ABSTRACT
In the following, M denotes a metallic element and X a nonmetallic element whose concentrations may vary between wide limits. In the case of mixtures, a specific element will be labeled Mj or Xj' The accessible lower limit for detection of amounts or concentrations of stable elements M and X is relatively low thanks to the sensitivity of present-day analytical methods. I -3 It is now a common practice to measure nanograms or picograms of an element. In terms of concentration, and with regard to constraints imposed by sample preparation, these figures correspond to parts per million (lLg/g or mg/kg) or parts per billion (ng/g or ILg/kg) levels. In extreme cases, the concentration may be of the order of lO-8 M for an element with atomic mass 100. Even at this dilution, however, the number of species per gram or milliliter is still enormous, and may amount to about lO12.
