Turnover rates in microorganisms by laser ablation electrospray ionization mass spectrometry and pulse-chase analysis

Biochemical processes rely on elaborate networks containing thousands of compounds participating in thousands of reaction. Rapid turnover of diverse metabolites and lipids in an organism is an essential part of homeostasis. It affects energy production and storage, two important processes utilized in bioengineering. Conventional approaches to simultaneously quantify a large number of turnover rates in biological systems are currently not feasible. Here we show that pulse-chase analysis followed by laser ablation electrospray ionization mass spectrometry (LAESI-MS) enable the simultaneous and rapid determination of metabolic turnover rates. The incorporation of ion mobility separation (IMS) allowed an additional dimension of analysis, i.e., the detection and identification of isotopologs based on their collision cross sections. We demonstrated these capabilities by determining metabolite, lipid, and peptide turnover in the photosynthetic green algae, Chlamydomonas reinhardtii, in the presence of ¹⁵N-labeled ammonium chloride as the main nitrogen source. Following the reversal of isotope patterns in the chase phase by LAESI-IMS-MS revealed the turnover rates and half-lives for biochemical species with a wide range of natural concentrations, e.g., chlorophyll metabolites, lipids, and peptides. For example, the half-lives of lyso-DGTS(16:0) and DGTS(18:3/16:0), t_1/2 = 43.6 ± 4.5 h and 47.6 ± 2.2 h, respectively, provided insight into lipid synthesis and degradation in this organism. Within the same experiment, half-lives for chlorophyll a, t_1/2 = 24.1 ± 2.2 h, and a 2.8 kDa peptide, t_1/2 = 10.4 ± 3.6 h, were also determined.     

Portable electrospray ionization mass spectrometry (ESI-MS) for analysis of contaminants in the field

Hitherto analysis of chemicals in the field using mass spectrometry (MS) has been limited to analysis of non-polar and thermally stabile organic compounds using either a direct gas leak or a membrane inlet as MS interface. Recently, Professor R. Graham Cooks’ group demonstrated that miniature mass spectrometers operating at elevated pressures (>0.13?Pa (1?·?10^?3??Torr)) can be combined with electrospray ionization (ESI) for analysis of polar as well as thermally labile organic compounds. We present a simple miniaturized ESI unit for analysis of small liquid samples using miniature mass spectrometry. The ESI unit operates without pumps and supplementary sheath gases, which makes it very simple to handle in the field. 20–30?µL of sample solution is simply dropped into a small cavity in the ESI unit, where after the spray is initiated by applying high voltage to it. The miniaturized ESI unit was tested in combination with a miniature mass spectrometer (the Mini 10 developed by Professor R. Graham Cooks, Purdue University, IN) and we found that common herbicides (Atrazine, Prometryne, Terbutryne and Triadimefone) could be detected with detection limits around 1?mg?L^?1 and with a quantitative reproducibility of +/?30%. These characteristics, although high for environmental samples, are comparable to detection limits obtained with other ESI units used with miniature mass spectrometers and represent an early step forward towards a future field instrument. A major advantage of the capillary spray cell is its direct compatibility with micro extraction techniques for sample pre-concentration.     

Parametric evaluation of laser ablation and ionization time-of-flight mass spectrometry with ion guide cooling cell

A novel laser ablation and ionization time-of-flight mass spectrometer has been used for direct elemental analysis of alloys. The system was incorporated with an ion guide cooling cell to reduce the kinetic energy distribution for the purpose of better resolution. Parametric studies have been conducted on the system with respect to the buffer gas pressure and the distance from sample to the nozzle to obtain the maximal signal intensities. In order to obtain satisfactory relative sensitivity coefficients (RSC) for different elements, the influence of the laser irradiance, nozzle voltage, rf frequency and voltage of the hexapole were also investigated. Under the optimized conditions, the RSC of different elements were available for direct semi-quantitative analysis. The mass resolving power (FWHM) of the spectrometer was approximately 7000 (m/Δm) and the limit of detection (LOD) was 10^− 6 g/g.     

A laser desorption ionization mass spectrometry investigation of triarylboranes and tri-9-anthrylborane photolysis products

Laser desorption ionization (LDI) mass spectra have been obtained for the photolysis products of tri-9-anthrylborane (TAB) in the solvents toluene, cyclohexene, and tetrahydrofuran; and for the solid triarylboranes: TAB, trimesitylborane (TMB), and tri-(2,6-dimethylphenyl)borane (TXyB). The major single solution photolysis product of TAB is 9,9′-dianthryl. Other products are rationalized in terms of an anthrylborylene intermediate (AnthB:). LDI mass spectrometry of the triarylboranes yields molecular ions in good abundance, providing a simple and selective method of characterization. Fragmentation patterns in some cases are interpreted in terms of photochemical reactions prior to ionization.     

Progress of laser ionization mass spectrometry for elemental analysis — A review of the past decade

Mass spectrometry using a laser ionization source has played a significant role in elemental analysis. Three types of techniques are widely used: high irradiance laser ionization mass spectrometry is capable of rapid determination of elements in solids; single particle mass spectrometry is a powerful tool for single particle characterization; and resonance ionization mass spectrometry is applied for isotope ratio measurements with high sensitivity and selectivity. In this review, the main features of the laser ablation process and plasma characterization by mass spectrometry are summarized. Applications of these three techniques for elemental analysis are discussed.     

Direct analysis of herbal powders by pipette-tip electrospray ionization mass spectrometry

Conventional electrospray ionization mass spectrometry (ESI-MS) is widely used for analysis of solution samples. The development of solid-substrate ESI-MS allows direct ionization analysis of bulky solid samples. In this study, we developed pipette-tip ESI-MS, a technique that combines pipette tips with syringe and syringe pump, for direct analysis of herbal powders, another common form of samples. We demonstrated that various herbal powder samples, including herbal medicines and food samples, could be readily online extracted and analyzed using this technique. Various powder samples, such as Rhizoma coptidis, lotus plumule, great burdock achene, black pepper, Panax ginseng, roasted coffee beans, Fructus Schisandrae Chinensis and Fructus Schisandrae Sphenantherae, were analyzed using pipette-tip ESI-MS and quality mass spectra with stable and durable signals could be obtained. Both positive and negative ion modes were attempted and various compounds including amino acids, oligosaccharides, glycosides, alkaloids, organic acids, ginosensides, flavonoids and lignans could be detected. Principal component analysis (PCA) based on the acquired mass spectra allowed rapid differentiation of closely related herbal species.     

Desorption electrospray ionization mass spectrometry in the analysis of chemical food contaminants in food

Since its introduction, desorption electrospray ionization (DESI) mass spectrometry (MS) has been mainly applied in pharmaceutical and forensic analysis. We expect that DESI will find its way in many different fields, including food analysis. In this review, we summarize DESI developments aimed at controlling chemical contaminants in food. Data are given for analysis of pesticides, natural toxins, veterinary drugs, food additives, adulteration, packaging migrants, and for applications of food forensics.We discuss practical aspects of DESI, including its strengths and weaknesses, highlighting specific features of performing chemical reactions during the desorption/ionization process in order to enhance sensitivity and selectivity.Finally, we discuss the position of DESI with respect to current food-analysis regulation and legislation. We envisage that DESI can be a rapid, qualitative or semi-quantitative, screening tool, ultimately being applied on site prior to sampling and transport of samples to food-control laboratories.     

Rapid analysis of raw solution samples by C18 pipette-tip electrospray ionization mass spectrometry

A C18 pipette-tip electrospray ionization mass spectrometry technique was developed for rapid analysis of raw solution samples. In this technique, a C18 pipette tip was employed for rapid purification and enrichment of analytes in raw sample solutions. The adsorbed analytes were eluted by solvents supplied by a syringe and a syringe pump, and a high voltage was applied onto the syringe needle to induce electrospray ionization at the pipette tip end for mass spectrometric analysis. This technique is simple, easy to assemble, enables generation of stable and reproducible signals, and can be conveniently used for qualitative and quantitative analysis of raw solution samples. Analysis by the technique only involved simple sample preparation procedures followed by direct mass spectrometric detection, all of which could be completed within minutes, while the analytical performances of the technique, including the limit of detection, limit of quantitation, liner range, accuracy and precision, were comparable to those by conventional methods.     

Coffee-ring effects in laser desorption/ionization mass spectrometry

This report focuses on the heterogeneous distribution of small molecules (e.g. metabolites) within dry deposits of suspensions and solutions of inorganic and organic compounds with implications for chemical analysis of small molecules by laser desorption/ionization (LDI) mass spectrometry (MS). Taking advantage of the imaging capabilities of a modern mass spectrometer, we have investigated the occurrence of “coffee rings” in matrix-assisted laser desorption/ionization (MALDI) and surface-assisted laser desorption/ionization (SALDI) sample spots. It is seen that the “coffee-ring effect” in MALDI/SALDI samples can be both beneficial and disadvantageous. For example, formation of the coffee rings gives rise to heterogeneous distribution of analytes and matrices, thus compromising analytical performance and reproducibility of the mass spectrometric analysis. On the other hand, the coffee-ring effect can also be advantageous because it enables partial separation of analytes from some of the interfering molecules present in the sample. We report a “hidden coffee-ring effect” where under certain conditions the sample/matrix deposit appears relatively homogeneous when inspected by optical microscopy. Even in such cases, hidden coffee rings can still be found by implementing the MALDI-MS imaging technique. We have also found that to some extent, the coffee-ring effect can be suppressed during SALDI sample preparation.     

Frontiers in elemental analysis by mass spectrometry

New developments in inductively coupled plasma mass spectrometry (ICP-MS) and laser desorption-time-of-flight mass spectrometry (LD-TOF-MS) for inorganic analysis are described. These include fundamental studies of the ion extraction, process in ICP-MS, development of a highly efficient nebulizer, isotope tracer studies, measurement of elemental speciation by liquid chromatography with ICP-MS detection and characterization of the structures of solids by ion association. The possibilities of determining inorganic species in solutions by electrospray MS are also described.     

Rapid detection of pesticide residues in Chinese herbal medicines by molecularly imprinted membrane electrospray ionization mass spectrometry

Chinese herbal medicines(CHMs) play an increasingly important role in the field of medicine and affects public health in the world.Although more and more strict has been employed to ensure the quality and safety of CHMs,pesticide residues in CHMs remain a serious issue and are the bottleneck for the global development of CHMs.In this work,we applied molecularly imprinted membrane electrospray mass spectrometry(MIM-ESI MS) for rapid detecting 4 classes of pesticide residues in CHMs,including organophosphorus(OPP),carbamates,pyrethroids and neonicotinoids in CHMs.Compared with our previous ambient ionization method MESI,MIM-ESI is capable of achieving a ～50-fold increase in the detection limit of conventional analytical methods owing to the specificity recognition and unique enrichment of MIM.The optimal experimental conditions were determined,and the method was further validated for its sensitivity and specificity.Our data showed that MIM-ESI MS is applicable for the direct quantitation of pesticide residues in CHMs.This detection technology may help to ensure the quality of CHMs in the future.     

Ultraviolet femtosecond laser ionization mass spectrometry

For this study, multiphoton ionization/mass spectrometry using an ultraviolet (UV) femtosecond laser was employed for the trace analysis of organic compounds. Some of the molecules, such as dioxins, contain several chlorine atoms and have short excited-state lifetimes due to a "heavy atom" effect. A UV femtosecond laser is, then, useful for efficient resonance excitation and subsequent ionization. A technique of multiphoton ionization using an extremely short laser pulse (e.g., <10 fs), referred to as "impulsive ionization," may have a potential for use in fragmentation-free ionization, thus providing information on molecular weight in mass spectrometry.     

Small molecule analysis using laser desorption/ionization mass spectrometry on nano-coated silicon with self-assembled monolayers

Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) is an emerging technique for the determination of the molecular weight of biomolecules and their non-covalent complexes without fragmentation. One problem with this technique is the use of excess amounts of matrices, which may produce intense fragment ions and/or clusters at low mass ranges between 1 and 800 Da. These fragments lead to interference, especially concerning the signals of small target molecules. Here, a simple, reusable, and quite inexpensive approach was demonstrated to improve the effectiveness of laser desorption/ionization mass spectrometry (LDI-MS) analysis, especially for small molecules, without using matrix molecules. In this study, substrates with controllable morphologies and thicknesses were developed based on the self-assembly of silane molecules on silicon surfaces using N-(3-trimethoxysilylpropyl)diethylenetriamine (TPDA) and octadecyltrichlorosilane (OTS) molecules. Prepared substrates with nano-overlayers were successfully used in the analysis of different types of small target molecules, namely acrivastine, l-histidine, l-valine, l-phenylalanine, l-arginine, l-methionine and angiotensin I. Our substrates exhibited clear peaks almost without fragmentation for all target molecules, suggesting that these surfaces provide a number of important advantages for LDI-MS analysis, such as ease of preparation, costs, reusability, robustness, easy handling and preventing fragmentation.     

Multiphoton ionization spectroscopy in surface analysis and laser desorption mass spectrometry

The application of resonance-enhanced multiphoton ionization (REMPI) spectroscopy for the ultrasensitive detection of molecules originating from laser desorption experiments performed on a variety of substrates is reviewed. Laser-induced desorption from surfaces is capable of producing intact gas-phase molecules, even from polar, non-volatile, high-molecular-weight and thermally labile substances. REMPI is a highly efficient and optically selective ionization method, which, coupled with laser desorption allows the direct chemical analysis of complex mixtures, without the need for previous sample purification and separation steps. The use of REMPI spectroscopy is discussed in two contexts: (1) for the direct chemical analysis of complex mixtures, e.g., environmental samples, by laser desorption/laser postionization mass spectrometry and (2) for measurements of internal state distribution of molecules laser-desorbed from sub-monolayers surface films to gain insight into the laser desorption mechanism.Presented at the 13th International Symposium on Microchemical Techniques (ISM), held in Montreux, Switzerland, May 16–20,1994     

Field-induced wooden-tip electrospray ionization mass spectrometry for high-throughput analysis of herbal medicines

This study demonstrates the first application of field-induced wooden-tip electrospray ionization (ESI) mass spectrometry (MS) for high-throughput analysis of herbal medicines. By application of an opposite and sample-contactless high voltage on the MS inlet rather than wooden tips, a high-throughput analysis device is easily set up, and a relatively fast analysis speed of 6 s per sample was successfully achieved. In addition, fast polarity switching between positive and negative ion detection mode is readily accomplished, which provides more complete chemical information for quality assessment and control of herbal medicines. By using the proposed method, various active ingredients present in different herbal medicines were rapidly detected, and the obtained mass spectra were served as the samples' fingerprints for tracing the origins, establishing the authenticity, and assessing the quality consistency and stability of herbal medicines. Our experimental results demonstrated that field-induced wooden-tip ESI-MS is a desirable method for high-throughput analysis of herbal medicines, with promising prospects for rapidly differentiating the origin, determining the authenticity, and assessing the overall quality of pharmaceuticals.     

Application of electrospray ionization mass spectrometry for studies of anionic σ-adducts of aromatic nitrocompounds

It has been found that anionic σ-adducts formed in the reactions of highly electrophilic nitroarenes with selected carbanions, alkoxide anions and amines can be transferred to the gas phase using an electrospray ion source and the resulting ions can be studied using various mass spectrometry techniques in the solvent-free environment. This method can also be used for estimating the relative equilibrium constants of the σ-adduct formation reactions in a liquid phase.     

Rapid authentication of Gastrodiae rhizoma by direct ionization mass spectrometry

In this study, direct ionization mass spectrometry (DI-MS) for rapid authentication of Gastrodiae rhizoma (known as Tianma in Chinese), a popular herbal medicine, has been developed. This method is rapid, simple and allows direct generation of characteristic mass spectra from the raw herbal medicines with the application of some solvents and a high voltage. The acquired DI-MS spectra showed that gastrodin, parishin B/parishin C and parishin, the major active components of Gastrodiae rhizoma, could be found only in genuine Gastrodiae rhizoma samples, but not in counterfeit samples, thus allowing rapid authentication of Gastrodiae rhizoma. Moreover, wild and cultivated Gastrodiae rhizoma could be classified and Gastrodiae rhizoma from different geographical locations could be differentiated based on their different intensity ratios of characteristic ions or principal component analysis (PCA). This method is simple, rapid, reproducible, and can be extended to analyze other herbal medicines.     

Gold nanoparticles bridging infra-red spectroscopy and laser desorption/ionization mass spectrometry for direct analysis of over-the-counter drug and botanical medicines

With a coating of gold nanoparticles (AuNPs), over-the-counter (OTC) drugs and Chinese herbal medicine granules in KBr pellets could be analyzed by Fourier Transform Infra-red (FT-IR) spectroscopy and Surface-assisted Laser Desorption/Ionization mass spectrometry (SALDI-MS). FT-IR spectroscopy allows fast detection of major active ingredient (e.g., acetaminophen) in OTC drugs in KBr pellets. Upon coating a thin layer of AuNPs on the KBr pellet, minor active ingredients (e.g., noscapine and loratadine) in OTC drugs, which were not revealed by FT-IR, could be detected unambiguously using AuNPs-assisted LDI-MS. Moreover, phytochemical markers of Coptidis Rhizoma (i.e. berberine, palmatine and coptisine) could be quantified in the concentrated Chinese medicine (CCM) granules by the SALDI-MS using standard addition method. The quantitative results matched with those determined by high-performance liquid chromatography with ultraviolet detection. Being strongly absorbing in UV yet transparent to IR, AuNPs successfully bridged FT-IR and SALDI-MS for direct analysis of active ingredients in the same solid sample. FT-IR allowed the fast analysis of major active ingredient in drugs, while SALDI-MS allowed the detection of minor active ingredient in the presence of excipient, and also quantitation of phytochemicals in herbal granules.     

Interferences and contaminants encountered in modern mass spectrometry

With the invention of electrospray ionization and matrix-assisted laser desorption/ionization, scientists employing modern mass spectrometry naturally face new challenges with respect to background interferences and contaminants that might not play a significant role in traditional or other analytical techniques. Efforts to continuously minimize sample volumes and measurable concentrations increase the need to understand where these interferences come from, how they can be identified, and if they can be eliminated. Knowledge of identity enables their use as internal calibrants for accurate mass measurements. This review/tutorial summarizes current literature on reported contaminants and introduces a number of novel interferences that have been observed and identified in our laboratories over the past decade. These include both compounds of proteinaceous and non-proteinaceous nature. In the supplemental data a spreadsheet is provided that contains a searchable ion list of all compounds identified to date.     

Development of a new multi-residue laser diode thermal desorption atmospheric pressure chemical ionization tandem mass spectrometry method for the detection and quantification of pesticides and pharmaceuticals in wastewater samples

A new solid phase extraction (SPE) method coupled to a high throughput sample analysis technique was developed for the simultaneous determination of nine selected emerging contaminants in wastewater (atrazine, desethylatrazine, 17β-estradiol, ethynylestradiol, norethindrone, caffeine, carbamazepine, diclofenac and sulfamethoxazole). We specifically included pharmaceutical compounds from multiple therapeutic classes, as well as pesticides. Sample pre-concentration and clean-up was performed using a mixed-mode SPE cartridge (Strata ABW) having both cation and anion exchange properties, followed by analysis by laser diode thermal desorption atmospheric pressure chemical ionization coupled to tandem mass spectrometry (LDTD-APCI-MS/MS). The LDTD interface is a new high-throughput sample introduction method, which reduces total analysis time to less than 15 s per sample as compared to minutes with traditional liquid-chromatography coupled to tandem mass spectrometry (LC–MS/MS). Several SPE parameters were evaluated in order to optimize recovery efficiencies when extracting analytes from wastewater, such as the nature of the stationary phase, the loading flow rate, the extraction pH, the volume and composition of the washing solution and the initial sample volume. The method was successfully applied to real wastewater samples from the primary sedimentation tank of a municipal wastewater treatment plant. Recoveries of target compounds from wastewater ranged from 78% to 106%, the limit of detection ranged from 30 to 122 ng L⁻¹ while the limit of quantification ranged from 90 to 370 ng L⁻¹. Calibration curves in the wastewater matrix showed good linearity (R² ≥ 0.991) for all target analytes and the intraday and interday coefficient of variation was below 15%, reflecting a good precision.