Practical Aspects of HOD IMS Implementation, Limitations on the Separation Order

2 Practical Aspects of HOD IMS Implementation, Limitations ON THE Separation Order 

Characteristic Parameters of the Optimum (Rectangular) Asymmetric Waveforms for Differential IMS Up to the Fourth Order  

In summary, the optimum waveform is unique for HOD IMS of lowest order, but not higher orders where the best segment sequence is determined by interplay of several criteria. The compromise wUl have to be selected depending on the specific hardware limitations. The values of Ap, AUtot/Ur , and AUjaax./Ur for HOD IMS are overall close to those for FAIMS (Table 5.2), suggesting a similar difficulty of implementation at equal field intensity. 

However, effective differential IMS must generally require stronger fields for higher separation orders, with HOD IMS involving greater E/N than FAIMS. In view of the electrical breakdown limitations on E/N (1.3.3), this trend will preclude useful operation above certain order, limiting the theoretically infinite progression of 

HOD IMS methods (5.2.1). The magnitude of necessary for HOD IMS analyses of order n depends on the a values for ions of interest (rigorously, on the spreads between for the species to be resolved, 3.1.7). The most extensive compilations of 02 values are the measurements for 17 amino acid cations and anions that we looked at in the context of FAIMS waveform optimization (3.1). In that set, the means (medians) are 6.8x10 (6.0x10 ) Td for a-[ and 1.5x10 ° for fl2 the similarity of means and medians for either suggests that the selection of a and 02 values is representative.  

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