Mahmoud H. El-Maghrabey

Micellar Liquid Chromatography from Green Analysis Perspective

Abstract Micellar liquid chromatography (MLC) is a simple well-established branch of high-performance liquid chromatography. The applications of MLC for the determination of numerous compounds in pharmaceutical formulations, biological samples, food, and environmental samples have been growing very rapidly. MLC technique has several advantages over other techniques, such as simultaneous separation of charged and uncharged solutes, rapid gradient capability, direct on-column injection of physiological fluids, unique separation selectivity, high reproducibility, robustness, enhanced luminescence detection, low cost, and safety. This review is devoted to the evaluation of the agreement of MLC with the principles of green chemistry which recently represents a universal trend. Also, it provides an overview on the basics of MLC, in addition to a survey of MLC methods published in the past five years for the assay of various compounds in different matrices. Graphical Abstract

Synchronous fluorescence spectrofluorimetric method for the simultaneous determination of metoprolol and felodipine in combined pharmaceutical preparation

A rapid, simple and sensitive synchronous specrtofluorimetric method has been developed for the simultaneous analysis of binary mixture of metoprolol (MTP) and felodipine (FDP). The method is based upon measurement of the synchronous fluorescence intensity of the two drugs at Δλ of 70 nm in aqueous solution. The different experimental parameters affecting the synchronous fluorescence intensities of the two drugs were carefully studied and optimized. The fluorescence intensity-concentration plots were rectilinear over the ranges of 0.5-10 μg/mL and 0.2-2 μg/mL for MTP and FDP, respectively. The limits of detection were 0.11 and 0.02 μg/mL and quantification limits were 0.32 and 0.06 μg/mL for MTP and FDP, respectively. The proposed method was successfully applied for the determination of the two compounds in their commercial tablets and the results obtained were favorably compared to those obtained with a comparison method.

9,10-Phenanthrenequinone as a mass-tagging reagent for ultra-sensitive liquid chromatography-tandem mass spectrometry assay of aliphatic aldehydes in human serum.

9,10-Phenanthrenequinone (PQ) was successfully used as a new mass-tagging reagent for sensitive labeling of aliphatic aldehydes (C3-C10) prior liquid chromatography-electrospray ionization-tandem mass spectrometry (LC/ESI-MS/MS). This reagent could overcome the drawbacks of previous amine or hydrazine-based reagents, such as lower sensitivity, formation of two stereoisomeric reaction products for each single analyte, need for longer derivatization time, and poor reactivity with aliphatic aldehydes. The PQ-aldehyde derivatives exhibited intense [M+H](+) and a common product ion with ESI in the positive-ion mode. The derivatives were monitored at the transition of [M+H](+)→m/z 231.9 with detection limits from 4.0 to 100 pM (signal to noise ratio=3). 3-Phenylpropanal was used as an internal standard (IS) and the separation of the eight aldehydes and IS was achieved in less than 10min employing gradient elution with methanol and ammonium formate buffer (20mM, pH 4.0). The method employed salting out liquid-liquid extraction for aliphatic aldehydes form serum for the first time with excellent recoveries (92.6-110.8%). The developed method was validated and applied for quantification of the target aldehydes in serum of healthy volunteers (n=14).

SIMULTANEOUS DETERMINATION OF METOCLOPRAMIDE HYDROCHLORIDE AND PYRIDOXINE HYDROCHLORIDE IN SYRUP USING HPLC METHOD WITH FLUORESCENCE DETECTION: APPLICATION TO HUMAN PLASMA

A simple, sensitive, and rapid HPLC method was developed and validated for the simultaneous determination of metoclopramide hydrochloride (MCA) and pyridoxine hydrochloride (PDX). The analysis was carried out on CLC Shim-pack C8 column (250 × 4.6 mm, 5 µm particle size) using a mobile phase consisting of methanol:0.02 M phosphate buffer mixture (45:55, v/v) of pH 3.0. The mobile phase was pumped at a flow rate of 1 mL/min with fluorescence detection at 308/374 nm. The method showed good linearity over the concentration ranges of 0.004–0.20 and 0.05–1.0 µg/mL for MCA and PDX, respectively, with limits of detection of 0.9 and 11.2 ng/mL. The proposed method was applied for the simultaneous determination of the two studied drugs in their combined syrup with average % recoveries of 100.31 ± 1.19 and 99.63 ± 1.27 for MCA and PDX, respectively. By virtue of its high sensitivity, the developed method was further applied to the determination of MCA in human plasma with mean % recovery of 101.00 ± 7.00.

Ultrasensitive determination of pyrroloquinoline quinone in human plasma by HPLC with chemiluminescence detection using the redox cycle of quinone

Graphical abstract Figure. No Caption available. HighlightsHPLC‐CL method was developed for PQQ analysis using the redox cycle of quinone.The method was ultrasensitive to PQQ with LOD of 1.08 nmol/L plasma (0.27 nM).A novel solid phase extraction (SPE) method was developed for PQQ from human plasma.The developed SPE method was simple, fast, and efficient (recovery >95%).The method was applied to monitor PQQ in human plasma after administration of PQQ. Abstract A fast, accurate, and ultrasensitive high‐performance liquid chromatography method with chemiluminescence detection (HPLC‐CL) was optimized and validated for the determination of pyrroloquinoline quinone (PQQ) concentration in human plasma following solid‐phase extraction (SPE). This method is based on the redox cycle of the reaction between PQQ and dithiothreitol, which generates reactive oxygen species that can be detected using luminol as a CL probe. The isocratic HPLC system comprised an ODS column and 4.0 mM tetra‐n‐butylammonium bromide in Tris‐HNO3 buffer (pH 8.8; 50 mM)‐acetonitrile (7:3, v/v) as mobile phase. A novel, rapid, and simple SPE method was also developed providing excellent %recovery (≥95.2%) for PQQ from human plasma samples. The proposed method was linear over the range of 4.0–400 nmol/L plasma of PQQ with a lower detection limit (S/N=3) of 1.08 nmol/L plasma (0.27 nM). The method was successfully implemented to determine PQQ concentration in the plasma of healthy individuals after administration of PQQ supplements.

A novel dual labeling approach enables converting fluorescence labeling reagents into fluorogenic ones via introduction of purification tags. Application to determination of glyoxylic acid in serum

Pre-column derivatization with fluorescence labeling reagents involves many problems including crowded chromatograms, possibility of the introduction of analytical errors, and poor selectivity. Herein we report a novel purification tag/fluorophore dual labeling approach based on a multi-component reaction to solve this major problem. Glyoxylic acid was recently identified as an early biomarker for diabetes, thus it was selected as a model analyte for our new dual labeling approach. Using the multi-component Petasis reaction, we could introduce a fluorophore (1-pyreneboronic acid, 1-PyBA) and a purification tag (taurine) to our target analyte (glyoxylic acid) in one step reaction. Using taurine as the amine reactant in Petasis reaction leads to the formation of a reaction product with a terminal sulfonic acid group which can be selectively retained on an anion exchange sorbent allowing excess fluorescent 1-PyBA reagent and its fluorescent decomposition products to be washed away. Then, quantification of the formed analyte-fluorophore-purification tag adduct was carried out by a simple isocratic HPLC-fluorescence detection method. The newly developed technique allowed highly selective, very rapid and efficient determination of glyoxylic acid in human serum eliminating endogenous components and excess reagent interference. Glyoxylic acid was determined in serum at a final concentration down to 30nM (600 fmol/injection) with good recovery (87.0%), accuracy (- 2.2 to 9.2) and precision (%RSD ≤ 8.7).

Aromatic aldehydes as selective fluorogenic derivatizing agents for α‐dicarbonyl compounds. Application to HPLC analysis of some advanced glycation end products and oxidative stress biomarkers in human serum

ABSTRACT &agr;‐Dicarbonyl compounds (&agr;‐DCs) are very clinically important as they are considered as advanced glycation end products (AGEs) precursors and biomarkers for many chronic diseases such as diabetes and vascular diseases, in addition to their major role in progression of complications of such diseases. Aromatic aldehydes and ammonium acetate were productively used as a one‐pot co‐reagents for fluorogenic derivatization of &agr;‐DCs yielding fluorescent imidazole derivatives. Among the tried aromatic aldehydes, 4‐carbomethoxybenzaldehyde yielded the products with best fluorescent characters. This approach for fluorogenic derivatization of &agr;‐DCs overcome the selectivity problem of the most commonly used derivatization reagent for &agr;‐DCs, &agr;‐diamino compounds, that can react unselectively with &agr;‐DCs and aldehydes. Separation of the formed imidazole derivatives of five &agr;‐DCs including glucosone, 3‐deoxyglucosone, glyoxal, methyl glyoxal and dimethyl glyoxal together with ethylmethylglyoxal as an internal standard was carried out on an octyl column using a mobile phase consisted of methanol‐water (15:85, v/v%) containing 0.2% formic acid with time programed flow, followed by fluorescence detection at excitation/emission wavelengths of 310/410nm. The method showed excellent sensitivity for the targeted &agr;‐DCs with limits of detections ranging from 0.4 to 5.0nM in human serum. Simple protein precipitation procedure was used for human serum treatment yielding very good recovery (91–105%) for the targeted &agr;‐DCs. The developed method was fully validated, then applied to the analysis of the five above mentioned clinically important &agr;‐DCs in serum samples of healthy, diabetic, rheumatic and cardiac disorders human volunteers. Due to the excellent analytical features of the developed method, including high selectivity and sensitivity, it was able to detect the pattern of the targeted &agr;‐DCs serum levels under the investigated different clinical conditions. HIGHLIGHTSA novel approach for fluorogenic derivatization of &agr;‐dicarbonyls was developed.Ammonium acetate and aromatic aldehydes are used as one‐pot fluorogenic co‐reagents.The method was selective for &agr;‐dicarbonyls even vs. &bgr;‐dicarbonyls and aldehydes.&agr;‐Dicarbonyls could be determined in human serums samples down to 0.4nM.The levels of &agr;‐dicarbonyls were measured at different clinical conditions.