Detection: International update, and some emerging di-lemmas involving calibration, the blank, and multiple detection decisions

Detection and quantification capabilities represent fundamental performance characteristics of measurement processes, yet there have been decades of confusion and miscommunication regarding the underlying concepts and terminology. New, co-ordinated documents prepared by the International organization for standardization (ISO) [1] and the International union of pure and applied chemistry (IUPAC) [2] promise to alleviate this situation by providing, for the first time, a harmonized position of standards and recommendations for adoption by the international scientific community. The first section of this paper contains a brief introduction to the events leading to the ISO and IUPAC efforts. Section 2 consists of (1) a brief review of the history of 'detection limits' in chemistry, illustrating the critical need for the development of a sound and uniform system of terms and symbols; and (2) a review of the ISO-IUPAC deliberations and the ensuing harmonized position on concepts and nomenclature. Section 3 treats fundamental applications of the underlying concepts, together with a series of unresolved or 'open' questions involving: detection and quantification capabilities in the signal and concentration domains, respectively; and the link between calibration and detection and quantification limits, together with the blank-intercept dichotomy. Also included are special treatments and approximations, developed in part for the IUPAC document, involving the non-central-t, and the exact (non-normal) distribution of the estimated concentration. The final section (Section 4) introduces issues and approaches to multiple independent and multivariate detection decisions and limits, and concludes with a glimpse at some challenges involving the multivariate blank and non-monotonic calibration functions.