Obtaining Accurate Isotopic Compositions with the Double Spike Technique: Practical Considerations

Ever‐increasing precision in isotope ratio measurements requires a concomitant small bias and minimisation of inter‐laboratory bias. The double spike technique is the most suitable method to obtain reliable isotope composition data that are accurately corrected for instrumental mass fractionation. Compared with other methods, such as sample‐calibrator bracketing, only the double spike technique can correct for all sources of fractionation after equilibration of the sample with the double spike, such as that incurred during chemical separation and measurement. In addition, it is not dependent on a priori assumptions of perfect matrix matching of samples to reference materials or quantitative recovery of the sample through the chemical separation procedure to yield accurate results. In this review article, we present a detailed discussion of the merits of the double spike technique, how to design and calibrate a suitable double spike and analytical strategies. Our objective is to offer a step‐by‐step introduction to the use of the double spike technique in order to lower potential barriers that researchers new to the subject might face, such that double spiking will replace sample‐calibrator bracketing as the measurement method of choice.