CRMs can be used for instrument calibration but also verification of calibration . There are CRMs with only the major elements certified or CRMs that offer certified values for almost all elements that may be present in aluminum alloys. Make sure you choose the CRM with elemental concentrations similar to the alloys you are analyzing. Should you need to proof the absence of elements in your alloy make sure you possess a CRM that contains these elements in a concentration right at or slightly below the limit for this element. Only with such a standard you can proof that you would actually detect the element should it be present in your alloy. Should you need to determine the content on minor elements (not the absence of an element), make sure the CRM you are using has a slightly higher concentration of the element in question so that your measurement takes place in a calibrated range. It is not good practice to extrapolate calibration to higher content. In the certificates of analysis for certified reference materials the concentration and uncertainty for each certified element is given. These values are usually based multiple wet chemical analyses in some cases from different laboratories. Certified reference materials from Suisse TP are certified in house using at least two independent analytical methods and several analyses to provide statistical data for uncertainty determination.