Isotopic Analogs as Internal Standards for Quantitative GC/MS Analysis--Molecular Abundance and Retention Time Difference as Interference Factors PDF Download

Author: WT. Chang
Publisher:
ISBN:
Category : Barbiturate
Languages : en
Pages : 9

Get Book Here

Book Description
The following analyte/isotope-labeled internal standard (IS) systems areadapted to further study the interference phenomenon previously reported fromour laboratory-the intensity ratio of the ion-pair designated for aspecific analyte/2H-analog system increases as the solvent used to reconstitutethe extraction/derivatization residue is increased: (a) Three analyte/2H-analogpairs with 2H-atoms positioned at allylic sites (butalbital, secobarbital,methohexital); (b) Two analyte/2H-analog pairs without these structural features(pentobarbital, phenobarbital); and (c) Two analyte/13C-analog pairs (butalbital,secobarbital) Major experimental parameters adapted in this study include:(a) Varying reconstitution solvent volume while keeping a constant analyte/ISconcentration ratio; (b) Varying analyte/IS concentration ratio; (c) Varyinggas chromatograph (GC) injection port temperature; and (d) Varying GC columntemperature programming conditions, rendering difference in the degree ofoverlap of the peaks derived from the analyte and the 2H-analog. This studyresults in the following observations: (a) Changes in the intensity ratioof the ionpair designated for a specific analyte/2H-analog system depend onmolecular abundance, regardless of whether the 2H-atoms are positioned atactive allylic positions or not-thus, ruling out hydrogen/deuteriumexchange as the cause of the observed interference phenomenon; (b) Variationsin GC injection port temperature do not alter the observed interference phenomenon-thus,ruling out chemical reactions at the injection port as the underlying cause;(c) Variations in peak-overlapping between the analyte and the 2H-analog,facilitated by changing GC column programming conditions, alter the observedinterference phenomenon. Abundance of the analyte and the 2H-analog and theiroverlapping characteristic in the mass spectrometer ion source are believedto be the underlying cause of the observed interference phenomenon. The interferencephenomenon observed for a specific analyte/2H-analog system has significantconsequences on the linearity of the thereby generated calibration curves.Nonlinear approaches can better describe the calibration data and are neededmore in comparison to systems in which 13C-analogs are used as the ISs.