An apparatus for determining the volume of liquid in a probe tip of an aspirating or dispensing probe, such as those used in a diagnostic analyzer, includes: two electrodes on opposite sides of the probe tip and the electrodes and liquid form a
variable capacitor; a
resistor; a
voltage source and the electrodes,
resistor, and solenoid are in electrical communication in at least one of series, parallel or series and parallel to form an
RC circuit; and a
microprocessor in electrical communication with the
RC circuit for converting an electrical
signal to a volume of liquid in the probe tip. In a preferred embodiment, the probe tip is separate from the probe and is adapted to be fitted on the end of a probe for aspirating and dispensing a liquid. In another preferred embodiment, the apparatus further includes a solenoid, and the
voltage source, electrodes,
resistor, and solenoid are in electrical communication in at least one of series, parallel or series and parallel to form an
RLC circuit, and the
microprocessor is in electrical communication with the
RLC circuit for converting an electrical
signal to a volume of liquid in the probe tip. The apparatus can be used with a liquid have a known or unknown
dielectric constant and can be used to determine the presence of bubbles in the liquid.