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1、How Does the Reaction Cell Work?Featuring the Agilent Octopole Reaction System1What is a Collision/Reaction Cell?lThe Octopole Reaction System (ORS) is an octopole ion guide contained within a stainless steel vessel and pressurized with a gas, most often H2 or He. The ORS is positioned between the i
2、on lens assembly and the quadrupole mass filter. As ions from the sample enter this cell, they interact with the gas, resulting in the reduction of the molecular interference normally below the level of the blank solution.lEliminates key interferences arising from the sample matrix that are not argo
3、n based and cannot be eliminated using “traditional” approaches.2Why use an Octopole? (1)= analyte ionOctopole Reaction SystemInitial Ion Energy Energy After CollisionSmall diameterIons entering the reaction cell have an ion energy in the radial direction corresponding to the dotted line labelled In
4、itial Ion Energy. As ions enter the cell and interact with the reaction gas, energy transfer takes place and the analyte ions lose energy. When ions lose energy (Energy After Collision), the voltages placed on the reaction cell force the ions to move along the potential energy distribution (drawn in
5、 black) and the ions are subsequently confined within the shaded region. Note that the confinement area in the Octopole design is relatively diffuse. A small diameter Octopole can be used to physically confine the ions into a tightly focused ion beam.3Why use an Octopole? (2)= analyte ionQuadrupole
6、Based Reaction CellsInitial Ion EnergyEnergy After CollisionCollisional FocusingIn contrast to the Octopole design, ions which lose energy in a quadrupole reaction cell are confined to a narrow potential field. This effect is known as collisional focusing and is required in systems having inherently
7、 low sensitivity or in which the reaction cell and the mass analyzer are of the same physical diameter. Collisional focusing requires a large number of ion molecule interactions within the cell to ensure ion energy loss. Therefore, highly reactive, heavy molecular gases are often required with these
8、 designs to prevent dramatic loss of sensitivity. Complex ion filtering techniques are often utilized with this configuration to remove reaction by-products caused by highly reactive gases used in the cell increases complexity and reduces sensitivity.4Processes in the CelllORS can be operated withou
9、t using highly reactive gases. Octopole design allows higher cell pressures increasing reaction cross section due to better ion beam focussinguHe ModeuCollisionally Induced Dissociation the interference is broken apart when it impacts the He atomuEnergy Discrimination the larger polyatomic species (
10、greater ionic radii) loose more energy than the smaller analyte species and cannot enter the QP effectively a molecular filteruAided by the Agilent ShieldTorch System all ions enter the Octopole with well-defined narrow energy distributionuH2 ModeuCharge Transfer electron transferred from (or to) hy
11、drogen, producing a neutral speciesuActually both modes use Energy Discrimination, at least in part5Collisionally Induced Dissociation (CID) Helium ModeArNaHeHeHeHeHeHeArNaHeHeHeHeHeMolecular species enter the cellThey collide with the He atomsThe collision breaks the species apartThe collision brea
12、ks the species apartThe interference has been neutralised6Energy Discrimination Ionic RadiiAs+ArCl+V+ClO+Ionic Radii (pm)Any polyatomic species will have a larger-cross section than single ionsThe larger polyatomics will collide with the cell gas a greater number of times than the smaller analyte io
13、ns and loose energyLow energy ions cannot enter the QPm/z 75m/z 517Energy Discrimination Ionic RadiiCuS2SO2NOClArMgCaOHIonic Radii (pm)Energy Discrimination is NOT a reaction process does NOT rely on reaction pathways that are species dependantSimply acts as a physical filter for the larger polyatom
14、ic ionsIs applicable for ANY polyatomicm/z 658Energy Discrimination (ED)Helium ModeHeHeHeHeHeHeHeHeHeAs+ArCl+HeHeSmaller analytes loose less energy than polyatomicsThey collide with few He atoms and can enter the QPLarger polyatomic species collide more timesEach collision reduces ion energyQP at +3
15、 Vc.f. OPPositive QP repels low energy polyatomic species Polyatomic cannot enter QP9ED & CID In Action 7500c Tune ScreenScreen capture of He-mode tuning.Solution contains 1.1g l-1 NaCl.System set to monitor 40Ar23Na (interferes with 63Cu) and 40Ar35Cl (interferes with 75As) and 65Cu (background con
16、tamination)Cell is pressurized and depressurized with He (at 0.0 & 4.0ml min-1)Note residual Cu contamination in NaCl saltClick Image to play movie10Charge TransferHydrogen ModeHHeeInterfering ion enters Octopole and collides with H2An electron is transferred to the interferenceArAr+The interference
17、 is neutralised and hydrogen gains the chargeHeeH+Neutral species cannot enter off-axis QP11Reaction Mode 7500c Tune ScreenClick Image to play movieScreen capture of H2-mode tuning.Solution contains 10ppb Tl and no Se.System set to monitor 40Ar38Ar (interferes with 78Se) and 40Ar40Ar (interferes with 80Se)Cell is pressurized and depressurized with H2 (at 0.0 & 4.5ml min-1)12
