QUALITY ASSURANCE AND QUALITY CONTROL
Prior to any analysis, the isotope ratio mass spectrometers are checked for several parameters (signal stability, sample count, peak jumping, etc.). Necessary adjustments are performed if the instruments fail to meet minimum tolerances.
For EA and TCEA analyses, samples are placed in a zero blank autosampler to keep samples dry and avoid atmospheric water vapor changes.
SIRFER uses a two-point normalization routine to correct raw instrument data. The normalization is based on the analysis of two primary laboratory reference materials (PLRM) with very different delta values. These primary laboratory reference materials are calibrated annually against NIST and IAEA certified reference materials. For quality control, SIRFER uses a secondary laboratory reference material (SLRM). The SLRM are chosen to have a similar elemental composition as the samples. To minimize linearity issues, the amount of each sample, PLRM, and SLRM is selected to yield signals of approximately the same peak area.