Accuracy and precision of a robotic sample processor

The accuracy and precision of the Packard Probe 1000, a computer-driven robotic sample processor, were determined using NCCLS Guideline 18-P, employing a rigorous gravimetric procedure. For volumes of 25, 100, and 200 muL, inaccuracy ranged from -0.5 to +0.6% (saline) and -0.8 to +0.7% (human serum), and imprecision from 0.1 to 0.6% (saline) and 0.02 to 0.8% (human serum), in the dip and sip mode of pipetting. For the same volumes of saline in the dispense-through pipetting mode, inaccuracy ranged from -0.1 to -0.9% and imprecision from 0.1 to 0.5%. To obtain this level of performance, the instrument's operating parameters were changed from the factory default settings. This automated liquid-handling system is capable of impressive accuracy and precision, but it must be calibrated in the same manner as any other volumetric device. Performance varies with the volume, type of liquid, and mode of pipetting. Inaccuracy of less than or equal to 1.0% and imprecision of less than =1.0% can be attained along with rapid, walkaway pipetting of calibrators, controls, and large numbers of patient samples.