COOLING OF CCD.

TECHNICAL FIELD

The present invention relates Gas Chromatography, GC - Ultraviolet absorption, UV - spectroscopy, GC-UV, to detect, identify and analyze gases, liquids and solid unknown substances from high to very low concentrations. The basic technology is known and used for various purposes. The invention relates to physical, mechanical and software control solutions. The invention solves one of the major problems to achieve in order to detect absorption of very short wavelengths (typically down to 120nm) for identification of unknown substances in gas phase.

The invention is very versatile and can be used in various applications such as hand held portable and laboratory based bench top instruments. One particu- lar use is for detection of metabolic or other substances emanating from living cells, tissues and in particular that can be found in exhaled air, saliva, sweat, blood and urine from humans, animals, organisms and plants etc. for detection of various deceases and metabolic activities like stress. Substances can be such as nitrogen oxide, urea, acetone, isoprene, carbon disulfide coming from diseases like cancer, gastric ulcers, asthma, diabetes, psychiatric disorders, drug abuse, stress conditions and intoxications, etc.

Many of those metabolic substances have significant high absorption of UV light in a spectrum ranging from about 120 nm wave length and longer.

BACKGROUND ART

Gas chromatography UV - spectroscopy is used for identification and quantification of various substances that can be transformed into gas. The technology is based on that substances in gas phase first passes through a heated column where the gas has a substance dependent velocity through the column and when the gas to be analyzed leaves the first heated column and enters a chamber where UV light passes the gas, absorb light when the light passes the gas, in a spectral way, so the photonic spectrum relates with very high accuracy to the identity of the substance.

The light used for the absorption shall preferably have a broad spectrum of wavelengths to allow absorption over a broad spectrum of wavelengths. The passage, chamber, where light penetrates the gas shall be designed to have the gas absorb as much light as possible and to achieve maximum resolution in analyzing, the chamber volume shall be kept as small as possible.

The process is basically a gas chromatography where a chamber with a light path is added in the end of the column so the gas passes through the cham- ber and absorbs light with a spectrum that is related to the gas. The remaining lights then passes into a spectrograph and further on to a light sensitive sectioned array preferably a CCD, Charge Coupled Device, so the spatial light components hits individual light sensitive elements enabling spatial detection of the light and thereby allows identification of the substance to be analyzed. Light is directed in to the spectrograph through a passage that can be a window made out of a photon transparent material that allows passage of the required wavelengths or a non-physical window or a slit. A CCD has the ability to collect photons and convert them to electrons to be red out by electronics, but has also a self-generated flow of electron, electron noise.

Such electron flow is a background noise which is temperature dependent with an increased current by increased temperature. It is in many cases of major importance to have a low background noise to be able to detect low - weak photonic signals and differentiate the signals from noise.

SUMMARY OF THE INVENTION

An object of the present invention is to eliminate at least one of the drawbacks mentioned above, which is achieved by assigning to the characteristics in accordance with claim 1- 10. By lowering the temperature the electron flow from the CCD is decreased. So, if the temperature of the CCD is lowered the CCD will have an increased ability to detect lower number of photons i.e. a higher sensitivity and a higher signal to noise ratio, S/N. The invention is a combination of barrier gas preventing substances in gas phase to be analyzed form entering the spectrograph and cooling of CCD or cooling of the CCD by expansion of gas in close proximity of a CCD only. The photon collecting device, that can be a CCD, has a self-generated tempera- ture dependent noise in its electrical output signal that can be reduced by lowering the temperature, i.e. lowering the temperature will increase the S/N ratio in favor of a more precise and accurate read out.

In various embodiments the photon collecting device, the CCD is cooled by expansion of carrier gas released through nozzles into the spectrograph cavity in proximity to and in thermal contact with the CCD. This design and arrangement combines the cooling of the CCD with the gas flow through the spectrograph and out through the light entrance slit so by using the same gas and gas source, cooling of the CCD does not require any major separate arrangement and is simply made by the position if the inlet of gas into the spec- trograph in proximity to the CCD.

The highest temperature decrease, the best cooling effect, takes place where highest rise of pressure is, i.e. where the largest expansion of the gas is. Pressurized gas is normally available as carrier gas for gas chromatography and it can as one solution of this invention also be used for cooling by having the expansion of the photon collecting device like a CCD. The pressure of the carrier gas in a gas chromatography is normally just in the region of single digit bar or less, but the gas normally comes from far higher pressure from up to two or three digit bar pressure.

After expansion of the gas in close proximity to the CCD or in good thermal contact with the CCD, the gas can be led through a spectrograph and out through a slit preventing substances in gas phase to enter the spectrograph and / or be led to be used as carrier gas for the gas chromatography column.

By having the expansion take place away from the entrance to the gas chromatography column the gas temperature will increase. A higher temperature of the gas is favorable as the gas enters the column to be further heated.

According to a first aspect of the invention, the photon collecting device, the CCD is cooled by expansion of carrier gas released through nozzles in to the spectrograph cavity in proximity to and in thermal contact with the CCD. This design and arrangement combines the cooling of the CCD with the gas flow through the spectrograph and out through the light entrance slit so that by using the same gas and gas source, cooling of the CCD does not require any major separate arrangement and is simply made by the position if the inlet of gas into the spectrograph in proximity to the CCD. Expansion of gas in proximity to the CCD can take place at one place or at multiple places and cooling effect can be directed by local flow and expansion of gas.

According to a second aspect of the invention, the gas that is used for cooling a photon collecting device like a CCD can be used after expansion as carrier gas of a gas chromatography column.

According to a third aspect of the invention, part of or the full gas flow after expansion and cooling a photon collecting device like a CCD can be used for preventing undesired gas to enter the spectrograph if the spectrograph does not have a physical window for light entrance. According to this aspect the gas after expansion leaks out through the light entrance.

According to a fourth aspect of the invention the photon collecting device like a CCD will have a higher S/N ration due to lowered temperature.

According to a fifth aspect of the invention it allows the photon collecting de- vice like a CCD to have a higher S/N ration due to its lower temperature by letting the expanded gas out to the open air.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to explain the invention, a number of embodiments of the invention will be described below with reference to the drawings, in which:

Fig. 1 shows schematically a first embodiment of an apparatus (9) in accordance with the invention, comprising a spectrograph (8) with a dispersive element (1 ) with light beams (3, 5) passing through a small slit (7) and reflects at the dispersive element (1 ) and hits a light sensitive element (2) like a CCD (2). The gas flows (4) into the spectrograph and then out of the spectrograph through a slit (7). The pressure of the gas decline from where it enters (4) the spectrograph to where then the gas exit from the spectrograph through the slit (7). The drop of pressure over the slit (7) creates a velocity of the gas that prevents gas or particles to enter through the slit (7) in the reverse direction.

Fig 2 shows schematically a second embodiment of an apparatus (9) in accordance with the invention, comprising a spectrograph (8) with a dispersive element (1 ) with light beams (3, 5) passing through a small slit (7) and reflects at the dispersive element (1 ) and hits a light sensitive element (2) like a CCD (2). The gas flows (4) in to the spectrograph in close proximity to a photon sensitive element like a CCD and then out of the spectrograph through a slit (7) and or a duct (12) leading to the entrance of a gas chromatography column to be used as carrier gas in the column. The pressure of the gas decline from where it enters (4) the spectrograph to where then the gas exit from the spectrograph through the slit (7) or through the duct (12) leading to the entrance of the gas chromatography column.

The drop of pressure over the slit (7) creates a velocity of the gas that pre- vents gas or particles to enter through the slit (7) in the reverse direction. The drop of pressure by expansion of the gas in close proximity to the CCD will transport heat away from the CCD and thereby lower its temperature and thereby increase the signal to noise ratio.

Same reference numerals have been used to indicate the same parts in the figures to increase the readability of the description and for the sake of clarity. The figures are not made to scale, and the relative dimensions of the illustrated objects may be disproportional.

Fig. 3 shows schematically a third embodiment of an apparatus (9) in accordance with the invention, comprising a spectrograph (8) with a dispersive ele- ment (1 ) with light beams (3, 5) passing through a slit (7) and a physical window (13) and reflects at the dispersive element (1 ) and hits a light sensitive element (2) like a CCD (2). The gas flow (4) that enters through the duct and that will be expanded in close proximity to the CCD and has its exit from the spectrograph through a duct (12) leading to the entrance of a gas chromatog- raphy column to be used as carrier gas or to the open air. DETAILED DESCRIPTION

The invention relates to a method of increasing the transparency of very short wavelength photons in GC-UV applications.

The embodiment of an apparatus shown in Fig. 1 comprises a spectrometer apparatus (9) comprising a spectrograph (8) with a dispersive element (1 ) with light beams (3, 5) passing through a slit (7) and being reflected at the dispersive element (1 ) and hitting a light sensitive element (2) like a CCD (2). Gas (4) flows from an inlet into the spectrograph and then out of the spectrograph through a slit (7). The pressure of the gas decline from the inlet of the gas (4) to where the gas exits from the spectrograph through the slit (7) and or through the duct leading to a gas chromatography column. (12). The drop of pressure through the slit (7) creates a velocity of the gas that prevents gas and particles to enter through the slit (7) in the reverse direction (6). As long as the pressure is higher at the point where the gas enters into the spectrome- ter than the point where it leaves the spectrometer there will be a gas flow where the gas has a velocity preventing gas or particles to enter the spectrograph. As the spectrograph - spectrometer in the shown embodiment does not comprise a physical window, but only a dynamic gas flow that does not filter any of the light (5) that enters through the slit (7) the full spectrum of in- coming lights (5) will enter the spectrograph - spectrometer.

Fig. 2 shows schematically a spectrometer apparatus (9) comprising a spectrograph (8) with a dispersive element (1 ) with light beams (3, 5) passing through a slit (7) and being reflected at the dispersive element (1 ) and hitting a light sensitive element (2) like a CCD (2). The slit (7) is so small that the flow of gas from outside the spectrograph into the same is so small that it will only marginally affect the function of the spectrograph and spectrometer. The gas flow (4) that enters through an inlet or duct and that will be expanded in close proximity to the CCD can either be divided into a flow out from the spectrograph through the light entrance slit into the spectrograph. Fig. 3 shows schematically a spectrometer apparatus (9) comprising a spectrograph (8) with a dispersive element (1 ) with light beams (3, 5) passing through a slit (7) and a physical window (13) and being reflected at the disper- sive element (1 ) and hitting a light sensitive element (2) like a CCD (2). The gas flow (4) that enters through the duct and that will be expanded in close proximity to the CCD and has its exit from the spectrograph through a duct (12) leading to the entrance of a gas chromatography column to be used as carrier gas or to the open air.

Definitions: A spectrograph is consisting of a slit (7) where light enters, a dispersive element that reflects the fractioned light.

A spectrophotometer is a spectrograph that has a photon collecting device (2) to collect the fractioned light (10) for read out and measurement of spectra. The Photon collecting device can be a CCD - Charge Collecting Device (2). Additionally, although individual features may be included in different embodiments, these may possibly be combined in other ways, and the inclusion in different embodiments does not imply that a combination of features is not feasible. In addition, singular references do not exclude a plurality. The terms "a", "an" does not preclude a plurality. Reference signs in the claims are provided merely as a clarifying example and shall not be construed as limiting the scope of the claims in any way.