Chromatographic resolving power

Today, IMS is often coupled to multicapillary columns to better match the flow rates of several milliliters per minute while maintaining good chromatographic resolving powers. Figure 3.8 shows a commercially available multicapillary column, and a schematic representation of the device is shown in Figure 3.9. 

As a secondary consideration, the chromatographer may also need to know the minimum value of the separation ratio (a) for a solute pair that can be resolved by a particular column. The minimum value of (a) has also been suggested [8] as an alternative parameter that can be used to compare the performance of different columns. There is, however, a disadvantage to this type of criteria, due to the fact that the value of (a) becomes less as the resolving power of the column becomes greater. Nevertheless, a knowledge of the minimum value of (cxa/b) can be important in practice, and it is of interest to determine how the minimum value of (aA/B) is related to the effective plate number. 

Sometimes, the resolving power attainable with a single chromatographic system is still insufficient for the analysis of complex matrices. An approach commonly used to obtain greater resolution is multidimensional chromatography. 

FTICR-MS is capable of powerful mixture analysis, due to its high mass range and ultrahigh mass resolving power. However, in many cases it is still desirable to couple a chromatographic interface to the mass spectrometer for sample purification, preconcentration, and mixture separation. In the example given above, DTMS under HRMS conditions provides the elementary composition. Apart from DTMS, PyGC-MS can be performed to preseparate the mixture of molecules and to obtain the MS spectrum of a purified unknown. Direct comparison with the pure reference compound remains the best approach to obtain final proof. 

More experienced chromatographers may refer to the McReynolds constants for a given stationary phase as a measure of its resolving power. A complete discussion of this subject, however, is beyond the scope of this text. 

---