Reproducibility weighing

The descriptions of the first isolation and first weighing of plutonium that appeared in Metallurgical Laboratory Reports at that time have been reproduced in a Benchmark Book of reprints (Seaborg, 1978). 

Example 59 (102.0-101.04)/0.47 = 2.04, (102.0-101.10)/0.115 = 7.8). Thus, the interpretation could have been that a fantastic reproducibility had been achieved, and that three of the 10 results could not be relied upon because of operator error (pipetting, weighing, whatever. .. ). 

Precision. The choice of 400 mg of soil is arbitrary. It was chosen in order to keep the entire cleanup step within a 2 cc vial. A test of replication was done on one field sample contaminated with about 20,000 ppm of 1254. Three samples of 50, 54, and 54 mg were weighed into separate vials, extracted, and then diluted 1 1000 into hexane in a separate vial. The three chromatograms are shown in Figure 7. Two peaks were quantified to demonstrate how reproducible a measurement can be, even in a field sample. 

There are several sources of irreproducibility in kinetics experimentation, but two of the most common are individual error and unsuspected contamination of the materials or reaction vessel used in the experiments. An individual may use the wrong reagent, record an instrument reading improperly, make a manipulative error in the use of the apparatus, or plot a point incorrectly on a graph. Any of these mistakes can lead to an erroneous rate constant. The probability of an individual s repeating the same error in two successive independent experiments is small. Consequently, every effort should be made to make sure that the runs are truly independent, by starting with fresh samples, weighing these out individually, etc. Since trace impurity effects also have a tendency to be time-variable, it is wise to check for reproducibility, not only between runs over short time spans, but also between runs performed weeks or months apart. 

Fig. 10 The powder x-ray diffraction pattern of ground carbamazepine tablets containing lithium fluoride (20% w/w) as the internal standard. Each tablet weighed 333 mg and contained 200 mg of anhydrous carbamazepine (/3-form). The peaks at 38.5° 20 (2.34 A line) and 45.0° 20 (2.01 A line) were due to lithium fluoride, while all other peaks were due to carbamazepine. (Reproduced with permission of the copyright owner, Plenum Press, from Ref. 56.)...

The number of influences in a thermobalance, which is a continuously weighing balance , is relatively large. To a great extent these are dependent on the construction of the balance. Normal macro balances are not affected by small vibrations if they are properly installed, regardless of whether this is on an upper or lower floor. Important for good reproducibility are good thermostated housing reproducible gas flow conditions... 

To assess the reproducibility of spray volume delivery, a series of preweighed weigh boats were placed on the instrument s carousel, and the instrument was programmed to spray a single time into each. After spray delivery, the boats were reweighed, and the volume of liquid calculated. The maximum amount of fluid dispensed was 105.1 pL, and the minimum was 65.7 pL The average of 20 separate determinations was 88.8 pL, yielding an error of 11.2%. 

Reproducibility is often used in the way that repeatability has been defined above but this does not leave room for a term defining what happens when an analytical procedure is handed over to another analyst. Since in the art world reproduction relates to copying of an original by another artist it would seem appropriate to use the term in the same way in analytical chemistry. If an assay is carried out in a laboratory by several analysts it is unlikely that these analysts will weigh out identical amounts of sample and use identical items of equipment. A clearly defined assay procedure should be capable of being reproduced by a number of analysts in a laboratory. Furthermore, having confidence in its reproducibility should facilitate... 

Calculation of peak area versus weighing for injection reproducibility... 

Figure 2.16—A miniature chromatograph. Instrument using a capillary column and a photoionisation detector. The instrument, weighing 4 kg including the carrier gas (C02), is mainly used for the analysis of volatile organic compounds (VOCs) in air pollution. The photoionisation detector, which is of limited use because of its variable sensitivity, is well suited for the analysis of hydrocarbons. The high powered UV source emits photons that have energies between 10 and 11 eV, ionising the compounds that exit the column, with the exception of the carrier gas. The ionic current generated is amplified using an electrometer and is proportional to the concentration of analytes (reproduced by permission of Photovac).

A 25-mL Class A volumetric pipet is certified by the manufacturer to deliver 25.00 0.03 mL. The volume delivered by a given pipet is reproducible, but can be anywhere in the range 24.97 to 25.03 mL. The difference between 25.00 mL and the actual volume delivered by a particular pipet is a systematic error. It is always the same, within a small random error. You could calibrate a pipet by weighing the water it delivers, as in Section 2-9. 

DSC has the advantage of being fast (results typically obtained within 1 hr) and suitable for any consistency of fat. However, perhaps because of the difficulty in accurately weighing the small (5 to 15 mg) samples required, precision and reproducibility tend to be poor. DSC instruments can be programmed to accurately reproduce the thermal environment the fat will... 

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