1. What is a counting chamber and what is it used for?
A counting chamber is a precision measuring instrument made of special optical glass. It is used to count cells or other particles in suspensions under a microscope.
Counting chambers are mainly used for blood analysis (counting leucocytes, erythrocytes and thrombocytes) and to count cells ofliquor. Counting chambers are also used, however, to count bacteria and fungus spores.
2. Design principle
All counting chambers have the same basic design principle.
There are four longitudinal grooves in the central third of a rectangular and thick base plate made of special optical glass.
The grooves are parallel to the short sides of the base plate and the central third hasthe same size as the coverglass used with the counting chamber. The two larger external surfaces are unfinished and are used for marking purposes.
The central support and the two external supports are ground smooth and polished. The surface of the central support is deeper than that of the two external supports. The counting nets are engraved in the central support (chamber base).
If acover glass is placed on the external supports, a capillary gap is produced between the underside of this cover glass and the central support of the counting chamber.
3. Design and identification of a counting chamber
Single net ruling: middle support without division (one counting net)
Double net ruling: middle support with one division (two counting nets)standard: the counting net is directly engraved in the glass
bright-lined: the chamber base is initially coated with rhoidum and the counter net is then etched into the coating of rhodium. By shifting the contrast, colour inversion under the microscope is possible so that the counter net can be viewed either in light or dark colouring
The following details are printed on bothunworked surfaces of the counting chamber
• counting net system
• name and trademark of the manufacturer
• chamber depth in mm
• area of the smallest square in mm2
4. Production and quality descriptions
Counting chambers are precision instruments. They are predominantly used in medical laboratories.
Counting chambers and cover glasses used in Germany and Austria have to beofficially tested and stamped whilst for exportation to other countries, no official tests are required
All the counting chambers sold by Marienfeld are manufactured in compliance with the relevant Calibration Ordinance and DIN standard. Therefore, we make a distinction between officially tested and stamped ones and those which are suitable for official testing.
The production ofcounting chambers is described herewith briefly only. It includes several individual processes, each of which is followed by stringent checks.
The internal support (chamber base) as well as the two external supports are ground a nd polished. The flatness and the accuracy are the most important requirements. They are described in the standard DIN 12874.
The central support (chamber base) islowered acc. to the system, for example the depth of the system Neubauer must be 0.1 mm. Besides the standard depth there are special depths available (f.e. 0.2 mm / 0.5 mm).
After these processes the counting net is engraved in the chamber base which is followed by the lettering on the unworked surfaces and by the stoving. The production of the counting chamber is now finished by the final checkwhich makes sure that the counting chamber is in accordance with the DIN standards resp. the regulations of weights and measures.
Requirements on quality controls
The maximum deviations allowed according DIN 12847 are as follows:
• for the chamber depth in the area of a counting net ± 2% of the nominal value
• for distances of less than 0.4 mm between any net lines ± 2µm