Development Of Gas Distribution System For VOCs As Lung Cancer Markers Based On Static Volumetric Method

Currently, lung cancer is one of human malignant tumors with the highest incidence rate and mortality rate. The screening and early diagnosing of people at high risk of having lung cancer can increase the survival rate of patients. At present breath test method has been widely concerned by researchers, and it is with a great possibility to become to one of the effective detection methods of lung cancer, just like puncture biospy and other methods based on instruments such as CT and MRI. However, one of the keys to being successfully applied in breath test is how to get VOCs in trace levels as lung cancer markers.Based on the static volumetric method, a gas distribution system has been designed and developed in this paper with requirement analysis. This system is designed for directly preparing VOCs as lung cancer in trace level from VOCs liquids when they are in normal temperature and pressure. The related principle, scheme, hardware, software and test results of the gas distribution system have given in the body of this paper. They include:1. Selection of gas distribution method. After analyzing and comparing the advantages and drawbacks of dynamic methods to these aspects of static methods, the static volumetric method has been chosen to meet the requirements and to prepare VOCs in trace level. A related gas distribution system has been fabricated based on the static volumetric method. And the specific process of gas distribution has been given.2. Description and development of distribution model. Taking actual working conditions into consideration, a proper multi-parameters model of gas distribution system has designed and described. This system is designed for various kinds of VOCs as lung cancer markers. Comparing with the equations under ideal conditions, the correlative equations in actual situations are developed to provide the relationships among the different objective concentrations, the constant temperatures of vaporizing chamber, the mixing times in blending chamber, the injector size and the pump stroke of syringe pump.3. Designing and development of instrument. Based on the idea of module designing, we departed the designing work of gas distribution system into three main parts: the designing of a vaporizing chamber and a blending chamber and a syringe pump. After summing up the selection of key components and plotting the hardware scheme, we designed the gas path system and the circuit system, and developed the total hardware system designing and fabricated the system. In the same time, we defined the function modules of the software system. The PIC16F877 control program files, such as temperature controlling with PID algorithm, controlling of the air pump and the electromagnetic valve group and driving of stepper motor, are written in this paper as well as the control software based on Visual Basic language on PC.4. System test. Benzene was chosen in this paper as the sample of VOCs as lung cancer markers. The preparation of gas mixtures of benzene and nitrogen in trace level and in multi-group was completed in the static gas distribution system. These gas mixtures were tested with gas chromatography by Agilent 7890 A. After analyzing the chromatograms of GC test, comparing the parameters, such as the delay time and peak areas and response values of concentration in single unit and etc., we verify that the validity, accuracy and stability of the gas distribution system are all in good condition. In a word, the gas distribution system designed and developed in this paper does really preform well.