Strategies When Analytical Standards are not Available

Unfortunately situations can arise in which not only is a suitable internal standard not available, neither is an analytical standard. A common occurrence is in environmental analyses for groups of closely related compounds, e.g., the polychlorinated biphenyls (PCBs), where a laboratory may not have access to standards (analytical or internal) for all 210 congeners in such multi-residue analyses a limited number of standards are used and quantitation of a congener for which no standard is available uses data for one that is believed to have chemical and physical properties as closely similar as possible. Of course this does introduce possible systematic errors into the determination. 

Another example where this problem can arise involves drug discovery requiring bioanalytical quantitation of drug metabolites in plasma when reference standards are not available. Two innovative approaches to this fairly common problem were proposed recently. The first of these approaches (Valaskovic 2006) exploits very low flow rate nanospray ionization that exhibited a distinct trend towards equimolar responses of similar compounds (in this case a set of well known drugs) when the flow rate was reduced from 25 to less than lOnL.min (see also Section 5.3.5b). A more uniform response between 

2006) to ensure complete total solvent consumption (Section 5.3.5b). This strategy is discussed further in Section 11.5.1. 

However, in general it is obvious that analyses in which no analytical standard is available can be classed as heroic and the reliability of data thus obtained can not match that of data acquired using calibrations with standards. 

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