SpheriCal -ESI: A dendrimer-based nine-point calibration solution ranging from m/z 273 to 1716 for electrospray ionization mass spectrometry peptide analysis.

Rationale: A calibration solution for mass spectrometry needs to cover the range of interest with intense and sufficiently narrowly spaced peaks. Limited options fulfilling this may lead to compromises between performance and ease of use. SpheriCal -ESI was designed to combine high calibration performance for electrospray ionization (ESI) mass spectrometric analysis of peptides in positive mode with quick and easy use.

Methods: The developed calibration solution was tested using three mass spectrometers: two ion traps and one tandem quadrupole. The m/z errors of SpheriCal -ESI itself and of a tryptic digest of cytochrome C were measured after calibration. The results were compared with those achieved with ESI Tuning Mix. The memory effects of the dendrimers, and contamination from Na in the calibration solution, were evaluated.

Results: SpheriCal -ESI showed good shelf life as powder and was quickly reconstituted for use. Achieving intense and stable signals was straightforward. The accuracies and precisions were as expected for the instruments. SpheriCal -ESI was more precise and at least as accurate as ESI Tuning Mix. The memory effects and Na contamination were found to be negligible in typical peptide solvents. In addition, the dendrimers showed predictable dissociations with product ions common to collision-induced dissociation in both ion trap and tandem quadrupole mass spectrometers.

Conclusions: SpheriCal -ESI provided easily accessible calibration by showing intense signals at low infusion rates and at source settings equal or similar to those used in peptide analysis. Nine calibration points in the range of interest gave precise and accurate results. Memory effects and contamination were negligible even without rinsing.