Liquid handling apparatus

A system for analyzing a biological fluid comprising

• an analysis region,
• a measurement system connected in sensing relation to said analysis region,
• a sample flow path connected between a sample inlet port and said analysis region,
• a pump for flowing sample to be analyzed through said sample flow path to said analysis region,
• a gas-liquid interface sensor in said flow path, said sensor having a first output when blood is in said flow path, a second output of magnitude different from the magnitude of said first output when serum is in said flow path, and a third output of magnitude intermediate the magnitudes of said first and second outputs when air is in said flow path, and
• control means for operating said pump at a first rate and responsive to said interface sensor for positioning the leading edge of a sample of fluid to be analyzed at a predetermined location in said sample flow path and then operating said pump at a second rate different from said first rate determined by the type of fluid detected by said sensor for positioning the sample in said analysis region with the trailing edge of the sample at a second predetermined location in said sample flow path.