On-line restricted access molecularly imprinted solid phase extraction of ivermectin in meat samples followed by HPLC-UV analysis

Magnetic solid-phase extraction based on restricted-access molecularly imprinted polymers for ultrarapid determination of ractopamine residues from food samples by capillary electrophoresis

An ultrafast, efficient, and eco-friendly method combining magnetic solid phase extraction and capillary electrophoresis with diode array detection have been developed to determine ractopamine residues in food samples. A restricted access material based on magnetic and mesoporous molecularly imprinted polymer has been properly synthesized and characterized, demonstrating excellent selectivity and high adsorbent capacity. Short-end injection capillary electrophoresis method was optimized: 75 mM triethylamine pH 7 as BGE, -20 kV, 50 mbar by hydrodynamic injection during 8 s, and capillary temperature at 25 °C; reaching ultrafast ractopamine analysis (∼0.6 min) with good peak asymmetry, and free from interfering and/or baseline noise. After sample preparation optimization, the conditions were: 1000 µL of sample at pH 6, 20 mg of adsorbent, stirring time of 120 s, 250 µL of ultrapure water as washing solvent, 1000 µL of methanol: acetic acid (7: 3, v/v) as eluent, and the adsorbent can be reused four times. In these conditions, the analytical method showed recoveries around to 100 %, linearity ranged from 9.74 to 974.0 µg kg-1, correlation coefficient (r) ≥ 0,99 in addition to adequate precision, accuracy, and robustness. After proper validation, the method was successfully applied in the analysis ractopamine residues in bovine milk and bovine and porcine muscle.

Plasmonically-enhanced competitive assay for ultrasensitive and multiplexed detection of small molecules

Novel methods that enable facile, ultrasensitive and multiplexed detection of low molecular weight organic compounds such as metabolites, drugs, additives, and organic pollutants are valuable in biomedical research, clinical diagnosis, food safety and environmental monitoring. Here, we demonstrate a simple, rapid, and ultrasensitive method for detection and quantification of small molecules by implementing a competitive immunoassay with an ultrabright fluorescent nanolabel, plasmonic fluor. Plasmonic-fluor is comprised of a polymer-coated gold nanorod and bovine serum albumin conjugated with molecular fluorophores and biotin. The synthesis steps and fluorescence emission of plasmonic-fluor was characterized by UV-vis spectroscopy, transmission electron microscopy, and fluorescence microscopy. Plasmon-enhanced competitive assay can be completed within 20 min and exhibited more than 30-fold lower limit-of-detection for cortisol compared to conventional competitive ELISA. The plasmon-enhanced competitive immunoassay when implemented as partition-free digital assay enabled further improvement in sensitivity. Further, spatially multiplexed plasmon-enhanced competitive assay enabled the simultaneous detection of two analytes (cortisol and fluorescein). This simple, rapid, and ultrasensitive method can be broadly employed for multiplexed detection of various small molecules in research, in-field and clinical settings.

Preparation of monodisperse, restricted-access, media-molecularly imprinted polymers using bi-functional monomers for solid-phase extraction of sarafloxacin from complex samples

Monodisperse restricted-access media bi-functional monomers with molecularly imprinted polymers (RAM-MIPs) were constructed using surface-initiated atom transfer radical polymerization. They were used as solid-phase extraction (SPE) adsorbents to enrich sarafloxacin (SAR) residues from egg samples, and influences on their performance were investigated. Optimum synthesis of RAM-MIPs was achieved by combining a bi-functional monomer (4-vinylpyridine-co-methacrylic acid, 1:3) with an 8:1:32:8 ratio of a template molecule, cross-linker, and restricted-access functional monomer. The SAR imprinting factor of RAM-MIPs was 6.05 and the selectivity coefficient between SAR and other fluoroquinolones was 1.86-2.64. Compared with traditional MIPs, the RAM-MIPs showed better SAR enrichment and selectivity during extraction of a complex protein-containing solution. Empty SPE cartridges were filled with RAM-MIP microspheres as SPE adsorbents. The limit of quantitation for SAR was 4.23 ng g^-1 (signal-to-noise ratio = 10) and the mean SAR recovery from spiked egg samples was 94.0-101.3%. Intra-day and inter-day relative standard deviations were 1.1-9% and 1.5-3.3%, respectively.

New and sensitive HPLC-UV method for concomitant quantification of a combination of antifilariasis drugs in rat plasma and organs after simultaneous oral administration

A combination treatment comprising ivermectin (IVM), albendazole (ABZ) and doxycycline (DOX) is often prescribed for lymphatic filariasis patients. Nevertheless, there has not been an analytical method established and documented to determine these compounds simultaneously. Herein, we report a new high-performance liquid chromatographic method coupled with a UV detector (HPLC-UV) to quantify these drugs in plasma and organs. This developed analytical method was validated according to the International Conference on Harmonization (ICH) and US Food and Drug Administration (FDA) guidelines. The validated method was successfully employed to analyze IVM, ABZ along with its metabolites (albendazole sulfoxide (ABZ-OX) and albendazole sulfone (ABZ-ON)), and DOX in the plasma and organs of Wistar rats after simultaneous oral administration. An Xselect CSH™ C₁₈ HPLC column was utilized as a stationary phase, with a mobile phase consisting of 0.1% v/v trifluoracetic acid in water and acetonitrile with a run time of 20 min. The calibration curves in biological samples were found to be linear across the concentration range of 0.01-5 μg mL^-1 for IVM, ABZ and ABZ metabolites, and 0.025-10 μg mL^-1 for DOX with an R value ≥0.998 in each case. The validated method was found to be selective, precise and accurate. Finally, the method developed in this study was deployed to assess the pharmacokinetic profiles and biodistribution of the combination of drugs after oral administration to Wistar rats. The validated HPLC-UV method in this study provides an extensive range of prospective applications for pharmacokinetic-based studies, therapeutic drug monitoring and toxicology.

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.

Toxicological analyses: analytical method validation for prevention or diagnosis

The need for reliable results in Toxicological Analysis is recognized and required worldwide. The analytical validation ensures that a method will provide trustworthy information about a particular sample when applied in accordance with a predefined protocol, being able to determine a specific analyte at a distinct concentration range for a well-defined purpose. The driving force for developing method validation for bioanalytical projects comes from the regulatory agencies. Thus, the approach of this work is to present theoretical and practical aspects of method validation based on the analysis objective, whether for prevention or diagnosis. Although various legislative bodies accept differing interpretations of requirements for validation, the process for applying validation criteria should be adaptable for each scientific intent or analytical purpose.

Targeted analysis of six emerging derivatives or metabolites together with 25 common macrolides in milk using Quick, Easy, Cheap, Effective, Rugged and Safe extraction and ultra-performance liquid chromatography quadrupole/electrostaticfield orbitrap mass spectrometry

An analytical method for the determination of six emerging derivatives or metabolites together with 25 common macrolides antibiotics in milk by ultra-performance liquid chromatography quadrupole/electrostaticfield orbitrap mass spectrometry was established. The samples were purified with optimized Quick, Easy, Cheap, Effective, Rugged, Safe methods. The amounts of primary-secondary amine, C18, and sodium acetate adsorbent materials were optimized by response surface method to obtain the best purification effect. The chromatographic separation was carried out using the XBridge-C18 (2.1 × 100 mm, 3.5 µm, Waters) column with mobile phase of acetonitrile with 0.1% v/v formic acid-water solutions (containing 10 mmol/L ammonium acetate), separated by gradient elution. The instrument was operated in the detection mode of electrospray positive and negative ions with Full MS/data dependent MS² acquisition mode detection, external standard method was used for quantitative analysis. The limits of detection and limits of quantitation of 31 compounds were 0.1-0.5 µg/L and 0.5-2.0 µg/L, respectively. A total of 31 compounds performed a good linearity in the range of 1 to 200 µg/L, and the correlation coefficient was greater than 0.990. The spiked recoveries in milk samples were 81.07-110.1% and the relative standard deviation was less than 5.1%. The method was successful applied to actual sample testing in the market.

Preconcentration and post-column fluorescent derivatization for the environmental water monitoring of an antihelmintic macrocyclic drug used in livestock

In this paper, a green analytical methodology based on fluorescence derivatization is proposed for the anti-helminthic drug monitoring ivermectin as environmental emergent contaminant. After sample clean-up, ivermectin was converted into a highly fluorescent derivative through a catalytic oxidation process followed by dehydration and tautomerization. Under optimal experimental conditions, a linear response was obtained for ivermectin within the range 0.38–600 μg L⁻¹, with detection and quantification limits of 0.11 and 0.38 μg L⁻¹, both values are lower than other previously reported. This method has been applied for ivermectin determination in environmental water samples at trace levels, showing its potential for contamination monitoring.

Evaluation of the tubing material and physical dimensions on the performance of extraction columns for on-line sample preparation-LC-MS/MS

Nowadays, high analytical throughputs are required considering an increasing demand for faster, simple and improved methods to analyze contaminants in a considerable number of samples. Generally, these compounds are present in complex matrices in contact with a high number of interferents becoming their determination difficult at low concentration. In this context, on-line extraction techniques arose to improve the extraction as well as separation power, while minimizing errors related to human sample manipulation. This paper describes a study regarding the development and optimization of columns used as an extraction device in multidimensional liquid chromatography. The main goals were the evaluation of the material used as column body as well as the investigation of the tube dimensions (internal diameter and length) in the extraction performance. Firstly, several tube materials were tested (steel, fused silica, PEEK, among others) being steel whose reported the best performance and was consequently chose for further studies. The investigation about the effects of the columns physical dimensions revealed a linear relationship between performance and the amount of sorbent utilized as extractive phase. However, when different columns with same amount of sorbent were tested results suggests that both i.d. and lengths play an important role in extraction efficiency. The longest columns with lower internal diameter showed the best results favoring the radial as well as axial analytes diffusion into the extraction column. After evaluation of these column variables, applications were carried out employing several different analytes belonging to various chemical classes and practical utilization, in order to reinforce the versatility as well as the robustness of this proposed study.

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.

Advancements of molecularly imprinted polymers in the food safety field

Molecularly imprinted technology (MIT) has been widely employed to produce stable, robust and cheap molecularly imprinted polymer (MIP) materials that possess selective binding sites for recognition of target analytes in food, such as pesticides, veterinary drugs, mycotoxins, illegal drugs and so on. Because of high selectivity and specificity, MIPs have drawn great attention in the food safety field. In this review, the recent developments of MIPs in various applications for food safety, including sample preparation, chromatographic separation, sensing, immunoassay etc., have been summarized. We particularly discuss the advancements and limitations in these applications, as well as attempts carried out for their improvement.

Packed in-tube solid phase microextraction with graphene oxide supported on aminopropyl silica: Determination of target triazines in water samples

On-line in-tube solid phase microextraction (in-tube SPME) coupled to high performance liquid chromatography and tandem mass spectrometry (HPLC-MS/MS) was successfully applied to the determination of selected triazines in water samples. The method based on the employment of a packed column containing graphene oxide (GO) supported on aminopropyl silica (Si) showed that the extraction phase has a high potential for triazines extraction aiming to its physical-chemical properties including ultrahigh specific surface area, good mechanical and thermal stability and high fracture strength. Injection volume and loading time were both investigated and optimized. The method validation using Si-GO to extract and concentrate the analytes showed satisfactory results, good sensitivity, good linearity (0.2-4.0 µg L^-1) and low detection limits (1.1-2.9 ng L^-1). The high extraction efficiency was determined with enrichment factors ranging from 1.2-2.9 for the lowest level, 1.3-4.9 intermediate level and 1.2-3.0 highest level (n = 3). Although the analytes were not detected in the real samples evaluated, the method has demonstrated to be efficient through its application in the analysis of spiked triazines in ground and mineral water samples.

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.

Newest applications of molecularly imprinted polymers for extraction of contaminants from environmental and food matrices: A review

This paper presents an overview of the recent applications of molecularly imprinted polymers (MIPs) to sample preparation. The review is thought to cover analytical procedures for extraction of contaminants (mainly illegal/noxious organic compounds) from food and environmental matrices, with a particular focus on the various pre-concentration/cleanup techniques, that is offline and online solid-phase extraction (SPE), dispersive SPE (d-SPE), magnetic SPE (MSPE), solid-phase microextraction (SPME) and stir-bar sorptive extraction (SBSE), applied before instrumental quantification. The selectivity and extraction efficiency of MIP-based sorbent phases are critically discussed, also in relation to the physical-chemical properties resulting from the synthetic procedures. A variety of molecularly imprinted sorbents is presented, including hybrid composites embedding carbon nanomaterials and ionic liquids. The analytical performance of MIP materials in sample preparation is commented as function of the complexity of the matrix, and it is compared to that exhibited by (commercial) aspecific and/or immunosorbent phases.