Instant Notes: Analytical Chemistry

Errors are associated with every measurement made in an analytical procedure,

and these will be aggregated in the final calculated result. The accumulationor

propagationof errors is treated similarly for both determinate (systematic) and

indeterminate (random) errors.

Determinate (systematic) errors can be either positive or negative, hence some

cancellation of errors is likely in computing an overall determinate error, and in

some instances this may be zero. The overall error is calculated using one of two

alternative expressions, that is

● where only a linear combination of individual measurements is required to

compute the result, the overall absolute determinate error, ET, is given by

ET=E 1 +E 2 +E 3 +.......

E 1 and E 2 etc., being the absolutedeterminate errors in the individual

measurements taking sign into account

● where a multiplicative expression is required to compute the result, the

overall relativedeterminate error, ETR, is given by

ETR=E1R+E2R+E3R+.......

E1Rand E2Retc., being the relativedeterminate errors in the individual measure-

ments taking sign into account.

The accumulated effect of indeterminate (random) errors is computed by

combining statistical parameters for each measurement (Topic B2).

Accumulated
errors

B1 – Errors in analytical measurements 25