JP2842477B2 - Electrothermal reactor - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a furnace for atomic absorption spectroscopy, in particular for the electrothermal atomization of a sample of atomic absorption spectroscopy.

BACKGROUND OF THE INVENTION Electrothermal atomizers, typically heated graphite atomizers or graphite furnaces, are useful for atomically decomposing a sample with an atomic absorption spectrophotometer. Typically, the atomizer consists of an annular graphite contact or a tubular graphite member clamped between electrodes. A radial opening in the longitudinal center of the side wall of the tubular graphite member serves as a sample port for inserting the substance to be analyzed into the tubular graphite member.

In general, the contacts mounted in the cooling jacket are pressed by elastic resilient members or servomotors into tight engagement with the ends of the tubular graphite member. A strong current is passed axially through the tubular graphite member between the contacts, heating the graphite member to the high temperatures required to convert the sample into an "atomic cloud."

A light beam emitted from the light source passes through the annular graphite contact and the longitudinal hole of the graphite tube.
This light source has the resonance spectral lines of the target. The amount of target in the sample can be determined from the absorption of the measurement light flux. In order to prevent the rapid degradation of the tubular graphite member due to the high temperature oxidation required for the atomization of the analyte, measures are taken to enclose the graphite member in a flow of inert protective gas. In short, the graphite tube is surrounded by an inert gas so that oxygen does not come into contact with the graphite tube.

If the graphite tube is held at both ends, a non-uniform temperature distribution along the graphite tube will result. The graphite tube has a higher temperature in the central region than in the end region where heat is discharged to the cooler contact. This uneven temperature causes sample deposition on the cooler end of the tubular graphite member. The sediment redevaporates the tubular graphite member the next time it is used, contaminating the new sample.

A graphite furnace of the type described above is disclosed in U.S. Pat. No. 4,022,530. In this graphite furnace, the contacts are tubular rather than annular. Two contacts extend around the graphite tube and across the length of the graphite tube between the contact surfaces except for the separation gap. An inert gas flow is passed from both ends of the graphite tube into the graphite tube.
This inert gas stream is fed to the center through radial holes in the graphite tube. One of the tubular contacts is provided with a radial hole, which coincides with the radial hole of the graphite tube.

In order to obtain a more favorable temperature distribution along the graphite tube, it has been proposed to pass a heating current through the graphite in a transverse direction instead of a longitudinal direction. For this purpose,
According to U.S. Pat. No. 4,407,582, two pairs of interconnected contacts are used, which are formed as fork-shaped contact pieces and engage radially opposite graphite tubes. The heating current flows circumferentially through the graphite tube in the graphite end region. The graphite tube is heated in its end region and the heating current flows from the end to the center, resulting in a more uniform temperature distribution.

In this known contact configuration, the electrodes engage the hot portion of the graphite tube. Therefore, the repeatability of the contact characteristics is poor. Furthermore, it is difficult to protect the graphite tube from atmospheric oxygen by an inert protective gas stream.

U.S. Pat. No. 4,726,678 and the publication "Analytica
l Chemistry "58 (1986), 1973 discloses a graphite furnace in which a tubular furnace body has a rectangular cross section and has contact projections extending transversely to the axis of the furnace body. And the contact projections are formed as a single piece, the contacts being formed in the cold region by flat contact surfaces.

According to the prior art disclosed in U.S. Pat. No. 4,726,678, the contact protrusion between the contact surface and the furnace body has a reduced area of section. In one embodiment (FIG. 3), a recess is provided which extends in the longitudinal direction with respect to the furnace body, parallel to the furnace axis. These recesses or slots reduce the flow of heat from the furnace body to the contact protrusions and adapt the electrical resistance to the output of the electrical power supply. In another embodiment (FIG. 4), the contact projection has multiple openings. This configuration is said to be particularly suitable for setting a predetermined temperature profile. Current is supplied at appropriate points and flows through the furnace body to produce Joule heat. This arrangement is similar to the arrangement according to U.S. Pat. No. 4,407,582 except that the contact has been transferred to the cooler area.

In this known configuration, power is supplied unevenly along the tubular furnace body.

It is an object of the present invention to provide an improved new furnace for electrothermal atomization.

Another object of the present invention is to provide an electrothermally atomizing furnace capable of obtaining a uniform temperature distribution along a tubular furnace body.

It is yet another object of the present invention to provide a furnace that reduces the heat discharge of a tubular furnace body.

Yet another object of the present invention is to provide such a furnace which effectively protects against exposure to atmospheric oxygen.

[Means for Solving the Problems] According to one configuration of the present invention that has solved the above problems, there is provided an electrothermal atomization furnace unit for atomizing a sample for analysis by atomic absorption spectrophotometry, A tube-shaped furnace body for passing a light beam is provided, and the furnace body has a vertical hole and a central axis, and the furnace body is provided on opposite sides of the furnace body along the longitudinal direction of the furnace body. A contact projection is formed integrally, whereby a uniform current is supplied to the furnace body over the length of the furnace body, and the contact projection protrudes outward from the furnace body and has a terminal portion. A contact surface at the end of the contact protrusion is adapted to support the furnace body between the cooperating current supply contacts, the contact protrusion having a transverse central axis with respect to the furnace body, The contact protrusion has a reduced area between the end of the contact protrusion and the furnace body about the transverse central axis, the reduced area reducing heat discharge from the furnace body. And configured to increase the relative temperature of the reduced area during atomization of the sample, the reduced area including a portion of the contact protrusion, the portion being contacted along the lateral central axis. It has a cross-section that decreases progressively from the contact surface at the end of the projection toward the furnace body and then progressively increases toward the furnace body, and is substantially uniform along the central axis of the furnace body. Extending. The area of reduced cross-section is formed by cylindrical recesses on the upper and lower surfaces of the contact projection.

[Operation / Effect of the Present Invention] The substantially uniform current supply to the furnace body over the length of the furnace body is performed so that the furnace body is uniformly heated. The reduction in the cross section of the contact protrusion hinders the discharge of heat. In one aspect, the cross-section for heat dissipation is reduced. On the other side, Joule heat is generated in the area of reduced cross section, which acts to reduce the discharge of heat from the furnace body to the contact surface. Thus, a significantly more uniform temperature distribution in the furnace body with relatively cold contact surfaces results.

[Embodiment] According to FIG. 1 to FIG. 3, the furnace for performing electrothermal atomization of the present invention includes a tubular furnace body 10.
10 comprises a conductive material such as graphite which does not affect the absorption measurement. The contact protrusions 12 and 14 are formed integrally with the furnace body 10 so as to be diametrically opposed to each other. The contact projections 12 and 14 have contact ribs 16 and 18, respectively. As can be seen from FIG. 1, the contact ribs 16 and 18 have a trapezoidal shape as seen in FIG. 1, and the long sides 20 and 22 of the trapezoid face each other parallel to each other and in the longitudinal direction of the tubular furnace body. Located along. 24,2 cylindrical contact members
6 is formed integrally with the contact ribs 16 and 18 on the short side of the trapezoid. The cylindrical contact members 24, 26 have conical contact surfaces 28, 30 at their ends.

As can be seen from FIG. 2, the tube-shaped furnace body 10 and the contact projections 12, 14 are formed of substantially plate-shaped solid members, and have a substantially octagonal shape having an upper surface 31, a lower surface 33, and opposed side surfaces 35, 37. It is formed in a shape (see FIG. 1). Furnace axis 46
A longitudinal hole 32 is formed between the upper surface 31 and the lower surface 33 along the axis, which forms a tubular furnace. The contact members 24, 26 extend perpendicularly to the side surfaces 35, 37 as can be seen in FIG.

The axes of the contact members 24, 26 define a transverse central plane 47 which extends through the contact members 24, 26 transversely to the furnace axis 46 for convenience of description. The contact projection 12 has a pair of cylindrical recesses 34 and 38 on the upper surface 31 thereof. The recesses 34, 38 extend substantially parallel to the furnace axis 46 and are spaced apart from the transverse mid-plane 47, forming a reinforcing rib 48 therebetween. Corresponding cylindrical recesses 42, 43 (not shown) are likewise provided in the lower surface 33, and these recesses are likewise located away from the lateral center plane 47 to form reinforcing ribs 52. I'm sorry. Similarly, the contact projection 16 has cylindrical concave portions 36, 40 on the upper surface 31, between which a reinforcing rib 50 is similarly formed, and corresponding concave portions 44, 45 ( (Not shown) is formed on the lower surface 33, and reinforcing ribs 54 are similarly formed between these concave portions.

The recesses 34, 38, 42, 43 reduce the cross-section of the contact protrusion 16 and create a constricted or reduced-area 56 in the contact protrusion 16 that extends substantially uniformly along the length of the contact protrusion. . Similarly, the concave portions 36, 40, 44, 4
5 also creates a constricted or reduced-profile area 58 in the contact projection 18. The reduced cross-sectional areas 56, 58 are shaped and dimensioned to provide a substantially uniform power supply to the furnace over the length of the furnace body, thereby uniformly heating the furnace body. The reduced-section areas 56 and 58 prevent heat discharge to the furnace body. In one aspect, the cross-section for heat conduction is reduced by this cross-sectional reduction area. On the other side, the Joule heat increases in the area of reduced cross section, which acts on the reduced mass and keeps the reduced area of area hot, thereby reducing the heat discharge from the furnace body to the contact surface. Therefore, a very uniform temperature distribution is obtained in the furnace body and the contact surface is kept at a relatively low temperature.

Adjacent cylindrical contact members 24, 26 have axial holes 60, 62, respectively. The holes 60, 62 intersect the cylindrical recesses 34, 38, 42, 43, 36, 40, 44, 45 on both sides of the reinforcing ribs, whereby the openings 64, 66, 68, 70 (the 1) and a correspondingly formed lower opening (not shown) are formed for the outflow of the inert gas.

Reinforcing rings 72, 74 are formed in the bore 32 and spaced from its ends. The reinforcing rings 72, 74 support and guide the sample platform 76. For this purpose, the reinforcing rings 72, 74 are provided with U-shaped matching notches 78, 80. In particular, as can be seen from FIG. 2, a radial hole 82 is provided above the furnace body.

As can be seen from FIGS. 7-9, the sample platform 76 forms a square trough 84 with a cylindrical bottom. Protrusions 90,92 are provided on the end faces 86,88 of the trough 84, through which the sample platform 76 is supported in U-shaped cutouts 78,80. Protrusions 90,92
Has parallel sides 94, 96 and a bottom 98 with a trapezoidal cross section. Cross sections 94, 96 parallel to each other are U-shaped notches 78, 80
The bottom 98 is supported on the U-shaped curved portion 83 of the notches 78, 80. Thus, the sample platform 76 is supported in the furnace only by the projections 90,92. In that case, the sample platform 76 is heated primarily by direct radiation of the furnace, and no current is passed through the sample platform to generate heat within the sample platform.

In operation, the above-mentioned tubular furnace is supported between the two current supply contacts 100, 130, so that current is supplied to both current supply contacts 100, 130, contact members 24, 26 and contact ribs 1.
It is passed laterally through the furnace body 10 via 6,18. The electric current flows around the tubular furnace body 10 in the circumferential direction.

As shown in FIG. 4 and FIG.
100 has a cylindrical shaft 102 and a head 104. Head 1
A notch 108 is formed in the end surface 106 of the 04. This notch 108
Are formed so as to be compatible with the furnace body 10, the contact ribs 16 and the contact members 24, as indicated by broken lines in FIG. A conical contact surface 110 is formed at the bottom of the notch 108 so as to make electrical contact with the conical contact surface 28 of the cylindrical contact member 24 of the contact rib 16.

An inert gas conduit 112 opens at the bottom of the notch 108 adjacent to the conical contact surface 110. This inert gas 1
12 extends along the axis of the shaft 102 and has two holes 1
It is connected to the outer annular groove 118 via 14,116. Hole 1
14, 116 extend obliquely with respect to the axis of the shaft 102. The annular groove 118 is connected to an inert gas source when the current supply contact 100 is mounted in the atom supply spectrometer.

The head 104 is provided with a hole 120 in its peripheral wall, which matches the sample guide hole 82 of the furnace body 10 when the furnace is inserted into the current supply contact 100. Sample is hole 120
And into the furnace through a sample guide hole 82, which is also guided on a sample platform 76 located in the furnace.

The head 104 is provided on two opposite sides with two parallel flat parts 122,124. The plane portions 122 and 124 are parallel to the axis of the hole 120 and are aligned with each other.
It has. The axes of the holes 126 and 128 and the axis of the hole 120 lie in planes perpendicular to each other. The axes of the holes 126, 128 coincide with the axis 46 of the furnace, so that the measurement flux of the atomic absorption spectrometer passes through the holes 126, 128 and through the hole 32 of the furnace body 10 along the axis 46 of the furnace.

FIG. 6 shows a second current supply contact 130, which cooperates with the current supply contact 100 for furnace support. The second current supply contact 130 comprises a shaft 132 and a head 13
4 and the head 134 has an end face 136. In the assembled state, the end face 136 is the end face 10 of the first current supply contact 100.
6 short distance away. In that case, the two current supply contacts 100, 130 form a cavity containing the furnace. Furthermore, a cutout 138 is formed in the end face 136, which cutout 138 fits the contact ribs 18 and the contact members 26 of the furnace, as indicated by the dashed lines in FIG. The current supply contact 130 has a conical contact surface 140 adjacent to the notch 138, which contact surface 140
Engages the conical contact surface 30 of the contact member 26 in the assembled state.

An inert gas conduit 142 is provided on the shaft 132 adjacent the conical contact surface 140. This inert gas conduit 142 extends along the axis of the shaft 132 and opens into a conical contact surface 140. The inert gas conduit 142 communicates with the annular groove 148 of the shaft 132 through the oblique holes 144 and 146. The annular groove 148, like the annular groove 118, is connected to an inert gas source when the current supply contact 130 is installed in the atomic absorption spectrometer.

In the assembled state, the furnace is supported between the current supply contacts 100, 130, and the holes 60, 62 of the furnace are connected to the inert gas conduits 112, 142 of the current supply contacts 100, 130, respectively. Inert gas is supplied from the inert gas conduits 112, 142 to the holes 60, 62 and the openings 64, 66, 6
8,70 and further through the corresponding opening on the other side to the cavity formed between the current supply contacts 100,130, flowing through the furnace enclosure and surrounding the furnace with inert gas.
Thus, the furnace is isolated from contact with the atmosphere and combustion of the furnace at high temperatures is prevented.

As described above, in the electrothermal atomization furnace according to the present invention, a uniform temperature along the furnace body is obtained and the heat emission is reduced. In addition, there is an effective barrier to atmospheric oxygen.

As will be apparent to those skilled in the art, the above configuration is one example, and the present invention is not limited to this embodiment.

[Brief description of the drawings]

FIG. 1 is a plan view of one embodiment of the present invention, FIG. 2 is a side view of the embodiment as viewed from below in FIG. 1, and FIG. 3 is a portion taken along a vertical axis 46 shown in FIG. FIG. 4 is a side view partially showing one of the contact members of the spectrometer, FIG. 5 is an end view of the contact member viewed from the right side of FIG. 4, and FIG. 6 is a spectrometer. FIG. 7 is a plan view of a sample platform used in a furnace, FIG. 8 is a view of the sample platform viewed from the left side in FIG. 7, FIG. 9 is a side view showing the sample platform partially in section, and FIG. 10 is a longitudinal sectional view showing one embodiment of the present invention in an assembled state. 10 Furnace body, 12, 14 Contact protrusion, 16, 18 Contact rib, 24, 26 Contact member, 28, 30 Contact surface, 46 Axis, 48, 50 Reinforcing rib , 56,58 ……
Cross-section reduction area, 60, 62 ... hole, 72, 74 ... reinforcing ring, 76
…… Sample platform, 78,80 …… Notched, 90,92
…… protrusion, 100,130 …… Current supply contact

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Gunter Radel Aubingen Hinter den Garten, Federal Republic of Germany 13 (56) References JP-A-1-288755 (JP, A) JP-A-58- 41338 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G01N 21/00-21/74

Claims (11)

(57) [Claims] 1. A furnace unit for atomizing electrothermally for atomizing a sample for analysis by atomic absorption spectrophotometry, comprising a tubular furnace body through which a light beam passes. The furnace body has a vertical hole and a central axis, and contact projections are integrally formed on the mutually facing sides of the furnace body along the longitudinal direction of the furnace body, whereby the length of the furnace body is reduced. A uniform current supply to the furnace body, the contact protrusions projecting outwardly from the furnace body and having terminal portions, and the contact surfaces at the terminal portions of the contact protrusions cooperate with each other. Adapted to support the furnace body between the supply contacts, wherein the contact protrusions have a transverse central axis with respect to the furnace body, each contact protrusion being between an end of the contact protrusion and the furnace body. A reduced cross-sectional area about the transverse central axis, which reduces heat removal from the furnace body and increases the relative temperature of the reduced cross-sectional area during sample atomization. Wherein the reduced cross-sectional area includes a portion of a contact protrusion, the portion being progressively progressive from the contact surface at the end of the contact protrusion to the furnace body along the transverse central axis. An electrothermal atomizer, characterized in that it has a cross-section that decreases gradually and then increases progressively towards the furnace body and extends substantially uniformly along the central axis of the furnace body. 2. Each of the contact projections has an upper surface and a lower surface arranged opposite to each other, and the cross-sectional reduction region has a plurality of pairs of mutually spaced cylindrical recesses provided on the upper surface and the lower surface. 2. The reactor according to claim 1, wherein the recess is formed by a hollow portion, and the concave portion extends parallel to a vertical hole of the furnace body. 3. The contact projection comprises two longitudinal contact ribs located opposite to each other, said contact ribs forming a reduced cross-sectional area, and a cylindrical contact member is provided with said contact rib. The atomization furnace according to claim 1, wherein the terminal rib is formed integrally with the contact rib. 4. The reactor according to claim 3, wherein the contact member has a conical tapered end forming a contact surface. 5. Each of the contact ribs has a trapezoidal upper surface and a lower surface facing the upper surface, and the trapezoidal upper and lower surfaces of the trapezoid have long sides parallel to each other adjacent to the furnace body. 4. The contact rib according to claim 3, wherein the contact rib has a cylindrical recess extending from the trapezoidal short side, and the upper and lower surfaces of the contact rib are parallel to the furnace body and form a reduced cross-sectional area. Nuclear reactor. 6. A central reinforcing rib is provided on each side of the contact rib, the reinforcing rib extending perpendicular to the central axis of the furnace body and being connected to the furnace body and the contact rib. The reactor according to claim 5. 7. A gas supply hole extends transversely to the furnace body through said cylindrical contact members and contact ribs, intersecting cylindrical recesses on both sides of the reinforcing ribs. 7. The reactor according to claim 6, wherein an opening for flowing an inert gas is formed in the furnace. 8. The reactor according to claim 3, wherein a pair of reinforcing rings integrally formed at positions away from the ends of the furnace body are provided in the furnace body in longitudinal holes. 9. A stiffening ring having a mating U-shaped notch, a substantially rectangular sample platform provided, said sample platform having support projections extending from each end, said support platform comprising The protrusion is
Claimed within the notch of the stiffening ring for support of the sample platform, the support protrusions form the only area of contact with the furnace body, whereby the sample platform is heated, for the most part, by radiation Item 10. A nuclear reactor according to item 8. 10. A current supply contact unit for supporting a furnace body and for supplying an electric current through a contact surface, the current supply contact unit comprising a cooperating first and second contact member. A first contact and a second contact, wherein both contact members are configured to form a cavity between the contact members and cooperate with each other to receive a furnace body within the cavity. A member has first and second conical contact surfaces opposing each other, each contact surface tapering to the conical shape of the cylindrical contact member for mounting a furnace body in the cavity. The reactor according to claim 4, wherein the reactor is formed so as to engage with the terminal portion. 11. A first contact member comprising a head having an end face, said end face being provided with a first notch, said first notch forming part of said cavity and a furnace. The first part is configured to receive a part of a body;
Notch has an inner surface forming a first cylindrical contact surface, the first contact member has a first conduit for flowing an inert gas to the first notch, and a second Has a head with an end face, a second notch is provided in this end face, and this second notch is
A second notch configured to form a portion of the cavity and receive a portion of the furnace body, the second notch having an inner surface forming a second conical contact surface; 11. The reactor according to claim 10, wherein the contact member has a second conduit for flowing an inert gas into the second notch.