Chemistry: analytical and immunological testing – Nitrogen containing – Amine and quaternary ammonium
Reexamination Certificate
2000-07-24
2003-01-21
Warden, Jill (Department: 1743)
Chemistry: analytical and immunological testing
Nitrogen containing
Amine and quaternary ammonium
C436S106000, C422S083000, C422S091000
Reexamination Certificate
active
06509194
ABSTRACT:
BACKGROUND OF THE DISCLOSURE
1. Field of the Invention
The invention relates generally to a method and apparatus of determining gas phase species concentration, and more particularly, to a method and apparatus for detecting concentration of NH-containing species.
2. Description of the Background Art
The use of ammonia (NH
3
), a corrosive and toxic gas, in industrial processes is wide spread. Trace amount of NH
3
has also been shown to adversely impact the use of chemically activated deep ultraviolet photoresists in advanced semiconductor fabrication. The need for worker protection, from either acute exposure to high NH
3
concentrations or long term exposure to very low concentration levels, has resulted in the development of sampling methods for the detection and quantitative measurement of NH
3
in ambient air. Some existing analytical techniques for NH
3
detection are briefly described below.
a. Electrochemical Method
In this method, gaseous NH
3
is absorbed into an electrochemical sensor assembly with a resultant change in the electrical conductivity of the sensor cell. The increased current flow allowed by the sensor is fairly linear over the concentration range of 1-50 ppm. A lower detection limit is about 500 ppb, but reproducibility of the sensor to periodic exposure of NH
3
is only fair.
b. Ozone Method
This method uses a reaction between ozone (O
3
) and ammonia, in which NH
3
is first converted to NO
2
, followed by a chemiluminescent reaction between NO
2
and O
3
. The reaction with O
3
results in the formation of excited state NO
2
molecules, denoted as NO
2
*, and the intensity of emission from NO
2
* is used to determine the original NH
3
concentration. However, difficulties in quantitative measurement result from side reactions during the conversion from NH
3
to oxides of nitrogen (forming NO and, perhaps, NO
3
or HNO), and also from non-stoichiometric side reactions between NO
2
and O
3
. In addition, the emission from excited NO
2
species (NO
2
*—the asterisk “*” is used in this disclosure to designate an excited state of a species) extends from the near UV into the yellow-green region of the visible spectrum (this emission is the well known “air afterglow” in the night sky, and results from the reaction: NO+O
2
→NO
2
*+O). Detection of this very diffuse emission over a broad spectral region is susceptible to interference from other emitting species, and may pose difficulties in accurate concentration determination.
c. Air Sampling Method
In this method, air samples are collected via a carefully prepared evacuated sampling ampoule and injected into a gas chromatograph (GC) for comparison against analyzed standards by well known methods. Careful selection of the GC column and temperature settings are necessary in order to obtain reliable results. A number of detectors are available for this method. One very sensitive detection method is mass spectrometry, but calibration for quantitative work is very difficult. Additionally, the GC/MS method is very expensive, and it is difficult to configure in a continuous sampling mode.
d. Laser Induced Emission
This method has the potential for great sensitivity, but requires great expertise and expense due to its sophistication. NH
3
, or a fragment thereof, is electronically (or vibrationally) excited by a pulsed, tunable dye laser, thereby creating observable fluorescence. However, non-linear optical effects and saturation effects tend to make quantitative measurements extremely complex, if at all possible.
Each of these prior art techniques has its own limitation and varying degrees of experimental complexities. Therefore, a need exists in the art for alternative analytical methods which allow continuous on-line determination of low level of ammonia in ambient air or gas samples.
SUMMARY OF THE INVENTION
Embodiments of the invention generally provides a method and apparatus for determining the concentration of an NH-containing species in a gas sample. The method comprises detecting radiation from excited imidogen radicals (NH*) generated from the gas sample, and determining the concentration of the NH-containing species from calibration data correlating detected NH* radiation intensity with concentration of the NH-containing species. In one embodiment, the NH-containing species is ammonia (NH
3
), and the NH* radiation is generated by reacting NH
3
with a gas sample containing fluorine. Using a bandpass optical device, NH* radiation around 336 nm can be selectively transmitted and detected, with minimal interference from other emitting species.
REFERENCES:
patent: 4432939 (1984-02-01), Watanabe et al.
patent: 5739038 (1998-04-01), Burrows
Matsuda et al. “Formation and quenching of imidogen (NH) fragments in excited states by high energy electron irradiation of helium-ammonia gas mixture”, Appl. Radiat. Isot. (1990), 41(8), 757-61.*
Hikida, T. et al. “Formation of imidogen(c1.Pl.) and (A3.Pl.) in the photolysis of ammonia, hydrazoic acid, and isocyanic acid a 121.6 nm”, Chem. Phys. (1988), 121(1), 63-71.*
Kenner, R. D. et al. “Two-photon formation of imidogen (NH/ND)(A3.Pl.) in the 193 nm photolysis of ammonia. I. Mechanism and identification of the intermediate species”, Chem. Phys. (1987), 118(1), 141-52.*
Hochard, L. et al. “Imidogen (NH) production in an argon + ammonia glow discharge” Symp. Proc.—Int. Symp. Plasma Chem., 6th (1983), vol. 2, 473-7.*
Chowdhury et al. “Isocyanic acid as a laser fuel”, Proc. SPIE-Int. Soc. Opt. Eng. (1988), 875 (Short Ultrashort Wavelength Lasers), 173-82.*
Qi et al. “: Direct production of excited fluoroimidogen (NF)(b1.SIGMA.+) in the atomic fluorine -molecular florine—ammonia system via a supersonic regime”, Conf. Ser.—Int. Phys. (1985), 72(Gas Flow Chem. Lasers, 1984), 149-52.*
Hack et al. “Reaction of imidogen (X3.SIGMA.-) with dioxygen(3.SIGMA.g-) and dioxygen(1.DELTA.g) in the gas phase”, J. Chem. Soc., Faraday Trans. 2 (1985), 81(6), 949-61.*
Hack et al. “Production of electronically excited fluoroimidogen radicals in the system NH3-F-O2 (1Dg)”, Chem. Phys. Lett. (1981), 82(2), 327-30.*
Bower et al. “Qenching of NH (a 1D)”, J. Chem. Phys., 1987 v. 86 (4), pp. 1954-1956.*
Hack “NH RAdical Reactions”, N-Cent. Radicals (1998), 413-466, Ed. Alfassi et al.*
Durie, “The Spectra of Flames Supported by Fluorine”, Proceedings of the Royal Society of London, Series A, vol. 211, Mar. 20, 1952, pp. 110-121.
Gaydon, “The Spectroscopy of Flames”, Flames with Nitrogen, Halogens, etc., pp. 219-220, 1957.
Cheung Wan-Yee
Gakh Yelena
Moser Patterson & Sheridan LLP
Verlangieri Patricia A.
Warden Jill
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