154 | Chapter 5: Qualification
Washer Liquid Tests
Dispense Precision Test
Dispense precision is a measure of the variability of volumes dispensed from tube
to tube across the manifold. The optical density of the solution in a well is
proportional to the total volume of the solution in the well. If the % Coefficient of
Variation (%CV) is calculated, the result is a measure of the uniformity of the
distribution of dispensed volumes across the manifold. It is the ratio, expressed in
percent, of the standard deviation of the distribution of fluid volumes in the wells
to the mean value of volume per well. The uniformity of distribution across the
manifold improves as the %CV is lowered.
Annual Buffer Switching Test: The dispense test is also conducted for the buffer
switching module to ensure that each valve (A, B, C, D) is calibrated to deliver the
same volume of fluid.
Evacuation Efficiency Test
The Evacuation Efficiency test measures the residual volume (mean residual
weight) per well after aspiration is performed. The lower the residual per well, the
better the evacuation efficiency of the washer. A known solution is dispensed into
all wells of a previously weighed microplate. Aspiration is performed and the plate
is re-weighed. The total residual fluid is calculated based on the weight difference,
and this value is divided by 96or 384 as appropriate, to obtain the mean residual
weight.
In addition, a diagnostic tool is provided for use, if necessary, to identify problem
wells: a known dye concentration is dispensed to and evacuated from the wells,
and the plate is weighed. Buffer is then dispensed to all wells to bring the volume
of fluid to a more optically measurable volume. The optical density (OD) of each
well is measured and the background is subtracted to account for scratches on the
plate or particulates in a well. Each well’s residual volume is calculated using its
OD and a calibration factor derived from the mean residual weight and the mean
OD of all wells on the plate. It is assumed that 1 mg = 1 µL of fluid for this
calculation.
Predefined Test Protocols
Several 405 LS protocols are shipped onboard the instrument and with the LHC
and installed on your computer during LHC installation.
405™ Microplate Washer LS
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