Ion mobility and liquid chromatography/mass spectrometry strategies for exhaled breath condensate glucose quantitation in cystic fibrosis studies

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Abstract
RATIONALE: Cystic fibrosis related diabetes (CFRD) is an important complication of cystic fibrosis (CF) because it causes acceleration in the decline in lung function. Monitoring concentrations of key metabolites such as glucose in airway lining fluid is necessary for improving our understanding of the biochemical mechanisms linking diabetes and CF. Targeted‐metabolomic strategies for glucose quantitation in exhaled breath condensate (EBC) from healthy individuals are presented. METHODS: Three different electrospray ionization mass spectrometry (ESI‐MS)‐based methods were developed for EBC sample interrogation and glucose quantitation without derivatization. Two methods utilized ultra‐high‐performance liquid chromatography (UHPLC) coupled to either time‐of‐flight (TOF) MS or triple quadrupole (QqQ) tandem MS (MS/MS). A third approach involved direct‐infusion traveling wave ion mobility spectrometry (TWIMS) with TOF‐MS detection. UHPLC/QqQ‐MS/MS was used for urea quantitation as the EBC dilution marker. Matrix effects were mitigated using isotopically labeled glucose and urea as internal standards. RESULTS: All the developed methods allowed glucose and urea quantitation in EBC with high accuracy and precision. The UHPLC/TOF‐MS and UHPLC/QqQ‐MS/MS methods provided similar analytical figures of merit. UHPLC/QqQ‐MS/MS provided the highest sensitivity and the lowest limit of detection (LOD) of 1.5 nM in EBC for both glucose and urea. The TWIMS‐TOF‐MS‐based method provided the highest sample throughput capability; however, the glucose LOD was ~3‐fold higher than with the two chromatographic methods. CONCLUSIONS: Mass spectrometric methods for the quantitative analysis of trace EBC glucose levels are reported and compared for the first time. The analytical figures of merit demonstrate the applicability of these methods to metabolite analysis of airway samples for CF and CFRD research. Copyright © 2013 John Wiley & Sons, Ltd.

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