Title: Radio frequency induced plasma excitation of optical emission spectroscopic samples

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Claims: What is claimed is:

1. A radio frequency excitation apparatus for exciting a spectroscopic sample, said excited spectroscopic sample emitting characteristic radiation, said apparatus comprising:

a. radio frequency power oscillator means having a plate tank circuit and a grid tank circuit defining a single resonant circuit including an induction coil and a tuning capacitor, said induction coil in parallel with said turning capacitor, said plate tank circuit and said grid tank circuit having a common inductance;

b. plasma torch means, said induction coil externally and coaxially encircling a portion of said plasma torch means, said encircled portion of said plasma torch means defining a plasma forming region, said radio frequency power oscillator means exciting a plasma forming gas within said plasma forming region; and

c. means for introducing the spectoroscopic sample into said excited plasma, the spectroscopic sample introduced into said excited plasma emitting characteristic radiation.

2. A radio frequency excitation apparatus for exciting a spectroscopic sample, said excited spectroscopic sample emitting characteristic radiation, said apparatus comprising:

a. radio frequency power oscillator means having a plate tank circuit and a grid tank circuit defining a single resonant circuit including an induction coil and a tuning capacitor, said induction coil in parallel with said tuning capacitor, said plate tank circuit and said grid tank circuit having a common inductance;

b. plasma torch means, said induction coil externally and coaxially encircling a portion of said plasma torch means, said encircled portion of said plasma torch means defining a plasma forming region, said radio frequency power oscillator means exciting a plasma forming gas within said plasma forming region;

c. means for introducing the spectroscopic sample into said excited plasma, the spectroscopic sample introduced into said excited plasma emitting characteristic radiation; and

d. power supply means operativley connected to said radio frequency power oscillator means.

3. A radio frequency excitation apparatus for exciting a spectroscopic sample, said excited spectroscopic sample emitting characteristic radiation, said apparatus comprising:

a. radio frequency power oscillator means having a plate tank circuit and a grid tank circuit defining a single resonant circuit including an induction coil and a tuning capacitor, said plate tank circuit and said grid tank circuit having a common inductance, said radio frequency power oscillator means including a dc isolation capacitor and vacuum tube means having a plate, a grid, and a cathode, said induction coil in parallel with said tuning capacitor, one side of said induction coil and said tuning capacitor operatively connected to said plate, the other side of said induction coil and said tuning capacitor operatively connected to said grid via said dc isolation capacitor, and induction coil having a tap, said cathode and said tap operatively connected to a return, said induction coil being common to said plate tank circuit and said grid tank circuit;

b. plasma torch means, said induction coil externally and coaxially encircling a portion of said plasma torch means, said encircled portion of said plasma torch means defining a plasma forming region, said radio frequency power oscillator means exciting a plasma forming gas within said plasma forming region; and

c. means for introducing the spectroscopic sample into said excited plasma, the spectroscopic sample introduced into said excited plasma emitting characteristic radiation.

4. A radio frequency excitation apparatus for exciting a spectroscopic sample, said excited spectroscopic sample emitting characteristic radiation, said apparatus comprising:

a. radio frequency power oscillator means having a plate tank circuit and a grid tank circuit defining single resonant circuit including an induction coil and a tuning capacitor, said plate tank circuit and said grid tank circuit having a common inductance, said radio frequency power oscillator means including a capacitor for dc isolation and vacuum tube means having a plate, a grid, and a cathode, said induction coil in parallel with said tuning capacitor, one side of said tuning capacitor operatively connected to said plate, the other side of said induction coil and the other side of said tuning capacitor operatively connected to said grid via said dc isolation capacitor, said induction coil having a tap operatively connected to a return, said induction coil being common to said plate tank circuit and said grid tank circuit;

b. plasma torch means, said induction coil externally and coaxially encircling a portion of said plasma torch means, said encircled portion of said plasma torch means defining a plasma forming region, said radio frequency power oscillator means exciting a plasma forming gas within said plasma forming region;

c. means for introducing the spectroscopic sample into said excited plasma, the spectroscopic sample introduced into said excited plasma emitting characteristic radiation; and

d. power supply means operatively connected to said radio frequency power oscillator means.

5. The radio frequency excitation apparatus as claimed in claim 4 wherein said plasma torch means includes:

a. an outer tubular vessel opened at one end and closed at an opposite end, a tangential inlet port for an insulating gas formed near the closed end of said outer tubular vessel; and

b. an inner tubular vessel coaxial mounted within said outer tubular vessel, a chamber for said insulating gas formed between said outer tubular vessel and said inner tubular vessel, said inner tubular vessel opened at one end, the opened end of said inner tubular vessel in registration with the opened end of said outer tubular vessel, said inner tubular vessel projecting from said closed end of said outer tubular vessel, said projecting portion of said inner tubular vessel having a narrowed portion defining a coaxial inlet port for introduction of the spectroscopic sample, a tangential inlet port for a plasma forming gas formed in said projecting portion of said inner tubular vessel.

6. The radio frequency excitation apparatus as claimed in claim 5 wherein said means for introducing the spectroscopic sample includes nebulizer means for providing a desolvated aerosol containing the spectroscopic sample, said desolvated aerosol introduced into said coaxial inlet port formed in said inner tubular vessel.

7. A radio frequency excitation apparatus for exciting a spectroscopic sample, said excited spectroscopic sample emitting characteristic radiation, said apparatus comprising:

a. radio frequency power oscillator means having a plate tank circuit and a grid tank circuit defining a single resonant circuit including an induction coil and a tuning capacitor, said plate tank circuit and said grid tank circuit having a common inductance, said radio frequency power oscillator means including vacuum tube means having a plate, a grid, and a cathode, first and second capacitors for dc isolation, a plate RF choke, and a grid RF choke, said plate RF choke connected to said plate and one side of said first capacitor, the other side of said first capacitor connected to one side of said tuning capacitor and one side of said induction coil, said tuning capacitor and said induction coil in parallel, the other sides of said tuning capacitor and said induction coil connected to one side of said second capacitor, the other side of said second capacitor connected to said grid and said grid Rf choke, said induction coil having a tap which is connected to ground;

b. plasma torch means, said induction coil externally and coaxially encircling a portion of said plasma torch means, said encircled portion of said plasma torch means defining a plasma forming region, said radio frequency power oscillator means exciting a plasma forming gas within said plasma region;

c. means for introducing the spectroscopic sample into said excited plasma, the spectroscopic sample introduced into said excited plasma emitting characteristic radiation; and

d. power supply means operatively connected to said radio frequency power oscillator means.

8. The radio frequency excitation apparatus as claimed in claim 7 wherein said power supply means includes:

a. circuit breaker means through which input power is applied;

b. filament supply means operatively connected to said circuit breaker means and said vacuum tube means, said filament supply means generating filament voltage for said vacuum tube means;

c. power regulator means operatively connected to said circuit breaker means; and

d. rectifier means operatively connected to said power regulator means and said vacuum tube means, said rectifier means generating plate voltage for said vacuum tube means, said power regulator means controlling the level of said plate voltage.

9. A spectroscopic apparatus comprising:

a. a radio frequency excitation apparatus for exciting a spectroscopic sample, said excited spectroscopic sample emitting characteristic radiation, said radio frequency excitation apparatus including a radio frequency power oscillator and an associated power supply, a plasma torch, and injection means, said radio frequency power oscillator comprising a single resonant circuit which includes an induction coil and a tuning capacitor, said induction coil in parallel with said tuning capacitor, a plate tank circuit and a grid tank circuit of said radio frequency power oscillator having a common inductance, said induction coil externally and coaxially encircling a portion of said plasma torch, said encircled portion of said plasma torch defining a plasma forming region, said radio frequency power oscillator exciting a plasma forming gas within said plasma forming region, said injection means introducing said spectroscopic sample into said excited plasma, said introduced spectroscopic sample being excited and emitting characteristic radaition;

b. entrance slit means through which said characteristic radiation is directed;

c. grating means for diffracting said characteristic radiation from said entrance slit means into a distribution of spectrum lines;

d. a plurality of exit slit means on which said spectrum lines are imaged; and

e. means for detecting and processing said spectrum lines imaged on said exit slit means for indicating the chemical composition of said spectroscopic sample; and

f. servo means operatively connected to said grating means for alignment of said grating means with respect to said entrance slit means and said exit slit means.

10. A spectroscopic apparatus comprising:

a. a radio frequency excitation apparatus for exciting a spectroscopic sample, said excited spectroscopic sample emitting characteristic radiation, said radio frequency excitation apparatus including a radio frequency power oscillator and an associated power supply, a plasma torch, and injection means, said radio frequency power oscillator comprising a single resonant circuit which includes an induction coil and a tuning capacitor, a plate circuit and a grid tank circuit of said radio frequency power oscillator having a common inductance, said radio frequency power oscillator including a capacitor for dc isolation and vacuum tube means having a plate, a grid, and a cathode, said induction coil in parallel with said tuning capacitor, one side of said tuning capacitor operatively connected to said plate, the other side of said induction coil and the other side of said tuning capacitor operatively connected to said grid via said dc isolation capacitor, said induction coil having a tap operatively connected to a return, said induction coil being common to said plate tank circuit and said grid tank circuit, said induction coil externally and coaxially encircling a portion of said plasma torch, said encircled portion of said plasma torch defining a plasma forming region, said radio frequency power oscillator exciting a plasma forming gas within said plasma forming region, said injection means introducing said spectroscopic sample into said excited plasma, said introduced stpectroscopic sample being excited and emitting characteristic radiation;

b. entrance slit means through which said characteristic radiation is directed;

c. grating means for diffracting said characteristic radiation from said entrance slit means into a distribution of spectrum lines;

d. a plurality of exit slit means on which said spectrum lines are imaged;

e. means for detecting and processing said spectrum lines imaged on said exit composition of said spectroscopic sample; and

f. servo means operatively connected to said grating means for alignment of said grating means with respect ot said entrance slit means and said exit slit means.

11. The radio frequency excitation apparatus as claimed in claim 10 wherein said plasma torch means includes:

a. an outer tubular vessel opened at one end and closed at an opposite end, a tangential inlet port for an insulating gas formed near the closed end of said outer tubular vessel; and

b. an inner tubular vessel coaxial mounted within said outer tubular vessel, a chamber for said insulating gas formed between said outer tubular vessel and said inner tubular vessel, said inner tubular vessel opened at one end, said inner tubular vessel projecting from said closed end of said outer tubular vessel, said projecting portion of said inner tubular vessel having a narrowed portion defining a coaxial inlet port for introduction of the spectroscopic sample, a tangential inlet port for a plasma forming gas formed in said projecting portion of said inner tubular vessel.

12. The radio frequency excitation apparatus as claimed in claim 11 wherein said injection means includes means for providing a desolvated aerosol containing the spectroscopic sample, said desolvated aerosol introduced into said coaxial inlet port formed in said inner tubular vessel.

Other info:

Inventors: Turner, Arthur S. (Carlisle, MA, US)

Application Number: 487168
Filing Date: 1974-07-10
Publication_date: 1976-05-25
Assignee: Baird-Atomic, Inc. (Bedford, MA)
Primary Class(es): 356/316 219/121.36, 315/111.51, 356/248, 356/305
Other Classes:
US Patent Ref:

3467471	Sep, 1969	Greenfield et al.	356/85.
3633990	Jan, 1972	Baierlein	356/80.
3846024	Nov, 1974	Turner	356/80.

Other Refs:
Primary Examiner: McGraw, Vincent P.
Assistant Examiner:
Attorney: Morse, Altman, Oates & Bello