Replicate determinations in Chemical Analysis

Replicate determinations in Chemical Analysis
Always carry more than one determination
Always carry more than one determination

It is a well accepted fact that a single determination will seldom provide the true value. Chemical measurements involve several variables and there is a potential scope for more errors in comparison to physical measurements. The various contributing factors that result in errors in chemical measurements are:

  • Errors inherent in method resulting from adoption of non-validated methods
  • Equipment errors resulting from non-calibration at specified time intervals
  • Use of reagents not meeting required purity specifications
  • Personal errors such as perception of colour changes at end point of titrations, reading of volumes in burettes,accurate transfer of reagent volumes, washing and transfer of precipitates, etc.

As a trained and responsible chemist you have to ensure that the results reported are not questioned by any other individual or laboratory. Take all the required precautions and follow guidelines laid down in the standard operating procedures. However, it is an established fact that in-spite of all the precautions that you take a single determination will not necessarily lead to the true value of the parameter under determination so it is essential to carry out more than one replicate analysis .

Replication of Analysis

Your confidence on results reported increases with the replication of analysis. Statistically speaking the larger the number of replicates the closer will be the experimental mean to the true mean or in other words the actual value of the parameter to be determined. This in principle is an ideal solution but in a chemical laboratory it is not practical to carry out infinite number of measurements for any single analysis parameter for the following obvious reasons:

Limitation of Time

As a chemist you will be always be hard pressed for time and it is not possible to carry out 10, 100, 1000 or even more replicates on a single sample.

Cost Considerations

No laboratory would be willing to conduct any particular analysis more number of times than required because it can involve extra expenditure on expensive reagents, standards and solvents in addition to loss in laboratory productivity.

Limitations on Resources

Every chemical analysis requires use of glassware, weighing balances and required instrument facilities. Due to limited availability of such resources their use for further essential activities gets blocked.

The accuracy and precision of results can be improved significantly through use of high quality reagents, use of calibrated equipments, validated working standards, calibrated volumetric glassware and weighing analytical balances and upgradation of skills of chemists through regular training schedules.

Majority of quantitative methods require establishing a calibration plot comprising of at least six known standard concentrations to determine the unknown concentration falling within the calibration concentration range so under routine analysis 6-8 replicate determinations fulfill the analytical requirements.

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