Declustering potentials

Chovan et al.30 described a system that integrates different components of bioanalysis including automatic in vitro incubation, automatic method development (mainly SRM transitions for LC/MS/ MS analysis), and a generic LC method for sample analysis to minimize human intervention and streamline information flow. Automaton software (Applied Biosystems) was used for automatic MS method development. Flow injection was used instead of a HPLC column to decrease run time to 0.8 min per injection. Two injections were performed. The first was performed to locate the precursor ion and optimal declustering potential (DP). The second injection was performed to locate the product ion and optimal collision energy (CE). 

Notes DP, declustering potential CE, collision energy. The CE values were optimized in such a way that the sensitivity of the multiple reaction monitoring signal was at the maximum. 

The spectrum shown in Figure 13.13 demonstrates how a PEG spectrum can be dominated by doubly charged ions ([M + 2 NH4]2"1") if the wrong conditions are chosen. In this case the concentration of ammonium acetate in the reference solution was too high (5 mM ammonium acetate is the maximum that should be used) and the declustering potential is too low. Doubly charged ions can be... 

Detector MS, Perkin Elmer Sciex API Ill-Plus triple quadrupole, APCI, nebulizer 400° and 80 psi, auxiliary nitrogen 1.2 L/min, curtain gas 1.2 L/min, interface 55°, collision gas argon, electron multiplier 3000 V, declustering potential 35 V, collision energy 35 eV... 

Figure 9.13 Positive ion spray mass spectrum of galactosyl ceramide (Galcer) (50 nmol ml" ) with (500 nmol ml" ) in methanol. The declustering potential was 80 V. Reproduced with permission from Koshy, K. M. and Boggs, J. M., Investigation of the calcium-mediated association between the carbohydrate head groups of galactosylceramide and galactosylceramide I sulphate by electrospray ionization mass spectrometry, J. Biol Chem., 271(7), 3496-9, 1996.

CE, collision energy CEP, cell entrance potential CXP, cell exit potential DP, declustering potential EP, entrance potential. 

Table 12.2 hsts the MRM transition ions (w/z) for each compound, along with their corresponding declustering potentials (DP), collision energies (CE), and exit... 

Molecule Ion selected in Q1 (m/ Declustering potential (V) Focusing potential (V) Declustering potential 2 (V) Collision energy (V) Collision gas (arb units) Scan range in the TOF analyzer (m/z)... 

Detector MS, Sciex API 3000 turbo ionspray, electrospray, positive mode at 400, m/z 705 to 335, lonSpray 4600 V, declustering potential 56 V, entrance potential —10 V, focusing potential 220 V, Turbolon gas nitrogen 8 L/min, collision energy 42 V, collision cell exit potential 24 V, dwell time 500 ms, pause time 5 ms... 

Detector MS, PE Sciex API-Ill, APCI, tandem triple quadrupole, positive ion mode, declustering potential 38 V, sprayer 4600 V, multiplier —4200 V, nebulizer gas nitrogen at 60 psi, curtain gas nitrogen at 1.2 L/min, collision gas argon, m/z 496-160... 

Detector MS, Applied Bios5retems API365, APCI, ionspray 4500 V, declustering potential 1 V, focusing potential 120 V, entrance potential -2.5 V, collision entrance potential 8.57 V, collision energy 13 V, collision exit potential 16 V, probe 450°, turbo gas flow 7 L/min, m/z 285.1—163.2... 

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