INTERLABORATORY QUALITY ASSURANCE STUDIES - THEIR USE IN CERTIFYING NATURAL-WATERS FOR MAJOR CONSTITUENTS AND TRACE-ELEMENTS

Environmental programs throughout North America have demonstrated a st rong awareness of the usefulness of interlaboratory studies for disclo sing the quality of analytical results. The Ecosystem Interlaboratory Quality Assurance Program offered by the National Water Research Insti tute has a wide participation base of laboratories. Many of these labo ratories are accredited and employ a number of recognized analytical m ethods. The interlaboratory study data archives contain a wealth of da ta for natural surface and rain waters from across the continent. Thes e archives have proven to be a reliable means of characterizing a vari ety of constituents. Data assessments from these studies accurately id entify the variability of data and the presence of any outliers. Repea ted use of selected samples in a regular QA program confirms their sta bility. Time charts and statistical techniques are used to illustrate this stability and yield the precision of pooled analyses. The availab ility of archived data from interlaboratory studies has enabled the In stitute to develop and certify natural water and trace element standar ds. The natural water CRM, ION-911, has been available for several yea rs. Its historical aspects are discussed as well as the processes lead ing to the certification of TMRain-95, a soft water standard certifyin g 22 trace elements. This paper focuses on the use of select laborator ies in round-robin evaluations to provide accurate values for constitu ent concentrations. Natural water and fortified trace element CRMs mee t a recognized need in the generation of accurate data for environment al programs.