%0 Journal Article %J J Am Soc Mass Spectrom %D 2015 %T Electron Capture Dissociation of Sodium-Adducted Peptides on a Modified Quadrupole/Time-of-Flight Mass Spectrometer. %A Voinov, Valery G %A Peter D Hoffman %A Bennett, Samuel E %A Beckman, Joseph S %A Barofsky, Douglas F %K Amino Acid Sequence %K Electrons %K Equipment Design %K Mass Spectrometry %K Models, Molecular %K Peptides %K Sodium %X

Electron capture dissociation (ECD), which generally preserves the position of labile post-translational modifications, can be a powerful method for de novo sequencing of proteins and peptides. In this report, ECD product-ion mass spectra of singly and doubly sodiated, nonphosphorylated, and phosphorylated peptides are presented and compared with the ECD mass spectra of their protonated counterparts. ECD of doubly charged, singly sodiated peptides yielded essentially the same sequence information as was produced by the corresponding doubly protonated peptides. The presence of several sodium binding sites on the polypeptide backbone, however, resulted in more complicated spectra. This situation is aggravated by the zwitterionic equilibrium of the free acid peptide precursors. The product-ion spectra of doubly and triply charged peptides possessing two sodium ions were further complicated by the existence of isomers created by the differential distribution of sodium binding sites. Triply charged, phosphorylated precursors containing one sodium, wherein the sodium is attached exclusively to the PO4 group, were found to be as useful for sequence analysis as the fully protonated species. Although sodium adducts are generally minimized during sample preparation, it appears that they can nonetheless provide useful sequence information. Additionally, they enable straightforward identification of a peptide's charge state, even on low-resolution instruments. The experiments were carried out using a radio frequency-free electromagnetostatic cell retrofitted into the collision-induced dissociation (CID) section of a hybrid quadrupole/time-of-flight tandem mass spectrometer. Graphical Abstract ᅟ.

%B J Am Soc Mass Spectrom %V 26 %P 2096-104 %8 2015 Dec %G eng %N 12 %R 10.1007/s13361-015-1230-y %0 Journal Article %J Environ Sci Technol %D 2008 %T Field trial and modeling of uptake rates of in situ lipid-free polyethylene membrane passive sampler. %A Kim A Anderson %A D Sethajintanin %A Gregory J Sower %A Quarles, L %K Lipids %K Membranes, Artificial %K Models, Molecular %K Models, Theoretical %K Polyethylene %K Quality Control %X

Lipid-free polyethylene membrane tubing (LFT) has been further developed in response to a growing need for an inexpensive and simple time-integrative sampling device for dissolved hydrophobic contaminants in water. The LFT sampler is based on the diffusion of dissolved hydrophobic target compounds through the aqueous boundary layer and into the polyethylene membrane, mimicking uptake by organisms. We demonstrate through laboratory and field validation studies that LFT provided the same benefits as many other passive sampling devices, withoutthe potential of analytical interference from lipid impurities. A total of 370 LFTs and semipermeable membrane devices were deployed for 21 days in paired studies at highly urbanized, undeveloped, and two Superfund sites, representing several river conditions. A simple internal surrogate spiking method served as an in situ calibration indicator of the effects of environmental conditions on the uptake rates. A modified extraction method for the LFT increased recoveries while decreasing solvent use and labor compared to other organic extraction procedures. LFT sampling rates were estimated using ratios, in situ calibration and modeling for over 45 target analytes, including PAHs, PCBs, and pesticides.

%B Environ Sci Technol %V 42 %P 4486-93 %8 06/2008 %G eng %N 12 %1 http://www.ncbi.nlm.nih.gov/pubmed/18605575?dopt=Abstract