Use of ionic liquids as headspace gas chromatography diluents for the analysis of residual solvents in pharmaceuticals

Deep eutectic solvents as green and sustainable diluents in headspace gas chromatography for the determination of trace level genotoxic impurities in pharmaceuticals

Genotoxic impurities (GTIs) are potential carcinogens that need to be controlled down to ppm or lower concentration levels in pharmaceuticals under strict regulations. The static headspace gas chromatography (HS-GC) coupled with electron capture detection (ECD) is an effective approach to monitor halogenated and nitroaromatic genotoxins. Deep eutectic solvents (DESs) possess tunable physico-chemical properties and low vapor pressure for HS-GC methods. In this study, zwitterionic and non-ionic DESs have been used for the first time to develop and validate a sensitive analytical method for the analysis of 24 genotoxins at sub-ppm concentrations. Compared to non-ionic diluents, zwitterionic DESs produced exceptional analytical performance and the betaine : 7 (1,4- butane diol) DES outperformed the betaine : 5 (1,4-butane diol) DES. Limits of detection (LOD) down to the 5-ppb concentration level were achieved in DESs. Wide linear ranges spanning over 5 orders of magnitude (0.005-100 µg g-1) were obtained for most analytes with exceptional sensitivities and high precision. The method accuracy and precision were validated using 3 commercially available drug substances and excellent recoveries were obtained. This study broadens the applicability of HS-GC in the determination of less volatile GTIs by establishing DESs as viable diluent substitutes for organic solvents in routine pharmaceutical analysis.

Thermodynamic characterization of interactions between environmental contaminants and room temperature ionic liquids using static headspace gas chromatography with vacuum ultraviolet detection

Understanding the thermodynamic interactions between an analyte and the sample phase is of paramount importance when choosing a co-solvent in headspace analysis. A sample phase - gas phase equilibrium partition coefficient (Kp) is used fundamentally to describe the distribution of the analyte between the two phases. Kp determinations by headspace gas chromatography (HS-GC) were acquired by two methods: vapor phase calibration (VPC) and phase ratio variation (PRV). Here, we demonstrated a pressurized - loop headspace system in conjunction with gas chromatography vacuum ultraviolet detection (HS-GC-VUV) to directly calculate the concentration of analytes in the gas phase from room temperature ionic liquids (RTILs) sample phases, using pseudo-absolute quantification (PAQ). PAQ, an attribute of VUV detection, allowed for quick determination of Kp and other thermodynamic properties, such as enthalpy (ΔH) and entropy (ΔS) of the system through the use of van't Hoff plots in the temperature range of 70-110 °C. The Kp determinations by PAQ were comparable to those obtained using the VPC method with percent difference ranging from ≤ 1-33%. Kp determinations were made for analytes (cyclohexane, benzene, octane, toluene, chlorobenzene, ethylbenzene, m-,p-, and o-xylene) at the varying temperatures (70-110 °C) using different RTILs (1-ethyl-3-methylimidazolium ethylsulfate ([EMIM][ESO₄]), 1-ethyl-3-methylimidazolium diethylphosphate ([EMIM][DEP]), and tris(2-hydroxyethyl)methylammonium methylsulfate ([MTEOA][MeOSO₃])) and (1-ethyl-3-methylimidazolium bis(trisfluoromethanesulfonyl)imide ([EMIM] [NTF₂])). The results from the van't Hoff analysis revealed that [EMIM] cation-based RTILs exhibit strong solute-solvent interactions with analytes that have π- electrons.

Platform headspace gas chromatography method for high-throughput determination of residual solvents in pharmaceutical materials

Static headspace capillary gas chromatography (HSGC) has been employed to monitor the level of residual solvents in the pharmaceutical materials. Most of the HSGC methods, however, consume significant amounts of diluents and require considerable amount of sample preparation time. Accordingly, a HSGC method featured with fast turnaround time, and minimal amount of solvent use has been developed for the quantitative analysis of 27 residual solvents frequently used in the development and manufacturing processes of pharmaceutical industry. This HSGC-FID method employs a commercially available fused silica capillary column, a split injection (40:1), and a programmed temperature ramp. It was qualified for specificity, accuracy, repeatability/precision, linearity, LOQ, solution stability, and robustness using two representative sample matrices. The standards, samples and spiked samples were demonstrated to be stable for at least 10 days at room temperature in sealed headspace vials with a recovery of ≥ 93%. The method was also shown to be robust, and its performance was not affected by small changes of carrier gas flow rate, initial oven temperature or the headspace oven temperature. In this new approach, the analytical sample was prepared by dissolving the sample into 1 mL of the diluent and the standard solution was prepared by diluting 1 mL of the custom-made stock into 9 mL of the diluent whereas the traditional approach requires liters of the diluent, making the new approach environmentally friendly, sustainable, economical, agile, error-proofing and thus appropriate for a variety of pharmaceutical applications.

Quantitation of Conjugation-related Residual Solvents in Antibody Drug Conjugates using Headspace Gas Chromatography

Background:

Antibody Drug Conjugates (ADCs) are complex hybrid molecules comprised of a monoclonal antibody (mAb) connected to a small molecule drug through a linker. The key step in the production of ADCs is bringing together the protein in an aqueous buffer with a hydrophobic small molecule in order to achieve conjugation of the molecules. This step involves dissolving the small molecule portion of the compound in an aqueous miscible organic solvent. These solvents and unconjugated small molecules are ideally cleared by downstream processing in order to achieve the desired product quality. As part of the control system to ensure product quality, the determination of residual solvents in pharmaceuticals is of significant importance in order to protect patient safety and ensure an efficacious drug.

Objective:

Headspace gas chromatography (HS-GC) is the most widely used tool for quantification of residual solvents for small molecule active pharmaceutical ingredients (APIs) but is not widely used for the analysis of protein-containing samples. In this study, the detection of residual solvents in headspace injections was explored using various conditions in order to detect commonly used conjugation solvents including N,N-dimethylacetamide (DMA), N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), Ethylene Glycol (EG), and Propylene Glycol (PG) in an ADC drug product sample.

Methods:

Various organic solvents were explored to enhance the response observed with complex protein and residual solvent matrixes. As EG and PG do not partition into the headspace efficiently in the ADC drug product samples that contain large amounts of water, ionic liquids and other ionic compounds were screened with the ADC samples to see if they could improve the partitioning of the key solvents EG and PG.

Results:

Following headspace and chromatographic optimization, we have developed an approach for the detection and quantification of several conjugation reaction solvents in ADC samples.

Conclusion:

This new approach is an HS-GC method that simplifies Gas Chromatography (GC) analysis and sample preparation and can be readily implemented in quality control testing for bioconjugated products.

[Simultaneous determination of 18 chlorinated hydrocarbon organic solvents in cosmetics by gas chromatography-mass spectrometry]

建立了同时测定化妆品中18种氯代烃类有机溶剂的气相色谱-质谱(GC-MS)检测方法。样品在饱和氯化钠溶液中由正十四烷振荡提取后,以Agilent J&W DB-624超高惰性毛细管柱(30 m×0.25 mm×1.4 μm)为分离色谱柱进行分析,以电子轰击(EI)源、SIM模式进行质谱监测,外标法定量。结果表明,18种化合物在19 min内完成色谱分离分析,检出限(LOD, S/N=3)和定量限(LOQ, S/N=10)分别为0.033~0.049 mg/L和0.10~0.15 mg/L, 18种氯代烃类有机溶剂在0.2~100 mg/L线性范围内线性关系良好,相关系数(R²)均不小于0.9992。以阴性样品口红(固体)和漱口水(液体)为样品基质,在不同添加水平下,18种氯代烃类有机溶剂的平均回收率分别为92.4%~103.1%和93.3%~102.4%,相对标准偏差(RSD, n=6)分别为3.1%~5.3%和2.8%~5.4%。采用该方法对115个化妆品样品进行测定,3个指甲油样品均检测出四氯乙烯,测定值为11.4~42.0 g/kg。研究建立的方法采用高沸点溶剂作为进样溶剂,取消溶剂延迟时间,使只能在溶剂延迟时间出峰的化合物得到有效色谱分离,分析时间短,且重复性好,灵敏度高,可同时检测各种化妆品中多种氯代烃类有机溶剂。该方法的建立为我国化妆品中氯代烃类有机溶剂检测标准的制订和质量安全监控提供了参考。

Validation of chemometric-assisted single-drop microextraction based on sustainable solvents to analyze polyaromatic hydrocarbons in water samples

Chemometric and statistic approaches were applied to optimize and validate headspace-single drop microextraction-based deep eutectic solvents combined with gas chromatography-mass spectrometry. The proposed technique was used for the pre-concentration, separation, and detection of polyaromatic hydrocarbons in aqueous samples. The efficacy of the independent variables on the extraction efficiency was studied via chemometric methods in two steps. The method exhibits good linearity for the analytes (R2 ≥ 0.9989). Under optimal conditions, the analytical signal was linear in the range of 0.01-50 μg L-1. The limit of detection and limit of quantitation were evaluated in the concentration range of 0.003-0.012 and 0.009-0.049 μg L-1, respectively. The precision consisting of repeatability and reproducibility were assessed by estimating the relative standard deviation (RSD%), and their values were found to be lower than 7.1% and 11.7%, respectively. Consequently, the proposed procedure was used to extract and analyze 19 polyaromatic hydrocarbons in real aqueous samples, which demonstrated satisfactory recoveries (94.40-105.98%).

Capillary zone electrophoresis of proteins applying ionic liquids for dynamic coating and as background electrolyte component

The use of ionic liquids in capillary electrophoresis, either as coating material or as components of the background electrolyte needs systematic standardization to set up optimal conditions. Excellent separation of the proteins was achieved using 1-ethyl-3-methylimidazolium tetrafluoroborate ([emim][BF4]) or 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]) ionic liquids using the properly made ionic-liquid-water binary mixtures for the experiments. The binary mixture has a distinctly stable and well perceptible low pH, which depends on the concentration of the ionic liquid, and on the preparation time of the mixture. Optimal conditions for the electrophoretic separation were obtained upon a multivariate analysis of the experimental parameters (applied voltage, migration time, concentration, and type of the ionic liquid). The standardized condition provides a low electroendosmotic flow toward the anode, which, however, did not hinder the proteins to migrate toward the cathode. The migration of cytochrome c, lysozyme, myoglobin, trypsin, and apo-transferrin at a pH around 2, far below the isoelectric points of the proteins, showed RSD values of the migration times less than 7.5% and less than 6.5% when using [emim][BF4] or [bmim][BF4], respectively, either in run-to-run or day-to-day experiments. The determination of the extent of the EOF is not possible with the commonly used EOF markers, due to interaction with the ionic-liquid constituents. The interaction of the ionic liquids with the proteins influences the migration order in zone electrophoresis. This method has been applied successfully for the analyses of real biological samples such as proteins from egg whites and human tears.

Deep eutectic solvent-based headspace single-drop microextraction of polycyclic aromatic hydrocarbons in aqueous samples

An improved deep eutectic solvent (DES)-based headspace single-drop microextraction procedure has been developed as a green procedure for gas chromatography-mass spectrometric analysis of polycyclic aromatic hydrocarbons (PAHs) in aqueous samples. The stability of the micro-drop was significantly improved using a DES as an extraction phase and a bell-shaped tube as a supporter. These strategies helped to perform the extraction process in higher temperatures and stirring rates. Finally, the back-extraction of the analytes into a proper solvent that is compatible with the chromatography system was applied. The efficacy of the independent variables on the extraction efficiency was evaluated via chemometric methods in two steps. The best result was obtained with choline chloride-oxalic acid at the molar ratio of 1:2, a stirring speed of 2000 rpm for 10 min as well as a sample temperature of 50 °C and with ionic strength prepared by using a 10% (w/v) NaCl. The method indicated a good linearity for the analytes (R²≥0.9989). Under optimal conditions, the analytical signal was linear in the range of 0.01-50 μg L^-1. Limit of detection (LOD) and limit of quantification (LOQ) were evaluated at the concentration levels of 0.003-0.012 and 0.009-0.049 μg L^-1, respectively. Intraday and interday precision for all targeted compounds was less than 7.2% and 11.3%, respectively. Consequently, the proposed procedure was efficiently applied to extract and analyze the 16 target compounds in real aqueous samples representing satisfactory recoveries (94.40-105.98%).

The Influence of Ionic Liquids on the Effectiveness of Analytical Methods Used in the Monitoring of Human and Veterinary Pharmaceuticals in Biological and Environmental Samples-Trends and Perspectives

Recent years have seen the increased utilization of ionic liquids (ILs) in the development and optimization of analytical methods. Their unique and eco-friendly properties and the ability to modify their structure allows them to be useful both at the sample preparation stage and at the separation stage of the analytes. The use of ILs for the analysis of pharmaceuticals seems particularly interesting because of their systematic delivery to the environment. Nowadays, they are commonly detected in many countries at very low concentration levels. However, due to their specific physiological activity, pharmaceuticals are responsible for bioaccumulation and toxic effects in aquatic and terrestrial ecosystems as well as possibly upsetting the body's equilibrium, leading to the dangerous phenomenon of drug resistance. This review will provide a comprehensive summary of the use of ILs in various sample preparation procedures and separation methods for the determination of pharmaceuticals in environmental and biological matrices based on liquid-based chromatography (LC, SFC, TLC), gas chromatography (GC) and electromigration techniques (e.g., capillary electrophoresis (CE)). Moreover, the advantages and disadvantages of ILs, which can appear during extraction and separation, will be presented and attention will be given to the criteria to be followed during the selection of ILs for specific applications.

Experimental study on explosion characteristics of ethanol gasoline-air mixture and its mitigation using heptafluoropropane

Ethanol gasoline is being widely used as a new environmentally friendly and energy-saving alternative energy, and the control/reduction of its fire/explosion risk has become an important aspect, not only for its production and storage, but also for its transport and application. This study aims to investigate the explosion characteristics of ethanol gasoline and its mitigation using heptafluoropropane in a restricted vessel. The flame propagation was visualized using a Phantom high-speed camera at 3000 fps, the explosion overpressure was measured using PCB pressure sensors, and the gas released from the vent was collected and analyzed using a gas chromatography-mass spectrometer. The results indicate that heptafluoropropane has a good suppression effect on the flame propagation speed and the explosion overpressure. The maximum overpressure of an ethanol gasoline explosion is approximately 456 kPa, and the overpressure reduction exceeds 60% when the concentration of heptafluoropropane addition is 10%, whereas an explosion is completely mitigated when the concentration of heptafluoropropane continuously increases. In addition, different flame colors during the mitigation process, such as blue, yellow, and purple, were observed and analyzed. The results of this study will be valuable for further understanding ethanol gasoline explosion mitigation and designing optimum heptafluoropropane explosion mitigation systems.

Rapid and Sensitive Analysis of Volatile Components of Different Parts of Clausena lansium by Ionic Liquid Based Headspace Gas Chromatography-Mass Spectrometry

A rapid and sensitive ionic liquid (IL) based headspace gas chromatography-mass spectrometry (HS-GC-MS) method was developed for analyzing volatile components in leaf, pericarp, and seed of Clausena lansium from different areas in Hainan Province, China. HS efficiencies were carefully investigated by using three ILs and water as matrix media. Extraction parameters, including equilibrium temperature, equilibrium time, and stirring rate had been evaluated and optimized by using an orthogonal design with OA₉(3³) table. Under the optimized condition of IL-based HS-GC-MS, only 100 mg of sample and 2 mL of [Bmim][BF₄] were needed to comprehensively and accurately analyze the volatile components in Clausena lansium. By utilizing a cluster analysis, six clusters were obtained for ninety components. This method was simpler, more rapid, and more sensitive when compared with previously reported methods for analyzing and identifying volatile components in Clausena lansium. The results may provide a theoretical basis for further exploitation of Clausena lansium.