Determination of histidine in human serum and urine by cation exchange chromatography coupled to selective on-line post column derivatization

A Copper-Incorporated meso-(N'-acetyl-hydrizide)-BODIPY as a "Off-On" Fluorescent Probe for Histidine

We present a highly sensitive and selective fluorescence "turn-on" sensor for l-histidine (His) detection in aqueous solutions utilizing a 1-Cu2+ complex. This sensing platform employs a fluorescence-based ligand displacement approach, featuring a meso-(N'-acetyl-hydrizide)-based BODIPY derivative (1) complexed with Cu2+. Initially highly fluorescent, compound 1 is selectively quenched by Cu2+ ions, forming the 1-Cu2+ complex. The high affinity between His and Cu2+ effectively displaces 1 from the complex, restoring fluorescence. The system exhibits rapid response (within 5 minutes), excellent sensitivity (detection limit of 78 nM), operational simplicity, and a large fluorescence "turn-on" signal. It demonstrates remarkable selectivity for His over other amino acids, with maleimide masking cysteine interference. Notably stable in complex biological matrices, the sensor has successfully quantified His in artificial urine samples. Its practical applicability extends to paper-based test strips, offering portability and potential for real-time His monitoring in clinical diagnostics and biological systems.

Selective colorimetric sensing of histidine in aqueous media via Ag nanotriangles in the presence of HgCl2

Silver nanotriangles (AgNTs) were successfully synthesized as a colorimetric probe for selective and sensitive histidine detection in aqueous media within a 15-100 µM range and a detection limit of 330 nM using UV-Vis spectroscopy. The interaction of HgCl2 with AgNTs would lead to the formation of disk-shaped Ag/Hg amalgam as observed from the transmission electron images and X-ray diffraction patterns. Histidine prevents these structural and morphological changes and accordingly, the detection approach was developed based on the correlation between the histidine concentration and the in-plane dipole plasmon resonance (DPR) intensity.

Analysis Profiling of 48 Endogenous Amino Acids and Related Compounds in Human Plasma Using Hydrophilic Interaction Liquid Chromatography-Tandem Mass Spectrometry

Analyzing and detecting endogenous amino acids in blood is of crucial importance for the diagnosis of medical conditions and scientific research. Considering the lack of UV chromophores in most of these analytes and the presence of several interfering substances in plasma, the quantification of quite a few amino acids and related compounds presents certain technical challenges. As a blank plasma matrix lacking these endogenous substances does not exist, the surrogate matrix method is used, as well as isotopic internal standards for calibration, to ensure the accuracy and reliability of the study. Method validation was conducted for 48 target analytes, giving the following results: linearity (R2 at least 0.99), limit of quantification (from 0.65 to 173.44 μM), precision (intra-day and inter-day RSD for LQC ranged from 3.2% to 14.2%, for MQC from 2.0% to 13.6%, and for HQC from 1.6% to 11.3%), accuracy, recovery, and stability of the method (all complied with the guidelines). To further investigate the applicability of this method to large-scale sample analysis, the method was successfully applied to the analysis of amino acids in plasma samples collected from 20 control individuals, demonstrating its wide application scope for clinical diagnosis and metabolic research.

Photoluminescence-Electrochemiluminescence Dual-Mode Sensor Arrays for Histidine and Its Metabolite Discrimination and Disease Identification

Histidine (His) and its metabolite analysis is significant due to their vital roles in the diagnosis of diseases. In practical applications, simple and effective detection and discrimination of these metabolic species are still a great challenge due to their highly similar structures. Herein, photoluminescence (PL)-electrochemiluminescence (ECL) dual-mode sensor arrays consisting of a series of sensing elements were proposed for simultaneous quantitation and accurate discrimination of His and its four key metabolites (including histamine, imidazole-4-acetic acid, N-acetylhistamine, and imidazole propionate). The sensing elements of these sensor arrays were constructed by employing two solvent iridium(III) complexes ([Ir(pbz)2(DMSO)Cl] and [Ir(ppy)2(DMSO)Cl], pbz = 3-(2-pyridyl)benzoic acid, ppy = 2-phenylpyridine) with excellent PL and ECL performances as cross-responsive sensing units. Based on diverse coordination abilities of the two complexes with the imidazole group of the five targets, PL and ECL responses of each sensing unit can be enhanced to various degrees, which generate unique fingerprint patterns for the corresponding targets. Through principal component analysis, the multifarious patterns (two-, three-, and four-element sensor arrays) can be transformed into simple visualization modes, from which His and its four key metabolites can be effectively discriminated against each other. Moreover, the quantitation of an individual metabolic species at different concentrations and the recognition of the mixtures with different ratios were also accurately achieved. Notably, His and its four key metabolites in urine can also be successfully discriminated by the as-fabricated sensor arrays, and the patients with kidney diseases can be identified clearly, providing a promising way for disease diagnosis.

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.

Smartphone-Based High-Throughput Fluorimetric Assay for Histidine Quantification in Human Urine Using 96-Well Plates

A high-throughput fluorimetric assay for histidine was developed, using a 96-well plates platform. The analyte reacts selectively with o-phthalaldehyde under mild alkaline conditions to form a stable derivative. Instrumental-free detection was carried out using a smartphone after illumination under UV light (365 nm). The method was proved to be linear up to 100 μM histidine, with an LLOQ (lower limit of quantification) of 10 μM. The assay was only prone to interference from glutathione and histamine that exist in the urine samples at levels that are orders of magnitude lower compared to histidine. Human urine samples were analyzed following minimum treatment and were found to contain histidine in the range of 280 to 1540 μM. The results were in good agreement with an HPLC corroborative method.

Development and evaluation of pulsed - Post column derivatization in liquid chromatography as a concept to minimize reagent consumption

In the current article, we propose an alternative approach to reduce the consumption of the reagents in liquid chromatography coupled to on-line post column derivatization. In our proposal post column reagents do not flow continuously but they are instead introduced as well-defined pulses (at microliter levels) that are merged on-line with the eluted analytes through precise tuning (Pulsed-Post Column Derivatization, Pulsed-PCD). The profiles of the pulses in terms of time and flow rate were investigated "visually" using caffeine as model compound (at 274 nm). The robustness of the procedure was evaluated by Monte Carlo simulations and was verified taking into account the precisions of typically used propulsion systems. As a proof of concept, we selected the determination of histidine in human urine after separation by cation exchange chromatography and Pulsed-PCD derivatization with o-phthalaldehyde. The consumption of the derivatizing reagent was downscaled to the microliter level per run, while the analytical results were within the expected ranges (110 - 1520 µmol L^-1) and with good agreement with the corroborative method based on classic HPLC-PCD.

Determination of Free Histidine in Complex Hair Care Products with Minimum Sample Preparation Using Cation-Exchange Chromatography and Post Column Derivatization

In this communication, we describe the first analytical method for the determination of free histidine in hair care products (shampoos and conditioners). Cation-exchange chromatography combined with postcolumn derivatization and fluorimetric detection enabled the accurate (recovery: 83.5-114.8%) and precise (2.4-5.6% RSD) determination of free histidine without matrix interferences at concentration levels down to 1.5 mg kg^-1. Real commercially available samples were found to contain the amino acid at levels ranging between 70 and 535 mg kg^-1.

Development of an equipment free paper based fluorimetric method for the selective determination of histidine in human urine samples

A direct fluorimetric method, employing μicro-analytical paper-based devices (μ-PADs) for the selective determination of histidine (HIS) is described. The suggested method exploits the fluorescence emission of histidine after its rapid reaction with o-phthalaldehyde (OPA) at a basic medium (pH = 10) on the surface of a paper device with the application of a UV lamp at 354 nm. The devices are inexpensive and are composed of chromatographic paper and wax barriers. The analytical protocol is easily applicable with minimal technical expertise and without the need of expensive experimental apparatus. The user has to add a test sample, illuminate the device with a UV lamp, and read the fluorescence of the sensing area using a simple imaging device such as a cell-phone camera. The method is free from common interferences likely to affect the measurement of histidine and is selective among all other amino acids. This analytical procedure was optimized and validated, paying special attention to its intended application. The detection limits are as low as 1.8 μM with very satisfactory precision ranging from 6.4% (intra-day) to 8.9% (inter-day). Random urine samples from adult volunteers (n = 5) were successfully analyzed and HIS content ranged between 260 and 1114 μmol L^-1 with percentage recoveries in the range of 78.2 and 124.6%.

HPLC method with post-column derivatization for the analysis of endogenous histidine in human saliva validated using the total-error concept

Histidine (His) is an essential amino acid that plays an important biological role and associated with various pathological conditions. A simple and reliable method for the determination of endogenous histidine in human saliva was optimized and validated. The analyte was separated from the saliva matrix by cation exchange chromatography and detected fluorimetrically (λ_ex/λ_em = 360/440 nm) after online, specific post-column derivatization (PCD) reaction with o-phthalaldehyde. The chemical and instrumental variables of the post-column reaction were optimized using Box-Behnken experimental design to achieve maximum sensitivity. Method validation was carried out employing the total-error concept. Histidine could be analyzed reliably in the range of 0.5-5.0 μΜ, with an LOD (S/N = 3) of 50 nM. Monte Carlo simulations and capability analysis were used to investigate the ruggedness of the PCD reaction. The sampling strategy, sample preparation and stability were also investigated. Seventeen saliva samples were successfully analyzed with histidine levels being in the range of 2.7-19.5 μΜ.