Considerations on adsorbent materials for in vitro and ex vivo VOCs (bio-)sampling

Thermal desorption (TD) tubes are often used to trap and extract VOCs in many
applications, from biomonitoring to food aroma characterization [1-3]. Recently, there is
a general growing interest in VOCs from biological fluids (breath, serum etc), specially as
possible biomarkers of specific disease states.
Because of the wide variety of adsorbent materials, the tube can be filled with, it may be
challenging to select the optimal tube for biological samples. Indeed, these trapping
materials can be used alone or in combination, and depending on the characteristics
(chemical and physical), the selectivity can be tuned, as well as the sensitivity and
repeatability.
In this study, TD adsorbent materials sampling performance were compared in biological
samples, both in in vitro and ex vivo situations. Specifically, 7 different adsorbents (Tenax
TA, Tenax GR, Carbopack B, 5TD, 1016, X and Sulphicarb) were used, packed singularly
and in combination, on Fetal Bovine Serum (FBS) and human breath. A mix of 19
standards were employed to monitor and evaluate the sensitivity and repeatability.
Regarding the in vitro sampling, spiked FBS was used to mimic the biological matrix, and
a dynamic headspace extraction was performed. For the in vivo part, breath was collected
in Tedlar bags in which standards were successively flash-vaporized. In both cases, after
extraction, the tubes were thermally desorbed on a comprehensive two-dimensional gas
chromatography system coupled to a time-of-flight mass spectrometer (GC×GC-TOF MS).
For both sample matrices and in the targeted analysis on selected VOCs, the tubes packed
with Tenax TA alone resulted the most sensitive with the highest repeatability, in the
range of 2-22 RSD % for in vivo and 2-32 RSD % for in vitro sampling. In untargeted
analysis on serum and breath, Tenax TA confirmed to be the most suitable material for
sampling in terms of analyte coverage, recovery, and repeatability.
References:
[1] Woolfenden E., Gas Chromatography, DOI:10.1016/b978-0-12-385540-4.00010-9,
2012.
[2] Franchina F.A., Purcaro G., et al. Anal. Chim. Acta, DOI:10.1016/j.aca.2019.03.027,
2019.
[3] Franchina F.A., Zanella D., et al. J. Sep. Sci., DOI:10.1002/jssc.201900902, 2019.