This is an analyte-specific qualifier. X indicates very biased data. Surrogate recovery qualifier application is sample-specific and matrix spike recovery qualifiers are applied to all samples in the associated QC batch. G indicates low biased data wherein the analyte concentration may be greater than the reported value. L indicates high biased data wherein the analyte concentration may be lower than the reported value.
R indicates that the associated data are judged unusable by the data reviewer.
The qualifier is applied based on the professional judgment of the data reviewer rather than any specific set of QC parameters and is applied when the reviewer feels that the data may not or will not provide any useful information to the data user. This qualifier may or may not be analyte-specific.