FUTURE POTENTIAL OF TARGETED COMPONENT ANALYSIS BY MULTIDIMENSIONAL LIQUID-CHROMATOGRAPHY MASS-SPECTROMETRY

Multidimensional liquid chromatography (MDLC) may be used in either (i ) the profiling mode where it is the objective to fractionate all comp onents in a mixture or (ii) the targeted component mode in which it is the objective to determine specific analytes. This paper focuses on t argeted component analysis from complex mixtures, addressing the criti cal operations of analyte selection and transport from the first to th e second dimension. Although the physical operation of switching a com ponent into the second dimension with computer controlled valving is s imple, it is shown that changes in analyte retention time and peak wid th with column age and fouling are a serious problem. The analyte move s out of the preselected time window for valve switching and quantitat ion is compromised in the second dimension. It is proposed that a solu tion to the ''drifting peak'' phenomenon in targeted component analysi s is to use binary mobility elution in the first dimension. Binary mob ility refers to those systems, such as affinity chromatography, in whi ch analyte mobility is generally either 0 or 1 relative to mobile phas e velocity. Coupling these binary changes in analyte mobility in the f irst dimension with valve switching eliminates the ''drifting peak'' p henomenon. In addition, it is shown that a wide time window may be use d in affinity separations without compromising the separation or accum ulating contaminants. Several cases are described in which immunosorbe nts were used with reversed phase columns to provide quantitative targ eted component analyses from complex mixtures.