In figure 1, the z-values calculated for cadmium represent concentrations ranging from 0 to 50 micrograms per liter. Intercomparison Program for Marine Sediment and Tissue. The USGS warehouses stock sample containers, filters, and preservatives for collecting environmental samples. Inorganic blank water is also available for customer use. All supplies are rigorously tested to ensure compliance with quality standards.
Contamination is tested using the lowest detection methodology for the constituents of interest.
Certificates of analysis are provided with each manufacturer's lot. Other field QC supplies, such as inorganic spike materials, are available on request. Method Performance Organic compounds may be degraded by heat, light, temperature, microorganisms, and other factors. Because the NWQL analyzes a wide range of samples and specializes in trace and ultratrace compound concentrations, there is an increased need for QC information compared to inorganic analyses. Samples received for organic determinations are grouped together for similar analyses.