title: Influence of electrolytes and a supercharging reagent on charge state distribution and response of neuropeptide ions generated during positive electrospray ionisation mass spectrometry.
abstract: To aid in the detection of trace quantities of neuropeptides in a biological matrix (as saliva), the influence of different electrolytes and a supercharging reagent on the positive electrospray ionisation mass spectrometry (ESI-MS) response was investigated. Ammonium acetate, sodium chloride and sodium bicarbonate (10(-7) M to 10(-3) M) and the supercharging reagent m-nitrobenzyl alcohol (m-NBA) was added to the mobile phase and the effect on the ESI response and charge-states distribution (CSD) was studied in a group of peptides (molecular weight range 2.2kDa to 3.5kDa; CGRP, VIP, GLP1, CRF and PrRP). As expected, the result indicates that the ESI response is affected by the presence of additives: ammonium acetate shifted the observed charge states ratio whereas the addition of m-NBA resulted in the appearance of higher maximum charge state ions. This increase in higher charge state for all the peptide ions, [M + nH]n+ to [M + (n + 1)H](n+1), was atttributed to protonation of the C-terminal. However, when the composition of MeCN in a mobile phase containing m-NBA was increased, an enhancement of the total ion signal was observed for non-polar peptide samples. This is a very interesting observation as this is not observed in samples without m-NBA and could be a result of how these peptide ions are solubilised and positioned relative to the droplet surface/air interface.
authors.forename: Birthe V
authors.initials: BV
authors.lastname: Nielsen
authors.forename: Daniel A
authors.initials: DA
authors.lastname: Abaye
mesh_terms: D000085:Acetates / Q000737:chemistry; D001592:Benzyl Alcohols / Q000737:chemistry; D004573:Electrolytes / Q000737:chemistry*; D007477:Ions / Q000737:chemistry*; D008970:Molecular Weight; D009479:Neuropeptides / Q000737:chemistry*; D017693:Sodium Bicarbonate / Q000737:chemistry; D012965:Sodium Chloride / Q000737:chemistry; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*
chemical_list: D000085:Acetates; D001592:Benzyl Alcohols; D004573:Electrolytes; D007477:Ions; D009479:Neuropeptides; D012965:Sodium Chloride; D017693:Sodium Bicarbonate; C046886:3-nitrobenzyl alcohol; C018824:ammonium acetate