What is the role of current mass spectrometry in pharmaceutical analysis?

The role of mass spectrometry (MS) has become more important in most application domains in recent years. Pharmaceutical analysis is specific due to its stringent regulation procedures, the need for good laboratory/manufacturing practices, and a large number of routine quality control analyses to be carried out. The role of MS is, therefore, very different throughout the whole drug development cycle. While it dominates within the drug discovery and development phase, in routine quality control, the role of MS is minor and indispensable only for selected applications. Moreover, its role is very different in the case of analysis of small molecule pharmaceuticals and biopharmaceuticals. Our review explains the role of current MS in the analysis of both small-molecule chemical drugs and biopharmaceuticals. Important features of MS-based technologies being implemented, method requirements, and related challenges are discussed. The differences in analytical procedures for small molecule pharmaceuticals and biopharmaceuticals are pointed out. While a single method or a small set of methods is usually sufficient for quality control in the case of small molecule pharmaceuticals and MS is often not indispensable, a large panel of methods including extensive use of MS must be used for quality control of biopharmaceuticals. Finally, expected development and future trends are outlined.

Identification of a nematic pair density wave state in Bi2Sr2CaCu2O8+x.

Electron-pair density wave (PDW) states are now an intense focus of research in the field of cuprate correlated superconductivity. PDWs exhibit periodically modulating superconductive electron pairing that can be visualized directly using scanned Josephson tunneling microscopy (SJTM). Although from theory, intertwining the d-wave superconducting (DSC) and PDW order parameters allows a plethora of global electron-pair orders to appear, which one actually occurs in the various cuprates is unknown. Here, we use SJTM to visualize the interplay of PDW and DSC states in Bi2Sr2CaCu2O8+x at a carrier density where the charge density wave modulations are virtually nonexistent. Simultaneous visualization of their amplitudes reveals that the intertwined PDW and DSC are mutually attractive states. Then, by separately imaging the electron-pair density modulations of the two orthogonal PDWs, we discover a robust nematic PDW state. Its spatial arrangement entails Ising domains of opposite nematicity, each consisting primarily of unidirectional and lattice commensurate electron-pair density modulations. Further, we demonstrate by direct imaging that the scattering resonances identifying Zn impurity atom sites occur predominantly within boundaries between these domains. This implies that the nematic PDW state is pinned by Zn atoms, as was recently proposed [Lozano et al., Phys. Rev. B 103, L020502 (2021)]. Taken in combination, these data indicate that the PDW in Bi2Sr2CaCu2O8+x is a vestigial nematic pair density wave state [Agterberg et al. Phys. Rev. B 91, 054502 (2015); Wardh and Granath arXiv:2203.08250].

Spatially Dependent in-Gap States Induced by Andreev Tunneling through a Single Electronic State.

By using low-temperature scanning tunneling microscopy and spectroscopy (STM/STS), we observe in-gap states induced by Andreev tunneling through a single impurity state in a low carrier density superconductor (NaAlSi). The energy-symmetric in-gap states appear when the impurity state is located within the superconducting gap. In-gap states can cross the Fermi level, and they show X-shaped spatial variation. We interpret the in-gap states as a consequence of the Andreev tunneling through the impurity state, which involves the formation or breakup of a Cooper pair. Due to the low carrier density in NaAlSi, the in-gap state is tunable by controlling the STM tip-sample distance. Under strong external magnetic fields, the impurity state shows Zeeman splitting when it is located near the Fermi level. Our findings not only demonstrate the Andreev tunneling involving single electronic state but also provide new insights for understanding the spatially dependent in-gap states in low carrier density superconductors.

Magnetic-Field Response and Giant Electric-Field Modulation of Cu2S.

Cu2S likely plays an important role in the sharp resistivity transition of LK-99. Nevertheless, this immediately arouses an intriguing question of whether the extraordinary room-temperature colossal magnetoresistance in the initial reports, which has been less focused, originates from Cu2S as well. To resolve this issue, we have systematically investigated the electrical transport and magnetotransport properties of near-stoichiometric Cu2S pellets and thin films. Neither Cu2S nor LK-99 containing Cu2S in this study was found to exhibit the remarkable magnetoresistance effect implied by Lee et al. This implies that Cu2S could not account for all of the intriguing transport properties of the initially reported LK-99, and the initially reported LK-99 samples might contain magnetic impurities. Moreover, based on the crystal-structure-sensitive electrical properties of Cu2S, we have constructed a piezoelectric-strain-controlled device and obtained a giant and reversible resistance modulation of 2 orders of magnitude at room temperature, yielding a huge gauge factor of 160,000.

Uncovering the Nonequilibrium Evolution Mechanism between Na2+2 δFe2- δ(SO4)3 Cathode and Impurities in the Na2SO4-FeSO4·7H2O Binary System for High-Voltage Sodium-Ion Batteries.

Sodium-ion batteries are increasingly recognized as ideal for large-scale energy storage applications. Alluaudite Na2+2 δFe2- δ(SO4)3 has become one of the focused cathode materials in this field. However, previous studies employing aqueous-solution synthesis often overlooked the formation mechanism of the impurity phase. In this study, the nonequilibrium evolution mechanism between Na2+2 δFe2- δ(SO4)3 and impurities by adjusting ratios of the Na2SO4/FeSO4·7H2O in the binary system is investigated. Then an optimal ratio of 0.765 with reduced impurity content is confirmed. Compared to the poor electrochemical performance of the Na2.6Fe1.7(SO4)3 (0.765) cathode, the optimized Na2.6Fe1.7(SO4)3@CNTs (0.765@CNTs) cathode, with improved electronic and ionic conductivity, demonstrates an impressive discharge specific capacity of 93.8 mAh g-1 at 0.1 C and a high-rate capacity of 67.84 mAh g-1 at 20 C, maintaining capacity retention of 71.1% after 3000 cycles at 10 C. The Na2.6Fe1.7(SO4)3@CNTs//HC full cell reaches an unprecedented working potential of 3.71 V at 0.1 C, and a remarkable mass-energy density exceeding 320 Wh kg-1. This work not only provides comprehensive guidance for synthesizing high-voltage Na2+2 δFe2- δ(SO4)3 cathode materials with controllable impurity content but also lays the groundwork of sodium-ion batteries for large-scale energy storage applications.

Nonlinear models based on leaf architecture traits explain the variability of mesophyll conductance across plant species.

Mesophyll conductance ( g m ${g}_{{\rm{m}}}$ ) describes the efficiency with which CO 2 ${\mathrm{CO}}_{2}$ moves from substomatal cavities to chloroplasts. Despite the stipulated importance of leaf architecture in affecting g m ${g}_{{\rm{m}}}$ , there remains a considerable ambiguity about how and whether leaf anatomy influences g m ${g}_{{\rm{m}}}$ . Here, we employed nonlinear machine-learning models to assess the relationship between 10 leaf architecture traits and g m ${g}_{{\rm{m}}}$ . These models used leaf architecture traits as predictors and achieved excellent predictability of g m ${g}_{{\rm{m}}}$ . Dissection of the importance of leaf architecture traits in the models indicated that cell wall thickness and chloroplast area exposed to internal airspace have a large impact on interspecific variation in g m ${g}_{{\rm{m}}}$ . Additionally, other leaf architecture traits, such as leaf thickness, leaf density and chloroplast thickness, emerged as important predictors of g m ${g}_{{\rm{m}}}$ . We also found significant differences in the predictability between models trained on different plant functional types. Therefore, by moving beyond simple linear and exponential models, our analyses demonstrated that a larger suite of leaf architecture traits drive differences in g m ${g}_{{\rm{m}}}$ than has been previously acknowledged. These findings pave the way for modulating g m ${g}_{{\rm{m}}}$ by strategies that modify its leaf architecture determinants.

Purification of recombinantly produced somatostatin-28 comparing hydrochloric acid and polyethyleneimine as E. coli extraction aids.

Peptides are used for diagnostics, therapeutics, and as antimicrobial agents. Most peptides are produced by chemical synthesis, but recombinant production has recently become an attractive alternative due to the advantages of high titers, less toxic waste and correct folding of tertiary structure. Somatostatin-28 is a peptide hormone that regulates the endocrine system, cell proliferation and inhibits the release of numerous secondary hormones in human body. It is composed of 28 amino acids and has one disulfide bond, which makes it to an optimal model peptide for a whole downstream purification process. We produced the peptide in the periplasm of E. coli using the CASPON™ technology, an affinity fusion technology system that enables high soluble expression of recombinant proteins and cleaves the fusion tag with a circularly permuted human caspase-2. Furthermore, purification of the products is straight forward using an established platform process. Two different case studies for downstream purification are presented, starting with either hydrochloric acid or polyethyleneimine as an extraction aid. After release of affinity-tagged somatostatin-28 out of E. coli's periplasm, several purification steps were performed, delivering a pure peptide solution after the final polishing step. The process was monitored by reversed-phase high-performance liquid chromatography as well as mass spectrometry to determine the yield and correct disulfide bond formation. Monitoring of impurities like host cell proteins, DNA and endotoxins after each downstream unit confirmed effective removal for both purification pathways.

Identification, synthesis, and characterization of an unprecedented N-(2-carboxyethyl) adduct impurity in an injectable ganirelix formulation.

Ganirelix, a peptide-based drug used to treat female infertility, has been in high market demand, which attracted generic formulation. A hitherto unknown impurity of ganirelix was observed in our formulation process, which reached ~0.3% in 6 months and led to a detailed investigation of its structure. In-depth analysis of ESI-MS/MS data of this impurity coupled with an artificial intelligence prediction tool led to a highly unusual putative structure, that is, N-(2-carboxyethyl)-ganirelix (NCE-GA), which was authenticated by chemical synthesis from ganirelix and NMR analysis and via corroborated HPLC and MS/MS data with the formulation-derived impurity.

A new HPLC method with multiple detection systems for impurity analysis and discrimination of natural versus synthetic cannabidiol.

Cannabidiol (CBD) is the main non-psychoactive phytocannabinoid derived from Cannabis sativa L. It is now an active pharmaceutical ingredient (API), given its usage in treating some types of pediatric epilepsy. For this reason, this compound requires a deep characterization in terms of purity and origin. Previous research work has shown two impurities in CBD samples from hemp inflorescences, namely, cannabidivarin (CBDV) and cannabidibutol (CBDB), while abnormal-cannabidiol (abn-CBD) has been described as the primary by-product that is generated from CBD synthesis. Both natural and synthetic CBD samples exhibit the presence of Δ9-tetrahydrocannabinol (Δ9-THC) and Δ8-THC. This study aimed to develop a new analytical method based on high-performance liquid chromatography (HPLC) with different detection systems to study the purity of CBD and to define its origin based on the impurity profile. In addition to the above-mentioned cannabinoids, other compounds, such as cannabigerovarin (CBGV), cannabigerol (CBG), cannabichromevarin (CBCV), and cannabichromene (CBC), were examined as potential discriminating impurities. Qualitative and quantitative analyses were carried out by UHPLC-HRMS and HPLC-UV/Vis, respectively. Principal component analysis was applied for statistical exploration. Natural CBD samples exhibited purities ranging between 97.5 and 99.7%, while synthetic samples were generally pure, except for three initially labeled as synthetic, revealing natural-derived impurities. To further confirm the origin of CBD samples, the presence of other two minor impurities, namely cannabidihexol (CBDH) and cannabidiphorol (CBDP), was assessed as unequivocal for a natural origin. Finally, an enantioselective HPLC analysis was carried out and the results confirmed the presence of the (-)-trans enantiomer in all CBD samples. In conclusion, the HPLC method developed represents a reliable tool for detecting CBD impurities, thus providing a clear discrimination of the compound origin.

Development of an SI-traceable N-terminal pro-B-type natriuretic peptide certified reference material using structure-based impurity-corrected isotope dilution mass spectrometry approaches.

N-Terminal pro-B-type natriuretic peptide (NT-proBNP) is a pivotal biomarker for the diagnosis and prognosis of heart failure (HF). However, no SI-traceable certified reference material (CRM) or reference measurement procedure (RMP) is available for this biomarker, and so clinical testing results obtained in different laboratories cannot be traced to a higher-order standard, leading to incomparable measurements. Protein hydrolysis and protein cleavage isotope dilution mass spectrometry (AAA-IDMS and PepA-IDMS) were used to develop a CRM. Structurally related impurities were identified by high-resolution mass spectrometry. The quantitative AAA-IDMS results were corrected according to the amino acid compositions of the impurities. Using PepA-IDMS, two peptides from the proteolyzed product were confirmed as signature peptides. To obtain traceable and accurate results, the signature peptides were quantified using impurity-corrected AAA-IDMS. The candidate NT-proBNP solution was denatured and enzymatically digested using the Glu-C endoproteinase. The released signature peptides were measured using an isotopic dilution approach. The homogeneity and stability of the candidate CRM were characterized, and their uncertainties were combined with the value assignment process. The developed CRM can be considered a unique SI-traceable NT-proBNP reference material and is expected to be used as a primary calibrator for matrix NT-proBNP CRM development.

Sources and control of impurity during one-pot enzymatic production of dehydroepiandrosterone.

Dehydroepiandrosterone (DHEA) has a promising market due to its capacity to regulate human hormone levels as well as preventing and treating various diseases. We have established a chemical esterification coupled biocatalytic-based scheme by lipase-catalyzed 4-androstene-3,17-dione (4-AD) hydrolysis to obtain the intermediate product 5-androstene-3,17-dione (5-AD), which was then asymmetrically reduced by a ketoreductase from Sphingomonas wittichii (SwiKR). Co-enzyme required for KR is regenerated by a glucose dehydrogenase (GDH) from Bacillus subtilis. This scheme is more environmentally friendly and more efficient than the current DHEA synthesis pathway. However, a significant amount of 4-AD as by-product was detected during the catalytic process. Focused on the control of by-products, we investigated the source of 4-AD and identified that it is mainly derived from the isomerization activity of SwiKR and GDH. Increasing the proportion of glucose in the catalytic system as well as optimizing the catalytic conditions drastically reduced 4-AD from 24.7 to 6.5% of total substrate amount, and the final yield of DHEA achieved 40.1 g/L. Furthermore, this is the first time that both SwiKR and GDH have been proved to be promiscuous enzymes with dehydrogenase and ketosteroid isomerase (KSI) activities, expanding knowledge of the substrate diversity of the short-chain dehydrogenase family enzymes. KEY POINTS: • A strategy of coupling lipase, ketoreductase, and glucose dehydrogenase in producing DHEA from 4-AD • Both SwiKR and GDH are identified with ketosteroid isomerase activity. • Development of catalytic strategy to control by-product and achieve highly selective DHEA production.

Determining recommended acceptable intake limits for N-nitrosamine impurities in pharmaceuticals: Development and application of the Carcinogenic Potency Categorization Approach (CPCA).

N-Nitrosamine impurities, including nitrosamine drug substance-related impurities (NDSRIs), have challenged pharmaceutical industry and regulators alike and affected the global drug supply over the past 5 years. Nitrosamines are a class of known carcinogens, but NDSRIs have posed additional challenges as many lack empirical data to establish acceptable intake (AI) limits. Read-across analysis from surrogates has been used to identify AI limits in some cases; however, this approach is limited by the availability of robustly-tested surrogates matching the structural features of NDSRIs, which usually contain a diverse array of functional groups. Furthermore, the absence of a surrogate has resulted in conservative AI limits in some cases, posing practical challenges for impurity control. Therefore, a new framework for determining recommended AI limits was urgently needed. Here, the Carcinogenic Potency Categorization Approach (CPCA) and its supporting scientific rationale are presented. The CPCA is a rapidly-applied structure-activity relationship-based method that assigns a nitrosamine to 1 of 5 categories, each with a corresponding AI limit, reflecting predicted carcinogenic potency. The CPCA considers the number and distribution of α-hydrogens at the N-nitroso center and other activating and deactivating structural features of a nitrosamine that affect the α-hydroxylation metabolic activation pathway of carcinogenesis. The CPCA has been adopted internationally by several drug regulatory authorities as a simplified approach and a starting point to determine recommended AI limits for nitrosamines without the need for compound-specific empirical data.

New limits proposed for the management of non-mutagenic impurities.

Multiple international guidelines exist that describe both quality and safety considerations for the control of the broad spectrum of impurities inherent to drug substance and product manufacturing processes. However, regarding non-mutagenic impurities (NMI) the most relevant ICH Q3A/B guidelines are not applicable during early phases of drug development leading to confusion about acceptable limits at this stage. Thus, there is need for more flexible approaches that ensure that patient safety remains paramount, while taking into consideration the limited duration of exposure. An EFPIA survey, which collected quantitative data from different types of studies applied to qualify impurities in accordance with ICH Q3A, shows that no toxicities could be attributed to any of the 467 impurities at any tested level in vivo. This data combined with earlier published toxicological datasets encompassing drug substances and intermediates, food related substances and chemicals provide convincing evidence that for NMIs, the application of a generic 5 mg/day limit for an exposure duration <6 months, and a 1 mg/day generic limit for life-long exposure, provides sufficient margins to ensure patient safety. Hence, application of these absolute limits to trigger qualification studies (instead of the relative limits described in Q3A/B), is considered warranted. This approach will prevent conduct of unnecessary dedicated impurity qualification studies and the resulting use of animals.

Simultaneous and trace-level quantification of four benzene sulfonate potential genotoxic impurities in doxofylline active pharmaceutical ingredients and tablets using high-performance liquid chromatography with ultraviolet detection.

In the production of doxofylline, the common occurrence of toxic p-toluene sulfonate generation prompted the development and validation of a method using HPLC with ultraviolet detection (HPLC-UV). This method is designed for detecting four potential genotoxic impurities (PGIs) present in both doxofylline drug substance and tablets, with a focus on the UV-absorbing group p-toluene sulfonate. The four impurities were methyl 4-methylbenzenesulfonate (PGI-1), ethyl 4-methylbenzenesulfonate (PGI-2), 2-hydroxyethyl 4-methylbenzenesulfonate (PGI-3), and 2-(4-methylphenyl)sulfonyloxyethyl 4-methylbenzenesulfonate (PGI-4). In this method, chromatographic separation was achieved using a Waters Symmetry C18 column (250 mm × 4.6 mm, 5 µm). The mobile phases consisted of 20% acetonitrile as mobile phase A and pure acetonitrile as mobile phase B, operating in gradient elution mode at a flow rate of 1.0 mL/min. According to the guidelines of the International Conference on Harmonization, it was determined that this method could quantify four PGIs at 0.0225 µg/mL in samples containing 60 mg/mL. The validated approach demonstrated excellent linearity (R2 > 0.999) across the concentration range of 30%-200% (relative to 0.075 µg/mL doxofylline) for the four PGIs. The accuracy of this method for the four PGIs ranged from 94.8% to 100.4%. The reverse-phase-HPLC-UV analytical method developed in this study is characterized by its speed and precision, making it suitable for the sensitive analysis of benzene sulfonate PGIs in doxofylline drug substances and tablets.

A novel liquid chromatography with quadrupole time-of-flight-tandem mass spectroscopy method for ultra-trace level identification and quantification of the genotoxic impurity 2,6-diamino-5-nitropyrimidin-4(3H)-one in valganciclovir hydrochloride.

In the present study, the main objective is to develop an analytical method for ultra-trace level measurement of 2,6-diamino-5-nitropyrimidin-4(3H)-one (DMNP) in valganciclovir hydrochloride (VAL) using liquid chromatography-quadrupole time-of-flight-tandem mass spectroscopy (LC-QTOF-MS/MS). In the early stages of guanine synthesis, DMNP is formed, and guanine is known to be the key starting material for the synthesis of VAL. Taking into consideration DMNP potential genotoxicity, this analytical method has been developed. This method is time saving and suitable for confirming the masses of parent and fragment ions by MS and MS/MS further fragmentation. An isocratic program and Acquity UPLC HSS cyano column (100 × 2.1 mm × 1.8 µm) were used to achieve optimal separation between VAL and the DMNP impurity. A 0.1% ammonia solution in Milli-Q water was used as mobile phase A, and methanol was used as mobile phase B in the ratio 90:10 v/v in isocratic mode. In accordance with the International Conference on Harmonization's requirements, the developed method was validated. The detection and quantification levels were found to be 0.028 and 0.083 ppm respectively. The DMNP impurity is linear from 0.083 to 1.245 ppm levels with correlation coefficient (R2 ) of 0.9960. The recoveries were found to be 97.0-107.9%.

Identification, trace level quantification, and in silico assessment of potential genotoxic impurity in Famotidine.

Potential genotoxic impurities in medications are an increasing concern in the pharmaceutical industry and regulatory bodies because of the risk of human carcinogenesis. To prevent the emergence of these impurities, it is crucial to carefully examine not only the final product but also the intermediates and key starting material (KSM) used in drug synthesis. During the related substances analysis of KSM of Famotidine, an unknown impurity in the range of 0.5-1.0% was found prompting the need for isolation and characterization due to the possibility of its to infiltrate into the final product. In this study, the impurity was isolated and characterized as 5-(2-chloroethyl)-3,3-dimethyl-3,4-dihydro-2H-1,2,4,6-thiatriazine 1,1-dioxide using multiple instrumental analysis, uncovering a structural alert that raises concern. Considering the potential impact of impurity on human health, an in silico genotoxicity assessment was established using Derek and Sarah tool in accordance with ICH M7 guideline. Furthermore, molecular docking and molecular dynamics simulation were performed to evaluate the specific interaction of the impurity with DNA. The findings reveal consistent interaction of the impurity with the dG-rich region of the DNA duplex and binding at the minor groove. Both in silico prediction and molecular dynamic study confirmed the genotoxic character of the impurity. The newly discovered impurity in famotidine has not been reported previously, and there is currently no analytical method available for its identification and control. A highly sensitive HPLC-UV method was developed and validated in accordance with ICH requirements, enabling quantification of the impurity at trace level in famotidine ensuring its safe release.

Reversal of Band-Ordering Leads to High Hole Mobility in Strained p-type Scandium Nitride.

Low hole mobility of nitride semiconductors is a significant impediment to realizing their high-efficiency device applications. Scandium nitride (ScN), an emerging rocksalt indirect band gap semiconductor, suffers from low hole mobility. Utilizing the ab initio Boltzmann transport formalism including spin-orbit coupling, here we show the dominating role of ionized impurity scattering in reducing the hole mobility in ScN thin films. We suggest a route to increase the hole mobility by reversing band ordering through strain engineering. Our calculation shows that the biaxial tensile strain in ScN lifts the split-off hole band above the heavy hole and light hole bands, leading to a lower hole-effective mass and increasing mobility. Along with the impurity scattering, the Fröhlich interaction also plays a vital role in the carrier scattering mechanism due to the polar nature of ScN. Increased hole mobility in ScN will lead to higher efficiencies in thermoelectric, plasmonics, and neuromorphic computing devices.

Identification and Structural Characterization of Degradation Products of Linagliptin by Mass Spectrometry Techniques.

As part of the development and production of pharmaceuticals, the purity of Active Pharmaceutical Ingredients stands as a fundamental parameter that significantly influences the quality, safety, and efficacy of the final drug product. Impurities in Active Pharmaceutical Ingredients are various unwanted substances that can appear during the whole manufacturing process, from raw materials to the final product. These impurities can stem from multiple sources, including starting materials, intermediates, reagents, solvents, and even degradation products resulting from exposure to environmental factors such as heat, light, or moisture. Their presence can potentially compromise the therapeutic effect of the drug, introduce unexpected side effects, or even pose safety risks to patients. This study aims to conduct the forced degradation of linagliptin and subsequently attempt to identify the resulting degradants. The degradation procedures were carried out in accordance with the guidelines of the International Committee for Harmonization. The degradation profile of linagliptin was investigated under various conditions, including acid hydrolysis, alkaline hydrolysis, oxidation, heat, and light exposure, utilizing ultra-performance liquid chromatography connected to a photo array detector. Identification and characterization of the degradation products were achieved using an ultra-performance liquid chromatography coupled with a single quadrupole detector mass spectrometer and also a liquid chromatography coupled with a high-resolution mass spectrometry. The identified degradation products demonstrate that linagliptin is particularly susceptible to degradation when exposed to acid and peroxide. Whereas, no significant degradation effects were observed under alkali, thermolytic, and photolytic conditions.

Facile Access to Solifenacin Impurity K: One-Step Synthesis and an HPLC-MS Method for Its Determination.

Solifenacin (SFC) is a potent muscarinic antagonist that effectively reduces bladder muscle contraction, thereby alleviating symptoms such as frequency of micturition and urgency. Oxidation of SFC leads to the formation of impurities like Impurity K. Effective analysis and control of this impurity is crucial for ensuring compliance with regulatory standards and safeguarding patient health. To address these challenges, we propose a novel one-step synthesis of Impurity K from SFC. Impurity K was synthesized using cerium(IV) ammonium nitrate (CAN) in water/acetonitrile as the solvent. Additionally, we describe a new HPLC-MS method for the detection of Impurity K in solifenacin succinate tablets.

Binding Energies and Optical Properties of Power-Exponential and Modified Gaussian Quantum Dots.

We examine the optical and electronic properties of a GaAs spherical quantum dot with a hydrogenic impurity in its center. We study two different confining potentials: (1) a modified Gaussian potential and (2) a power-exponential potential. Using the finite difference method, we solve the radial Schrodinger equation for the 1s and 1p energy levels and their probability densities and subsequently compute the optical absorption coefficient (OAC) for each confining potential using Fermi's golden rule. We discuss the role of different physical quantities influencing the behavior of the OAC, such as the structural parameters of each potential, the dipole matrix elements, and their energy separation. Our results show that modification of the structural physical parameters of each potential can enable new optoelectronic devices that can leverage inter-sub-band optical transitions.