Optics: measuring and testing – By dispersed light spectroscopy – Utilizing a spectrophotometer
Patent
1995-05-02
1997-10-21
Evans, F. L.
Optics: measuring and testing
By dispersed light spectroscopy
Utilizing a spectrophotometer
356327, 356328, 356246, 250373, G01J 302, G01J 342, G01J 3447
Patent
active
056802099
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
The invention relates to spectroscopic systems for the analysis of small and very small quantities of substance, particularly in the HPLC range.
Spectroscopic methods are frequently employed for analyzing substances in the fields of chemistry and biology.
Reference FR 2643147 A1 discloses a process and an apparatus for spectral photometry of liquids. Radiation vertically traverses the liquid to be tested in the direction of flow thereof by means of cone-shaped bodies. For this purpose, the large end faces of the cone-shaped bodies are directed at the liquid to be tested.
References DE-U-9013325 and GB-A 2116707 disclose optical systems for testing liquids, wherein the essential optical elements used for guiding the light are lenses.
None of the cited references are directed at a process for analyzing small and very small quantities of substance, however; nor do they refer to specific problems in micro-analytical procedures.
Reference U.S. Pat. No. 4,379,235 discloses the use of fiber-optical bundles in a scanner head for improving the spatial resolution of the scanner.
The inventive complex is directed to the analysis of very small quantities of substance. This automatically means that the sample spaces shrink to filament-shaped cylinders because of the largest possible path length. As there there can be no parallel irradiation, one has to rely on approximate solutions, preferred variants of which are described whithin the framework of this invention.
The simultaneous spectrometer developed by the applicant comprises a higher aperture than any other similar device and, as a result, achieves maximum energy efficiency and optimum spectral resolution. The high aperture entails one limitation: so-called "complete image formation" (in microscopy: Koehler's principle) is no longer possible with a lens system, as the spherical and chromatic errors limit the degree of transmission. (In microscopy, one can resort to immersion.) Hence, the solution resides in an aspherical mirror optical system.
FIG. 1 shows a prior art spectroscopy system wherein the spectrometer is a simultaneous spectrometer.
The core or main feature of the simultaneous spectrometer 1 is the use of self-scanning lines of diodes 2 which were developed by Snow in 1975 and comprise 512 single diodes over a length of 1.27 cm. The silicon diodes determine the effective spectral range of the simultaneous spectrometer 1 of about 200 to 1000 nm. The use of the lines of diodes 2 in a spectrometer as developed by the applicant is determined by the line geometry, a diode width of 25 .mu.m defining the width of the exit slit 3 of the spectrometer. In the formation of images subject to the minimum error rate, i.e. 1:1, this is also the width of the entrance slit 3. The 12.52 mm spectrum length is extremely short for a spectrum of analytical interest, e.g. the visible range of from 400 to 800 nm, while the bandwidth of 0.8 nm is satisfactory. Said unusually small linear dispersion signifies a very short focal distance of the spectroscopic instrument, which would primarily result in a small dispersion element. The spectral resolution (Rayleigh criterion) for the 0.8 nm bandwidth cannot be realized in this manner, however, so that solutions based on prisms are ruled out. For a grating arrangement, short bandwidth, low groove density and large grating area, i.e. a small spectrograph having an extremely high relative aperture, are required. This automatically leads to a light conductance capable of competing with conventional instruments. The afore-said requirements of the grating 5 are met by holographically generated concave gratings.
A lighting unit 6 adapted to the design of the simultaneous spectrometer 1 is shown in FIG. 1. In order that the spectrometer 1 may be utilized with the highest efficiency possible, the arrangement is basically the same as in the spectrometer; an aspherical (ellipsoidal) mirror 7 having the same aperture replaces the high-aperture hologram grating 5. So as to achieve "complete image formation", i.e. the strictly conjug
REFERENCES:
patent: 2790081 (1957-04-01), Munday
Stromberg et al, The Review of Scientific Instruments, vol. 41, No. 12, Dec. 1970, pp. 1880-1881.
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