GB2152234A

GB2152234A - Atomizer cuvette for use in flameless atomic absorption spectrometry

Info

Publication number: GB2152234A
Application number: GB08432823A
Authority: GB
Inventors: Berndt Findeisen; Klaus-Peter Schmidt; Klaus Eichardt; Heinz Falk
Original assignee: Carl Zeiss Jena GmbH
Current assignee: Jenoptik AG
Priority date: 1983-12-30
Filing date: 1984-12-31
Publication date: 1985-07-31
Also published as: GB8432823D0; GB2152234B; DD221279A1; DE3442073C2; DE3442073A1

Abstract

An atomizer cuvette for use in flameless atomic absorption spectrometry comprising an open-ended hollow cylindrical body (1) with contact faces (10) at the open ends and a dosaging port (2) provided in the cuvette wall substantially in the central plane of symmetry (y-y). The cuvette has a cylindrical external shape and an internal shape which is defined by two collars (5,5') substantially at equal distances to one another and to the place of symmetry (y-y). The collars (5,5') subdivide the interior of the hollow cylindrical body into a central section (3) which is adapted to receive a sample material to be analysed and two lateral sections (4,4') adjacent to a respective one of the collars. The collars each have a "knife" edge (6,6') adjacent the central section. The ratio of the length of the central section to each end portion is 3:1, and the ratio of the wall thickness of the central section to one of the lateral sections is in a range of from 1.3:1 to 2.4:1. <IMAGE>

Description

SPECIFICATION Atomizer cuvette for use in flameless atomic absorption spectometry The invention relates to an electrically heated atomizer cuvette for use in flameless atomic absorption spectrometry. The atomizer cuvette serves to receive, to thermally decompose and to atomize a sample material, as well as to hold together a resulting atomic vapour cloud.

Atomizer cells which consist of graphite or pyrolitically coated graphite are generally known. These are of a tubular shape with smooth external and internal wall faces and provided with a dosaging port in the central portion of the tubular cell.

Electric current is fed in via both end portions of the cell which is supported by cooled electrodes, the contacting faces of which are matched to respective ones at the end portions of the tubular cell. The atomizer cell therefore has a temperature distribution with a higher temperature in the central portion and a lower temperature at both end portions.

Hence, a part of the sample material or of its components, after heating, condenses at the cooler cell portions and is again vaporized during the atomizing phase or, when very strongly wetting matter is concerned, is sucked in between the contacting faces and the electrodes, by capillary action.

Such effects prove to be disadvantageous in relation to the correctness and the reproducibility of the measuring data. There are already solutions known which try to overcome the temperature drop towards the end portions of the cell and the resulting measuring value departures. A substantially constant temperature course over the longitudinal extension of the atomizer tube is achieved according to DE PS 2148777, G 01 N. 21/54 by applying different electric resistances per unit length.

One embodiment of the latter Patent Specification comprises a tubular hollow cell which has a cylindrical external shape and an internal geometry which is adapted to realize a desired temperature gradient and which departs from the cylindrical shape. A central section has a comparatively thick wall; both end portions have a wall-thickness which at least corresponds to that of the central section; and in-between sections have a comparatively thin wall-thickness. This solution has the disadvantage that a sample material disposed within the cell upon the central section runs along the tube axis when heated or when very strongly wetting materials are concerned, particularly, when large sample volumina are involved so that the advantage obtained by the constant temperature course is at least partially lost.In order to prevent the sample material from running along the tube axis, another known atomizer cell disclosed in DE PS 2323774, G 01 N, 21/54 has at least a portion of the interior face of the cell provided with grooves, the courses of which are substantially at right angles to the axis of the tubular cell.

This solution has also the disadvantages of a non-uniform temperature distribution considered along the tube.

In DE-OS 2924123, G01 N, 21/74 a graphite tube is disclosed having a sample insert which is a flat mount made of pyrocarbon with an indentation for receiving the sample material. Though this graphite tube prevents the sample material from creeping along the internal wall of the tube, condensation of the sample material at the cooler end portions of the tube arising from a non-uniform temperature distribution is not eliminated.

It is an object of the present invention to obviate the above disadvantages.

It is a feature of the present invention to provide an atomizer cuvette which ensures correct and reproducible measuring results which are substantially independent of matrices in atomic spectrometrical measurements of sample materials, particularly of measuring volumina of greater 1 00 jul .

It is a further feature of the present invention to provide an atomizer cuvette for the flameless atomic absorption spectrometry which permits evaporation of a sample material at a place within the atomizer cuvette where it is disposed by a dosaging operation.

In accordance with the present invention, there is provided an open-ended atomizer cuvette of tubular shape and having a longitudinal axis of symmetry. A dosaging port is provided in the cuvette wall substantially in a plane of symmetry which is at right angles to said axis of symmetry. The cuvette has a cylindrical external shape symmetrical to said axis, an internal chamber which is subdivided by two collars equally spaced from said plane of symmetry into three sections, a first central section being enclosed by said collars, and two end portions, adjacent to a respective one of said two collars. The central section is defined at both ends by knife-edged collars which are necked-down relative to the central section.

The ratio of the length of the central section to the length of one of the two lateral sections is 3;1, and the ratio of the wall thickness of the central section to the wall thickness to one of the end sections lies in a range of from 1.3:1 to 2.4:1.

The ratio to be selected of the wall thickness of the central section to the lateral section depends on whether the sample to be analyzed is easily vapourized or not.

An element with typical vapourization behaviour is silver which has a boiling point of about 2200 K and requires a ratio of 1.7:1, whereas with elements which do not easily vapourize such as molybdenum with a boiling point of about 4800 K the ratio is 2.4:1. The collars and in particular the knife-edges provide an additional barrier against creep of the sample material in the direction of the longitudinal axis.

Advantageously, the collar faces in opposition to the open ends are curved, the centre of curvature being located within the respective lateral section. By this measure a continuous course of temperature and a better mechanical strength of the range of the cuvette where the wall thickness changes is obtained.

The invention is described further hereinafter, by way of example only, with reference to the accompanying drawing, which is a schematic sectional view of one embodiment of an atomizer cuvette in accordance with the present invention.

A tubular open ended cuvette 1, forming an atomizer cuvette for use in the flameless atom absorption spectrometry, has an external cylindrical shape and a longitudinal axis of symmetry x-x. The internal geometry of the cuvette 1 is defined by two collars 5 and 5' which are equally spaced in relation to a central plane (axis y-y) whch, in turn, is perpendicular to the axis x-x. The internal chamber of the cuvette 1 is subdivided by the collars 5 and 5' into a central section 3-which is provided with a dosaging port 2 for insertion into the central section 3 of a sample material to be analyzed, the dosaging port 2 being arranged substantially in the central plane (y-y)-and into a first lateral section 4, adjacent the collar 5 and a second lateral section 4' which is adjacent the collar 5'.The lateral faces 7 and 7' which are in opposition to one another form "knife" edges 6 and 6', respectively, with the circumferential portions 8 and 8' of the collars 5 and 5', respectively.

The lateral faces 9 and 9' of the collars 5 and 5', respectively, are curved so that the transition from the collar 5 and 5' tops to the respective interior walls of the lateral sections 4 and 4' is a gradual one. The centres of the curved lateral faces 10 and 10' lie substantially within the lateral sections 4 and 4', respectively.

The lateral sections 4 and 4' are provided with contact faces 10 and 10', respectively, for connection to heating electrodes (not shown).

According to the internal geometry, a practical embodiment of the atomizer cuvette 1 can have the following parameters: The external diameter of the cuvette 1 is 7.9 mm and the length 28 mm. The central section 3 has a length 12 1 5 mm and a wall thickness d, = 0.725 mm. The collars 5 and 5' have each a thickness d2 = 1.025 mm. The length of each lateral section 4 and 4' is 11 = 5.0 mm. measured up to the smallest part of the collars 5 and 5'. The wall thickness is d3 = 0.6 mm.

Accordingly, the wall thicinesses of the collars 5 and 5' the central section 3. and the lateral sections 4 and 4' satisfy the condition d2 > d, > d3 with respect to their wall thicknesses.

In operation, a sample material (not shown) is inserted through port 2 into the central section 3 of the cuvette 1. Upon the application of electric heating to the cuvette 1 via the contact faces 10 and 1 0', the sample material to be analyzed tries to move along the axis x-x over the entire cuvette 1 interior, but is.

however. retained by the edges 6 and 6', respectively. After vapour formation, the sample material cloud is substantially retained in the central section 3. Any cloud portions which evade into the lateral sections 4 and 4', respectively, do not condense on the walls of the sections 4 and 4' by virtue of the lengths and wall thicknesses selected so that a temperature distribution results having a slightly higher temperature in the lateral sections 4 and 4' than in the central section 3. The otherwise necessary components for an atom absorption spectrometry have been omitted for the sake of simplicity. These are well known in the art.

The invention is not retricted to the above described embodiment and the specific dimensional data given.

Also the curved faces 9 and 9' which serve to increase the mechanical strength of the cuvette 1 may have their centres of curvature outside of the respective lateral sections 4 and 4'.

An atomizer cuvette 1 according to the present invention enables precise and reproducible measuring results to be achieved in flameless atom absorption spectrometry.

Claims

1. An atomizer cuvette for use in flameles atomic absorption spectrometry, comprising an open-ended hollow cylindrical body having a longitudinal axis, and a wall symmetrically to said axis, a first and a second collar, a central plane of symmetry arranged at right angles to said axis, said first and said second collar being arranged within-said hollow body in parallel and equally spaced relation to one another and to said plane of symmetry, said first and said second collar each forming a narrowed passage in the interior of said hollow cylindrical body, said first and said second collar subdividing the interior of said hollow cylindrical body into three sections, namely, a central section included by said first and said second collar, and first and second lateral sections adjacent to said first collar and said second collar, respectively, said first and said second collar each having a lateral face in common with said central section, and an interior top face concentrically to said axis, the top face and the lateral face of said first collar and said second collar, respectively, forming a first and a second "knife" edge, said first and said second collar each having a curved lateral face in common with said first and said second lateral section, respectively, the curved lateral faces each having a centre of curvature, a port for introducing a sample material into said central section, said port being provided in said wall, substantially in said central plane, said central section, said first and said second collar, and said first and second lateral section having different lengths, considered along said axis, and different wall thicknesses, considered at right angles to said axis, the ratio of lengths of said central section to said first and second lateral section, respectively, being 3:1, the ratio of wall thicknesses of said central section to said first and second lateral section, respectively, being in a range of from 1.3:1 to 2.4:1, and the wall thickness of said first and said second collar, respectively, being greater than that of said central section.

2. An atomizer cuvette as claimed in claim 1, wherein said hollow cylindrical body is provided with contact faces for electrical contact.at the open ends of said cuvette, said contact faces coinciding with the respective end portions of said first and second lateral section remote from said first and second collars, respectively.

3. An atomizer cuvette as claimed in claim 2, wherein the centres of curvature of said curved faces lie within said first and said second lateral sections, respectively.

4. An atomizer curvette as claimed in claim 2, wherein the centres of curvature of said curved faces lie substantially on said axis outside of said first and said second lateral section, respectively.

5. An atomizer tube for use in flameless atom absorption spectrometry having a central dosaging hole and contact faces at its ends, the tube having a cylindrical external surface and a non-cylindrical internal surface, the structure of which defines different sections of the tube, namely a central portion for receiving a sample material and two end portions symmetrically disposed relative to a central plane of symmetry, the central portion being defined at both ends by knife-edged collars which are necked-down relative to the central section and the relation of the central portion to each end portion being substantially 3:1, as concerns their lengths and from 1.3:1 to 2.4:1 as concerns their wall thicknesses.

6. An atomizer cuvette substantially as hereinbefore described with reference to and as illustrated in the accompanying drawing.