Sample introduction assembly

Details Sample introduction assembly Sample introduction assembly

2000-11-03

2001-09-18

Pelham, Joseph (Department: 3742)

Electric heating

Heating devices

Combined with container, enclosure, or support for material...

C219S392000, C373S118000, C414S200000

Reexamination Certificate

active

06291802

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a sample introduction assembly for loading small samples into analytical crucibles for subsequent analysis and particularly to a seal system which prevents the admission of contaminants.
In analytical furnaces for combusting relatively small (1 mg to 0.5 gram) samples of, for example, steel pins, chips, or the like, typically resistance or induction furnaces are employed. Graphite crucibles are employed for resistance heating of a crucible directly when placed between a pair of electrodes. Ceramic crucibles are employed in furnaces in which heating is by an induction field provided by an RF coil. In either furnace, it is necessary initially to outgas the crucible and assure no contaminant gases are mixed with the specimen gases during loading of the sample.
In several prior art systems, it is necessary to open the combustion chamber area after the outgassing to gain access to a crucible for insertion of a sample to be analyzed. In doing so, the crucible is exposed to atmospheric gases which can contaminate the crucible to an extent that the analytical results can be adversely effected. In order to prevent the introduction of contaminants, one solution has been to provide a sample loading mechanism which allows the introduction of a sample into a movable hopper which is subsequently sealed and the area purged with an inert gas. The jaws of the hopper are subsequently opened to allow admission of the sample into the crucible through an electrode assembly. U.S. Pat. No. 4,371,971 discloses such an apparatus which, although preventing a direct communication path with the atmosphere during admission of the sample, may allow a small amount of atmospheric gases to enter the combustion chamber during the sample loading operation through the dynamic seals on the movable jaw actuator. With analyzers designed to measure oxygen and nitrogen content of a specimen, even miniscule amounts of atmospheric oxygen and nitrogen adds inaccuracy to analytical results, particularly for low concentration samples. Even with sealed sample dropped mechanisms where linear acting pistons move through radial seals, gases trapped in imperfections on the shaft surface are introduced to the analytical specimen, degrading the precision and accuracy of the measured amount of oxygen and nitrogen. Also, with time, atmospheric leakage increases as dynamic seals wear due to high cyclical use.
Accordingly, there exists a need for an improved sample introduction system in which contamination from atmospheric contaminants can be eliminated.
SUMMARY OF THE INVENTION
The system of the present invention solves this need by providing a sample introduction system in which a sample is introduced into a drop chamber which can be sealed and purged and which includes a movable jaw selectively holding the sample in position above a conduit communicating with an open crucible for receiving a sample once the jaw has been moved to an open position releasing the sample. The jaw is actuated by a magnetic field which moves the jaw in an enclosed environment, thereby preventing the introduction of atmospheric contaminants during the operation of the sample dropping jaw from a closed, sample holding position to an open sample releasing position. By providing a magnetic actuator, such as a solenoid, for operation of the jaw, the sample chamber remains sealed during the sample dropping operation preventing contaminants from interfering with the analytical results.
These and other features, objects and advantages of the present invention will become apparent upon reading the following description thereof together with reference to the accompanying drawings.


REFERENCES:
patent: 3899627 (1975-08-01), Sitek et al.
patent: 3936587 (1976-02-01), Sitek et al.
patent: 4056677 (1977-11-01), Berk et al.
patent: 4371971 (1983-02-01), Bredeweg
patent: 4510610 (1985-04-01), Hosokawa et al.
patent: 5314662 (1994-05-01), Hemzy et al.
patent: 5395586 (1995-03-01), Hemzy et al.

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