Errors Pharmaceutical Analysis Unit-I

Sources of errors 

Errors in the results in an analysis can be resulted from various sources. Some major sources of error in pharmaceutical analysis are described here under.

1. Human Source: The qualification and experience of an analyst performing the analysis has major impact on error in results. If an experiment is performed by inexperience person the chances of error are more as compared to same experiment performed by the experienced analyst.
2. Instrumental, Apparatus and glassware: If the instrument, glassware as well as apparatus used in analysis is of low quality and uncalibrated the chances of error are increased at significant extent.
3. Experimental conditions: If the analysis is carried out in the conditions which are unfavorable for particular experiment or analysis the desirable result will not obtained.
4. Constituents used in analysis: If various constituents like standard, solvents, reagents etc. used in analysis are not of desired quality and purity the results will be obtained with errors.
5. Procedure: If the analytical procedure used in analysis is not validated and if validated but not followed carefully the errors in the results will obtained.

Types of Errors

Errors occurs in analysis can be majorly classified into two types:-

 1. Systemic errors:- 

Systemic errors is also known as determinate errors. These are the errors whose source or cause as well as magnitude is known and can be avoided or minimized by following proper procedure carefully and taking necessary precautions. Systemic errors can be classified as follows:-

 a) Personal errors: For these errors the person carrying operation or experiment is responsibly. These errors occurs When the procedure is not properly followed or done carefully.

Some of the examples of personal errors are:- 

1. Person carrying titration cannot able to detect endpoint by color change clearly and always add some more amount of titrant that actually  required which result in positive error i.e. measured value is always bit more than standard value.
2. Person is not washing precipitate properly in gravimetric determinations that result's error in final result.
3. Person performing assay has not free hand in making dilutions and add more or less solvent in dilution preparations that directly give error in results.
4. Person carrying titrations is unable to read burette properly and always note incorrect values that also cause error in results.

  b) Instrumental errors:- Instrumental errors are seen when the instrument used in the operation doesn't give accurate measurement which it need to be give. These are due to use of uncalibrated or improperly calibrated glassware's like pipette, burette etc. and instruments like spectrometers, pH meters, potentiometers etc.

 c) Reagents errors:- Reagent errors are due to the reagents used in analysis. These errors are seen when contaminated reagents are employed in analysis or the reagents attacks on the apparatus or glassware and introduce impurities in analyte sample under analysis.

d) Additive errors:- These errors are independent of the amount of substances present in the sample. For example, use in the weight of crucible during the incineration of precipitate gives error in final results.

e) Proportional errors:- The magnitude of proportional error depends upon the amount of sample. Proportional error is usually due to the materials that interferes the analytical procedure.

Methods of Minimizing errors:-