Determination of cannabinoids in hair using high-pH* non-aqueous electrolytes and electrochemical detection. Some aspects of sensitivity and selectivity

Applications of Capillary Electrophoresis for the Determination of Cannabinoids in Different Matrices

Cannabinoids, terpenophenolic chemicals found only in cannabis, are primarily responsible for cannabis pharmacologic effects; nearly 150 distinct cannabinoids have been identified thus far. Among these, the main psychoactive molecule, tetrahydrocannabinol (THC), and the non-psychoactive counterpart, cannabidiol (CBD) are distinguishable. In the past decade, a CBD-containing pharmaceutical preparation was approved by Food and Drug Administration (FDA) for the treatment of drug-resistant epileptic seizures in children, and research trials for a variety of additional medical conditions for which CBD has been suggested as a therapy are being conducted. Additionally, the number of "CBD-containing" dietary supplements, largely available online, is increasing rapidly. Consequently, the necessity for the development of qualitative and quantitative methodologies for the analysis of the bioactive components of Cannabis is rising because of the increase in the production of therapeutic cannabis products. One of the analytical methods with good potential in cannabinoids analysis is capillary electrophoresis (CE). It has advantages related to high separation efficiency, relatively short analysis time, and the small consumption of analytes and reagents which generates relatively lower operational costs than other methods. This review focuses on the use of CE techniques to examine biological matrices and plant materials for the presence of cannabinoids and other bioactive compounds found in cannabis. The advantages, drawbacks, and applicability of the various electromigration approaches are also assessed. The article provides an overview of the "state of the art" and the latest trends in CE-based methods for the determination of cannabinoids.

Affinity Assays for Cannabinoids Detection: Are They Amenable to On-Site Screening?

Roadside testing of illicit drugs such as tetrahydrocannabinol (THC) requires simple, rapid, and cost-effective methods. The need for non-invasive detection tools has led to the development of selective and sensitive platforms, able to detect phyto- and synthetic cannabinoids by means of their main metabolites in breath, saliva, and urine samples. One may estimate the time passed from drug exposure and the frequency of use by corroborating the detection results with pharmacokinetic data. In this review, we report on the current detection methods of cannabinoids in biofluids. Fluorescent, electrochemical, colorimetric, and magnetoresistive biosensors will be briefly overviewed, putting emphasis on the affinity formats amenable to on-site screening, with possible applications in roadside testing and anti-doping control.

An Electrochemical Sensor Based on Amino Magnetic Nanoparticle-Decorated Graphene for Detection of Cannabidiol

For detection of cannabidiol (CBD)—an important ingredient in Cannabis sativa L.—amino magnetic nanoparticle-decorated graphene (Fe₃O₄-NH₂-GN) was prepared in the form of nanocomposites, and then modified on a glassy carbon electrode (GCE), resulting in a novel electrochemical sensor (Fe₃O₄-NH₂-GN/GCE). The applied Fe₃O₄-NH₂ nanoparticles and GN exhibited typical structures and intended surface groups through characterizations via transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray powder diffraction (XRD), vibrating sample magnetometer (VSM), and Raman spectroscopy. The Fe₃O₄-NH₂-GN/GCE showed the maximum electrochemical signal for CBD during the comparison of fabricated components via the cyclic voltammetry method, and was systematically investigated in the composition and treatment of components, pH, scan rate, and quantitative analysis ability. Under optimal conditions, the Fe₃O₄-NH₂-GN/GCE exhibited a good detection limit (0.04 μmol L⁻¹) with a linear range of 0.1 μmol L⁻¹ to 100 μmol L⁻¹ (r² = 0.984). In the detection of CBD in the extract of C. sativa leaves, the results of the electrochemical method using the Fe₃O₄-NH₂-GN/GCE were in good agreement with those of the HPLC method. Based on these findings, the proposed sensor could be further developed for the portable and rapid detection of natural active compounds in the food, agricultural, and pharmaceutical fields.

Single-Run Separation and Quantification of 14 Cannabinoids Using Capillary Electrophoresis

Quantification of major cannabinoids in cannabis products is normally performed using high-pressure liquid chromatography (HPLC)-based methods. We propose a cost-effective alternative method that successfully separates and quantifies 14 cannabinoids in a single run using capillary electrophoresis (CE) coupled with a UV detector in 18 min. The separation is carried out in 60% acetonitrile in the presence of 6.5 mM sodium hydroxide and 25 µM β-cyclodextrin, resulting in good separation of cannabinoids. Our CE method demonstrated the limit of detection between 1.2–1.8 µg/mL, with the linear range reaching up to 50 µg/mL. We validated the method performance by testing a plant extract and quantifying cannabinoid content. This method is the first to separate 14 cannabinoids in one run using a CE system with UV detection.

Emerging challenges in the extraction, analysis and bioanalysis of cannabidiol and related compounds

Cannabidiol (CBD) is a bioactive terpenophenolic compound isolated from Cannabis sativa L. It is known to possess several properties of pharmaceutical interest, such as antioxidant, anti-inflammatory, anti-microbial, neuroprotective and anti-convulsant, being it active as a multi-target compound. From a therapeutic point of view, CBD is most commonly used for seizure disorder in children. CBD is present in both medical and fiber-type C. sativa plants, but, unlike Δ⁹-tetrahydrocannabinol (THC), it is a non-psychoactive compound. Non-psychoactive or fiber-type C. sativa (also known as hemp) differs from the medical one, since it contains only low levels of THC and high levels of CBD and related non-psychoactive cannabinoids. In addition to medical Cannabis, which is used for many different therapeutic purposes, a great expansion of the market of hemp plant material and related products has been observed in recent years, due to its usage in many fields, including food, cosmetics and electronic cigarettes liquids (commonly known as e-liquids). In this view, this work is focused on recent advances on sample preparation strategies and analytical methods for the chemical analysis of CBD and related compounds in both C. sativa plant material, its derived products and biological samples. Since sample preparation is considered to be a crucial step in the development of reliable analytical methods for the determination of natural compounds in complex matrices, different extraction methods are discussed. As regards the analysis of CBD and related compounds, the application of both separation and non-separation methods is discussed in detail. The advantages, disadvantages and applicability of the different methodologies currently available are evaluated. The scientific interest in the development of portable devices for the reliable analysis of CBD in vegetable and biological samples is also highlighted.

Electrochemical Sensing of Cannabinoids in Biofluids: A Noninvasive Tool for Drug Detection

Cannabinoid sensing in biofluids provides great insight into the effects of medicinal cannabis on the body. The prevalence of cannabis for pain management and illicit drug use necessitates knowledge translation in cannabinoids. In this Review, we provide an overview of the current detection methods of cannabinoids in bodily fluids emphasizing electrochemical sensing. First, we introduce cannabinoids and discuss the structure and metabolism of Δ⁹-THC and its metabolites in relation to blood, urine, saliva, sweat, and breath. Next, we briefly discuss lab based techniques for cannabinoids in biofluids. While these techniques are highly sensitive and specific, roadside safety requires a quick, portable, and cost-effective sensing method. These needs motivated a comprehensive review of advantages, disadvantages, and future directions for electrochemical sensing of cannabinoids. The literature shows the lowest limit of detection to be 3.3 pg of Δ⁹-THC/mL using electrochemical immunosensors, while electrodes fabricated with low cost methods such as screen-printing and carbon paste can detect as little as 25 and 1.26 ng of Δ⁹-THC/mL, respectively. Future research will include nanomaterial modified working electrodes, for simultaneous sensing of multiple cannabinoids. Additionally, there should be an emphasis on selectivity for cannabinoids in the presence of interfering compounds. Sensors should be fully integrated on biocompatible substrates with control electronics and intelligent components for wearable diagnostics. We hope this Review will prove to be the seminal work in the electrochemical sensing of cannabinoids.

Absorptive stripping voltammetry for cannabis detection

BACKGROUND

Given that Δ(9)-tetrahydrocannabinol, the active constituent of cannabis, has been shown to greatly reduce driving ability, thus being linked to many drug driving accidents, its reliable detection is of great importance.

RESULTS

An optimised carbon paste electrode, fabricated from graphite powder and mineral oil, is utilised for the sensitive detection of Δ(9)-tetrahydrocannabinol (THC) in both aqueous solutions of pH 10.0 and in synthetic saliva solutions. "Absorptive Stripping Voltammetry" is exploited to that effect and the paste is used to pre-concentrate the carbon paste electrode with the target molecule. Practical limits of detection of 0.50 μM and 0.10 μM are determined for THC in stationary and stirred aqueous borate buffer solutions, respectively. Theoretical limits of detection are also calculated; values of 0.48 nM and 0.41 nM are determined for stationary and stirred THC aqueous borate buffer solutions, respectively. THC concentrations as low as 0.50 μM are detected in synthetic saliva solutions. The sensitivity of the sensor was 0.12 μA μM(-1), 0.84 μA μM(-1) and 0.067 μA μM(-1) for the stationary buffer, the stirred buffer and the saliva matrix, respectively.

CONCLUSIONS

"Absorptive Stripping Voltammetry" can be reliably applied to the detection of Δ(9)-tetrahydrocannabinol, after suitable optimisation of the assay. Usefully low practical limits of detection can be achieved.

Detecting cannabis use on the human skin surface via an electronic nose system

The most commonly used drug testing methods are based on the analysis of hair and urine using gas chromatography-mass spectrometry, liquid chromatography-mass spectrometry or immunoassay screening. These methods are time-consuming and partly expensive. One alternative method could be the application of an “electronic nose” (eNose). We have developed an eNose to detect directly on the human skin surface metabolic changes in the human body odor caused by cannabis consumption. Twenty cannabis-smoking and 20 tobacco-smoking volunteers were enrolled in this study. For the sensor signal data processing, two different methods were applied: Principle component analysis (PCA) with discriminant analysis, and the method of pattern recognition with subsequent support vector machines (SVM) processing. The PCA analysis achieved a correct classification of 70%, whereas the SVM obtained an accuracy of 92.5% (sensitivity 95%, specificity 90%) between cannabis-consuming volunteers and tobacco-smoking subjects. This study shows evidence that a low-cost, portable and fast-working eNose system could be useful for health protection, security agencies and for forensic investigations. The ability to analyze human body odor with an eNose opens up a wide field for diagnosing other drugs and also various diseases.

Nonaqueous capillary electrophoresis in pharmaceutical analysis

This review presents different solvents and electrolytes commonly used as BGEs in NACE for the analysis of pharmaceutical compounds. Most NACE applications carried out since 1998 for the analysis of compounds of pharmaceutical interest are presented in four tables: (i) analysis of drugs and related substances, (ii) analysis of chiral substances, (iii) analysis of phytochemical extracts and (iv) analysis of drugs in biological fluids. These selected examples are used to illustrate the interest in NACE versus conventional aqueous CE.

Determination of enkephalin peptides by nonaqueous capillary electrophoresis with electrochemical detection

Nonaqueous capillary electrophoresis with electrochemical detection (NACE-ED) was applied to the analysis of enkephalin peptides. The effect of different buffer compositions on the electrophoretic behavior of methionine enkephalin, leucine enkephalin, and [D-Ala2]-leucine enkephalin was studied. Separation of the protonated and the deprotonated peptides was obtained using ACN/methanol-based electrolyte systems. The electrochemical behavior of the enkephalins was studied by the capillary batch injection analysis technique. NACE-ED yielded well-defined signals in the oxidation mode only for the negatively charged analytes. The optimized BGE for the counterelectroosmotic separation consisted of 10 mM ammonium acetate in ACN/methanol (3:1 v/v). Using a platinum microdisk electrode set to an actual potential of +0.65 V detection limits in the submicromolar range were observed which are about one order of magnitude lower compared to UV detection. Problems concerning EOF instability and electrode fouling caused by water and other neutral sample impurities transported by the EOF can be avoided in the EOF-inverted mode using poly(ethylene glycol)-coated capillaries and an actual working electrode potential of +1.0 V. For the quantification of the enkephalins [D-Ala2]leucine enkephalin was used as internal standard. The practical utility for the determination of enkephalins in spiked plasma samples after SPE was demonstrated.

Pulsed amperometric detection with poly(dimethylsiloxane)-fabricated capillary electrophoresis microchips for the determination of EPA priority pollutants

A miniaturized analytical system for separation and detection of three EPA priority phenolic pollutants, based on a poly(dimethylsiloxane)-fabricated capillary electrophoresis microchip and pulsed amperometric detection is described. The approach offers a rapid (less than 2 min), simultaneous measurement of three phenolic pollutants: phenol, 4,6-dinitro-o-cresol and pentachlorophenol. The highly stable response (RSD = 6.1%) observed for repetitive injections (n > 100) reflects the effectiveness of Au working electrode cleaned by pulsed amperometric detection. The effect of solution conditions, separation potential and detection waveform were optimized for both the separation and detection of phenols. Under the optimum conditions (5.0 mM phosphate buffer pH = 12.4, detection potential: 0.7 V, separation potential: 1200 V, injection time: 10 s) the baseline separation of the three selected compounds was achieved. Limits of detection of 2.2 microM (2.8 fmol), 0.9 microM (1.1 fmol), and 1.3 microM (1.6 fmol) were achieved for phenol, 4,6-dinitro-o-cresol and pentachlorophenol, respectively. A local city water sample and two over-the-counter sore-throat medicines were analyzed in order to demonstrate the capabilities of the proposed technique to face real applications.

Nonaqueous capillary electrophoretic assays ofp-phenylene-bis-4,4'-(1-aryl-2,6-diphenylpyridinium) molecular wires

A nonaqueous CE system for separation and detection of novel electron-dopable molecular wires based on p-phenylene-bis-4,4'-(1-aryl-2,6-diphenylpyridinium) oligomers is described. The method is based on the coupling of CE separation in pure organic solvent, DMF with 50 mM acetic acid, and UV detection at 338 nm. The system offers a rapid measurement in less than 20 min for two priority nanowires and their impurities. Calibration data confirmed linear response for all compounds of interest in the concentration range 0.1-1.0 mg/mL. A highly stable response was observed for repetitive injections (RSD < or = 2.8%, n = 10).

Recent applications of capillary electrophoresis-electrospray ionisation-mass spectrometry in drug analysis

A critical review of applications for the period 2000-2004, taken from the Web of Knowledge database, of the technique capillary electrophoresis-electrospray ionisation-mass spectrometry (CE-ESI-MS) in drug analysis is presented. The review is concerned with molecules of mass less than 500 Da, chosen according to selected structural classes in which they give ESI signals primarily as [M+H](+) ions although other ions, such as [M-H](-), [M+Na](+), and [M+NH(4)](+), are also reported. These structural classes are drugs with amine-containing side chains, drugs with N-containing saturated ring structures, 1,4-benzodiazepines, other heterocyclic hypnotics, carbohydrates, sulphonylureas, anthracyclines, sulphonamides, penicillins, cephalosporins, tetracyclines, nitrocatechols, steroids, flavonoids/polyphenols, cannabinols, and miscellaneous molecules. Details are given on the fragmentations, where available, that these ionic species exhibit in-source and in ion-trap, triple quadrupole, and time of flight-mass spectrometers. The review gives a critical evaluation of these recent CE-ESI-MS analytical methods in drug analysis. Analytical information on, for example, sample concentration techniques, CE separation conditions, recoveries from biological media and limits of detection (LODs) are provided. Potential applications of CE-MS to particular drugs or drug classes are also briefly discussed in the text.

Indirect detection of substituted phenols and cannabis based on the electrochemical adaptation of the Gibbs reaction

The voltammetric behaviour of 2,6-dichloro-p-aminophenol (PAP) in aqueous solution at an edge plane pyrolytic graphite electrode was explored and its sensitivity to additions of substituted phenols examined. Proof of concept is shown for the electrochemical adaptation of the Gibbs reaction, where reaction of the oxidised form of PAP with substituted phenols provides an indirect methodology for the analytical detection of these compounds. This indirect protocol provides an attractive alterative to the direct electrochemical oxidation of phenolic compounds, since the latter is plagued by electrode passivation, leading to low sensitivity. It is observed that phenol, 4-phenoxyphenol, methylphenol (para and meta), nitrophenol and most importantly, tetrahydrocannabinol, can be detected voltammetrically. Such a protocol is particularly attractive for roadside testing for cannabis in drug drivers.

Amperometric and voltammetric detection for capillary electrophoresis

The focus of this article is amperometric and voltammetric detection coupled with capillary electrophoresis. Fundamental concepts and progress in the field of capillary electrophoresis with electrochemical detection (CEEC) that have occurred within the past three years, including new methodologies and unique applications, are highlighted. This review contains 95 references.

A chip-based electrophoresis system with electrochemical detection and hydrodynamic injection

A simple capillary electrophoresis system in the planar format that uses a new, hydrodynamic injection principle is described. The system was realized with poly(dimethylsiloxane)-glass chips and microdisk electrodes for amperometric detection. Using a double-tee injector, no precise voltage control of the electrolyte reservoirs was needed, thus making the microchip CE system more user-friendly. The analytical characteristics of chip-based CE-EC were evaluated using ascorbic acid as the model analyte. The reproducibility of migration time and signal height was expressed by relative standard deviations of 1.2% and 5.1%, respectively (n = 5). The limit of detection for ascorbic acid was approximately 5 microM at a signal-to-noise ratio of 3. Practical application concerning the determination of physiologically relevant compounds such as noradrenaline and L-dopa are discussed.