Extraction Technologies for Medicinal and Aromatic ... - Capacity4Dev

EXTRACTION TECHNOLOGIES FOR MEDICINAL AND AROMATIC PLANTS
cedure has a suitable level of accuracy, precision and linearity. It is normally
derived from linearity studies.
14.3.3.4 Accuracy
The accuracy of an analytical procedure is the closeness of
agreement between the conventional true value (or an accepted reference
value) and the value calculated. It tells how closely the analyte amount is
determined to its true amount present in the test sample. Accuracy should
be specifi ed across the range of analytical procedure and inferred from 9
measurements (triplicates of three concentrations in the range).
Accuracy can be demonstrated by application of the proposed
procedure to an analyte of known purity or by comparing the results of the
proposed analytical procedure with those of a second well-characterized procedure,
whose accuracy is already known. Application of the procedure to
test samples after spiking at three different levels of 50%, 100% and 150%
of expected analyte concentration helps to determine the accuracy of the
procedure.
A sample containing 1.0 mg analyte may, in different analyses,
be found to contain 1.2, 0.9 and 0.8 mg. The assay procedure determining
0.9 mg is more accurate than the two other procedures.
14.3.3.5 Precision
The precision of an analytical method is closeness of results
for a series of measurements of multiple samples from the same homogeneous
material. The precision may suffer upon varying the experimental
conditions, which are therefore assumed to be kept constant. System precision
demonstrates error in recording the response and can be determined
by repeatedly analyzing a sample within a short period of time.
It is possible that the results are precise but not accurate or
vice versa. Triplicate measurements of 1.0 mg true quantity as 0.6, 1.0 and
1.4 result in an average value of 1.0 mg which is accurate but the three
measurements themselves are not precise. Similarly, triplicate measurements
of the same quantity as 0.6, 0.7 and 0.6 are precise but not accurate.
Triplicate measurements of 1.0, 0.9 and 1.0 are precise as well as
accurate.
Precision is expressed at three levels of short, medium and
long intervals, which are respectively referred to as repeatability, intermediate
precision and reproducibility.
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