Hollow-fibre liquid-phase microextraction: investigation into the potential use in clinical and forensic toxicology

Venson, Rafael (2017) Hollow-fibre liquid-phase microextraction: investigation into the potential use in clinical and forensic toxicology. PhD thesis, University of Glasgow.

Abstract

Hollow-fibre liquid-phase microextraction (HF-LPME) was introduced in 1999 as a miniaturised version of liquid-liquid extraction (LLE) in order to reduce the consumption of organic solvents and offer an environmentally-friendly approach to extraction procedures. Since then, several studies have been published in the field of forensic and clinical toxicology applying the technique to a broad range of analytes; however more studies are necessary regarding its applicability to bioanalyses. The principle of HF-LPME is the extraction of analytes across a thin supported liquid membrane within the walls of a hollow fibre from a donor phase (DP) into an acceptor phase (AP). It is an extraction technique that encompasses several parameters that require optimisation for an efficient method; this is most effectively achieved by utilising a design of experiment (DoE) approach rather than the conventional one-factor-at-a-time (OFAT) approach.
The main aim of this work is to further investigate the applicability of HF-LPME to the fields of forensic and clinical toxicology by developing and validating methods to extract various drugs from different biological matrices.
Complex matrices, such as whole blood, are commonly used in forensic toxicology. Considering that not many studies have been performed on the application of HF-LPME to whole blood (only 10 up to the present day), this is an aspect that requires further investigation. For this, a fast, accurate and precise 3-phase HF-LPME method followed by LC-MS/MS analysis was developed and validated to simultaneously quantify 5 NBOMe drugs in human whole blood. NBOMe drugs are a group of substances part of the so-called “novel psychoactive substances” (NPS); drugs that have been emerging with increasing frequency over the last few years. NBOMes are associated to deaths as the causa mortis, and due to their high potency, these drugs are normally abused in micrograms. For that reason, the HF-LPME method developed had to present high sensitivity (LOD of pg/mL).
The aim of the second part of this project was to challenge HF-LPME further by developing and validating methods to assess the potential application of HF-LPME in multi-drug analyses. Urine was selected as biological matrix, and the group of chosen analytes were 14 anti-hypertensive drugs and their metabolites with very different physical-chemical properties. HF-LPME has never been applied to such a broad spectrum of substances in previous bioanalytical studies. These drugs were divided into two groups (acidic and basic/neutral), and a total of four extraction methods (two for each group of analytes) were developed and optimised using chemometrics (DoE) then analysed by LC-MS/MS. Two of these methods were liquid-liquid extraction (LLE) methods that were developed and validated to be used as reference to which the two HF-LPME methods were compared. The LLE methods were sensitive, accurate, precise, and valid for application to real case samples. The HF-LPME methods presented some limitations due to the lack of isotopically-labelled analogues of each specific analyte as internal standards (IS); for non-exhaustive methods the use of these IS should be adopted as standard practise. Real urine samples from genuine patients were extracted using all 4 methods followed by LC-MS/MS analysis. By applying the methods to real case samples, it was possible to define that the HF-LPME methods were suitable for qualitative screening of urine to determine the level of compliance of patients under anti-hypertensive pharmacotherapy. However, for quantification of the drugs applying HF-LPME, further development is required to incorporate the use of isotopically labelled analogues.
This study proved that HF-LPME is a potential asset not only for forensic but also for clinical toxicology. It can be a very powerful tool which, mainly due to its green-chemistry approach and pre-concentration capabilities, which allows direct injection into the analytical instrument, could potentially become a more used technique in the future. However, the analyst should be careful when developing HF-LPME methods, to bear in mind its limitations so that methods that are fit-for-purpose can be developed.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Keywords: microextraction methods, HF-LPME, liquid-phase microextraction, NBOMe, method development, forensic toxicology, clinical toxicology, method validation, method optimisation, design of experiment, DoE.
• Subjects: Q Science > Q Science (General); Q Science > QD Chemistry; R Medicine > RA Public aspects of medicine > RA1001 Forensic Medicine. Medical jurisprudence. Legal medicine
• Colleges/Schools: College of Medical Veterinary and Life Sciences > School of Medicine, Dentistry & Nursing
• Supervisor's Name: Torrance, Dr. Hazel and McKeown, Ms. Denise
• Date of Award: 2017
• Embargo Date: 24 January 2022
• Depositing User: Dr Rafael Venson
• Unique ID: glathesis:2017-8697
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 25 Jan 2018 08:46
• Last Modified: 25 Jan 2021 09:10
• URI: https://theses.gla.ac.uk/id/eprint/8697