气相色谱2_2016.ppt

Thermal conductivity detector Thermal Conductivity(mW/m?K) Malor Mass(g/mol) inorganic compounds Hydrogen(H2) 240 2.02 Helium(He) 193 4.00 Nitrogen(N2) 34 28.01 Argon(Ar) 23 39.95 Oxygen(O2) 37 32.00 Carbon Dioxide(CO2) 29 44.01 Organic compounds Methane(CH4) 54 16.04 Ethane(CH3CH3) 39 30.07 Propane(CH3CH2CH3) 34 44.10 n-Butane(CH3CH2CH2CH3) 32 58.12 n-Pentane(CH3CH2CH2CH2CH3) 29 72.15 Thermal Conductivities of Representative Compounds and Carrier Gases Advantages of a TCD Respond tp any analyte that is different from the carrier gas and is present in a sufficient quantity to be measured. A TCD is nondestructive. It is possible to pass analyte onto a second type of detector for further analysis or to collect these analytes after they exit the TCD. Disadvantages of a TCD Respond to impurities in the carrier gas, to a stationary phase that is bleeding from the column, or to air that is leaking into the GC system. Be sensitive to changes in separation conditions, which will result in baseline drift. Has a relative poor lower limit of detection compared to other common GC detectors. 4．Factors that affect TCD （1）桥流↑，灵敏度↑ 灵敏度足够时，桥流应尽可能小（100~200mA） 先通载气，再给桥流 （2）⊿λ↑，灵敏度↑，选λ大的做载气 λ载 λ组，出正峰 λ载 = λ组，不出峰 λ载 λ组，出倒峰 λH2 λHe λN2——选氢气做载气 （3）T池↓，池体与热丝温差↑，灵敏度↑ 保证T检 T柱，以免造成检测器污染 （4）浓度型检测器， A ∝ 1/u， 以A定量，应保持u一定 （峰面积定量依据） （二）氢焰检测器（FID） 1．Structure of TCD 2．Advantagements and Disadvantagements 3．Operation conditions Flame Ionization Detector Advantage of FID Gives little or no signal for many small inorganic compounds. Provides lower background signal and creates limits of detection for organic compounds that are 100- to 1000-fold lower than those that can be obtained with a TCD. Can use temperature program. Disadvantage of FID It is a destrutive detector that breaks down analytes during the process of their measurement. How to overcome: split the carrier gas stream a