A simplified guide for charged aerosol detection of non-chromophoric compounds—Analytical method development and validation for the HPLC assay of aerosol particle size distribution for amikacin

RP-CAD for Lipid Quantification: Systematic Method Development and Intensified LNP Process Characterization

Lipid nanoparticles (LNPs) and their versatile nucleic acid payloads bear great potential as delivery systems. Despite their complex lipid composition, their quality is primarily judged by particle characteristics and nucleic acid encapsulation. In this study, we present a holistic reversed-phase (RP)-charged aerosol detection (CAD)-based method developed for commonly used LNP formulations, allowing for intensified LNP and process characterization. We used an experimental approach for power function value (PFV) optimization termed exploratory calibration, providing a single PFV (1.3) in an appropriate linearity range for all six lipids. Followed by the procedure of method calibration and validation, linearity (10-400 ng, R2 > 0.996), precision, accuracy, and robustness were effectively proven. To complement the commonly determined LNP attributes and to evaluate the process performance across LNP processing, the developed RP-CAD method was applied in a process parameter study varying the total flow rate (TFR) during microfluidic mixing. The RP-CAD method revealed a constant lipid molar ratio across processing but identified deviations in the theoretical lipid content and general lipid loss, which were both, however, entirely TFR-independent. The deviations in lipid content could be successfully traced back to the lipid stock solution preparation. In contrast, the observed lipid loss was attributable to the small-scale dialysis following microfluidic mixing. Overall, this study establishes a foundation for employing RP-CAD for lipid quantification throughout LNP processing, and it highlights the potential to extend its applicability to other LNPs, process parameter studies, or processes such as cross-flow filtration.

A Novel high throughput 96-well based Fluorimetric Method to Measure Amikacin in Pharmaceutical Formulations: Development using Response Surface Methodology

An aminoglycoside antibiotic, amikacin, is used to treat severe and recurring bacterial infections. Due to the absence of a chromophore, however, amikacin must be extensively derivatized before being quantified, both in analytical and bioanalytical samples. In this study, for the first time, we developed a simple and sensitive method for measuring amikacin sulfate by spectrofluorimetry using a 96-well plate reader, based on the design of the experiment's approach. To develop a robust and reproducible spectrofluorimetric method, the influence of essential attributes, namely pH of the buffer, heating temperature, and concentration of reagents, were evaluated by univariate analysis followed by multivariate analysis (central composite design). ICH guidelines were used to validate the optimized method. The developed technique is linear from 1.9 to 10 μg/mL with a regression coefficient of 0.9991. The detection and quantification limits were 0.649 μg/mL and 1.9 μg/mL, respectively. For the developed method, both intra- and inter-day precision (%RSD) were below 5%. Using the method, amikacin concentrations were quantified in prepared amikacin liposomes and commercial formulations of Amicin®. The developed method greatly reduces sample volume and is a rapid, high throughput microplate-based fluorescence approach for the convenient and cost-effective measurement of amikacin in pharmaceutical formulations. In comparison to previously published approaches, the suggested method allowed for quick analysis of a high number of samples in a short amount of time (96 samples in 125 seconds), resulting in an average duration of analysis of 1.3 seconds per sample.

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.

Monitoring polysorbate hydrolysis in therapeutic proteins using an ultrasensitive extraction-free fatty acid quantitation method

Polysorbates (PSs) are surfactants commonly added to therapeutic protein drug product formulations to protect proteins from denaturation and aggregation during storage, transportation, and delivery. However, enzymatic hydrolysis of PSs has been recognized as the primary route of PS degradation in monoclonal antibody formulations, resulting in the release of free fatty acids that drive undesired particulate formation. Here, we present a rapid lipase activity assay with optimized incubation conditions for accurate quantitation of free fatty acids without a fatty acid extraction step. This assay can detect low levels of PS degradation (0.000024% PS20 degradation) within 1 day with minimal sample preparation. The levels of released free fatty acids were found to strongly correlate with the degree of PS20 degradation. The case study described herein suggests that this approach can detect low levels of PS20 degradation caused by sub-ppm lipase levels within 1 day, compared with the duration of 14 days needed for PS degradation assays based on two-dimensional liquid chromatography-charge aerosol detection.

Performance of ion pairing chromatography and hydrophilic interaction liquid chromatography coupled to charged aerosol detection for the analysis of underivatized amino acids

The charged aerosol detector (CAD) is frequently employed in liquid chromatography for the analysis of small polar and ionizable compounds such as amino acids and amino sugars, which provide a weak chromophore only. Separation of these compounds is achieved by means of ion pair chromatography (IPC), and, more recently, hydrophilic interaction chromatography (HILIC) techniques. However, as the CAD's response is highly dependent on the mobile phase composition, the substantial differences in the mobile phase composition of IPC and HILIC have a distinct impact on the detector's performance. This study was aimed at systematically comparing the performance of IPC and HILIC when coupled to the CAD. Therefore, the separation techniques characterized by their specific mobile phase compositions were evaluated for their influence on the CAD response and the signal-to-noise ratio (S/N) of the amino acids L-alanine, L-leucine, and L-phenylalanine applying the response surface methodology (RSM). The RSM results derived from flow injection analysis (FIA) indicated that the CAD response and thus the obtainable S/N are significantly higher in HILIC compared to IPC where the S/N decreased with the chain length of the applied ion-pairing reagent. In addition, an IPC and a HILIC method, respectively, were developed for the impurity profiling of the branched-chain amino acids (BCAAs) L-leucine, L-isoleucine, and L-valine. The beneficial effects of the HILIC conditions on the S/N observed under FIA conditions were partly offset by moderate column bleed effects when using an amide functionalized column, which facilitates the separation in the HILIC method. Satisfactory LOQs (3-10 ng on column) were obtained with both methods; however, the HILIC method was found to be slightly superior in terms of sensitivity and separation efficiency.

Quantitative analysis of impurities in leucomycin bulk drugs and tablets: A high performance liquid chromatography-charged aerosol detection method and its conversion to ultraviolet detection method

Toxic impurities were found in leucomycin and its preparation, however the content determination of impurities was challengeable due to the lacking of their reference standards. In this study, we developed high-performance liquid chromatography method coupled with charged aerosol detection (CAD) for the quantification of related substance of leucomycin (kitasamycin) bulk drugs and tablets, however, the CAD was not yet popular. In order to carry out quantitation work conveniently in the laboratory without CAD instruments, a high-performance liquid chromatography method coupled with ultraviolet (UV) detection was developed with the assistant of the HPLC-CAD results. The relative response of impurities on CAD chromatogram was used for guiding the establishment of HPLC-UV method, which could achieve the quantitation task in the absence of impurity reference standards. The developed HPLC-UV method was validated according to the ICH guideline and showed good precision, reproducibility and linearity with determination coefficient higher than 0.9999. The limit of detection and quantitation were 0.3 and 0.5 μg mL^-1, respectively. The recoveries were 92.9 %-101.5 % at the spiked concentration levels of 0.1 %, 0.8 %, 1.0 and 1.2 % with relative standard deviations (RSDs, n = 3) lower than 2.0 %. Finally, the developed HPLC-CAD and -UV methods were compared by the determination of impurities in several batches of leucomycin bulk drugs and tablets. The results demonstrated that the developed HPLC-UV method was simple and reliable. This study developed methods to quantify the related substance in leucomycin and tablets, and discussed a strategy of the conversion of HPLC-CAD method to HPLC-UV method. The developed methods could be considered for implementation into pharmacopeial monographs in the future.

Charged aerosol detection in early and late-stage pharmaceutical development: selection of regressionmodels at optimum power function value

In recent years, the use of quantitative liquid chromatography (LC) coupled charged aerosol detection (CAD) for poor UV absorbing analytes in multicomponent mixtures has grown exponentially across academic and industrial sectors. The ballpark of previous LC-CAD reports is focused on practical applications, as well as optimization of critical parameters such as: response dependencies on temperature, nebulization process, analyte volatility, and mobile-phase composition. However, straightforward approaches to deal with the characteristic nonlinear response of CAD still scarce. A highly overlooked parameter is the power function value (PFV), whose optimization enables a detection signal that is more linear with higher signal-to-noise ratio (S/N) and lower relative standard deviation (RSD) of area counts. Herein, a systematic investigation of different regression models (log-log, first-and second-degree polynomial) by both interpolation and extrapolation process in conjunction with PFV optimization throughout the development of LC-CAD assays is reported. The accuracy of the results via interpolation is always good (< 5%) when operating in the vicinity of the optimum PFV regardless the regression model choice. On the contrary, extrapolation process only worked when applying log-log regression at the optimum PFV (accuracy <5%). This outcome indicates that a first-order regression via interpolation can be a safe and simple choice for quantitative LC-CAD in highly regulated laboratories (GLP, GMP, etc.). Whereas a straightforward extrapolation combined with log-log regression can enable the deployment of high-throughput LC-CAD assays, especially but not limited to laboratories where the synthetic process route is undergoing rapid change and optimization (medicinal chemistry, discovery, biocatalysis, process chemistry, etc.). This approach is crucial in developing quantitative LC-CAD assays for poor UV absorbing pharmaceuticals that are sensitive, precise, accurate and robust across early and late-stage pharmaceutical development.

Universal response method for the quantitative analysis of multi-components in josamycin and midecamycin using liquid chromatography coupled with charged aerosol detector

Josamycin and midecamycin are consisted of three groups of components with different ultraviolet maximum absorption wavelengths (λ_max), which are 231 nm, 280 nm and 205 nm. The quantitative analysis of all these components is challengeable due to the absence of the respective reference substances. To address this problem, universal and reliable methods were developed using high performance liquid chromatography coupled with charged aerosol detector (HPLC-CAD) for the quantitative analysis of components in josamycin and midecamycin. The chromatographic conditions and CAD parameters setting were optimized. Subsequently, the components were identified using HPLC coupled with ion trap/time-of-flight mass spectrometry (IT/TOF MS). The developed methods were validated by assessing linearity, limit of quantitation (LOQ), accuracy, precision and robustness. Good separations were achieved for all components and the adjustment of the filter valve and power function value efficiently improved sensitivity. The developed methods were more comprehensive than current HPLC-UV method. The experimental results demonstrated good linearity with coefficients of determination (R²) greater than 0.999 in the range of 0.002-0.30 mg mL^-1. The limits of detection (LOD) were ranging from 1.8 to 2.0 μg·mL^-1. The intra-day and inter-day RSD values were less than 2.0 % (n = 6) and 5.6 % (n = 9) respectively. The recoveries were 95.0 %-124.0 % at the spiked concentration levels of 0.05 %, 0.50 %, 0.10 % and 2.5 % with relative standard deviations (RSDs, n = 3) lower than 2.0 %. Finally, the developed methods were successfully applied to the quantitative analysis of minor components and used main components (leucomycin A₃ and midecamycin A₁) as alternative reference substance of minor components. The overall results demonstrated that the HPLC-CAD was a good alternative for the quantitative analysis of multi-components in 16-membered macrolides.

A Status Update on Pharmaceutical Analytical Methods of Aminoglycoside Antibiotic: Amikacin

Amikacin (AMK) is one of the commonly used aminoglycoside antibiotics, introduced for clinical use in patients suffering from bacterial infections especially life-threatening gram-negative infections. Due to lack of chromophore in the molecule, the detection of AMK during analysis is a challenge. Thus, pre and post-column derivatization techniques are generally used for AMK estimation. This review focuses on different analytical methods used for detection and quantification of AMK in pure or fixed dose combination pharmaceutical formulations and biological samples. Various reported methods described in the literature include high-performance liquid chromatography techniques, pulsed electrochemical detection techniques, Chemiluminescence techniques, Capillary electrophoresis and immunological methods. High-performance-liquid-chromatography based methods with UV/Vis spectrophotometric, fluorescence and mass spectrometric detection are the most prevailing methods employed for the analysis of AMK. This review could be of significant importance in the area of future AMK analytical method development studies.

Determination and Identification of Antibiotic Drugs and Bacterial Strains in Biological Samples

Antibiotics were initially natural substances. However, nowadays, they also include synthetic drugs, which show their activity against bacteria, killing or inhibiting their growth and division. Thanks to these properties, many antibiotics have quickly found practical application in the fight against infectious diseases such as tuberculosis, syphilis, gastrointestinal infections, pneumonia, bronchitis, meningitis and septicemia. Antibiotic resistance is currently a detrimental problem; therefore, in addition to the improvement of antibiotic therapy, attention should also be paid to active metabolites in the body, which may play an important role in exacerbating the existing problem. Taking into account the clinical, cognitive and diagnostic purposes of drug monitoring, it is important to select an appropriate analytical method that meets all the requirements. The detection and identification of the microorganism responsible for the infection is also an essential factor in the implementation of appropriate antibiotic therapy. In recent years, clinical microbiology laboratories have experienced revolutionary changes in the way microorganisms are identified. The MALDI-TOF MS technique may be interesting, especially in some areas where a quick analysis is required, as is the case with clinical microbiology. This method is not targeted, which means that no prior knowledge of the infectious agent is required, since identification is based on a database match.

A strategy for test article selection and phytochemical characterization of Echinacea purpurea extract for safety testing

Botanical dietary supplements (BDS) are used around the world for many purported therapeutic properties. The selection of an authentic product and it's phytochemical characterization is critical to generate robust safety data. Because botanicals are complex mixtures with variable quality, identification of a representative product for testing has been challenging. Echinacea is used for its purported immune stimulant properties and was listed as the 2nd top-selling BDS in 2018. However, there are limited safety data for Echinacea. Hence, the National Toxicology Program (NTP) has selected Echinacea for safety testing using rodent models. Here, we describe selection and comprehensive characterization of an Echinacea purpurea root extract to be used in the NTP testing program. Using non-targeted chemical analyses combined with chemometric analysis, a potential unfinished product (i.e., an extract that serves as source material for finished products) of Echinacea purpurea was selected. The product was then authenticated using chemical and DNA techniques and characterized, including the phytochemical composition. Among numerous constituents identified, caftaric acid, chicoric acid, chlorogenic acid and dodeca-2(E),4(E),8(Z),10(E/Z)-tetraenoic acid isobutylamide made up a small fraction of the extract. Based on these analyses, an approach is proposed for test article selection for Echinacea research which can be adapted to other botanicals.

Development and Validation of a Pre-Column Derivatization HPLC Method for the Assay of Amikacin Sulfate in Pure and Parenteral Dos age Forms

Background:

Amikacin sulfate (AMK) belongs to the class of aminoglycoside antibiotics. It is effective against the infections caused by Gram-negative and positive bacteria. AMK lacks a chromophore group in its structure and, therefore, it does not absorb light in the 200-800 nm region which makes it a difficult molecule to analyze by UV detector using high performance liquid chromatography (HPLC).

Objective:

This study has been carried out to develop and validate a relatively simple, accurate, precise, rapid, economical, and stability-indicating pre-column derivatization HPLC method for the determination of AMK in pure and parenteral dosage forms.

Methods:

The stock solution of AMK was derivatized prior to its analysis. The mobile phase used for the analysis was acetonitrile and water in the ratio of 50:50 (v/v) at pH 6.0. The method has been validated according to the guideline of International Council for Harmonization (ICH) and different parameters such as linearity, range, accuracy, precision, sensitivity, robustness, solution stability, specificity and system suitability have been studied. AMK was subjected to stress degradation studies including thermolysis, humidity exposure, acid-base hydrolysis, and oxidation in order to determine the specificity of the test method.

Results:

The retention time of AMK has been found to be 4.7 min. The results indicated that the method is linear in the concentration range of 12.5-125% and possesses high accuracy (99.88±0.42%), precision ((<1.2%) and robustness (<0.5%). The obtained results are compared statistically with a reference method.

Conclusion:

It was observed that the stress degradation studies do not affect the accuracy of the method. Hence the proposed method can be used for the assay of AMK and its parenteral dosage form.

Specific fluorometric assay for direct determination of amikacin by molecularly imprinting polymer on high fluorescent g-C3N4 quantum dots

Here, a specific and reliable fluorometric method for the rapid determination of amikacin was developed based on the molecularly imprinting polymer (MIP) capped g-C₃N₄ quantum dots (QDs). g-C₃N₄ QDs were obtained by facile and one-spot ethanol-thermal treatment of bulk g-C₃N₄ powder and showed a high yield fluorescence emission under UV irradiation. The MIP layer was also created on the surface on QDs, via usual self-assembly process of 3-aminopropyl triethoxysilane (APTES) functional monomers and tetraethyl ortho-silicate (TEOS) cross linker in the presence of amikacin as template molecules. The synthesized MIP-QDs composite showed an improved tendency toward the amikacin molecules. In this state, amikacin molecules located adjacent to the g-C₃N₄ QDs caused a remarkable quenching effect on the fluorescence emission intensity of QDs. This effect has a linear relationship with amikacin concentration and so, formed the basis of a selective assay to recognize amikacin. Under optimized experimental conditions, a linear calibration graph was obtained as the quenched emission and amikacin concentration, in the range of 3-400 ng mL^-1 (4.4-585.1 nM) with a detection limit of 1.2 ng mL^-1 (1.8 nM). The high selectivity of MIP sites as well as individual fluorescence properties of g-C₃N₄ QDs offers a high specific and sensitive monitoring method for drug detection. The method was acceptably applied for the measurement of amikacin in biological samples.

Revealing the inner workings of the power function algorithm in Charged Aerosol Detection: A simple and effective approach to optimizing power function value for quantitative analysis

In recent years, charged aerosol detection (CAD) has become a valuable tool for fast and efficient quantitative chromatographic analysis of drug substances with weak UV absorption. In analytical method development using CAD, the power function settings available in the instrument software are key for linearization of the signal response with respect to analyte concentration. However, the relatively poor understanding of the power function algorithm has limited a more widespread use of CAD for quantitative assays, especially in the late stage of method validation and GMP laboratories. Herein, we present an approach to understand the inner workings of the power function value (PFV), the PFV optimization algorithm, as well as a method to determine the optimum PFV based on the signals acquired at PFV = 1 (default CAD settings). The exponent and the constant in the PFV equation used for modeling follow a trend as a function of PFV. The CAD signal at any PFV was modeled based on the signal acquired at PFV = 1, the modelling was successful for two analytes at different concentration levels on two different CAD detectors of the same model. This method reveals the functionality of the PFV which substantially simplifies the workflow needed to optimize the detector signal. The accuracy between the experimental and theoretical results showed high correlation and always resulted in the same optimum PFV determined by both ways. The approach described in this investigation simplifies the selection of the optimum PFV at which the signal is more linear, the signal-to-noise is higher, and the area reproducibility is better. The power function algorithm elucidated herein enables determination of optimum PFV from minimal experimental output and excellent overall accuracy. This paper provides an approach that includes no data transformation outside the vendor software, a very important requirement to easily validate and report results in a GMP environment.