Thin layer chromatography coupled with electrospray ionization mass spectrometry for direct analysis of raw samples

Improved Point-of-Care Mass Spectrometry Analysis with Thin-Layer Chromatography-Based Two-Dimensional Separation and Spray Ionization

Point-of-care testing (POCT) involves administering rapid on-site analysis to provide fast biochemical testing results. POCT reduces delays in clinical decision-making and eliminates the need to transport and prepare clinical samples for immediate diagnosis or clinical intervention by healthcare professionals. Herein, a novel methodology integrating thin-layer chromatography-based two-dimensional separation with miniature mass spectrometry was developed for rapid on-site clinical analysis. As a proof-of-concept demonstration, γ-aminobutyric acid, 2-hydroxyglutarate, and N-acetyl-l-aspartic acid, which are widely known as biomarkers for brain gliomas, were selected as model analytes for method development and validation. The proposed approach exhibited satisfactory analytical performance, with 1 ng/mL limits of detection, 2 ng/mL limits of quantitation, and recoveries in the range of 85.9-107.2%. Additionally, on-TLC derivatization and reactive spray ionization strategies were utilized to enhance the mass spectrometric signals compared to underivatized analysis. This method was applied to analyze clinical samples, showcasing its attractive potential outside the laboratory.

Thin layer chromatography/desorption flame-induced atmospheric pressure chemical ionization/mass spectrometry for the analysis of volatile and semi-volatile mixtures

Flame-induced atmospheric pressure chemical ionization (FAPCI) has been used to directly characterize chemical compounds on a glass rod and drug tablet surfaces. In this study, FAPCI was further applied to interface thin layer chromatography (TLC) and mass spectrometry (MS) for mixture analysis.

METHODS

A micro-sized oxyacetylene flame was generated using a small concentric tube system. Hot gas flow and primary reactive species from the micro-flame were directed toward a developed TLC gel plate to thermally desorb and ionize analytes on the gel surface. The resulting analyte ions subsequently entered the MS inlet for detection.

RESULTS

A 1-1.5-mm-wide light-brown line was observed on the TLC plate after the desorption FAPCI/MS (DFAPCI/MS) analysis, revealing that the gel surface withstood a high temperature from the impact of the micro-flame. Volatile and semi-volatile chemical compounds, including amine and amide standards, drugs, and aromatherapy oils, were successfully desorbed, ionized, and detected using this TLC/DFAPCI/MS. The limit of detection of TLC-DFAPCI/MS was determined to be 5 ng/spot for dibenzylamine and ethenzamide.

CONCLUSIONS

TLC/DFAPCI/MS is one of the simplest TLC-MS interfaces showing the advantages such as low costs and an easy set up. The technique is useful for characterizing thermally stable volatile and semi-volatile compounds in a mixture.

Review of Thin-Layer Chromatography Tandem with Surface-Enhanced Raman Spectroscopy for Detection of Analytes in Mixture Samples

In the real world, analytes usually exist in complex systems, and this makes direct detection by surface-enhanced Raman spectroscopy (SERS) difficult. Thin layer chromatography tandem with SERS (TLC-SERS) has many advantages in analysis such as separation effect, instant speed, simple process, and low cost. Therefore, the TLC-SERS has great potential for detecting analytes in mixtures without sample pretreatment. The review demonstrates TLC-SERS applications in diverse analytical relevant topics such as environmental pollutants, illegal additives, pesticide residues, toxic ingredients, biological molecules, and chemical substances. Important properties such as stationary phase, separation efficiency, and sensitivity are discussed. In addition, future perspectives for improving the efficiency of TLC-SERS in real sample detecting are outlined.

Electrospray ionization mass spectrometry with wooden tips: A review

Electrospray ionization (ESI) is a powerful ionization technique in mass spectrometry (MS). There has been an increasing interest for the new development of ESI technique to extend its applications. ESI-MS with wooden tips (wooden-tip ESI-MS), an ESI technique invented in 2011, enabled not only new applications but also new insights into the ESI mechanism. In this review, the technical aspects of wooden-tip ESI-MS are described, the new features of wooden-tip ESI-MS for sampling and ionization of analytes are highlighted, and the important applications of wooden-tip ESI-MS in various fields in the past 10 years, including food safety, forensic investigation, environmental analysis, biomedical analysis and protein study, are summarized. The perspectives on the further development and applications of wooden-tip ESI-MS are also discussed.

Recent Advances in Combinations of TLC With MALDI and Other Desorption/Ionization Mass-Spectrometry Techniques

The combination of planar chromatography with desorption/ionization mass-spectrometry (MS) techniques provides chemists with unique tools for fast and simple separation of mixtures followed by the detection of analytes by the most powerful analytical method. Since its introduction in the early 1990s, thin-layer chromatography (TLC)/matrix-assisted mass spectrometry (MALDI) has been used for the analysis of a wide range of analytes, including natural and synthetic organic compounds. Nowadays, new desorption/ionization approaches have been developed and applied in conjunction with planar chromatography competing with MALDI. This review covers recent developments in the combination of TLC with various desorption/ionization MS methods which were made in recent several years.

Direct coupling of solid phase microextraction with electrospray ionization mass spectrometry: A Case study for detection of ketamine in urine

Electrospray ionization mass spectrometry (ESI-MS) is a commonly used technique for analysis of various samples. Solid phase microextraction (SPME) is a simple and efficient technique that combines both sampling and sample preparation into one consolidated step, preconcentrating extracted analytes for ultra-sensitive analysis. Historically, SPME has been coupled with chromatography-based techniques for sample separation prior to analysis, however more recently, the chromatographic step has been omitted, with the SPME device directly coupled with the mass spectrometer. In this study, direct coupling of SPME with ESI-MS was developed, and extensively validated to quantitate ketamine from human urine, employing a practical experimental workflow and no extensive hardware modification to the equipment. Among the different fibers evaluated, SPME device coated with C₁₈/benzenesulfonic acid particles was selected for the analysis due to its good selectivity and signal response. Different approaches, including desorption spray, dripping, desorption ESI and nano-ESI were attempted for elution and ionization of the analytes extracted using the SPME fibers. The results showed that the desorption spray and nano-ESI methods offered better signal response and signal duration than the others that were evaluated. The analytical performance of the SPME-nano-ESI-MS setup was excellent, including limit of detection (LOD) of 0.027 ng/mL, limit of quantitation (LOQ) of 0.1 ng/mL, linear range of 0.1-500.0 ng/mL (R² = 0.9995) and recoveries of 90.8-109.4% with RSD 3.4-10.6% for three validation points at 4.0, 40.0 and 400.0 ng/mL, far better than the performance of conventional methods. The results herein presented, demonstrated that the direct coupling of SPME fibers with ESI-MS-based systems allowed for the simple and ultra-sensitive determination of analytes from raw samples such as human urine.

Coupling of micro-solid-phase extraction and internal extractive electrospray ionization mass spectrometry for ultra-sensitive detection of 1-hydroxypyrene and papaverine in human urine samples

Quantification of ultra-trace analytes in complex biological samples using micro-solid-phase extraction followed by direct detection with internal extractive electrospray ionization mass spectrometry (μSPE-iEESI-MS) was demonstrated. 1-Hydroxypyrene (1-OHP) and papaverine at attomole levels in human raw urine samples were analyzed under negative and positive ion detection mode, respectively. The μSPE was simply prepared by packing a disposable syringe filter with octadecyl carbon chain (C18)-bonded micro silica particles, which were then treated as the "bulk sample" after the analytes were efficiently enriched by the C18 particles. Under the optimized experimental conditions, the analytes were readily eluted by isopropanol/water (80/20, V/V) at a high voltage of ± 4.0 kV, producing analyte ions under ambient conditions. The limit of detection (LOD) was 0.02 pg/L (9.2 amol) for 1-hydroxypyrene and 0.02 pg/L (5.9 amol) for papaverine. The acceptable linearity (R² > 0.99), signal stability (RSD ≤ 10.7%), spike recoveries (91-95%), and comparable results for real urine samples were also achieved, opening up possibilities for quantitative analysis of trace compounds (at attomole levels) in complex bio-samples. Graphical abstract.

High-throughput polymer tip-electrospray ionization mass spectrometry for enhanced detection of neopterin and biopterin in clinical urine samples

Urinary biopterin (Bio) and neopterin (Neo) are important markers for clinical diagnosis of hyperphenylalaninemia. Herein, we developed a high-throughput analysis method based on electrospray ionization mass spectrometry (ESI-MS) with polymer tips for the rapid quantitative detection of Bio and Neo in clinical urine samples. Different polymer tips were investigated. It is found that the best detection sensitivity was achieved with hydrophobic polymer tip, ie, polyethylene tips. The high-throughput polymer tip-ESI-MS method allowed a rapid analysis speed at ~40 seconds per sample. The limits of quantification (LOQ) (S/N ≥ 10) for the detection of Bio and Neo were improved to be 5.0 ng/mL. Acceptable relative standard deviation (RSD) values for Neo and Bio were measured to be 12.2% and 13.4% for direct measurement of Bio and Neo in raw urine samples, respectively. Furthermore, Bio and Neo were directly quantified from 18 clinical urine samples by presented method. The ratios of urinary Bio-to-Neo were analyzed for diagnosis of hyperphenylalaninemia. The results demonstrated that the present polymer tip-ESI-MS method is a promising strategy for the rapid analysis of clinical samples.

Electrostatic field-induced tip-electrospray ionization mass spectrometry for direct analysis of raw food materials

Rapid characterization of metabolites and risk compounds such as chemical residues and natural toxins in raw food materials such as vegetables, meats, and edible living plants and animals plays an important part in ensuing food quality and safety. To rapidly characterize the analytes in raw food materials, it is essential to develop in situ method for directly analyzing raw food materials. In this work, raw food materials including biological tissues and living samples were placed between an electrode and mass spectrometric (MS) inlet under a strong electrostatic field; analytes were rapidly induced to generate electrospray ionization (ESI) from the sample tip by adding a drop of solvent onto the sample. Therefore, the electrostatic field-induced tip-ESI-MS allows raw samples to avoid contacting high voltage, and thus this method has the advantage for in vivo analysis of food living plants and animals. Metabolite profiling, residues of pesticides and veterinary drugs, and natural toxins from raw food materials have been successfully detected. The analytical performances, including the linear ranges, sensitivity, and reproducibility, were investigated for direct sample analysis. The ionization mechanism of electrostatic field-induced tip-ESI was also discussed in this work.

Recent Development of Quality Control Methods for Herbal Derived Drug Preparations

Pharmaceutical industries should apply rigorous QC (quality control) to ensure the consistency, safety, and efficacy of their herbal derived drug-preparations. QC must be performed at every stage of the production line i.e. incoming raw materials, extractions, in-process control, finished products and keeping samples. Due to the complex nature of the chemical content of herbal drugs, two approaches to QC should be taken, that is quantitative determination of the selected marker(s) compound(s), and metabolite profiling. Contamination of herbal medicines by heavy metals, pesticides, toxic metabolites, microbial toxins, pathogenic microorganisms and other foreign matter should also be evaluated. A combination of chemical profiling and multivariate analysis (MVA) is recommended as the QC tool for the botanical identification method (BIM) of herbs, extracts, herb materials, and herbal drug preparations. Microscopic methods, DNA profiling or chemical marker(s) are not recommended for use as the sole BIM due to the lack of specificity. Only markers that meet certain criteria i.e. quality active (QA) markers can be utilized as a QC tool. The limit specification range of markers used as QC tools should be described in the analytical target profile (ATP). To gain reliable results of any analysis that has been performed at any QC laboratory, the analysis method must be validated according to the newest guidance. Sample detection limit of any toxic compound(s) should be lower than its cut-off value and MPL. The reliability of any results of analysis of a QC laboratory must be evaluated by using QC-samples for each series of measurements.

Analyte-substrate interactions at functionalized tip electrospray ionization mass spectrometry: Molecular mechanisms and applications

Conventional electrospray ionization mass spectrometry (ESI-MS) commonly uses capillary tip for sample introduction and ionization. In recent years, ESI-MS using noncapillary substrate tips has attracted growing interest as it allows separation and enrichment of analytes from complex samples due to analytes-substrate interactions. In this work, model mixtures and functionalized tips were employed to investigate the molecular mechanism of the analyte-substrate interactions. The mixtures were directly loaded on substrate tips, and then temporal responses of analytes were investigated by monitoring selected ion chromatogram (SIC) responses of each analyte. It is found that all analytes are sprayed out together when bulk solution loaded substrate surface and then sequential ionization of analytes were observed. Sequential ionization of analytes was affected by the analytes-substrate interactions which caused analytes of weaker-interaction to be faster moved and the analytes of stronger-interactions to be retained on the substrate. The main molecular mechanisms of analyte-substrate interactions were revealed to be hydrophobic interactions and electrostatic interactions. Furthermore, based on the mechanistic insights, functionalized tips were further applied for rapid extractive sampling of target analytes from complex samples with good analytical performances. Overall, this study on the mechanism and applications of analyte-substrate interactions is useful for understanding the fundamental principles and further developments of functionalized tip electrospray ionization (TESI).

HPTLC-FLD-SERS as a facile and reliable screening tool: Exemplarily shown with tyramine in cheese

The serious cytotoxicity of tyramine attracted marked attention as it induced necrosis of human intestinal cells. This paper presented a novel and facile high performance thin-layer chromatography (HPTLC) method tailored for screening tyramine in cheese. Separation was performed on glass backed silica gel plates, using methanol/ethyl acetate/ ammonia (6/4/1 v/v/v) as the mobile phase. Special efforts were focused on optimizing conditions (substrate preparation, laser wavelength, salt types and concentrations) of surface enhanced Raman spectroscopy (SERS) measurements directly on plates after derivatization, which enabled molecule-specific identification of targeted bands. In parallel, fluorescent densitometry (FLD) scanning at 380</400 nm offered satisfactory quantitative performances (LOD 9 ng/zone, LOQ 17 ng/zone, linearity 0.9996 and %RSD 6.7). Including a quick extraction/cleanup step, the established method was successfully validated with different cheese samples, both qualitatively (straightforward confirmation) and quantitatively (recovery rates from 83.7 to 108.5%). Beyond this application, HPTLC-FLD-SERS provided a new horizon in fast and reliable screening of sophisticated samples like food and herb drugs, striking an excellent balance between specificity, sensitivity and simplicity.

Rapid determination of carbendazim in complex matrices by electrospray ionization mass spectrometry with syringe filter needle

The determination of pesticide residues is an indispensable task in controlling food safety and environment protection. Carbendazim is one of the extensive uses of pesticides in the agricultural industry. In this study, a simple method utilizing syringe filter has been applied as electrospray ionization emitter for mass spectrometric identification and quantification of carbendazim in complex matrices including soil, natural water, and fruit juice samples, which contain many insoluble materials. With online syringe filter of the complex samples, most of insoluble materials such as soil were excluded in spray ionization process due to the filter effect, and analytes were subsequently sprayed out from syringe needle for mass spectrometric detection. The pore sizes of filters and diameters of syringe needles also were investigated. The analytical performances, including the linear range (1-200 ng·mL^-1 ), limit of detection (0.2-0.6 ng·mL^-1 , S/N > 3), limit of quantitation (3.5-8.6 ng·mL^-1 , S/N > 10), reproducibility (6.4%-12.5%, n = 6), and recoveries (72.1%-91.0%, n = 6) were well acceptable for direct analysis of raw samples. Matrix effect for detection of carbendazim in soil samples also was experimentally investigated. This study demonstrated that syringe filter needle coupled with electrospray ionization mass spectrometry is a simple, efficient, and sensitive method for detection of pesticide residues in water, soil, and fruit juice for risk assessment.

Characterization and Analysis of Paper Spray Ionization of Organic Compounds

Paper spray ionization has arisen relatively recently as a complement and alternative to electro- and nanospray ionization with silica capillaries. A majority of the work in the present literature focuses on the chemical aspect of paper spray. In order to study the physical and phenomenological facet of its implementation, we measured current and voltage distributions of Taylor cones. To study transport phenomena on filter paper, we addressed the behavior of large, sparingly soluble tetraalkylammonium ions, which are usually used as mobility standards, in paper spray. The variation of intensity with time of monomers and dimers of these ions was measured with a differential mobility analyzer and compared with that produced by contamination in the paper. At the same time, we evaluated the proficiency of different paper spray techniques for protein analysis using nano spray as a reference. Experiments suggest that Taylor cones in paper spray are subject to hysteresis, whereas transport phenomena in the porous substrate notably affects the ionization of the sample. Additionally, we observed that paper spray tends to favor lower charge states in proteins. Graphical Abstract.

New approach for the quantification of metallic species in healthcare products based on optical switching of a Schiff base possessing ONO donor set

A new method is reported for the quantification of some metallic components of healthcare products utilizing a Schiff base chelator derived from 2-hydroxyacetophenone and ethanolamine. The Schiff base chelator recognizes some metallic species such as iron, copper and zinc (important components of some healthcare products), and cadmium (common contaminant in healthcare products) giving colorimetric/fluorimetric response. It coordinates with Fe²⁺/Fe³⁺ and Cu²⁺ ions via ONO donor set and switches the colour to bright red, green and orange, respectively. Similarly, it switches 'ON' a fluorometric response when coordinates with Zn²⁺ and Cd²⁺ ions. In the present approach, detailed studies on the colorimetric and fluorimetric response of ONO Schiff base is investigated in detail. The Job plot for the complexation of ONO switch with various metal ions suggested formation of 1:1 (metal-chelator) complex with Fe²⁺, Fe³⁺, and Cu²⁺ while 1:2 (metal-chelator) for Zn²⁺ and Cd²⁺ ions. The limit of detection, limit of quantification are 6.73, 18.0, 25.0, 0.65, 1.10μM and 27.0, 72.0, 100.0, 2.60 and 4.40μM for Fe²⁺, Fe³⁺, Cu²⁺, Zn²⁺ and Cd²⁺ ions, respectively. Under the optimized conditions, chelator was used for the quantification of important metals present in healthcare products via direct dissolution and furnace treatment during sample preparation. The results were found precise and accurate for both sample preparation techniques using the developed method.

Determination of Sulfonamides in Chicken Muscle by Pulsed Direct Current Electrospray Ionization Tandem Mass Spectrometry

A simple and rapid approach for the simultaneous detection of trace amounts of six sulfonamides in chicken muscle was developed using pulsed direct current electrospray ionization tandem mass spectrometry (pulsed-dc ESI-MS/MS). The pretreatment of chicken muscle samples consisted of two steps: acetonitrile extraction and n-hexane delipidation. Sulfonamides do not need to be derivatized or chromatographed prior to pulsed-dc ESI-MS/MS. The factors affecting the performance of pulsed-dc ESI-MS/MS were studied. Under optimum conditions, the quantitative performance of pulsed-dc ESI-MS/MS was validated according to European Union Decision 2002/657/EC, and the sensitivity of pulsed-dc ESI-MS/MS was 3 times higher than that of ultrahigh-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). The limits of detection obtained by pulsed-dc ESI-MS/MS were in the range of 0.07-0.11 μg/kg. The proposed method was simple, rapid, and sensitive, and was successfully used for quantitation and rapid screening of sulfonamides in real chicken muscle samples.

Medical swab touch spray-mass spectrometry for newborn screening of nicotine and cotinine in meconium

Newborn screening is one of public health concerns designed to screen infants shortly after birth. Prenatal exposure to tobacco smoke such as nicotine has been reported to affect babies. Levels of nicotine and cotinine in meconium were widely used to evaluate the tobacco exposure of foetuses during pregnancy in a polluted environment. In this study, medical swabs were applied by using touch spray-mass spectrometry (TS-MS) to collect meconium from newborn infants for detection of nicotine and cotinine. Parameters such as choice of spray solvents, solvent volume and collision energy for screening of nicotine and cotinine were optimized. The limits of detection, reproducibility and matrix effect for analysis of meconium were also investigated. In this study, the levels of nicotine and cotinine in 54 puerpera volunteers were screened by TS-MS and were validated by using traditional liquid chromatography-mass spectrometry. These results showed that medical swab TS-MS would be useful for newborn screening of nicotine and cotinine in meconium with high reproducibility, speed, sensitivity and specificity. The use of disposable medical swabs involves no sample preparation and no chromatographic separation, significantly reducing the cost and time required for screening a large number of clinical sample. Copyright © 2016 John Wiley & Sons, Ltd.

Thermal-assisted gasification injector for analyzing high-salt solution samples: a novel device developed for online coupling of liquid chromatography with direct analysis in real time mass spectrometry

A thermal-assisted gasification injector was designed for online coupling of liquid-chromatography to direct-analysis-in-real-time mass-spectrometry. The method can be used in analysis with an inorganic salt matrix and weak polar solvent.