end point to the titration is detected. The titre reading is automatically calculated from
the piston travel multiplied by the cross-sectional area of the burette.
3.2.5 Syringes
Syringes used in laboratories fall into two broad categories: high precision metal and
glass instruments, often designed for a specific application, and disposable, general
purpose, low precision, plastic items. High precision syringes often have a claimed
volumetric accuracy and precision of better than 1%. Plastic syringes normally have
relatively low volumetric accuracy, typically 5%.
3.3 OPERATION
3.3.1 The performance of these instruments, in particular syringes, may be user of
application dependent. For this reason, it is important that suitable operating
procedures are documented and followed, and that operators are specifically trained
in the correct use of the instruments. Users should be cautious in relying on
manufacturers’ performance figures. It is more appropriate for the laboratory to
determine its own data, taking different users into account.
3.4 CALIBRATION INTERVALS
3.4.1 The time taken for the calibration of a particular instrument to become invalid should
be monitored and the re-calibration interval set accordingly. For instruments with a
variable volume setting, it may be advisable that the volume is always set from the
same direction and the accuracy of the set volume checked every time the setting is
altered. The tolerance specified by the manufacturer should give a guide to the
achievable performance.
3.5 CALIBRATION REQUIREMENTS
3.5.1 These instruments should be checked for the accuracy of the delivered volume
against the set volume (at several different settings in the case of variable volume
instruments), and the precision of repeat deliveries should be measured (at several
different settings in the case of variable volume instruments). In the case of variable
volume instruments, the accuracy of the selected volume setting may be dependent
on whether the adjustment is made from ‘up-volume’ or ‘down-volume’.
3.5.2 For syringes used for chromatographic sample injection, the absolute accuracy of the
volume delivered is relatively unimportant, provided that the injected volume of
sample standard are the same, since the syringe is used in a comparative way, ie,
one injection will be compared with another. Precision is important, but it is normally
sufficient to determine the overall precision of the syringe and the application for
which it is being used. This can be achieved from repeat injections and the
determination of the variation of the results obtained. Clearly, for optimum results,
the user needs to develop a reliable injection technique. An alternative approach is to
use an internal standard which can be used to calculate the relative volumes of each
injection.
3.5.3 For some syringes, the volumetric capacity is so small that problems may occur
because of factors such as surface tension, and difficulty in eliminating carry-over.
3.6 CARE OF APPARATUS
3.6.1 Although these instruments are generally made of inert materials, care should be
taken when handling corrosive solvents, or in microbiological or clinical applications.
Volatile solvents may damage seals. In all cases, care should be taken that the