Which CRM should I choose for my method ?
In this week's blog post, we would like to discuss a point in the label information of certified reference materials (CRMs), which are frequently used in laboratories for calibration, control or product development, and which some users may overlook.
There is no limiting framework for manufacturers in ISO 17034 for the nomenclature of certified reference materials. As a general practice, designations containing a basic property or measurable value that provide the definition of the reference substance are preferred. However, there is a detail about this naming, which can lead to misconceptions and/or wrong choices for users. As an example, let's examine the names of the following 2 reference standard substances:
A. Magnesium standard solution / traceable to NIST 1000 mg/l Mg(NO₃)₂ in HNO₃
B. Magnesium standard solution for ICP / traceable to NIST 1000 mg/l Mg(NO₃)₂ in HNO₃
When we look at the label information of these two reference standards, it is seen that both are magnesium standard solutions, their contents and values are exactly the same. The only difference is the “ICP” information on the label. This little information means:
Standard A was prepared gravimetrically as a magnesium standard solution. The 1000 mg/l value was obtained by mathematical calculations using raw material weighing and volumetric solution data. It is a reference standard suitable for mostly wet chemistry studies.
Standard B was prepared gravimetrically as a magnesium standard solution. The value of 1000 mg/l was obtained theoretically with mathematical calculations using raw material weighing and volumetric solution data, and this value was confirmed by ICP analysis.
As a user, if you need a magnesium reference standard solution to use in ICP analysis and you have chosen the A standard, you should remember that you will be working with a standard whose assigned value has not been verified by ICP analysis, even though the label information says "Magnesium Reference Standard Solution". This does not necessarily mean that you will be working with an erroneous result or a result with a high margin of bias. However, for each different lot of CRM you will use, you may encounter different ICP result deviation ranges. For this reason, the standard we can recommend to use is the B reference standard. Similarly, it may be advisable to choose standards with IC code for ion chromatography studies and GC code for gas chromatography studies, for example.
Of course, an important factor affecting this choice between A and B reference standard solutions is the price of the product. The selling price of standard A is lower than the selling price of standard B as it does not include additional instrumental analysis verifications. The low price of the A standard may also lead to preference for ICP users who misunderstand that the A and B standards are equivalent to each other.
A. Magnesium standard solution / 1000 mg/l Mg(NO₃)₂ in HNO₃ / 100 ml / 22 Euro
B. Magnesium standard solution for ICP / 1000 mg/l Mg(NO₃)₂ in HNO₃ / 100 ml / 34 Euro