Analytical Chem istry - DePauw University

70 Analytical Chemistry 2.0be traced back to the SI standard kilogram. Volumetric glassware and digitalpipets can be calibrated by determining the mass of water that it deliversor contains and using the density of water to calculate the actual volume. Itis never safe to assume that a calibration will remain unchanged during ananalysis or over time. One study, for example, found that repeatedly exposingvolumetric glassware to higher temperatures during machine washingand oven drying, leads to small, but significant changes in the glassware’scalibration. 2 Many instruments drift out of calibration over time and mayrequire frequent recalibration during an analysis.2 Castanheira, I.; Batista, E.; Valente, A.; Dias, G.; Mora, M.; Pinto, L.; Costa, H. S. Food Control2006, 17, 719–726.Table 4.2 Measurement Errors for Type A Volumetric Glassware †Transfer Pipets Volumetric Flasks BuretsCapacity(mL)Tolerance(mL)Capacity(mL)Tolerance(mL)Capacity(mL)Tolerance(mL)1 ±0.006 5 ±0.02 10 ±0.022 ±0.006 10 ±0.02 25 ±0.035 ±0.01 25 ±0.03 50 ±0.0510 ±0.02 50 ±0.0520 ±0.03 100 ±0.0825 ±0.03 250 ±0.1250 ±0.05 500 ±0.20100 ±0.08 1000 ±0.302000 ±0.50† Tolerance values are from the ASTM E288, E542, and E694 standards.Table 4.3 Measurement Errors for Digital Pipets †Pipet Range Volume (mL or mL) ‡ Percent Measurement Error10–100 mL 10 ±3.0%50 ±1.0%100 ±0.8%100–1000 mL 100 ±3.0%500 ±1.0%1000 ±0.6%1–10 mL 1 ±3.0%5 ±0.8%10 ±0.6%† Values are from www.eppendorf.com.‡ Units for volume match the units for the pipet’s range.