Tolerance volumetric flask

Accuracy tolerances for volumetric flasks at 20°C are given by ASTM standard E288. 

Using the tolerance values for pipets and volumetric flasks given in Table 4.2, the overall uncertainties in Ma and Mb are... 

What is essential in establishing traceability is that the measurand is specified unambiguously. This may be, e.g. in terms of extractable cadmium from soil by using a named acid mix or the concentration of a metal in a particular oxidation state, e.g. Fe(n) or Fe(m). The units used to report the result should also be known and acceptable SI units are preferred. The method used will be validated and if used in accordance with the written procedures should produce results that are fit for purpose . The class of glassware to be used will be specified in the method procedure, e.g. Class A pipettes and volumetric flasks, as these are manufactured to a specified tolerance. Instruments will be regularly calibrated and their performance verified daily. In terms of the chemicals used, these will... 

The Indian Standard Institution (ISI) has laid down the tolerances on capacity of volumetric flasks (with different capacities) calibrated at 27°C as stated in Table 2.6. 

The British Standards Institution (BSI) and the National Physical Loaboratory (NPL) have laid down the tolerances in the capacity of volumetric flasks (i.e., measuring flask) at 20°C by two sets of tolerances viz., Grade A and Grade B respectively, evidently to indicate the class of accuracy to which the flask has been subjected to for graduation, followed by the manufacturer s name and finally the BS standard number. However, the permitted tolerances for volumetric flasks commonly used in analytical laboratories are depicted in Table 2.8. 

Various Official Compendia viz., IP, BP, USP, NF and NBS (National Bureau of Standards) have laid down tolerance on capacity for Burettes, Pipettes, Volumetric Flasks. Discuss its importance in volumetric quantitative analysis. 

An estimate of compound random errors is obtained from the square root of the sum of the squares of the RSDs attributed to each component or operation in the analysis. If the analysis of paracetamol described in Box 1.3 is considered then, assuming the items of glassware are used correctly. Assuming the items of glassware are used correctly the errors involved in the dilution steps can be simply estimated from the tolerances given for the pipette and volumetric flasks. The British Standards Institution (BS) tolerances for the grade A glassware used in the assay are as follows ... 

Figure 2-9 (a) Class A glass volumetric flask. [Courtesy A. H. Thomas Co., Philadelphia, PA.] (fc>) Class B polypropylene plastic volumetric flask for trace analysis. [Courtesy Fisher Scientific, Pittsburgh, PA.] Class A flasks meet tolerances of Table 2-3. Class B tolerances are twice as big as Class A tolerances, (c) Short-form volumetric flask with Teflon-lined screw cap fits in the analytical balance in Figure 2-3a. Teflon protects the cap from chemical attack. 

Do not let the designation Class A mean more than it was meant to. Class A can only mean that it is the best tolerance readily available for that specific type of volumetric ware. Class A volumetric ware is not consistent across volumetric ware type. For example, a Class A volumetric pipette does not have the same degree of tolerance as a Class A measuring pipette. Equally, a Class A graduated cylinder does not have the same degree of tolerance as a Class A volumetric flask. See Table 2.6 for a representative cross comparison of Class A tolerances. 

Volumetric flasks are used to measure very precise volumes of liquids for making standard solutions or weighing for density calibrations. Each flask has one measurement line for the specific volume of the flask (see Fig. 2.18). Volumetric flasks are of either Class A or Class B quality the tolerances for Class B are twice those for Class A. There are no general purpose volumetric flasks. The tolerances... 

Standards of Accuracy The capacity tolerances for volumetric flasks, transfer pipets, and burets are those accepted by the National Institute of Standards and Technology (Class A),1 as indicated in the accompanying tables. Use Class A volumetric apparatus unless otherwise specified in the individual monograph. For plastic volumetric apparatus, the accepted capacity tolerances are Class B.2... 

The uncertainty involved in weighing the solutes was small. The balance has a certified accuracy of 5 X 10 4 or 0.05% (49). Class A 500-mL volumetric flasks have tolerances of less than 0.05% (50). The uncertainty associated with the preparation of these solutions is estimated to be less than 0.1%. 

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