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Rapid Commun Mass Spectrom. 2016 May 15;30(9):1101-7. doi: 10.1002/rcm.7544.

Use of captive spray ionization to increase throughput of the data-independent acquisition technique PAcIFIC.

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Department of Medicinal Chemistry, School of Pharmacy, University of Washington, Seattle, WA, USA.
Department of Pharmaceutical Sciences, School of Pharmacy, University of Maryland, Baltimore, MD, USA.



The Precursor Acquisition Independent From Ion Count (PAcIFIC) method is a data-independent acquisition technique capable of identifying proteins over eight orders of magnitude in a single analysis in human plasma. Widespread application of this technique in proteomic studies is hindered by its time-intensive nature. There exists a need to explore strategies to increase the throughput of the PAcIFIC method.


The PAcIFIC acquisition technique was optimized for use with an Orbitrap mass spectrometer fitted with a captive spray ionization (CSI) source. Chromatographic methods, PAcIFIC acquisition parameters, for example, channels interrogated per chromatographic gradient, time span of chromatographic gradient, and sample loading amount, were investigated to achieve a maximum number of peptide and protein identifications on a yeast proteome where protein copy number had been previously determined.


A 24-hour CSI PAcIFIC method was developed with minimal reduction of peptide and protein identifications from the 4.2-day nano-electrospray ionization (nESI) PAcIFIC method. Analysis of a yeast cell lysate with the 4.2-day nESI PAcIFIC method resulted in 13,468 peptide and 2120 protein identifications. A 24-hour CSI PAcIFIC method resulted in 11,277 peptide and 1753 protein identifications. Increased sample loading of the CSI system allowed for an 8% increase in peptide and protein identifications.


A dramatic decrease in the overall analysis time of the PAcIFIC method (24 h with CSI versus 100.8 h with nESI) was achieved with minimal reduction of peptide and protein identifications. Furthermore, the CSI PAcIFIC method demonstrated a high degree of sensitivity and capability of identifying proteins across a large dynamic range observed with the nESI PAcIFIC method (CSI PAcIFIC identified proteins as low as 46 molecules per cell).

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