Use ELIT plug-in all-solid-state
Ion-Selective Electrodes with our
8mm Reference Electrodes
and dual Electrode Heads for a practical and cost-effective alternative to conventional combination electrodes.

Ammonium
NH₄⁺ (NH₃)

Barium
Ba⁺⁺

Bromide
Br ^-

Cadmium
Cd⁺⁺

Calcium
Ca⁺⁺

Chloride
Cl^-

Copper
Cu⁺⁺

Cyanide
CN^-

Fluoride
F^-

Iodide
I^-

Lead
Pb⁺⁺

Mercury
Hg⁺⁺

Nitrate
NO₃^-

Nitrite
NO₂^-

Perchlorate
CLO₄^-

Potassium
K⁺

Silver
Ag⁺

Sodium
Na⁺

Sulphide
S^--

Thiocyanate
SCN^-

(Sulphate)
SO₄^-- Indirect:
using Ba electrode.

General
Operating
Instructions

Sample
Preparation

The main advantages of Ion-Selective Electrodes are:

• Inexpensive and simple to use, in the field as well as the laboratory.
  
  
• Wide concentration range - typically from less than one to several thousand parts per million.
  
  
• Unaffected by sample colour or turbidity.
  
  
• Ideal for monitoring environmental pollution or water quality etc. - where the operator simply wants to be sure that a certain ion is below a particular threshold value, or where only the order of magnitude may be required.
  
  
• Ideal for long term monitoring of changes in ion concentration (e.g. for measuring rates of reaction or nutrient uptake etc.) - particularly when used in conjunction with an ELIT Ion Analyser (electrode-computer Interface), to link electrodes directly to a desk-top or lap-top PC.

Note: ISEs are not generally used as precise analytical tools. Nevertheless, routine, rapid measurements can usually be expected to have an accuracy of around ± 10% and with careful analysis under ideal conditions some can achieve an accuracy and precision of better than ± 2% (1-sigma) - see chapter on Accuracy and Precision in our Beginners Guide to ISE measurements.

Ion-Selective Electrodes measure the activity (or effective concentration) of ions in a solution, rather than the actual concentration; the activity is always less than the concentration because of
inter-ionic interactions and the difference between concentration and activity increases as the
Ionic Strength increases. (Note that the Ionic Strength is a measure of the total effect of all the ions in the solution, both positive and negative, of the measured ion as well as any other contaminants.) In practice, however, the measured activity is not significantly different from the concentration in dilute solutions (i.e. with total Ionic Strength of less than about 0.01 Molar for monovalent ions and 0.001 Molar for divalent ions), and steps can be taken to minimize the difference at higher concentrations (e.g. by adding Ionic Strength Adjustment Buffer, diluting the sample, or, most effectively, by using Standard Addition or Sample Addition techniques).

ELIT ion selective electrodes

· All solid-state construction.
· Simple gold-plated plug-in connectors.
· Robust and Durable.
· Easy to handle.
· Stable electrochemical potential.
· Fast response time.
· Function in any position.
· No leaking of fluids.
· Long shelf life and working life.
· Can be stored and transported below 0°C.

ELIT Electrode Heads are manufactured from a robust plastic material and fitted with low noise cables and connectors which are compatible with any standard mV/pH/ion meter.
The standard version, for use with an ELIT Ion Analyser / Computer Interface, has a BNC plug, but DIN, US or S7 versions are available if required.
The sockets on the head and the pins on the plug-in electrodes are gold plated to assure good contact.

Advantages of this 'electrode combination' over conventional combination electrodes:

• Use of one reference electrode for several ion-selective electrodes.
• Replacement of a defective reference system without sacrificing the more expensive ISE.
• Expensive low-noise cable and connector are attached to the re-usable head and do not need to be replaced if the ISE becomes defective.
• ISE is less expensive than conventional types with cable & connectors permanently attached.
• ISE can be stored dry and the RE wet.
• Increased distance between the ISE and the reference system reduces electrical interference and increases the precision of measurement.

• Mono Head for inserting one ELIT ISE or Redox electrode, for use with a conventional reference electrode
  (or a combination pH electrode).
  
  
• Mono Head with 2mm plug connector for using one ELIT reference electrode with any ISE which is not compatible with an ELIT head.
  
  
• Dual Head for use as an electrode combination: one ISE or Redox and one ELIT reference electrode.
  
  
• Triple, Four or Seven-electrode head for connecting up to six sensors with one reference, for use in simultaneous multi-component analysis using an ELIT four or eight-channel Ion Analyser / computer interface.

Nico2000 Ltd can also supply Mini ISEs with a range of tube diameters and lengths for special applications. These electrodes are fitted with a simple wire connector to allow maximum flexibilty for connecting to other equipment and are not suitable for use with the ELIT electrode head system.

These electrodes are of a robust design with 8mm diameter PVC bodies and gel electrolytes. Made to be compatible with ELIT ISEs, they must also be connected to the measuring system via an ELIT Electrode Head.
Leak rates are very low and the electrolytes do not require replacing, therefore these electrodes are manufactured as maintenance-free sealed units which should have an active (or shelf) life of several years - provided that the porous frit is kept moist by immersing in a solution with the same composition as the gel electrolyte when not in use. This is normally done by keeping a few drops of solution in the protective black plastic cap which must always be replaced when the electrode is not in use.

The choice of which reference electrode to use depends on the likely interferences with the ISE - i.e. the outer filling solution of the RE, which comes into contact with the sample solution, must not contain any ions which would interfere with the target ionophore - for more details see Reference Electrodes in our Beginners Guide to ISE Measurements.

Nico2000 Ltd currently offer the following three types of Reference electrodes - named according to the composition of the filling solution (gel) :

Please click on code number to see operating instructions.
• Single Junction potassium/silver chloride.
  (code number ELIT 001n - for Ba, Ca, F, NO₂, Na, ClO₄).
  
  
• Double Junction potassium nitrate.
  ( 002n - for Br, Cd, Cl, Cu, CN, I, Pb, Hg, Ag, S, SCN).
  
  
• Double Junction lithium acetate ( 003n - suitable for all ions.)

ELIT pH electrodes are basic combination electrodes with glass membranes and AgCl reference systems. They are fitted with cable and BNC connector for connection to any type of measuring system and do not require an ELIT electrode head connector or separate reference electrode.

pH measuring range: 0 - 14. Dimensions: 120mm long by 12mm diameter.

ELIT PHE-10P has a plastic body and gel electrolyte (which does not require replenishing) and a "Pelon Film" liquid junction between the reference system and the external sample which has a very low leak rate. Thus there is little contamination of the sample solution with K or Cl ions as is the case with conventional liquid electrolytes and this makes it ideal for simultaneous pH/Ion measurements, even with ISEs which might be affected by K or Cl contamination. Despite this low leak rate the electrode still achieves sufficient accuracy and response time to be suitable for use in many applications of pH measurements. Temp Range 0 - 60°C.
For more details please see: Leak Rate of pH electrode.htm

ELIT P11 has a glass body, refillable liquid electrolyte and annular ceramic junction.
Temp Range 0 - 80°C.

ELIT P14 has an epoxy body, refillable liquid electrolyte and porous teflon junction.
Temp Range 0 - 60°C.

Introduction to DO sensors:
There are two types of dissolved oxygen sensors: polarographic and galvanic. Both involve the use of a thin organic membrane over an electrolyte and metal electrode. Oxygen diffuses through the membrane, and the resulting partial pressure is directly proportional to the volume of oxygen flowing through the membrane. The measured oxygen is reduced at the cathode, producing a current that is directly proportional to the concentration of dissolved oxygen. In polarographic sensors, a polarizing voltage is applied across the electrodes which stimulates the reduction of oxygen, which produces a current. Galvanic sensors require no external voltage, the oxygen present will spontaneously activate the reaction to produce a corresponding current. Thus, a galvanic sensor is like a battery (fuel cell) that is fueled by oxygen. Galvanic sensors typically have faster response times than polarographic sensors and are more stable and more accurate at low dissolved oxygen levels. They can last for several months without needing to replace the membrane or the electrolyte, resulting in lower maintenance costs. Polarographic probes need to be recharged every few weeks after heavy use.

ELIT Dissolved Oxygen Sensors:
Nico2000 can supply three types of DO electrodes: two polarographic types and one galvanic. All are designed for laboratory measurements and have a standard 12mm body diameter.
The two versions of the polargraphic type differ in their output currents. In air-saturated water (20.9% Oxygen), one has an output current of 600nA, the other 60nA.
The output of the galvanic electrode at saturation is 33-40mV.
The residual output in zero oxygen solutions for all the electrodes is less than 1% of the output in saturated water.
One or two Automatic Temperature Control (ATC) sensors (Thermistor or Pt100/1000) may be fitted to customers specific requirements.
Replacing the Teflon membrane is quick and easy. Simply unscrew the old assembly, load the new one with fill solution and screw on to the electrode.
The electrode is supplied with 2 membrane assemblies and a 50 ml bottle of filling solution.
A 50ml bottle of Zero Oxygen solution is available for calibration purposes.

For more information please see: DO Operating instructions (PDF file).

Type	Output at Saturation	Output at Zero Oxygen	Polarisation Voltage	Membrane
601 Polargraphic	600nA +25%	<1% Saturation	800 mV	Teflon
602 Polargraphic	60nA +25%	<1% Saturation	800mV	Teflon
603 Galvanic	33-40mV	<1% Saturation	N/A	Teflon