AU715545B2

AU715545B2 - Improved method of spectroscopy

Info

Publication number: AU715545B2
Application number: AU14835/97A
Authority: AU
Inventors: Alan Eastgate
Original assignee: Varian Australia Pty Ltd
Current assignee: Varian Australia Pty Ltd
Priority date: 1996-02-23
Filing date: 1997-02-21
Publication date: 2000-02-03
Anticipated expiration: 2017-02-21
Also published as: AU1483597A

Description

P/00/0oII Regulation 3.2

AUSTRALIA

Patents Act 1990

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT

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Invention Title: IMPROVED METHOD OF SPECTROSCOPY Applicant: VARIAN AUSTRALIA PTY LTD S. S 5* 0c The following statement is a full description of this invention, including the best method of performing it known to me: -2- IMPROVED METHOD OF SPECTROSCOPY This invention relates to spectroscopy and is particularly concerned with spectroscopic systems in which the sample to be analysed is introduced into the analysis zone in the form of a fine mist or spray (aerosol). The invention will be hereinafter described with reference to inductively coupled plasma emission (ICP) spectroscopy, but it is to be understood that the invention is not limited to that use. The invention is applicable to any spectroscopic system in which the sample to be analysed is presented in the form of an aerosol.

In ICP systems the aerosol is introduced into a spray chamber and passes from thereto an analysis zone. In the event that several samples are sprayed in succession the chamber needs to be purged of the residue of one .sample before analysis of a succeeding sample can be conducted with the oo expectation of accurate results. The purge time is typically in the order of tens of seconds and during that time the aerosol issuing from the spray chamber is 15 a mixture of the newly introduced sample and the preceding sample. The analytical instrument cannot be used productively during the time required to purge the residue of a preceding sample and it is therefore important to keep 00 that time to a minimum.

Various methods have been employed in an attempt to accelerate 0000* 20 purging of the aerosol chamber and thereby achieve a higher level of efficiency of use of the instrument. One method involves increasing the rate of up-take of 0**00: oooo:a blank liquid solution between the introduction of successive samples into the So• spray chamber. Another method involves the use of two or more nebulizers, or two or more spray chambers, in a single instrument so that a new sample can be introduced by means of one nebulizer or spray chamber while the other nebulizer or spray chamber is being cleaned of the residue of a previous sample. That method necessarily involves a relatively high equipment cost.

It is an object of the present invention to overcome or at least minimise the aforementioned problem. In particular, it is an object of the invention to provide means whereby the time lost between analysis of successive samples is kept to a minimum.

The invention is characterised in that purging or cleaning of the spray -3chamber is accelerated by subjecting the aerosol to an electrical field. All natural and artificially created aerosols are electrically charged to some extent and that has been considered an adverse factor in the field of ICP spectroscopy to the extent that positive steps have been taken to combat its presence. The present invention involves application of a relatively large electrical field to the aerosol (much larger than naturally occurring fields) during the non-analysis period when changing from one sample to the next.

Application of such a field causes rapid movement of aerosol droplets to the walls of the aerosol chamber and thereby typically reduces the purge period by approximately 50%. That permits a significant increase in sample through-put in systems utilising a single spray chamber and a single nebulizer.

*In accordance with one aspect of the invention there is provided a *oooo method of spectroscopy in which two or more samples to be analysed are successively presented in aerosol form to an analysis zone, including the steps 15 of, introducing a first said sample aerosol into a spray chamber which is connected to said analysis zone, analysing said first sample aerosol received at said analysis zone from said spray chamber, subjecting the aerosol *remaining in said chamber to an electrical field so as to thereby induce rapid movement of droplets of that aerosol towards a wall or walls of said chamber S" 20 and hasten removal of residue of said first sample from the chamber, introducing a second said sample aerosol into said spray chamber, and analysing said second sample after said first sample residue has been at least substantially removed from said spray chamber.

In accordance with another aspect of the invention there is provided a method of spectroscopy in which two or more samples to be analysed are successively presented in aerosol form to an analysis zone, including the steps of, introducing each said sample aerosol in turn into a spray chamber, analysing each said sample aerosol in turn at an analysis zone connected to said spray chamber, and between said analysis of each two successive samples subjecting the aerosol remaining in said spray chamber to an electrical field so as to thereby induce rapid movement of droplets of that aerosol towards a wall or walls of said chamber and hasten removal of residue -4of the relevant said sample from the chamber, whereby the residue of a preceding said sample is at least substantially removed from said spray chamber before analysis of an immediately succeeding sample commences.

In accordance with still another aspect of the invention there is provided a spectroscopic apparatus including, a spray chamber for sequentially receiving two or more samples each of which is to be analysed individually at an analysis zone connected to said chamber, sample feed means operable to successively introduce each said sample in aerosol form into said chamber, and a power source operable to generate an electrical field within said chamber and thereby induce rapid movement of aerosol droplets towards a wall or walls of said chamber and hasten removal of the relevant sample from said chamber, wherein aerosol remaining within said chamber after said analysis of one said sample is at least substantially removed from said chamber before analysis of another said sample commences.

15 A method in accordance with the invention preferably involves creation of an electrical field at a moderate voltage, such as a voltage in the range of volts to several hundreds of volts, and the polarity of the field can be either negative or positive. The time span of maintenance of the field can vary, but i :something in the range of two to ten seconds inclusive is generally satisfactory to achieve substantially complete wash-out of a previous sample.

The invention will be hereinafter described in greater detail by reference to the attached drawing which diagrammatically illustrates one possible application of the invention. The particularity of that drawing and the related description is not to be understood as superseding the generality of the preceding broad description of the invention.

In the arrangement shown a nebulizer 1 is operable in a known manner to introduce a sample in aerosol form into a spray chamber 2. The nebulizer 1 is connected to a body 3 of a liquid sample contained in a vessel 4. In the preferred arrangement shown the nebulizer 1 is connectable to two or more sample sources in succession. Each of those sample sources includes a respective vessel 4 supported by part of an auto-sampler 12 (part only shown) of a known kind, and each vessel 4 contains a different sample 3, 3a and 3b.

Auto-samplers are typically arranged to enable each of a variety of samples to be accessed individually and in a selected order, and the number of samples may be greater than or less than three as shown in the attached drawing.

The spray chamber 2 as shown has an aerosol outlet 5 and a waste drain 6. The nebulizer 1 is connected to the sample body 3 through a conduit 7. The outlet 5 communicates with an analysis zone 13 in a known manner. In the arrangement shown an electrical field is generated within the chamber 2 by connecting an appropriate power source 8 to the input to the nebulizer 1 and to the drain outlet 6 of the chamber 2. This arrangement requires the sample solution to be conductive, which is generally the case. Non-conductive samples could be handled by connecting the power source directly to the nebulizer 1. Other arrangements are possible.

o It is preferred that the power source 8 is a DC power source, but AC power would be suitable. The power source 8 is preferably connected into the 15 fluid streams at the drain 6 of the chamber 2 and the inlet to the nebulizer 1 respectively, and that may be achieved in any appropriate fashion. In the *.oarrangement shown an electrode 9 is exposed to the fluid stream at the drain 6 and an electrode 10 is exposed to the fluid stream at the inlet to the nebulizer 1, and the power source 8 is connected to each of the electrodes 9 and Other arrangements are clearly possible. For example, if the conduit 7 is metal it may be adequate to connect the power source 8 direct to the conduit 7, and the same applies to the drain 6.

The connection between the power source 8 and the drain 6 is preferably of a low resistance, and something less than 100 ohms is most preferred.

In the particular arrangement shown in the attached drawing, a peristaltic pump 11 or other pumping means is provided at the inlet side of the nebulizer 1. Such pumping means may not be necessary in all applications of the invention.

When apparatus as shown by the attached drawing is in use sequential analysis of different samples is carried out generally in the same manner as adopted with prior apparatus not incorporating the present invention. That is, -6sample aerosol received at the analysis zone 13 from the spray chamber 2 is analysed and the aerosol remaining within the chamber 2 is purged, at least to a substantial extent, before another sample aerosol is subjected to analysis.

Introduction of the second aerosol sample into the chamber 2 may commence before purging of residual aerosol of the first or preceding sample aerosol is completed.

In one method according to the invention an electrical field as referred to above is generated substantially the entire period of time during which a sample is being purged from the spray chamber. That is, the electrical field is applied from the time a new sample is introduced into the spray chamber until purging of the previous sample is completed. The field could however, be generated before or after introduction of the new sample is initiated. The field *oovoltage can be selected to suit requirements, but a voltage in the range 20 to *"200 volts inclusive is preferred and the range 20 to 100 volts inclusive is most 15 preferred. It is also preferred that the voltage is maintained substantially constant during the time that the electrical field is in existence. The time duration of the field may be also selected to suit requirements, and in particular to suit the type of spray chamber being used. In the case of a Varian "Liberty" ICP AES spray chamber a field duration in the order of 2 to 10 seconds 20 inclusive has been found satisfactory, but a duration of 3 to 5 seconds inclusive is usually preferred. It is also preferred that analysis of a sample takes place *oo :during a period of time aerosol in the spray chamber is not subjected to an electrical field.

In a preferred method according to the invention the sequence of steps is as follows: analyse a first sample, apply an electrical field to the aerosol remaining within the chamber to accelerate purging, commence introduction of a second sample into the chamber, deenergise the electrical field, and analyse the second sample.

It has been found that generation of an electrical field as described -7causes droplets within the chamber 2 to move rapidly towards the walls of the chamber and thereby hasten removal of residue of the sample from the chamber. The effect is substantially the same with an electrical field of either polarity. The rapid movement of the droplets greatly facilitates the purging of the chamber 2 which needs to be completed before accurate measurement of a newly introduced sample can be commenced. The time lost in purging the chamber 2 is generally in the order of 50% less than that required in convention systems.

Various alterations, modifications and/or additions may be introduced into the constructions and arrangements of parts previously described without departing from the spirit or ambit of the invention as defined by the appended claims.

a a.

Claims

1. A method of spectroscopy in which two or more samples to be analysed are successively presented in aerosol form to an analysis zone, including the steps of, introducing a first said sample aerosol into a spray chamber which is connected to said analysis zone, analysing said first sample aerosol received at said analysis zone from said spray chamber, subjecting the aerosol remaining in said chamber to an electrical field so as to thereby induce rapid movement of droplets of that aerosol towards a wall or walls of said chamber and hasten removal of residue of said first sample from the chamber, introducing a second said sample aerosol into said spray chamber, and analysing said second sample after said first sample residue has been at least substantially removed from said spray chamber. o

2. A method according to claim 1, wherein said electrical field is generated a. within said chamber at substantially the same time as said second aerosol is 000# 15 introduced into the chamber.

3. A method according to claim 1 or 2, wherein said analysis occurs during 0* a period of time aerosol in said chamber is not subjected to said electrical field. a.

4. A method of spectroscopy in which two or more samples to be analysed are successively presented in aerosol form to an analysis zone, including the 0. 20 steps of, introducing each said sample aerosol in turn into a spray chamber, analysing each said sample aerosol in turn at an analysis zone connected to :said spray chamber, and between said analysis of each two successive samples subjecting the aerosol remaining in said spray chamber to an electrical field so as to thereby induce rapid movement of droplets of that aerosol towards a wall or walls of said chamber and hasten removal of residue of the relevant said sample from the chamber, whereby the residue of a preceding said sample is at least substantially removed from said spray chamber before analysis of an immediately succeeding sample commences.

A method according to claim 4, wherein said electrical field is not generated for a period of time between said introduction of successive said samples.

6. A method according to any preceding claim, wherein said electrical field -9- voltage is in the rangeof 20 to 200 volts inclusive.

7. A method according to any preceding claim, wherein said electrical field voltage is in the range 20 to 100 volts inclusive.

8. A method according to claim 6 or 7, wherein said voltage is maintained substantially constant.

9. A method according to any preceding claim, wherein said electrical field is generated for a predetermined period of time during the residence of each said sample aerosol in said chamber.

A method according to claim 9, wherein said predetermined period of time is 2 to 10 seconds inclusive.

11. A method according to claim 9, wherein said predetermined period of time is 3 to 5 seconds inclusive.

12. Spectroscopic apparatus including, a spray chamber for sequentially receiving two or more samples each of which is to be analysed individually at 15 an analysis zone connected to said chamber, sample feed means operable to successively introduce each said sample in aerosol form into said chamber, and a power source operable to generate an electrical field within said chamber and thereby induce rapid movement of aerosol droplets towards a wall or walls of said chamber and hasten removal of the relevant sample from 20 said chamber, wherein aerosol remaining within said chamber after said analysis of one said sample is at least substantially removed from said Ole.li chamber before analysis of another said sample commences.

13. Apparatus according to claim 12, including a plurality of sample sources each of which contains a different said sample, and means for connecting said sample feed means to two or more said sample sources in succession. DATED: 21 February, 1997 PHILLIPS ORMONDE FITZPATRICK Attorneys for: VARIAN AUSTRALIA PTY LTD OAAS;t %Lt44