MEASUREMENT OF ALCOHOL

Abstract: The alcohol content of a solution (36) can be determined by passing a gas into said solution from supply means (33, 34, 35), to remove at least a portion of alcohol as vapour, and passing the resulting gas/alcohol mixture over a sensor (31) adapted to determine the alcohol content in the mixture, and processing and displaying the results, the processor (41) receiving inputs determined by the alcohol content of the mixture, and ambient temperature and humidity.

Description: MEASUREMENT OF ALCOHOL This invention relates to an apparatus and a method for the measurement of alcohol concentration in an aqueous solution. More specifically, the invention relates to such an apparatus and method using semi-conducting gas sensors in conjunction with a sample presentation system. The apparatus and method are particularly suited for the estimation of the alcohol content of beer or other alcoholic beverages. It is envisaged that this instrument may be used as a quality control tool in the alcoholic beverages industries, and also as a means for testing the alcoholic content of beverages at point of sale, for example Trading Standards Officers. The present recommended method for measuring alcohol concentrations (see "The Institute of Brewing Recommended Methods of Analysis 1986") relies on a distillation procedure followed by measurement of the specific gravity of the resultant alcoholic distillate. In the case of beer, a sample must be degassed by filtration before distilling, and the distillate then made up to the original sample volume with distilled water. The specific gravity of distillate is determined at 20°C using a density bottle. The alcohol content, either by mass or by volume, is obtained by reference to a Laboratory Alcohol Table issued by HM Customs and Excise. This is a lengthy procedure, a single determination of alcohol content taking approximately thirty minutes. Examples o; other methods employed in the brewing industry rely on the use of the following instrumentation: - gas liquid chromatography (see Cutaia, A.J., J. Assoc. Off. Anal. Chem. Jan/Feb, 1984, 67(i), 192-193). The equipment needed for this procedure is expensive and is not portable. A skilled technician is required to operate the equipment and the analysis time is about 12 minutes. In addition a supply, usually from gas cylinders, of nitrogen, hydrogen and air is required. - combustion and electrical measurement of heat generated (see SCABA, ServoChem AB, PO Box 110, 5-162 12 Stockholm, Sweden). This instrumentation is very expensive, not portable and requires a skilled technician for its operation and maintenance. - near infrared spectroscopy (see Halsey, S.A., J. Inst. Brew. 1985, 91(5), 306-312). This instrument is expensive, not portable and requires a skilled technician for its operation and maintenance. biochemical cell (see Waites, M.J. & Ba forth, C.W., J. Inst. brew., 1984, 90(i), 33-36). The enzyme required for use in the biochemical cell is not commercially available. A skilled technician is needed to prepare the enzyme which is a fairly complicated and lengthy procedure. - Oxidase electrode in a flow injection system (see Schelter-Graf A. et al, Z. Lebensm. ϋnters. Forsch., 1983, 177(5), 356-358). The equipment is expensive, not portable and requires a skilled technician. - immobilised enzyme electrode (see Mason M., J. Assoc. Off. Anal. Chem., July, 1983, 66(4), 981-984). The associated equipment is fairly expensive and the electrodes have a relatively short working life. low pulsed nuclear magnetic resonance (see Guillou, M. & Tellier, C, Anal. Chem., 1988m 60, 2182-2185). The equipment needed is relatively expensive and needs a skilled operator. high performance liquid chromatography (see Cieslak, M.E. & Herwig, W.C., J.Am.Soc.Brew.Chem., 1982, 40(2), 43-46). Instrumentation is expensive, not portable and requires a skilled technician for its operation. Total analysis time is about 20 to 30 minutes per sample. In addition to the above described techniques, many studies have been carried out to determine alcohol concentrations using gas sensitive detectors in combination with gas permeable membranes. A simple gas sensor has been used for the direct measurement of alcohol in culture broth (see Vorlop, K.D., Becke, J.W. & Klein, J., Biotechnology Letters, 1983, Vol 5(8), 509-514). The probe was used as a dip-type electrode and employed a Figaro sensor TGS 812 and a silicone semi-permeable membrane (0.5mm). This probe was used for the on-line measurement of ethanol for a period of 2 months, during a continuous fermentation with immobilised cells. The response time using a 0.5mm thin silicone membrane was 10 minutes. However, it was reported that the response time might be improved if a thinner membrane was employed. A similar dip-type probe was constructed by Kerape and Schallenberger for the on-line measurement of alcohol from fermentation processes (see Kempe, E. & Schallenberger, W., Process Biochemistry, 1983, December 7-12). These workers used a Figaro gas sensor in combination with a probe consisting of silicone tubing. Air was employed as a carrier gas to transport the alcohol permeating through the membrane to the sensor. A microcomputer was used to process the data. Mandenius et al have developed an on-line sensor for monitoring the ethanol content of beer. Measurements were carried out on bottled beer and also continuously during fermentation (see Mandenius, C.F., Hedman, T. & Mattiasson, B., J. Inst. Brew., 1984, 90, 77-80). In this application a Figaro sensor was used in combination with a gas permeable membrane of silicone tubing, which covered a stainless steel probe. In order to obtain accurate values for the levels of alcohol encountered in beer, however, it was necessary to dilute the headspace gas and nitrogen carrier gas with a further volume of pure nitrogen gas. The response time for the signal to rise to 90% of its final value was calculated to be 12-15 minutes at a dilution of 550 for the carrier gas. Other studies reported in which alcohol has been monitored in fermentation media using gas sensitive sensors include Bach et al (see Bach,. HP, Woehrer, W. & Roehr, M., Biotechnol Bioeng, 1987, 20, 799) and Picque and Corrieu (see Picque, D and Corrieu, G., Ind. Aliment. Agric, Oct 1988, 105(10), 899-903). In the paper by /. B c l_r£ Censor was fixed in a glass tube fitted with a water circulation jacket in order to maintain a constant temperature. Picque & Corrieu employed a gas sensitive sensor in combination with a hydrophobic polytetrafluoroethylene membrane with a pore diameter of 0.2 micron. ' Lee et al also used hydr ophobi c poly tet raf l uor oethylene membr anes in conjunction with a gas sens itive sensor (see Lee , J.H. , Woodward, J.C. , Pagan, R.J. and Rogers P.L. , Biotechnology letters, 1981, 3 (5) , 251-256) . Fuel cells have also been employed for the measurement of alcohol (see Cr iddle, W.J. , Parry, K.W. & Jones, T.P. , Analyst 1986 , 111 (5) , 507-510) . In this system air at 300 ml/minute is passed through a headspace generating vessel containing the diluted sample. A standard volume of the emerging air is drawn into a fuel cell and the increase in electr ical potential is measured. The procedure is calibrated using standard solutions of aqueous alcohol. Problems due to temperature changes are overcome by use of a correction factor, and the effect of dissolved solids is negligible due to sample dilution. The total analysis time for each sample using this method, however, is about six minutes , and moreover it is necessary to calibrate the instrument before each sample analysis. Also, beer samples need to be degassed before analysis. The use of an on-line alcohol sensor (fuel cell) for fermentation monitoring and control has been reported by Birch et al (see Birch S.W. , Turner , A.P.F. 6 Ashby A.E. , Process Biochemistry, 1987 , April, 37-42) . The fuel cell was used to monitor headspace gas from a fermenter at a sampling frequency of once every five minutes. The above described techniques for the measurement of alcohol by means of gas sensitive detectors, whilst being on the whole simpler and quicker than such techniques as are descr ibed at the beginning of this specif ication, never theless still require fairly lengthy analys is times for each sample. Many require sample preparation, for instance degassing or dilution, before analysis. Many also rely on the use of relatively complicated equipment and skilled personnel to run it. Calibration of instruments between sample analyses represents yet another frequently occurring problem. It is an object of the present invention to provide an apparatus and method for the determination of alcohol concentrations which is simple and relatively inexpensive to use, does not rely on the presence of skilled technicians and yet produces accurate and reliable results from a relatively small sample analysis time period. Further objects of the present invention are to provide a method of alcohol measurement which requires little or no sample preparation; which relies on simple and portable apparatus; which does not require calibration of instruments between each sample analysis and which may be used for the analysis of beer or any other alcoholic beverage. This method can be used for the batchwise analysis of discrete samples, or for continuous on-line monitoring during production. One embodiment of this invention provides a method of determining alcohol concentration in an aqueous solution using a sensing means capable of detecting alcohol in the vapour phase which comprises passing a gas through said aqueous solution to remove at least a portion of any alcohol present in said solution, passing the resultant vapour over said sensing means, and processing and displaying the output from said sensing means, a reference means being used to detect ambient temperature and humidity, the output from said reference means being processed with the output from said sensing means to compensate for changes in ambient temperature and humidity. In a preferred variation of this embodiment, the reference means is contained in the sensing means, in a single sensor the vapour is passed over said sensor, and the outputs are processed and displayed. In another variation, two identical parallel systems are provided, one containing the aqueous solution to be tested, the other containing a solution of identical composition except that it contains no alcohol, the respective sensing means are connected in a Wheatstone Bridge circuit, whereby the difference in output from the two sensing means is measured, and then processed and displayed. The invention also provides apparatus for determining alcohol concentration in an aqueous liquid comprising a container for a liquid to be tested, gas-supply means for passing a gas into the container, an alcohol sensing means for sensing alcohol in gas issuing from said liquid, and means for processing and displaying the output from the sensing means. Preferably, there is a temperature sensor in said container connected to said processing and display means. In a preferred apparatus the gas-supply means comprises a pump controlledl by microcomputer which receives outputs from alcohol sensing means, and temperature sensor and whose output is displayed by screen. Another embodiment of the apparatus according to the invention comprises a test solution vessel and a blank solution vessel, respective gas-supply means, for conducting gas from said vessels to respective sensors, and means for determining and displaying the difference in output from said sensors. Preferably the gas sensing means comprises a semi-conductor gas sensor or heated platinum catalytic sensor. Preferably the air emerging from the said solution is passed through a means for removing moisture before it is passed through the gas sensing means. This means for removing moisture is preferably a filter or gas-permeable membrane comprising a hydrophobic component. More preferably, the means for removing moisture comprises a polytetrafluoroethane filter of pore s i ze about 0.5 microns, su itably suppor ted in the flow of air upstream of the gas sensor to filter out water droplets . Pref erably an antifoaming agent is added to the sample unde r tes t be f o r e analys is i s car r i ed out. Th is is necessary particulary when the sample under test is a beer, when the addition of an antifoaming agent removes the need to degas and/or dilute the sample before analys is. The antifoaming agent is preferably a s il icone antif oaming fluid. The air flow passed through the sample under test is preferably a constant air flow, maintained by the use of a regulated supply from an electric pump. The air supply is regulated by use of a needle valve in the flow of air before the sampling system. Preferably the ai r is initially passed thr ough a small aperture having an internal diameter of about 0.5 mm, which is immersed in the sample under test. This provides a stream of small bubbles of air , which passes through the solution and emerges as water-saturated air containing a quantity of dissolved alcohol which is proportional to the amount of alcohol in the sample under test. According to one embodiment of the invention, the air/alcohol mixture, passing from the sample to the sensor, can be diluted by combining it with a bleed stream of air. This embodiment is especially suitable when the sample under test is a distilled spirit, since the alcohol content of the stream passing to the sensor may in that instance be too high to be accurately measured by the sensor. Alternatively, the pumped air supply can be replaced by compressed air from cylinders. It is also possible to strip alcohol from a sample by bubbling a compressed inert gas, such as nitrogen, through the sample. In this case, however, air should also be supplied, for instance by using a bleed stream as described above, since it will be required for operation of the sensor. Since temperature influences the amount of alcohol released from the solution, a semiconducting temperature sensor is preferably incorporated into the sample vessel so that readings may be automatically corrected. A mathematical correction is carried out by means of a microcomputer, which compensates for the logarithmic increase of alcohol concentration in the vapour with increasing temperature. In one embodiment of the present invention, the reference means is provided by the use of a first reference sample of an aqueous solution containing no alcohol. A flow of air is passed through this reference sample, the emergent water saturated air is then passed through a filter or gas- permeable membrane comprising a hydrophobic component so as to remove moisture and then through a first semi-conductor gas sensor capable of detecting any alcohol present in the said water saturated air. The emergent air is then passed through the sample solution under test as described above as being in accordance with the present invention. This method thus makes use of two gas sensors, the first acting as a reference to compensate for changes in background environment such as temperature and humidity and the second detecting alcohol vapour from the sample under test. These two gas sensors are, in this first embodiment of the present invention, configured in a Wheatstone bridge circuit. The difference in the response from the two sensors is measured, preferably electronically, and the output signal can be processed and recorded in a suitable manner. The output signal may for instance be displayed on a voltmeter, which can be monitored either by a strip chart recorder or by a suitable equipped microcomputer. The difference in response from the two sensors can be related to the concentration of alcohol in the test solution. In a second and more preferred embodiment of the present invention, use is made of a gas sensor such as the FGS 7712 type sensor, manufactured by Fuji of Japan and marketed by Hakuto, Waltham Cross, Hertfordshire which comprises two sensing elements, the first of which is capable of detecting alcohol in vapour passed through the sensor and the second of which is sensitive to changes in ambient temperature and humidity, use of this type of gas sensor provides a built in reference means, obviating the need to use a reference solution, and the output from the sensor is automatically corrected for fluctuations in the ambient temperature and humidity. Methods and apparatus according to the present invention will now be described by means of the following examples and with reference to the accompanying drawings, of which: Figure 1 is a schematic representation of the layout of apparatus for a method of alcohol measurement according to the present invention which makes use of both a sample solution and a reference solution; Figure 2 is a schemati c representat ion of the layout of apparatus in a second method of alcohol measurement according to the present invention, in which use is made of a semi-conductor gas sensor having two sens ing elements , one of which compensates for changes in ambient temperature and humidity; Figure 3 is a schematic representation of internal detail of a gas se nsor such as could be used in the appar atus shown in Figure 2 ; and F igure 4 is a schematic representation of an apparatus constituting a preferred variant of the apparatus shown in Figure 2. Example 1 This example relates to a first embodiment of the present invention which makes use of both a sample solution and a reference solution and two semi-conductor gas sensors configured in a Wheatstone bridge circuit. The apparatus used in this method of measurement is shown schematically in Figure 1. The semi-conductor detectors (7 & 8) are of the type TGS 816 manufactured by Figaro Engineering Inc of Osaka, Japan, and have a high sensitivity to alcohol. Each consists of an N-type sintered tin oxide electrode which is electrically heated. The semi-conductor and the measuring electrodes are attached to a ceramic tube, which is electrically heated by a coil of a noble metal. The detector is enveloped by a cage of steel gauze to prevent the possibility of an explosion. The electrical resistance of the sensing element is decreased in the presence of alcohol vapour and other volatile organic compounds. The change in resistance of the sensing element can then be converted into a voltage output by the component in the electronic module (2). A stabilised low voltage power supply, of between 4 and 10 volts, is also housed in the electronic module (2) and is used to heat the sensing element of the sensor. The two sensors (7 & 8) are configured in a Wheatstone bridge circuit and are sealed in a sensor block housing (10) . One of the two sensors (8) detects the alcohol in the vapour from the test sample (5) , whilst the other (7) acts as a reference to compensate for changes in the ambient temperature, humidity and background environment. Semi¬ conductor gas sensors of this type are not specific for detecting ethanol, but since this is a major component of the headspace gas resulting from beer and similar alcoholic beverages, such sensors are nevertheless inherently suitable for this experimental application. A constant air flow (3) is maintained through the system by the use of a regulated supply from a gas cylinder. Air is initially passed through a small aperture (9) , of internal diameter 0.6 mm (0.025 inches), to give a stream of small bubbles which pass through the solution (4) in the reference vessel (11). This reference solution (4) contains dissolved material similar to that of the solution under test (5), but without any alcohol. The water saturated air emerging from the reference sample (4) is passed through a filter (13) of Vyon (1 mm) plus polytetraf luoroethylene (0.5 microns) in order to filter out water droplets, before being passed through the reference sensor (7). The water-saturated air is then passed through the solution under test (5) contained in the sample vessel (12). Again, the air enters the sample vessel through a small aperture (6) of internal diameter 0.6 mm (0.025 inches) to produce a steady stream of small bubbles. The emergent water-saturated air-ethanol vapour is passed through a Vyon and polytetrafluoroethylene filter (13) as before, and then through the sample sensor (8). This sequence has the dual effect of producing a fast response time (about 60 seconds), and also of reducing instrumental drift. The difference in the response from the two sensors (7, 8) is electronically amplified at (2) and the output signal can be displayed on a voltmeter, which can be monitored either by a strip chart recorder or by a suitably equipped microcomputer (1). The difference in response of the two sensors can then be related to the concentration of alcohol in the solution (5) under test. The following experiment for the measurement of alcohol concentrations using the apparatus as described above and shown in Figure 1 was carried out on five samples of beer, A-E. The method may also be used to measure alcohol contents of other alcoholic beverages such as wine or spirits. Each sample was firstly degassed by filtration, and diluted so that the alcohol content was in the range from 0.5% v/v to 2.0% v/v. Alternatively, the beer samples could have 14 been analysed without the need to degas or dilute provided a silicone antifoaming agent had been added before analysis. The instrument was switched on and allowed to equilibrate. The reference vessel (11) was filled with distilled water and an empty vessel (12) for holding the sample was inserted. Air was passed through the system. Calibration was achieved by using two standard alcohol solutions of known concentration, in this case, 0.5% v/v for the lower calibration point and 2.0% v/v for the higher. In this application, beer samples of known alcohol contents were used for calibration purposes. The sample under test was then transferred to the sample vessel (12) which was placed in the system. After 60 seconds, the response was recorded and the alcohol content of the sample was calculated from the calibration responses given by the two standard solutions. For comparision purposes, the following Table 1 gives alcohol values of beers analysed using (a) the above procedure and (b) a gas liquid chromatographic procedure. TABLE 1 Sample (a) Gas Sensor (b) Gas/Liquid Procedure Chromatographic Procedure A 4.14% v/v 4.13% v/v B 3.43% v/v 3.40% v/v E 4.08% v/v 4.07% v/v Example 2 This example relates to a method of alcohol measurement according to the present invention which makes use of one gas sensor comprising two sensing elements. The layout of the instrumentation is represented schematically in Figure 2, and internal detail of the sensor used is shown schematically in Figure 3. The sensor used in this experiment was an FGS 7712 type sensor (20), supplied by Hakuto of Waltham Cross in Hertfordshire. This sensor comprises two heated platinum wires, (23.24), one of which (23) is coated with special catalytic materials for sensing gas (alcohol) and the other of which (24) compensates for changes in ambient temperature and humidity. Both elements are housed in double wire-mesh for preventing explosions which may otherwise result from the internally heated platinum wires. The platinum electrodes are electrically heated using a three volt DC supply from an amplifier module (21). The electrical resistance of the sensing element is decreased in the presence of alcohol vapour and other volatile compounds. This change in resistance of the sensing element is converted into a voltage output by the components in the amplifier module (21). In the present experiment, the sensor (20) is sealed in a block housing (19) made from a suitable plastics material, such as a poly methacrylate. A constant air flow (22) is maintained throughout the system either by the use of a regulated supply from a gas cylinder or by a small electrically driven pump. This air passes through a small aperture (16) of internal diameter 0.6 mm (0.025 inches), to give a stream of small bubbles which pass through the solution under test (15) contained in a screw-capped glass vessel (14). The emergent alcohol-water saturated air is passed through a filter system (18) consisting of Vyon (1 mm) and a hydrophobic polytetrafluoroethylene membrane (0.5 micrometers) to remove droplets of moisture. The alcoholic vapour is then allowed to pass through the sensor unit (19), (20). The difference in the response from the sensing and compensating elements of the sensor is electronically amplified at (21) and the output signal can be displayed on a voltmeter, which in turn can be monitored either by a strip chart recorder or by a suitable equipped micro-computer. The response of the sensor exhibits a linear relationship with the alcohol content of the sample. The response time is between 1 and 2 minutes. Calibration of this instrument is achieved using solutions of known alcohol content. To compensate for changes in temperature of the sample under test, a thermistor (17) is incorporated in the electronic system, the probe of which is inserted directly into the sample contained in the glass vessel. The following experiment was carried out using the apparatus described above and shown in Figure 2. The instrument was switched on and allowed to equilibrate. Air was passed through the system. Calibration was achieved using two standard alcohol solutions of known concentration, iin this case 1.0% v/v and 5.0% v/v. The sample under test (e.g. beer) was poured from the bottle, without the need for degassing or diluting, into the glass vessel (14). One drop of silicone antifoaming fluid was added and the sample vessel (14) was placed in the system. After about 1 to 2 minutes, the response was recorded and the alcohol in the sample was calculated from the responses given by the two calibration solutions. A correlation coefficient of 0.9999 was obtained from a plot of instrument response against alcohol content measured by a gas chromatographic procedure, for a range of beer samples. As an example, for a beer sample, a value of 3.34% v/v was obtained by the instrument of the present invention as shown in Figure 2 and a value of 3.35% v/v by a gas chromatographic procedure. The precision of the measurement using the instrument shown in Figure 2 was determined for three samples of beers from ten replicate determinations. Sample E Sample F Sample G Mean 2.05 3.65 3.34 Standard Deviation 0.037 0.040 0.060 Repeatability (rgg-* 0.015 0.110 0.170 All alcohol contents are reported in units of % v/v. Repeatability (rg 5 ) is defined as the difference that would be expected between repeat analyses carried out by the same operator, on the same instrument, over a short period of time at a confidence level of 95%. EXAMPLE 3 A further instance of a preferred instrument according to the invention is illustrated in Figure 4 of the accompanying Drawings. This employs a sensor of similar type to that shown in Figure 2, the instrument being under microcomputer control, with the results being displayed on a screen, suchas an LCD screen. The FGS sensor (31) (see Example 2) is sealed in a nylon block housing (22a,b). A constant air flow is maintained throughout the system, bv means of an electrically driven pump (33) and/ fcloonwtrol valve (34) controlled by microcomputer (41). This air passes through a small aperture (35) having an internal diameter of about 0.5 mm, to give a small stream of bubbles which pass through the solution under test (36), contained in a polycarbonate vessel (37), which is pushed into the nylon housing (32b) and abuts a rubber seal (38). The emergent alcohol-water saturated air is passed through a polytetrafluoroethylene filter membrane (39) which is supported against the face of the sensor (31) by means of a rubber o-ring (4D). The alcoholic vapour is then allowed to pass through the sensor unit. The difference in response between the sensing and compensating elements of the sensor (31) is passed to a microcomputer (41) by means of an 8-bit analog-to-digital interface. The response from the temperature sensor (42), is similarly passed to the microcomputer (41). The computer can then carry out a calculation to compensate for temperature, and the resulting alcohol concentration is displayed on the LCD screen (43). The response of this sensor exhibits a linear relationship with the alcohol content of the sample. The response time is between 1 and 1.5 minutes. Calibration of this instrument is achieved by the use of solutions of known alcohol content. The above-described apparatus was used as follows: The instrument was switched on, and the sensor (21) was allowed to equilibrate for 30 seconds. Calibration was achieved by using the sensor response from two standard alcohol solutions of known concentration. The sample under test was poured into the sample vessel. One drop of silicone antifoaming agent (e.g. Dow Corning Antifoam RD. Emulsion) was added and the vessel was placed in the system. When the microcomputer detected no further increase in the response from the FGS sensor, this maximum response was recorded, as was the temperature of the sample. The microcomputer calculated the concentration of alcohol in the solution under test and displayed this result on the LCD screen. A correlation coefficient of 0.9999 was obtained from a regression plot of instrument response against alcohol content measured by a gas chromatographic procedure. The precision of the measurement using the instrument was determined for three samples of beer from ten replicate determinations. Mean: 0.98 3 .24 4.11 Standard Deviation: 0.02 0.03 0 .01 Repeatability (r95) : 0.05 0.09 0.03 Result from G.C. Analysis: 0.94 3.29 4.11 EXAMPLE 4 The results of testing a series of 90 samples of beer using the apparatus shown in Fig.4, are set out below in 20 the following Table 2, compared with the results obtained using gas chromotography (GC) and distillation. The technique provided by the present invention, as described above, has distinct advantages over presently known methods for determining alcohol content. These can be summarised as: (a) Rapid response times of 1 to 2 minutes (approximately 1 minute in the case of the use of Figaro sensors) . (b) No need for sample preparation such as degassing or dilution of beer samples. (c) Accurate and reliable results which correlate well with those obtained using previously known techniques. (d) Simple and portable equipment which can be used by non-skilled personnel. (e) Low cost. (f) Applicability to the analysis of many different alcoholic beverages. TABLE 2 Code ALCOHOL DISTILL Number SCABA GC METER ATION 1 -0.05 0.00 0.01 0.30 2 -0.03 0.00 0.05 0.16 3 0.79 0.82 0.62 0.96 4 0.95 0.96 0.85 1.37 0.99 1.04 1.01 1.10 1.00 1.02 0.97 1.15 1.03 1.03 1.01 1.23 2.79 2.78 2.86 2.83 2.83 2.77 2.82 2.76 2.88 2.89 2.73 2.89 3.01 2.97 3.10 3.32 3.17 3.05 2.97 3.18 3.24 3.13 3.23 3.08 3.26 3.17 3.19 3.32 3.27 3.26 3.18 3.47 3.30 3.21 3.11 3.04 3.31 3.30 3.18 3.61 3.34 3.33 3.25 3.32 3.36 3.25 3.18 3.47 3.36 3.38 2.97 3.32 3.38 3.23 2.98 3.04 3.42 3.30 3.24 3.39 3.46 3.39 3.17 3.47 3.47 3.40 3.33 3.47 3.49 3.40 3.40 3.32 3.52 3.37 3.36 3.61 3.53 3.37 3.30 3.47 3.56 3.38 3.32 3.61 3.60 3.53 3.53 3.54 3.61 3.54 3.43 3.54 3.63 3.55 3.55 3.54 3.64 3.56 3.63 3.54 3.65 3.53 3.57 3.32 3.79 3.64 3.97 3.76 3.88 3.84 3.59 3.90 3.90 3.78 3.70 4.10 3.99 3.96 3.96 4.05 4.02 4.07 3.83 4.12 4.11 4.05 3.93 4.19 4.15 4.05 4.14 4.12 4.18 4.07 3.84 4.05 4.19 4.13 4.12 4.05 4.23 4.13 4.16 4.34 4.25 4.16 4.12 4.70 4.30 4.29 4.28 4.34 4.37 4.22 4.34 4.34 4.39 4.42 4.55 4.40 4.43 4.43 4.42 4.34 4.46 4.44 4.55 4.48 4.51 4.32 4.39 4.48 4.57 4.47 4.43 4.34 4.64 4.51 4.71 4.93 4.73 4.72 4.91 4.78 4.73 4.68 4.57 4.78 4.79 4.66 3.61 5.53 4.81 4.72 4.72 3.70 4.82 4.83 4.77 4.93 4.84 4.94 4.92 3.32 4.85 4.84 5.04 5.00 4.88 4.96 4.92 4.93 4.89 4.70 4.64 4.78 4.89 4.81 4.80 4.93 4.90 4.92 4.80 4.93 4.94 4.97 4.96 5.00 4.97 4.94 4.45 5.00 5.00 5.02 5.20 4.78 5.02 5.03 5.03 4.84 5.08 5.07 5.07 5.00 5.13 5.13 5.10 5.08 5.14 5.11 5.05 5.15 5.15 5.22 5.16 5.23 5.15 5.16 5.06 5.23 73 5.17 5.04 5.17 5.38 74 5.18 5.19 5.19 5.16 75 5.18 5.12 5.12 5.15 76 5.29 5.29 5.19 5.38 77 5.35 5.27 5.36 5.38 78 5.39 5.47 5.37 5.47 79 5.43 5.46 5.35 5.23 80 5.93 5.88 5.67 5.90 81 6.02 6.02 6.20 6.13 82 6.07 6.13 6.07 6.13 83 6.26 6.32 6.21 6.29 84 6.86 6.96 6.76 7.06 85 8.27 8.52 8.62 8.51 86 8.45 8.82 9.00 8.65 87 8.65 8.93 9.25 8.65 88 8.95 9.16 9.36 9.14 89 9.00 9.38 9.64 8.81 90 11.37 10.20 10.54 10.20 The SEP, a measure of the precision of a metho d compare d with a reference method, was determined for the method employed, using the equation: SEP [ 95 ] = 2 x(SEP) = SEP at 95% Confidenee Level. The results obtained were as follows: Regression of Distillation Results vs Alcohol Meter results Regression Output: Constant -0. 2569 Std Err of Y Est 0.35852 R Squared 0.96464 No. of Observations 90 Degrees of Freedom 88 X Coefficient(s) 1.0452 Std Err of Coef. 0.0213 Regression of GC Results vs Alcohol Meter Results Regression Output: Constant 0. , 1412 Std Err of Y Est 0. .17431 R Squared 0. .99164 No. of Observations 90 Degrees of Freedom 88 X Coefficient(s) 1. .0261 Std Err of Coef. 0. .0100 Regression of SCABA Results vs Alcohol Meter Results Regression Output: Constant -0. 1756 Std Err of Y Est 0.23496 R Squared 0.98481 No. of Observations 90 Degrees of Freedom 88 X Coefficien (s) 1.0258 Std Err of Coef. 0.0135 SUBSTITUTESHEET Standard Errors of Prediction SEP and SEP[95] for Alcohol Meter Against Distillation SEP 0.3692 SEP[95] 0.7384 Against GC SEP 0.181 SEP[95] 0.362 Against SCABA SEP " 0.2452 SEP[95] 0-4904 SUBSTITUTESHEET

Claims: CLAIMS 1. A method of determining alcohol concentration in an aqueous solution using a sensing means capable of detecting alcohol in the vapour phase which comprises passing a gas through said aqueous solution to remove at least a portion of any alcohol present in said solution, passing the resultant vapour over said sensing means, and processing and displaying the output from said sensing means, a reference means being used to detect ambient temperature and humidity, the output from said reference means being processed with the output from said sensing means to compensate for changes in ambient temperature and humidity. 2. A method according to Claim 1 characterized in that the reference means is contained in the sensing means in a single sensor, the vapour is passed over said sensor, and the outputs are processed and displayed. 3. A method according to claim 1 characterized in that two identical parallel systems are provided, one containing the aqueous solution to be tested, the other containing a solution of identical composition except that it contains no alcohol, the respective sensing means are connected in a Wheatstone Bridge circuit, whereby the difference in output from the two sensing means is measured, and then processed and displayed. 4. Apparatus for determining alcohol concentration in an aqueous liquid comprising a container (14, 37) for a liquid (15, 36) to be tested, gas-supply means (22, 16; 33, 34, 35) for passing a gas into the container, an alcohol sensing means (20, 31) for sensing alcohol in gas issuing from said liquid, and means (21; 41, 43) for processing and displaying the output from the sensing means. 5. Apparatus according to Claim 4 characterized by a temperature sensor (17, 42) in said container connected to said processing and display means (21; 41). 6. Apparatus according to Claim 4 or 5 characterized in that said sensing means (20, 31) comprises two heated platinum wires (23, 24), one platinum wire (23) having a catalytic coating. 7. Apparatus according to any one of Claims 4 to 6 characterized in that the gas-supply means comprises a pump (33) controlled by microcomputer (41) which receives outputs from alcohol sensing means (31), and temperature sensor (42) , and whose output is displayed by screen (43) . 8. Apparatus according to Claim 4 characterized by a test solution vessel (11) and a blank solution vessel (12), respective gas-supply means (9, 6), means for conducting gas from said vessels (11, 12) to respective sensors (7, 8), and means (2, 1) for determining and displaying the difference in output from 1 said sensors.

Inventors: BROWNE ANDREW JONATHAN, BUCKEE GEOFFREY KERSWILL, NYE JOHN WILLIAM SIDNEY, BROWNE, ANDREW, JONATHAN, BUCKEE, GEOFFREY, KERSWILL, NYE, JOHN, WILLIAM, SIDNEY
Applicants: CRISP INSTRUMENTATION LTD
Application year: 1990
Main classification: G01N33
IPC codes: G01N33