Measuring and testing – Sampler – sample handling – etc. – Analyzer supplier
Patent
1984-04-27
1986-03-25
Swisher, S. Clement
Measuring and testing
Sampler, sample handling, etc.
Analyzer supplier
239338, G01N 3500
Patent
active
045775176
DESCRIPTION:
BRIEF SUMMARY
This invention relates to improvements in and relating to nebulizers and instruments utilizing same and to methods of operating such instruments.
Nebulizers are used in a variety of chemical analysis equipment to transport a liquid sample into various flames, plasmas, etc. whereby selected characteristics of the liquid may be observed. Such instruments include but are not limited to atomic absorption instruments, flame photometers and inductively coupled plasma instruments. There are various types of nebulizers. However common forms utilize pneumatic means or ultra-sonic means to form an aerosol from the sample liquid. In each case the aerosol is contained in a cloud or mist chamber having an outlet arranged to select a fine mist like sample for analysis while the larger size particles, droplets and liquid are directed to a drain at the bottom of the chamber. Furthermore in both the above types of nebulizers the rate of sample uptake remains constant throughout the duration of an analytical sequence, and the means for forming the aerosol, i.e., the gas supply in the case of pneumatic nebulizers, and the electrical energy supplied to the R.F. transducer in the case of ultrasonic nebulizers, also remains constant.
This arrangement has led to operating inaccuracies which result from what are called memory effects whereby an erroneous result may occur due to contamination from the previous sample. This contamination can be due to residual aerosol sample or to residual liquid at the gas/liquid interface in the case of a pneumatic nebulizer, or at the transducer block in the case of an ultrasonic nebulizer. Furthermore in pneumatic nebulizers the calibration of the instrument can change during use as a result of a sample precipitation at the gas/liquid interface. This may be due to local cooling at the gas/liquid interface caused by the constant operation of the instrument whereby the high velocity gas flow at the interface causes a sufficient reduction in temperature to precipitate salts from the sample liquid. This effect is particularly noticeable when testing high concentration solutions and it may result in markedly labourious procedure being adopted in order to achieve acceptable results. At present the means of dealing with the above inaccuracies is to make allowances for same in the test results. This can result, however, in inaccurate results being obtained. Further inaccuracies may result from both long and short term changes in the instrument condition. These inaccuracies may be reduced by the use of an internal standard. In the past the method of using an internal standard has been to introduce a fixed amount of solution, containing a known concentration of a substance, into the liquid sample prior to the introduction to the nebulizer. The instrument would then analyse the liquid sample containing both the unknown substance and the known substance. Any variation in output in respect of the known substance is monitored, and these variations are used to correct for variation in results of the unknown substance.
This procedure is time consuming in that the internal standard needs to be added very accurately to each liquid sample container in turn prior to introduction to the nebulizer. This procedure can lead to errors if care is not taken to ensure that precise amounts of internal standards are added. Additionally, in prior art nebulizers, problems associated with the introduction of dirty or turbid samples can manifest themselves in several ways. For example, the sample introduction tube can become clogged up with deposited precipitated material or all wetted parts can be coated with the suspended or otherwise matter, causing problems with drainage and/or blockages.
One feature of an ultrasonic nebulizer is that, due to its very high nebulization efficiency, desolvation of the aerosol may be necessary before analysis can take place. The desolvation apparatus can have a large volume which will need to be purged in order to reduce memory from one sample to the next. This is a disadvantage in that it inc
REFERENCES:
patent: 3385522 (1968-05-01), Kock
patent: 3806250 (1974-04-01), George
patent: 3929291 (1975-12-01), Ladisch
patent: 4125225 (1978-11-01), Venghiattis
patent: 4206160 (1980-06-01), Suddendorf
Labtest Equipment Co. (S.E. Asia) Pty. Ltd.
Swisher S. Clement
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