Pre‑cleaned bare wooden toothpicks for the determination of drugs in oral fluid by mass spectrometry
Our latest article, published as a paper in the forefront in Analytical and Bioanalytical Chemistry, presents a deep study of the reduction of the intrinsic components of wooden toothpicks (WTs) towards their use as a sorptive phase in the determination of six tricyclic antidepressants (amitriptyline, clomipramine, desipramine, imipramine, nortriptyline, and trimipramine) in saliva by direct infusion mass spectrometry (DI-MS) and LC-MS, and the in vivo qualitative analysis of acetaminophen in saliva samples.
In the sample preparation context, WTs
are used as sorbents according to their superficial -OH groups that provide
electrostatic and hydrogen bond interactions with the target compounds.
Moreover, they can be surface-modified to establish or improve the
sorbent-analyte interaction. However, the presence of intrinsic components or
impurities provided by the biosorbents can present a negative effect on the
instrumental determination of the target compounds.
To minimize this limitation, different
consecutive washing cycles with boiling tap water have been evaluated, avoiding
using organic solvents during the synthesis process. Moreover, the introduction
of chromatographic separation reduces the hindering of the ionization of the
target analytes.
TCAs analysis
The proposed extraction process
allows the simultaneous extraction, elimination of the interferences, and
elution of the samples, providing a high sample throughput in the analysis of
biosamples (Figure 1). The pb-WTs are simultaneously conditioned with Milli-Q water,
transferred to glass vials with 5 mL of the sample, and stirred at 500 rpm for 60
min. The pb-WTs are washed with 1 mL of Milli-Q water at 500 rpm for 10 min.
Finally, the pb-WTs are eluted with 200 μL of methanol in an HPLC insert into
the vial, and the extracts are analyzed by DI-MS or LC-MS.
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| Figure 1. Extraction procedure. |
The effect of the variables is
corrected by using internal standards, making the sample pH and ionic strength
not necessary to be adjusted. The extraction time was established at 60 min for
aqueous standards and saliva samples.
The proposed method was
satisfactorily validated for DI-MS and LC-MS in terms of linear range, LODs,
LOQs, inter-and-intra-day precision, and accuracy. The limits of detection were
in the range of 0.1-0.5 ng/mL and 0.1-0.3 ng/mL, respectively, while the linear
range spanned from 0.4 to 800 ng/mL. The intra-day precision (expressed as relative
standard deviation) was better than 12.1% and 8.6%, for DI-MS and LC-MS,
respectively. Accuracy values spanned from 94-133% and 77-114% for DI-MS and LC-MS,
respectively. Blind samples were analyzed to demonstrate the applicability of
the method.
In vivo analysis
The potential of pb-WTs as a tool
for in vivo sampling was preliminarily presented towards the qualitative
analysis of acetaminophen in saliva. A healthy volunteer took orally 1 g of acetaminophen,
followed by rinsing the mouth with 100 mL of water to remove potential
residues. Aftewarss, a pb-WT was introduced in the mouth and sucked for 5 min.
The pb-WT was collected, washed with Milli-Q water, and eluted in 200 µL of
methanol. The eluate was finally analyzed by DI-MS/MS, showing a
pharmacokinetic profile of the presence of the analyte at different times from
the ingest.
Reference
Millán-Santiago J, Lucena R, Cárdenas
S (2022) Pre-cleaned bare wooden toothpicks for the determination of drugs in
oral fluid by mass spectrometry. Anal Bioanal Chem.
https://doi.org/10.1007/s00216-022-03977-w
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Keywords
Bioanalysis, high sample
throughput, in vivo, mass spectrometry, microextraction, prescription drugs, pre-cleaned
bare wooden toothpicks.
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