Chemometric experimental design based optimization techniques in capillary electrophoresis: a critical review of modern applications

Introduction of an electrospun nanofibrous membrane incorporated by metal-organic framework-199 (MOF-199) with Lewis acid property for efficient extraction of sulfonamides in on-chip electromembrane extraction

In this study, a new supporting polymeric membrane having Lewis acid nature was introduced for immobilizing organic solvent in on-chip electromembrane extraction (on-chip EME). For this aim, a polymeric nanofibrous membrane incorporated by a copper based metal-organic framework (MOF-199), with coordinatively unsaturated metal sites and Lewis acid property, was prepared by electrospinning a mixture of polycaprolactone (PCL) and MOF-199. Based on the field emission scanning electron microscopy images, the obtained polymeric membrane consisted of intertwined nanofibers having empty space between the fibers which could provide a suitable place for immobilizing the organic solvent. To demonstrate remarkable extractability of the proposed membrane (PCL/MOF-199 nanofibers) via executing Lewis acid-base interactions, three sulfonamide drugs was selected as anionic polar analytes with Lewis base feature. The parameters affecting the extraction efficiency of the method were optimized through the experimental design method using the orthogonal and rotatable central composite design (CCD). Under optimum conditions, the extraction recoveries ranging from 35.5 to 71.2 %, the relative standard deviations (RSD%) less than 6.45 %, and the detection limits in the range of 0.2-0.5 μg L-1 were achieved. The comparison of the extraction efficiency of the on-chip EME method using the electrospun PCL/MOF-199 nanofibers and PCL nanofibers membranes indicated that the proposed membrane was more efficient for extraction of sulfonamides because of the significant Lewis acid-base interactions of sulfonamides with copper uncoordinated open sites in MOF-199. Finally, the performance of the proposed method for extraction and determination of sulfonamides in three real samples was assayed.

A chemometric experimental design with three-step stacking capillary electrophoresis for analysis of five tobacco-specific nitrosamines in cigarette products

Tobacco-specific nitrosamines (TSNAs) as carcinogens endanger our health and life from cigarette products. However, the safe range of TSNAs levels in commercial cigarette products has not yet been established. For the purpose of safety and supervision, a three-step stacking approach including field amplified sample injection (FASI), sweeping, and analyte focusing by micelle collapse (AFMC), was developed for the simultaneous determination of five TSNAs levels in cigarette products. This approach also involved aspects of chemometric experimental design, including fractional factorial design and central composite design. After the multilevel optimization of the experimental design, the five TSNAs were well separated. The LOD (S/N = 3) values of the N´-nitrosonornicotine (NNN), N´-nitrosoanatabine (NAT), N´-nitrosoanabasine (NAB), 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL), and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) in the FASI-sweeping-AFMC CE approach were 1.000 ng/mL, 0.500 ng/mL, 0.125 ng/mL, 1.000 ng/mL, and 0.500 ng/mL respectively. The results of relative standard deviation (RSD) and relative error (RE) were all less than 3.35%, demonstrating good precision and accuracy. Finally, this novel approach was further applied to monitor three commercial cigarette products, and a range of 250.1-336.6 ng/g for NNN, 481.6-526.7 ng/g for NAT, 82.2-247.6 ng/g for NAB, 167.7-473.7 ng/g for NNAL, and 39.4-246.7 ng/g for NNK could be observed among these. Based on these results, the novel CE stacking strategy was successfully applied for the analysis of five TSNAs levels in cigarette products and could serve as a tool for assays of quality control of nitrosamines.

Application of Experimental Design Methodologies in the Enantioseparation of Pharmaceuticals by Capillary Electrophoresis: A Review

Chirality is one of the major issues in pharmaceutical research and industry. Capillary electrophoresis (CE) is an interesting alternative to the more frequently used chromatographic techniques in the enantioseparation of pharmaceuticals, and is used for the determination of enantiomeric ratio, enantiomeric purity, and in pharmacokinetic studies. Traditionally, optimization of CE methods is performed using a univariate one factor at a time (OFAT) approach; however, this strategy does not allow for the evaluation of interactions between experimental factors, which may result in ineffective method development and optimization. In the last two decades, Design of Experiments (DoE) has been frequently employed to better understand the multidimensional effects and interactions of the input factors on the output responses of analytical CE methods. DoE can be divided into two types: screening and optimization designs. Furthermore, using Quality by Design (QbD) methodology to develop CE-based enantioselective techniques is becoming increasingly popular. The review presents the current use of DoE methodologies in CE-based enantioresolution method development and provides an overview of DoE applications in the optimization and validation of CE enantioselective procedures in the last 25 years. Moreover, a critical perspective on how different DoE strategies can aid in the optimization of enantioseparation procedures is presented.

Chemo-metric engineering designs for deciphering the biodegradation of polycyclic aromatic hydrocarbons

Polycyclic aromatic hydrocarbons (PAHs) are non-polar organic compounds that are omnipresent in the environment and released due to anthropogenic activities through emissions and discharges. PAHs, being xenobiotic and exerts health impacts, thus they attract serious concern by the environmentalists. The stringent regulations and the need of sustainable development urges the hunt for a technically feasible and cost-effective wastewater treatment. Although the conventional physico-chemical treatment are widely preferred, they cause secondary pollution problems and demand subsequent treatment options. This comprehensive review intends to address the (a) different PAHs and their associated toxicity, (b) the remedial strategies, particularly biodegradation. The biological wastewater treatment techniques that involve microbial systems are highly influenced by the different physio-chemical and environmental parameters. Therefore, suitable optimization techniques are prerequisite for effective functioning of the biological treatment that sustains judiciously and interpreted in a lesser time. Here we have aimed to discuss (a) different chemo-metric tools involved in the design of experiments (DoE), (b) design equations and models, (c) tools for evaluating the model's adequacy and (d) plots for graphically interpreting the chemo-metric designs. However, to best of our knowledge, this is a first review to discuss the PAHs biodegradation that are tailored by chemo-metric designs. The associated challenges, available opportunities and techno-economic aspects of PAHs degradation using chemo-metric engineering designs are explained. Additionally, the review highlights how well these DoE tools can be suited for the sustainable socio-industrial sectors. Concomitantly, the futuristic scope and prospects to undertake new areas of research exploration were emphasized to unravel the least explored chemo-metric designs.

Experimental Design Methodologies for the Optimization of Chiral Separations: An Overview

In this chapter, the application of design of experiments (DoE) for chiral separation optimization using supercritical fluid chromatography (SFC), liquid chromatography (LC), capillary electrophoresis (CE), and capillary electrochromatography (CEC) methods is reviewed. Both screening and optimization steps are covered, including a discussion of each aspect, such as factor-, level-, and response selection. Different designs are also presented, highlighting their applications.

Electrophoretic Separations on Parafilm-Paper-Based Analytical Devices

Microfluidic paper-based analytical devices (mPADs) have gained significant attention in recent years for applications ranging from clinical diagnostics to environmental testing. However, separation on mPADs remain challenging to implement, particularly in complex samples. This has revived interest in revisiting paper chromatography and paper electrophoresis in mPADs to address these needs. Here, laminated Parafilm-paper (l-paper) is applied to fabricate electrophoretic devices. This approach yields a free-standing channel, leading to improved peak resolution relative to previous electrophoretic separations in traditional wax-printed mPADs. Major factors influencing the separation, including Joule heating, electroosmotic flow, and electrophoretic mobility, were investigated. As a result of paper's high ratio of surface area (78%) to pore volume (22%) resulting in slow heat dissipation, a usable applied field strength range of 0 - 200 V cm^-1 was employed to avoid Joule heating. The electroosmotic flow of the system was found to be 2.5 × 10^-5 ± 7.7 × 10^-7 cm² V^-1s^-1 and the electrophoretic mobility of chlorophenol red was 1.2 × 10^-4 ± 7.7 × 10^-7 cm² V^-1s^-1. Basic separation protocols were optimized using colorimetric detection of chlorophenol red and indigo carmine dyes as representative molecules. Paper type, channel width, and applied potential were then used to optimize the separations. Addition of an injection port to the device improved resolution and reduced peak broadening. Finally, the separation of fluorescein isothiocyanate (FITC) and L-glutamic acid (Glu) labeled with FITC, was successfully carried out using the l-paper electrophoretic device. Imaging with a microscope was found to achieve reduced peak broadening and increased resolution relative to imaging with a mobile camera, due to elimination of background signal, achieving a 72 ± 4% conjugation of Glu and FITC.

Enantioselective analysis of fluoxetine in pharmaceutical formulations by capillary zone electrophoresis

Fluoxetine is an antidepressant, a selective serotonin reuptake inhibitor (SSRI) used primarily in the treatment of major depression, panic disorder and obsessive compulsive disorder. Chiral separation of racemic fluoxetine is necessary due to its enantioselective metabolism. In order to develop a suitable method for chiral separation of fluoxetine, cyclodextrin (CD) modified capillary electrophoresis (CE) was employed. A large number of native and derivatized, neutral and ionized CD derivatives were screened to find the optimal chiral selector. As a result of this process, heptakis(2,3,6-tri-O-methyl)-β-CD (TRIMEB) was selected for enantiomeric discrimination. A factorial analysis study was performed by orthogonal experimental design in which several factors are varied at the same time to optimize the separation method. The optimized method (50 mM phosphate buffer, pH = 5.0, 10 mM TRIMEB, 15 °C, + 20 kV, 50 mbar/1 s, detection at 230 nm) was successful for baseline separation of fluoxetine enantiomers within 5 min. Our method was validated according to ICH guidelines and proved to be sensitive, linear, accurate and precise for the chiral separation of fluoxetine.

Chiral Separation of Uncharged Pomalidomide Enantiomers Using Carboxymethyl-β-Cyclodextrin: A Validated Capillary Electrophoretic Method

The racemic mixture of pomalidomide (POM), a second-generation immunomodulatory uncharged drug, was separated into enantiomers by capillary zone electrophoresis for the first time. Seven different chargeable cyclodextrin (CD) derivatives were screened as complexing agents and chiral selectors, investigating the stability of the POM-CD inclusion complexes and their enantiodiscriminating capacities. Based on preliminary experiments, carboxymethyl-β-CD (CM-β-CD) was found to be the most effective chiral selector. Factors influencing enantioseparation were systematically optimized, using an orthogonal experimental design. Optimal parameters (background electrolyte [BGE]: 50 mM Tris-acetate buffer, pH 6.5, containing 15 mM CM-β-CD; capillary temperature: 20°C; voltage applied +15 kV) allowed baseline separation of POM enantiomers with a resolution as high as 4.87. The developed method was validated, in terms of sensitivity (limit of detection and limit of quantification), linearity, accuracy, repeatability, and intermediate precision.

Leuco-crystal-violet micelle gel dosimeters: II. Recipe optimization and testing

In this study, recipe optimization of Leuco Crystal Violet (LCV) micelle gels made with the surfactant Cetyl Trimethyl Ammonium Bromide (CTAB) and the chemical sensitizer 2,2,2-trichloroethanol (TCE) was aided by a two-level three-factor designed experiment. The optimized recipe contains 0.75 mM LCV, 17.0 mM CTAB, 120 mM TCE, 25.0 mM tri-chloro acetic acid (TCAA), 4 wt% gelatin and ~96 wt% water. Dose sensitivity of the optimized gel is 1.5 times higher than that of Jordan's standard LCV micelle gel. Spatial integrity of the 3D dose distribution information in 1L phantoms filled with this recipe is maintained for >120 d. Unfortunately, phantoms made using the optimized recipe showed dose-rate dependence (14% difference in optical attenuation at the peak dose using electron beam irradiations at 100 and 400 MU min(-1)). Further testing suggests that the surfactant CTAB is the cause of this dose rate behaviour.

A rapid method for total Β-escin analysis in dry, hydroalcoholic and hydroglycolic extracts of Aesculus hippocastanum L. by capillary zone electrophoresis

INTRODUCTION

Seeds of Aesculus hippocastanum L. are used in European phytotherapy to treat inflammatory and vascular problems, and also to help in the regulation of the microcirculation. Thus, the quality control of herbal medicines using this species is important.

OBJECTIVE

To develop and to optimise a capillary zone electrophoresis method to determine total β-escin in different extracts of A. hippocastanum L.

METHODS

The optimal condition found through chemometric approach was: 25 mmol/L of bicarbonate-carbonate buffer, pH 10.3; +20 kV of voltage; 20°C of cartridge temperature; direct ultraviolet detection at 226 nm; 13 mbar injection for 5 s and analysis time within 6 min.

RESULTS

Repeatability, coefficient of variation (CV; %) = 3.19, 3.07 and 1.89 (n = 12), and intermediate precision, CV (%) = 3.05, 3.53 and 2.99 (n = 24) for dry, hydroalcoholic and hydroglycolic extracts, respectively were achieved. The accuracy was evaluated through recovery tests in concentration levels of 100, 150 and 200 g/L, ranging from 98.17 to 104.68%. The proposed method exhibited linearity (r = 0.9983) in the concentration range from 101.4 to 907.2 g/L and limits of detection and quantification equal to 11.63 and 38.76 g/L respectively.

CONCLUSION

A fast and reliable methodology for determination of total β-escin was successfully validated and applied on extracts of A. hippocastanum L. demonstrating its usefulness to quality control of medicines containing this plant species.

Multivariate optimization of capillary electrophoresis methods: a critical review

In this article a review on the recent applications of multivariate techniques for optimization of electromigration methods, is presented. Papers published in the period from August 2007 to February 2013, have been taken into consideration. Upon a brief description of each of the involved CE operative modes, the characteristics of the chemometric strategies (type of design, factors and responses) applied to face a number of analytical challenges, are presented. Finally, a critical discussion, giving some practical advices and pointing out the most common issues involved in multivariate set-up of CE methods, is provided.

Differentiation of enantiomers by capillary electrophoresis

Capillary electrophoresis (CE) has matured to one of the major liquid phase enantiodifferentiation techniques since the first report in 1985. This can be primarily attributed to the flexibility as well as the various modes available including electrokinetic chromatography (EKC), micellar electrokinetic chromatography (MEKC), and microemulsion electrokinetic chromatography (MEEKC). In contrast to chromatographic techniques, the chiral selector is mobile in the background electrolyte. Furthermore, a large variety of chiral selectors are available that can be easily combined in the same separation system. In addition, the migration order of the enantiomers can be adjusted by a number of approaches. In CE enantiodifferentiations the separation principle is comparable to chromatography while the principle of the movement of the analytes in the capillary is based on electrophoretic phenomena. The present chapter will focus on mechanistic aspects of CE enantioseparations including enantiomer migration order and the current understanding of selector-selectand structures. Selected examples of the basic enantioseparation modes EKC, MEKC, and MEEKC will be discussed.

Optimisation of a capillary zone electrophoresis methodology for simultaneous analysis of organic aliphatic acids in extracts of Brachiaria brizantha

INTRODUCTION

Aluminum toxicity is commonly verified in acidic soils, and poses a severe limitation to plant growth and development. Therefore, Al complexation by the root system mucilage, Al complexation by organic compounds that are exuded by the roots and internal metabolic processes must be monitored by organic acids (OA), since they play a central role in these aluminum tolerance mechanisms.

OBJECTIVE

To optimise a capillary zone electrophoresis method able to perform simultaneous separation of acetic, citric, formic, lactic, malic, oxalic, pyruvic, succinic, tartaric and aspartic acid in plant extract solutions.

METHODOLOGY

Method optimisation was achieved by a chemometric approach through experimental designs. The optimal condition found was: 20 mmol/L phthalic acid buffer; 0.8 mmol/L cetyltrimethyl-ammonium bromide; pH 3.4 adjusted with tris(hydroxymethyl)aminomethane (around 16 mmol/L); -15 kV of voltage; 25 °C of cartridge temperature; indirect ultraviolet detection at 240 nm; and 25 mbar injection for 2 s, within an analysis time of 4 min.

RESULTS

As a repeatability test of the optimal condition, 30 replicates were carried out with the same working electrolyte, where the relative standard deviation of each peak ranged from 0.081 to 0.36% (for migration time) and from 2.4 to 4.6% (for peak area).

CONCLUSION

The methodology was successfully applied to simultaneously determine citric, malic and aspartic acid in roots and leaves extract solutions of Brachiaria brizantha, demonstrating its usefulness to study aluminum tolerance.

Optimization of micellar electrokinetic capillary chromatography method using central composite design for the analysis of components in Yangwei granule

Central composite design (CCD), together with multiple linear regression, was successfully used to optimize the electrophoretic buffer system of micellar electrokinetic capillary chromatography (MEKC) for the determination of albiflorin, paeoniflorin, liquiritin, and glycyrrhizic acid in the traditional Chinese medicine (TCM) prescription, Yangwei granule. Concentrations of sodium deoxycholate (SDC) and borate, and proportions of ammonia, acetonitrile, and methanol were optimized. The total resolutions of peaks between the analytes and their adjacent peaks in real samples were integrated into the evaluation index of separation efficiency. The optimum electrophoretic buffer contained 80 mmol/L SDC, 20 mmol/L borate, 5% (v/v) methanol, 0.5% (v/v) ammonia, and 5% (v/v) acetonitrile. The correlation coefficients (R(2)) between the peak areas and the corresponding concentrations of analytes were greater than 0.9956. The limits of detection (LODs) (S/N=3) of the analytes were 0.97-4.00 μg/ml. The results indicate the superiority of CCD in optimizing the separation conditions of complex samples such as TCM prescriptions.

CE and CEC of nucleosides and nucleotides in food materials

Dietary nucleosides and nucleotides play an important role in the maintenance of functions of bone marrow hematopoietic cells, intestinal mucosa, and brain. Therefore, analysis of those compounds in food is very important for improving and assuring food quality. This review summarized the application of CE and CEC in the analysis of nucleosides and nucleotides in food. The sample preparation and detection are also discussed.

Optimization of capillary electrophoresis conditions for a glucagon competitive immunoassay using response surface methodology

The capillary electrophoresis (CE) conditions for a competitive immunoassay of glucagon were optimized for highest sensitivity of the immunoassay and resolution of the electrophoretic peaks using a Box-Behnken design. Injection time, voltage ramp time, and separation voltage were varied between three levels and two responses, bound-to-free (B/F) ratio of the immunoassay peaks and resolution between the peaks, were measured. Analysis of variance was applied to fit a predictive model, and a desirability function was used to simultaneously optimize both responses. A 10-s injection, 1.6-min ramp time, and a 22-kV separation voltage were the conditions found when high B/F was given more emphasis than high resolution. To test the model, calibration curves of a glucagon immunoassay were measured at the optimum and least optimum CE conditions. Optimal conditions increased the sensitivity of the immunoassay by 388% compared to the least optimum conditions while maintaining adequate resolution.