glance

11. Red-rod benefits
Additional KCl crystals maintaining saturation of the reference electrolyte at higher
temperatures 
Stable reference system for best pH results up to 100°C
Glass probe body
withstands heat and
organic chemicals 
Enlarging the application range
to difficult matrices and use
models
Probes with various designs
and diaphragms (liquid
junctions) 
Higher flexibility in selecting the
best pH probe for your sample
pH measurement 
Combining both technologies for
reliable results and highest
comfort
Red-Rod pH probes now with
digital technology