Working Standards

One of the major time consuming elements of developing an isotope ratio monitoring method is obtaining and calibrating suitable working standards. Remember that the IAEA will only supply a lab with each international standard only once every three years. So it is important to find a good batch of working standards and to do a good job of characterizing them using the international standards.

What makes a good working standard?

    The first concern is that the working standard has the elements of interest and is in a form that is useful for your analytical techniques. For example,  a fine powder for EA work would be great.

    Isotopic homogeneity is probably the most important characteristic. If a batch of material is not isotopically homogenous, then its measured isotope ratio will vary with each measurement. Hence, the way to check a working standard is to make multiple measurements of it using a variety of sample sizes. If it is sufficiently homogenous, then you should get the same isotope ratio within acceptable precision over multiple measurements. As a rule of thumb, mixed liquids are homogenous. Hence, if you can dissolve the working standard in a solution for your analyses (for example making a large batch of standard for the TOC analyzer) then you can be sure that the homogeneity is ok.

More detailed information on the working standards we use are provided below by analysis type:

Waters

Bulk Carbon and Nitrogen on the EA and total organic/inorganic carbon on the TOC analyzer

Bulk Oxygen on the TC/EA

Bulk Hydrogen on the TC/EA

GC-C/TC: So far we have no standards for GC-C or GC-TC work.

Page last updated: Feb. 27, 2006