ABSTRACT
An impurity in a material is something that does not belong there. As the requirements for pure materials in demanding applications grow, so does the need to identify and measure trace contaminants. The very definition of the word “trace” has varied as improvements in detection limits have been made through technological advances in instrumentation. In 1962, Pinta [1] defined “trace” as a concentration of analyte below 10 3—10–4 in a given material. In 1962 the abbreviation ppt meant parts per thousand. Today’s analytical chemistry student will tell you that ppt stands for parts per trillion. The idea of routinely measuring concentrations at or below the parts per trillion level would have been unthinkable 40 years ago, but it is commonly done today. The term “ultratrace analysis” has been added to the vocabulary for concentrations below 10–9. In general, trace impurities are considered here to be those that are present at concentrations of less than 10–1 in the material and includes “ultratrace” concentrations.
