IE46941B1 - Sample tube mounting - Google Patents

Abstract

The graphite tube cuvette for flameless atom absorption spectroscopy holds the graphite tube between two annular contact pieces connected to current conductors and allows axial passage of measurement beams along the tube. The contact pieces are arranged in relatively movable and differently biassed housing components. The cuvette is designed to facilitate replacement of graphite tubes. Both housing components contain slots for press-in cooling pipes. Each component has parallel opposite faces with circular borings for contact piece insertion. U-shaped cooling pipe slots are positioned about the circular portions and connected together via an external U-shaped tube.

Description

This invention relates to graphite tube atomisers for flameless atomic absorption spectroscopy and is particularly concerned with the mounting structure for the graphite sample tube used therein. Such mounting structure includes a pair of electrode members for supporting the ends of the sample tube and for applying heating current therethrough and each supported by a respective cooling jacket housing.

It has been proposed to make the structure in two 10 relatively movable portions each including an electrode member and its associated cooling jacket housing. The cooling jacket housings have needed machined passages for coolant and these have presented certain problems. When used over extended periods, eddies are generated within the passages and have prevented the necessary cooling of the cooling jacket assembly and electrodes. Furthermore, since the cooling jackets are subjected to heavy, thermal stresses, very fine pockets and crevices in the material may develop and may result in leaks in the passages and the corresponding development of steam or vapourised coolant.

According to the present invention the cooling jacket housings have co-axial apertures, each for supporting one of said electrodes, with power actuating means for separating the housings to enable the removal of the sample tube and each housing includes in close proximity to the respective electrode supporting aperture, a channel containing a seamless coolant tubing for carrying a flow of cooling liquid. Such a structure provides greatly improved cooling without the possibility of coolant leakage, and the cooling jacket housings are separable to permit easy inspection of their bores. - 3 An example of a structure in accordance with the invention is illustrated in the accompanying drawings, in which:Figure 1 is a sectional elevation? Figure 2 is a perspective view illustrating the positioning of coolant tubes within cooling housing channels; and Figure 3 is an elevation of the apparatus illustrated in Figure 1 showing cooling jacket housings in a pivotally separated position.

Xn flameless atomic absorption spectroscopy, a sample material to be analyzed is admitted into the bore of a sample tube which is subjected to a very high heat, so that the sample, upon entering the tube, is atomized. The analyzing beam of the spectroscope is then directed through the bore of the sample tube and the atomized contents may then be quantitatively analyzed. In most instances, the sample tube is a graphite tube that is electrically heated to temperatures that range up to approximately 3,000°C. It is therefore apparent that the apparatus closely associated with the sample tube must be provided with adequate cooling facilities to prevent damage from the high heat.

FIG. 1 is a sectional elevation view of the apparatus for supporting and heating a graphite sampler tube 10 provided with a radial sample inlet aperture 12 located near the center of the tube. The ends of graphite tube 10 are slightly tapered to provide a flat beveled surface that engages the conical internal surfaces 14 of electrodes 16 and 18 at the opposite ends of tube 10. Electrodes 16 and 18 are circular in cross-section and are fitted into corresponding apertures in cooling jacket housings 20 and 22, respectively. Housings 20 and 22 are preferably rectangular with parallel end faces 24 and 26 on housing 20 and parallel faces 28 and 30 on housing 22. Electrodes 16 and 18 are provided with flanged inner ends 32 and 34 and end faces 26 and 28 are normally separated from each other by the amount necessary to provide for the - 4ίι flanges 32 and 34. Flange 34 is wider than corresponding flange 32, since flange 34 must be provided with a sample admitting port 36 which is co-axial with the aperture 12 in the sample tube 10.

When electrical current is applied to the electrodes 16 and 18 and the sample tube 10 is heated to its elevated temperature, it is apparent that heat will be readily conducted from the tube 10 through the electrodes 16 and 18, the housings 20 and 22, and also to the tubular inserts 38 and 40 which may be provided to carry transparent windows (not shown). This excessive heat will obviously cause damage to the component parts of the apparatus unless adequately cooled. Therefore, housings 20 and 22 are provided with U-shaped cooling channels, such as the channels 42 in the end face 24, channel 44 in the end face 26, channel 46 in the end face 28, and channel 48 in the end face 30. Each of these channels is in close proximity with the respective housing apertures containing the electrodes 16 or 18.

FIG. 2 is a perspective view of the cooling jacket housing 20 and illustrates the U-shaped channel 42 in the surface 24 and the channel 44 in the surface 26, each surrounding and co-axial with the aperture 50 which supports the electrode 16 and tubular insert 40 of FIG.1.

It will be noted from an examination of FIG. 1 that cooling jacket housings 20 and 22 are identical in order to simplify and therefore reduce the cost of manufacture.

As best illustrated in FIG. 2, the U-shaped channels 42 and 44 do not directly carry a coolant but support a seamless tubing 52 which is tightly pressed into the channels 42 and 44. Prior to its installation, tube 52 is preferably filled with a low melting point bismuth alloy, such as Wood's metal, and the tube is then firmly pressed into the channel to thereby insure good heat transfer.

After installing the tube 52 first in the U-shaped channel on one surface, such as surface 24, and then bending the tube to engage the channel 44 in the second surface 26, the bismuth alloy is melted from the tube 52. Thereafter, 40941 when in operation, liquid coolant is supplied to and drawn off through connectors 54 in the tube 52.

As previously indicated, the housings 20 and 22 are identical and are mounted in a base unit in the channel between two parallel structures, such as the structure 56 of FIG. 1. The structures are interconnected by connecting block 58 at the end of the base unit adjacent housing 22 and by an intermediate connecting block 60, which is positioned to prevent the stationary housing 22 from moving about its pivot pin 62 which extends between the two parallel structures and through the bottom portion of the housing 22. The housing 20, which is identical with housing 22, is connected between the base structures, such as structure 56, by a pivot pin 64.

As shown in FIG. 2, each of the housings, such as the housing 20, contains a circular aperture 66, which extends completely through the housing. A hole 68 is drilled laterally through the center of the aperture 66 and, as illustrated in FIG. 1, supports a pin 70 within a slot 72 in a crosshead member 74. The aperture in housing 22 that corresponds to the aperture 66 in the housing 20, carries a reversible actuator 76 which is preferably pneumatic and contains a cylinder (not shown) that drives a piston rod 78 connected to the crosshead member 74. Air pressure applied to, or air withdrawn from the actuator 76 through its connector 80, will exert a force against pin 70 which will force the housing 20 to rotate about its pivot pin 64, as best illustrated in FIG. 3.

FIG. 3 is an elevation view showing housings 20 and 22 separated so that the graphite sample tube 10 may be readily removed from the electrode 34 and also to facilitate inspection of the bores or apertures in the electrodes 32 or 34. As shown in the figure, actuator 76, which is secured in the aperture of housing 22 by a pin 82, is extended so that its rod 78 and attached crosshead member 74 can exert a force against the pin 70 in housing 20 so that the housing 20 pivots about its pivot pin 64. - 6 Since the base of the housing 20 pivots in a channel between two base structures 56, it is free to move so that the bores of the electrodes 32 and 34 may readily be inspected for possible damage.

Claims (12)

1. CLAIMS:1. A sample tube mounting structure for flameless atomic absorption spectroscopy, including a pair of electrode members for supporting the ends of a sample tube and for applying heating current therethrough, the electrode members being supported by respective cooling jacket housings having co-axial apertures, each for supporting one of said electrodes, with power actuating means for separating the housings to enable the removal of the sample tube and in which each cooling jacket housing includes, in close proximity to the respective electrode supporting aperture, a channel containing a seamless coolant tubing for carrying a flow of cooling liquid.

2. A mounting structure as claimed in Claim 1 wherein each of the housings has two parallel surfaces substantially perpendicular to the axis of the aperture in the housing, each surface having a substantially U-shaped channel wherein the coolant tubing is fitted.

3. A mounting structure as claimed in Claim 1 or Claim 2 wherein one coolant jacket housing is in the form of an elongated rectangular member having the electrode supporting aperture adjacent one end and a pivot member adjacent the other end.

4. A mounting structure as claimed in Claim 3,and further including a power actuator coupled between the ends of the housing for pivotally moving the end remote from the pivot member away from the other housing.

5. A mounting structure as claimed in Claim 4 wherein the actuator is a pneumatic actuator.

6. A mounting structure as claimed in Claim 4 or Claim 5 wherein the two housings are substantially identical in structure and have a second pair of co-axial apertures. 941 - 8 that in the pivoted housing having a transverse pin engaging a slotted crosshead member attached to the piston rod of the power actuator, which is located in the aperture in the other housing.

7. A sample tube mounting structure for flameless atomic absorption spectroscopy substantially as described and as illustrated with reference to the accompanying drawings.

8. An electrode for use with a structure as claimed in any of claims 1-7 wherein the electrode comprises a sleeve shaped part having a cylindrical outer surface, an inner surface and a radial flange located at one end thereof, the radial flange having an end face, the inner surface having a cylindrical portion adjacent the flange', and first and second conical portions extending on the side of the cylindrical portion remote from the flange and wherein the inner surface of the first conical portion tapers inwardly from the cylindrical portion and the inner surface of the second conical portion flares outwardly towards the end of the part remote from the flange.

9. An electrode as claimed in claim 8 wherein, in use, the cylindrical outer surface is housed within one of the apertures of the structure so that the end face of the flange of the electrode faces the end face 469 41 of the flange of a second electrode of a type as claimed in claim 8, which second electrode is housed in the other aperture of the structure, the arrangement being such that a narrow slot is defined 5 between the faces of the flanges, and the sample tube is held between opposing first conical portions.

10. A pair of electrodes of the type as claimed in claim 8 or 9 wherein the flange of one of the electrodes is substantially thicker than the flange 10 of the other electrode so that, in use, the thicker flange extends beyond the middle of the Bample tube, and wherein a radial bore is provided in the thicker flange and is aligned, in use, with a radial bore of the sample tube. 15

11. An electrode as claimed in any of claims 8 10 wherein an annular groove is provided in the outer surface which, in use, communicates with an inert gas port in the housing and wherein an inclined inwards extending passage emerges from the annular groove 20 which opens into the annulus which is defined between the sample tube and the electrode.

12. An electrode as claimed in any of claims 811 substantially as hereinbefore described and with reference to the accompanying drawings.