Structural elucidation of amino amide-type local anesthetic drugs and their main metabolites in urine by LC-MS after derivatization and its application for differentiation between positional isomers of prilocaine

Determination of Local Anesthetic Drugs in Human Plasma Using Magnetic Solid-Phase Extraction Coupled with High-Performance Liquid Chromatography

In this work, magnetic tetraethylenepentamine (TEPA)-modified carboxyl–carbon nanotubes were synthesized, characterized, and used as adsorbents to conduct magnetic solid-phase extraction (MSPE) for the preconcentration of seven local anesthetic drugs (procaine, lidocaine, mepivacaine, oxybuprocaine, bupivacaine, tetracaine, and cinchocaine) from human plasma. The separation and determination of analytes were performed on high-performance liquid chromatography with UV detection. Several factors affected the extraction efficiency, such as the amount of adsorbents used, extraction time, sample pH, and optimization of elution conditions. Under optimal conditions, satisfactory linear relationships were obtained in the range of 0.02–5.00 mg/L, with the limits of detection (LOD) ranging from 0.003 mg/L to 0.008 mg/L. The recoveries of analytes for spiked human plasma were in the range of 82.0–108%. Moreover, the precision with intra-day and inter-day RSD values were obtained in the range of 1.5–7.7% and 1.5–8.3%. The results indicated that this method could determine the concentration of seven local anesthetic drugs in human plasma with high precision and repeatability and provide support for the clinical monitoring of the concentration of local anesthetic drugs in human plasma.

Oxidative derivatization of V-type nerve agents as a tool for their structural elucidation by liquid chromatography/tandem mass spectrometry

RATIONALE

The identification of V-type nerve agents poses an analytical challenge. Their spectra obtained by electron ionization mass spectrometry (EI-MS) and electrospray ionization tandem mass spectrometry (ESI-MS/MS) are dominated by ions originating from the N,N-dialkylaminoethyl moiety, while ions representative of the alkyl phosphonothiolate part are absent from the spectra or present at negligible abundance. Hence, analogs or isomers with the same amine residue exhibit similar mass spectral patterns, leading to unavoidable ambiguity in their identification.

METHODS

Chemical derivatization was utilized for the structural elucidation of a series of five V-type nerve agents, including O-ethyl S-(2-diisopropylamino)ethyl methylalkyl phosphonothiolate (VX), O-isobutyl S-(2-diethylamino)ethyl methylalkyl phosphonothiolate (RVX) and O-ethyl S-(2-diethylamino)ethyl methylalkyl phosphonothiolate (VM). The procedure consisted of "in-vial" oxidation of the tertiary amine group with 3-chloroperbenzoic acid (m-CPBA) at ambient temperature followed by liquid chromatography (LC)/Orbitrap-ESI-MS/MS analysis with no other sample preparation.

RESULTS

The generated N-oxide of the V-type nerve agents altered the charge distribution occurring during fragmentation and produced informative ESI-MS/MS spectra characteristic of the alkyl phosphonothiolate structure, enabling a higher degree of certainty in their identification. Moreover, two VX isomers possessing an identical tertiary amine moiety that coeluted at practically the same retention time and displayed high mass spectral similarity were easily differentiated, and their structures elucidated once derivatized.

CONCLUSIONS

In contrast to the ESI-MS/MS spectra of the V-type nerve agents, which exhibited mostly/only information on the amine-containing residue, the ESI-MS/MS spectra of the V-type nerve agent N-oxides revealed ions indicative of both the alkyl phosphonothiolate and the amine parts, enabling their reliable structural elucidation.

Structural elucidation of dipeptides displaying limited mass spectral information by liquid chromatography-electrospray ionization-tandem mass spectrometry

Small peptides, such as dipeptides, have attracted attention in many research fields because of their important biological functions and potential roles as disease biomarkers. However, the identification of many of them by implementation of liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-ESI-MS/MS) is a challenging task. This is because many dipeptides display limited mass spectral information in LC-ESI-MS/MS analyses, which leads to unavoidable ambiguity in determinations of their structures. In this study, two useful analytical techniques were developed for the structural elucidation of 10 representative dipeptides exhibiting a dominant/single product ion in the ESI-MS/MS spectra of the protonated molecules [M + H]⁺ . Structural elucidation was obtained instantaneously through LC-ESI-MS/MS fragmentation of the accompanying sodium adducts [M + Na]⁺ or alternatively by "in-vial" chemical derivatization with isobutyl chloroformate. The sodium adducts and the resulting carbamate derivatives altered the charge distribution occurring during ESI-MS/MS fragmentation, enabling detailed structural elucidation and unambiguous identification of such dipeptides at ng/ml levels. These quick, simple, and easy techniques can be implemented to identify various dipeptides or confirm their identities without the need for complex sample handling.