Total Aspirate and Dispense Monitoring: TADM

During crucial sample transfers, the STAR can monitor aspiration and dispense steps in real time. TADM verifies with a traceable digital audit trail that a sample has been transferred, which is particularly beneficial for In Vitro Diagnostic (IVD) laboratories.  High and low pressure limit bands are first predetermined from multiple test sample runs.   During routine pipetting, errors are time reported in real-time when the measured pressure exceeds these bands.  The system can then simply record the errors or react to them. 

 

Aspiration Error Detection

Tip blockage (2) is detected when the pressure drops below the minimum set values.  The minimum set values vary with aspiration/dispense time and are predetermined by the results of test runs.  Limits can be widened or tightened to minimize false errors.

Insufficient sample (3) or incorrect aspiration is detected when the pressure rises above the maximum limit during aspiration.

Dispense Error Detection

Blocked tip (1) is detected when dispense pressure rises above the maximum pressure limit during dispense.

Leaking seals (2) are detected when the pressure declines below the minimum pressure limit during dispense.

Error event handling

Pressure data is continuously recorded during pipetting for Chain of Custody.  When the pressure goes outside the pressure limits prescribed for different times during the aspiration or dispense cycles, an error event is registered and communicated to the script.  Venus scripts can be written in a variety of ways to handle these events.  It can ignore them, stop the method, ask for user intervention or intelligently attempt to deal with the error without user intervention.  For example, in the event of a clog or too low pressure during aspiration, the script could evacuate the tip or needle and try to aspirate again.  It could even move the tip slightly to avoid a swab in a tube and perhaps be programmed to make several aspiration attempts before requesting user intervention or flag the sample as an error and automatically move on to the next sample. 


TADM - Typical curves

Typical TADM curves (mbar vs msec) for various dispense volumes.


TADM - Typical curves - 50 successful runs

TADM  curves (mbar vs msec) from aspirating 50 samples of the same volume with no errors.  Maximum and minimum error bands are set just outside this range of data to allow for variation within observed successful dispenses.  Band settings are stored in the software by liquid class.  A unique liquid class can be created for each liquid type and pipetting volume range.


TADM - Typical curves - Insufficient sample

Insufficient sample aspiration detected in three samples when the pressure abruptly increased above the maximum TADM error band.


TADM - clots

Clots detected and aspiration aborted in two samples when the pressure gradually decreased below the minimum TADM error band.


TADM - foam

Foam detected and aspiration aborted in two samples when the pressure abruptly dropped below the minimum TADM error band at the beginning of the aspiration cycle.

 
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