FR2563915A1 - SAMPLE HOLDER FOR FLAME-FREE ATOMIC ABSORPTION AND EMISSION SPECTROSCOPY AND MANUFACTURING METHOD THEREOF - Google Patents

Abstract

THE SAMPLE HOLDER IS CONSTITUTED BY RELAXED COLD PRESS OR COLD ROLLED UNDER HIGH PRESSURE GRAPHITE. PREFERREDLY, THE REALIZATION WAS CARRIED OUT BY STAMPING OF A GRAPHITE SHEET OBTAINABLE IN COMMERCE. THIS MANUFACTURING PROCESS IS VERY SIMPLE AND PARTICULARLY ADVANTAGEOUS.

Description

-1 - "Sample holder for absorption and emission spectroscopy

  flameless atomics and its manufacturing process ".

  The invention relates to a sample holder for spec-

  flameless atomic absorption and emission troscopy as well

  than a process for its manufacture.

  For flameless atomic absorption and emission spectroscopy with electrothermal excitation, a cuvette is used, in most cases a graphite tube, which fulfills a double function. It serves as a reservoir for receiving the sample, among others as a resistance element, that is to say as an oven for electric heating. In general, the sample to

  analyze is brought into solution and from this solution whatever

  ques / ul are injected, at the start of the analysis, into a lateral opening (filling opening) of the cuvette. Then, after a

  temperature-time program determined, the bowl is brought to

  temperatures up to the atomization temperature, which can reach up to 3000 C, depending on the element to be determined, and is then cooled. The following effects may occur with

  negative consequences for the achievement and outcome of the analysis

  lysis, during the immediate injection of the sample solution into the cuvette tube: Following infiltration of the sample substance into the wall of the cuvette, there may remain residues of a sample. Under certain conditions, these residues influence the result of the subsequent analysis carried out with the same cuvette (called "memory effect"). As a result of particle wetting process

  of the sample may extend over larger remote areas

  from the inner wall of the bowl and are therefore partially lost for determination. There is always a certain reactive interaction between the sample and the wall of the cuvette, which ultimately results in a reduction in service life

of the bowl.

  Spectrochim. Acta 35 B (1980) 701 is known a tech-

  sample entry nick, avoiding immediate contact

  -2- diat between the test substance and the wall of the cuvette. This is done by using small separate containers, which are placed in the bowl (slid, suspended). Such containers are indicated as sample holders, "platforms", "inserts" or "sample holders". The heating of the sample holder is preferably carried out by radiation through the wall of the cuvette and to a lesser extent also by thermal conduction. Given the

  extreme high temperatures of up to 3200 K used for the ab-

  sorption by flame-free atomic emission and absorption, the carriers

  The samples must be made of a material correspondingly resistant to high temperatures. On the other hand, the

  heating must be carried out for a very short time. He re-

  sulte the requirement that the mass of the sample holder in the case of a

  sufficient mechanical stability is kept as low as possible

  sible. Another necessity, that is to say making the sample holder

  as small (flat) as possible, results from the fact that once introduced into the bowl, it weakens as little as possible or

  otherwise affects the measurement radius passing through the cuvette.

  The volumes necessary for the reception of the sample are according to the system - from a few / μl up to approximately ul. As is customary, the sample to be analyzed can be introduced by injection into the sample holder already engaged, it can however also be introduced first outside the cuvette in the sample holder and introduced with this last in the bowl functioning as an atomization device. This cannot in particular be avoided when the sample is not present in dissolved form in an acid or other solvent but in a way

  direct as a solid body - for example as a metal - or mineral -

  shards of glass or stone, organic solid body, part of fabric

  su animal etc. Generally speaking, solid body samples

  have irregular shapes for volumes from 1 to

  ques mat. From this shape and irregular quantities, it results that an introduction by the filling opening most often

  very narrow (diameter approximately 1.5 to 2.0 m) is in practice

  sible. For the latter metering technique with separate filling -3-

  and insertion by following sliding in the atomizing device

  sation called "solid sampling" or "solid state sampling" by

  specialists, sample holders are essential.

  During "solid sampling", the function of the sample holder

  is reduced in many cases - where the substance of

  sample does not pass through a liquid phase with low viscosity or

  melting, for example during heating - at the respective fixing -

  ment to the location of the sample in the cuvette. Thus, it is possible to make the sample holder as a very flat cuvette-shaped reservoir with a useful volume of a few mm3 up to mm3 and thus satisfy the requirement of a passage also

  free as far as possible from the measuring radius.

  The sample holders offered by the manufacturers consist of very pure electrographites, which are carried in the form required by mechanical treatment - for example in the form of flat blades with a thickness of 1 mm, of rectangular shape, for example 5 mm x 12 mm with a cup-shaped recess obtained by milling and having a depth of 0.5 mm for a

  mass of about 80 to 100 mg. These sample holders are very com-

  pliqu6s for the realization, machining and further processing and

  are therefore relatively expensive. In addition, it presents the

  advantage of a fairly large thermally inert mass.

  The invention aims to provide sample holders (in-

  serts, platforms), which are at least equivalent, in terms of their performance, to known products, but which are very

  simple and which lend themselves in particular to a little costly realization.

  In accordance with the invention, this object is achieved by the fact that the sample holder consists of graphite expanded press6 to

  cold or cold rolled under high pressure.

  Preferably, the sample holder consists of a graphite sheet. In this case, a commercially obtainable graphite sheet offered by several manufacturers "Papyex" from Carbone Lorraine, "Sigraflex" from Sigri, "Grafoil" from Union Carbide) is used as starting material in different qualities and several dimensions. What these products have in common -4- is that they are made of pure graphite without the addition of binders

  by rolling loose graphite flakes under high pressure.

  The sheets and strips, which can be obtained in widths of 50 cm and lengths up to 50 m, have a very smooth surface. The thicknesses obtainable are between 0.1 to 0.35 mm. Of

  remarkable properties are the relatively low densities of

  about 1.0 g / em3 and the more or less intense anisotropy which is obtained

  is due to the fact that the graphite particles are preferably oriented parallel to the rolling direction as a result of the

  layer structure under the influence of rolling pressure.

  According to the manufacturer's instructions, these sheets of gra-

  phites are particularly suitable for cable gland seals and seals resistant to corrosion and high temperatures, but also as linings for ovens and protective screens

  thermal (in non-oxidizing atmospheres).

  However, it has been found that in the cold state, sheets of gra-

  phite of the kind described can be plastic deformed without destroying their structure to a degree sufficient to

  making small containers like the 4-sample holder.

  As a particularly suitable process, stamping has been found, by which sample holders are produced which satisfy

  all the requirements both with regard to the properties ggner-

  them as the useful volumes obtainable.

  A certain disadvantage of the leaves consists in the re-

  low mechanical resistance and, therefore, its susceptibility to

  damage during handling. In the normal state, among others, the leaves are quite active from the chemical point of view, especially at higher temperatures. This is explained by the fact that the edges of the reactive reticular plane of the laminated graphite particles whose

  the leaves are made up, represent a high number of cen-

  very active, both on the surface of the leaves and in the volume

  due to the high porosity. -

  In the case of sample holders made from

  sheets in which the mentioned reactivity is not express6-

  ment desired, for example as a reducer for oxide, it is -5effective to achieve an at least partial coating with graphite

  pyrolitic after the stamping process.

  Thus in reality three things are obtained: 1) As a result of heating to a separation temperature of approximately 2300 K under vacuum (pressure of 1073 mbar or a lower value), there is degassing of the fairly large volume of

  approximately 56% pore and subsequent vaporization

  tion of impurities which may be volatile under these conditions.

  2) The pyrolitic graphite layer acts in the direction of a passi-

  chemical vation of the leaf surface and ensures the seal

  as a barrier strongly limiting the diffusion of the volume

inside the pores.

  3) As a result of the presence of the pyrolitic graphite wrap

  that, the base sheet is reinforced mechanically. Thus, it can be more easily handled and is not subject to damage. When drawing the graphite sheet used as starting material, cracks may occur when the

  degree of deformation exceeds a certain upper limit. An au-

  be drawback occurs when the die (punch) has

  sharp edges as for example in the case of indentations

  sample cell holder. In this case, the cracks do not

  are hardly avoidable, especially at angles, curvatures and edges.

  Deformation free from damage has been found

  graphite sheet is also possible in the case of pro-

  wires with more or less sharp edges when the graphite sheet is

  provided with a stabilizing surface film. This is obtained by application

  cation by bonding a thin plastic sheet. For graphite tapes (characteristic dimensions: width 20 mm, thickness 0.2 to 0.3 mm for lengths up to 50 m) preferably used for the production of sample holders, suitable for example the self-adhesive tape like Tésa tape . Oddly enough, the possibility of stamping the graphite strip can be improved

  notably by a coating, carried out on one side or on both sides.

  During the graphite coating, process which follows the process -6-

  forging and cushioning, the applied strip is again

  practically quantitative lifting by depolymerization and evaporation, with care for the graphite sheet, in

  the heating phase (up to 2100 C under vacuum).

  For another preferred manufacturing process, the stabilizing film instead of a sheet applied by bonding - is applied by impregnation by immersion in a solution of

  polymeric substance. As particularly usable have been found

  impregnation with aqueous solutions of poly- alcohol

  vinyl and as preferred also the aqueous solutions of

  methyl cellulose (modified). A single immersion in a solu-

  Concentrated or saturated aqueous water of this kind already allows matri-

  drilling of a sample holder without cracks or other damage

  essential magements. The impregnation process can be repeated several times, each time with intermediate drying. The film

  polyvinyl alcohol or methyl cellulose which is not necessary

  that for the mastering process, is practically quantitative

  tively removed during the heating phase before the pyrolytic coating. Another advantage for intermediate stabilization using a film of polymeric substances is that the tensile strength and, therefore, the workability of the

  graphite sheet, preferably strip-shaped, are notable-

  improved. This last fact is very important for a coat-

  ment in continuous band mode.

  The invention offers the advantage of allowing, in a way

  particularly simple and advantageous, the production of

  samples as used for absorption anisotropy and

  atomic emission - especially for the so-called "solid state sam-

  pling "by cold rolling of expanded graphite under high pressure

  or by stamping graphite sheets obtainable in the com-

  thank you. This applies all the more since the process can be carried out

  also killed continuously, while the raw material is

  obtainable in practically endless strips (up to 50 m). In principle

  eg, it is possible to make two kinds of sample holders: -7- a) the stamped shape not covered

  b) the form subsequently covered with pyrolitic graphite.

  Form a) it is not very stable from the mechanical point of view, it is true, and, therefore, easily prone to damage; from the chemical point of view it is however relatively reactive and can act in a reducing manner at temperatures

  raised on a range of substances.

  Form b) it is more compact mechanically, therefore

  made, easier to handle and less prone to damage-

is lying.

  Compared to Form a), it is chemically passive. In addition, the infiltration of an analytical substance

  in the porous base material is blocked.

  What the two forms have in common is their low thermally inert mass. Given the low costs

  of manufacture, the question of recovery is not important

this (tank to throw away).

  The stamping process allows the rational realization-

  the and extremely advantageous (compared to other processes

  shaping, such as turning, milling and sawing. The por-

  The samples can be used immediately or after recoating.

  a protective layer of pyrolitic graphite. The plastic

  city of leaves is limited, so the bodies present

  quite often damage like holes and cracks.

  When these damages are of little importance, they can

  be covered in general during pyrolitic recovery (fi-

  nissage). The sensitivity to damage is significantly reduced when, before deformation, the graphite sheet is provided with a stabilizing film of deformable soluble volatile polymer material

  and volatile when using high temperatures (e.g.

times under vacuum).

  The invention will be explained in detail using the drawings and several exemplary embodiments. On the drawing

  Figure 1 shows in section in sample holder in form

me of a cap.

  Its figure 2 represents in perspective a sample holder

in the shape of a basket.

  Ia 2a shows in section along line A-A 'the sample holder according to Figure 2 and

  Figure 2b in section along line B-B 'the holder

sample according to figure 2.

Example 1

  As a starting material for temperature stamping

  ambient tite graphite sheets are used in the form of strips with a width of 20 and 25 mm, a thickness of 0.2 mm and

  0.3 mm and any length up to 15 m (product: "pa-

  Pyex N 'of Carbon Iorraine). When pressing "sinking" in the form of caps (Figure 1) it is determined that no damage occurs to the sheet structure when the ratio between the

  deformation depth t and the diameter of the cap D does not exceed

  if not the value t / D = 0.1 At values> 0.1i, cracks or

  ruptures. We carried sample holders fitted with such

  shell-shaped cements with diameters of 5, 9 and 11

  min. Of t%) ldiamntres corresponded to depths of deformation

  corresponding 0.5 and 1.0 to 1.1 mm. The depths of

  fundamentally h the caps necessary for the calculation of the "useful volumes" emerge from

  h = t - cS (cP = sheet thickness).

  For the values mentioned were calculated volumes

  useful of the sample holder of in = 3 mm3, 22 mm3 and 38 mm3.

  In addition, sample holders with shaped depressions

  bowl Vn = 10 mm3 and 20 m3 were made in a

  very fast and exact size lesson using a simple stamping device. The weight of such "bowls" is

about 20, respectively 35 mg.

  The sample holder was sealed according to the

  known methods of hot gas pyrolysis. The thicknesses of the layers

-9-

  applied graphite layers may vary within further limits

  tests between 1 and 100 / µm, depending on the requirement.

Example 2

  A strip of graphite sheet with a width of

  20 mm and a thickness of 0.2 mm was immersed once in a so-

  aqueous saturation of polyvinyl alcohol at room temperature

  biante (20 C) and dried. By determination of the weight, the thickness of the surface film thus produced was established at approximately 2 μmn. This

  film thickness is sufficient for pressing without cracks in a pen

  bowl-shaped cement with a length of about 10 mm, a width of 3 mm and a depth of 0.5 mm with sharp edges (R 0.5 mm), R being the radius of curvature inside the edges in question. By repeating, several times, the impregnation

  by immersion polyvinyl alcohol films were made (re-

  clothes) from 20 to 30 mm thick.

  By immersion, 10 times, in a saturated solution of metallic cellulose were obtained layers with a thickness of

  / um. During the following coating by a deposition process chi-

  mique from steam at 2000 C in C3H8 under a pressure of 2.0 mbar, duration 1 h, this "basket" (Figure 2) was covered

  a dense, corrosion-resistant layer of pyrolitic graphite

  than. This sample holder thus has a mass of approximately 30 mg.

-10-

Claims (7)

CLAIMS:   1. Sample holder for absorption spectroscopy and   flameless atomic emission, characterized in that it is made up of   killed by cold pressed cold rolled graphite or cold rolled under high pressure.   2. Sample holder according to claim 1, characterized in   what it consists of is a graphite sheet.   3. Sample holder according to claim 2, characterized in   what it consists of is a stamped graphite sheet.   4. Sample holder according to claim 2 or 3, character-   laughed at in that it is constituted at least partially by graphi- you pyrolitic.   5. Method for producing the sample holder according to a   or more of the preceding claims, characterized in that a   Before deformation, the graphite sheet is provided with a static film.   stabilizer made of deformable polymer material soluble and volatile in   the case of using high temperatures.   6. Proc6dé according to claim 5, characterized in that a   adhesive tape is glued to the graphite sheet.   7. Process according to claim 5, characterized in that the stabilizing film is applied by impregnation by immersion in   a solution of a polymeric substance.