A problem arises when determining the decision and detection limits in a series of results where the variance of the error distribution of the analytical signals around their expectation is not a constant when applying a method proposed by Hubaux and Vos6. In this paper an approach is proposed to overcome this difficulty, that involves the use of a transform method to convert heteroscedastic data to homoscedastic data so that the limit of detection can be obtained by projection of the confidence band about the linear regression. This approach is applied to the case of a gravimetric determination of sulphate ion in the 1 – 5 mgL−1SO42-range. The results obtained from this approach are compared from others obtained previously.