|Methodologies to determine b-term coefficients revisited
|Challenges in Quantitative Analysis
| Huiying Song
|University in Leuven
Abstract Information :
The accuracy of the longitudinal diffusion term (b-term) plays a vital role in the study of mass transfer mechanisms in high performance liquid chromatography (HPLC). In this presentation, three commonly used methodologies (peak parking; fitting of an experimental plate height curve; and the so-called dynamic method) for the determination of the b-term constant will be discussed in detail. The three methods will be compared based on their mutual agreement, the intra- and inter-day variation of the obtained values and the time required to measure them. It will be demonstrated that whereas the dynamic method is often plagued by impractically long waiting times and concomitant baseline variations compromising accurate measurements of the band broadening, the two other methods lead to very similar b-values, i.e., well within the 1% RSD inter-day variation typically marking both methods in the present study. It will moreover be shown that the best way to study the agreement of the peak parking and plate height fitting method is in a plot of h.v versus v, providing a much better zoom on the b-term region of the van Deemter curve than the customarily employed h versus v-curve and hence allowing to identify any anomalous measurement values (usually related to measurements with a long experimentation time). Finally, the implications of a certain variation in b-term value for the further determination of column performance parameters will be discussed.