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Carry-over

Carry-over can be a problem in screening small molecules which are analysed at relatively high concentration and may have limited solubility in aqueous buffers. A carry-over control injection (buffer injection) over the surface after regeneration could be included to check that analyte is not carried over to the next cycle. If you know that your screening assay does not suffer from carry-over problems, you may delete this inject from the cycle so that cycle time is reduced and sample throughput is faster.

This plot shows the binding level at the end of the carry-over control injection.

In this run, one compound (encircled) causes consistently high carry-over, which increasingly affects subsequent cycles as the run progresses.

Watch for compounds that reproducibly cause carry-over. One such is highlighted in the example illustrated above: the carry-over binding is consistently high, and shows an increasing effect on subsequent samples as the run progresses.

Consistent carry-over may be caused by too high sample concentrations, precipitation of the sample or by binding of the sample compound to the walls of the flow system. An extra wash with 50% DMSO after sample injection can help in reducing carry-over.

Another possible source of carry-over is the use of high viscosity regeneration solutions, which may not be adequately washed out of the system. This results in carry-over of the regeneration solution rather than sample, but it may be difficult to distinguish between these in practice.

If precipitation is suspected, lower the sample concentration or increase the DMSO concentration. If you do this, increase the DMSO concentration in running buffer and in all samples (including control samples) and remember to adjust the solvent correction range.

If carry-over problems appear randomly and are not associated with specific substances, there may be a malfunction in the sample handling.

See also

List of help files

Assay design for small molecule screening