Inaccuracy volume measurement

Maximal measurement uncertainty at volume measurements could be calculated as well. However volume measurements are generally only performed as second choice if weighing would pose too many drawbacks for the reliability of the preparation process (see Sect. 29.1.2). Therefore, the acceptable measurement uncertainty for volume measuring depends strongly on the nature of the process in question. Usually only inaccuracy is taken into consideration. It is limited by requiring a minimum filling of the device to be used, as is explained in Sect. 29.1.7. More exact calculations would be irrelevant. 

The measurement uncertainty of weighing will usually lead to a deviation due to inaccuracy and imprecision of not more than 1 % [10]. Volume measurements however, may show a deviation of 1.5 % under the most favourable conditions. Under less favourable conditions this can easily rise to 3 % or more (see Sect. 29.1.7). 

For some steps of the preparation processes, however, weighing is not or hardly possible or volume measurement has advantages for reasons that outweigh inaccuracy. Examples include the adjustment to volume of large amoimts of solutions, working in a laminar flow cabinet, and preparing parenterals prior to administration on the ward. 

It is likely that volumetric measures were used for quantity deterrnination when commodities were first bartered however, it has been established with certainty that weighing scales or balances have been in use for at least 7,000 years (1). Measuring by weight instead of by volume eliminates some very considerable inaccuracies from, for example, changes in specific gravity of liquids with temperature, or changes in density of solids owing to voids. 

Student 2 has obtained a set of results which are closely clustered but give a mean which is less than the correct answer. Thus although this assay is precise it is not completely accurate. Such a set of results indicates that the analyst has not produced random errors which would produce a large scatter in the results but has produced an analysis containing a systematic error. Such errors might include repeated inaccuracy in the measurement of a volume or failure to zero the spectrophotometer correctly prior to taking the set of readings. The analysis has been mainly well controlled except for probably one step which has caused the inaccuracy and thus the assay is precisely inaccurate. 

If a barbotage technique is employed in foam formation and the foams produced are of low stability, it is possible to reach a steady-state at which the rate of foam formation becomes equal to the rate of the decrease in foam column height, and during a long period of time the volume of the foam remains constant. It should be emphasised that a certain inaccuracy in the measurement of the foam column height can originate from an non-distinct (diffuse) liquid/foam boundary or roughness of the upper foam boundary (especially in structured foams, e.g. from proteins). 

Measurement Procedure. IGC measurements were started after the thermal and flow equilibrium in the column were stable (2 to 3 h). To facilitate rapid vaporization of the probe (0.01 yL), the injector temperature was kept 30°C above the boiling point of the probe. Measurements were made at five carrier gas flow rates. The retention volumes of six injections for each probe and twenty injections of the marker (H2) at a given flow rate were averaged. The values obtained were extrapolated to zero flow rate to eliminate the flow rate dependence of the retention data. The net retention time (tR) is defined as the time difference between the first statistical moment of the solvent peak and that of the marker gas. Thus, tR was calculated by an on-line computer statistical peak analysis rather than the retention time at the peak maximum (tp,maY). This eliminated inaccuracies arising from slight peak asymmetry, which occurs even for inert and well-coated supports. The specific retention volumes (Vg°) derived from tR and tR max differed by as much as 5% for small retention times and slightly skewed peaks (11,12). 

Any device or system that has one or more physical properties (e.g., electrical resistance, electrical potential, length, pressure at constant volume, or volume at constant pressure) that vary monotonically and repro-ducibly with temperature may be used to measure temperature. The science of the measurement of temperature is called thermometry. In the past, the measurement of high temperature was known as pyrometry but now that term usually refers to radiation thermometry at any temperature. Although the accuracy of a measurement refers to the difference between the measured value and the true value of the quantity being measured, and the precision of measurement refers to the degree of agreement among repeated measurements of the same quantity, it follows that a set of measurements of the same quantity, it follows that a set of measurements may be very precise but terribly inaccurate. Since in many instances the word accuracy is used when inaccuracy is meant and the word precision is used when imprecision is meant, perhaps it would be better always to refer to uncertainties of measurement, statistical and systematic, rather than to accuracy and precision. 

Compared to the 355-mL value shown on a typical soda can, the approximated value seems reasonable. The difference between the approximated value and the indicated value may be explained in a number of ways. First, the soda container does not represent a perfect cylinder. If you were to look closely at the can you would note that the diameter of the can reduces at the top. This could explmn our overestimation of volume. Second, we measured the outside diameter of the can, not the inside dimensions. However, this approach will introduce smaller inaccuracies because of the small thickness of the can. 

Because retention volume is the most important factor in SEC (it is related to the logarithm of the molecular mass, even small inaccuracies in the determination of Vr are magnified), the pump must deliver a very constant flow which can be controlled by a continuous flow measurement system, for example. Further information on SEC can be found in [19], [24], [87], [88]. 

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