DD275922B5 - ARRANGEMENT FOR ELECTROTHERMIC ATOMIZATION - Google Patents

Description

For this 1 page drawing

The invention relates to an arrangement for electrothermal atomization according to the preamble of claim 1. It can be used in the device technology for atomic absorption, atomic emission and atomic fluorescence spectroscopy. In flameless atomic absorption spectroscopy, it is customary to use so-called semi-open furnace systems according to the Massman principle, according to which a cylindrical graphite tube of 20-30 mm in length and 4-8 mm in inner diameter simultaneously acts as heating element and analysis cuvette.

The graphite tube is clamped at the front between two graphite electrodes and is completely surrounded by a cylindrical graphite protective sheath in two water-cooled metal blocks. From both sides of the tube, the graphite tube is surrounded inside and outside by inert gas. The protective gas supply, which takes place symmetrically to the tube end faces, is designed so that the protective gas enters the cavity between the cuvette window and the tube end face and gas flow channels as an inner gas flow in the space between the cuvette window and tube face and as an outer gas flow between the graphite protective jacket and outer tube surface. Both gas streams are directed towards the center of the graphite tube and leave the cell system via a dosing channel. The function and task of the gas streams is to protect the graphite pipe and all other graphite parts from burns caused by atmospheric oxygen, dissipate interfering sample decomposition products which are produced in the pretreatment stages drying and incineration as smoke or vapor and, if necessary, the density distribution of the released analysis atoms in the cuvette space spatially and temporally to control. Known solutions are described in DE-PS 2413782 and DE-OS 3228245 and DD-WP 200050 and DE-AS 2413782. It is also known that the internal gas flow shortly before the release of the analysis atoms, d. H. shortly before the atomization step, to interrupt, in order to achieve a spatially limited, symmetrical atomic vapor volcano with a high density and residence time in the tube center region (DE-AS 2314 207). This is supported in DD-PS 213063 in that during the atomization phase, an increase in pressure takes place. The invention is now based on the task to increase the analytical sensitivity and reproducibility in a simple manner and with little technical effort.

For this purpose, the loss mechanisms acting on the atomic cloud in the atomization phase should be further reduced or eliminated

 The object is achieved in a generic arrangement by the characterizing features of the first claim.

It is particularly advantageous in this case that the inner and outer SchuUg & sstrom with fixed ratio to each other can be regulated

and both are interrupted at the same time in a defined manner, and thus an at least iweKe acting, the thermal expansion of the

Protective gas and thus also a dilution of the analyte atom density in the Atomisatorinnonraum counteracting separation

the resting inert gas volume between the atomizer interior and the supply channels takes place.

The invention further relates to an arrangement for electrothermal atomization, which in a two-part,

coolable housing feeds for an internal Schutzgssstrom in the axial direction through an atomizer tube with radial

Center hole containing, between two hermetically interconnected, centrally perforated electrodes and axial

angre'-end, closed by windows closed cavities and surrounded by an annular space, the

Guiding an outer protective gas flow through holes in the electrodes with one concentric to the tube axis

extending annular channel in each housing part is in communication.

Pie supplies for the inner protective gas flow have a fixed aspect ratio to the holes in the electrodes

and are formed by at least one outgoing from each annular channel connecting channel which opens into the cavity. Each connecting channel has at least temporarily acting, a thermal expansion of the protective gas and the

Atomic cloud mitigating resistance elements. Advantageously, at least one nozzle is provided in each connecting channel as an expansion-reducing element

simultaneously establishes a fixed ratio of internal to external inert gas flow.

In other advantageous embodiments, each connecting channel has flow resistances at its outlet opening Form of porous means, or each connecting channel is mechanically controllable temporarily vorschließbar. By the solution according to the invention, the effective residence time of the atomic cloud in the Meßstrahlengang is further increased because the

thermal expansion of the inert gas, which transports the atoms from the hot zone of the atomizer tube in the direction of the pipe ends to the cuvette window and in the gas supply system is limited. In addition, the suction effect via the pipetting opening is canceled by a simultaneous throttling or interruption of inner and outer inert gas flow.

It expand the measures according to the invention the applications of flameless atomization

Previously in the border area of the Nechweisvermögens lying applications, or an analysis is made possible in the first place.

Ausfuhrungsbeltplel The invention will be explained in more detail below with reference to the schematic drawing. The figure shows a cut

through a graphite tube cuvette.

An atomizer tube 1 designed as a graphite tube and having a radial center bore 2 as the pipetting opening is used by

two, provided with openings 3.4 electrodes 5, β, which are fitted in cooled housing parts 7,8 and connected to the outside hermetically held. At the openings 3, 4 borders axially by Küvettonfonster 9,10 vorschlossene

Cavities) 11,12 on. With the center hole 2 a Doslerkanal 13 is aligned. An annular space 14, the Atomisatorrohr the first

surrounds, is about holes 15 in the electrodes 5.6, each with a tube x-x concentric to the tube axis

Ring channel 16,17 and with the pipette opening 13 in conjunction. Of the Ringkanälon 16,17, which serves for gas supply Have connection piece (not shown), go connection channels 18,19 to another, axially offset in the window direction Ring channels 20,21, which open into the cavities 11,12. In the connecting channels 18,19 nozzles 22,23 are introduced,

which are in a fixed aspect ratio in a range of 1: 5 to 1:15 to the holes 15.

To change the atomizer tube 1, the graphite tube cuvette is to be opened by separating the housing parts 7, 8 from each other. The temperature in the atomizer tube 1 is connected by a non-illustrated temperature sensor in conjunction with elnor Control unit controlled or determined by a temperature adjustment algorithm, not the subject of this invention

is. In the latter variant can also be dispensed with the temperature sensor.

Such a temperature setting is z. B. in DD-WP 200823 described. The inert gas of an adjustable by computer Gasquello (not shown) is about the connecting pieces in equal amounts

divided on each of the ring channels 16,17, which serve as collecting channels. There is a splitting into outer

Protective gas streams 24 and inner Schutzgasströmo 25, the ratio of each other by the cross-sectional ratios

the bores 15 is determined to the nozzles 22,23. The nozzles 22, 23 also have a limiting effect on the expansion

Atomic cloud in the atomization phase, since the acting gas outlet surface of the nozzles 22,23 is very small in relation to Area cross section of the cavities 11,12. The nozzles 22,23 form over the very fast expiring gas expansion

infinitely large flow resistance.

The entering into both cavities 11,12 inner protective gas streams 25 first wash around the cuvette window 9,10 and

then proceed to the center of the atomizer tube 1 before the common exit with the outer protective gas streams 24 takes place through the metering channel 13.

If you work with gas in the gas phase or reduced gas flow during the atomization phase, pass through the common

and simultaneous regulation of external and internal inert gas streams 24, 25 does not have a suction effect on the atomic cloud. The simultaneous gas stop or the reduction of the gas flow of the protective gas streams 24,25 can therefore be realized, since the graphite tube cuvette Ober has a highly effective lip seal 26 for shielding against atmospheric oxygen. The inert gas volume of the outer protective gas streams 24 that is expanding in the atomization phase prevents the short-term

Entry of atmospheric oxygen via the metering 13th Another possibility, during the atomization expansion restricting on the gas volume and thus on the Atomic cloud to act, can be realized that in the connecting channels 18,19 flow resistance in the form of

porous agents, such as. B. frits, sintered bronze o. 8, are provided.

Finally, it is possible in a further variant, the connection channels 18,19 mechanically and controllable to temporarily

preclose.

Since these two possibilities are readily realizable by the person skilled in the art, let me turn to a graphic representation

waived.

Claims (7)

An electrothermal atomization apparatus comprising an electrically heatable atomizing tube in which an atomizing cloud is produced and gas guide channels for generating an inner and outer shielding gas flow, characterized in that between the atomizing tube and the gas supply channels for the inner and outer shielding gas flow Resistance elements are arranged to reduce the thermal expansion of the inert gas formed from inert gas and the cloud of analytical gas volume. 2. Arrangement for electrothermal atomization according to claim 1, characterized in that the provided with a radial center hole atomizing tube is surrounded by a two-part, coolable housing with the gas supply channels for the inner gas flow in the axial direction through the atomizing tube, wherein the atomizing tube between two hermetically with each other connected, centrally perforated electrodes and axially adjacent, closed by window cavities and is surrounded by an annular space which communicates with the supply channels for the outer protective gas flow in the form of holes in the electrodes, each extending concentrically to the tube axis annular channel in each Guide housing part, communicating. 3. Arrangement for electrothermal atomization according to claims 1 and 2, characterized in that the gas supply channels for the internal gas flow are formed by at least one outgoing from each annular channel connecting channel to the cavity and having a fixed relationship to the holes in the electrodes, wherein the resistance element is arranged in the connecting channel. 4. Arrangement for electrothermal atomization according to claims 1 to 3, characterized in that the fixed ratio between the inner and outer protective gas flow is in a range of 1: 5 to 1:15. 5. An arrangement for electrothermal atomization according to claims 3 or 4, characterized in that a nozzle is provided as the resistance element, which simultaneously establishes a fixed ratio of inner to outer gas flow. 6. An arrangement for electrothermal atomization according to claims 3 or 4, characterized in that there are provided as resistance element flow resistances at the outlet opening of the connecting channels in the form of porous means. 7. An arrangement for electrothermal atomization according to claims 3 or 4, characterized in that the resistance element is mechanically controllable and temporarily closed.