van Holde - Weischet Tutorial

Range of S - values is too large

For some cases the distribution of components in the system display a range of S - values simply too large for successful analysis with the van Holde - Weischet analysis. In such cases, the slowest material has not yet cleared the meniscus, but the fastest components already started to pellet and lose their stable plateau:

Figure 26: A heterogeneous system with a large range of S-values. All scans have either not cleared the meniscus or no stable plateau, or both.

Such a condition makes it impossible to analyze with the van Holde - Weischet analysis, since the boundary conditions are not met. It may be possible to analyze a portion of the boundary at the beginning of the experiment by limiting the range and percent offset from the baseline using the UltraScan software:

Figure 27:Only the first 4 scans of the above sample are analyzed, and 17% of the boundary near the baseline have been excluded from the analysis, since the meniscus was not cleared in that range.

Under the proper run conditions, the van Holde - Weischet analysis can be used for S-value ranges of 10-20 fold difference in S.