بررسي رفتار زماني پاسخ دستگاه طيف سنج تحرك يوني

چكيده انگليسي :

Time Evolution of Ion Mobility Spectrometer Signals Elham Fadaei Tirani ef iut@yahoo com Date of Submission 2012 02 29 Department of Chemistry Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language FarsiMahmoud Tabrizchi m tabriz@cc iut ac ir Abstract Like any other sensor the response time of ion mobility spectrometer IMS is important especiallywhen it is coupled to other analytical devices such as GC HPLC or TLC In this thesis the time behavior ofthe IMS signals was evaluated under different conditions At first the IMS response to a gas sample foranisole and ammonia that was quickly injected by a Lit syringe was studied The injection profile wasassumed as a square pulse However the response was found in a Gaussian shape followed by a long tail The Gaussian response was referred to distortion of the injected square pulse under diffusion in gas phase The long tail was attributed to desorption of the sample from the internal surfaces of the injection port Sample adsorbs on the walls of the injection port as soon as it is injected and releases after the injection isfinished In fact the fresh carrier gas is flowing continuously and washes out the adsorbed sample slowly The desorption kinetics is a first order reaction hence it creates an exponential long tail in the responsecurve The time behavior of solid samples for papaverine and acridine was also evaluated Like gas sample the response curve of the solid included a Gaussian peak due to diffusion and a long exponential decay dueto desorption However the middle part of the response curve did not fit well This new part in comparisonto the gas sample was attributed to the evaporation of the solid sample from the injection needle Theevaporation process was assumed to be a first order desorption reaction Based on the assumption an extrafast exponential decay function was added to the response curve In summary the response curve of thesolid sample included a Gaussian function for the rise time a fast exponential decay for the desorption ofthe sample from the injection needle and a slow exponential decay for the desorption of the sample fromthe internal surfaces of the injection port Although in this model the evaporation process was consideredat constant temperature the experimental data well agreed with the model In reality the needle temperaturerises exponentially to reach the injection port temperature A more complete model was also presentedconsidering a first order evaporation or desorption kinetics under an exponentially rising temperature plus along decay function Experimental data for different final temperatures were fitted to this new model andthe activation energy of desorption and pre exponential factors were obtained The fittings were very goodand the results agreed well with the values reported in the literature In the second part of this work the influence of the experimental factors such as sample type oventemperature type and length of the carrier tubes and the amount of sample on the response curve wereevaluated The response time is shorter for samples with lower melting points The length of the tail wasalso found to be proportional to the sample amount The cell temperature had no considerable effect on theresponse curve

فدايي تيراني، الهام

بررسي رفتار زماني پاسخ دستگاه طيف سنج تحرك يوني

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