Twenty Years of Evaporative Light Scattering Detection

Lipid loss and compositional change during preparation of liposomes by common biophysical methods

Liposomes are widely used as model lipid membrane platforms in many fields, ranging from basic biophysical studies to drug delivery and biotechnology applications. Various methods exist to prepare liposomes, but common procedures include thin-film hydration followed by extrusion, freeze-thaw, and/or sonication. These procedures have the potential to produce liposomes at specific concentrations and membrane compositions, and researchers often assume that the concentration and composition of their liposomes are similar to, if not identical, to what would be expected if no lipid loss occurred during preparation. However, lipid loss and concomitant biasing of lipid composition can in principle occur at any preparation step due to nonideal mixing, lipid-surface interactions, etc. Here, we report a straightforward method using HPLC-ELSD to quantify the lipid concentration and membrane composition of liposomes, and apply that method to study the preparation of simple POPC/cholesterol liposomes. We examine many common steps in liposome formation, including vortexing during re-suspension, hydration of the lipid film, extrusion, freeze-thaw, sonication, and the percentage of cholesterol in the starting mixture. We found that the resuspension step can play an outsized role in determining the overall lipid loss (up to ~50% under seemingly rigorous procedures). The extrusion step yielded smaller lipid losses (~10-20%). Freeze-thaw and sonication could both be employed to improve lipid yields. Hydration times up to 60 minutes and increasing cholesterol concentrations up to 50 mole% had little influence on lipid recovery. Fortunately, even conditions with large lipid loss did not substantially influence the target membrane composition more than ~5% under the conditions we tested. From our results, we identify best practices for producing maximum levels of lipid recovery and minimal changes to lipid composition during liposome preparation protocols. We expect our results can be leveraged for improved preparation of model membranes by researchers in many fields.

Comprehensive mass spectrometric metabolomic profiling of a chemically diverse collection of plants of the Celastraceae family

Natural products exhibit interesting structural features and significant biological activities. The discovery of new bioactive molecules is a complex process that requires high-quality metabolite profiling data to properly target the isolation of compounds of interest and enable their complete structural characterization. The same metabolite profiling data can also be used to better understand chemotaxonomic links between species. This Data Descriptor details a dataset resulting from the untargeted liquid chromatography-mass spectrometry metabolite profiling of 76 natural extracts of the Celastraceae family. The spectral annotation results and related chemical and taxonomic metadata are shared, along with proposed examples of data reuse. This data can be further studied by researchers exploring the chemical diversity of natural products. This can serve as a reference sample set for deep metabolome investigation of this chemically rich plant family.

Application of the HPLC-ELSD technique for the determination of major metabolites of ibuprofen and creatinine in human urine

The report presents robust and high throughput methods, based on liquid chromatography coupled with evaporative light scattering detection (HPLC-ELSD), for the simultaneous determination of major metabolites of ibuprofen (IBU), namely 2-hydroxyibuprofen and carboxyibuprofen (method A) as well as creatinine (Crn) (method B) in human urine. The assays primarily involve straightforward sample purification. For both methods, the chromatographic separation of the analytes is achieved within 8 min at room temperature on Poroshell 120 SB-C18 (75 × 4.6 mm, 2.7 µm) column using gradient elution. The eluents consisted of 0.1% formic acid in water and acetonitrile (method A) or water and methanol (method B) delivered at a flow rate of 1 or 0.5 mL/min, respectively. In relation to metabolites of IBU, the assay linearity was observed within 0.06-0.5 g/L in urine, while the Crn assay linearity was demonstrated within 0.5-30 mmol/L in urine. The limit of quantification for IBU metabolites was determined to be 0.06 g/L, and 0.5 mmol/L for Crn. These methods were successfully applied to urine samples delivered by ten apparently healthy donors showing that the HPLC-ELSD assays are suitable for human urine screening.

Determination of End-Group Functionality of Propylene Oxide-Based Polyether Polyols Recovered from Polyurethane Foams by Chemical Recycling

Chemical recycling of polyurethane foams (PUFs) leads to partially aromatic, amino-functionalized polyol chains when the urethane groups in the PUF structure are incompletely degraded. Since the reactivity of amino and hydroxyl groups with isocyanate groups is significantly different, information on the type of the end-group functionality of recycled polyols is important to adjust the catalyst system accordingly to produce PUFs from recycled polyols of suitable quality. Therefore, we present here a liquid adsorption chromatography (LAC) method using a SHARC 1 column that separates polyol chains according to their end-group functionality based on their ability to form hydrogen bonds with the stationary phase. To correlate end-group functionality of recycled polyol with chain size, LAC was coupled with size-exclusion chromatography (SEC) to form a two-dimensional liquid chromatography system. For accurate identification of peaks in LAC chromatograms, the results were correlated with those obtained by characterization of recycled polyols using nuclear magnetic resonance, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, and SEC coupled with a multi-detection system. The developed method allows the quantification of fully hydroxyl-functionalized chains in recycled polyols using an evaporative light scattering detector and appropriate calibration curve.

In vitro anti-obesity activity by pancreatic lipase inhibition - Simple HPLC approach using EVOO as natural substrate

BACKGROUND

Pancreatic lipase (PL) is a key lipolytic enzyme in humans for the digestion and absorption of dietary fats. Thereby, PL is a well-recognized target in the management of obesity and its inhibition attracts the interest of researchers globally. The screening of new natural PL inhibitors as alternative strategy to the synthesis of chemical ones represents nowadays a hot topic in research. The main challenge in this matter is the lack of a universal analytical method allowing the monitoring of PL activity and the reliable quantification of lipid digestion products.

RESULTS

The (normal phase)-high-performance liquid chromatography-evaporative light scattering detector [(NP)-HPLC-ELSD] method proposed in this work represents a direct and rapid strategy to simultaneously quantify the products obtained from in vitro PL digestion. As one of the main novelties, the triacylglycerol (TAG) fraction from extra-virgin olive oil was selected as natural substrate. The PL activity was measured by monitoring the levels of remaining TAGs and formed free fatty acids (FFAs), using Orlistat as known inhibitor. The method validation confirmed the adequacy of the analytical method for quantitative purposes, showing high recovery percentage values (between 99% and 103%) and low relative standard deviation (RSD%) values (between 2% and 7%) for triolein and oleic acid standard solutions, as well as appreciably low limit of detection (LOD) and limit of quantification (LOQ) values (respectively 58 and 177 ng mL-1 for triolein; 198 and 602 ng mL-1 for oleic acid). Finally, the developed HPLC-ELSD method was successfully applied to evaluate the inhibitory effect of a polyphenolic extract obtained from apple pomace. The results showed a comparable inhibition degree between a 4.0 mg mL-1 apple pomace solution and a 1.0 μg mL-1 Orlistat solution.

CONCLUSION

The proposed innovative method reveals highly sensitive and simple to follow the fate of PL digestion, thus opening the way to further investigations in the research of new potentially anti-obesity compounds. © 2022 Society of Chemical Industry.

Choice of buffer in mobile phase can substantially alter peak areas in quantification of lipids by HPLC-ELSD

Evaporative light scattering detectors (ELSD) are commonly used with high-performance liquid chromatography (HPLC) to separate and quantify lipids, which are typically not easily detectable by more conventional methods such as UV-visible detectors. In many HPLC-ELSD methods to analyze lipids, a volatile buffer is included in the mobile phase to control the pH and facilitate separation between lipid species. Here, we report an unintended effect that buffer choice can have in HPLC-ELSD analysis of lipids - the identity and concentration of the buffer can substantially influence the resulting ELSD peak areas. To isolate this effect, we use a simple isocratic methanol mobile phase supplemented with different concentrations of commonly used buffers for ELSD analysis, and quantify the effect on peak width, peak shape, and peak area for seven different lipids (POPC, DOPE, cholesterol, sphingomyelin, DOTAP, DOPS, and lactose ceramide). We find that the ELSD peak areas for different lipids can change substantially depending on the mobile phase buffer composition, even in cases where the peak width and shape are unchanged. For a subset of analytes which are UV-active, we also demonstrate that the peak area quantified by UV remains unchanged under different buffer conditions, indicating that this effect is particular to ELSD quantification. We speculate that this ELSD-buffer effect may be the result of a variety of physical phenomenon, including: modification of aerosol droplet size, alteration of clustering of analytes during evaporation of the mobile phase, and mass-amplification or ion-pair effects, all of which could lead to differences in observed peak areas. Such effects would be expected to be molecule-specific, consistent with our data. We anticipate that this report will be useful for researchers designing and implementing HPLC-ELSD methods, especially of lipids.

The potency of HPLC-DAD and LC-MS/MS combined with ion chromatography for detection/purification of levulinic acid and bio-compounds from acid hydrolysis of OPEFB

This work reports a new strategy for the detection and purification of levulinic acid (LA) and bio-compounds from the acid hydrolysis and enzymatic treatment of oil palm empty fruit bunch (OPEFB) through high-performance liquid chromatography (HPLC) techniques combined with ion/ligand chromatography. The detections of LA, biomass-saccharides, hydroxymethylfurfural (HMF), and furfural were successfully elucidated by optimizing the multiple reaction monitoring mode (MRM) and liquid chromatography conditions using a Pb²⁺ ligand exchange column in the liquid chromatography with tandem mass spectrometry (LC-MS/MS) approach. High-performance liquid chromatography with diode-array detection (HPLC-DAD) combined with an H⁺ ion exchange column also showed potency for detecting chromophoric compounds such as LA, HMF, furfural, and acid (by-products) but not biomass-saccharides. Both techniques showed acceptable validation in terms of linearity, limit of detection (LOD), limit of quantitation (LOQ), accuracy, precision, and stability in both quantitative and qualitative analysis. However, the LC-MS/MS approach showed higher sensitivity for detecting LA and HMF compared with HPLC-DAD. Samples comprised of cellobiose, glucose, HMF, and LA from the acid hydrolysis of cellulose to LA with a mineral acid, and the biocatalysis of cellulase and β-glucosidase catalyzed cellulose (from OPEFB) to glucose were successfully monitored through the LC-MS/MS approach. In addition, using the optimal HPLC conditions obtained from LC-MS/MS, the purification of LA from other substances obtained from the hydrolysis reaction of cellulose (5 g) was successfully demonstrated by HPLC-DAD equipped with a fraction collector combined with an H⁺ ion exchange column at gram-scale of 1 g LA with a purification rate of 0.63 g ml⁻¹ min⁻¹.

The analytical approach for detection and purification levulinic acid from and bio-compound in hydrolysis biomass.

Simultaneous Quantification of Commonly Used Counter Ions in Peptides and Active Pharmaceutical Ingredients by Mixed Mode Chromatography and Evaporative Light Scattering Detection

In academia and industry, the analysis of counter ions in small molecules and synthetic peptides represents a great challenge. Due to the frequent use of salt forms and the application of a wider range of counter ions in pharmaceutically used substances, simple and generic methods for quantification are required. Especially, the analysis of trifluoracetic acid (TFA) in synthetic peptides is of high interest. Quantification of TFA is needed to assess the content and safety of synthetic peptides and for the interpretation of functional assay results, respectively. In here, a full quantitative mixed mode high performance liquid chromatography based method coupled to evaporative light scattering detection is presented. Finally, 14 positively and negatively charged counter ions were simultaneously quantified within 30 minutes. The method was validated in terms of specificity, accuracy, precision, limit of quantification, sample stability and carry over as proposed by the International Council of Harmonization. In order to prove the applicability of the procedure, small molecules reference substances and synthetic peptides were analyzed, respectively. The obtained results indicated a successful determination of counter ions in small molecules and differences to expected concentrations of prepared peptide solutions. Furthermore, an unexpectedly high content of sodium was observed for synthetic peptides.

Automated Programmable Generation of Broad pH Range Volatile Ionic Eluents for Liquid Chromatography

Many of the universal detectors in liquid chromatography, including mass spectrometry, must completely volatilize the chromatographic eluent first before further processing and detection of the analytes. A basic requirement is that the eluent does not contain a nonvolatile dissolved component. However, separation of biomolecules must be conducted in mostly aqueous media of compatible pH and ionic strength if their biological activity must survive the separation process. Combinations of ammonia with acetic and formic acids are commonly used as eluent for this purpose but generally maximum concentrations that can be tolerated are relatively low. Further, buffering is good only over a limited pH range. We describe a system where the eluent is generated in an automated pressure-programmed manner from high-purity gaseous NH₃ and CO₂ through gas-permeable membrane devices. This can be aided by the prior presence of formic/acetic acids in the mobile phase to extend the attainable low pH limit. We outline the fundamental pH, ionic strength, and buffer intensity considerations and demonstrate the application of such eluents in the separation of amino acids, proteins, and monoclonal antibodies. We also demonstrate the use of dissolved CO₂ as an ion-pairing agent in the separation of chiral amines.

Normal-Phase HPLC-ELSD to Compare Lipid Profiles of Different Wheat Flours

Normal-phase high-performance liquid chromatography (HPLC) is widely used in combination with evaporative light scattering detection (ELSD) for separating and detecting lipids in various food samples. ELSD responses of different lipids were evaluated to elucidate the possibilities and challenges associated with quantification by means of HPLC-ELSD. Not only the number and type of polar functional groups but also the chain length and degree of unsaturation of (free or esterified) fatty acids (FAs) had a significant effect on ELSD responses. Tripalmitin and trilinolein yielded notably different ELSD responses, even if their constituting free FAs produced identical responses. How FA structure impacts ELSD responses of free FAs is thus not predictive for those of triacylglycerols and presumably other lipids containing esterified FAs. Because ELSD responses of lipids depend on the identity of the (esterified) FA(s) which they contain, fully accurate lipid quantification with HPLC-ELSD is challenging and time-consuming. Nonetheless, HPLC-ELSD is a good and fast technique to semi-quantitatively compare the levels of different lipid classes between samples of comparable FA composition. In this way, lipid profiles of different flours from near-isogenic wheat lines could be compared.

Detection challenges in quantitative polymer analysis by liquid chromatography

Accurate quantification of polymer distributions is one of the main challenges in polymer analysis by liquid chromatography. The response of contemporary detectors is typically influenced by compositional features such as molecular weight, chain composition, end groups, and branching. This renders the accurate quantification of complex polymers of which there are no standards available, extremely challenging. Moreover, any (programmed) change in mobile-phase composition may further limit the applicability of detection techniques. Current methods often rely on refractive index detection, which is not accurate when dealing with complex samples as the refractive-index increment is often unknown. We review current and emerging detection methods in liquid chromatography with the aim of identifying detectors, which can be applied to the quantitative analysis of complex polymers.

Semiquantitation of Paralytic Shellfish Toxins by Hydrophilic Interaction Liquid Chromatography-Mass Spectrometry Using Relative Molar Response Factors

Paralytic shellfish toxins (PSTs) are a complex class of analogs of the potent neurotoxin saxitoxin (STX). Since calibration standards are not available for many PSTs, including C-11 hydroxyl analogs called M-toxins, accurate quantitation by liquid chromatography–mass spectrometry (LC-MS) can be challenging. In the absence of standards, PSTs are often semiquantitated using standards of a different analog (e.g., STX), an approach with a high degree of uncertainty due to the highly variable sensitivity between analytes in electrospray ionization. Here, relative molar response factors (RMRs) were investigated for a broad range of PSTs using common LC-MS approaches in order to improve the quantitation of PSTs for which standards are unavailable. First, several M-toxins (M1-M6, M9 and dcM6) were semipurified from shellfish using preparative gel filtration chromatography and quantitated using LC-charged aerosol detection (LC-CAD). The RMRs of PST certified reference materials (CRMs) and M-toxins were then determined using selective reaction monitoring LC-MS/MS and full scan LC-high-resolution MS (LC-HRMS) methods in positive and negative electrospray ionization. In general, RMRs for PSTs with similar chemical structures were comparable, but varied significantly between subclasses, with M-toxins showing the lowest sensitivity. For example, STX showed a greater than 50-fold higher RMR than M4 and M6 by LC-HRMS. The MS instrument, scan mode and polarity also had significant impacts on RMRs and should be carefully considered when semiquantitating PSTs by LC-MS. As a demonstration of their utility, the RMRs determined were applied to the semiquantitation of PSTs in contaminated mussels, showing good agreement with results from calibration with CRMs.

Improving chromatographic separation of polyolefins on porous graphitic carbon stationary phases: effects of adsorption promoting solvent and column length

The chromatographic separation of complex polyolefins on porous graphitic carbon stationary phases is strongly influenced by the composition of the mobile phase. Of particular interest is the effect of the chemical structure of the adsorption promoting solvent as this component of the mobile phase determines the adsorption–desorption behavior of the polyolefin molecules. In a systematic study, alkyl alcohols and linear alkanes are used as adsorption promoting solvents and the effect of the molecules' carbon chain length on chromatographic resolution is investigated. As representative examples, solvent gradient interaction chromatography experiments on polypropylene stereoisomers and ethylene-co-1-octene copolymers are presented. In a further study, the effect of increasing chromatographic column length on the solvent gradient separation of ethylene-co-1-octene copolymers is investigated. In summary, it is shown that the polypropylene stereoisomers are retained in 1-octanol as well as in n-decane and n-dodecane, allowing for identification of the individual stereoisomers in complex blends. For ethylene-co-1-octene copolymers it is shown that separation improves with increasing carbon chain length of the adsorption promoting solvent. Maximum resolution is obtained when a column length of 300 mm is used with 1-dodecanol as the adsorption promoting solvent.

The chromatographic separation of complex polyolefins on porous graphitic carbon stationary phases is strongly influenced by the composition of the mobile phase.

Method development in interaction polymer chromatography

Interaction polymer chromatography (IPC) is an umbrella term covering a large variety of primarily enthalpically-dominated macromolecular separation methods. These include temperature-gradient interaction chromatography, interactive gradient polymer elution chromatography (GPEC), barrier methods, etc. Also included are methods such as liquid chromatography at the critical conditions and GPEC in traditional precipitation-redissolution mode. IPC techniques are employed to determine the chemical composition distribution of copolymers, to separate multicomponent polymeric samples according to their chemical constituents, to determine the tacticity and end-group distribution of polymers, and to determine the chemical composition and molar mass distributions of select blocks in block copolymers. These are all properties which greatly affect the processing and end-use behavior of macromolecules. While extremely powerful, IPC methods are rarely employed outside academic and select industrial laboratories. This is generally because most published methods are "bespoke" ones, applicable only to the particular polymer being examined; as such, potential practitioners are faced with a lack of inductive information regarding how to develop IPC separations in non-empirical fashion. The aim of the present review is to distill from the literature and the author's experience the necessary fundamental macromolecular and chromatographic information so that those interested in doing so may develop IPC methods for their particular analytes of interest, regardless of what these analytes may be, with as little trial-and-error as possible. While much remains to be determined in this area, especially, for most techniques, as regards the role of temperature and how to fine-tune this critical parameter, and while a need for IPC columns designed specifically for large-molecule separations remains apparent, it is hoped that the present review will help place IPC methods in the hands of a more general, yet simultaneously more applied audience.

Current status and contemporary approaches to the discovery of antitumor agents from higher plants

Higher plant constituents have afforded clinically available anticancer drugs. These include both chemically unmodified small molecules and their synthetic derivatives currently used or those in clinical trials as antineoplastic agents, and an updated summary is provided. In addition, botanical dietary supplements, exemplified by mangosteen and noni constituents, are also covered as potential cancer chemotherapeutic agents. Approaches to metabolite purification, rapid dereplication, and biological evaluation including analytical hyphenated techniques, molecular networking, and advanced cellular and animal models are discussed. Further, enhanced and targeted drug delivery systems for phytochemicals, including micelles, nanoparticles and antibody drug conjugates (ADCs) are described herein.

Droplet probe: coupling chromatography to the in situ evaluation of the chemistry of nature

Covering: up to 2019The chemistry of nature can be beautiful, inspiring, beneficial and poisonous, depending on perspective. Since the isolation of the first secondary metabolites roughly two centuries ago, much of the chemical research on natural products has been both reductionist and static. Typically, compounds were isolated and characterized from the extract of an entire organism from a single time point. While there could be subtexts to that approach, the general premise has been to determine the chemistry with very little in the way of tools to differentiate spatial and/or temporal changes in secondary metabolite profiles. However, the past decade has seen exponential advances in our ability to observe, measure, and visualize the chemistry of nature in situ. Many of those techniques have been reviewed in this journal, and most are tapping into the power of mass spectrometry to analyze a plethora of sample types. In nearly all of the other techniques used to study chemistry in situ, the element of chromatography has been eliminated, instead using various ionization sources to coax ions of the secondary metabolites directly into the mass spectrometer as a mixture. Much of that science has been driven by the great advances in ambient ionization techniques used with a suite of mass spectrometry platforms, including the alphabet soup from DESI to LAESI to MALDI. This review discusses the one in situ analysis technique that incorporates chromatography, being the droplet-liquid microjunction-surface sampling probe, which is more easily termed "droplet probe". In addition to comparing and contrasting the droplet probe with other techniques, we provide perspective on why scientists, particularly those steeped in natural products chemistry training, may want to include chromatography in in situ analyses. Moreover, we provide justification for droplet sampling, especially for samples with delicate and/or non-uniform topographies. Furthermore, while the droplet probe has been used the most in the analysis of fungal cultures, we digest a variety of other applications, ranging from cyanobacteria, to plant parts, and even delicate documents, such as herbarium specimens.

Development and validation of a novel UPLC-ELSD method for the assessment of lipid composition of nanomedicine formulation

Lipid nanocarriers incorporating glycerides, polyethylene glycol (PEG)-stearates and phospholipids have attracted great attention for in vivo diagnostic, in vivo imaging, activated or non-activated targeted drug delivery. For quality control purposes, the development of appropriate methods for the quantification of their lipid components is needed. In the present study, we developed an analytical method for lipid quantification in formulated nanoparticles. PEG-stearates and glycerides were analyzed in a single run by RP-UPLC-ELSD using a two-step gradient elution program, while the analysis of phospholipids was accomplished by HILIC-UPLC-ELSD after isolation using an SPE silica column. Using both isolated compounds and commercial lipid standards, calibration curves were produced using second-order polynomials to attain the quantitative evaluation of each lipid excipient. Relative standard deviation of all analytes was between 0.9% and 5.3% for intra-day precision and recovery ranged from 83.5% to 112.2%. The presented method was successfully implemented to study the manufacturing process and stability of the formulated lipid excipients during long-term storage and accelerated conditions. The formulation lipid yield was determined and found equal to 82.5%.

Comparative Analysis of Protein Quantification Methods for the Rapid Determination of Protein Loading in Liposomal Formulations

Advances in manufacturing processes provide the ability for the high throughput production of liposomes containing a range of moieties, from small molecules to large biologicals (including proteins and nucleic acids for prophylactic and therapeutic applications). Whilst rapid quantification methods for small molecules are generally well established, the ability to rapidly quantify liposomal entrapment of proteins is limited. Indeed, most standard protein quantification techniques (including the BCA assay and Reverse phase-high performance liquid chromatography (RP-HPLC)) measure protein encapsulation indirectly, by measuring the amount of non-incorporated drug, and subtracting from the initial amount of protein added. However, this can give inaccurate and misrepresentative results. To address this, we have developed a range of methods to directly quantify protein entrapment within liposomes. The encapsulation efficiency within neutral, anionic and cationic liposome formulations was determined by three techniques; BCA assay, RP-HPLC and HPLC coupled to an evaporative light scattering detector, (HPLC-ELSD). All three methods are reliable for the quantification of protein, with linear responses and correlation coefficients of 0.99, and LOQ for all three methods being less than 10 µg/mL. Here within, we provide three methods for the rapid and robust quantification of protein loading within liposomal (and other bilayer) vesicle systems.

Multidimensional chromatographic analysis of carboxylic acid-functionalized polyethylene

Carboxy-functionalized polyethylene is comprehensively analysed using a multidimensional fractionation approach based on high-temperature HPLC, two-dimensional liquid chromatography and selective infrared detection.

Automated solubility and crystallization analysis of non-UV active compounds: integration of evaporative light scattering detection (ELSD) and robotic sampling

The integration of high-performance liquid chromatography-evaporative light scattering detection with robotic sampling allows for the acquisition of reliable and data-rich solubility and crystallization profiles of minimally- or non-UV active compounds in an automated manner.

Determination of residual poly diallyldimethylammonium chloride (pDADMAC) in monoclonal antibody formulations by size exclusion chromatography and evaporative light scattering detector

The cationic polyelectrolyte pDADMAC is widely used in biopharmaceutical industry as a flocculating agent to enhance clarification throughput and downstream filtration operations. Due to the possible toxicity, pDADMAC should be assessed for an acceptable residual level to ascertain the safety of the product to patients. The strong protein-polyelectrolyte interaction, however, can negatively affect sensitivity and accuracy of measurements. This paper reports on the application of size exclusion (SE) chromatography coupled to evaporative light scattering detector (ELSD) to the quantitative determination of pDADMAC in monoclonal antibody formulations and in process intermediates during downstream purification. The SE chromatography was performed under isocratic condition with a mobile phase consisting of 0.1% TFA in water (90%) and acetonitrile (10%) at a flow rate of 0.4 ml/min. A quantification limit (S/N = 10) of 0.85 ppm was achieved in sample matrix, which is sufficiently low for the trace analysis of this compound in protein-containing samples.

Comprehensive Analysis of Oxidized Waxes by Solvent and Thermal Gradient Interaction Chromatography and Two-Dimensional Liquid Chromatography

This report addresses the comprehensive analysis of oxidized/functionalized polyethylene waxes according to chemical composition and molar mass by selective chromatographic methods. For the first time, tailored high-temperature interaction chromatography in solvent gradient (HT-SGIC) and thermal gradient (HT-TGIC) modes are used for the chemical composition separation of these materials. Separation protocols are developed using three model wax samples with different degrees of oxidation. For the chromatographic separations polar silica gel is used as the stationary phase. Solvent gradients of decane and cyclohexanone are used in HT-SGIC at 110 °C to separate the bulk waxes into several heterogeneous fractions according to polarity and the type of functionality. Column temperature and gradient manipulation are shown to influence chromatographic resolution and retention. The HT-SGIC investigations are complemented by HT-TGIC separations where a solvent mixture of decane and cyclohexanone is used as the mobile phase in isocratic mode. It is shown that HT-SGIC and HT-TGIC provide different types of separation, however, both are predominantly based on differences in functionality. To provide comprehensive information on chemical composition (functionality) and molar mass, HT-SGIC and HT-TGIC are coupled to HT-SEC, using ortho-dichlorobenzene as the second dimension mobile phase. Clear differences between oxidized and nonoxidized waxes are detected in HT-2D-LC providing comprehensive information on the molecular heterogeneity of these materials.

A multidimensional fractionation protocol for the oligomer analysis of oxidized waxes

Oxidized waxes possess far superior properties as compared to the alkanes they are derived from. The separation of alkane oligomers via gas chromatography (GC) becomes a challenge when polar oxygen-containing functional groups are introduced or when higher molar masses are targeted. In the present study, the separation and analysis of oligomers in oxidized and non-oxidized waxes using different liquid chromatographic techniques are investigated. Oligomers in two oxidized waxes and a non-oxidized wax from which they are derived, are separated using high-temperature solvent gradient interaction chromatography (HT-SGIC) and high-temperature two-dimensional liquid chromatography (HT-2D-LC). Evaporative light scattering detector conditions are tailored to provide the best detection with the solvent system at use. It is shown that oligomers in oxidized and non-oxidized waxes can be separated and identified using the mentioned techniques. It has been found that the ELSD detector response systematically decreases as the oxidation levels of the waxes increase. Coupling of HT-HPLC and high-temperature size exclusion chromatography (HT-SEC) in a comprehensive 2D-LC setup shows a broadening of the molar mass distributions of the lower oligomer fractions as a consequence of the modification indicating changes in the oligomer chain microstructures. A preparative fractionation technique is utilized to collect specific oligomer fractions from the bulk waxes followed by hyphenation to HT-HPLC and other techniques. HPLC is shown to provide more detailed information on the oligomer composition of waxes when coupled to a pre-fractionation technique.

Determination of Propionylbrassinolide and Its Impurities by High-Performance Liquid Chromatography with Evaporative Light Scattering Detection

The discovery of brassinolide in 1979, a milestone in brassinosteroids research, has sparked great interest of brassinolide analogs (BLs) in agricultural applications. Among these BLs, propionylbrassinolide has captured considerable attention because it shows plant growth regulating activity with an excellent durability. Two impurities of propionylbrassinolide were isolated and purified by semi-preparative high-performance liquid chromatography (HPLC), and the chemical structures were confirmed. For simultaneous separation and determination of propionylbrassinolide and impurities, an efficient analytical method based on HPLC with evaporative light scattering detector (HPLC-ELSD) was developed. The optimized analysis was performed on a C18 reversed phase column (250 mm × 4.60 mm, 5 μm) with isocratic elution of acetonitrile and water (90:10, v/v) as the mobile phase. The drift tube temperature of the ELSD system was set to 50 °C and the auxiliary gas pressure was 150 kPa. The regression equations demonstrated a good linear relationship (R² = 0.9989-0.9999) within the test ranges. The limits of detection (LODs) and quantification (LOQs) for propionylbrassinolide, impurity 1 and 2 were 1.3, 1.2, 1,3 and 4.3, 4.0, 4.2 mg/L, respectively. The fully validated HPLC-ELSD method was readily applied to quantify the active ingredient and impurities in propionylbrassinolide technical concentrate. Moreover, the optimized separation conditions with ELSD have been successfully transferred to mass spectrometry (MS) detector for LC-MS determination.

A rapid method for analysis of fermentatively produced D-xylonate using ultra-high performance liquid chromatography and evaporative light scattering detection

An ultra-high performance liquid chromatography (UHPLC) based method for the analysis of d-xylonate was developed using an amide column in combination with an evaporative light scattering (ELS) detector. Separation of d-xylonate from other components of the fermentation medium was achieved. The dynamic range of the method was 0.2-7.0 g/L.

Development of a Robust Method for Simultaneous Quantification of Polymer (HPMC) and Surfactant (Dodecyl β-D-Maltoside) in Nanosuspensions

This report describes the development of a chromatographic method for the simultaneous quantification of a polymer, hydroxypropyl methylcellulose (HPMC), and a surfactant, dodecyl β-D-maltoside (DM), that are commonly used in the physical stabilization of pharmaceutical formulations such as nanosuspensions and solid dispersions. These excipients are often challenging to quantify due to the lack of chromophores. A reverse phase size exclusion chromatography (SEC) with evaporative light scattering detector (ELSD) technique was utilized to develop an accurate and robust assay for the simultaneous quantification of HPMC and DM in a nanosuspension formulation. The statistical design of experiments was used to determine the influence of critical ELSD variables including temperature, pressure, and gain on accuracy, precision, and sensitivity of the assay. A robust design space was identified where it was determined that an increase in the temperature of the drift tube and gain of the instrument increased the accuracy and precision of the assay and a decrease in the nebulizer pressure value increased the sensitivity of the assay. In the optimized design space, response data showed that the assay could quantify HPMC and DM simultaneously with good accuracy, precision, and reproducibility. Overall, SEC-ELSD proved to be a powerful technique for the simultaneous quantification of HPMC and DM. This technique can be used to quantify the amount of HPMC and DM in nanosuspensions, which is critical to understanding their effects on the physical stability of nanosuspensions.

Isolation and Analysis of Phospholipids in Dairy Foods

The lipid fraction of milk is one of the most complex matrixes in foodstuffs due to the presence of a high number of moieties with different physical and chemical properties. Glycerolipids include glycerol and two fatty acids esterified in positions sn-1 and sn-2 with higher concentration of unsaturated fatty acids than in the triglyceride fraction of milk. Sphingolipids consist of a sphingoid base linked to a fatty acid across an amide bond. Their amphiphilic nature makes them suitable to be added into a variety of foods and recent investigations show that phospholipids, mainly phosphatidylserine and sphingomyelin, can exert antimicrobial, antiviral, and anticancer activities as well as positive effects in Alzheimer's disease, stress, and memory decline. Polar lipids can be found as natural constituents in the membranes of all living organisms with soybean and eggs as the principal industrial sources, yet they have low contents in phosphatidylserine and sphingomyelin. Animal products are rich sources of these compounds but since there are legal restrictions to avoid transmission of prions, milk and dairy products are gaining interest as alternative sources. This review summarizes the analysis of polar lipids in dairy products including sample preparation (extraction and fractionation/isolation) and analysis by GC or HPLC and the latest research works using ELSD, CAD, and MS detectors.

Chemical profiling of the major components in natural waxes to elucidate their role in liquid oil structuring

Elucidating the composition of waxes is of utmost importance to explain their behavior in liquid oil structuring. The chemical components (hydrocarbons - HCs, free fatty acids - FFAs, free fatty alcohols - FALs and wax esters - WEs) of natural waxes were analyzed using HPLC-ELSD and GC-MS followed by evaluation of their oil structuring properties. The gel strength, including the average storage modulus and oscillation yield stress, displayed a negative correlation with FALs and a positive correlation with HCs, FFAs and WEs. The components dictating the gel strength are HCs, FFAs and WEs in a descending order of importance. The consistency of the oleogels increased with the increasing amount of FFAs and HCs and the decreasing amount of WEs and FALs. The presence of more WEs results in a strong but brittle gel with a high initial flow yield stress. We believe these results might be useful in selecting the right waxes to combine in certain fat-based food products.

Systematic development of a group quantification method using evaporative light scattering detector for relative quantification of ginsenosides in ginseng products

The determination for the contents of multi-components in ginseng products has come to the fore by demands of in-depth information, but the associated industries confront the high cost of securing pure standards for the continuous quality evaluation of the products. This study aimed to develop a prospective high-performance liquid chromatography-evaporative light scattering detector (HPLC-ELSD) method for relative quantification of ginsenosides in ginseng products without a considerable change from the conventional gradient analysis. We investigated the effects of mobile phase composition and elution bandwidth, which are potential variables affecting the ELSD response in the gradient analysis. Similar ELSD response curves of nine major ginsenosides were obtained under the identical flow injection conditions, and the response increased as the percentage of organic solvent increased. The nine ginsenosides were divided into three groups to confirm the effect of elution bandwidth. The ELSD response significantly decreased in case of the late eluted ginsenoside in the individual groups under the isocratic conditions. With the consideration of the two important effects, stepwise changes of the gradient condition were carried out to reach a group quantification method. The inconsistent responses of the nine ginsenosides were reconstituted to three normalized responses by the stepwise changes of the gradient condition, and this result actualized relative quantification in the individual groups. The availability was confirmed by comparing the ginsenoside contents in a base material of ginseng products determined by the direct and group quantification method. The largest difference in the determination results from the two methods was 8.26%, and the difference of total contents was only 0.91%.