Electricity: measuring and testing – Particle precession resonance – Using an electron resonance spectrometer system
Reexamination Certificate
2000-11-21
2002-10-08
Arana, Louis (Department: 2862)
Electricity: measuring and testing
Particle precession resonance
Using an electron resonance spectrometer system
C324S317000
Reexamination Certificate
active
06462546
ABSTRACT:
The invention is related to a method for investigating the imperishability of liquid foodstuffs by means of electron spin resonance (ESR), wherein a sample of the foodstuff is exposed to an elevated temperature, as compared to room temperature, for an extended period of time, wherein during the period of time an ESR signal of the sample is measured in predetermined time intervals, the intensity of the ESR signal is plotted vs. time and the moment in time is detected when the intensity shows a superproportional increase.
The invention is, further, related to an apparatus for investigating the imperishability of liquid foodstuffs by means of electron spin resonance (ESR), wherein a sample of the foodstuff is exposed to an elevated temperature, as compared to room temperature, for an extended period of time, wherein during the period of time an ESR signal of the sample is measured in predetermined time intervals, the intensity of the ESR signal is plotted vs. time and the moment in time is detected when the intensity shows a superproportional increase.
When doing so, the samples are provided with a so-called spin-trap-substance or a spin-label-substance or a corresponding intrinsic substance is already comprised in the sample anyhow.
A method of the afore-mentioned kind is disclosed in an article by Kaneda, H. et al. “Free Radical Reactions in Beer during Pasteurization”, International Journal of Food Science and Technology (1994), 29, pp. 195 to 200. A corresponding method as well as an apparatus for executing same is also disclosed in EP 0 720 026 A2. Still another description of such a method together with a corresponding apparatus may be found in an application note by Barr, D. “Measuring Flavor Stability of Beer using the Bruker EMX Spectrometer”, Bruker EPR Application Note (1998).
For a better understanding of the present method the underlying measuring technology of electron spin resonance shall be briefly discussed.
Electron spin resonance (ESR) is a partial field within the general field of magnetic resonance. In ESR, a sample substance is simultaneously exposed to a high frequency electromagnetic field as well as to a strong constant magnetic field of high homogeneity. By varying the field strength of the constant magnetic field various electron spin resonances are excited within the sample and may be plotted as a spectrum. Typically a high frequency electromagnetic field within X-band, i.e. at about 10 GHz is utilized, which means that the strength of the constant magnetic field is about 0.32 T. It is, however, also known to conduct ESR measurements on the one hand at frequencies being ten times as high or, on the other hand, being only one tenth of the afore-mentioned frequeny.
As mentioned before, for exciting ESR it is only necessary to expose the sample substance to a magnetic high frequency field. When the measuring frequencies are within the microwave range, hollow cavities are conventionally utilized for that purpose. Such cavities are mostly rectangular cavities of the oscillation mode TE
10n
, however, in some instances also cylindrical cavities of the oscillation mode TE
011
are utilized.
Such rectangular cavities are conventionally configured in double length, i.e. as TE
102
cavities. The sample container having the shape of a sample tube is then inserted at the cavity center where the H-lines of both oscillation loops extend parallel to each other. In such a situation the sample, is, hence, located within the area of maximum magnetic high frequency field strength. Due to the characteristics of such oscillation mode, this is also the area of minimum electric high frequency field strength. This is of particular advantage for lossy samples because in such a way the dielectric losses are at a minimum.
When liquid samples are to be investigated with ESR measurements, one has to bear in mind that such samples per se are subject to substantial dielectric losses. One has, therefore, to take care that the liquid sample substance is as much as possible arranged within the plane within which the magnetic high frequency field strength is at a maximum and the electric high frequency field strength is at a minimum. For achieving that one may either utilize one single thin capillary, however, it is also well known to utilize so-called “flat cells”, i.e. sample tubes which have been flattened within the measuring area. By doing so the liquid sample substance is essentially distributed within an area so that one may place relatively much sample substance within the afore-mentioned plane of maximum magnetic and minimum electric high frequency field strength.
Sample heads of the afore-mentioned kind are generally known and are also commercially available from the competent manufacturers.
It is, furthermore, well known in the field of magnetic resonance to arrange a plurality of different samples within independent vessels or at least at individual locations within the same probe head being distant from each other, for conducting comparative measurements. By doing so one may either conduct direct comparative measurements between two sample substances or one may utilize one of the substances, being a reference substance, as a standard, whereas only the other substance is investigated. This standard may be utilized for quantitative scaling purposes or one may use same for effecting a field control (so-called “internal lock”). Within this context various probe heads have been disclosed, permitting that two distinct sample substances are received within a sample area or within two independent sample areas, respectively.
An example of such a prior art probe head is disclosed in an article by DALAL et al. “The effects of lossy solvents on quantitative EPR studies”, Journal of Magnetic Resonance, 44, pp. 415-428 (1981).
In this prior art probe head (cf. FIG. 3 in the afore-mentioned article) a sample tube arrangement is utilized in which within a thin-walled NMR-sample tube of 0.5 cm outer diameter a first capillary having an inner radius of 0.05 cm and, either a quartz tube having a radius of 0.064 cm or another capillary having an inner radius of 0.05 cm are utilized. The first capillary contains the sample substance being dissolved within a non-lossy solvent as a reference substance, whereas the second capillary or the tube contains the lossy solvent being conventionally used. Both samples may be arranged within the plane of minimum electric high frequency field strength.
U.S. patent specification No. 5,552,709 discloses a probe head for nuclear magnetic resonance (NMR). This prior art probe head is of elongate design and comprises a plurality of parallel capillaries. The capillary walls consist of a non-conductive material so that the quality factor Q of the resonance system shall be increased by reducing the electrical losses caused by currents flowing radially with respect to the sample container axis.
In another sample container for an NMR-spectrometer, as disclosed in U.S. Pat. specification No. 5,469,061 a plurality of laterally adjacent capillaries is likewise used as a sample container. These capillaries are switched in series such that a flow cell is configured in which the liquid sample substance enters through one capillary, then flows through all of the remaining capillaries under repetitive change of flow direction and, finally, is discharged from another capillary.
Finally, U.S. Pat. specification No. 5,596,276 discloses a standard rectangular cavity as used for electron spin resonance spectrometers.
The afore-mentioned probe heads, therefore, are exclusively intended to be used for making comparative measurements between two samples, one of which being conventionally known for reference purposes.
While ESR measurements on liquid samples have only played a secondary role in the past, because ESR was mostly used as an analytical instrument in connection with solids, various applications have gained attention in the recent past in which ESR was utilized on liquid samples.
One of these applications is the investigation of the imperishability of beer. One has found t
Heiss Arthur H.
Jiang JinJie
Kamlowski Andreas
Schmalbein Dieter
Weber Ralph T.
Arana Louis
Bruker Analytik GmbH
Weingarten Schurgin, Gagnebin & Lebovici LLP
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