3 RELATED APPARATUS
density of powders, or in the measurement of the volume of liquid distillates, etc. In
such cases, the level of calibration shall be appropriate to the application.
3.1 SCOPE
3.1.1 The following types of apparatus are dealt with in this Section:
(a) mechanical hand-pipettes
(b) dispensers
(c) diluters
(d) piston burettes
(e) syringes
3.1.2 Procedures for calibrating mechanical hand-pipettes are covered by British Standards
(see Appendix A). The accuracy and precision of these items vary according to
manufacturer, but will normally be quoted in the specification.
3.1.3 In all cases, the level of calibrations should be appropriate to the use of the
equipment and should have traceability to national standards.
3.2 APPARATUS
3.2.1 Mechanical hand-pipettes
These provide a convenient alternative to traditional glass pipettes. They may be
fixed or variable volume. The sample volume is drawn by suction into a disposable
tip, usually of polypropylene, and then fully expelled. The accuracy of the volume
drawn in this manner is dependent on the density and viscosity of the liquid, and
other factors such as surface tension, speed of filling, etc. The manufacturer’s
operating instructions should be taken into consideration when performing
calibrations.
3.2.2 Dispensers
These are devices for repetitive dispensing of liquids, and consist of a reservoir and a
dispenser head which normally has a variable volume adjustment. A pre-set amount
of the reagent is drawn into the head using a plunger. Depression of the plunger then
discharges the liquid through a spout into the receiving vessel. Flow is controlled by
check valves.
3.2.3 Diluters
These devices take up a measured amount of reagent and then discharge it together
with a measured amount of diluent, taken from a reservoir. The principle of operation
is very similar to that for mechanical hand pipettes and dispensers.
3.2.4 Piston burettes
These are used in auto-titration systems, and operate on very similar principles to
diluters and dispensers. The burette barrel consists of a precision cylinder which is
filled by titrant using a moving piston. The same piston discharges the titrant until an