Contamination control for liquid handling

An apparatus for reading machine-readable labels disposed on receptacles and associating receptacle data read from each machine-readable label with a location within the system, said apparatus comprising:

• a plurality of rack-receiving locations, each configured to receive a rack holding at least one receptacle;
• a label reading device configured to read a rack-identifying machine-readable label disposed on the rack and a machine-readable label disposed on the at least one receptacle held on the rack, wherein said label reading device is disposed adjacent to a first of said rack-receiving locations;
• and
• a data processing system, which includes data storage media and is configured to:
• read the machine-readable label of each receptacle having a machine-readable label and read the rack-identifying machine readable label when the rack is placed into said first rack-receiving location to obtain receptacle data for each receptacle having a machine-readable label and to obtain rack identifying data;
• store the receptacle data and the rack identifying data and associate the receptacle data with the rack identifying data;
• read the rack-identifying machine readable label when the rack is placed in a second of said rack-receiving locations to obtain rack identifying data, wherein the first and second rack-receiving locations are different locations;
• acquire location data identifying the second rack-receiving location in which the rack was placed;
• and
• retrieve the stored receptacle data that is associated with the rack-identifying data and associating the retrieved receptacle data with the location data to thereby associate the retrieved receptacle data with the rack-receiving location in which the rack was placed.