Measuring and testing – Sampler – sample handling – etc. – Capture device
Patent
1993-08-05
1996-04-09
Noland, Thomas P.
Measuring and testing
Sampler, sample handling, etc.
Capture device
B01L 302
Patent
active
055050972
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention concerns a pipette comprising a cylinder which constitutes a cylinder volume with liquid passage; a plunger placed to be reciprocatingly movable in said cylinder volume; and a plunger-operating means for moving the plunger within the cylinder; said operating means comprising a body, a threaded rod, an operating member in cooperation by means of a thread with said threaded rod, and a power means for rotating the threaded rod and the operating member relative to each other; said body being connectable to the cylinder and the threaded rod/operating member combination, to the plunger, for moving the plunger by mediation of the threaded rod and the operating member when the threaded rod and the operating member are rotated relative to each other with the aid of the power means.
The filling of a pipette is based on producing a vacuum in the cylinder volume of the pipette by moving the plunger in the cylinder volume. At the same time, liquid which one wants to fill is conducted into the cylinder volume through the tip of the pipette. The true filling volume of the pipette, i.e., the volume of the liquid quantity that has entered the pipette, depends on quite a number of factors, e.g. the displacement volume of the plunger, ambient air pressure, which in turn is due to temperature and gravity, height of the liquid column inside the pipette, air space inside the pipette, inclination of the pipette (which affects the liquid column height), resilience of the plunger sealing, lifting of the pipette (which gives rise to a downward inertia force of the liquid column), tip leakage, adhesion forces between tip and liquid, etc. The air volume of the pipette, in particular, exerts a great effect on the pipetting accuracy.
For the reasons mentioned, the liquid volume, the true filling volume in connection with pipetting, differs from the corresponding displacement volume of the plunger by even as much as several per cent. The error is highest in high precision pipettes which are meant to be used in a wide operating range, e.g. from 10 .mu.l to 100 .mu.l or 100 to 1000 .mu.l. The highest error percentages are encountered at the lowest rated volumes, even up to 2 to 3%.
In practice, when the true filling volume of the pipette is considered in relation to the displacement volume of the plunger, at the beginning too little liquid enters the pipette, compared with the displacement volume of the plunger, possibly mainly owing to the air volume of the pipette. As operating the pipette is continued, its true filling volume approaches relatively the theoretical displacement volume of the plunger. Therefore the relative error is highest expressly at the lowest filling volume of the pipette.
SUMMARY OF THE INVENTION
The object of the present invention is to eliminate the above-mentioned drawback. It is in particular an object of the invention to provide a novel kind of pipette in which the difference between true filling volume and theoretical filling volume can be minimized.
It is in particular an object of the invention to provide a high precision pipette in the case of which the relative error between its true filling volume and its theoretical filling volume can be eliminated with substantially higher efficiency than in prior art also at low rated volumes.
The invention is based on that the thread of the threaded rod and/or the operating member is non-linear. The thread is advantageously non-linear in such a way that the non-linearity of the thread causes a non-linear, that is non-uniform, motion of the plunger. Thus, in the pipette of the invention, when the threaded rod and operating member are rotated relative to each other with constant speed, the true movement of the plunger, that is the displacement volume, is not uniformly consistent with the rotary movement, owing to the non-linearity of the thread and, for instance, the plunger displacement volumes corresponding to a given angle of rotation of the threaded rod/operating member combination are not consistent throughout t
REFERENCES:
patent: 3707107 (1972-12-01), Bier
patent: 4101283 (1978-07-01), Sundstrom
patent: 4346920 (1982-08-01), Dailey et al.
patent: 4554134 (1985-11-01), Tervamaki et al.
patent: 4671123 (1987-06-01), Magnussen, Jr. et al.
Ekholm Pertti
Suovaniemi Osmo
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