八級桿工作原理(ICP-MS).ppt

1、,How Does the Reaction Cell Work? Featuring the Agilent Octopole Reaction System,Page 2,What is a Collision/Reaction Cell?,The 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 betw

2、een the ion 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. Eliminates key interferences arising from the sample matrix that are

3、 not argon based and cannot be eliminated using “traditional” approaches.,Page 3,Why use an Octopole? (1),Ions entering the reaction cell have an ion energy in the radial direction corresponding to the dotted line labelled Initial Ion Energy. As ions enter the cell and interact with the reaction gas

4、, 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 black) and the ions are subsequently confined within the shaded region. No

5、te 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.,Page 4,Why use an Octopole? (2),= analyte ion,Quadrupole Based Reaction Cells,Initial Ion Energy,Energy After Collision,Col

6、lisional Focusing,In 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 low sensitivity or in which the reaction cell and the mass an

7、alyzer 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 designs to prevent dramatic loss of sensitivity. Complex ion

8、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.,Page 5,Processes in the Cell,ORS can be operated without using highly reactive gases. Octopole design allows h

9、igher cell pressures increasing reaction cross section due to better ion beam focussing He Mode Collisionally Induced Dissociation the interference is broken apart when it impacts the He atom Energy Discrimination the larger polyatomic species (greater ionic radii) loose more energy than the smaller

10、 analyte species and cannot enter the QP effectively a molecular filter Aided by the Agilent ShieldTorch System all ions enter the Octopole with well-defined narrow energy distribution H2 Mode Charge Transfer electron transferred from (or to) hydrogen, producing a neutral species Actually both modes

11、 use Energy Discrimination, at least in part,Page 6,Collisionally Induced Dissociation (CID) Helium Mode,Molecular species enter the cell,They collide with the He atoms,The collision breaks the species apart,The collision breaks the species apart,The interference has been neutralised,Page 7,Energy D

12、iscrimination Ionic Radii,As+,ArCl+,V+,ClO+,Ionic Radii (pm),Any polyatomic species will have a larger-cross section than single ions The larger polyatomics will collide with the cell gas a greater number of times than the smaller analyte ions and loose energy Low energy ions cannot enter the QP,m/z

13、 75,m/z 51,Page 8,Energy Discrimination Ionic Radii,Cu,S2,SO2,NOCl,ArMg,CaOH,Ionic Radii (pm),Energy Discrimination is NOT a reaction process does NOT rely on reaction pathways that are species dependant Simply acts as a physical filter for the larger polyatomic ions Is applicable for ANY polyatomic

14、,m/z 65,Page 9,Energy Discrimination (ED)Helium Mode,Smaller analytes loose less energy than polyatomics,They collide with few He atoms and can enter the QP,Larger polyatomic species collide more times,Each collision reduces ion energy,QP at +3 V c.f. OP,Positive QP repels low energy polyatomic spec

15、ies,Polyatomic cannot enter QP,Page 10,ED & CID In Action 7500c Tune Screen,Screen 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 contamination) Cell is pressurized and depress

16、urized with He (at 0.0 & 4.0ml min-1) Note residual Cu contamination in NaCl salt,Click Image to play movie,Page 11,Charge TransferHydrogen Mode,Interfering ion enters Octopole and collides with H2,An electron is transferred to the interference,The interference is neutralised, and hydrogen gains the charge,Neutral species cannot enter off-axis QP,Page 12,Reaction Mode 7500c Tune Screen,