Quantitative comparison of a corona-charged aerosol detector and an evaporative light-scattering detector for the analysis of a synthetic polymer by supercritical fluid chromatography

Quantitation of polyethylene glycol by size exclusion chromatography with charged aerosol, differential refractive index, and multi-angle light scattering detectors

Polyethylene glycol (PEG) has found tremendous applications in pharmaceutical products and has played a critical role in PEGylated drug modalities to improve pharmacokinetic properties and biological efficacy. The characterization and quantitation of PEGs are essential to control manufacture process and drug product quality. However, the assay value of PEG could change dramatically depending on the structures of the PEG and the detection techniques used. In this study, we developed a size exclusion chromatographic (SEC) method for quantitative PEG analysis, and we systematically evaluated the performance of three online detectors with different operating principles: a charged aerosol detector (CAD), a differential refractive index (dRI) detector, and a multi-angle light scattering detector (MALS). Fourteen PEG compounds covering a wide range of molecular weight (MW, 1 - 40 kDa) and molecular architectures (linear, branched, Y-shaped and multi-arm geometries) were evaluated by these three detection techniques. Our study revealed that the dRI showed the most universal responses among all the PEGs regardless of their molecular weight or geometries. In the contrast, CAD and MALS detector showed MW-dependent and semi-universal geometry-dependent responses. Another key finding is that the relative response factor for each multi-arm PEG in the CAD and the MALS were inversely correlated, suggesting both can be applied to qualitatively assess polymers of different architectures, including the ones with subtle differences in their core structures. The comparison of the three detectors not only provides the fundamental and comprehensive understanding of PEG quantitation but also enables the process development and control of high-quality PEGs in producing PEGylated therapeutics in the pharmaceutical industry.

Separation of Molar Weight-Distributed Polyethylene Glycols by Reversed-Phase Chromatography—Analysis and Modeling Based on Isocratic Analytical-Scale Investigations

The separation of polyethylene glycols (PEGs) into single homologs by reversed-phase chromatography is investigated experimentally and theoretically. The used core–shell column is shown to achieve the baseline separation of PEG homologs up to molar weights of at least 5000 g/mol. A detailed study is performed elucidating the role of the operating conditions, including the temperature, eluent composition, and degree of polymerization of the polymer. Applying Martin’s rule yields a simple model for retention times that holds for a wide range of conditions. In combination with relations for column efficiency, the role of the operating conditions is discussed, and separations are predicted for analytical-scale chromatography. Finally, the approach is included in an efficient process model based on discrete convolution, which is demonstrated to predict with high accuracy also advanced operating modes with arbitrary injection profiles.

Quality evaluation of Codonopsis Radix and processed products based on the analysis of monosaccharides and oligosaccharides by liquid chromatography coupled with charged aerosol detector

INTRODUCTION

Codonopsis Radix (CR) is an edible food and traditional Chinese herb medicine that is widely used in China and Southeast Asia. Saccharides, including fructo-oligosaccharides (FOS) and polysaccharides, are among the most important active substances in CR. However, a quality evaluation of CR based on oligosaccharides has not been conducted.

OBJECTIVE

This study aimed to establish a high-performance liquid chromatography coupled with charged aerosol detector method (HPLC-CAD) for the quality evaluation of CR and processed products based on analysis of monosaccharides and oligosaccharides.

METHOD

A sensitive and rapid HPLC-CAD method for the simultaneous determination of two monosaccharides (D-fructose and D-glucose), sucrose, and FOS (GF2-GF6) was established to evaluate the quality of CR for the first time. In the present study, 65 batches of CR from three species of the genus Codonopsis were analysed using multivariate statistical techniques. Furthermore, the effects of cultivation management measures (plant growth retardants supply, harvesting time, and growth period) and primary process (drying methods) in the production areas on the target compounds were studied by analysing 34 batches of processed samples.

RESULTS

Different varieties of CR resulted in considerably different saccharide contents. Cultivation management measures and processing method remarkably affected the quality of CR. Low concentration of plant growth retardants was recommended. The best harvest time is in October after 4 years of growth. Dryer-drying was suggested to meet the requirement for large-scale processing.

CONCLUSION

This method would provide an efficient analytical tool for monosaccharides and oligosaccharides of CR and contribute to the improvement of CR quality.

Investigation of hydrophilic interaction liquid chromatography coupled with charged aerosol detector for the analysis of tromethamine

Tromethamine (TMM), often encountered in a final drug product, exhibits interesting chemical properties as a counter ion, buffer, or active ingredient. European and US pharmacopeias propose titration against hydrogen chloride for TMM assays. However, this method can be a hindrance when using drugs containing low concentrations of TMM in complex buffered formulations. Due to the lack of chromophores and the high hydrophilicity of TMM, we performed a simple and reliable hydrophilic interaction chromatography coupled with a charged aerosol detector (HILIC-CAD) separation approach as an alternative for TMM analysis. An amide stationary phase and a mobile phase consisting of a binary mixture of acetonitrile and 10 mM ammonium formate, pH 3 (80/20, V/V) were used. As the CAD response deeply depends on parameters such as stationary phases and pH buffer, we investigated their impact and explored the optimal signal conditions. Including TMM analogs such as tris(hydroxymethyl) nitromethane and 2-amino-2-ethyl-1,3-propanediol allowed us to select these parameters appropriately. The effects of the evaporation temperature, flow rate, and power function value (PFV) on the CAD signal response were also studied and optimized. The method was validated according to the ICH Q2 R1 guidelines. A linear response (mean R² > 0.997) covering the range for low TMM concentrations (170-520 μg/mL) was achieved. Satisfactory intra-day and inter-day precisions were obtained with RSDs lower than 1.9% and 2.8%, respectively. The trueness ranged from 99.6% to 101.2%, and the LOD was found to be 1.1 μg/mL. The HILIC-CAD method has been applied to a sterile TMM solution for injection.

Determination of Free Amino Acids in Banlangen Granule and its Fractions by Solid Phase Extraction Combined with Ion-pair Hig-h Perfor mance Liquid Chromatography using a Corona-charged Aerosol Detector (SPE-HPLC-CAD)

Background:

Banlangen granules are broad-spectrum effective antiviral drugs, and have a large clinical demand in China. Free amino acid is one of the main antiviral active ingredients of Banlangen granules. The pre-processing of samples by the existing pre-column derivatization reversed- HPLC method is complicated. Therefore, the determination of free amino acids (AAs) by underivatized ion-pair HPLC-CAD is advantageous for simplifying the preparation process and improving sensitivity.

Objective:

To better optimize AAs analysis methods, here a sensitive SPE-HPLC-CAD method with a better resolution was established for the determination of underivatized AAs in Banlangen Granule for the first time.

Method:

The analytes were separated only by HPLC using a Hypercarb column with gradient elution of solvent A (20 mM nonafluorovaleric Acid in water) and solvent B (0.3% trifluoroacetic acid in acetonitrile-0.3% trifluoroacetic acid in water (1:9, v/v)) at a flow rate of 0.15 mL/min. N2 gas pressure and evaporation temperature of CAD were held at a constant 58.6 psi and 60 ℃, respectively.

Results:

This method was linear over the respective concentration range of six amino acids. The precision, accuracy, stability and recovery were satisfactory in all samples examined. And the method was successfully applied to determination of free amino acids in Banlangen granules and its fractions. The total contents of six amino acids in 28 batches of Banlangen Granule were between 1.36 mg/g-11.62 mg/g.

Conclusion:

The proposed method could be a simple, accurate and sensitive alternative approach for the determination of free AAs in Banlangen Granule.

Comprehensive ethoxymer characterization of complex alcohol ethoxy sulphate products by mixed-mode high-performance liquid chromatography coupled to charged aerosol detection

The present work describes a simultaneous mixed-mode high performance liquid chromatography (HPLC) method combined with a universal and non-selective-response detector for the complete ethoxymer profiling of alcohol ethoxy sulphate mixtures. The optimized HPLC methodology combines the dual hydrophilic (HILIC) and reversed-phase selectivity of a surfactant-type column in order to render a comprehensive and simultaneous separation of more than 50 endogenous ethoxymers in a single analysis. Furthermore, an accurate quantitation of every single analyte was achieved using a final universal charged aerosol detector (CAD) including specific mathematical processing tools. Results obtained helped describing a complete alkyl chain and ethoxymer distribution of the investigated AES samples. Method validation evidences provided reliability of the individual ethoxymer contributions determined with the proposed HPLC-CAD methodology. Regarding accuracy including independent nuclear magnetic resonance (NMR) experiments, an excellent correlation was found between the structural information provided by a COSY NMR spectrum and the CAD results regarding the mono/polyethoxylated and the non-ethoxylated/ethoxylated distribution. Additional calculations including the average molecular weight and the degree of ethoxylation for the reference AES sample showed minimum differences (relative error < 1 %) between the two considered techniques. An outstanding precision and linearity along the working concentration range (r²>0.999) was also observed. The individual limit of detection for the target sulphate ethoxymers was determined to be in the low ppm range. Further validated distribution profiles for a large number of AES samples demonstrated the applicability of the optimized HPLC-CAD methodology to routine surfactant screenings. Therefore, the hereby developed methodology provided extensive information regarding the detailed individual ethoxymer profile of AES formulations, which can be extremely useful for the surfactant industry in order to gain information on specific synthesis routes and/or detergency properties.

Towards improved characterisation of complex polyethylene glycol excipients using supercritical fluid chromatography-evaporative light scattering detection-mass spectrometry and comparison with size exclusion chromatography-triple detection array

The application of supercritical fluid chromatography (SFC) coupled to an evaporative light scattering detector (ELSD) and mass spectrometer (MS) was evaluated for the characterisation of three analogues of functionalised polyethylene glycol (PEG) 2000 (m-PEG-OH, m-PEG-cm and cm-PEG-cm (where m = OCH₃ and cm = OCH₂COOH)). These polymers are common excipients in drug product formulations for pharmaceuticals as they help provide the desired pharmacokinetic profile for successful drug delivery. A SFC-ELSD-MS method was developed which was selective to all three polymers, and allowed visualisation of these low UV chromophore materials. The method provided baseline resolution of the individual oligomers which allowed facile calculation of the polymer dispersity. A number of molecular weight characteristics were calculated, which showed the SFC-ELSD-MS methodology to be comparable with the current standard of analysis using size exclusion chromatography (SEC) with a triple detector array (TDA). The increased resolving power of SFC compared to SEC revealed a bimodal distribution of oligomers in the cm-PEG-cm 2000 polymer, which was not observed using SEC-TDA and exemplified SFC-ELSD as an orthogonal approach for polymer characterisation with the potential for much simpler, reduced sample and instrument preparation, calibration-less dispersity determination. When combined with SEC-TDA data, this combination allows a more complete characterisation of complex formulations excipients.

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.

Unusual effect of flow rate on retention in analytical supercritical fluid chromatography exemplified by polyethylene glycol separation

We report a case of a peculiar effect of flow rate on retention in a separation of polyethylene glycol oligomers via supercritical fluid chromatography. During method development, we tested flow rate gradients and notices that for some PEG oligomers retention times at flow rate gradient were lower than at constant flow with the largest flow rate value used in a gradient. For instance, at BEH stationary phase and CO₂-MeOH gradient from 10 to 35% at 20 min a PEG oligomer having mass of 1225 Da has a retention time 14 min at 1 mL/min flow rate, 10.3 at 2 mL/min and 9.5 min at 1-2 mL/min flow rate gradient. The effect is not unified for all PEG oligomers, it occurs only starting from a particular PEG molecular weight which depends on the stationary phase type and/or mobile phase conditions. We believe that such an unusual flow rate effects can happen in SFC on various occasions, not exclusively for flow rate gradients, and thus should be taken into account during method development or method transfer.

A linear mass concentration detector for solvent gradient polymer separations

Silicon photonic microring resonators are an optical sensor utilized here as a detector for gradient elution liquid chromatography of polymers. Universal refractive index based detection and a linear mass concentration response is observed.

Development of a rapid and reliable analytical method for screening poloxamer 188 for use in cell culture process

Poloxamer P188 is a common nonionic surfactant additive used in cell culture media as a cellular protectant from the hydrodynamic forces and shear stress during bioprocessing. Presence of a hydrophobic high molecular weight impurity contaminant has been shown to compromise its protective properties and lead to batch failure. In this work we present, a reliable, sensitive, and rapid analytical method to detect and quantify the contaminant impurity in poloxamer 188. This method replaces a laborious and time-consuming functional test in the form of a shake flask assay. The method is based upon reversed-phase liquid chromatography with charged aerosol detection, simple mobile phase compositions, and a three-step gradient. The method was optimized to resolve the impurity from the main P188 fraction in less than 10 min. Analytical method qualification and functional test comparison demonstrate equivalent or better high throughput impurity screening performance. Attempts to identify the impurity and establish suitable method positive control standards are also discussed.

Silicon Photonic Microring Resonator Arrays for Mass Concentration Detection of Polymers in Isocratic Separations

Molecular weight distribution (MWD) is often the most informative analytical parameter in polymer analysis, with gel permeation chromatography (GPC) being the most common approach for determining the MWD for polymer samples. Many industrially relevant polymers lack chromogenic or fluorogenic signatures, precluding use of spectroscopy-based detection. Universal detectors, such as evaporative light scattering and charged aerosol detectors, are nonlinear, limiting quantitative polymer analysis. Differential refractive index (dRI) detectors show linear mass concentration sensitivity but are limited for some analyses given that they are incompatible with gradient-based separations, have a limited dynamic range, and require extended thermal equilibration times. In this study, we investigated the utility of silicon photonic microring resonator arrays as a quantitative mass concentration detector for industrial polymer analysis. Microring resonators have optical properties that are sensitive to changes in refractive index, offer an extended dynamic range, have a broad solvent compatibility, and have a linear mass concentration detection for a range of molecular weights. Linear mass concentration detection for microrings was demonstrated through a series of isocratic GPC separations using narrow MWD polystyrene (PS) standards. This detection technology was then utilized in conjunction with conventional GPC detectors to analyze a series of broad MWD PS standards, with results in good agreement with dRI and UV/visible. These results demonstrate the potential of the microring resonator platform as a detector for industrial polymer analysis.

A multi-detector chromatographic approach for characterization and quantitation of botanical constituents to enable in silico safety assessments

An approach has been developed to characterize the individual chemical constituents of botanicals. The challenge was to identify and quantitate the significant analytes in these complex mixtures, largely in the absence of authentic standards. The data-rich information content generated by this three-detector configuration was specifically intended to be used to conduct safety and/or quality evaluations for complex botanical mixtures, on a chemical constituent basis. The approach utilized a broad gradient UHPLC chromatographic separation. Following the chromatographic separation and UV detection, the eluent was split and sent into a charged aerosol detector (CAD), for quantitation, and a quadrupole/time-of-flight high-resolution mass spectrometer for component identification. The known bias of the otherwise universal CAD response, for organic solvent composition of the mobile phase, was compensated by the addition of an inverse gradient make-up stream. This approach and the orthogonal information content from the chromatography and three different detectors was specifically designed to enable in-silico safety assessments. These guide, minimize, or even eliminate the need for in vivo and in vitro safety assessments. The methodology was developed and demonstrated using standardized extracts of Ginkgo biloba. Results from the development of this novel approach and the characterization example reported here demonstrate the suitability of this instrumental configuration for enabling in-silico safety assessments and proving general quality assessments of botanicals.

Self-Assembled Curved Macroporous Photonic Crystal-Based Surfactant Detectors

Surfactants are extensively used as detergents, dispersants, and emulsifiers. Thus, wastewater containing high-concentration surfactants discharged to the environment pose a serious threat to the ecosystem. Unfortunately, conventional detection methods for surfactants suffer from the use of sophisticated instruments and cannot perform detections for various surfactants by a single analysis. The article reports the development of simple and sensitive surfactant detection using doctor-blade-coated three-dimensional curved macroporous photonic crystals on a cylindrical rod. The photonic crystals exhibit different hydrophobicities at various angular positions after surface modification. The penetration of aqueous surfactant solutions in the interconnected macropores causes red-shift as well as reduction in amplitude in the optical stop bands, resulting in surfactant detection with visible readout. The correlation between the surface tension, as well as the solution-infiltrated angular position, and the concentration of aqueous surfactant solutions has also been investigated in this study.

A non-derivative method for the quantitative analysis of isosteroidal alkaloids from Fritillaria by high performance liquid chromatography combined with charged aerosol detection

A non-derivative method was developed for the qualitative and quantitative analysis of isosteroidal alkaloids from Fritillaria thunbergii. During method development the performance of two universal detectors, the charged aerosol detector (CAD) and evaporative light scattering detector (ELSD), were evaluated. The CAD was found to be 30 to 55 times more sensitive than ELSD enabling the measurement of low levels of reference compound impurities that could not be detected by ELSD. The peak area percent of the reference compound, peimisine, obtained by CAD was 50.10%, but 91.66% by ELSD showing that CAD is suitable to estimate the presence of impurities. The CAD showed good reproducibility with overall intra- and inter-day peak area RSD values of less than 1.8% and 2.7%, respectively and had a linear dynamic range of up to 4 orders of magnitude (0.06-44mg/L) for peimine and peiminine. The optimized method was used for the quantitative analysis of peimine and peiminine from F. thunbergii.

Charged aerosol detection to characterize components of dispersed-phase formulations

Colloidal formulations based on biocompatible phospholipids, emulsifiers, and oils are employed in a wide range of applications including medicine, food, and cosmetics. However, characterization of these dispersed-phase components may be difficult to analyze by traditional HPLC with UV, visible, or fluorescence detection modalities due to lack of chromophores or fluorophores. Charged aerosol detection (CAD) is increasingly used for analysis of dispersed-phase components due to its broad applicability and high sensitivity for non-chromophore containing components found in many colloidal systems, such as lipid-based molecules. In this review, we summarize the recent applications of CAD reported in the literature as well as our own laboratory for the analysis of widely used components of dispersed-phase systems. In particular, we discuss the advantages and disadvantages of CAD compared to other HPLC detection methods, as well as the various sample preparation methods suitable for colloidal formulations prior to HPLC-CAD analysis.

Analysis of Sucrose Esters by HPLC Using Charged Aerosol Detector

A high performance liquid chromatographic method has been developed for separation and quantitation of sucrose esters using charged aerosol detection (CAD) combined with mobile phase compensation. Two Acclaim120 C18 columns (75×3.0mm, 3μm) and the gradient composition (0 min – 72% A + 25% B + 3%C, 7.5 min – 75% A + 25% B + 3%C, 19.5 min – 97% A + 3%C, 30 min – 97% A + 3%C, where A is methanol, B is water and C is tetrahydrofuran) were applied. A precisely inverse gradient composition (0 min – 97% A + 3%C, 7.5 min – 97% A + 3%C, 19.5 min – 72% A + 25% B + 3%C, 30 min – 72% A + 25% B + 3%C) was also used. The mobile phase compensation was performed by mixing of the column effluent with the mobile phase of exactly reverse composition provided by a second pump before introduction into the CAD. Introduction