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Trích:
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One of the difficulties in using LC retention for sample analysis is uncertainty that the entire sample has eluted from the column, even for the case of gradient elution (Section 16.2). Thus the possibility exists of missing a major component of the sample, and (worse) confusing the structure of a minor eluting band with that of the main sample constituent.
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và
Trích:
It is easy to see that combining uncertainties in this way overestimates the total uncertainty. Adding the uncertainty for the first delivery to that of the second delivery assumes that both volumes are either greater than 9.992 mL or less than 9.992 mL. At the other extreme, we might assume that the two deliveries will always be on opposite sides of the pipet’s mean volume. In this case we subtract the uncertainties
for the two deliveries,
(9.992 mL + 9.992 mL) ± (0.006 mL – 0.006 mL) = 19.984 ± 0.000 mL
underestimating the total uncertainty.
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