| BackgroundOccupational and non-occupational poisonous substance affect human healthgreater and greater nowadays. With china becoming a world machine factory after innovation and opening, producing mode and living style have changed greatly. The extension and degree of damage made by toxicant become greater and greater. The cost of examining curing and healing are very expensive. These will bring great losing to the country, company and individual. Alcohol is a poisonous substance we often use which scientific name is ethanol. It was often used in foodstuff industry, chemical industry, new energy source industry and all kinds of social location. Alcohol is absorbed in stomach and small intestine mainly. It will reach different kinds of tissue after passing through liver lung and heart. The main affecting part of it in brain, especially affect consciousness, action, capacity of judge and long short term influence of physiology and psychology. It is perhaps the most command fatal factor. The reason of it not only because of its own toxicity but also because its synergetic effect to other toxic chemicals. Blood alcohol concentration is a kind of important contacting index. It is used wildly. It is regarded as a more accurate detecting means than breath alcohol concentration. The means of detecting blood alcohol concentration are enzymatic method, chemistry method and gas chromatographic method at present. The operation of enzymatic method is complex and it has low precision, so does chemistry method. Though the technique of gas chromatographic methods has a mature development with a high precision, but it will take a long time to pretreatment, and equipments and testing cost are very expensive. It is difficult to promote when the equal income is not high in our country for now. So it has very important significance for preventing and curing alcohol poison to design a kind of instrument that is of simple operation, high sensitivity, high precision and low cost.ObjectiveBy designing the Gas Sensor Blood Alcohol Concentration Instrument and estimating the measuring method of it, looking for a kind of instrument that are of convenient operation, online test, high sensitivity, high precision and low cost for measuring blood alcohol concentration, looking for a kind of instrument that can reduce the labour cost and equipment cost.MethodsThe experimental theory is that making use of the equation of steam-liquid balance in a liquid alcohol container, using a gas-sensor to measure the density of alcohol steam in the container and then calculate the corresponding liquid concentration. By introducing a computer into the experiment, we try to develop an interface circuit with singlechip technique which handles data acquisition, ADC and serial communication (in that the stability and accuracy of our experimental circuit can not meet the specification yet, we use Art Technology's USB2006 and Advantech's PCL818HD devices in the real work instead), and build a supporting program under Win32 to assist our work. There are two use of the computer aid. First, it supports the experiment by easing the operations. Second, it helps the research work by automatically recording data and doing some analysis of sensor characteristics. In the aspect of the measuring method in practical application, the sampling method is taking out 2ml vein blood in the aseptic vacuum anticoagulant test tube, adding enough sodium fluoride and sodium oxalate in it. Conserving in 4℃refrigeratory. Mixing 0.5ml blood and 9.5ml pure water. Conducting accuracy experiment by methodology experiment of comparing the result of gas-sensor method and gas chromatogram method, by recovery experiment in three groups of high middle and low concentration. Conducting precious experiment by recurrence experiment in three groups of high middle and low concentration, by doing reappearance experiment in the first third seventh fourteenth days from sampling, and using different sensor. The slope of the standard curve is the sensitivity of the method. The detection limit is 3 times concentration STD of the vacant solution which be tested 11 times. Taking the scope of the standard curve which correlation coefficient more than 0.995 as beeline authentic range. Conducting the stability experiment in the first third seventh fourteenth days from Sampling. Conducting disturbance experiment by adding sodium chloride, sugar, calcium, magnesium, zinc and copper.Results1.Principle The sensor we research in this paper is belong to semiconductor gas sensor that has been passivated, it doesn't touch the sample when testing. Making use of unilateral transmission characteristic and gas-liquid balance of volatile compound, target gas pass through the sensor, producing signal direct ratio to gas volume integral. Measuring the density of alcohol steam in the container and then compute the corresponding liquid concentration2.Instrument basic configuration The basic configuration of the experimental sample instrument involving sensor; sensor bracket; constant temperature sample pool; manostat; USB interface; computer.3.Characterisitic of application software Application software include two functions: assisting experiment and assisting research. Assisting experiment function easy the operation very much. It made the experimental course rapid and accuracywhich hard to complete by handwork. Assisting research function of it provides necessary means for experimental data accumulation, analysis and sensor characteristic research.4.Estimation of experimental method Among the response range assigned, having stabile electric signal, having perfect line relation and recurrence, having many merit for example operation convenient rapid and high precision low cost and so on. 5.Sampling and preservation Stabile experiment show that it can be preserved for 3 days under room temperature and in 4℃refrigeratory.6.Sensor initialization time Peak value is higher than common for the first initialization time, its time is between 220 seconds and 300 seconds. Afterward, the peak value will fall greatly because of activation of the sensor surface, then the initialization time will be shorten greatly, between 120 seconds and 180 seconds commonly.7. Estimation of accuracy and precision By means of methodology experiment with average value t-testing of comparing the result of gas-sensor method and gas chromatogram method, it showed that they have not remarkable difference in statistics. It means that there is not statistics significance in two methods' difference. The recovery rate of high concentration is 101.6%, the recovery rate of middle concentration is 101.6%, the recovery rate of low concentration is 100.3 %.8. Estimation of precision The RSD of three concentration groups from 0.76% to 8.17%.9.In the reappearance experiment with different sensor, P＞0.0510.Estimation of linearity range and relative coefficient The curve has a good linearity relation in the range of 0～1.58mg/ml. The correlative coefficient is 0.9998.11. Estimation of sensitivity and detection limit Using of the standard cure slop as sensitivity, d=375.26. The STD of the vacant solution is 0.0014mg/ml, so the detection limit is 0.004mg/ml (0.5ml blood account).2.Disturbing experiment Sodium chloride, sugar, calcium, magnesium, zinc and copper in human blood do not have disturbance to experiment.Conclusions1.The cost of instrument is low, the total expense of instrument and computer are about RMB10000 only. It is much lower than the Gas Chromatogram which expense is more than RMB100000. It is more fit for our country that is short of medical spending generally. It is much easy to promote in community hospitals and country hospitals.2.Operations of it are convenient and rapidly, there is no necessary to especial pretreatment. Therefore, it is easy to master, so the cost of person material and time can be reduced greatly, it is easy to promote too. More time can be shortened for experiment, more time can be saved for cure.3.The application software not only can assist experimental operation but also can assist research work, for instant data analysis and so on.4.Time of stability is short, not like some other big equipment that need long time for stability. It needs less than 5 minutes to stabile for the first time. Afterward, it only needs about 3 minutes to stabile. The judge of initialization is computer's job. Therefore it need little time and easy to operate.5.The results of methodology comparing experiment and recovery experiment are all suit for the corresponding index in "Rule for development of biomaterial analysis method (Urine and Blood)". It shows that it has the accuracy according with criterion request, and its accuracy is not less than GC's. Because it has few steps of pretreatment, operation convenient, so it has little operation error and has high accuracy. This is the reason it has little system error.6.It has high precious in high middle and low concentration groups showed by recurrence experiment result. There is no statistical significance for the results of using different sensor showed by reappearance experiment.7.The detection limit is low relativity of this method. When sampling 5ml blood, the detection limit reach 0.003mg/L, which lower than request of the WS/T 68-1996 that detection limit ought to less than 0.3 times of biological contact limit.8.Experiment has a good linearity relation in some defined ranges. Its correlative coefficient is above to 0.999. This method allow multinomial curve plot involving conic plot and cubic plot. So it has wider detection range than that only has linear plot. The result of alcohol is acquired by the means of alcohol volume fraction in the steam, dilution of the blood will not affect the detection result, and it has a high sensitivity, so it has a wide detection range.9.This method can be used widely, involving clinic examination, legal medical examination, execution of the law by traffic police and medical study department.
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