Bipolar Mass Spectrometry of Labile Coordination Complexes, Redox Active Inorganic Compounds, and Proteins Using a Glass Nebulizer for Sonic-Spray Ionization

In this study, we report on the development of a novel nebulizer configuration for sonic-spray ionization (SSI) mass spectrometry (MS), more specifically for a version of SSI that is referred to as Venturi easy ambient sonic-spray ionization (V-EASI) MS. The developed nebulizer configuration is based on a commercially available pneumatic glass nebulizer that has been used extensively for aerosol formation in atomic spectrometry. In the present study, the nebulizer was modified in order to achieve efficient V-EASI-MS operation. Upon evaluating this system, it has been demonstrated that V-EASI-MS offers some distinct advantages for the analysis of coordination compounds and redox active inorganic compounds over the predominantly used electrospray ionization (ESI) technique. Such advantages, for this type of compounds, are demonstrated here for the first time. More specifically, a series of labile heptanuclear heterometallic [Cu^II ₆Ln^III] clusters held together with artificial amino acid ligands, in addition to easily oxidized inorganic oxyanions of selenium and arsenic, were analyzed. The observed advantages pertain to V-EASI appearing to be a “milder” ionization source than ESI, not requiring electrical potentials for gas phase ion formation, thus eliminating the possibility of unwanted redox transformations, allowing for the “simultaneous” detection of negative and positive ions (bipolar analysis) without the need to change source ionization conditions, and also not requiring the use of syringes and delivery pumps. Because of such features, especially because of the absence of ionization potentials, EASI can be operated with minimal requirements for source parameter optimization. We observed that source temperature and accelerating voltage do not seem to affect labile compounds to the extent they do in ESI-MS. In addition, bipolar analysis of proteins was demonstrated here by acquiring both positive and negative ion mass spectra from the same protein solutions, without the need to independently adjust solution and source conditions in each mode. Finally, the simple and efficient operation of a dual-nebulizer configuration was demonstrated for V-EASI-MS for the first time.

Stability-Indicating High-Performance Thin-Layer Chromatographic Method for Simultaneous Estimation of the Active Pharmaceutical Ingredients Metolazone and Spironolactone

JPC – Journal of Planar Chromatography – Modern TLC - This work represents the validation of a stability-indicating thin-layer chromatographic technique for the simultaneous estimation...     

Development of mass spectrometric methods for detecting arsenic-glutathione complexes

It has been suggested recently that arsenic-glutathione (As-GSH) complexes play an important role in the methylation of arsenic. The present study describes the development of high-performance liquid chromatography (HPLC)-electrospray tandem mass spectrometry (ES-MS/MS), operated in the selected reaction monitoring (SRM) mode, and HPLC-inductively coupled plasma mass spectrometry (ICP-MS) methods suitable for the sensitive and selective identification of four As-GSH complexes. Method optimization was carried out using a series of synthetically prepared standards, i.e., three As-GSH species containing trivalent arsenic: tri(glutamyl-cysteinyl-glycinyl)trithio-arsenite (ATG), di(glutamyl-cysteinyl-glycinyl)methyl-dithio-arsonite (MADG), and (ã-glutamyl-cysteinyl-glycinyl) dimethyl-thio-arsinite (DMAG), as well as one As-GSH species containing pentavalent As: dimethylthioarsinic acid-glutathione (DMTA^V-GSH). The collision induced dissociation behavior of these compounds was investigated in detail to identify optimum SRM transitions for each complex. Both methods were based on reversed-phase chromatography using gradient elution with methanol, formic acid, and water as solvents. The amount of methanol that was used with this HPLC method (up to 12% vol/vol) was compatible with ICP-MS, without the need of a specially adapted interface. Subsequently, these analytical methods were applied to carry out a preliminary investigation about the role of As-GSH complexes in the methylation of arsenite by methylcobalamin (CH₃B₁₂) in the presence of glutathione (GSH). For the first time, the complexes ATG, MADG, and trace amounts of DMAG were detected as products of this reaction.     

Precursor ion scanning for the non-targeted detection of individual arsenosugars in extracts of marine organisms

Arsenosugars are a group of arsenic compounds reported to be present in a wide variety of marine organisms. Numerous such compounds have been identified and characterized in marine organisms; however, unknown arsenosugar species may also be present. This indicates the need for an analytical technique suitable for their non-targeted detection. One such technique is tandem mass spectrometry operated in the precursor ion scanning mode. This technique is based on scanning for precursor ions that give specific product ions, characteristic of the compounds under investigation. In the present study two subgroups of arsenosugar species were examined, the oxo- and the thioarsenosugars, the CID behavior of which is well known from previous studies. In the case of the oxoarsenosugars characteristic product ions were observed at m/z 237 and 97, and for the thioarsenosugars at m/z 253 and 97. Validation of this approach was carried out by analyzing extracts of two commercial kelp powders with known contents of arsenosugar species. All arsenosugars reported to exist in these materials were detected successfully using the precursor ion scanning approach. The limits of detection for the oxo- and the thioarsenosugar species, and the selectivity and sensitivity of the method, strongly indicate the suitability of this approach for the non-targeted detection of arsenosugars in extracts of marine origin.     

Fingerprint analysis of Shankhpushpi for species discrimination by HPLC coupled with chemometric methods

Abstract

Shankhpushpi, traded in the Indian market is having different controversial botanical sources, that is, Convolvulus pluricaulis Choisy (Convulvulaceae), Clitoria ternatea Linn. (Papilionaceae), and Evolvulus alsinoides Linn. (Convulvulaceae). Simple, accurate and precise RP-HPLC-PDA method was established for quality assessment and discrimination of Shankhpushpi samples using chromatographic profiling method. In distinction to the routine method of quality assessment which uses single or dual marker peaks, all chromatographic data (retention times/variables) were used. Fifteen shankhpushpi samples were purchased from the market including authenticated samples of all three C. pluricaulis, C. ternatea, E. alsinoides. A total of 18 samples were analyzed by HPLC and the dataset was then treated with multivariate analyses like PCA and HCA by using MINITAB software. Thus, the developed method was useful in discriminating the Shankhpushpi samples and for the perseverance of quality control.     

Development and validation of a thin-layer chromatography-densitometric method for the quantitation of alliin from garlic (Allium sativum) and its formulations

A selective, precise, and accurate high-performance thin-layer chromatographic (HPTLC) method has been proposed for the analysis of garlic and its formulations for their alliin content. The method involves densitometric evaluation of alliin after resolving it by HPTLC on silica gel plates with n-butanol-acetic acid-water (6 + 2 + 2, v/v) as the mobile phase. For densitometric evaluation, peak areas were recorded at 540 nm after derivatizing the resolved bands with ninhydrin reagent. The relation between the concentration of alliin and corresponding peak areas was found to be linear within the range of 250 to 1500 ng/spot. The method was validated for precision (interday and intraday), repeatability, and accuracy. Mean recovery was 98.36%. The method was applied for the quantitation of alliin in bulbs of Allium sativum Linn. (garlic) and its formulations. The proposed TLC method was found to be precise, specific, sensitive, and accurate and can be used for routine quality control of garlic and its formulations.     

Differential scanning calorimetry and a thermogravimetric analysis of nanozirconia-based powder systems

Results obtained from differential scanning calorimetry and a thermogravimetric analysis of zirconia-based nanocrystalline powder systems are presented. Heating is found to cause intense mass loss that increases with increase in the MgO content. Differential scanning calorimetry has revealed that the total energy expended for reactions involved in the powder heating process increases with increase in the MgO content. The heated powders are characterized by desorption of water. For 10 wt. % MgO, residual nitrates are seen to decompose into NO₂, N₂O, or NO.     

Simultaneous Quantitation of Piperine and Piperlongumine in the Fruit of Piper longum Linn. by Validated High-Performance Thin-Layer Chromatography—Densitometric Method

JPC – Journal of Planar Chromatography – Modern TLC - The fruit of Piper longum Linn. (family: Piperaceae), known as pippali in India, is a reputed drug of Ayurveda (the Indian system...     

Hg(OTf)2-catalyzed vinylogous semi-pinacol rearrangement leading to 1,4-dihydroquinolines

An efficient method for the construction of dihydroquinoline derivatives possessing a quaternary carbon center is developed by an application of Hg(OTf)(2)-catalyzed vinylogous semi-pinacol-type rearrangement. The reaction was found to be specifically catalyzed by mercury salt and to proceed via a bicyclic aminal.