A MODEL TO ESTABLISH THE LIMIT OF DECISION AND THE LIMIT OF DETECTIONFOR STRAIGHT-LINE CURVES IN A CASE OF HETEROSCEDASTICITY

A problem arises when determining the decision and detection limits in a series of results where the variance of the error distribution of t he analytical signals around their expectation is not a constant when applying a method proposed by Hubaux and Vos6. In this paper an approa ch is proposed to overcome this difficulty, that involves the use of a transform method to convert heteroscedastic data to homoscedastic dat a 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-1 SO42- range. The results obtained from this approach are compa red from others obtained previously.