Detection of Volatile Organic Compounds in a Drop of Urine by Ultrasonic Nebulization Extraction Proton Transfer Reaction Mass Spectrometry

Detection of volatile organic compounds (VOCs) in human urine has potential application value in screening for disease and toxin exposure. However, the current technologies are too slow to detect the concentration of VOCs in fresh urine. In this study, we developed a novel ultrasonic nebulization extraction proton transfer reaction mass spectrometry (UNE-PTR-MS) technology. The urinary VOCs can be rapidly extracted to gaseous VOCs using the UNE system and then delivered using a carrier gas to the PTR-MS instrument for rapid detection. The carrier gas flow and sample size were optimized to 100 mL/min and 100 μL, respectively. The limits of detection (LODs) and response time of the UNE-PTR-MS were evaluated by detecting three VOCs that are common in human urine: methanol, acetaldehyde, and acetone. The LODs determined for methanol (4.47 μg/L), acetaldehyde (1.98 μg/L), and acetone (3.47 μg/L) are 2–3 orders of magnitude lower than the mean concentrations of that in healthy human urine. The response time of the UNE-PTR-MS is 34 s and only 0.66 mL of urine is required for a full scan. The repeatability of this UNE-PTR-MS was evaluated, and the relative standard deviations of 5 independent determinations were between 4.62% and 5.21%. Lastly, the UNE-PTR-MS was applied for detection of methanol, acetaldehyde, and acetone in real human urine to test matrix effects, yielding relative recoveries of between 88.39% and 94.54%. These results indicate the UNE-PTR-MS can be used for the rapid detection of VOCs in a drop of urine and has practical potential for diagnosing disease or toxin exposure.