GB2088054A

GB2088054A - Improvements Relating to Atomic Absorption Spectroscopy

Info

Publication number: GB2088054A
Application number: GB8133984A
Authority: GB
Original assignee: NPP BALKAN
Current assignee: NPP BALKAN
Priority date: 1980-11-12
Filing date: 1981-11-11
Publication date: 1982-06-03
Also published as: JPS57149948A; ATA478181A; JPH0158452B2; FR2493988B1; GB2088054B; DE3144997C2; SU1219959A1; AT389766B; FR2493988A1; CA1163463A; DE3144997A1; BG33390A1

Abstract

A device for pulse dosage of liquid microsamples into the flame of an atomic absorption spectrophotometer (AAS) comprises a three-way distributor and an electromagnetic valve acting on one of the three channels of the distributor, the second of the three channels being for connection to a source of the sample to be analysed by the atomic absorption spectrophotometer and the third of the three channels being for connection to the atomiser unit of the atomic absorption spectrophotometer. In one embodiment, the device is constructed of two units at most, said units being located at different levels in respect to the atomiser of the atomic absorption spectrophotometer, the three-way distributor of the higher level unit being connected to a container for the sample, to the atmosphere through its electromagnetic valve and to the three-way distributor of the lower level unit, said distributor of the lower level unit being connected through its valve to a container for solvent, and to the atomiser. <IMAGE>

Description

SPECIFICATION Improvements Relating to Atomic Absorption Spectroscopy This invention relates to atomic absorption spectroscopy and more particularly but not exclusively is concerned with a device for pulse dosage of liquid microsamples into the flame of an atomic absorption spectrophotometer (AAS).

Several forms of device for the pulse dosage of liquid microsamples into the flame of an AAS are known. One of these consists of a polytetrafluoroethylene funnel which is connected to the aggregate head for spraying of the sample by means of a special capillary. The dosage of the solution in a volume range of 50-100 microliters is effected manually, using microliter pipettes provided with special movable plastic nozzles (see Anal. Chem., 264, 105 (1973)-article by E. Sebastiani, K. Ohis, G.

Reimer and Z. Fresenius).

Another known device for automatic pulse dosage of liquid mocrosamples into the flame of an AAS has a design which is based on the studies performed by Berndt and Jackwerth (see Spectrochimica Acta, 30B, 169 (1975); Atomic Absorption Newsletter, 15, 109 (1976); and Anal.

Chem., 290, 105 (1978) and is used by Perkin Elmer. It consists, in combination, of a Teflon (Registered Trade Mark) funnel provided with a microliter pipette and a small pump; and a system for stepwise rotation of a table, which carries beakers containing samples to be tested. The operation of the device depends on the electronics of the AAS. It permits an automatic dosage of samples of volumes 50 or 100 microliters.

A manual device for pulse dosage is also known, which comprises a small container with a conical bottom. The sample of preliminary known volume in the range 50-500 microliters is pumped only once by the capillary, said capillary being connected to the atomiser of the AAS (see Atomic Absorption Newsletters, 17, 113(1978)-A. Eaton and E. Schiemer).

It is a common disadvantage of the well known automatic pulse dosage devices that they are extremely expensive. In manual devices for pulse dosage, relatively high cost microliter pipettes with movable nozzles are used and the dosage is both inconvenient and tiresome when large numbers of samples are to be tested, which results in lower reproducibility.

An object of the present invention is to provide a device for pulse dosage of liquid microsamples into the flame of atomic absorption spectrophotometers, said device being such as to enable simple, fast, reliable, precise and convenient handling of the samples both with good reproducibility and at low cost.

According to the present invention, there is provided a device for the variable pulse dosage of liquid samples into the flame of an atomic absorption spectrophotometer, which device comprises a three-way distributor and an electromagnetic valve acting on one of the three channels of the distributor, the second of the three channels being for connection to a source of the sample to be analysed by the atomic absorption spectrophotometer and the third of the three channels being for connection to the atomiser unit of the atomic absorption spectrophotometer.

The device of the invention will generally be associated with, or it may include, a pump for delivering a quantity of the sample to the second channel of the distributor. Advantageously, the device is also associated with, or includes, timing means which controls the electromagnetic valve (and preferably also the pump) so as to control accurately the closure time of the said valve (and preferably also simultaneously the operating time of the said pump).

In several embodiments, the second and third of the three channels are formed as a single conduit, and said one of the three channels has an axis making an angle of from 15 to 1650 with the axis of said conduit. Such a conduit can be of uniform cross-section or it can be stepped to provide two regions differing in cross-section.

In some embodiments of the invention, the device comprises a single unit constituted by the said distributor and electromagnetic valve. In other embodiments, the device includes two units each having a three-way distributor and an electromagnetic valve. The two distributors will then be interconnected, so that the third channel of the first distributor is connected to the AAS via the second distributor.

According to a second aspect of the invention, there is provided a device for pulse dosage of a liquid microsample into the flame of an atomic absorption spectrophotometer, which device includes a distributor and an electromagnetic valve, wherein the said device is constructed of two units at most, said units being located at different levels in respect to the pulverizer of the atomic absorption spectrophotometer, wherein the distributors are of the three-way type and there is a connection provided between said distributors and the electromagnetic valves, the three-way distributor of the higher level unit being connected (i) to a container for the sample, (ii) to the atmosphere by means of an electromagnetic valve, and (iii) to the pulverizer of the atomic absorption spectrophotometer by means of the three-way distributor of the lower level unit, said distributor of the lower level unit being connected to a container for the sample solvent.

In a first embodiment of the device, there are two distributors each having three intercommunicating channels and with an electromagnetic valve operable to close the first of the three channels in each case. The third channel of the first distributor is connected to the second channel of the second distributor; the first channel of the first distributor communicates with the atmosphere; the second channel of the first distributor is for receiving the sample to be analysed; the first channel of the second distributor communicates with a source of solvent (which will be the same solvent as is used to dissolve the material for analysis); and the third channel of the second distributor is for direct connection to the atomiser unit of an atomic absorption spectrophotometer.

In a second embodiment of the device, only one unit is used, where the first channel (with the electromagnetic valve) of its three-way distributor communicates with the atmosphere and another channel is connected directly to the atomiser of the atomic absorption spectrophotometer.

In a third embodiment of the device, only one unit is used, where the first channel of its three-way distributor and its associated electromagnetic valve is connected to a container for the sample solvent and another channel is connected directly to the container for the sample under test.

Each of the three-way distributors in the various embodiments has one channel which is associated with the electromagnetic valve, said channel preferably being connected to a conduit the axis of which makes an angle of between 15 and 1650 (e.g. 900) with that of said channel. The conduit can be of a uniform or stepped cross section, and acts as the second and third channels in the threeway distributor.

The invention also provides an atomic absorption spectrophotometer including a device as defined above. In one such spectrophotometer, there are two distributors arranged and interconnected as in the first embodiment of the invention set forth above; the first distributor is mounted at a higher level than the second distributor. Preferably, the spectrophotometer further comprises a pump for delivering a quantity of sample to the second channel of the first distributor, and timing means associated with the electromagnetic valves of the first and second distributors and with the said pump, for accurately controlling the closure time of the two electromagnetic valves and simultaneously controlling the operating time of the said pump.

The invention also provides a method of operating an atomic absorption spectrophotometer, which comprises introducing a liquid sample to be analysed into the flame of the atomic absorption spectrophotometer through a device as hereinbefore described.

Embodiments of the device of the invention possess the following advantages: there is no need for microliter pipettes; dosed volumes can be smoothly varied starting from 50 microliters to a continuous atomisation; the device is expected to have universal applicability; the possibility of working in a mode of integration of the signals at a minimal volume is provided; zeroing in the flame according to the respective solvent used, followed by a pulse dosage of a microsample in the same solvent, is possible; a continuous dosage of the solvent and pulse dosage of the sample is possible, thereby maintaining the flame stoichiometry and ensuring simplicity, convenience, reliability, rapidity and exactness in operation. Moreover, the device can be constructed readily and at relatively low cost.

Embodiments of the invention are shown by way of example in the accompanying drawings in which: Figure 1 is a diagrammatic representation of a first embodiment of the invention; Figure 2 is a diagrammatic representation of a second embodiment of the invention; and Figure 3 is a diagrammatic representation of part of a third embodiment of the invention.

Referring now to Figure 1, the device for pulse dosage of liquid microsamples into the flame of an AAS comprises two units located at different levels over the AAS atomiser unit. Three-way distributors connected to electromagnetic valves are used in this embodiment. The three-way distributor 1 of the higher unit is connected to a container for the sample by means of an opening 21 in conduit 2 and is connected by means of an electromagnetic valve 6 to the atmosphere through channel 31. The distributor 1 is also connected via opening 22 of conduit 2 and a tube 4 to an opening 23 in a conduit 20 forming part of the three-way distributor 10 of the lower unit. The distributor 10 is also connected firstly to a container 5 for the sample solvent through a channel 32 by means of an electromagnetic valve 60, and secondly to the atomiser of the AAS by means of an opening 24 of conduit 20.

There is an angle of 900 between the axes firstly of conduit 2 and channel 31, in the upper threeway distributor 1, and secondly of conduit 20 and channel 32, in the lower three-way distributor 10.

The device operates as follows: the flame of the AAS is ignited. Both electromagnetic valves 6 and 60 are opened. Pure solvent contained in the container 5 passes through the electromagnetic valve 60, channel 32, opening 24 and by means of a suitable plastics tube (not shown) enters the atomiser (or, respectively, flame of the AAS). A portion of the solvent ascends along the tube 4 (which is conveniently formed of a plastics material), thereby forming a hydraulic seal against the air inlet from the electromagnetic valve 6. No suction of solution of the liquid sample occurs. Thus, calibration or zeroing of the apparatus can then take place under these conditions. A higher rate of solvent admission is ensured compared with the liquid consumption of the atomiser because of the higher level of the container 5 compared with the level of the atomiser and by the proper choice of the cross sections of channels 32 and 2.

The two electromagnetic valves 6 and 60 are closed during a short, strictly defined time by means of electro-magnetic relays actuated by a signal initiated by the operator. The dosage of pure solvent in the manner described above then stops. The liquid sample is pumped by a suitabie pump (not shown) and enters the AAS atomiser after being passed through a plastics tube (not shown) connected to the opening 21, thence through the conduit 2, the opening 22, the plastics tube 4, the opening 23, the conduit 20 and opening 24 where it enters a further plastics tube (not shown) leading to the atomiser. Atomisation of the pure solvent is restored after the opening of the electromagnetic valves 6 and 60 which occurs simultaneously with the cessation of the pumping of sample to conduit 2. The sample dosage volume is controlled by the duration of the closure time of the electromagnetic valves.

The device permits a continuous dosage of the solvent and pulsed dosage of the sample or a continuous supply of liquid to the flame of the AAS, i.e. sample-solvent-sample...without any air feeding, which results in an improvement of the flame parameters and/or of the efficiency of atomization of a number of elements, while making it possible to work without deuterium correction.

Results obtained using the above outlined device are given in Example 1 below.

Example 1 Relative absorption values obtained from 1 5 measurements performed with solutions in the flame of an AAS after a pulse dosage of the type sample-solvent-sample... using a device of the invention as described above with reference to Figure 1 of the drawings were as shown in Table 1 below:: Table 1 Concentration Element mg.mF1 Solvent A SR % Cu 2.0 MMK 0.147 5.32 10.0 H2O 0.197 2.26 Cd 0.4 MMK 0.141 2.24 4.0 H2O 0.248 3.32 Te 4.0 MMK 0.224 6.29 - H2O - - Pb 10.0 MMI 0.518 0.70 10.0 H2O 0.095 5.20 Fe 4.0 MMK 0.284 1.42 4.0 H2O 0.042 6.47 Al 50.0 xylene 0.280 50.0 H2O 0.300 Sn 50.0 MIBK 0.790 50.0 H2O 0.120 MMK=methylmethacrylate MlBK=methylisobutyl ketone SR %=relative standard shift Organic solutions of Cu, Cd, Te and Pb were obtained by extraction of their diethyldithiocarbamate complexes with methylmethacrylate. The Fe was extracted as a hydrochloric acid complex, and the Sn and Al were extracted as standard caproate solutions.

Figure 2 is a diagram of a device in accordance with invention for pulse dosage of liquid microsamples into the flame of an AAS, said device being constructed as a single unit. The three-way distributor 1 of the unit communicates with the atmosphere by means of a channel 31 and electromagnetic valve 6; with the container (not shown) for the sample under test by means of opening 21 of conduit 2; and directly with the atomiser of the AAS by means of opening 22 of the conduit 2.

This device operates as follows: the opening 22 is connected, in use, to the atomiser of an AAS by means of a plastics tube (not shown). Then, the control panel of the electromagnetic valve 6 is switched on to the electric set. The flame of AAS is ignited. Zeroing of the apparatus can be made either on the flame or corresponding solvent used.

A signal initiated by the operator closes the electromagnetic valve for a short, strictly defined .time, this time being controlled by electronic timers. The air access to the conduit 2, coming from the eWctromagnetic valve 6 through the channel 31, is thus disconnected. The sample solution under test is then pumped for a short time and passes through a plastics tube (not shown) leading to opening 21, thence through conduit 2, the opening 22 and then, by means of a further plastics tube, enters the atomiser of the AAS. Thus, pulse dosage of liquid microsamples is accomplished, which stops at the moment of opening of the electromagnetic valve 6, i.e. a dosage of the type sample-air-sample... is performed. The sample dosage volume is determined by the closure time of the electromagnetic valve 6.

Results obtained using the above device are given in Example 2 below.

Example 2 Absorption values of solutions in the flame of an AAS, measured after pulse dosage of the type sample-air-sample... with a device of this invention as described above with reference to Figure 2 of the drawings, were compared with those obtained using a prior art funnel method.The results obtained are given in Table 2 below: Table 2 maX324nm max-228.8nm max-2l7.Onm split-0.7 split-0.7 split-0.7 Cu-1 .5 mg.ml-' Cd-0.4mg.ml-1 Pb-5.0mg.ml1 A SR% A SR% A SR% device 0.065 1.58 0.032 7.08 0.093 1.65 aqueous solutions funnel P.E. 0.058 4.33 0.027 9.48 0.074 4.88 device device 0.253 0.66 0.127 2.82 0.076 4.60 solutions MjnBK funnel P.E. 0.256 0.86 0.100 3.28 0.081 5.04 device device 0.221 1.18 0.107 3.53 0.061 5.67 solutions MMK funnel P.E. 0.220 1.18 0.105 3.68 0.062 7.50 device 0.118 1.73 0.084 7.88 - - solutions * in 0.108 0.91 - - - - toluene funnel P.E. 0.126 1.92 0.048 7.68 - MlBK=methylisobutyl ketone MMK=methylmethacrylate SR %=relative standard shift Absorption values are averaged over 25 measurements (II).

*Zeroing performed on organic solvent. In other cases, zeroing is accomplished based on the flame.

In a third embodiment of the device of the invention, the device is in the form of a single unit which is constructed substantially in the same form as the lower unit of the device shown in Figure 1.

In this third embodiment, the three-way distributor 10 of said unit is connected to a container 5 for the sample solvent, via the electromagnetic valve 60 and channel 32; to a container for the sample under test by means of the opening 23 of the conduit 20; and to the atomiser of the AAS by means of the opposite opening 24 of the same conduit 20. The mode of working of this embodiment will be apparent in view of the preceding descriptions relating to Figures 1 and 2.

In all possible embodiments of the device, the conduits 2 and 20 can either be of constant crosssection (as in Figures 1 and 2) or with stepped, variable cross-sections (as shown in Figure 3, where conduit 2 is stepped to a narrower bore at the region of the junction with channel 31 which in turn is formed of a narrow bore portion 3 and a wide bore portion 34).

Claims

1. A device for the variable pulse dosage of liquid samples into the flame of an atomic absorption spectrophotometer, which device comprises a three-way distributor and an electromagnetic valve acting on one of the three channels of the distributor, the second of the three channels being for connection to a source of the sample to be analysed by the atomic absorption spectrophotometer and the third of the three channels being for connection to the atomiser unit of the atomic absorption spectrophotometer.

2. A device as claimed in claim 1, which further comprises a pump for delivering a quantity of the sample to the said second of the three channels.

3. A device as claimed in claim 1, which further comprises timing means associated with the electromagnetic valve for accurately controlling the closure time of the said valve.

4. A device as claimed in claim 2, which further comprises timing means associated with the electromagnetic valve and with the said pump, the timing means being for accurately controlling the closure time of the valve and simultaneously the operating time of the said pump.

5. A device as claimed in claim 1, 2, 3 or 4, wherein said one of the three channels of the distributor communicates with the atmosphere.

6. A device as claimed in claim 1, 2,3, or 4, wherein said one of the three channels of the distributor communicates with a source of solvent.

7. A device as claimed in any preceding claim, wherein said second and third of the three channels are formed as a single conduit, and wherein said one of the three channels has an axis making an angle of from 1 5 to 1 650 with the axis of said conduit.

8. A device as claimed in claim 7, wherein the said conduit is of constant cross-section.

9. A device as claimed in claim 7, wherein the said conduit is stepped to provide two regions differing in cross-section.

10. A device as claimed in any preceding claim, wherein the device comprises a single unit constituted by the said distributor and electromagnetic valve.

11. A device as claimed in any preceding claim, wherein the third of the three channels of the said distributor is connected directly to the atomiser unit of an atomic absorption spectrophotometer.

12. A device as claimed in any of claims 1 to 9 wherein the third of the three channels of the said distributor is connected to the second channel of a second three-way distributor, the first channel of the second distributor including an electromagnetic valve, and the third channel of the second distributor being for direct connection to the atomiser unit of an atomic absorption spectrophotometer.

13. An atomic absorption spectrophotometer including a device as claimed in any of claims 1 to 11.

14. An atomic absorption spectrophotometer including a device as claimed in claim 12.

1 5. A spectrophotometer as claimed in claim 14, wherein said first distributor is mounted at a higher level than said second distributor.

1 6. A spectrophotometer as claimed in claim 14 or 15, wherein said one of the three channels of the first distributor communicates with the atmosphere when its associated electromagnetic valve is open, and wherein said one of the three channels of said second distributor communicates with a source of solvent when its associated electromagnetic valve is open.

1 7. A spectrophotometer as claimed in claim 16, which further comprises a pump for delivering a quantity of sample to the second channel of the first distributor, and timing means associated with the electromagnetic valves of the first and second distributors and with the said pump, for accurately controlling the closure time of the two electromagnetic valves and simultaneously controlling the operating time of the said pump.

1 8. A spectrophotometer as claimed in claim 16 or 1 7, wherein the second and third channels of each of the two distributors are formed as a single conduit, and wherein the axis of the first channel makes an angle of from 1 5 to 1 650 with that of the said conduit of each of the first and second distributors.

19. A spectrophotometer as claimed in claim 18, wherein the said angle is 900.

20. A spectrophotometer as claimed in claim 18 or 19, wherein the said conduits are of constant cross-section.

21. A spectrophotometer as claimed in claim 1 8 or 19, wherein the said conduits are stepped to provide regions of different cross-section.

22. A device for the pulse dosage of liquid samples into the flame of an atomic absorption spectrophotometer, substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawing.

23. A method of operating an atomic absorption spectrophotometer, which comprises introducing a liquid sample to be analysed into the flame of the atomic absorption spectrophotometer through a device as claimed in any one of claims 1 to 13.

24. A method of operating an atomic absorption spectrophotometer, substantially as hereinbefore described with reference to the accompanying drawing.

25. A device for pulse dosage of a liquid microsample into the flame of an atomic absorption spectrophotometer, which device includes a distributor and an electromagnetic valve, wherein the said device is constructed of two units at most, said units being located at different levels in respect to the pulverizer of the atomic absorption spectrophotometer, wherein the distributors are of the three-way type and there is a connection provided between said distributors and the electromagnetic valves, the three-way distributor of the higher level unit being connected (i) to a container for the sample, (ii) to the atmosphere by means of an electromagnetic valve, and (iii) to the pulverizer of the atom absorption spectrophotometer by means of the three-way distributor of the lower level unit, said distributor of the lower level unit being connected to a container for the sample solvent.

26. A device according to claim 25, wherein when a single unit is used, where the electromagnetic valve of said unit is connected to the atmosphere, the three-way distributor is connected directly to the pulverizer of the atom absorption spectrophotometer.

27. A device according to claim 25 wherein when a single unit is used, where the electromagnetic valve of said unit is connected to a container for the sample solvent, the three-way distributor is connected directly to the container for the sample.

28. A device according to ciaim 25, 26 or 2i; wherein each of the three-way distributors is provided with a channel connecting said distributors with the electromagnetic valves, said channel being connected to a conduit, wherein an angle of from 150 up to 1650 is concluded between said two channels

29. A device according to claim 28, wherein the conduit is of a constant cross-section.

30. A device according to claim 28, wherein the conduit is of a stepwise variable cross-section.