title: Use of modified Doehlert-type experimental design in optimization of a hybrid electrospray ionization ion trap time-of-flight mass spectrometry technique for glutathione determination.
abstract: BACKGROUND
  The capabilities of modified non-spherical Doehlert-type experimental designs to optimize the performance of a hybrid mass spectrometer were investigated in this paper for the first time. The optimization process was completed in three successive steps with groups of variables avoiding any univariable approach. Glutathione (GSH, reduced) was selected as a very interesting analyte since it is considered to be one of the most abundant tripeptides in human organism and its action against xenobiotics and oxidative radicals is well known.
  
  
  METHODS
  In particular, a tandem technique based on sequential ion management by an ion trap followed by a time-of-flight mass analyzer (ITTOFMS) was introduced commercially in recent years and investigated for glutathione determination. Glutathione was injected in a stream of a typical mobile phase used in liquid chromatography (LC) and analyzed after electrospray ionization (ESI) in tandem MS.
  
  
  RESULTS
  The three main steps of the LC/MS system, namely the LC mobile phase, the ESI interface and the MS analyzer, were independently optimized in terms of maximum sensitivity. In this context quadratic models were found and their prediction power was evaluated. A calibration study was performed at default and optimum conditions in order to quantitatively estimate the sensitivity enhancement of the employed technique for this analyte. Satisfactory precision (RSD 5.7%) and detectability (LOD 0.07 µmol L(-1) ) were achieved.
  
  
  CONCLUSIONS
  The results highlighted the possibilities offered by the employment of multifactorial optimization towards the improvement of performance of tandem mass spectrometry techniques.
authors.affiliation: Laboratory of Analytical Chemistry, Department of Chemistry, Aristotle University, 54124, Thessaloniki, Greece.
authors.forename: George A
authors.initials: GA
authors.lastname: Zachariadis
authors.forename: Erwin
authors.initials: E
authors.lastname: Rosenberg
mesh_terms: D000097:Acetonitriles / Q000737:chemistry; D005978:Glutathione / Q000032:analysis* / Q000737:chemistry; D057230:Limit of Detection; D012044:Regression Analysis; D015203:Reproducibility of Results; D012107:Research Design; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*; D053719:Tandem Mass Spectrometry / Q000379:methods; D013696:Temperature
chemical_list: D000097:Acetonitriles; D005978:Glutathione; C032159:acetonitrile