The functional form of instrumentally produced mass fractionation associated with MC-ICP-MS analysis is not accurately known and therefore cannot be fully corrected by traditional approaches of internal normalization using power, linear, or exponential mass-bias laws. We present a method for robust correction of instrumentally produced mass-fractionation of both spiked and unspiked samples that can be applied to mass analysis of Hf as well as Nd, Sr, Os, etc. Correction of 176Hf/177Hf for unspiked samples follows a traditional approach of internal normalization using an exponential law, followed by normalization to a standard of known composition, such as JMC-475. For spiked samples, standards are used to characterize a linear instrumental mass-bias coefficient; the mass-bias coefficient is defined by the slope of a tie-line between measured and true values of a standard. This approximation results in identical precision and accuracy of measurements for spiked and unspiked samples (¿0.005% 2σ, external reproducibility). The effects of the spike on the 176Hf/177Hf ratio and calculation of the molar spike-sample ratio is determined by a closed-form solution modified from the double-spike approach used for Fe isotope analysis by TIMS <Johnson and Beard, 1999>. The measured 176Lu/175Lu ratios are corrected by doping the sample with Er and using the 167Er/166Er ratio to externally normalize the 176Lu/175Lu ratio using an exponential law. Finally, spike-sample equilibration is confirmed for our sample dissolution protocol through analysis of varying physical mixtures of 1 Ga garnet and hornblende, where all the data lie on a mixing-line, within error, on a 176Lu/177Hf-176Hf/177Hf diagram. Precision of 176Lu/177Hf ratios is determined to be ¿0.2% (2σ) for standards and for physical mixtures of garnet and hornblende.