Innovative Solid-Phase Extraction Strategies for Improving the Advanced Chromatographic Determination of Drugs in Challenging Biological Samples

In the past few decades, considerable scientific strides have been made in the subject of drug analysis in human biological samples. However, the risk caused by incorrect drug plasma levels in patients still remains an important concern. This review paper attempts to investigate the advances made over the last ten years in common sample preparation techniques (SPT) for biological samples based on solid sorbents, including solid-phase extraction (SPE) and solid-phase micro-extraction (SPME), and in particular in the field of molecularly imprinted polymers (MIPs), including non-stimuli-responsive and stimuli-responsive adsorbents. This class of materials is known as 'smart adsorbents', exhibiting tailored responses to various stimuli such as magnetic fields, pH, temperature, and light. Details are provided on how these advanced SPT are changing the landscape of modern drug analysis in their coupling with liquid chromatography-mass spectrometry (LC-MS) analytical techniques, a general term that includes high-performance liquid chromatography (HPLC) and ultra-high performance liquid chromatography (UHPLC), as well as any variation of MS, such as tandem (MS/MS), multiple-stage (MSn), and high-resolution (HRMS) mass spectrometry. Some notes are also provided on coupling with less-performing techniques, such as high-performance liquid chromatography with ultraviolet (HPLC-UV) and diode array detection (HPLC-DAD) detection. Finally, we provide a general review of the difficulties and benefits of the proposed approaches and the future prospects of this research area.

One-step synthesis of well-defined molecularly imprinted nanospheres for the class-selective recognition and separation of β-blockers in human serum

β-blockers are a class of medications that are used to treat abnormal heart rhythms and hypertension. Molecularly imprinted polymers (MIPs) capable of selective recognizing and extracting β-blockers from complex biological samples hold great promise in bioanalytical and biomedical applications, but developing such artificial receptor materials is still challenging. Herein, we introduce a simple one-step method for the synthesis of well-defined molecularly imprinted nanospheres in high yield (83.6-94.4%) via reversible addition-fragmentation chain transfer (RAFT) precipitation polymerization for the selective recognition and extraction of the β-blockers from human serum. The prepared MIPs are characterized in terms of morphology, pore properties, binding kinetics, capacity, selectivity, and recognition mechanisms. The uniform nanoscale-imprinted layer favored the rapid mass transfer of β-blockers. The binding studies showed the high adsorption capacity (126.8 μmol/g) and selectivity of the developed nanomaterial. The investigation on the recognition mechanism reveals that multiple driving forces participate in the binding between MIP and β-blockers, where hydrogen bonding plays as the dominating role for the specific recognition. The MIP was successfully applied for the direct enrichment of five β-blockers from human serum with HPLC recoveries ranging from 82.9 to 100.3% and RSD of 0.5-6.9% (n = 3).

An Update on the Use of Molecularly Imprinted Polymers in Beta-Blocker Drug Analysis as a Selective Separation Method in Biological and Environmental Analysis

Beta-blockers are antihypertensive drugs and can be abused by athletes in some sport competitions; it is therefore necessary to monitor beta-blocker levels in biological samples. In addition, beta-blocker levels in environmental samples need to be monitored to determine whether there are contaminants from the activities of the pharmaceutical industry. Several extraction methods have been developed to separate beta-blocker drugs in a sample, one of which is molecularly imprinted polymer solid-phase extraction (MIP-SPE). MIPs have some advantages, including good selectivity, high affinity, ease of synthesis, and low cost. This review provides an overview of the polymerization methods for synthesizing MIPs of beta-blocker groups. The methods that are still widely used to synthesize MIPs for beta-blockers are the bulk polymerization method and the precipitation polymerization method. MIPs for beta-blockers still need further development, especially since many types of beta-blockers have not been used as templates in the MIP synthesis process and modification of the MIP sorbent is required, to obtain high throughput analysis.

Recent advances and applications of molecularly imprinted polymers in solid-phase extraction for real sample analysis

Sample pretreatment is essential for the analysis of complicated real samples due to their complex matrices and low analyte concentrations. Among all sample pretreatment methods, solid-phase extraction is arguably the most frequently used one. However, the majority of available solid-phase extraction adsorbents suffer from limited selectivity. Molecularly imprinted polymers are a type of tailor-made artificial antibodies and receptors with specific recognition sites for target molecules. Using molecularly imprinted polymers instead of conventional adsorbents can greatly improve the selectivity of solid-phase extraction, and therefore molecularly imprinted polymer-based solid-phase extraction has been widely applied to separation, clean up and/or preconcentration of target analytes in various kinds of real samples. In this article, after a brief introduction, the recent developments and applications of molecularly imprinted polymer-based solid-phase extraction for determination of different analytes in complicated real samples during the 2015-2020 are reviewed systematically, including the solid-phase extraction modes, molecularly imprinted adsorbent types and their preparations, and the practical applications of solid-phase extraction to various real samples (environmental, food, biological, and pharmaceutical samples). Finally, the challenges and opportunities of using molecularly imprinted polymer-based solid-phase extraction for real sample analysis are discussed.

Restricted Access Molecularly Imprinted Polymers

The use of conventional molecularly imprinted polymers (MIPs) for biological sample preparation is a difficult procedure due to the presence of high concentrations of proteins which can obstruct the selective binding sites, decrease the adsorption capacity, and compromise the analytical validation. In this way, modifications of conventional MIPs have been carried out in order to give them the ability to exclude macromolecules. Superficial coverings with hydrophilic groups and/or proteins have been the main procedures to obtain these restricted access molecularly imprinted polymers (RAMIPs ). These materials have been efficiently used for the selective extraction of small molecules from untreated complex matrices (e.g., blood, plasma, serum, and milk), without the need of a pre-deproteinization step. In this chapter, we describe a generic synthesis protocol to obtain RAMIPs as well as the assays to evaluate the protein exclusion efficiency and possible applications in offline and online procedures.

Application of molecularly imprinted polymers in the anti-doping field: sample purification and compound analysis

The problem posed by anti-doping requirements is one of the great analytical challenges; multiple compound detection at low ng ml-1 levels from complex samples, with requirements for exceptional confidence in results. This review surveys the design, synthesis and application of molecularly imprinted polymers (MIPs) in this field, focusing on the templating of androgenous anabolic steroids (AASs), as the most commonly abused substances, but also other WADA prohibited substances. Commentary on the application of these materials in detection, clean-up and sensing is offered, alongside views on the future of imprinting in this field.

A new restricted access molecularly imprinted fiber for direct solid phase microextraction of benzodiazepines from plasma samples

Restricted access molecularly imprinted polymers (RAMIPs) are hybrid materials that present selective binding sites for a template (or similar molecules), and an external hydrophilic layer that avoids the binding of proteins to the material, making them appropriate for the sample preparation of protein fluids.

Development of a multi-functional concurrent assay using weak cation-exchange solid-phase extraction (WCX-SPE) and reconstitution with a diluted sample aliquot for anti-doping analysis

RATIONALE

In addition to the development of adequate screening methods for multiple compounds, the World Anti-Doping Agency (WADA) requires anti-doping laboratories to analyze prohibited substances and their metabolites from various classes. This task presents a difficult challenge for all agencies and interests involved in the field of doping control.

METHODS

A screening method is reported in which hybrid sample preparation was performed using a combination of weak cation-exchange solid-phase extraction (WCX-SPE) and the 'Dilute and Shoot' strategy in order to take advantage of both the methodologies. Target substances were extracted using a WCX cartridge and reconstituted with a diluted sample aliquot that included 20% of an untreated urine sample. The target substances were further analyzed by high-performance liquid chromatography/triple quadrupole mass spectrometry (LC/MS).

RESULTS

The SPE procedure was optimized using a cartridge-washing step, elution conditions, and elution volume. The cartridge-washing step, which was performed using 10% methanol, improved the overall recovery of target substances. Since the recovery was observed to vary according to the pH of the eluting solution, we applied an elution step using both an acid and a basic organic solvent to achieve complementary recovery. Reconstitution of the diluted aliquot sample was performed to recover the polar substances.

CONCLUSIONS

The method was validated and applied to real samples in accordance with the external quality assessment scheme of WADA and to the previously reported samples that had provided positive test results. This novel method using hybrid sample preparation and LC/MS could be useful to screen multiple classes of the 264 targeted substances in anti-doping analysis.

Online extraction of antihypertensive drugs and their metabolites from untreated human serum samples using restricted access carbon nanotubes in a column switching liquid chromatography system

A novel analytical method was developed to determine 5 antihypertensive drugs of different pharmacological classes (angiotensin-converting enzyme inhibitors, calcium channel blockers, α-2 adrenergic receptor agonists, angiotensin II receptor blockers, and aldosterone receptor antagonists) and some of their metabolites in human serum. The untreated samples were directly analyzed in a column switching system using an extraction column packed with restricted access carbon nanotubes (RACNTs) in an ultra-high performance liquid chromatography coupled to a mass spectrometer (UHPLC-MS/MS). The RACNTs column was able to exclude approximately 100% of proteins from the samples in 2.0min, maintaining the same performance for about 300 analytical cycles. The method was validated in accordance with Food and Drug Administration (FDA) guidelines, being linear for all the determined analytes in their respective analytical ranges (coefficients of determination higher than 0.99) with limits of detection (LODs) and quantification (LOQs) ranging from 0.09 to 10.85μgL^-1 and from 0.30 to 36.17μgL^-1, respectively. High recovery values (88-112%) were obtained as well as suitable results for inter and intra-assay accuracy and precision. The method provided an analytical frequency of 5 samples per hour, including the sample preparation and separation/detection steps. The validated method was successfully used to analyze human serum samples of patients undergoing treatment with antihypertensive drugs, being useful for pharmacometabolomic, pharmacogenomic, and pharmacokinetic studies.

Spectrofluorimetric determination of atenolol from human urine using high-affinity molecularly imprinted solid-phase extraction sorbent

This study presents a novel, sensitive and selective molecularly imprinted solid-phase extraction (MISPE)-spectrofluorimetric method for the removal and determination of atenolol from human urine. Molecularly imprinted and non-imprinted polymers were synthesized thermally using a radical chain polymerization technique and used as solid-phase extraction sorbents. Acrylic acid ethylene glycol dimethacrylate, dibenzoyl peroxide and dichloroethane were used as a functional monomer, cross-linker, initiator and porogen, respectively. The calibration curve was in the range of 0.10-2.0 μg/ml for the developed method. Limit of detection and limit of quantification values were 0.032 and 0.099 μg/ml, respectively. Owing to the selectivity of the MISPE technique and the sensitivity of spectrofluorimetry, trace levels of atenolol have been successfully determined from both organic and aqueous media. Relatively high imprinting factor (4.18) and recovery results (74.5-75.3%) were obtained. In addition, intra- and interday precision values were 0.38-1.03% and 0.47-2.05%, respectively, proving the precision of the proposed method. Thus, a selective, sensitive and simple MISPE-spectrofluorimetric method has been developed and applied to the direct determination of atenolol from human urine.

Detection of Metoprolol in Human Biofluids and Pharmaceuticals via Ion-Transfer Voltammetry at the Nanoscopic Liquid/Liquid Interface Array

Metoprolol (MTP) is one of the most widely used antihypertensive drugs yet banned to use in sport competition. Therefore, there has been an increasing demand for developing simple, rapid, and sensitive methods suited to the identification and quantification of MTP in human biofluids. In this work, ultrathin silica nanochannel membrane (SNM) with perforated channels was employed to support nanoscale liquid/liquid interface (nano-ITIES) array for investigation of the ion-transfer voltammetric behavior of MTP and for its detection in multiple human biofluids and pharmaceutical formulation. Several potential interfering substances, including small molecules, d-glucose, urea, ascorbic acid, glycine, magnesium chloride, sodium sulfate and large molecules, bovine serum albumin (BSA), were chosen as models of biological interferences to examine their influence on the ion-transfer current signal of MTP. The results confirmed that the steady-state current wave barely changed in the presence of small molecules. Although BSA displayed an apparent blockade on the transfer of MTP, the accurate determination of MTP in multiple human biofluids (i.e., urine, serum and whole blood) and pharmaceutical formulation were still feasible, thanks to the molecular sieving and antifouling abilities of SNM. A limit of detection (LOD) within the physiological level of MTP during therapy could be achieved for all cases, i.e., 0.5 and 1.1 μM for 100 times diluted urine and serum, respectively, and 2.2 μM for 1000 times diluted blood samples. These results demonstrated that the nano-ITIES array behaved as a simplified and integrated detection platform for ionizable drug analysis in complex media.

Analysis of tricyclic antidepressants in human plasma using online-restricted access molecularly imprinted solid phase extraction followed by direct mass spectrometry identification/quantification

The use of a new class of hybrid materials, called restricted access molecularly imprinted polymers (RAMIPs) seems to present a good strategy for the sample preparation of complex matrices, since these materials combine good protein elimination capacity with high degree selectivity. Mass spectrometers (MS) have been successfully used for polar drug identification and quantification. In order to combine the advantages of both RAMIPs and mass spectrometry, we proposed a study that joins these properties in a single system, where we could analyse tricyclic antidepressants from human plasma, without offline extraction or chromatographic separation. A RAMIP for amitriptyline was synthesised by the bulk method, using methacrylic acid as a functional monomer and glycidilmethacrylate as a hydrophilic co-monomer. Then, epoxide ring openings were made and the polymer was covered with bovine serum albumin (BSA). A column filled with RAMIP-BSA was coupled to a MS/MS instrument in an online configuration, using water as loading and reconditioning mobile phase and a 0.01% acetic acid aqueous solution: acetonitrile at 30:70 as elution mobile phase. The system was used for on-line extraction and simultaneous quantification of nortriptyline, desipramine, amitriptyline, imipramine, clomipramine and clomipramine-d3 (IS) (from 15.0 to 500.0μgL^-1) from plasma samples. The correlation coefficient was higher than 0.99 for all analytes. The CV (coefficient of variation) values ranged from 1.34% to 19.13% for intra assay precision and 1.32-19.77% for inter assay precision. The E% (relative error) values ranged from -19.15% to 19.51% for intra assay accuracy and from -9.04% to 16.22% for inter assay accuracy.

Annual banned-substance review: analytical approaches in human sports drug testing

The aim of improving anti-doping efforts is predicated on several different pillars, including, amongst others, optimized analytical methods. These commonly result from exploiting most recent developments in analytical instrumentation as well as research data on elite athletes' physiology in general, and pharmacology, metabolism, elimination, and downstream effects of prohibited substances and methods of doping, in particular. The need for frequent and adequate adaptations of sports drug testing procedures has been incessant, largely due to the uninterrupted emergence of new chemical entities but also due to the apparent use of established or even obsolete drugs for reasons other than therapeutic means, such as assumed beneficial effects on endurance, strength, and regeneration capacities. Continuing the series of annual banned-substance reviews, literature concerning human sports drug testing published between October 2014 and September 2015 is summarized and reviewed in reference to the content of the 2015 Prohibited List as issued by the World Anti-Doping Agency (WADA), with particular emphasis on analytical approaches and their contribution to enhanced doping controls.

Recent advances in flow injection analysis

A dynamic development of methodologies of analytical flow injection measurements during four decades since their invention has reinforced the solid position of flow analysis in the arsenal of techniques and instrumentation of contemporary chemical analysis.

Cardiovascular drug determination in bioanalysis: an update

The great impact of cardiovascular diseases in human health has led to the development of a huge number of drugs and therapies to improve the treatment of these diseases. Cardiovascular drug analysis in biological fluids constitutes an important challenge for analytical scientists. There is a clear need for reliable methods to carry out both qualitative and quantitative analysis in a short time of analysis. Different problems such as drug monitoring, analysis of metabolites, study of drugs interactions, drugs residues or degradation products, chiral separation, and screening and confirmation of drugs of abuse in doping control must be solved. New trends in sample preparation, instrumental and column technology advances in LC and innovations in MS are described in this work.

Restricted access molecularly imprinted polymers obtained by bovine serum albumin and/or hydrophilic monomers’ external layers: a comparison related to physical and chemical properties

RAMIP-BSA is the best material for sample preparation in terms of selectivity, protein exclusion, and adsorption.