Addition of surrogate standards in the routine analysis of investigating polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F)

Conclusion  Independent losses of internal standard by evaporation and/or sorption will increase both absolute and random errors for the native analyte. Thus, the internal standard should only be used for compensation of losses, variations and irregularities in the clean-up, dilution, transfer and instrument. This is achieved by addition of internal standard to the eluent after extraction, or avoiding direct contact between internal standards and suspected active matrices. The analytical results will then not guarantee a correct quantification of the true analyte concentration on the matrix, only maximise the precision of measurement of extracted analyte. In Soxhlet extraction, the internal standard can be added to the solvent reservoir. In supercritical fluid extraction (SFE), the internal standard might be added to an aliquot of reversed phase silica (C-8, C-18) located after the sample in the fluid direction.