Method for estimating viscosity

A method as claimed in 8, wherein the viscosity is estimated by:

• μ
• =
• 
• {
• -
• 1
• β
• 3
• 
• [
• β
• 2
• +
• ln
• 
• (
• β
• 1
• R
• -
• β
• 0
• -
• 1
• )
• ]
• }
• wherein β0, β1, β2, and β3 are constants determined by a non-linear calibration curve.

A method for aspirating a selected amount of liquid comprising:

• providing an aspirating probe which comprises a probe tip and a pump, wherein the probe tip and pump are in fluid communication;
• measuring a reference pressure which is the pressure inside a metering tip when no dispense or aspirate is occurring (Pref);
• moving the tip into the liquid, whereby a volume of gas is located between the top of the liquid and the pump, wherein the reference pressure is measured before or after the tip enters the liquid;
• actuating the pump for a duration or distance which corresponds to a selected volume of liquid to be aspirated;
• stopping the aspirate or dispense;
• measuring the pressure (Pstop) inside the tip at a time (t) which is the time when the aspirate or dispense is stopped;
• measuring the pressure (Pstop′) inside the tip at a time (t′) after t;
• estimating viscosity as a function of Pref, Pstop, and Pstop′;
• compensating for viscosity by either notifying an operator if the estimated viscosity is outside a predetermined range, or adjusting the actuation of the pump based on the estimated viscosity.

A method of analyzing a sample for an analyte, comprising:

• providing a source of a sample;
• providing an aspirating probe which comprises a probe tip and a pump, wherein the probe tip and pump are in fluid communication;
• measuring a reference pressure which is the pressure inside a metering tip when no dispense or aspirate is occurring (Pref);
• moving the tip into the liquid, whereby a volume of gas is located between the top of the liquid and the pump, wherein the reference pressure is measured before or after the tip enters the liquid;
• actuating the pump for a duration or distance which corresponds to a selected volume of liquid to be aspirated;
• stopping the aspirate or dispense;
• measuring the pressure (Pstop) inside the tip at a time (t) which is the time when the aspirate or dispense is stopped;
• measuring the pressure (Pstop′) inside the tip at a time (t′) after t;
• estimating viscosity as a function of Pref, Pstop, and Pstop′;
• compensating for viscosity by either notifying an operator if the estimated viscosity is outside a pre-determined range, or adjusting the actuation of the pump based on the estimated viscosity.