Certification examples elements

For example trace elements in milk powder are not consumed as milk, and moisture in transformer oil is not used in transformers, yet matrix reference materials based on milk are imported as food and are subject to health certification requirements and sometimes import quotas. Likewise a matrix based on oil is identified as fuel or lubricating oil and is both classified as a hazardous material and subject to mineral oil tax. These problems arise because RMs are frequently incorrectly classified by specific title of their matrix (as Reference Material of Trace Elements in Rice is classified as rice) and not as reference material which is the intended use. 

Example 1 NAA, a suitable method for trace element certification... 

Abstract An example is presented of a traceability protocol for the measurement of a single-element strontium reference material solution, executed by a primary method of measurement for certification. The method of measurement is briefly described together with the measurement equation and the associated calculations for the estimation of uncertainties. 

This example is of a traceability [1] protocol [2] for the chemical measurement of an element by a primary method of measurement [3]. It can be used for the certification of a single-element reference material by a national reference laboratory. This protocol relates to a very pure strontium nitrate solution, stabilized by 10% (by volume) nitric acid1. This solution is to be certified for the amount of strontium substance n(Sr) per unit mass of aqueous solution m (sol). The general measurement method described is based in part on the experience of certifying a currently available certified reference material (CRM) [4], Standard Reference Material (SRM) 3153a [5],... 

Figure 10.2. Examples of bar graphs obtained in the certification projects of trace elements in Antarctic krill.

UV). Consequently the reliability of the signal relies on the prior chromatographic separation. Matrix matching of the calibration solution or standard addition procedure can help to overcome matrix influences. An example of the too often neglected matrix effect is given in Table 2.1. These results were obtained in an interlaboratory certification study of trace elements in soils. It demonstrates the importance of matrix matching for the calibration [25]. Except for Co and Cu, for which another source of error remained, the matrix matching of the calibrant solutions allowed the laboratory to come closer to the certified values. 

Figure 2.3 An example of a certificate of analysis for elements in apple leaves. Reprinted from Certificate of Analysis, Standard Reference Material 1515, Apple Leaves, National Institute of Standards and Technology. Not copyrightable in the United States.

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