US3492074A - Atomic absorption spectroscopy system having sample dissociation energy control - Google Patents

Atomic absorption spectroscopy system having sample dissociation energy control Download PDF

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Publication number
US3492074A
US3492074A US685455A US3492074DA US3492074A US 3492074 A US3492074 A US 3492074A US 685455 A US685455 A US 685455A US 3492074D A US3492074D A US 3492074DA US 3492074 A US3492074 A US 3492074A
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sample
plasma
gas
energy
atomic absorption
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John F Rendina
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HP Inc
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Hewlett Packard Co
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
    • G01N21/71—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light thermally excited
    • G01N21/73—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light thermally excited using plasma burners or torches

Definitions

  • This invention relates to a method and apparatus for controlling the effective temperature of a plasma and, more particularly, to a method and apparatus for controlling the ability of a plasma to transfer energy.
  • a source of radiation which produces wave lengths of light which are characteristic of the element atoms under test.
  • This source of radiation is usually produced by a source capable of providing narrow lines.
  • One such source is the well known hollow cathode lamp.
  • Another such source is a metallic halide discharge tube of the type described in U.S. Patent 3,319,119 isssued May 9, 1967 to John F. Rendina.
  • characteristic radiation from the source is passed through a medium in which free atoms are available. These free atoms are obtained by dissociation of molecules of a sample of the substance under test.
  • the sample is introduced into the conversion zone as a spray, mist, or fog, or as solid small particles.
  • mist or fog energy is transferred to or absorbed by the droplets, drying off the more volatile components and leaving a solid particle.
  • Absorption of additional energy by the particle results in the particle reaching the boiling or sublimation point and it becomes independent molecules (a gas).
  • Further absorption of energy by the molecules can produce chemical bond splitting, resulting in free atoms in the ground or excited state, which are capable of absorbing electromagnetic radiation at a resonant frequency. If too much energy has been transferred to the particles or molecules, excitation or ionization may occur, producing an atom which cannot absorb resonant radiation.
  • the ideal condition for atomic absorption spectroscopy is that suflicient energy be imparted to the molecule to permit dissociation, but not so much so as to excite the sample atoms. This leaves a maximum number of ground state atoms available to absorb the resonant radiation from the source.
  • ions and electrons are accelerated in the intense electric fields produced by the RF supply and thereby possess considerable kinetic energy. If they collide with another species (third body inelastic collision) they may impart all or part of their kinetic energy to the third body which may absorb this energy in several ways, such as increased kinetic energy, ionization, excitation, chemical bond splitting, etc.
  • the amount of energy available per collision and the number of collisions per unit time define the power transferred from the plasma.
  • the factors affecting the available energy transfer per collision are a function primarily of the gas characteristics. When a monatomic gas is considered, these factors include gas pressure, gas ionization potential and mass of the gas atoms.
  • gas pressure When a monatomic gas is considered, these factors include gas pressure, gas ionization potential and mass of the gas atoms.
  • an additional form of energythe dissociation energy of the polyatomic gas molecules- is available to the third body during each collision.
  • the dissociation energy of a polyatomic gas is present in the free atoms in the form of additional kinetic energy.
  • the free atoms transfer this dissociation energy to the third body and then recombine to their original polyatomic molecule.
  • the dissociation energy of these gases is usually quite high compared to the kinetic energy normally available from monatomic gases or the free electrons.
  • a. polyatomic gas is frequently referred to as a hot gas and a monatomic gas is referred to as a cool gas.
  • the polyatomic gases are generally used as the plasma gas.
  • Monatomic gases sometimes are used to excite those more easily excited and dissociated substances.
  • Unfortunately there are not enough different gases available having dilferent dissociation energies to permit the matching of the plasma gas to the element under test. This problem is particularly apparent when testing the more easily excitable elements such as the alkali metals. Other metals of intermediate excitability are sometimes diflicult to detect.
  • the temperature of the plasma is usually mentioned. Actually this phase has no real meaning. Since the plasma has no equilibrium temperature, it cannot be accurately or meaningfully defined in terms of the conventional temperature units available. The temperature of the plasma often is arrived at through theoretical calculations or one can define the effective plasma temperature by observing the effect of the plasma on a sample introduced into it and correlating or extrapolating these results to those derived from the effect of a thermally heated gas in contact with a sample.
  • Another object of this invention is to provide a method of controlling a plasmas effective temperature.
  • An additional object of this invention is to provide an apparatus for controlling the temperature of a plasma for atomic absorption spectroscopy.
  • a preferred embodiment of this invention provides a method and apparatus for controlling the energy imparted to a sample by a plasma for use in spectroscopic analysis.
  • the method envisions the use of two different gases from which the plasma is formed. These two gases are mixed together and introduced into a plasma generator. The sample itself then is introduced into the plasma. By adjusting the ratio of the first gas to the second gas, the energy transferred from the plasma to the sample may be varied to impart the precise amount of energy to the sample required to dissociate the sample and yet leave the resulting free atoms at the ground state energy level. This provides the maximum number of available atoms which can absorb the characteristic radiation and reduces the amount of characteristic radiation emitted by the sample itself, thereby reducing system noise.
  • the preferred method of this invention may be performed using the apparatus seen in the sole figure in which there is provided a suitable radio frequency (R.F.) generator 10 capable of producing several hundred watts of RF. energy typically in the range of 10 to 1,000 megacycles.
  • the output of the RF. generator 10 is coupled to a tap 12 on an auto transformer 14 for the purpose of raising the RF. voltage.
  • One end 16 of the autotransformer 14, which is closest to the tap 12 in an electrical sense, is grounded.
  • the remaining end 18 of the autotransformer 14, at which the high voltage is available, is coupled to, in this case, a ring electrode 20.
  • a capacitor 22 is placed in parallel with the autotransformer 14 to provide a tank circuit 24 tuned to the frequency of the RF. generator 10.
  • the ring electrode 20 is placed over a quartz tube 28 or other shielding device for containing the plasma generator.
  • the plasma generator includes a flame tip 30, disposed coaxially within the tube 28 and may be formed of aluminum, silver, or other metal having a high thermal conductivity.
  • the flame tip 30 may be water cooled if desired.
  • the particular design of the plasma generator is not of importance to this invention. A typical design for a plasma generator that can be used is described, for example, in an article entitled Radio Frequency Plasma Emission Spectrophotometry by C. David West and David N. Hume appearing on page 412 of Analytical Chemistry, volume 36, No. 2, dated February 1964.
  • the upper terminal 18 of the autotransformer 14 could be connected to the flame tip 30 and the ring electrode 20 grounded.
  • the chamber within the tube 28 surrounding the flame tip 30 is supplied with the gas mixture from which the plasma is to be formed along with the sample which is to be dissociated into ground state atoms by the energy of the plasma.
  • the plasma generator is supplied simultaneously from a first gas supply denoted by the block 32 and a second gas supply denoted by the block 34.
  • the respective first and second gas supplies 32 and 34 are connected through suitable conduits and adjusting valves 36 and 38, respectively to a T junction 40, thence through a nebulizer system denoted by the block 42 to the lower portion of the shielding tube 28.
  • the nebulizer system may be any suitable mechanical or ultrasonic means of atomizing a fluid sample supplied to the fluid inlet 44, denoted sample inlet in the drawing.
  • the atomized or nebulized sample is entrained in the gas mixture flowing to the plasma flame generator through the conduit 46.
  • a suitable atomizer or nebulizer system for this purpose is described in a letter entitled Direct Continuous Quantitative Ultrasonic Nebulizer for Flame Photometry and Flame Absorption spectrophotometry by Wolfgang I. Kirstan and Groto B. Bertillson which was published in Analytical Chemistry in 1966.
  • the particular system used by Kirstan and Bertillson employs an ultrasonic transducer to which the solution is fed for atomization and subsequent entrainment in the carrier gas from the first and second gas supplies 32 and 34. It is to be noted that it is not necessary that the sample be introduced into the gases.
  • the sample may be introduced directly into the plasma generator if desired.
  • the particular plasma generator used does not form a part of this invention.
  • characteristic radiation denoted by the dashed line 45 is shown as passing through the shielding tube 28 to the atomic absorption spectrometer 48 for detection and measurement. It is understood that the complete atomic absorption instrument 48 includes a characteristic light source and the atomic vapor system as well as the detecting measuring components.
  • the method of this invention comprises selecting a gas for the first gas supply 32 which produces a relatively low effective plasma temperature.
  • gases of this type are monatomic gases such as helium, argon, and neon.
  • the gas selected for the second gas supply 34 should be one which produces a relatively high effective plasma temperature or at least a gas producing a higher effective plasma temperature than that of the first gas.
  • Gases of this latter type typically are the diatomic or polyatomic gases such as nitrogen, carbon dioxide, carbon monoxide, hydrogen, and oxygen which provide a relatively hot efiective plasma temperature compared to the first gas.
  • the volume ratio of the first gas to the second gas supplied to the T 40 may be varied in accordance with the sample under analysis. The ratio is varied until optimum sensitivity of the atomic absorption spectrophotometer 48 is obtained.
  • Optimum sensitivity is obtained when (1) the maximum number of free sample atoms are obtained by dissociation of the sample molecules and (2) the sample atoms are at the ground state rather than an excited state. Too high an energy transfer into the sample causes the sample to undergo an undesired amount of excitation. This reduces the sensitivity of the system. Too little energy transfer does not permit the breaking of the chemical bonds of the compounds containing the atoms under test. Too few atoms capable of absorbing the characteristic radiation are produced.
  • a mixture of nitrogen and argon gases can provide an effective plasma temperature that varies from that of an argon plasmas elfective temperature alone to that of a nitrogen plasmas eifective temperature alone, depending on the particular gas ratio employed.
  • Example I In the determination of calcium, whose atoms become excited at a relatively low energy level, a parts per million (ppm) sample of calcium chloride (CaCl was introduced into the plasma generator operating on pure nitrogen in accordance with the prior art teaching. No absorption could be detected using conventional atomic absorption techniques. On the other hand, considerable emission was evident from the atomic vapor. Next pure argon, a known low temperature plasma, was tried. Likewise, no atomic absorption due to the resulting vapor was detected. Next the nitrogen and argon gases were mixed and it was found that a ratio of about 1 part nitrogen to 6 parts argon by volume provided an atomic vapor having excellent atomic absorption characteristics. It was found further that this gas ratio for calcium determination was quite critical. Deviation on either side of this particular ratio reduced the sensitivity and accuracy of the atomic absorption measurement.
  • ppm parts per million
  • Example II A similar situation is observed in the determination of magnesium in a sample of magnesium nitrate (Mg (NO).
  • Mg magnesium nitrate
  • an optimum nitrogen to argon ratio was found to be approximately 6 parts argon to 2.5 parts nitrogen by volume. From this it can be stated that a hotter, more effective energy transfer plasma than that provided by argon alone is required for the proper measurement or detection of magnesium by atomic absorption techniques.
  • Example IH In still another case sodium from a solution of sodium bicarbonate (NaHCO was determined. Optimum absorption sensitivity was attained using a gas mixture of 1.3 parts argon to 2.3 parts nitrogen by volume.
  • the proper mixture of gases has permitted the formation of a plasma having the proper effective temperature to supply sufiicient energy to dissociate the sample molecules into free ground state atoms.
  • the precise mechanism providing the basis for this invention is not entirely understood, it is believed that the monatomic gases absorb a portion of the energy available in the diatomic gas plasma such that the average effective temperature of the plasma is lowered.
  • the particular gas ratio will vary not only with the element under determination but also with the bonding energy and boiling point of compound in which the element is contained. The optimum gas ratio in each case is determined empirically.
  • a ratio may be established for a particular element and used for subsequent determinations of that element. This is generally true regardless of the compound. The determinations can be made without excessive loss of sensitivity due to lack of sufiicient absorbing atoms and without excessive noise due to a large number of excited atoms. It is preferred however to establish a particular ratio of gases for each and every compound.
  • a diatomic and polyatomic gas may be mixed, two of the same types of gases may be mixed, i.e., two monatomic gases, a monatomic gas and a polyatomic gas may be mixed.
  • An atomic spectroscopy system for analyzing the atomic composition of a sample comprising:
  • a source of radiation characteristic to a selected element to be detected and measured in said sample said radiation being directed along a path of travel to said atomic absorption spectrometer;
  • Cited means for adjusting the ratio of said first: and second 5 v UNITED STATES PATENTS gases supphed to said plasma generating means to precisely control the energy transferred to said neb- 3,324,334 6/1967 Raid ulized sample to dissociate said sample and maximize I r n a the number of ground state atomsof a selected .ele- RAYMOND HOSSFELD Pnmary Exammer ment of said sample.
  • v 10 I 2.
  • said sec- 1' I 0nd gas is a polyatomic gas and said first gas is a mon- 313--23'1; 315111;356--96 atomic gas.

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US685455A 1967-11-24 1967-11-24 Atomic absorption spectroscopy system having sample dissociation energy control Expired - Lifetime US3492074A (en)

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Cited By (24)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3583844A (en) * 1969-06-09 1971-06-08 Instrumentation Labor Inc Atomic absorption spectroanalytical instrument control system
US3646308A (en) * 1969-07-09 1972-02-29 Philips Corp Method of heating a hollow article
US3648015A (en) * 1970-07-20 1972-03-07 Thomas E Fairbairn Radio frequency generated electron beam torch
US4654504A (en) * 1983-11-30 1987-03-31 Hewlett-Packard Company Water-cooled gas discharge detector
US4894511A (en) * 1986-08-26 1990-01-16 Physical Sciences, Inc. Source of high flux energetic atoms
US5086255A (en) * 1989-02-15 1992-02-04 Hitachi, Ltd. Microwave induced plasma source
US6046546A (en) * 1992-04-16 2000-04-04 Advanced Energy Industries, Inc. Stabilizer for switch-mode powered RF plasma
WO2000031513A1 (fr) * 1998-11-19 2000-06-02 Oseir Oy Procede et dispositif permettant d'analyser des substances par spectroscopie d'absorption atomique
US20060286492A1 (en) * 2005-06-17 2006-12-21 Perkinelmer, Inc. Boost devices and methods of using them
JP2008544454A (ja) * 2005-06-17 2008-12-04 パーキンエルマー・インコーポレイテッド 増強装置及びその使用方法
US20090166179A1 (en) * 2002-12-12 2009-07-02 Peter Morrisroe Induction Device
US20100062223A1 (en) * 2004-10-07 2010-03-11 Johnson Controls Gmbh Laser welded seat structure
US20100320379A1 (en) * 2005-06-17 2010-12-23 Peter Morrisroe Devices and systems including a boost device
US20110139751A1 (en) * 2008-05-30 2011-06-16 Colorado State Univeristy Research Foundation Plasma-based chemical source device and method of use thereof
US8786394B2 (en) 2010-05-05 2014-07-22 Perkinelmer Health Sciences, Inc. Oxidation resistant induction devices
US8829386B2 (en) 2010-05-05 2014-09-09 Perkinelmer Health Sciences, Inc. Inductive devices and low flow plasmas using them
US9117636B2 (en) 2013-02-11 2015-08-25 Colorado State University Research Foundation Plasma catalyst chemical reaction apparatus
US9259798B2 (en) 2012-07-13 2016-02-16 Perkinelmer Health Sciences, Inc. Torches and methods of using them
US9269544B2 (en) 2013-02-11 2016-02-23 Colorado State University Research Foundation System and method for treatment of biofilms
US9532826B2 (en) 2013-03-06 2017-01-03 Covidien Lp System and method for sinus surgery
US9555145B2 (en) 2013-03-13 2017-01-31 Covidien Lp System and method for biofilm remediation
US10237962B2 (en) 2014-02-26 2019-03-19 Covidien Lp Variable frequency excitation plasma device for thermal and non-thermal tissue effects
US10368427B2 (en) 2005-03-11 2019-07-30 Perkinelmer Health Sciences, Inc. Plasmas and methods of using them
US10524849B2 (en) 2016-08-02 2020-01-07 Covidien Lp System and method for catheter-based plasma coagulation

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3736368A1 (de) * 1987-10-27 1989-05-11 Msi Technik Gmbh Optogalvanisches spektrometer
JPH03282252A (ja) * 1990-03-30 1991-12-12 Hitachi Ltd プラズマ極微量元素分析装置

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3324334A (en) * 1966-03-15 1967-06-06 Massachusetts Inst Technology Induction plasma torch with means for recirculating the plasma

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3324334A (en) * 1966-03-15 1967-06-06 Massachusetts Inst Technology Induction plasma torch with means for recirculating the plasma

Cited By (39)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3583844A (en) * 1969-06-09 1971-06-08 Instrumentation Labor Inc Atomic absorption spectroanalytical instrument control system
US3646308A (en) * 1969-07-09 1972-02-29 Philips Corp Method of heating a hollow article
US3648015A (en) * 1970-07-20 1972-03-07 Thomas E Fairbairn Radio frequency generated electron beam torch
US4654504A (en) * 1983-11-30 1987-03-31 Hewlett-Packard Company Water-cooled gas discharge detector
US4894511A (en) * 1986-08-26 1990-01-16 Physical Sciences, Inc. Source of high flux energetic atoms
US5086255A (en) * 1989-02-15 1992-02-04 Hitachi, Ltd. Microwave induced plasma source
US6046546A (en) * 1992-04-16 2000-04-04 Advanced Energy Industries, Inc. Stabilizer for switch-mode powered RF plasma
WO2000031513A1 (fr) * 1998-11-19 2000-06-02 Oseir Oy Procede et dispositif permettant d'analyser des substances par spectroscopie d'absorption atomique
US20090166179A1 (en) * 2002-12-12 2009-07-02 Peter Morrisroe Induction Device
US9360430B2 (en) 2002-12-12 2016-06-07 Perkinelmer Health Services, Inc. Induction device
US8742283B2 (en) 2002-12-12 2014-06-03 Perkinelmer Health Sciences, Inc. Induction device
US8263897B2 (en) 2002-12-12 2012-09-11 Perkinelmer Health Sciences, Inc. Induction device
US8187721B2 (en) 2004-10-07 2012-05-29 Johnson Controls Gmbh Laser welded seat structure
US20100062223A1 (en) * 2004-10-07 2010-03-11 Johnson Controls Gmbh Laser welded seat structure
US10368427B2 (en) 2005-03-11 2019-07-30 Perkinelmer Health Sciences, Inc. Plasmas and methods of using them
JP2008544454A (ja) * 2005-06-17 2008-12-04 パーキンエルマー・インコーポレイテッド 増強装置及びその使用方法
AU2006259381B2 (en) * 2005-06-17 2012-01-19 Perkinelmer Health Sciences, Inc. Boost devices and methods of using them
US8289512B2 (en) 2005-06-17 2012-10-16 Perkinelmer Health Sciences, Inc. Devices and systems including a boost device
US8622735B2 (en) 2005-06-17 2014-01-07 Perkinelmer Health Sciences, Inc. Boost devices and methods of using them
US20060286492A1 (en) * 2005-06-17 2006-12-21 Perkinelmer, Inc. Boost devices and methods of using them
US9847217B2 (en) 2005-06-17 2017-12-19 Perkinelmer Health Sciences, Inc. Devices and systems including a boost device
US20100320379A1 (en) * 2005-06-17 2010-12-23 Peter Morrisroe Devices and systems including a boost device
US8896830B2 (en) 2005-06-17 2014-11-25 Perkinelmer Health Sciences, Inc. Devices and systems including a boost device
US9288886B2 (en) * 2008-05-30 2016-03-15 Colorado State University Research Foundation Plasma-based chemical source device and method of use thereof
US20110139751A1 (en) * 2008-05-30 2011-06-16 Colorado State Univeristy Research Foundation Plasma-based chemical source device and method of use thereof
US8786394B2 (en) 2010-05-05 2014-07-22 Perkinelmer Health Sciences, Inc. Oxidation resistant induction devices
US10096457B2 (en) 2010-05-05 2018-10-09 Perkinelmer Health Sciences, Inc. Oxidation resistant induction devices
US8829386B2 (en) 2010-05-05 2014-09-09 Perkinelmer Health Sciences, Inc. Inductive devices and low flow plasmas using them
US9686849B2 (en) 2012-07-13 2017-06-20 Perkinelmer Health Sciences, Inc. Torches and methods of using them
US9259798B2 (en) 2012-07-13 2016-02-16 Perkinelmer Health Sciences, Inc. Torches and methods of using them
US9117636B2 (en) 2013-02-11 2015-08-25 Colorado State University Research Foundation Plasma catalyst chemical reaction apparatus
US9269544B2 (en) 2013-02-11 2016-02-23 Colorado State University Research Foundation System and method for treatment of biofilms
US9532826B2 (en) 2013-03-06 2017-01-03 Covidien Lp System and method for sinus surgery
US10524848B2 (en) 2013-03-06 2020-01-07 Covidien Lp System and method for sinus surgery
US9555145B2 (en) 2013-03-13 2017-01-31 Covidien Lp System and method for biofilm remediation
US10237962B2 (en) 2014-02-26 2019-03-19 Covidien Lp Variable frequency excitation plasma device for thermal and non-thermal tissue effects
US10750605B2 (en) 2014-02-26 2020-08-18 Covidien Lp Variable frequency excitation plasma device for thermal and non-thermal tissue effects
US10524849B2 (en) 2016-08-02 2020-01-07 Covidien Lp System and method for catheter-based plasma coagulation
US11376058B2 (en) 2016-08-02 2022-07-05 Covidien Lp System and method for catheter-based plasma coagulation

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DE1808965C3 (de) 1975-12-04
FR1592470A (fr) 1970-05-11
DE1808965B2 (de) 1975-04-10
DE1808965A1 (de) 1969-06-26
GB1230160A (fr) 1971-04-28

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