title: Addition of CsCl reduces ion suppression effects in the matrix-assisted laser desorption/ionization mass spectra of triacylglycerol/phosphatidylcholine mixtures and adipose tissue extracts.
abstract: BACKGROUND
  Ion suppression is a known disadvantage in mixture analysis. Matrix-assisted laser desorption/ionization (MALDI) mass spectra of crude adipose tissue extracts are dominated by triacylglycerol (TAG) signals while less abundant phospholipids such as phosphatidylcholines (PC) and particularly phosphatidylethanolamines (PE) are suppressed. It is suggested that addition of an excess of cesium (Cs) ions helps to overcome this problem.
  
  
  METHODS
  Selected lipid mixtures of known compositions and organic adipose tissue extracts were investigated by positive ion MALDI-time-of-flight mass spectrometry (TOF MS). 2,5-Dihydroxybenzoic acid (DHB) in methanol was used as the matrix. In selected cases the methanolic DHB solution was saturated by the addition of different solid alkali chlorides (such as NaCl, KCl, RbCl and CsCl). Studies on the solubilities of these salts in methanol and the interaction with DHB (by13C NMR) were also performed.
  
  
  RESULTS
  Saturation of the DHB matrix with solid CsCl leads to tremendous intensity differences, i.e. the intensities of the TAG signals (which otherwise dominate the mass spectra) are significantly reduced. In contrast, the intensity of small signals of phospholipids increases considerably. Decrease in the TAG signal intensity is particularly caused by the considerable size of the Cs+ion which prevents successful analyte ionization.
  
  
  CONCLUSIONS
  The addition of CsCl improves the detectability of otherwise invisible or weak phospholipid ions. This is a simple approach to detect small amounts of phospholipids in the presence of an excess of TAG. No laborious and time-consuming separation of the total lipid extract into the individual lipid classes is required. Copyright © 2016 John Wiley & Sons, Ltd.
authors.affiliation: Leipzig University, Faculty of Medicine, Institute for Medical Physics and Biophysics, Härtelstr. 16-18, D-04107, Leipzig, Germany.
authors.forename: Yulia
authors.initials: Y
authors.lastname: Popkova
authors.affiliation: Leipzig University, Faculty of Medicine, Institute for Medical Physics and Biophysics, Härtelstr. 16-18, D-04107, Leipzig, Germany.
authors.forename: Jürgen
authors.initials: J
authors.lastname: Schiller
mesh_terms: D000273:Adipose Tissue / Q000737:chemistry*; D000818:Animals; D002586:Cesium / Q000737:chemistry*; D002712:Chlorides / Q000737:chemistry*; D005260:Female; D005841:Gentisates / Q000737:chemistry; D000432:Methanol / Q000737:chemistry; D051379:Mice; D008810:Mice, Inbred C57BL; D010713:Phosphatidylcholines / Q000032:analysis*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / Q000379:methods*; D014280:Triglycerides / Q000032:analysis*
chemical_list: D002712:Chlorides; D005841:Gentisates; D010713:Phosphatidylcholines; D014280:Triglycerides; D002586:Cesium; C028019:cesium chloride; C010925:2,5-dihydroxybenzoic acid; D000432:Methanol