Certified reference materials are indispensable for validating the results of analysis. Like any other laboratory reagents they involve a recurring cost but their costs are higher than regular reagents. The reason for the higher cost is because such materials bear traceability to global standardization bodies and are accompanied with a certificate that guarantees the concentration of the analyte of interest.
The cost of certified reference materials of rare compounds or elements can be prohibitive. A few hundred milligrams or milliliters may cost several hundred dollars. It becomes all the more necessary to use such materials judiciously so that analysis costs can be reduced. In this article some practices are recommended that can help bring down the recurring costs.
Make Use of Working Standards
Working standards are high purity compounds or reagents having similar chemical composition as the certified reference material. Such compounds are standardized against certified reference materials by adopting validated test procedures and calibrated instrumental techniques. Thus working standards get related to the certified reference materials in terms of traceability and the traceability chain will get further propagated when other pure compounds are standardized against such working standards. However, traceability records need to be maintained and all such correlations should be carried out within the expiry of the working standard. Such working standards need to be preserved in the conditions prescribed by the supplier of the original certified reference material.
Conduct Stability Studies
Certified reference materials and working standards have a shelf life. The material can degrade naturally over the shelf life or it can get contaminated through leaching or transpiration from the container during storage. It is strongly recommended that stability studies be carried out on a portion of the working standards prepared to establish the shelf life and new working standards be prepared within the validity established through such studies.
Store Diluted Solutions as Working Standards
Pure certified reference standards generally come in high concentrations ranging from 10,000 ppm to 1000 ppm. It is indeed very rare that such high concentrations will be used in routine analysis. You will require 10 – 100 fold or even higher dilution for the analysis. It would indeed be wasteful if every time the required quantity of original standard is taken.
A cost saving approach is explained through the example below:
Suppose you have a routine requirement of a standard of nickel at 10 ppm level. This will involve serial dilution 100 fold of a 1000 ppm standard solution. You will normally dilute 1 ml every time when an analysis is conducted so 10 ml quantity can be used only 8 to 9 times which in other words means the entire standard can get consumed in as little as one month.
The shelf life of the original reference standard plays a significant role. Suppose the shelf life is specified as two years. It will mean that one ml quantities can be withdrawn 8 to 9 times for use over the two year span. In the suggested approach take 1ml quantity at a time. Dilute 10 times to get 100 ppm strength and use this working standard over a period of time after a confirmation of analyte concentration through stability studies.
Over a period of time you will realize that there is a significant cost reduction as every time you will not be consuming the original standard for similar set of determinations.