Optimization of direct analysis in real time (DART) linear ion trap parameters for the detection and quantitation of glucose

Synthetic dyes: A mass spectrometry approach and applications

Synthetic dyes are found in a wide variety of applications today, including but not limited to textiles, foods, and medicine. The analysis of these molecules is pertinent to several fields such as forensics, environmental monitoring, and quality control, all of which require the sensitivity and selectivity of analysis provided by mass spectrometry (MS). Recently, there has been an increase in the implementation of MS evaluation of synthetic dyes by various methods, with the majority of research thus far falling under electrospray ionization and moving toward direct ionization methods. This review covers an overview of the chemistry of synthetic dyes needed for the understanding of MS sample preparation and spectral results, current fields of application, ionization methods, and fragmentation trends and works that have been reported in recent years.

Direct analysis in real time-mass spectrometry for rapid quantification of five anti-arrhythmic drugs in human serum: application to therapeutic drug monitoring

Therapeutic drug monitoring (TDM) is necessary for the optimal administration of anti-arrhythmic drugs in the treatment of heart arrhythmia. The present study aimed to develop and validate a direct analysis in real time tandem mass spectrometry (DART–MS/MS) method for the rapid and simultaneous determination of five anti-arrhythmic drugs (metoprolol, diltiazem, amiodarone, propafenone, and verapamil) and one metabolite (5-hydroxy(OH)-propafenone) in human serum. After the addition of isotope-labeled internal standards and protein precipitation with acetonitrile, anti-arrhythmic drugs were ionized by DART in positive mode followed by multiple reaction monitoring (MRM) detection. The use of DART–MS/MS avoided the need for chromatographic separation and allowed rapid and ultrahigh throughput analysis of anti-arrhythmic drugs in a total run time of 30 s per sample. The DART–MS/MS method yielded satisfactory linearity (R² ≥ 0.9906), accuracy (86.1–109.9%), and precision (≤ 14.3%) with minimal effect of biological matrixes. The method was successfully applied to analyzing 30 clinical TDM samples. The relative error (RE) of the concentrations obtained by DART–MS/MS and liquid chromatography-tandem mass spectrometry (LC–MS/MS) was within ± 13%. This work highlights the potential usefulness of DART for the rapid quantitative analysis of anti-arrhythmic drugs in human serum and gives rapid feedback in the clinical TDM practices.

Direct analysis in real time coupled with quadrupole-Orbitrap high-resolution mass spectrometry for rapid analysis of pyrethroid preservatives in wooden food contact materials

A methodology is presented for the determination of four pyrethroid (PYR) preservatives in wooden food contact materials (FCMs) using direct analysis in real time (DART) coupled with quadrupole-Orbitrap high-resolution mass spectrometry (Q-Orbitrap HRMS). The sampling mode and critical parameters of the DART-Q-Orbitrap HRMS protocol were systematically investigated. Good linearity was achieved for the four analytes with correlation coefficients all greater than 0.99. The limits of detection (LODs) and limits of quantitation (LOQs) of the method were in the range of 0.04-0.20 mg kg^-1 and 0.10-0.50 mg kg^-1, respectively. The mean recoveries ranged from 72.1% to 82.7% with relative standard deviations (RSDs) from 5.2% to 11.8% at three spiked levels. The developed method was proved to be suitable for rapid screening of PYRs in complex wooden FCM samples to ensure product safety and consumer health.

Simultaneous determination of multiple components in cigarettes by mechanochemical extraction and direct analysis in real time mass spectrometry in minutes

A simple, rapid and high throughput analytical approach with combination of mechanochemical extraction (MCE) and direct analysis in real time mass spectrometry (DART-MS) analysis was developed for the simultaneous determination of multiple chemical components in cigarette fillers. Different kinds of substances including nicotine, cigarette alkaloids, carbohydrates, organic acids, humectants and other additives were successfully extracted using MCE and detected by high resolution DART-MS. Six solvents of various polarities were compared during MCE process and significant differences were observed. Different brands of cigarettes as well as standard research cigarette exhibited distinctive chemical features and DART-MS fingerprints. Principle component analysis showed clear differentiation among different cigarettes extracted with the same solvent and different solvent extracts of the same type of cigarette. The putative chemical formulas were proposed based on accurate m/z values with <10 ppm mass errors. The relative contents of nicotine and other identified substances were compared and significant differences were observed among cigarettes of different locations. The whole procedure of MCE combined with DART-MS only takes minutes from raw cigarette fillers to obtaining the semi-quantitative results. The operation is simple and high throughput, providing an efficient method to analyze cigarette composition, and to establish a methodology to acquire the rapid cigarette fingerprints for quality control.

Studying Chemistry in Micro-compartments by Separating Droplet Generation from Ionization

Recent studies show that reactions inside micron-sized compartments (e.g., droplets, emulsions) can proceed at significantly accelerated rates and with different mechanisms compared to the same reactions in a macroscopic container. Many of these studies use electrospray ionization (ESI) to both generate droplets and to quantify, via mass spectrometry (MS), droplet reaction kinetics. The highly charged and rapidly evaporating droplets produced in ESI make it difficult to examine precisely the underlying cause for droplet-induced rate enhancements. Additionally, interpretation of the spectra from ESI-MS can be complicated by gas-phase ion-molecule and clustering reactions. Here, we use an approach where droplet generation is separated from ionization, in order to decouple the multiple possible sources of acceleration and to examine more closely the potential role of gas-phase chemistry. The production of sugar phosphates from the reaction of phosphoric acid with simple sugars (a reaction that does not occur in bulk solution but has recently been reported to occur in droplets) is measured using this approach to compare reactivity in droplets (i.e., with compartments) with that in the gas phase (i.e., without compartments). The same product ions that have been previously assigned to in droplet reactions are observed with and without compartmentalization. These results suggest that in some cases, gas-phase processes in the ionization region can potentially complicate the quantification and interpretation of accelerated reactions in droplets using ESI-MS (or one of its variants). In such cases, contributions from in-droplet chemistry cannot be ruled out, but we demonstrate that gas-phase processes can be a significant (and possibly dominant) reaction pathway. We suggest that future studies of rate acceleration in droplets be modified to better assess the potential for non-droplet-related processes. Graphical Abstract ᅟ.

Ambient desorption/ionization mass spectrometry: evolution from rapid qualitative screening to accurate quantification tool

In this article, some recent trends and developments in ambient desorption/ionization mass spectrometry (ADI-MS) are reviewed, with a special focus on quantitative analyses with direct, open-air sampling. Accurate quantification with ADI-MS is still not routinely performed, but this aspect is considered of utmost importance for the advancement of the field. In fact, several research groups are devoted to the development of novel and optimized ADI-MS approaches. Some key trends include novel sample introduction strategies for improved reproducibility, tailored sample preparation protocols for removing the matrix and matrix effects, and multimode ionization sources. In addition, there is significant interest in quantitative mass spectrometry imaging. Graphical abstract Conceptual diagram of the ambient desorption/ionization mass spectrometry approach with different desorption/ionization probes.

Ionization characteristics of glycosides by direct analysis in real time quadrupole-time of flight mass spectrometry

Glycosides were ionized via various different reactions including (de)protonation, molecular ion formation, ISD fragmentation, and the formation of adducts.

Rapid detection of bacterial endotoxins in ophthalmic viscosurgical device materials by direct analysis in real time mass spectrometry

Bacterial endotoxins are lipopolysaccharides bound to the bacterial cell wall and released when bacteria rupture or disintegrate. Possible contamination of endotoxin in ophthalmic devices can cause a painful eye inflammation or result in toxic anterior segment syndrome after cataract surgery. Measurement of bacterial endotoxin in medical device materials is difficult since endotoxin binds with polymer matrix and some of the materials are very viscous and non-water soluble, where traditional enzyme-based Limulus amebocyte lysate (LAL) assay cannot be applied. Here we propose a rapid and high throughput ambient ionization mass spectrometric (MS) method using direct analysis in real time (DART) for the evaluation of endotoxin contamination in medical device materials. Large and structurally complex endotoxin instantaneously breaks down into low-mass characteristic fragment ions using DART and is detected by MS in both positive and negative ion modes. This method enables the identification and separation of endotoxin from medical materials with a detection limit of 0.03 ng mL^-1 endotoxins in aqueous solution. Ophthalmic viscosurgical device materials including sodium hyaluronate (NaHA), non-water soluble perfluoro-n-octane (PFO) and silicone oil (SO) were spiked with different known concentrations of endotoxin and analyzed by DART MS, where the presence of endotoxin was successfully detected and featured small mass fragment ions were generated for NaHA, PFO and SO as well. Current findings showed the feasibility of measuring endotoxin contamination in medical device materials using DART-MS, which can lead to a one-step analysis of endotoxins in different matrices, avoiding any potential contamination during sample pre-treatment steps.

Effects of ion source operating parameters on direct analysis in real time of 18 active components from traditional Chinese medicine

Direct analysis in real time mass spectrometry (DART-MS) provides a new analytical method for traditional Chinese medicine (TCM). The present study investigated the effects of key ion source operating parameters on DART-MS analysis of various TCM active components. A total of 18 active components, including phenylpropanoids, alkaloids, saponins, flavones, volatile oils, and glycosides, were examined. For each substance, the peak area and signal-to-noise of its characteristic ions under different reagent gases and heater temperatures were compared. Based on the comparison, the relationships among chemical structures, ion source parameters and instrument responses were revealed. Finally, some suggestions about choosing reagent gas and heater temperature were proposed for types of TCM active substance, which offered a reference for the application of DART-MS on TCM analysis.

Differentiation of Disaccharide Isomers by Temperature-Dependent In-Source Decay (TDISD) and DART-Q-TOF MS/MS

Helium direct analysis in real time (He-DART) mass spectrometry (MS) of some compounds, polysaccharides, for example, usually tends to be challenging because of the occurrence of prominent in-source decay (ISD), which was considered as an undesired side reaction, as it complicated the resulting mass spectra. Our approach is to take advantage of an efficient and practical method termed the temperature-dependent ISD (TDISD) technique combined with fragmentation of the dehydrated dimers using DART Q-TOF tandem mass spectrometry for differentiation of disaccharide isomers. In this study, cross-ring cleavages and non-ovalent complexes were detected in the spectra of the saccharides. It was observed that the gas heater temperature had a significant effect on the absence or presence of signal in DART spectra. At high gas temperature, ions in high mass region began to appear. Based on the types of cross-ring cleavages and noncovalent complexes, disaccharide isomers with different linkage positions can be differentiated in both positive and negative ion modes at a lower DART gas temperature. Additionally, anomeric configurations were assigned on the basis of the relative abundance ratio of m/z 198:342 obtained by the comparison of the positive ion mode tandem mass spectrum of an α isomer dimer generated at higher DART gas temperature and that of the corresponding β one. In general, this method is easy, fast, effective, and robust for identifying disaccharide isomers.

Characterization of mustard seeds and paste by DART ionization with time-of-flight mass spectrometry

Direct analysis in real time (DART) is a novel technique with great potential for rapid screening analysis. The DART ionization method coupled with high-resolution time-of-flight mass spectrometry (TOF-MS) has been used for characterization of mustard seeds and table mustard. The possibility to use DART to analyse glucosinolates was confirmed on determination of sinalbin (4-hydroxybenzyl glucosinolate). The DART-TOF-MS method was optimized and validated. A set of samples of mustard seeds and mustard products was analyzed. High-performance liquid chromatography and DART-TOF-MS were used to determine glucosinolates in mustard seeds and compared. The correlation equation between these methods was DART = 0.797*HPLC + 6.987, R(2)  = 0.972. The DART technique seems to be a suitable method for evaluation of the quality of mustard seeds and mustard products.

Extraction-free in situ derivatisation of timosaponin AIII using direct analysis in real time TOF/MS

INTRODUCTION

Direct analysis in real time (DART) TOF/MS has been used for mass information of various non-polar phytochemicals in raw material with no sample preparation. However, low ionisation efficiency for polar compounds including glycosides limits its extensive use in the field of phytochemical analysis.

OBJECTIVE

In order to develop a direct analysis method for polar glycosides using in situ derivatisation, which improves ionisation efficiency of hydrophilic glycosides.

METHOD

Anemarrhena Rhizoma was used as a model plant targeting on Timosaponin AIII utilising a Dip-It module. Permethylation was applied to the powdered raw material with tetramethylammonium hydroxide in front of a DART ion source. Also, DART TOF/MS combined with permethylation was applied to timosaponin AIII standard solution to obtain the limit of detection (LOD).

RESULTS

In situ methylation of timosaponin AIII and Anemarrhena Rhizoma raw material were successfully used to ionise the glycoside. The LOD was found to be in the range of 2.4-4.8 ng for permethylated timosaponin AIII and this level is four times higher than the range of the underivatisation analysis. Direct analysis of permethylated timosaponin from Anemarrhena Rhizoma was also successfully performed.

CONCLUSION

A simple and quick derivatisation method with tetramethylammonium hydroxide was developed for the direct identification of a hydrophilic saponin from the plant tissue. Better ionisation efficiency conferred by in situ permethylation enabled ionisation of whole molecules of timosaponin AIII from the plant tissue. This simple analytical method will provide a solution to reduce tedious sample preparation steps, not only for non-polar but also hydrophilic natural products directly from the tissue.

Ambient surface analysis of organic monolayers using direct analysis in real time Orbitrap mass spectrometry

A better characterization of nanometer-thick organic layers (monolayers) as used for engineering surface properties, biosensing, nanomedicine, and smart materials will widen their application. The aim of this study was to develop direct analysis in real time high-resolution mass spectrometry (DART-HRMS) into a new and complementary analytical tool for characterizing organic monolayers. To assess the scope and formulate general interpretation rules, DART-HRMS was used to analyze a diverse set of monolayers having different chemistries (amides, esters, amines, acids, alcohols, alkanes, ethers, thioethers, polymers, sugars) on five different substrates (Si, Si3N4, glass, Al2O3, Au). The substrate did not play a major role except in the case of gold, for which breaking of the weak Au-S bond that tethers the monolayer to the surface, was observed. For monolayers with stronger covalent interfacial bonds, fragmentation around terminal groups was found. For ester and amide-terminated monolayers, in situ hydrolysis during DART resulted in the detection of ions characteristic of the terminal groups (alcohol, amine, carboxylic acid). For ether and thioether-terminated layers, scission of C-O or C-S bonds also led to the release of the terminal part of the monolayer in a predictable manner. Only the spectra of alkane monolayers could not be interpreted. DART-HRMS allowed for the analysis of and distinction between monolayers containing biologically relevant mono or disaccharides. Overall, DART-HRMS is a promising surface analysis technique that combines detailed structural information on nanomaterials and ultrathin films with fast analyses under ambient conditions.

Quality by design study of the direct analysis in real time mass spectrometry response

A mass spectrometry method has been developed using the Quality by Design (QbD) principle. Direct analysis in real time mass spectrometry (DART-MS) was adopted to analyze a pharmaceutical preparation. A fishbone diagram for DART-MS and the Plackett-Burman design were utilized to evaluate the impact of a number of factors on the method performance. Multivariate regression and Pareto ranking analysis indicated that the temperature, determined distance, and sampler speed were statistically significant (P < 0.05). Furthermore, the Box-Behnken design combined with response surface analysis was then employed to study the relationships between these three factors and the quality of the DART-MS analysis. The analytical design space of DART-MS was thus constructed and its robustness was validated. In this presented approach, method performance was mathematically described as a composite desirability function of the critical quality attributes (CQAs). Two terms of method validation, including analytical repeatability and method robustness, were carried out at an operating work point. Finally, the validated method was successfully applied to the pharmaceutical quality assurance in different manufacturing batches. These results revealed that the QbD concept was practical in DART-MS method development. Meanwhile, the determined quality was controlled by the analytical design space. This presented strategy provided a tutorial to the development of a robust QbD-compliant mass spectrometry method for industrial quality control.