1 Microextraction Techniques in Analytical Toxicology: An Overview
Rajeev Jain1, Ritu Singh2, and Abuzar Kabir3
1Central Forensic Science Laboratory, Directorate of Forensic Science Services, Ministry of Home Affairs, Govt. of India, India
2Department of Environmental Science, School of Earth Sciences, Central University of Rajasthan, NH8, Bandarsindri, Kishangarh, India.
3Department of Chemistry and Biochemistry, Florida International University, Miami, USA
DOI: 10.1201/9781003128298-1
Contents
- 1.1 Introduction to Analytical Toxicology
- 1.2 Nature of Specimens in Analytical Toxicology
- 1.2.1 Blood
- 1.2.2 Urine
- 1.2.3 Saliva / Oral Fluid
- 1.2.4 Hair and Nails
- 1.2.5 Vitreous Humour (VH)
- 1.2.6 Liver
- 1.2.7 Stomach Contents
- 1.2.8 Other Tissues
- 1.3 Microextraction Techniques in Analytical Toxicology: Classification, Theory, and Practical Applications
- 1.3.1 Classification of Microextraction Techniques Used in Analytical Toxicology
- 1.3.2 Theoretical Considerations
- 1.3.2.1 Solvent-Based Microextraction
- 1.3.2.2 Sorbent-Based Microextraction
- 1.3.3 Sorbent-Based Microextraction Techniques
- 1.3.3.1 Solid-Phase Microextraction (SPME)
- 1.3.3.2 Micro Solid-Phase Microextraction (µSPE)
- 1.3.3.3 Stir Bar Sorptive Extraction (SBSE)
- 1.3.3.4 Microextraction by Packed Sorbent (MEPS)
- 1.3.3.5 Electromembrane Extraction (EME)
- 1.3.3.6 Fabric Phase Sorptive Extraction (FPSE)
- 1.3.3.7 Molecularly Imprinted Polymer-Based Microextraction
- 1.3.4 Solvent-Based Microextraction Techniques
- 1.3.4.1 Single Drop Microextraction (SDME)
- 1.3.4.2 Liquid-Phase Microextraction (LPME)
- 1.3.4.3 Ionic Liquid-Based Microextraction
- 1.3.4.4 Deep Eutectic Solvent-Based Microextraction
- 1.4 Conclusion and Future Trends
- References
1.1 Introduction to Analytical Toxicology
Analytical toxicology involves detection, identification, and quantification of xenobiotic compounds (exogenous compounds), such as drugs, pesticides, poisons, pollutants, and their metabolites in various complex sample matrices, such as ante- and postmortem blood, urine, tissue, or vitreous humour (VH), or alternative samples, such as hair, nail, meconium, sweat, oral fluid, etc. Analytical toxicologists play an important role in diagnosis, management, and prevention of poisoning by detecting, identifying, and measuring the unknown drug or poison in the biological specimens (Maurer 2007; Maurer 2010). In most cases of analytical toxicology and doping control, the nature of the target analyte is usually unknown prior to analysis. Additionally, the presence of endogenous biomolecules and other xenobiotic compounds makes the matrix more complex, which raises the need for highly selective and sensitive analytical methods to determine unknown toxicants. Moreover, drugs and their metabolites are generally present at very trace levels in biological fluids, which further makes the whole analysis a daunting task. Since the analysis is usually untargeted and sample availability is also limited, sample preparation methodologies that require the least amount of sample and are capable of removing insoluble residues and interfering compounds are of the utmost importance in analytical toxicology (Flanagan 2007; Jain and Singh 2016).
1.2 Nature of Specimens in Analytical Toxicology
Various disciplines, such as clinical toxicology, forensic toxicology, therapeutic drug monitoring (TDM), screening of drugs of abuse, as well as occupational and environmental toxicology are covered under the aegis of analytical toxicology. However, there is considerable overlap between all the disciplines. Therefore, the specimens commonly encountered in analytical toxicology are basically of biological origin obtained under different conditions, which may range from liquid (e.g., pure solutions of a drug, blood, urine, cerebrospinal fluid, oral fluid) to semi-solid and solid material (e.g., tissue and pharmaceutical tablets). Analysis of liquid samples is generally easier in comparison to solid samples, which generally require homogenization, digestion, and protein precipitation.
1.2.1 Blood
Blood is the sample of choice in living humans as analyte concentrations in blood are closely related with their dose and biological effect. Beside blood, plasma and serum are also used for analysis of drugs. In postmortem toxicology, two blood specimens are collected: one from the heart and another from a peripheral site, e.g., femoral or ileac vein. These specimens may be significantly decomposed or contaminated from chest fluid, pericardial fluid, and gastric contents in the case of traumatic death (Jones 2008; Kerrigan and Levine 2020). Beside quantification, blood samples are also useful for screening of xenobiotics if their concentration is high enough. Postmortem blood has a high degree of haemolysis, and therefore direct analysis of whole blood is preferred.
1.2.2 Urine
Urine is an important specimen for targeted and non-targeted comprehensive screening of drugs and xenobiotic compounds as it represents a major route for their elimination from the body. Additionally, the collection process of urine samples is non-invasive, and the concentration of drugs is relatively high. Analysis of a urine specimen is also relatively simple as it comprises more than 99% water and is devoid of lipids, circulating serum proteins, and large molecular weight compounds due to the glomerular filtration process, which facilitates its analytical investigation by immunoassay, spot-tests, or sample preparation for instrumental analysis (Dinis-Oliveira et al. 2010). However, in forensic postmortem toxicology, urine is available only in 50% of deaths as the bladder usually voids during the dying process (Jones 2008).
1.2.3 Saliva / Oral Fluid
There has been growing interest in using saliva as a diagnostic medium of drug abuse since it can be obtained quickly and non-invasively without privacy violation, unlike urine sample collection. Saliva contains the free form of the drug, and its concentration can be correlated to the free drug concentration in plasma. For many drugs, only free fraction is physiologically active; therefore, saliva can better indicate the state of intoxication (Schramm et al. 1992).
1.2.4 Hair and Nails
Analysis of hair and nails is particularly useful for retrospective information of drug abuse and metal poisoning. The circulating drugs in the blood stream get incorporated into the cells of the hair and nails and get trapped when they are keratinized. The advantage of hair and nail testing is their non-invasive and easy collection, storage at room temperature, and small sample size requirement for analysis. The growth rate of nails is slower, which makes them suitable for retrospective analysis of drug abuse. Various drugs of abuse (e.g., amphetamines, cannabinoids, benzodiazepines, morphine, heroin, cocaine), trace elements (e.g., arsenic), and doping substances (e.g., ephedrine), etc., can be detected in hair and nails and can establish their chronic exposure (Daniel et al. 2004).
1.2.5 Vitreous Humour (VH)
VH is located between the lens and the retina of the eye and fills the eye chamber. VH is basically a salt solution that consists 99% of water and contains very little protein. Hence, any drug and metabolite present in VH can be easily extracted. VH is resistant to putrefactive changes as it resides in an anatomically isolated area; therefore, it has been used widely for estimation of ethanol and other drugs in postmortem forensic toxicology. The main drawback of VH is its small volume, i.e., up to 3–4 mL in each eye.
1.2.6 Liver
The liver is one of the most important and primary solid tissue used in postmortem toxicology for the analysis of drugs and poisons. The liver is the main metabolic organ of the body, where a higher concentration of basic drugs can be found in comparison to other body organs. The collection and sample preparation of the liver is easier; it is available in sufficient quantities for analysts, and unlike blood, it is not affected by postmortem redistribution as the concentration of drugs is relatively stable after death (Jones 2008; Dinis-Oliveira et al. 2010).
1.2.7 Stomach Contents
Stomach or gastric contents are mainly important for qualitative analysis in the case of oral overdose of drugs and poisons, especially when the specimen is obtained soon after the intoxication. The concentration of drug after oral ingestion may be high in the stomach contents; therefore, it is suitable for toxicological screening of xenobiotics. The drugs that are difficult to be detected in blood due to their extensive distribution can be easily detected in their parent form in stomach contents. In some cases where death occurred within a short time after oral ingestion, unabsorbed tablets or capsules may be detected in their intact form (Jones 2008; Dinis-Oliveira et al. 2010).
