Development of an accurate and sensitive method for lactate analysis in exhaled breath condensate by LC MS/MS

Exhaled breath condensate (EBC) is easily obtained for clinical diagnosis and prognosis for pulmonary diseases and has gained much interest in biomarker discovery research and studies. Lactate, a physiological material, is found in EBC and has been demonstrated to be a potential indicator of chronic obstructive pulmonary disease and other lung diseases. Several assays are available to detect lactate in human body fluids, and yet none is suitable for detecting lactate in EBC. Due to the very low concentration of lactate in EBC and low volume of EBC, it is very important to develop an assay to measure lactate with high sensitivity, accuracy and easy sample processing. We report here a novel LC-MS/MS based assay to measure lactate using HILIC column separation. Sample preparation was simple and straightforward through a "dilute and shoot" approach with a separation of 4min. The limit of quantification was determined to be 0.5μM. This assay was linear from 0.5μM to at least 100μM. The inter- and intra- day precision at the levels of 1μM, 10μM, and 100μM were less than 3% with recovery within 5.4% of expected values. There was no ion suppression for the assay, and no carry-over was observed up to 500μM. Furthermore, we discovered that lactate is ubiquitously present in the lab environment, which can create significant challenges for accurate detection of lactate at low concentrations. We provided practical approaches in this paper to overcome the challenges and ensure the accuracy of the assay. In summary, this article presents an accurate and sensitive method using LC-MS/MS for measuring lactate in EBC, and this method is suitable for measuring lactate concentrations for non-invasive monitoring of pulmonary functions.