Presentation on theme: "Method Building Essentials"— Presentation transcript:
1Method Building Essentials Source Parameter OptimizationExtracting the solution ion from the mobile phaseCompound Optimization for MRMGetting parent ion to the collision cell and smashing it to bitsMS optimization for EPIProducing reproducible full scan MS with lots of detail.Linking MRM with EPI using IDA
2Method Parameters TurboSpray Parameters The goal is to maximize ion formation based on the liquid matrix.Set globally in the method.In multi-compound methods should be generalizedCompound ParametersThe goal is two fold1st maximize parent ion reaching the collision cell2nd Optimize fragmentationMS experiment determines if generalized and set globallyMRM = drug specificEPI = generalized and set globally.MS ParametersThe goal is optimized resolution and sensitivity.Minimize scan time
3Infusion and FIA Infusion Flow Injection Analysis Syringe pump driven 10 mcL/minCompounds ~ 5mg/L in H20 mixed with a small amount of 50:50 A:B mobile phase.Flow Injection AnalysisSyringe pump still usedNo chromatographyLC mobile phase added at mixing-T on source.Syringe pump +A + B = 200 mcl/minMobile phase A & B: 0.95 mL/min eachSyringe Pump 10 mcl/min.
4TurboSpray Settings Ion Spray Voltage [IS] Nebulizer Gas [GS1] The “hairdryers”Heater [TEM]Heater Gas [GS2]Curtain Gas [CUR]Interface Heater [ihe]On or Off…we leave it on.
53200 Qtrap Overview: The Source ISiheGS1TEM &GS2Orifice PlateCurtain PlateVoltage, Temperature & Gas ParametersCUR
6Ion Spray Voltage [IS]100030005000Infusion200040005500FIA
7Nebulizer Gas [GS1] 20 10 30 50 70 9 Infusion 50 20 30 90 70 10 Infusion502030907010Increasing the GS1 from 10 to 50Increases cocaine ion flux ~20%FIA
8Heater [TEM] Infusion FIA TEM= 300 - 600 TEM= 600 TEM= 200 TEM= 500 TEM= 0 (no heat)TEM= 200TEM= 100TEM= 0 (no heat)Increasing TEM 0 to 500Increases cocaine flux >350%InfusionFIA
9Heater Gas [GS2]503070102090[LC Baseline: GS1 =10, GS2 = 0]
10TurboSpray Parameters The curtain gas [CUR] should be maximized to repel neutrals and droplets without dramatically impacting sensitivity.The geometry of the 3200 source makes it less important than on older sources.Mobile phase composition and flow affects source parametersIncreasing water content will require higher temperature and gas pressuresIncreasing flow rate will require increased temperature and gas pressures.Using FIA reproduces mobile phase conditions at compound elution and can help to maximize sensitivity.
11Compound Optimization Overview Select Mass [M+H]+Needs to be the exact mass of the most abundant isotopeOptimize compound voltagesmaximize parent ion abundanceDP,EP, & CEPOptimize compound fragmentationSelect and optimize transition massesCEQuantitative OptimizationInstrument’s automatic routine
12Compound Optimization Parameters Getting ions to the collision cellDeclustering Potential [DP]Entrance Potential [EP]Collision Cell Entrance Potential [CEP]Controlling FragmentationCollision Energy [CE]Collision Gas Setting [CAD]Collision Cell Exit Potential [CXP]Usually 4VCollision Energy Spread [CES]
133200 Qtrap: PotentialsQ0Q1Q2Q3EPCEPCXPDPCEMCEMost potentials are relative to the entrance potential (EP).CEM is the setting for the Cascade Electron Multiplier
14Declustering Potential “The potential applied to the orifice plate (OR) has the greatest effect on the amount of declustering in the orifice region of the interface.”“The working range of DP is typically 0 to 100 V, although it may be set higher.”Decluster what?Example clusters include: [M+H3O]+, [M+Na]+, [M+H+CH3OH]+If set too high DP can actually fragment a compound in the source… BAD for LC/MS/MS.
15Cocaine DP Ramp 5.0 to 100v Infusion (10 mcl/min) FIA 200 mcl/min 50:50 H2O: MeOH
17Entrance Potential [EP] The EP parameter controls the entrance potential, which guides and focuses the ions through the high-pressure Q0 region.It is typically set at 10 V (for positive ions) or–10 V (for negative ions) and affects the value of all the other instrument voltages.
19Collision Cell Entrance Potential CEP (Collision Cell Entrance Potential)The CEP parameter controls the collision cell entrance potential, which is the potential difference between Q0 and IQ2.It focuses ions into Q2 (collision cell). CEP is used in Q1, MS/MS-type, and LIT scans.Generally the most mass dependent.
21Fragmentation Parameters Controlling FragmentationCollision Energy [CE]Collision Gas Setting [CAD]Collision Cell Exit Potential [CXP]Usually 4VCollision Energy Spread [CES]
22Collision Energy (CE)Fragmentation of parent ion is caused by collision with low pressure N2 in the collision cell.The more energy generally results in greater fragmentation.The energy of that collision is controlled by the Collision Energy (CE) setting.CE is a voltage difference between the Q0 and Q2 (EP – RO2).CE can be optimized for each drug.(Quantitative Optimization)Higher CE results in greater fragmentation of the parent molecule.Consider dextromethorphan…
33Fragment Ion Selection In MRM screening, generally a single transition is selected for each drug.For example dextromethorphan 272 128The sensitivity of the method is directly proportional to the intensity of the fragment ion.Attention should also be given to the uniqueness or the transition.How do you select a transition ion to monitor?
34Fragment Ion Selection Quantitative OptimizationStarts with compound optimizationDP, EP, & CEPFragment parent mass at many different collision energies.Pick the four most intense ionsAvoid loss of H2O(fragments δm >19 amu of parent)Determine the collision energy that produces the maximum amount of each transition ion.
35Optimize These Fragments DXM : CE =10 to 100 [summed]Optimize These Fragments
36Optimizing 128, 147, 171, 215 171 128 215 147 CE Fragment CE Max 128 84171511474121532171128215147CE
37Dwell TimeDwell time is the amount of time (msec) the instrument spends at each transition.Effects sensitivity up to a point.Increasing the DT >50 msec produces little if any additional sensitivity.For most drugs DT> 25 has little effect.Also longer dwell times lengthen total MRM scan times.
38Method Building: MRM Optimization of source parameters Optimization of compound parametersCompoundFragmentationSelection of drug transitionsRepeated 130 times…..Congratulations You’re Ready to Build an MRM Method!
39MRM Method for DXM Parent [M+H]+ Daughter Transition Ion Dwell Time MRM Parameters
40MS Parameters Enhanced Product Ion Global Parameters Collision Energy Spread [CES]Collision Cell Gas Pressure [CAD]LIT SettingsFill TimesLIT Scan SpeedQ0 Trapping
41Dextromethorphan EPI Typical EPI output... CE =20 CES = 30 Q0 trap = OffScan Speed = 1000Fill time fixed 20ms
42EPI: Global Parameters Source Settings (TEM, GS1 etc…) are set globally and are the same for MRM and EPI.Compound parameters individualized to optimize transition ion formation (MRM) must be set globally for EPI. (DP,EP,CEP,CE,CXP)The goal of EPI optimization is to find the best settings to produce good MS data that is reproducible and library searchable.
43Collision Energy Spread [CES] “The CES parameter controls the spread of collision energies used when filling the LIT. It is used in conjunction with the Collision Energy (CE) parameter.”“The advantage of using a collision energy spread is that you do not have to optimize the collision energy.”“By specifying the CE and CES parameters, low, medium, and high collision energies are used in a single scan to provide maximum information in the product ion spectra (low and high mass fragments).”We have chosen CE 20:CES 30 (20/30) or (25/30)Provided the best fragmentation across the widest number of drugs.
45Collision Gas Pressure [CAD] Controls the pressure of the N2 gas in the collision cellIn simplified mode you get three settings:Variable by instrumentLow: 1.9x10-5 TorrMedium: 2.6x10-5 TorrHigh: 3.3x10-5 TorrCollision with the gas causes fragmentation, but also helps to “cool” fragment ions and focus them into the LIT.
46Collision Gas Pressure [CAD] CAD = High (3.3x10-5 Torr)CAD = Medium (2.6x10-5 Torr)CAD = Low (1.9x10-5 Torr)
47LIT Settings The LIT has four important settings Mass Range Scan Speed Set to cover the range dictated by compounds covered (e.g.50 to 500 amu)Scan SpeedSlower Scan Speed give better mass resolution but cost time and sensitivity.Qtrap has three 250, 1000 and 4000 amu/s
49LIT Settings The LIT has four important settings Fill Time The amount of time the trap remains open to accept ions.Can be fixed time (e.g. 50 msec) or DynamicDynamic fill time (DFT)Fill time based on presampling of incoming ion fluxPrevents over or under filling of the LIT.Q0 trapping [on or off]Like the LIT Q0 can store ions coming in from the source while the LIT is closed.Can increase sensitivity
50Fixed vs. Dynamic Fill Times Fixed 20ms Fill Time Q0 OnFixed 20ms Fill Time Q0 OFFDynamic Fill Time
51Building a Qualitative Method Use MRM as the survey methodEach compound setting optimized for sensitivity and specificityUse EPI to generate a full scan mass spectrum with a lot of detail to facilitate positive identification.Use standard parameters for reproducibility and library searching.Use Information Dependent Acquisition (IDA) to switch between MRM and EPI.
52Information Dependent Acquisition Allows on-the-fly software switching between MS modes.IDA examinesThe results of the MRM cycle to see if any drugs are above the a threshold.IDA determinesIF any drugs will be selected for EPIWhich drugs will be selectedIDA switchesThe instrument from MRM mode to EPI mode
53IDA Example For Example Experiment 1: MRM IDA (Decision Maker) Survey Scan of 100+ drugsIDA (Decision Maker)When a transition is above a threshold…And is the most intense transition…And is not on an exclusion list…Then trigger a second experimentExperiment 2: Product Ion ScanFull scan mass spectrum for compound identification.
54IDA: Dynamic Exclusion A software technique to handle coeluting peaks especially when one is much less intense.Dynamic Exclusion TimeThresholdProduct Ion Scans
55IDA Method Flowchart IDA On exclusion list ? Any over 1100 cps? YES NO 130 MRMTransitionsDo EPINOYES3rdEPI?Add to exclusionlist for 15 sec.Dynamic Exclusion
56Putting it all together… Overlay of 130 MRM transitionsXIC of oxycodone MRMMRM Triggered EPI