Ultrasensitive Direct Chemical Analysis of Human Hair Using Proton Transfer Reaction Time-of-Flight Mass Spectrometry (PTR-TOF-MS) for Nontargeted Exposure Profiling

Abstract

Exposure to air pollution plays a significant role in human health. Current methods of measuring human exposure are often limited to outdoor measurements, are time intensive, or are unable to accurately measure certain classes of compounds. This study proposes human hair as a promising indicator of pollution exposure. We present a novel method of hair analysis involving thermal extraction and detection of semivolatile organic compounds using a Vocus 2R proton transfer reaction time-of-flight mass spectrometer (Vocus PTR-TOF-MS). The hair samples were subjected to a temperature ramp spanning three different temperatures: 60 °C, 90 °C, and 120 °C. A hierarchical clustering approach was used to create "clustergrams", dendrograms comprising chemical fingerprints of the hair samples at each different temperature. Each clustergram grouped the chemicals in the samples by similarity, allowing the determination of potential sources of exposure. Multivariate factor analysis revealed the presence of phthalates and their corresponding metabolites, confirming that this method can detect biomarkers associated with pollution exposure. This method enables the rapid and sensitive detection of a wide spectrum of toxicologically relevant compounds in human hair, providing an initial screening tool for measuring human exposure and assessing health risks.

1

Average signal intensity (in cps) is shown across all subsamples of Hair A for three ions, tentatively identified as C₅H₆O (methylfuran), C₄H₇ON (methacrylamide), and C₉H₁₄O (isophorone). The consistency of signal across several days supports both interday and intraday reproducibility of the method.

2

Behavior of selected phthalates during thermal desorption.

3

Chemical fingerprints of HAIR1, HAIR2, and HAIR3 at 90 °C.

4

Clustergram of compounds released by hair samples at 90 °C and a subsection of the dendrogram containing compounds consistent with air pollution. Formulas and tentative compound identities are indicated in Table S3.