Bio-Rad BioFrac™ Fraction Collector - Manual (Page 91)

User Guide | 83
A Bubble Filter Time
The bubble filter time function is used in conjunction with the Peak Collection by
Threshold. The bubble filter time function distinguishes true chromatographic peaks
from unwanted signals such as electrical spikes or the passage of an air bubble.
Such false signals are characterized by extremely fast rise and fall times.
The bubble filter time function is entered at the end of the threshold programming
sequence. The default value is off (bubble filter = 0 seconds).
A signal that exceeds the set threshold value with a rise time of >6.0% full scale
(AUFS) in 0.1 seconds is perceived by the fraction collector as possibly signifying a
false peak. In such cases, the fraction collector looks for a bubble filter time set by
the user. If the signal falls to 2% of the pre-rise FS level within the set bubble filter
time, the signal is rejected and the false peak is not collected. Signals that exceed
the threshold value and are of a longer duration than the bubble filter time are
collected as true peaks.
Very sharp, true chromatographic peaks (such as those from an HPLC application)
may rise at a sufficient rate to trigger this function. As a consequence, if an
unsuitable bubble filter time has been set, then the early part of such peaks may not
be collected.
The bubble filter time can be set from 0 to 10 sec. For most chromatographic
applications, a filter time of 0 or 1 sec will suffice. The actual setting depends upon
both flow rate and peak duration and should be optimized for each type of
separation. Generally speaking, a very short bubble filter time should be used with
sharp peaks of short duration.