Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
  • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
  • G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
  • G01N33/02—Food
  • G01N33/14—Beverages
  • G01N33/146—Beverages containing alcohol
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
  • G01N33/02—Food
  • G01N33/14—Beverages

Definitions

• the present invention refers to techniques for the determination of the content of ethanol in liquid or aeriform substances.
• the invention has been developed paying particular attention to the possible application in determination of the ethanol content in wine or in alcoholic beverages.
• the known methods for the evaluation of the ethanol are essentially chromatographic methods, such as gas chromatography or high efficiency liquid chromatography, and such methods sometimes require distillation and subsequent density and refraction index measurements. Such methods require specialized personnel, sometimes pre-treatment of the samples to be analyzed and they must be performed in professional laboratories using expensive instrumentations. Such methods are therefore incompatible with the increasing necessities of field measurements and necessities determined by the automation of the food industry, since they do not allow continuous monitoring during the industrial processes and they are not very useful for rapid routine analysis.
• ITRM2002A000310 discloses the use of a solid state sensor, that exploits a porous material to detect concentrations of substances in liquids and vapors.
• a solid state sensor that exploits a porous material to detect concentrations of substances in liquids and vapors.
• Such sensor includes a porous silicon microcavity of the interferential type, that is set in a cell together with a test-tube containing the liquid or vapor to be measured.
• the vapors, or the vapors produced by the liquid, to be measured fill the pores of the microcavity, replacing the air previously there and condense inside such pores changing the optical properties of the microcavity.
• an optical detection apparatus including a light source and a photodetector to collect the light that is reflected or transmitted by the cavity.
• the present invention has for purpose to supply an apparatus for the determination of the ethanol content having good reproducibility and selectivity capabilities with respect to ethanol, as well as being effectively applicable in an industrial field.
• an apparatus for the determination of the ethanol content in liquid or aeriform substances comprising a sensing element comprising an optical resonant microcavity including layers of porous material suitable for receiving in its pores the vapors of said liquid or aeriform substances, whereas said porous material comprises porous silicon oxide.
• the apparatus includes a measuring module including means for emitting an optical radiation toward said sensing element; and means for detecting said optical radiation after an interaction with said sensing element, said means for detecting being associated to elaborating means suitable for identifying spectral features of said optical radiation determined by the interaction with said sensing element.
• elaborating means are configured for identifying said spectral features after the establishing of a phase of condensation and/or evaporation of said substances in/from the pores of said of porous silicon oxide.
• FIG. 1 represents a schematic diagram of a microcavity suitable for being used in the apparatus according to the invention
• FIG. 2 represents a schematic diagram of the apparatus according to the invention
• the Figures 3, 4 and 6 represent diagrams illustrating the operation of the apparatus according to the invention
• - the Figure 5 represents a preferred embodiment of a cell included in the apparatus of Figure 2.
• the proposed apparatus for the determination of the ethanol content is substantially based on the adoption of an optical microcavity comprising an active layer of porous silicon oxide.
• the detection through such porous silicon oxide microcavity includes a measurement operated during the process of evaporation or condensation of the ethanol inside or from the inside of the pores in the porous material.
• the adoption of such process allows to obtain, as it will better shown in the following, a high selectivity with respect to the ethanol and it also determines an elevated resistance to aging.
• sensing element 10 which includes a microcavity 13 of the Fabry Perot ⁇ /2 type, that is comprised between two Bragg reflectors (DBR) , respectively an upper Bragg reflector 11 and a lower Bragg reflector 12.
• DBR Bragg reflectors
• Such sensing element 10 is produced by an electrochemical etching of a wafer of boron doped crystalline silicon with ⁇ 100> orientation (resistivity 5/15 m ⁇ cm) .
• the etching solution used is a mixture of fluoridric acid (50% in water) and ethylic alcohol (>99.9%) with a 1:1 ratio.
• the reflectors 11 and 12 are obtained by stacks of layers, eight layers for the superior reflector 11 and six layers for the inferior reflector 12, in which two layers having different porosity, indicated with 11a and lib, and therefore having different refraction index, are alternated.
• the current densities used in the electrochemical etching are of 450 mA/cm 2 for the high porosity layer 11a and of 150 mA/cm 2 for the low porosity layer lib.
• the sensing element 10 is therefore designed so that to operate in the visible field with the cavity mode centered around a wavelength Of 600 nanometers.
• the thickness of the high porosity layer 11a is indicatively 132.9 nanometers and its refraction index nl is 1.1286, while for what regards the low porosity layer lib its thickness is 123.31 nanometers and its refraction index N2 is 1.2164. It is clearly possible also to design the cavity so that to operate to other wavelengths, for instance in the near infrared field, varying the thicknesses and the refraction indexes of the layers. As a further example, it is possible to operate in the infrared field with a structure presenting eleven layers for the upper reflector 11 and nine layers for the lower reflector 12.
• the current densities used in the electrochemical etching are here of 550 mA/cm 2 for the high porosity layer 11a and of 200 mA/cm 2 for the low porosity layer lib.
• the sensing element 10 is therefore designed so that to operate in the in the near infrared field with the cavity mode centered around a wavelength of 1500 nanometers.
• the ⁇ thickness of the high porosity layer 11a is indicatively of 341 nanometers and its refraction index nl is 1.101, while for what concerns the low porosity layer lib its thickness is 267 nanometers and its refraction index N2 is 1.406. '
• the sensing element 10 is oxidized in an oven by the followings steps:
• FIG 2 the apparatus of detection of ethanol content is schematically shown, indicated as a whole by the reference 20, comprising an optical radiation source 21 that it is substantially a optical radiation source operating in the visible field and a visible radiation detector 22.
• the source 21 and the detector 22 are associated to means 40 for elaborating the optic data.
• Such means for elaborating the optic data 40 elaborate an output signal of the detector 22, but they are able, at the same time, to drive the radiation source 21.
• the radiation source 21, the detector 22 and the means for elaborating the optic data 40 can preferably be obtained through a sole device, which is a visible spectrometer equipped with an optical fibre interface 23 for sending and collecting the radiation on the sensing element 10.
• the optical fibre 23 can operate in connection with respective collimating lenses 25, which convey the radiation on the surface of the sensing element 10 with an angle of 10° from the normal to the surface of such element 10.
• the sensing element 10 is placed with a quantity of wine inside a cell 30, in particular, in the example here shown, with 2 ml of wine placed in a special container or test-tube 24.
• the sensing element 10 and the container 24 of the wine are maintained, through respective Peltier-type heaters 26 and 27, to a fixed temperature of 35 0 C for the sensing element 10 and of 38 °C for the container 24 in order to perform tests that will be illustrated in the following. It appears that the solution must be maintained to a temperature higher than the temperature of the sensing element 10; a difference of 2-3 0 C is considered optimal.
• Figure 3 it is shown an inset table in which in the first column are inserted the references, from Wl to W17, of the samples, in the second column it is indicated the wine type (Barbera, Dolcetto, Barolo, etc.), in the third column it is indicated the alcoholic degree in volume percentage.
• Figure 4 it is shown a diagram that represents a shift of the maximum of the cavity mode of the element 10, as stimulated by means of the visible spectrometer embodying the source 21, the detector 22 and the elaborating means 40, as a function of the alcoholic degree.
• the points represented on such diagram are obtained with the wine samples W1..W17 of Figure 3.
• the parameters of the linear equation used for fitting the data where R is the regression value and SD the standard deviation.
• the measurement procedure includes therefore the followings steps : a) first measurement of the position of the maximum of the cavity mode; b) insertion of a quantity of wine (2 ml) in the container 24; c) insertion of the container 24 in the cell 30; d) waiting till the system wine / sensing element 10 of Figure 2 in porous silicon oxide reaches the equilibrium in the pores of said porous silicon oxide/ e) second measurement of the position of the maximum of the cavity mode; f) removal of the container 24 from the cell 30. Subtracting the values read by the spectral features respectively in the steps a) and e) , related to the initial measurement of the position of the maximum and to the measure at the equilibrium, a value of shift of the cavity mode is obtained as shown in Figure 4. The shifts obtained in condensation and evaporation are equivalent.
• Such cell 30 includes a lower half body 31 and a superior half body 32, apt for being joined through suitable screws, not shown here.
• the inferior half body 31 include a passing circular opening 33 that it is closed by an optical window suitable for allowing the passage of the optical radiation.
• Around the passing circular opening 33 is defined an annular concentric housing lodging 34 in which the wine container 24, also having a annular concentric shape complementary to that of the housing 34, is inserted.
• the Peltier heater 27 is consequently shaped in an annular concentric shape, in order to allow applying below the cell 30, leaving the passage for the measurement radiation.
• the superior half body 32 includes a square opening 35 in which a Peltier heater 26 of a square shape can be inserted.
• microcavity 10 is then glued by a thermal paste on the lower face of such Peltier heater 26, so that to receive the radiation coming from the opening 33 and further, to directly receive the vapors from the container 24, which is facing from above.
• This -latter decision of setting the sensing element 10 above the container 24 is particularly effective in making quick the
• Figure 6 a diagram is shown that represents the shift of the maximum of the cavity mode in function of the percentage of ethanol in water for a cavity in porous silicon according to the prior art (square symbols) and a cavity in silicon oxide according to the invention (circle symbols) .
• the adoption of silicon oxide not only improves the repeatability, but it determines remarkably greater shift values ensuring a greater sensibility.
• the apparatus and process according to the invention allow to determine the alcoholic degree, i.e. the ethanol content in liquids and aeriforms, in particular wines, beers and liqueurs, with a good approximation and it can be extremely useful for rapid routine analysis.
• the proposed apparatus and process advantageously introduce an high selectivity to ethanol, as well as a high stability, since it is not affected from problems of aging due the use of porous silicon oxide for the production of the sensing element.
• porous silicon oxide in comparison to the porous silicon involves a important advantage favouring, under the measurements conditions adopted for the sensor here described, the interaction with the ethanol also to low concentrations (from 1% to 20%) . This characteristic allows to effectively detect the ethanol concentrations for wines.
• a heater e.g. a Peltier heater
• a Peltier cell under the sensing element 19 with the purpose to make it operate at a temperature, e.g. 35°C, at which the efficiency is maximized.
• the visible spectrometer which, for the diagrams shown as example, is a Ocean Optics I model HR2000 spectrometer, can be in general of any type, in particular it can be a device integrated with the cell. It is also clear, moreover, that all the suitable techniques to identify the position of the maximum of the cavity mode of the sensing element fall within the scope of the invention. Further, as mentioned, the wavelengths range adopted can be also different, being for instance possible to operate to wavelengths in the infrared range using a FTIR spectrometer, for instance a FTIR Nicolet model Nexus spectrometer.

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• Physics & Mathematics (AREA)
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• Health & Medical Sciences (AREA)
• Life Sciences & Earth Sciences (AREA)
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Cited By (2)

Citations (3)

• 2006
  • 2006-03-21 IT ITTO20060213 patent/ITTO20060213A1/it unknown
• 2007
  • 2007-03-20 WO PCT/IB2007/000689 patent/WO2007107849A1/en active Application Filing

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