Dilutions play an important role in laboratories. The required accuracy depends on the purpose for which dilution is to be carried out. Simple school/ graduate level dilutions can be carried out using graduated measuring cylinders and pipettes. However, very low level determinations require use of precision devices such as micropipettes. For high level precision levels dilutions use of automated dilutions is strongly recommended.
A dilution can be a single step or can involve multiple steps depending on the required dilution factor. It should be kept in mind that error introduced at any stage of serial dilutions gets multiplied in subsequent stages. In view of the importance of dilutions a few suggestions are being forwarded.
Suggestions on carrying out dilutions
Separate zone for dilutions
A separate section should be provided in each lab for carrying out dilutions and sample preparation. This zone should have restricted entry and there should be complete restriction of mobile or intercom inside. The zone will permit the chemist to carry out the dilutions with full concentration and freedom from any distractions from other laboratory workers. Only one person should be permitted entry at any given time. This will also help protect the sophisticated instruments from coming in contact with solvent vapours and prolong their useful life.
Dilution glassware and devices
It goes without saying that glassware and devices should be clean up to the requirements of the study. Volumetric flasks and pipettes should also conform to Class A approved specifications.
Pipettes can be used for volume transfers in range of 5ml, 10 ml, etc but for sub ml or μl volume transfers use of micropipettes should be mandatory. Disposable tips should never be reused. When using micropipettes use hand gloves for prevention of sample contamination.
Maintain laboratory environment
A clean laboratory environment should always be maintained. The temperature of the laboratory should be maintained within [Latex]+/- 2^0C [/Latex] so that there are no significant changes in volume due to temperature fluctuations.
Validity of standards
Standards are available both as liquids composed of required analytes or in solid powder forms. The standards should be highest purity grade materials accompanied with a certificate of analysis and also bear traceability to its origin. Always ensure that the material is within its expiry period before use.
Weighing and transfer of standards
After taking the required weight or volume the excess amount should not be returned to the original container. This is necessary to prevent contamination of the remaining standard. Store the standard under its recommended storage conditions otherwise there is a risk that the standard can lose its potency even before the expiry period.
Dilution of strong acids
Always remember to add acid to water when there is requirement for dilution of strong acids otherwise due to heat of mixing the mixture can splash out and cause injury or burns.
Dilutions are commonly perceived as simple processes but if the critical points are overlooked the results of analysis can be misleading and of little significance.