Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – Distributive type parameters
Patent
1990-08-16
1991-10-15
Williams, Hezron E.
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
Distributive type parameters
324636, 73 232, 73 2341, 73 2342, G01N 2200
Patent
active
050577824
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to a spectrometer and in particular to a microwave spectrometer.
Microwave spectroscopy is known to measure changes in rotational energy of substances in the vapour state, it being possible to make measurements of each spectral line with such precision (at least to one part in 100,000 in the measurement of line frequencies) that accurate measurements of only a small number of lines (say 3 or 4) provides a unique fingerprint not shared by any other known chemical compound. The method of microwave spectroscopy therefore differs from virtually any other known analytical method in its uniqueness of identification.
The standard method of microwave spectroscopy has hitherto been limited to a small number of rather simple chemical compounds because the compound has had to be vaporized in order to study it whereas the great majority of chemicals of interest to business commerce, etc., such as pharmaceutical preparations, drugs etc., are involatile and normally thought of as not capable of being vaporized.
SUMMARY OF THE INVENTION
The object of this invention is to provide a spectrometer which is capable of use with at least some involatile substances.
The invention may be said to reside in a spectrometer for analyzing a sample substance, said spectrometer including:
(a) means for supporting the sample substance,
(b) means for providing a flow of gas through or over said substance such that molecules of said substance are entrained in said gas flow,
(c) nozzle means for receiving said gas flow entraining said molecules of the substance and for ejecting said flow of gas as a supersonic beam seeded with said molecules,
(d) means for creating an electric field in the vicinity of said beam which is ejected by said nozzle means,
(e) means for providing a source of electromagnetic radiation which passes through said beam in the vicinity of said electric field, and
(f) means for detecting said electromagnetic radiation to thereby detect an absorption signal of the molecules which has been modulated in frequency by said electric field.
Since the substance to be studied is entrained in a gas flow which is ejected in the vicinity of an electric field, substances which are generally involatile can be analyzed with the invention since sufficient numbers of molecules can be entrained in a gas flow and reduced to the desired pressure and temperature during supersonic expansion of the beam ejected from the nozzle means to enable analysis to take place.
Preferably said means for creating an electric field comprises a pair of electrodes between which the beam and said electromagnetic radiation pass.
Preferably the electrodes are supported in a vacuum cavity and pump means is provided to create a vacuum in said cavity.
Preferably a cold trap is provided in said cavity to facilitate trapping of gas molecules in the gas flow to thereby facilitate maintenance of the vacuum in the cavity.
Preferably the means for supplying a gas flow together with the sample is heated by a heating means to cause some vaporization of the substance so that it can be more easily entrained in the gas flow and wherein the gas flow is maintained at a predetermined temperature by the heating means to maintain the substance in the vapour state not allowing deterioration of the substance.
BRIEF DESCRIPTION OF THE DRAWINGS
A preferred embodiment of the invention will be described with reference to the accompanying drawings, in which:
FIG. 1 is a view of a measurement cavity of a spectrometer according to the preferred embodiment of the invention;
FIG. 2 is a view of the sample preparation device of the spectrometer; and
FIG. 3 is a view along the line 3--3 of FIG. 2.
DETAILED DESCRIPTION OF THE INVENTION
With reference to FIG. 1 a generally cylindrical housing 10 is shown which defines a cavity 20 and is maintained at a low pressure (about 0.1 Pa) and preferably at a vacuum by a diffusion pump 22. The housing 10 also has a cold trap 24 which is preferably in the form of a Chevron Baffle cold trap which
REFERENCES:
patent: 3889182 (1975-06-01), Easley et al.
patent: 4598577 (1986-07-01), Jowitt et al.
patent: 4607521 (1986-08-01), Saito et al.
patent: 4894603 (1990-01-01), Berger et al.
patent: 4896097 (1990-01-01), Berger et al.
Brown Ronald D.
Crofts Jonathan G.
Godfrey Peter D.
Francos William S.
Monash University
Williams Hezron E.
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