Derivatization procedures and their analytical performances for HPLC determination in bioanalysis

A Novel RP-UHPLC-MS/MS Approach for the Determination of Tryptophan Metabolites Derivatized with 2-Bromo-4'-Nitroacetophenone

Many biologically active metabolites of the essential amino acid L-tryptophan (Trp) are associated with different neurodegenerative diseases and neurological disorders. Precise and reliable methods for their determination are needed. Variability in their physicochemical properties makes the analytical process challenging. In this case, chemical modification of analyte derivatization could come into play. Here, we introduce a novel fast reversed-phase ultra-high-performance liquid chromatography (RP-UHPLC) coupled with tandem mass spectrometry (MS/MS) method for the determination of Trp and its ten metabolites in human plasma samples after derivatization with 2-bromo-4'-nitroacetophenone (BNAP). The derivatization procedure was optimized in terms of incubation time, temperature, concentration, and volume of the derivatization reagent. Method development comprises a choice of a suitable stationary phase, mobile phase composition, and gradient elution optimization. The developed method was validated according to the ICH guidelines. Results of all validation parameters were within the acceptance criteria of the guideline, i.e., intra- and inter-day precision (expressed as relative standard deviation; RSD) were in the range of 0.5-8.2% and 2.3-7.4%, accuracy was in the range of 93.3-109.7% and 94.7-110.1%, limits of detection (LODs) were in the range of 0.15-9.43 ng/mL, coefficients of determination (R2) were higher than 0.9906, and carryovers were, in all cases, less than 8.8%. The practicability of the method was evaluated using the blue applicability grade index (BAGI) with a score of 65. Finally, the developed method was used for the analysis of Alzheimer's disease and healthy control plasma to prove its applicability. Statistical analysis revealed significant changes in picolinic acid (PA), anthranilic acid (AA), 5 hydroxyindole-3-acetic acid (5-OH IAA), and quinolinic acid (QA) concentration levels. This could serve as the basis for future studies that will be conducted with a large cohort of patients.

Derivatization of carboxylic groups prior to their LC analysis - A review

Carboxylic acids (CAs) represent a large group of important molecules participating in various biologically significant processes. Analytical study of these compounds is typically performed by liquid chromatography (LC) combined with various types of detection. However, their analysis is often accompanied by a wide variety of problems depending on used separation system or detection method. The dominant ones are: i) poor chromatographic behavior of the CAs in reversed-phase LC; ii) absence of a chromophore (or fluorophore); iii) weak ionization in mass spectrometry (MS). To overcome these problems, targeted chemical modification, and derivatization, come into play. Therefore, derivatization still plays an important and, in many cases, irreplaceable role in sample preparation, and new derivatization methods of CAs are constantly being developed. The most commonly used type of reaction for CAs derivatization is amidation. In recent years, an increased interest in the isotopic labeling derivatization method has been observed. In this review, we comprehensively summarize the possibilities and actual trends in the derivatization of CAs that have been published over the past decade.

Quantifying acute changes in neurometabolism following blast-induced traumatic brain injury

Brain health is largely dependent on the metabolic regulation of amino acids. Brain injuries, diseases, and disorders can be detected through alterations in free amino acid (FAA) concentrations; and thus, mapping the changes has high diagnostic potential. Common methods focus on optimizing neurotransmitter quantification; however, recent focus has expanded to investigate the roles of molecular precursors in brain metabolism. An isocratic method using high performance liquid chromatography with electrochemical cell detection was developed to quantify a wide range of molecular precursors and neurotransmitters: alanine, arginine, aspartate, serine, taurine, threonine, tyrosine, glycine, glutamate, glutamine, and γ-Aminobutyric acid (GABA) following traumatic brain injury. First, baseline concentrations were determined in the serum, cerebrospinal fluid, hippocampus, cortex, and cerebellum of naïve male Sprague Dawley rats. A subsequent study was performed investigating acute changes in FAA concentrations following blast-induced traumatic brain injury (bTBI). Molecular precursor associated FAAs decreased in concentration at 4 h after injury in both the cortex and hippocampus while those serving as neurotransmitters remained unchanged. In particular, the influence of oxidative stress on the observed changes within alanine and arginine pathways following bTBI should be further investigated to elucidate the full therapeutic potential of these molecular precursors at acute time points.

Developments in on-line, post separation sample manipulation in the last 22 years: Pharmaceutical and biomedical applications

On-line post separation sample manipulation is a powerful approach increasing the sensitivity and selectivity in chemical analysis. Post separation sample manipulation includes the treatment of the analytes after their separation through a suitable separation technique, mainly liquid chromatography and capillary electrophoresis. Typically, post separation approaches include either the addition of a reagent/solvent to derivatize the analyte/enhance the sensitivity, pH change, or the conversion of the analyte through a photochemical/electrochemical system (reagent-free systems). This review focuses on the developed methods using post-column manipulation of sample with pharmaceuticals and biomedical applications, covering the period from 2000 to midle-2023. Chemistries combined with fluorescence, UV-vis and mass spectrometric detection are discussed employing both liquid chromatography and electrophoretic techniques for separation. Noteworthy instrumental modifications are also discussed.

How can I measure brain acetylcholine levels in vivo? Advantages and caveats of commonly used approaches

The neurotransmitter acetylcholine (ACh) plays a central role in the regulation of multiple cognitive and behavioral processes, including attention, learning, memory, motivation, anxiety, mood, appetite, and reward. As a result, understanding ACh dynamics in the brain is essential for elucidating the neural mechanisms underlying these processes. In vivo measurements of ACh in the brain have been challenging because of the low concentrations and rapid turnover of this neurotransmitter. Here, we review a number of techniques that have been developed to measure ACh levels in the brain in vivo. We follow this with a deeper focus on use of genetically encoded fluorescent sensors coupled with fiber photometry, an accessible technique that can be used to monitor neurotransmitter release with high temporal resolution and specificity. We conclude with a discussion of methods for analyzing fiber photometry data and their respective advantages and disadvantages. The development of genetically encoded fluorescent ACh sensors is revolutionizing the field of cholinergic signaling, allowing temporally precise measurement of ACh release in awake, behaving animals. Use of these sensors has already begun to contribute to a mechanistic understanding of cholinergic modulation of complex behaviors.

Advancements in Analyzing Tumor Metabolites through Chemical Derivatization-Based Chromatography

Understanding the metabolic abnormalities of tumors is crucial for early diagnosis, prognosis, and treatment. Accurate identification and quantification of metabolites in biological samples are essential to investigate the relationship between metabolite variations and tumor development. Common techniques like LC-MS and GC-MS face challenges in measuring aberrant metabolites in tumors due to their strong polarity, isomerism, or low ionization efficiency during MS detection. Chemical derivatization of metabolites offers an effective solution to overcome these challenges. This review focuses on the difficulties encountered in analyzing aberrant metabolites in tumors, the principles behind chemical derivatization methods, and the advancements in analyzing tumor metabolites using derivatization-based chromatography. It serves as a comprehensive reference for understanding the analysis and detection of tumor metabolites, particularly those that are highly polar and exhibit low ionization efficiency.

Simultaneous measurement of amino acid enantiomers in the serum of late-life depression patients using convenient LC–MS/MS method with Nα-(5-fluoro-2,4-dinitrophenyl)-l-leucinamide Derivatization

D-amino acids may be indicators of late-life depression but separation and quantification of enantiomers which differ only by optical rotation sign remain challenging due to their identical physical and chemical properties. A convenient LC-MS/MS method was developed for the simultaneous measurement of l- and d-amino acids based on the chiral derivatization reagent, N^α-(5-fluoro-2,4-dinitrophenyl)-L-leucinamide, and conventional octadecylsilane reversed-phase column. Methanol was used as the extraction solvent and a single-step derivatization reaction using volatile triethylamine eliminated the requirement for desalination prior to LC-MS/MS. Simultaneous separation and identification of 21 amino acids and the enantiomeric compositions of the 18 chiral proteogenic entities were achieved. Low limits of detection (0.03-4.0 nM), wide linear range (0.01-20 μM), good precision (RSDs < 10 %) and negligible matrix effects indicated the suitability of the method. Application of the method to the quantification of serum chiral amino acids in late-life depression patients (n = 40) and controls (n = 35) found a total of 17 L-amino acids, 14 D-amino acids, DL-asparagine, glycine and γ-aminobutyric acid. The statistical evaluation showed significant differences of glycine, L-threonine and D-methionine between late-life depression patients and controls, indicating that these are potential biomarkers of late-life depression.

Advances in solid-phase extraction techniques: Role of nanosorbents for the enrichment of antibiotics for analytical quantification

Antibiotics are life-saving medications for treating bacterial infections; however it has been discovered that resistance developed by bacteria against these incredible agents is the primary contributing factor to rising global mortality rates. The fundamental cause of the emergence of antibiotic resistance in bacteria is the presence of antibiotic residues in various environmental matrices. Although antibiotics are present in diluted form in environmental matrices like water, consistent exposure of bacteria to these minute levels is enough for the resistance to develop. So, identifying these tiny concentrations of numerous antibiotics in various and complicated matrices will be a crucial step in controlling their disposal in those matrices. Solid phase extraction, a popular and customizable extraction technology, was developed according to the aspirations of the researchers. It is a unique alternative technique that could be implemented either alone or in combination with other approaches at different stages because of the multitude of sorbent varieties and techniques. Initially, sorbents are utilized for extraction in their natural state. The basic sorbent has been modified over time with nanoparticles and multilayer sorbents, which have indeed helped to accomplish the desired extraction efficiencies. Among the current traditional extraction techniques such as liquid-liquid extraction, protein precipitation, and salting out techniques, solid-phase extractions (SPE) with nanosorbents are most productive because, they can be automated, selective, and can be integrated with other extraction techniques. This review aims to provide a broad overview of advancements and developments in sorbents with a specific emphasis on the applications of SPE techniques used for antibiotic detection and quantification in various matrices in the last two decades.

Thiol Quantification Using Colorimetric Thiol-Disulfide Exchange in Nonaqueous Solvents

A careful analysis of two (thiol-disulfide exchange) thiol quantification chromophores' behavior (Ellman's reagent and Aldrithiol-4) in nonaqueous solvents is presented. A wide range of kinetic profiles and response factors were measured to exhibit a large variance for nonaqueous systems. We report several robust benchtop and room-temperature methods using different organic solvents compared to aqueous conditions. Validation of analytical analyses in nonaqueous systems and quantification of the cysteine content of ovalbumin are also presented. This work serves as a treatise on the utilization of thiol-disulfide exchange chromophores under nonaqueous conditions for the quantification of thiols.

A regenerable electrochemical sensor for electro-inactive cyclovirobuxine D detection in biological samples

Based on the pK_a determination of cyclovirobuxine D (CVB-D) using the method of potentiometry, we predicted the ionization state of CVB-D at physiological pH. Thus, by taking advantage of the ionization state and consequent non-covalent interactions between protonated CVB-D and deprotonated polymerized bromothymol blue (poly-BTB) under physiological conditions, we developed a simple and reusable electrochemical sensor that contains a poly-BTB/SWNT-modified electrode for electro-inactive CVB-D detection in biological fluids using poly-BTB as both the recognition unit and the electrochemical probe. Upon being immersed in the solution of CVB-D, the poly BTB-based electrode shows a current decrease due to the interaction-driven binding of CVB-D on the electrode surface. The current decrease in the electrochemical sensor toward CVB-D concentration shows a linear relationship in the dynamic ranges of 0.01-1 μM and 1-50 μM with a detection limit of 1.65 nM based on 3σ. The sensor can be easily regenerated through the removal of the binding of CVB-D from the electrode surface by highly negatively charged heparin, and it presents high repeatability with an RSD of less than 4.0% for seven measurements. In animal experiments, the electrochemical sensor was selective and sensitive for CVB-D determination in plasma and liver homogenates. The electrochemical sensor is readily accessible, robust, and cost-effective and holds good promise for more applications in biological and clinical fields associated with CVB-D using less technically demanding and simple operating procedures.

Improved Ion Mobility Separation and Structural Characterization of Steroids using Derivatization Methods

Steroids are an important class of biomolecules studied for their role in metabolism, development, nutrition, and disease. Although highly sensitive GC- and LC-MS/MS-based methods have been developed for targeted quantitation of known steroid metabolites, emerging techniques including ion mobility (IM) have shown promise in improved analysis and capacity to better identify unknowns in complex biological samples. Herein, we couple LC-IM-MS/MS with structurally selective reactions targeting hydroxyl and carbonyl functional groups to improve IM resolution and structural elucidation. We demonstrate that 1,1-carbonyldiimidazole derivatization of hydroxyl stereoisomer pairs such as testosterone/epitestosterone and androsterone/epiandrosterone results in increased IM resolution with ΔCCS > 15%. Additionally, performing this in parallel with derivatization of the carbonyl group by Girard's Reagent P resulted in unique products based on relative differences in number of each functional group and C17 alkylation. These changes could be easily deciphered using the combination of retention time, collision cross section, accurate mass, and MS/MS fragmentation pattern. Derivatization by Girard's Reagent P, which contains a fixed charge quaternary amine, also increased the ionization efficiency and could be explored for its potential benefit to sensitivity. Overall, the combination of these simple and easy derivatization reactions with LC-IM-MS/MS analysis provides a method for improved analysis of known target analytes while also yielding critical structural information that can be used for identification of potential unknowns.

Analytical derivatizations in environmental analysis

Analytical derivatization is a technique that alters the structure of an analyte and produces a product more suitable for analysis. While this process can be time-consuming and add reagents to the procedure, it can also facilitate the isolation of the analyte(s), enhance analytes' stability, improve separation and sensitivity, and reduce matrix interferences. Since derivatization is a functional group analysis, it improves selectivity by separating reactive from neutral compounds during sample preparation. This technique introduces detector-orientated tags into analytes that lack suitable physicochemical properties for detection at low concentrations. Notably, many regulatory bodies, especially those in the environmental field, require these characteristics in analytical methods. This review focuses on note-worthy analytical derivatization methods employed in environmental analyses with functional groups, phenol, carboxylic acid, aldehyde, ketone, and thiol in aqueous, soil, and atmospheric sample matrices. Both advantages and disadvantages of analytical derivatization techniques are discussed. In addition, we discuss the future directions of analytical derivatization methods in environmental analysis and the potential challenges.

Experimental design of a stable isotope labeling derivatized UHPLC-MS/MS method for the detection/quantification of primary/secondary bile acids in biofluids

An efficient analytical platform is required to characterize the human metabolome in pathology. For this purpose, ultra-high performance liquid chromatography with tandem mass spectrometry (UHPLC-MS/MS) combined with chemical derivatization stands out as one of the most powerful techniques. A targeted metabolomics platform for 11 bile acids (BAs) profiling in human serum and bile samples using a stable isotope labeling derivatization (SILD) was applied. For SILD, the design of experiments (DoE) was employed to optimize the reaction conditions such five factors in three levels. The sample preparation built upon a liquid-liquid extraction requiring small volumes (20 μL). In application, the relation between the BA and short-chain fatty acid levels in human serum and bile samples from patients with bile duct diseases were investigated. The proposed method offers significant utility in the large-scale biological analyses of hepato-biliary-pancreatic-related diseases.

Applied Analytical Methods for Detecting Heavy Metals in Medicinal Plants

For thousands of years, medicinal plants (MPs) have been one of the main sources of drugs worldwide. However, recently, heavy metal pollution has seriously affected the quality and safety of MPs. Consuming MPs polluted by heavy metals such as Pb, Hg, and Cu significantly threaten the health of consumers. To manage this situation, the levels of heavy metals in MPs must be controlled. In recent years, this field has attracted significant attention, but few researchers have systematically summarized various analytical methods. Therefore, it is necessary to investigate methods that can accurately and effectively detect the amount of heavy metals in MPs. Herein, some important analytical methods used to detect heavy metals in MPs and their applications have been introduced and summarized in detail. These include atomic absorption spectrometry, atomic fluorescence spectrometry, inductively coupled plasma mass spectrometry, inductively coupled plasma atomic emission spectrometry, X-ray fluorescence spectrometry, neutron activation analysis, and anodic stripping voltammetry. The characteristics of these methods were subsequently compared and analyzed. In addition, high-performance liquid chromatography, ultraviolet spectrophotometry, and disposable electrochemical sensors have also been used for heavy metal detection in MPs. To elucidate the systematic and comprehensive information, these methods have also been briefly introduced in this review.