GB2066981A

GB2066981A - Introduction of sample material into a graphite tube in atomic absorption spectroscopy

Info

Publication number: GB2066981A
Application number: GB8034519A
Authority: GB
Original assignee: Bodenseewerk Perkin Elmer and Co GmbH
Current assignee: PE Manufacturing GmbH
Priority date: 1979-11-12
Filing date: 1980-10-27
Publication date: 1981-07-15
Also published as: DE2945646A1; GB2066981B; DE2945646C2

Abstract

A device for introducing a solid sample into a graphite tube of an atomic absorption spectrometer comprises basically a small diameter tube 10 capable of fitting into the dosing opening of the graphite tube and a rod-like piston 18. The free end of the tube 10 receives and retains the sample and movement to the right of the piston 18 ejects the sample into the dosing opening. Movement of the piston 18 is controlled by a larger piston 24 which operates in a cylinder 22 under pneumatic pressure. The piston 24 can be given a pre-selected range of movement by co-operation of a spring catch 36 with one of a number of grooves 28. A retractable needle and a retractable "spoon" are also disclosed by which the sample is physically introduced into the dosing opening. <IMAGE>

Description

SPECIFICATION Introduction of sample material into a graphite tube in atomic absorption spec troscopy This invention relates generally to the intro duction of a sample into a graphite tube of an atomic absorption spectrometer and, in parti cular, relates to an apparatus for this purpose for use with solid or semi-solid sample mate rial and to a method of using such apparatus.

The conventional arrangement consists of a housing with a pair of electrodes between which a graphite tube is held. A heating current is led via supply leads and the elec 'trodes through the graphite tube, whereby the graphite tube is heated up to high tempera tures. In order to avoid burning the graphite tube a stream of protective gas is caused to flow around the graphite tube. The graphite tube usually has a dosing opening in its shell through which liquid samples may be intro duced via a tube.Solid samples, however, have had to be introduced through the end of the tube, for which purpose the housing with the electrodes, the graphite tube and the flexible supply leads for heating current and protective gas (and if necessary cooling water) is arranged to be movable between two posi tions, in the first of which the graphite tube is located in the optical path of the rays of the atomic absorption spectrometer and in the second of which the graphite tube is accessi ble from its end through at least one elec trode. In order to introduce solid matter into the graphite tube it is necessary to bring the tube out of its adjusted operating position into this second position. This is very cumbersome and presupposes special measures in order to bring the graphite tube out of its adjusted operating position and make the graphite tube accessible from its end.

According to the present invention solid or semi-solid sample can be introduced through the dosing opening of the tube, without the need for changing the position of the latter, by means of apparatus comprising a hollow tube for receiving and retaining the sample at one end thereof and having an outer diameter which fits through the dosing opening and means for ejecting the sample from the end of the tube which is preferably a rod-like piston slidably positioned within the tube.

Examples of apparatus in accordance with the invention wills now be described with refer ence to the accompanying drawings, in which:- Figure 1 is a longitudinal sectional view of one embodiment, not drawn to scale; Figure 2 is a longitudinal sectional view of another embodiment, also not drawn to scale; Figure 3 is a longitudinal sectional view of a third embodiment; Figure 4 is a partial longitudinal sectional view of a fourth embodiment; and Figure 5 depicts one step in the operation of apparatus in accordance with Fig. 4.

The apparatus shown in Fig. 1 comprises a small hollow tube 10, preferably of glass or the like, having an outer diameter which is less than the diameter of- a dosing opening 1 2 (see Fig. 5) in a graphite tube 14. The apparatus also includes means for ejecting a solid or semi-solid sample from the tube 10 constituted by a rod-like piston 1 8 slidably mounted in the tube 1 0. The tube 10 is preferably transparent and the piston 1 8 is coloured so that the position of the piston is immediately clearly visible to the user. In operation, the tube 10 is inserted into a holder 20 which, on the side remote from the tube 10, comprises a cylinder 22.The cylinder 22 guides a piston member 24 which abuts the rod-like piston 1 8 and which for reasons of weight, is provided with a blind drilled hole 26. The piston member 24 is also provided with annular grooves 28 of triangular cross section on the outer surface thereof. The cylinder 22 has on its outer surface a circumferential groove 30 which is connected to the inside of the cylinder 22 via a longitudinal slit 32 intersecting the circumferential groove 30. An annular spring 34 has at one end a U-shaped bent portion 36 which extends in a longitudinal plane and projects through the longitudinal slit 32 into the inside of the cylinder 22. This bent portion 36 serves as a catch by means of which the piston member 24 can be located in different positions by co-operation with the annular grooves 28.

A recess 38 with a restricted entrance is provided in the end of the piston member 24 on the side remote from the blind drilled hole 26. In the cylindrical wider part of the recess 38 are seated two O-rings 40. One end 41 of the rod-like piston 1 8 is inserted into the recess 38 and bears against the bottom of the recess.

The holder 20 has a neck 44 extending from the end of the cylinder 22 which has a central bore 46 opening into the cylinder 22.

The bore 46 widens to form a shoulder 48 on the side remote from the cylinder 22. The neck 44 is joined to a pot shaped end piece 50 in which the widened bore 46 continues into a funnel shaped enlargement 52. The tube 10 is inserted into the bore 46 until it rests against the shoulder 48. A conical rubber plug 54 provided with a longitudinal channel, through which the tube 10 is introduced is inserted into the funnel shaped enlargement 52 in the end piece 50. A cap nut 56 is screwed onto the end piece 50 whereby the rubber plug 54 is compressed and held in firm frictional contact against the glass tube 10, which is thereby secured in position. The piston is inserted to the bottom of the recess 38 and thereby connected to the piston member 24.Re-producible positions of the rod-like piston 1 8 in the glass tube 10 are accomplished by the grooves 28 and the catch 36 For introducing a powdery sample material the piston member 24 and hence the rod-like piston 1 8 is pulled back until the bent catch portion 36 snaps into one of the annular grooves 28. An annular disc 58, e.g. of polytetrafluoroethylene is pushed onto the tube 10 to enclose the tube 10 tightly. The free end of the tube 10 is then pushed, usually repeatedly, into a vessel containing the powdery sample In this way the powdery material at each push slides step by step further into the tube 1 0. The maximum amount picked up by the tube 10 is thus determined by the position of the rod-like piston 18.After filling. the annular disc 58 is pulled off the tube 10 thereby wiping off any sample material adhering to the outside of the tube 10. The tube 10, the outer diameter of which is less than the diameter of the dosing opening 1 2 in the graphite tube 14, can then be introduced through this dosing opening 1 2 into the graphite tube 14. In doing so care should be taken that the end of the tube 10 does not foul the inner wall of the graphite tube 1 4. Preferably, therefore, the apparatus just described is inserted in an automatic sample feeder such as is known for the introduction of liquid samples and which, by an automatically controlled arm, introduces the glass tube 10 to the correct position into the graphite tube 14.

The piston member 24 and with it the rodlike piston 1 8 is then pushed forward so that the piston 1 8 slides the powdery sample material out of the tube 10 and into the graphite tube 14.

For quantitative measurements the apparatus may be weighed both with the sample before the introduction into the graphite tube and without the sample after the emptying, for the determination of the weight of sample introduced.

Fig. 2 shows an apparatus which is particularly suitable for pasty sample material. In this embodiment the apparatus also includes a small tube 60, the outer diameter of which is less than the diameter of the dosing opening in the graphite tube. Again, one end of the glass tube 60 is inserted in a holder 62. This arrangement is essentially the same as in Fig.

1 and corresponding parts are provided with the same reference numbers as there.

The holder 62 includes a cylinder 22 as in the embodiment shown in Fig. 1, containing a movable piston member 66. The piston member 66 likewise includes an annular groove 28 of triangular cross section which can form a catch with a U-shaped bent portion of an annular spring (not shown).

The piston member 66 includes, on its end face remote from the blind drilled hole, a stud 68 with a head 70. On the stud 68 is seated an annular sealing ring 72 which bears by lips 74 and 76 against the stud 68 and the inner wall of the cylinder 22 respectively.

In operation, the apparatus shown in Fig. 2 is likewise pushed a number of times into a vessel containing the sample substance, so that the sample substance slides up step by step into the tube 60. Thereafter, an annular disc which has been pushed onto the tube 60 in a similar way to the disc 58 as Fig. 1, is pulled off the tube 60 to remove excess material adhering to the outside of the tube 60. For introducing the sample material into the graphite tube the tube 60 is introduced through the dosing opening 1 2 in the graphite tube 1 4. The piston member 66, previously pulled back as far as the catch position, is then pushed forward to force out the sample material by means of compressed air.

Here too the apparatus having the sample is preferably weighed by means of an analytical balance. After the withdrawal of the emptied tube from the graphite tube re-weighing of the apparatus is effected. The apparatus just described is suitable for introducing pasty samples like fats, pastes, shoe polish, lipsticks or ointments.

The apparatus shown in Fig. 3 is suitable for sample material in the form of fabrics, paper, sheets, foils or the like. This apparatus includes a sleeve 104 and a needle 106 slidably guided therein. The sleeve 104 at the end of which the sharp end 108 of the needle 106 projects, includes a section 110 of reduced outer diameter which is less than the diameter of the dosing opening 1 2 in the graphite tube 14. The needle 106 preferably includes, at its blunt end, a knurled knob 112.

For introducing samples of the kind involved here the sample is first shredded into pieces the dimensions of which are smaller than the diameter of the dosing opening in the graphite tube. These pieces are impaled on the needle 106 and are then introduced with the needle 106 and the section 110 of the sleeve 104 into the dosing opening in the graphite tube. By retracting the needle 106 via the knurled knob 11 2 the pieces are stripped off the needle after the introduction thereof into the graphite tube.

The apparatus shown in Fig. 4 is particu larly advantageous for handling crumbs, bones, stones, steels, hair and other solid bodies. This apparatus includes a cylindrical rod 114, e.g. of graphite, the diameter of which is less than the diameter of the dosing opening 1 2 in the graphite tube 14. A hollow spoon-like cavity 11 6 which has a cylindrical shell 11 8 andand end wall 1 20 has the shell 11 8 slipped, by its open end, onto a reduced diameter end part of the rod 114 so that the outer diameter of the spoon-part 11 6 is essentially equal to the diameter of the rod 114.

The spoon-part 11 6 can pick up solid bodies of sample material which are to be tested. As is illustrated in Fig. 5, the dosing opening 1 2 in the graphite tube 14 is preferably arranged at an acute angle to the vertical. The appa ratus 1 28 (Fig. 5) is introduced with the sample through the obliquely arranged dosing opening 1 2. After the introduction, the spoon like apparatus is rotated about 1 80" about its axis so that the crumbs, or the like, drop out of the spoon-part 11 6 into the graphite tube.

Claims

1. In combination with a graphite tube for the flameless atomic absorption spectroscopy of a solid or semi-solid sample, apparatus for introducing the sample through the dosing opening of the graphite tube and comprising a hollow tube for receiving and retaining the sample at one end thereof and having an outer diameter which fits through the dosing .opening and means for ejecting the sample from the end of the tube.

2. Apparatus as claimed in claim 1 wherein the ejecting means is a rod-like piston slidably positioned with the tube.

3. Apparatus for introducing a solid or semi-solid sample through the dosing opening of a graphite tube for the flameless atomic absorption spectroscopy of the sample, the apparatus comprising a hollow tube for receiv ing and retaining the sample at one end thereof and having its other end fixed within a holder including a piston cylinder extending in a direction away from the tube, a piston slidably located within the piston cylinder and a rod-like piston extending from the piston cylinder through the holder and into the hol low tube where it forms a sliding fit.

4. Apparatus as claimed in claim 3 wherein the rod-like piston abuts the piston.

5. Apparatus as claimed in claim 3 wherein the rod-like piston is fixed to the piston.

6. Apparatus as claimed in any one of claims 3 to 5 wherein the piston is capable of being selectively snapped into position within the piston cylinder.

7. Apparatus as claimed in any one of claims 3 to 6 wherein the holder includes a central bore having a shoulder therealong against which one end of the tube abuts, the other end of the tube extending beyond the holder.

8. Apparatus as claimed in claim 7 wherein the tube is fixed to the holder via a conical plug secured in the holder via a cap.

9. Apparatus as claimed in claim 3 wherein the rod-like piston serves as a means for ejecting the solid or semi-solid material from the hollow tube.

10. Apparatus as claimed in Claim 1 wherein the tube is provided with a sharp ended, needle-like member slidably mounted therein so that the sharp end projects from the tube to receive and retain the sample.

11. Apparatus as claimed in claim 1 wherein the hollow tube is provided with a rod, slidably mounted within the tube and having a cavity adjacent one end, that end of the rod being extendable from the tube.

12. Apparatus as claimed in any one of the preceding claims further comprising means for removing sample material from the outside of the tube.

1 3. A method of introducing a solid or semi-solid sample through the dosing opening of a graphite tube for the flameless atomic absorption spectroscopy of the sample, the method comprising the steps of receiving and retaining the sample in a device having an outside diameter smaller than the dosing opening, inserting the device into the dosing opeing and ejecting the sample into the graphite tube.

14. A method as claimed in claim 1 3 further comprising the step of first charging the device with sample by pushing it into the sample and, prior to insertion in the dosing opening, wiping off sample material adhering to the outside of the device.

1 5. A method as claimed in claim 1 3 or claim 1 4 further including the step of weighing the device after the receiving and retaining step and again after the ejecting step to determine the weight of sample ejected into the graphite tube.