Genral Water Catalogue - Crison Instruments - #19

⁷S8, coaxial, for standard electrodes. MP-4, multiple, for CRISON electrodes with built-in tempe­rature sensor. Fixed cable, no connector.

Thread

PG 13.5-type, standard for all manufac­turers.

This is a "cell" that supplies a stable potential (mV). Various types are available: Silver wire (Ag)

Galvanically coated with AgCI. This is the typical reference element for low-cost electrodes.

^The silver wire comes into contact with a portion of the AgCI crystals inside a small glass tube. Ag⁺ ion barrier

/The tube with Ag/AgCI crystals is leng­thened to house a chemical substance which acts as a barrier to silver ions. This prevents diaphragms becoming conta­minated because of the formation and precipitation of AgCI and Ag₂S. "Sleeved" silver wire /Consists of a silver wire protected by a tube. This protects the standard element from possible alterations that may occur in the electrolyte.

This is the point of union between the sample and the electrolyte. It is the critical part of the electrode as it has a direct influence on its lifespan.

A wide range of diaphragms are available. They vary accor­ding to manufacturer, application, quality of electrode and price.

This catalogue features electrodes with ceramic, porous PTFE and open diaphragms.

The ceramic diaphragm is a chemically-inert, porous ceramic plate. These are the traditional diaphragms. They allow a small electrolyte flow towards the sample. The flow is greater if pres­surised electrodes are used.

Porous PTFE, consisting of a large ring of porous PTFE through which contact between the electrolyte and the sample is made. The \\/ \V J conductivity of the sample is hardly altered, VI^_J„/ thanks to the low level of flow provided by the polyacrylic electrolyte.

Open, which in fact should be called "without diaphragm". The sample and the electrolyte are in direct contact. There is no electrolyte flow. It is only used with electrodes with solid electro­lyte (polymerised). There are two types available:

- lateral orifice. This consists of an orifice in the body of the electrode.

- circular "ring-like" groove between the main body, the indicator electrode and the reference electrode.

Facilitates maximum contact with the sample.

This is a highly-concentrated saline solu­tion into which the reference element is

..Diaphragm

The composition of the glass membrane affects characte­ristics such as sensitivity, chemical, thermal and mechanical resistance of the electrode or the scale of measurement, e.g. a pH of 0...12, of 0...14. There are membranes with specific types of glass, e.g. to measure pH in the presence of a certain concentration of HF. There are also special membranes for measuring at extremely low temperatures (-30°C).

A large membrane is a symbol of quality.

The speed at which an electrode responds depends directly

on the quality of its membrane.

Membrane

submerged.

It comes in 3 forms: liquid, gel or solid (polymer), depending on the type of electrode.

Liquid electrolytes. Used for refillable electrodes.

There are various types for different applications. They are all

KCI-based.

Gel electrolytes. These are used in non-refillable or "low maintenance" electrodes. Most are glycerine gels.

Electrodes with wide PTFE diaphragm include a polyacrylic gel, thanks to which there is little electrolyte diffusion through the diaphragm.

Solid electrolytes. These are also used in "non-refillable" electrodes. They are made of a conducting polymer.