Automated clinical chemistry analyzers are well known in the art and are generally used for the automated or semi-automated analysis of patient samples. Typically, prepared patient samples, such as blood, urine, spinal fluid and the like, are placed onto such an analyzer in sample containers such a test tubes. The analyzer pipettes a patient sample and one or more reagents to a reaction cell or cuvette where a chemical analysis of the sample is conducted, usually for a particular analyte of interest, and the results of the analysis are reported.
Automated pipettors are employed on such analyzers to transfer the patient samples and reagents as required for the specified analysis. Such pipettors can include a hollow probe having an open end or tip. The probe is, for example, lowered into a sample container that holds a sample, a predetermined volume of sample is withdrawn from the sample container, and the probe is withdrawn from the sample container. The probe is moved, for example, to a position above a reaction cell, is again lowered, and the sample held in the probe is expelled into the reaction cell. Similar actions may be used to pipette and deliver one or more reagents from reagent containers to the reaction cell, either with the same probe or with one or more reagent delivery probes.
To prepare such a probe for a subsequent delivery, the probe is washed to eliminate as much as possible any residue from the prior samples or reagents that were handled by the probe. Probe washing may be accomplished by, for example, lowering the probe tip into a wash cell that contains a wash fluid such as water. The wash fluid washes the exterior of the probe tip, and the interior of the probe may be cleaned by aspirating and discharging the wash fluid or, alternatively, discharging a wash fluid through the probe into the wash cell.
A common problem with probe washing, however, is carryover, that is, the residual fluid or contaminates from a fluid that remain on or in or may be absorbed by the probe despite washing. This residue mixes with subsequent sample or reagents drawn into the probe and can interfere with subsequent analyses.
Another problem with probe washing is the time needed to move the probe to a wash station and accomplish the probe washing. Substantial time can be required to wash the probe. For example, if the probe has delivered a sample to a reaction cell, the probe must be raised, moved to a position over a wash cell, and lowered into the cell for washing. Once washing is done, the probe must again be raised and moved on to the next operation.
Still another drawback of prior systems is washing a probe that has been inadvertently inserted into, for example, a sample or reagent to a depth that conventional washing cups and cells can not clean. Probes often include or are provided externally with some form of liquid level detection. This allows the probe to be inserted until the tip touches the surface of the liquid, where liquid contact is sensed. The probe may then be lowered an additional distance sufficient for the volume of liquid to be drawn into the probe or may be lowered as liquid is drawn into the probe. In either instance, only a relatively short, predetermined portion of the outside of the probe tip is contaminated with the liquid. Thus, the probe tip can be cleaned in a conventional wash cell or cup that is required to clean only a short portion of the probe tip, reducing cleaning time and the volume of washing liquid required.
If the liquid level sensing used to detect the contact of the probe tip with the surface of the liquid should fail, however, the probe will be lowered some predetermined distance that may represent the maximum insertion distance permitted to avoid the probe tip striking the bottom of the liquid reservoir. If the vessel actually is full or substantially full of liquid, the entire length of the submerged probe exterior becomes contaminated with the liquid. This length may well exceed the probe length that can be accommodated by the washing cell or cup, requiring operator intervention to manually clean the probe and return the probe, and the automated analyzer in which the probe is used, to service.
Thus, there is a need for a probe washing apparatus and method of use of such an apparatus that overcomes these limitations of the prior art probe washing approaches, including but not limited to reduced carryover, decreased probe washing time, and variable exterior probe tip lengths that may be coated with contaminating liquids.