Determination of glucose in exhaled breath and saliva by ion chromatography

A novel noninasive method was developed for determining glucose levels in human exhaled breath and saliva using ion chromatography. This innovative approach involves collecting exhaled breath and saliva samples using a self-designed condensation device and non-stimulative method to ensure minimal participant discomfort. The glucose contents in both exhaled breath condensate (EBC) and saliva were analyzed using ion chromatography, which is highly sensitive and specific. The experimental conditions were optimized, including a condensation temperature of -14 ℃ and an expiratory flow of 15 L/min. A Dionex CarboPac MA1 ion chromatography column (250 mm×4 mm) was used to separate glucose, with the column temperature maintained at 30 ℃. Sodium hydroxide solution (0.8 mol/L) with a pump flow rate of 0.4 mL/min was used as the mobile phase for ion chromatography. Under these conditions, glucose exhibited a good linear relationship in the range of 0.01-20 mg/L, with a correlation coefficient of 0.9999, along with limits of detection (LOD) and quantification (LOQ) of 2.1 and 7.0 μg/L, respectively. The intra- and inter-day precisions of glucose content in exhaled breath and saliva samples of ≤7.5% (<i>n</i>=5) and ≤8.4% (<i>n</i>=5), respectively. The results reveal that the glucose levels in exhaled breath and saliva are strongly correlated with blood glucose levels. The method was validated by measuring the glucose contents of exhaled breath and saliva from six diabetic patients and six healthy subjects. Little variation in the glucose contents of the exhaled breath of the two groups was observed under fasting states. However, the exhaled breath of the diabetic patients exhibited significantly higher (by factors of 6-80) glucose contents (48.4-140.0 ng/L) than those of healthy subjects (1.7-7.9 ng/L) 1 h after glucose ingestion. Saliva samples from fasting diabetic patients contained 1.2-5.0-times more glucose contents (87.6-158 mg/L) than those of healthy subjects (31.6-70.9 mg/L). In addition, the saliva of the diabetic patients exhibited glucose contents (136-257 mg/L) that were 1.8-7.7-times higher than those of the healthy subjects (33.1-75.2 mg/L) 2 h after glucose ingestion. The developed method provides a simple, precise, and non-invasive means of detecting glucose contents in a manner that does not harm the human body; hence, it is a promising non-invasive metabolic-monitoring tool. This study opens new avenues for the development of innovative technologies for monitoring glucose and other biomarkers, which is expected to greatly enhance metabolic-study accuracy and ease, particularly in the context of managing diabetes and other metabolic disorders.