Quality Control Requirements for Sampling and Analysis

• Field duplicate sampling and analysis of replicates in a balanced analysis of variance (ANOVA) design (see figure below) for evaluation of geochemical relief in relation to sampling and analytical variability, and estimation of measurement uncertainty, and
• Duplicate field samples of each material must be taken from one geologically representative small catchment basin (either 1, 2, 3, 4 or 5) of the selected GTN grid cell in the case of the cost-effective 5 random point sampling design.
• Countries with less than 6 GTN grid cells, i.e., 30 drainage basins, should randomly select 2 drainage basins for duplicate field sampling, which must be in different GTN grid cells.
• Secondary Reference Materials (SRMs) to monitor analytical drift, and randomisation to convert any residual systematic drift to non-spatially related analytical variability. 

Data Storage

• Miscellaneous recommendations relate to analytical data reporting (maximum of 4 significant figures, and adequate resolution close to the detection limit), data formats, units of measurement, geographical coordinates, data transfer, and the availability of a standard query (command) language.