WO1998023952A1

WO1998023952A1 - Nebulizer

Info

Publication number: WO1998023952A1
Application number: PCT/GB1996/002908
Authority: WO
Inventors: Johannes David De Bruyn
Original assignee: Anglo American Research Laboratories (Proprietary) Limited; Dyer, Alison, Margaret
Priority date: 1996-11-26
Filing date: 1996-11-26
Publication date: 1998-06-04
Also published as: AU7635496A

Abstract

The method and nebulizer of the invention provide effective means for providing an atomised sample of a liquid such as an oil suitable for a variety of analytical methods such as, for example, introduction into an inductively coupled plasma atomic emission spectrometer. The method includes the step of heating the liquid prior to atomisation. The nebulizer includes a chamber (40), an inlet (46) for introducing a liquid into the chamber (40), a gas inlet (52) and a heater block (64) for heating the liquid and gas prior to entry into the chamber (40). Atomisation of the liquid is caused by entraining the liquid in a stream of fast-moving gas in region (54) of the chamber (40).

Description

NEBULI ZER

BACKGROUND OF THE INVENTION

This invention relates to a nebulizer.

In the analysis of liquids, many methods require conversion of a sample of the liquid into atomised form, i.e. in fine droplet form suitable for the analysis. Nebulizers are known and used to achieve this. In the case of viscous liquids such as oils, it is generally necessary to dilute the liquid prior to introduction into the nebulizer to ensure that a uniform atomised sample is produced. Dilution is not entirely satisfactory and can lead to variation in the sample produced giving rise to the possibility of inconsistent results, reduced sensitivity of analysis and limit of detection and increases the possibility of contamination or analyst error. SUMMARY OF THE INVENTION

According to the present invention, a method of producing an atomised sample of a liquid for analysis includes the step of heating the liquid prior to. and preferably immediately prior to, atomisation. Atomisation, e.g. fine droplet formation suitable for analysis, may be achieved by passing a liquid through a suitable atomising nozzle or entraining the liquid in a fast-moving gas or both.

Further according to the invention, a nebulizer for use in producing an atomised sample of a liquid for analysis includes a chamber, an inlet for introducing a liquid into the chamber, means to atomise the liquid entering the chamber, and heating means to heat the liquid introduced into the chamber. The heating means is preferably a heater in thermal contact with the inlet.

DESCRIPTION OF THE DRAWINGS

Figure 1 is a sectional plan view of a first embodiment of a nebulizer of the invention;

Figure 2 is a sectional plan view of a second embodiment of a nebulizer of the invention; and

Figure 3 is a graph of emission intensity as a function of temperature for a range of viscosities of an aluminium containing sample liquid. DESCRIPTION OF EMBODIMENTS

The method and nebulizer of the invention provide effective means for providing an atomised sample of a liquid such as an oil suitable for a variety of analytical methods such as, for example, introduction into an inductively coupled plasma atomic emission spectrometer. It has been found that heating the liquid immediately prior to atomisation greatly increases the output of atomised liquid and reduces output variation in emission intensity due to differences in liquid manufacture and viscosity.

The method and nebulizer of the invention have particular application to atomising a sample of a liquid which has a viscosity greater than that of water. As mentioned above, an example of such a liquid is oil. The method and nebulizer may be used for determining the metal content, both qualitatively and quantitavely, present in a used oil allowing for effective and controlled monitoring of the concentration of metals in the oil.

The atomised sample may be treated in whatever manner is needed for the subsequent analysis. For example, when the sample is to be introduced into an inductively coupled plasma atomic emission spectrometer, it is necessary to ionise the sample creating a plasma. Preferably, such ionisation takes place in the region where the atomised sample is produced.

Embodiments of the invention will now be described with reference to the accompanying drawings. Referring to Figure 1 , there is shown a nebulizer comprising a chamber 10 closed at one end 12 and open at the opposite end 14. A sample inlet 16 passes through side wall 18 of the chamber and is provided with an atomiser 20 at its end located in the chamber 10. Gas inlet 22 passes through the end 12. The chamber 10 also has an outlet 24 to drain waste material and prevent it accumulating in the chamber.

Heater block 26, provided with heating element 28. surrounds the sample inlet 16 while heater block 30, provided with heating element 32, surrounds the gas inlet 22. The nebulizer is provided with support 38 which is spaced from the two heater blocks 26, 30 by means of teflon or other insulating spaces 34, 36.

In use, liquid to be atomised is introduced into the chamber 10 through inlet 16. On passage through the inlet it is heated by the heater block 26 and passes through the atomising nozzle 20 in this heated form. At the same time, gas such as argon is passed into the chamber 10 through gas inlet 22 and is heated by the heater block 30 prior to entry into the chamber. This gas entrains the atomised liquid issuing from the atomiser 20 and carries the atomised sample out of the chamber 10 through open end 14 for analysis.

Figure 2 shows a nebulizer comprising a chamber 40 closed both ends 42, 44. A liquid inlet 46 passes through side wall 48 of the chamber 40 and a gas inlet 52 passes through the end 42.

The end 42 is provided with a v- shaped inner wall 55 which defines within it a zone 54. Ends 56 and 58 of the liquid inlet 46 and gas inlet 52, respectively open into the region 54. The chamber 40 is further provided with a drain 60 and an outlet 62.

Heater block 64, provided with heating element 66, surrounds the sample inlet 46 and the gas inlet 52. The heater block 64 is also provided with a thermocouple 68 for monitoring the temperature thereof. A teflon washer 70 is provided for sealing the gas inlet 52 in the event of dismantling the system for cleaning the atomiser.

In use, liquid to be atomised is introduced into the chamber 40 through inlet 46. On passage through the inlet it is heated by the heater block 64. At the same time, gas such as argon is passed through gas inlet 52 and is also heated by the heating block 64. The heated liquid and a fast moving stream of the heated argon make contact at right angles in the region 54. The heated liquid is entrained in the fast moving stream of gas and is thereby atomised. The atomised liquid is carried by the gas through the passage 72. located axially within the chamber 40, out of the open end 74 and then out through the outlet 62. Liquid which falls out of the stream of gas is removed through drain 60.

When the analysis is by way of an inductively coupled plasma atomic emission spectrometer, the atomised liquid must be ionised creating a plasma. Preferably, ionisation takes place in the region 54 where atomization takes place. A plasma is thus produced which is delivered to the spectrometer for analysis. The ionisation of the atomised liquid may be achieved by applying a suitable energy to the liquid using any known technique, e.g. by means of an electrical coil surrounding the region 54.

In an example, liquid samples containing a number of elements and having a range of viscosities were heated to various temperatures and atomised in a nebulizer such as that illustrated in Figure 2 and then analyzed to establish the intensity equalising temperature. The samples were not diluted or subjected to any pretreatment and all had a viscosity greater than water. The results of the changes in emission intensities with changes in temperature are set out in the following Tables 1 to 5.

The results given in the Tables show that the higher the temperature the higher or better the emission intensities. This is illustrated graphically by Figure 3 for aluminium. Figure 3 is a graph of emission intensity as a function of temperature which clearly illustrates the effect of heating a sample prior to analysis, in this case a sample containing aluminium, on the resultant emission intensities. At a temperature of between 100°C and 110°C, a range of viscosities had a relatively low slope indicating the intensity equalising effect of heating the oil samples to this temperature prior to atomisation.

The nebulizers described above are particularly effective for producing an atomised sample of a viscous liquid such as an oil. Heating avoids the necessity to pre-treat or dilute the oil, results in more consistent and better atomisation of the liquid and reduces the output variation in emission intensity due to differences in oil manufacture and viscosity.

STD 1 VISCOSITY SAE 20

TABLE 1

Std 2 Viscosity SAE 30

TABLE 2

Std 3 Viscosity SAE 50

TABLE 3

Std 4 Viscosity SAE 60

TABLE 4

Std 5 Viscosity SAE 70

TABLE 5

Claims

1.

A method of producing an atomised sample of a liquid for analysis includes the step of heating the liquid prior to atomisation.

2.

A method according to claim 1, wherein the liquid is heated immediately prior to atomisation.

J .

A method according to either claim 1 or claim 2, wherein the atomisation is achieved by passing the liquid through a suitable atomising nozzle.

4.

A method according to any one of claims 1 to 3 wherein the liquid is atomised by entraining it in a fast moving gas.

5.

A method according to claim 4, wherein the gas is heated prior to being contacted with the liquid.

6.

A method according to any one of claims 1 to 5, wherein the liquid has a viscosity greater than water.

7.

A method according to claim 6, wherein the liquid is an oil.

8.

A method according to any one of the preceding claims, wherein the atomised liquid is ionised in the region where it is produced.

9.

A nebulizer for producing an atomised sample of a liquid for analysis comprising a chamber, an inlet for introducing a liquid into the chamber, atomising means to atomise the liquid entering the chamber, and heating means to heat the liquid introduced into the chamber.

10,

A nebulizer according to claim 9, wherein the atomising means comprises an atomising nozzle.

11.

A nebulizer according either claim 9 or claim 10, wherein the heating means is in thermal contact with the inlet.

12.

A nebulizer according to claim 11 , wherein the heating means is a heating block including a heating element.

13.

A nebulizer according to claim 9, wherein the atomising means comprises a gas inlet arranged to direct a stream of fast moving gas across liquid introduced into the chamber through the inlet.

14.

A nebulizer according to claim 13, comprising heating means for heating the fast moving gas.

15.

A nebulizer according to claim 14, wherein the heating means is in thermal contact with the gas inlet.

16.

A nebulizer according to claim 15, wherein the heating means is a heating block including a heating element.

17.

A nebulizer according to any one of the preceding claims including means to ionise the liquid which is atomised in the chamber in the region in which atomisation of the liquid takes place.

18. A method of producing an atomised sample of a liquid for analysis substantially as hereinbefore described, with reference to any of Figures 1 to 3 of the accompanying drawings.

19. A nebulizer, substantially as hereinbefore described, with reference to and as shown in, any of Figures 1 to 3 of the accompanying drawings.

20. Any novel feature or combination of features described herein.