Fixed volume sequential standard addition calibration: Value assignment of impurities in zero gas

•A fixed volume sequential standard addition calibration is described mathematically.•This has been applied to the determination of impurities in blank gas.•A systematic bias during the extrapolation process is observed.•Best practice solutions for correction are proposed.

A fixed volume case of sequential standard addition calibration (S-SAC) for the value assignment of impurities in zero gas is described. A mathematical description of this technique has been derived and has been shown to exhibit a similar systematic bias during the extrapolation process to that seen for other S-SAC cases. The use of S-SAC in the gas phase has demonstrated that variation in the sample volume for S-SAC in the liquid phase is not the generalised cause of the bias experienced during extrapolation. Instead it is the variation in the volume of the original sample with respect to the overall volume of the mixture following the addition of standard. In addition, the requirement to perform a bias correction on the extrapolated values has been discussed and best practice solutions for correction proposed.