@article{148621,
  abstract     = {{Using human insulin (MW 5808 Da) as a model compound, the possible strategies towards optimization of sensitivity and selectivity of measurement by electrospray ionization with a standard triple quadrupole mass spectrometer were investigated. For measurement in selected ion-monitoring (SIM) mode, these strategies involved systematic variation of instrumental parameters and spray pH. In this investigation four different operating modes were used corresponding to positive/negative ionization modes with acidic/basic sprays and pH reversed (hereafter termed 'wrong-way-round' operation); the cone voltage was optimized for each mode of operation. When collision-activated dissociation (CAD) is employed, two additional operation modes are possible: namely, low collision energies (10-35 eV, CAD-1) for the generation of sequence-specific fragments and high collision energies (> 80 eV, CAD-h) for the generation of nonspecific fragments. Overall, this results in twelve different modes of operation.

Loop-injection of aqueous insulin standards were run for each of the twelve operating modes and measurements made for five different charge states (n = 2-6) observable with our instrument that has an upper mass limit of m/z 4000. The signal/noise (S/N) ratio was optimized for each charge state, resulting in 60 measurements. The best S/N ratios (20000) were achieved under positive SIM conditions with charge state 6 (m/z 969) and under 'wrong-way-round' negative SIM conditions with charge state 3 (m/z 1935). Lower S/N ratios were observed under positive CAD-h conditions with charge state 5 (m/z 1163, S/N 15000) and positive CAD-I conditions with charge state 6 (m/z 969, S/N 10000). All other operating modes gave maximum S/N ratios of 4000.

For measurement of insulin standards, the results obtained show SIM to give the best S/N ratio. However, for samples in complex matrices, our general experience suggests CAD to be the preferable operating mode. Consequently, for the development of a quantitative method for proteins in general, it might be advocated that all of the twelve operating modes and all relevant charge states be investigated to find the optimum S/N ratio. Copyright (C) 2001 John Wiley & Sons, Ltd.}},
  author       = {{Fierens, Colette and Stöckl, Dietmar and Thienpont, Linda and De Leenheer, Andreas}},
  issn         = {{0951-4198}},
  journal      = {{RAPID COMMUNICATIONS IN MASS SPECTROMETRY}},
  language     = {{eng}},
  number       = {{16}},
  pages        = {{1433--1441}},
  title        = {{Strategies for determination of insulin with tandem electrospray mass spectrometry : implications for other analyte proteins?}},
  url          = {{http://doi.org/10.1002/rcm.386}},
  volume       = {{15}},
  year         = {{2001}},
}

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