**6.2 Precision**

*Pharmaceutical Formulation Design - Recent Practices*

and validated procedures.

released by an authorized person.

cal distribution of values [27].

noticed and overcome. There are three types of errors:

burettes or pipettes (A, B, C types) etc.

25% result is 27.5%, 22% for 20% and 33% for30%.

linearity, working range, accuracy and precision [28].

to defined procedures.

**method**

Production and control operations are clearly specified in a written form i.e. standard operating procedures (SOP's) and GMP requirements are adopted.

Control procedures on starting materials, intermediate products and finished products and other in process controls should be carried out according to written

The finished products should be correctly processed, checked, packed according

Finished pharmaceutical products should not be sold or supplied unless they are

**6. Method validation and statistical interpretation of the analytical** 

The function of the analyst is to obtain a result as near to the true value as possible by the correct application of the analytical procedure employed. Quantitative analysis is not simply a case of taking sample, carrying out a single determination and then claim that the value obtained is irrefutable. It also requires knowledge of the chemistry involvements and the possibilities of the interferences from other ions, elements and compounds as well as of the statisti-

Different errors may occur during the analysis process which should be well

a.Gross errors: easily recognized as it leads to definite unreliable results: could be due to contaminated reagents, defective instruments, accidental loss of crucial sample etc. It is defined as a serious error so that there is no way to correct the experiment.

b.Random error (in determinate error): the average of the results are very close to the true value, so there is no evidence of bias i.e. some results could be high and some results could be low. Arises from sources that cannot be corrected i.e. the degree of sensitivity of the balance: fourth decimal, fifth decimal. Types of

c.Systematic (determinant errors): this causes all the results to be in error in the same sense (constant error). May be due to (1) faults in analytical procedure or (2) the equipment used. Observed result could be too low or too high i.e. inaccuracy should be constant (all answers are 10% too high or too low). Example: True value for three samples were 25, 20 and 30% assay result was 35, 30 and 40% respectively i.e. 10% too high. It makes the assay precise but inaccurate sometimes the inaccuracy may be proportional to the true answer, giving rise to proportional error such as 10% of the answer i.e. for the above example for

Validation of methods for the quantitative analysis of drugs involves determining as a minimum, their selectivity, and limit of detection, limit of quantification,

Accuracy is a measure of how closely the result of an experiment agrees with the expected result. The difference between the obtained result and the expected

**36**

**6.1 Accuracy**

Precision is a measure of how close a set of results are to each other [30]. It is often measured under repeatable (same analyst, same day, same instruments and same materials) and reproducible conditions. Precision always accompanies accuracy, but a high degree of precision does not imply accuracy.
