Instrument stability checks and necessary calibrations are performed prior to all analyses. Instruments are tuned to exceed factory specifications for linearity, or bias associated with amplitude. In addition, samples, reference material, and monitoring gasses are prepared to yield signals of the same amplitude.
Final isotopic data is calculated using multi-point normalization from at least two internal running standards or certified reference material with a wide span of delta values. We use the LIMS database for light stable isotopes developed and maintained by the USGS. All running standards are calibrated biannual to 3 or more NIST and IAEA certified reference material. Standards used are selected to be of a similar matrix and elemental ratio as your samples. For quality control, we include at least two blind QC samples of similar composition in all sample sequences. Summaries of these QC standards from multiple analyses, multiple days, and instruments are available upon request. Our laboratory also participates in periodic ring tests with multiple laboratories.
For a 49 sample EA sequence for CN analysis, this amounts to 12 calibrated references distributed throughout the run.