The quality control protocols applied to routine chromatographic analyses do not entirely fulfill the Good Laboratory Practice (GLP). The GLP requires th;lt the reliability of an analyser should be proven while the analyser performs the analysis. In addition the present protocols increase the analytical cost by duplicating the number of analyses. Both problems call be solved by using the Deferred Standard (DS) concept: on-line reliability checking and minimum analyses needed. Combined with dedicated software, the DS presents several advantages over conventional methods used in routine analysis: it allows on-line reliability checking of the analyser, increases credibility, allows calculation of a Reliability Level independent of the operator suggestivity, allows system certification, increases analytical throughput, allows a larger flexibility, an accreditation of laboratory and decreases the analytical cost.