Results (
Thai) 2:
[Copy]Copied!
2.7 CALIBRATION PROCEDURES
2.7.1 Calibration of capacity must be carried out using a suitable, documented procedure.
Detailed procedures for the calibration of volumetric glassware are given in BS 6696
(see Appendix A). The calibration of glassware is a skilled process, which should
only be carried out by experience or trained personnel. Where there is only an
occasional need for calibration of glassware, consideration should be given to the
sub-contracting of this work to a UKAS accredited calibration laboratory.
2.7.2 Volumetric capacity is normally determined gravimetrically, using water confirming to
BS EN ISO 3696. Before starting, scrupulous care must be taken to ensure that the
glassware is clean and, in particular, grease free. The amount of water that the
vessel contains, or delivers at a measured temperature, is accurately weighed, and
the volume calculated in cubic centimetres at standard temperature and pressure.
Tables to facilitate this calculation are available in BS 1797 (see Appendix A).
2.7.3 The balance used must be calibrated using an approved method (see LAB 14,
Calibration of Weighing Machines) with weights traceable to national standards.
Similarly, any temperature measurements shall be traceable to national standards
(see LAB 11, Traceability of Temperature Measurement).
2.7.4 For burettes, and all types of pipettes normally encountered, a 200 g capacity
balance reading to 0.1 mg can be used. The calibration of volumetric glassware
larger than 100 cm 3 capacity will require a balance of adequate sensitivity with a
capacity of 2 kg or more.
2.8 ENVIRONMENTAL CORRECTIONS TO VOLUME
2.8.1 The correct calibration, and subsequent use of volumetric glassware is critically
dependent on temperature. Volumetric glassware is normally calibrated at 20C
(27C in tropical countries). Errors resulting from the use of volumetric solutions at
temperatures different to the calibration temperature may be significant, although
thermal expansion of the glass itself over the same range is comparatively trivial.
Thermal expansion of volumetric solutions should be taken into account when
working at temperatures different from the reference temperature.
2.8.2 In Table 3, the temperature limits at which volumetric solutions fall outside their
Class A tolerances are shown for various volumes. For example, an aqueous
volumetric solution occupying 100 cm 3 at 20C will have a volume of 99.9 cm 3 at
13C or 100.1 cm 3 at 25C. Thus at temperatures below 13C, or above 25C, the
volume will exceed the Class A tolerance (100 cm 3 + 0.1%).
Table 3 Suggested operating temperature limits for Class A glassware
Volume / cm 3
Temperature limits / C
10 < 31
50 10 - 26
100 13 - 25
250 16 - 23
1000 17 - 22
Being translated, please wait..
