Analytical and Bioanalytical Chemistry (v.408, #21)
Jacob Fraden: Handbook of modern sensors: physics, designs, and applications, 5th ed. by Gerald Urban (5667-5668).
Andreas Manz, Petra S. Dittrich, Nicole Pamme, Dimitri Iossifidis: Bioanalytical chemistry, 2nd ed. by Joachim Wegener (5669-5670).
Self-aliquoting micro-grooves in combination with laser ablation-ICP-mass spectrometry for the analysis of challenging liquids: quantification of lead in whole blood by Winfried Nischkauer; Frank Vanhaecke; Andreas Limbeck (5671-5676).
We present a technique for the fast screening of the lead concentration in whole blood samples using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). The whole blood sample is deposited on a polymeric surface and wiped across a set of micro-grooves previously engraved into the surface. The engraving of the micro-grooves was accomplished with the same laser system used for LA-ICP-MS analysis. In each groove, a part of the liquid blood is trapped, and thus, the sample is divided into sub-aliquots. These aliquots dry quasi instantly and are then investigated by means of LA-ICP-MS. For quantification, external calibration against aqueous standard solutions was relied on, with iron as an internal standard to account for varying volumes of the sample aliquots. The 208Pb/57Fe nuclide ratio used for quantification was obtained via a data treatment protocol so far only used in the context of isotope ratio determination involving transient signals. The method presented here was shown to provide reliable results for Recipe ClinChek® Whole Blood Control levels I–III (nos. 8840–8842), with a repeatability of typically 3 % relative standard deviation (n = 6, for Pb at 442 μg L−1). Spiked and non-spiked real whole blood was analysed as well, and the results were compared with those obtained via dilution and sectorfield ICP-MS. A good agreement between both methods was observed. The detection limit (3 s) for lead in whole blood was established to be 10 μg L−1 for the laser ablation method presented here. Graphical Abstract Micro-grooves are filled with whole blood, dried, and analyzed by laser ablation ICP-mass spectrometry. Notice that the laser moves in perpendicular direction with regard to the micro-grooves
Keywords: Laser ablation-ICP-MS; Whole blood analysis; Lead quantification; Dried-droplet laser ablation; Transient signals
Combined use of direct analysis in real-time/Orbitrap mass spectrometry and micro-Raman spectroscopy for the comprehensive characterization of real explosive samples by Maxime C. Bridoux; Adrián Schwarzenberg; Sébastien Schramm; Richard B. Cole (5677-5687).
is a research scientist at the Commissariat à l’Energie Atomique et aux énergies alternatives (CEA). He received his PhD in 2008 from the State University of New York at Albany in the field of environmental and analytical chemistry and completed his postdoctoral training from 2008 to 2012 at the School of Oceanography, University of Washington (UW). His personal research interests are the analytical aspects (chromatography and mass spectrometry) related to the detection of trace amounts of organic compounds for forensic and environmental applications. is an R&D scientist of the Plant Nutrition unit at the Centre Mondial d’Innovation (CMI) in Saint-Malo, France. His PhD thesis at the Pierre and Marie Curie University (UPMC) focused on the development of high-resolution mass spectrometry-based methods for the characterization and accurate identification of organophosphorus compounds and explosives. is a postdoctoral researcher at the Commissariat à l'Energie Atomique et aux énergies alternatives (CEA). During his postdoctoral research, he developed mass spectrometry-based methods (Orbitrap, LC-QQQ, FTICRMS, qToF) for the identification and the quantification of small organic molecules for forensics and environmental applications. is a professor at Sorbonne Universities, UPMC Univ. of Paris 6. He has worked as a researcher in the field of mass spectrometry since 1983. His activities include pioneering the development of anion attachment mass spectrometry, investigations into what determines charge state distributions in electrospray ionization mass spectrometry, characterization of the electrochemistry inherent to ESI, and development of novel matrixes for MALDI. He has edited two major books in the MS field concerning fundamentals and applications of ESI, and of MALDI. Direct Analysis in Real Time (DART™) high-resolution Orbitrap™ mass spectrometry (HRMS) in combination with Raman microscopy was used for the detailed molecular level characterization of explosives including not only the charge but also the complex matrix of binders, plasticizers, polymers, and other possible organic additives. A total of 15 defused military weapons including grenades, mines, rockets, submunitions, and mortars were examined. Swabs and wipes were used to collect trace (residual) amounts of explosives and their organic constituents from the defused military weapons and micrometer-size explosive particles were transferred using a vacuum suction-impact collection device (vacuum impactor) from wipe and swap samples to an impaction plate made of carbon. The particles deposited on the carbon plate were then characterized using micro-Raman spectroscopy followed by DART-HRMS providing fingerprint signatures of orthogonal nature. The optical microscope of the micro-Raman spectrometer was first used to localize and characterize the explosive charge on the impaction plate which was then targeted for identification by DART-HRMS analysis in both the negative and positive modes. Raman spectra of the explosives TNT, RDX and PETN were acquired from micrometer size particles and characterized by the presence of their characteristic Raman bands obtained directly at the surface of the impaction plate nondestructively without further sample preparation. Negative mode DART-HRMS confirmed the types of charges contained in the weapons (mainly TNT, RDX, HMX, and PETN; either as individual components or as mixtures). These energetic compounds were mainly detected as deprotonated species [M–H]−, or as adduct [M + 35Cl]−, [M + 37Cl]−, or [M + NO3]− anions. Chloride adducts were promoted in the heated DART reagent gas by adding chloroform vapors to the helium stream using an “in-house” delivery method. When the polarity was switched to positive mode, DART-HRMS revealed a very complex distribution of polymeric binders (mainly polyethylene glycols and polypropylene glycols), plasticizers (e.g., dioctyl sebacate, tributyl phosphate), as well as wax-like compounds whose structural features could not be precisely assigned. In positive mode, compounds were identified either as protonated molecules or ammonium adduct species. These results clearly demonstrate the complementarity of micro-Raman microscopy combined with DART-MS. The former technique provides structural information on the type of explosives present at the surface of the sample, whereas the latter provides not only a confirmation of the nature of the explosive charge but also useful additional information regarding the nature of the complex organic matrix of binders, plasticizers, polymers, oils, and potentially other organic additives and contaminants present in the sample. Combining these two techniques provides a powerful tool for the screening, comprehensive characterization, and differentiation of particulate explosive samples for forensic sciences and homeland security applications. Graphical Abstract Comprehensive characterization of explosive particles collected from swipe samples by micro-Raman and DART™-HRMS
Keywords: Direct Analysis in Real Time; Orbitrap MS; Raman microscopy; Real weapons; Explosives; Polymers
Determination of endocrine disrupting compounds in fish liver, brain, and muscle using focused ultrasound solid–liquid extraction and dispersive solid phase extraction as clean-up strategy by Oihana Ros; Asier Vallejo; Maitane Olivares; Nestor Etxebarria; Ailette Prieto (5689-5700).
is a PhD student in analytical chemistry with experience in the development of analytical methods in the field of environmental chemistry. She is currently working at the University of the Basque Country (UPV/EHU) developing new analytical strategies for the uptake evaluation of emerging organic pollutants by fishes. is lecturer at the Analytical Chemistry Department of the UPV/EHU. He has published more than 30 publications in the analytical chemistry field and at this time he is working in the development of analytical methods and passive sampling technologies for the determination of priority organic compounds in sludge and compost matrices. is lecturer at the Department of Analytical Chemistry of the faculty of Science and Technology of the UPV/EHU. She is an analytical chemist with experience in the development of analytical approaches for organic compounds in environmental chemistry and cultural heritage fields, and has published about 40 novel manuscripts in these areas. is Professor in the Department of Analytical Chemistry at the University of the Basque Country. He also works at the Plentzia Marine Station (PIE). His research interests are in the development of analytical methods and in environmental chemistry, especially focused on the fate and the effects of contaminants. is a permanent researcher at the Department of Analytical Chemistry of the UPV/EHU. Her research interest focuses on the development of analytical methods for organic pollutants and its application in environmental samples analysis. She has published about 50 manuscripts in this area, mainly on the development of extraction methods, based on novel and green extraction techniques This study describes a new method for the simultaneous extraction of several endocrine disrupting compounds, including alkylphenols (APs), estrogen, bisphenol-A (BPA) and one phthalate metabolite (mono-2-ethylhexyl ester, MEHP) in fish liver, brain, and muscle. Parameters affecting the extraction (extraction solvent and temperature) and the clean-up (dispersive phase nature and amount) steps were evaluated. The extraction was performed by means of focused ultrasound solid–liquid extraction (FUSLE) using 10 mL of n-hexane:acetone (50:50, v/v) for 5 min at ~0 °C, and the clean-up was done by means of dispersive solid phase extraction (dSPE) using 100 mg of ENVI-CARB and 100 mg of MgSO4 for the cleaning of brain and muscle extracts together with 100 mg of PSA in the case of liver extracts. Good apparent recoveries were obtained in the case of liver (62–132 %), brain (66–120 %), and muscle (74–129 %), relative standard deviation (RSD%) was always below 26 %, and the method detection limits (MDLs) were at low ng/g level. The developed method was applied to fish captured in Urdaibai estuary (Bay of Biscay) in December 2015, and the concentrations obtained were in the range MDL-1115 ng/g in brain, MDL-962 ng/g in muscle, and MDL-672 ng/g in liver. In general, the highest concentrations were measured in liver, followed by brain and muscle. In addition, diethylstilbestrol was only detected in fish brain. Graphical Abstract MS method scheme for the/MS method scheme for the determination of EDCs in fish liver, brain and muscle
Keywords: Endocrine disrupting compounds; Focused ultrasound solid–liquid extraction; Dispersive solid phase extraction; Biota; Fish
Hyperspectral backscatter imaging: a label-free approach to cytogenetics by Karsten Rebner; Edwin Ostertag; Rudolf W. Kessler (5701-5709).
Current techniques for chromosome analysis need to be improved for rapid, economical identification of complex chromosomal defects by sensitive and selective visualisation. In this paper, we present a straightforward method for characterising unstained human metaphase chromosomes. Backscatter imaging in a dark-field setup combined with visible and short near-infrared spectroscopy is used to monitor morphological differences in the distribution of the chromosomal fine structure in human metaphase chromosomes. The reasons for the scattering centres in the fine structure are explained. Changes in the scattering centres during preparation of the metaphases are discussed. FDTD simulations are presented to substantiate the experimental findings. We show that local scattering features consisting of underlying spectral modulations of higher frequencies associated with a high variety of densely packed chromatin can be represented by their scatter profiles even on a sub-microscopic level. The result is independent of the chromosome preparation and structure size. This analytical method constitutes a rapid, cost-effective and label-free cytogenetic technique which can be used in a standard light microscope. Graphical abstract Hyperspectral backscatter imaging for label-free characterization
Keywords: Spectral karyotyping; Label-free; Human metaphase chromosomes; Dark-field imaging; Scattered light spectroscopy; Visible and short near-infrared spectroscopy
An analytical approach for the non-invasive selection of consolidants in rubber artworks by Marcello Manfredi; Elettra Barberis; Antonio Rava; Tommaso Poli; Oscar Chiantore; Emilio Marengo (5711-5722).
The effectiveness of five polymeric materials for the long-term conservation and restoration of rubber artworks was evaluated by accelerated photo-oxidative degradation studies. Two different ethylene vinyl-acetate resins, generally used in industry and uncommon in conservation field, a new water-based polyurethane, and two ethylene butyl-acrylate resins were assessed for the consolidation of rubber. By monitoring their degradation along time with LED imaging coupled to statistics and Fourier transform infrared spectroscopy (FTIR), the polymeric materials with the best properties that ensure the protection and security of the artwork were identified. The degradation was performed in solar box simulating the light exposure in a museum, under controlled temperature at no more than 35 °C in order to exclude the thermal effects that could influence the ageing of polymers. The mechanical stress of the treated samples was also investigated. The spectroscopic analyses, the chromatic changes study, and the mechanical degradation were used as indicators of the consolidant stability, allowing the evaluation of the materials selected for the consolidation and conservation of rubber. The ethylene-vinyl acetate copolymers resulted the most stable and suitable for the conservation of rubber artworks. Lastly, the conservation treatment identified in this research was employed for the restoration of the contemporary artwork “Presagi di Birnam” made with bicycle inner tubes by the artist Carol Rama.
Keywords: Non-invasive methods; Polymers; Rubber restoration; Consolidants; LED imaging
Identification of absorbed components and metabolites of Zhi-Zi-Hou-Po decoction in rat plasma after oral administration by an untargeted metabolomics-driven strategy based on LC-MS by Kaiwen Luo; Fang Feng (5723-5735).
In this study, a novel untargeted metabolomics-driven strategy based on LC-MS was used to rapidly screen and identify the absorbed components and metabolites of Zhi-Zi-Hou-Po decoction (ZZHPD) in rat plasma. The plasma sample was obtained from orbital venous of rats after oral administration and pretreated by protein precipitation before analysis. All sample data from total ion chromatograms (TICs) of LC-TOF/MS were aligned and peak picked by XCMS and MetAlign combined to extract three-dimensional datasets (peak code, t R –m/z pairs and ion intensity). Xenobiotics in rat plasma were differentiated from endogenous components by multivariate statistical analysis and then divided into prototype compounds and metabolites by comparing t R –m/z with the chemical compounds of ZZHPD. Combined with fragment ions and structure information of LC-TSQ/MS, a total of 61 compounds, including 35 prototype compounds and 26 metabolites, were rapidly identified or tentatively characterized in rat plasma. Results indicated that iridoid glycosides, monoterpenoids, flavonoids, and lignans were the main absorbed chemical components of ZZHPD. Glucuronidation and sulfation were the main metabolic pathways of ZZHPD compounds in vivo. In addition, there were ring-opening reactions and reduction reactions for iridoid glycosides, hydrolysis for flavonoids, as well as hydroxylation and stereoscopic conversion reactions for lignans. This study offers a systematically applicable approach for rapid screening and identification of xenobiotics and metabolites derived from multi-herb prescription in vivo, and provides useful information for ascertaining bioactive ingredients and action mechanisms of ZZHPD. Graphical Abstract Diagram of untargeted metabolomics-driven strategy for ZZHPD in rat plasma
Keywords: Untargeted metabolomics; Absorbed components; Metabolites; Identification; LC-MS; Zhi-Zi-Hou-Po decoction
Molecularly imprinted polymer as efficient sorbent of solid-phase extraction for determination of gonyautoxin 1,4 in seawater followed by high-performance liquid chromatography-fluorescence detection by Xiao-Qi Mei; Xiu-Ping He; Jiang-Tao Wang (5737-5743).
A kind of new molecularly imprinted polymer (MIP) was synthesized by bulk polymerization using guanosine as dummy template molecule, α-methacrylic acid as functional monomer and ethylene glycol dimethyl acrylic ester as crosslinker. Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM) showed that the MIP had homogenous and uniform-sized cavities. It was confirmed that the MIP had higher binding affinity and selectivity towards gonyautoxins 1,4 (GTX 1,4) than the non-imprinted polymer (NIP) according to the static equilibrium adsorption. An off-line molecularly imprinted solid-phase extraction (MISPE) method followed by high-performance liquid chromatography with fluorescence detection (HPLC-FLD) was established for the analysis of GTX 1,4. 0.1 mol/L acetic acid and 95:5 (v:v) methanol/water were optimized as the washing and elution solutions, respectively. The recoveries of spiked cultured seawater samples were satisfactory, as high as 88 %. Using this method, the concentrations of GTX 1,4 from cultured seawater samples of Alexandrium minutum and Alexandrium tamarense were detected to be 1.10 μg/L and 0.99 μg/L, respectively. Graphical Abstract The synthesis of molecularly imprinted polymer and molecularly imprinted solid-phase extraction analysis for gonyautoxin 1,4
Keywords: Gonyautoxins 1,4; Molecularly imprinted polymers; Solid-phase extraction; Alexandrium minutum ; Alexandrium tamarense
On-column entrapment of alpha1-acid glycoprotein for studies of drug-protein binding by high-performance affinity chromatography by Jeanethe Anguizola; Cong Bi; Michelle Koke; Abby Jackson; David S. Hage (5745-5756).
An on-column approach for protein entrapment was developed to immobilize alpha1-acid glycoprotein (AGP) for drug-protein binding studies based on high-performance affinity chromatography. Soluble AGP was physically entrapped by using microcolumns that contained hydrazide-activated porous silica and by employing mildly oxidized glycogen as a capping agent. Three on-column entrapment methods were evaluated and compared to a previous slurry-based entrapment method. The final selected method was used to prepare 1.0 cm × 2.1 mm I.D. affinity microcolumns that contained up to 21 (±4) μg AGP and that could be used over the course of more than 150 sample applications. Frontal analysis and zonal elution studies were performed on these affinity microcolumns to examine the binding of various drugs with the entrapped AGP. Site-selective competition studies were also conducted for these drugs. The results showed good agreement with previous observations for these drug-protein systems and with binding constants that have been reported in the literature. The entrapment method developed in this study should be useful for future work in the area of personalized medicine and in the high-throughput screening of drug interactions with AGP or other proteins. Graphical abstract On-column protein entrapment using a hydrazide-activated support and oxidized glycogen as a capping agent
Keywords: Alpha1-acid glycoprotein; High-performance affinity chromatography; Drug-protein binding; Entrapment; Immobilization method; Affinity microcolumn
Characterisation of the protein corona using tunable resistive pulse sensing: determining the change and distribution of a particle’s surface charge by Emma L. C. J. Blundell; Matthew J. Healey; Elizabeth Holton; Muttuswamy Sivakumaran; Sarabjit Manstana; Mark Platt (5757-5768).
The zeta potential of the protein corona around carboxyl particles has been measured using tunable resistive pulse sensing (TRPS). A simple and rapid assay for characterising zeta potentials within buffer, serum and plasma is presented monitoring the change, magnitude and distribution of proteins on the particle surface. First, we measure the change in zeta potential of carboxyl-functionalised nanoparticles in solutions that contain biologically relevant concentrations of individual proteins, typically constituted in plasma and serum, and observe a significant difference in distributions and zeta values between room temperature and 37 °C assays. The effect is protein dependent, and the largest difference between the two temperatures is recorded for the γ-globulin protein where the mean zeta potential changes from −16.7 to −9.0 mV for 25 and 37 °C, respectively. This method is further applied to monitor particles placed into serum and/or plasma. A temperature-dependent change is again observed with serum showing a 4.9 mV difference in zeta potential between samples incubated at 25 and 37 °C; this shift was larger than that observed for samples in plasma (0.4 mV). Finally, we monitor the kinetics of the corona reorientation for particles initially placed into serum and then adding 5 % (V/V) plasma. The technology presented offers an interesting insight into protein corona structure and kinetics of formation measured in biologically relevant solutions, i.e. high protein, high salt levels, and its particle-by-particle analysis gives a measure of the distribution of particle zeta potential that may offer a better understanding of the behaviour of nanoparticles in solution. Graphical Abstract The relative velocity of a nanoparticle as it traverses a nanopore can be used to determine its zeta potential. Monitoring the changes in translocation speeds can therefore be used to follow changes to the surface chemistry/composition of 210 nm particles that were placed into protein rich solutions, serum and plasma. The particle-by-particle measurements allow the zeta potential and distribution of the particles to be characterised, illustrating the effects of protein concentration and temperature on the protein corona. When placed into a solution containing a mixture of proteins, the affinity of the protein to the particle’s surface determines the corona structure, and is not dependent on the protein concentration
Keywords: Biosensor; TRPS; Zeta potential; Protein corona; Tunable pores
Analysis of non-steroidal anti-inflammatory drugs in milk using QuEChERS and liquid chromatography coupled to mass spectrometry: triple quadrupole versus Q-Orbitrap mass analyzers by Antoni Rúbies; Lili Guo; Francesc Centrich; Mercè Granados (5769-5778).
We developed a Quick, Easy, Cheap, Effective, Rugged, and Safe (QuEChERS) method for the high throughput determination of 10 non-steroidal anti-inflammatory drugs (NSAIDs) in milk samples using high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) with a triple quadrupole (QqQ) instrument and an electrospray ionization (ESI) source. The new extraction procedure is highly efficient, and we obtained absolute recoveries in the range 78.1–97.1 % for the extraction and clean-up steps. Chromatographic separation is performed in the gradient mode with a biphenyl column and acidic mobile phases consisting of water and acetonitrile containing formic acid. The chromatographic run time was about 12 min, and NSAID peaks showed a good symmetry factor. For MS/MS detection, we used multiple reaction monitoring (MRM) mode, using ESI in both positive and negative modes. Our method has been validated in compliance with the European Commission Decision 657/2002/EC, and we obtained very satisfactory results in inter-laboratory testing. Furthermore, we explored the use of a hybrid high resolution mass spectrometer, combining a quadrupole and an Orbitrap mass analyzer, for high resolution (HR) MS/MS detection of NSAIDs. We achieved lower NSAID quantification limits with Q-Orbitrap high resolution mass spectrometry (HRMS/MS) detection than those achieved with the QqQ instrument; however, its main feature is its very high selectivity, which makes HRMS/MS particularly suitable for confirmatory analysis.
Keywords: Liquid chromatography; Mass spectrometry; Triple quadrupole; Q-Orbitrap; Milk; Non-steroidal anti-inflammatory drugs
Ion sensors based on novel fiber organic electrochemical transistors for lead ion detection by Yuedan Wang; Zhou Zhou; Xing Qing; Weibing Zhong; Qiongzhen Liu; Wenwen Wang; Mufang Li; Ke Liu; Dong Wang (5779-5787).
Fiber organic electrochemical transistors (FECTs) based on polypyrrole and nanofibers have been prepared for the first time. FECTs exhibited excellent electrical performances, on/off ratios up to 104 and low applied voltages below 2 V. The ion sensitivity behavior of the fiber organic electrochemical transistors was investigated. It exhibited that the transfer curve of FECTs shifted to lower gate voltage with increasing cations concentration, the sensitivity reached to 446 μA/dec in the 10–5–10–2 M Pb2+ concentration range. The ion selective properties of the FECTs have also been systematically studied for the detection of potassium, calcium, aluminum, and lead ions. The devices with different cations showed great difference in response curves. It was suitable for selectively monitoring Pb2+ with respect to other cations. The results indicated FECTs were very effective for electrochemical sensing of lead ion, which opened a promising perspective for wearable electronics in healthcare and biological application. Graphical Abstract The schematic diagram of fiber organic electrochemical transistors based on polypyrrole and nanofibers for ion sensing.
Keywords: Organic electrochemical transistor; Polymer; Nanofiber; Ion sensor; Lead ions
Sensitive multiresidue method by HS-SPME/GC-MS for 10 volatile organic compounds in urine matrix: a new tool for biomonitoring studies on children by Arianna Antonucci; Matteo Vitali; Pasquale Avino; Maurizio Manigrasso; Carmela Protano (5789-5800).
A HS-SPME method coupled with GC-MS analysis has been developed for simultaneously measuring the concentration of 10 volatile organic compounds (VOCs) (benzene, toluene, ethylbenzene, o-, m-, and p-xylene, methyl tert-butyl ether, ethyl tert-butyl ether, 2-methyl-2-butyl methyl ether, and diisopropyl ether) in urine matrix as a biomonitoring tool for populations at low levels of exposure to such VOCs. These compounds, potentially toxic for human health, are common contaminants of both outdoor and indoor air, as they are released by autovehicular traffic; some of them are also present in environmental tobacco smoke (ETS). Thus, the exposure to these pollutants cannot be neglected and should be assessed. The low limits of detection and quantification (LODs and LOQs <6.5 and 7.5 ng L–1, respectively) and the high reproducibility (CVs <4 %) make the developed method suited for biomonitoring populations exposed at low levels such as children. Further, the method is cost-effective and low in time-consumption; therefore, it is useful for investigating large populations. It has been applied to children exposed to traffic pollution and/or ETS; the relevant results are reported, and the relevant implications are discussed.
Keywords: Volatile organic compounds; Biomonitoring; Urine; Children; HS-SPME; GC-MS
Multiplug filtration cleanup method with multi-walled carbon nanotubes for the analysis of malachite green, diethylstilbestrol residues, and their metabolites in aquatic products by liquid chromatography–tandem mass spectrometry by Yuhong Qin; Jingru Zhang; Yanjie Li; Yongtao Han; Nan Zou; Yanbin Jiang; Jihao Shan; Canping Pan (5801-5809).
The food safety supervision in aquatic products has raised public concern in recent years. In this study, a liquid chromatographic–tandem mass spectrometric (LC-MS/MS) method for the simultaneous quantification and identification of four residues of the ever widely used analytes (including malachite green, leucomalachite green, diethylstilbestrol, and dienestrol) in aquaculture samples was developed. For sample preparation, a modified QuEChERS (quick, easy, cheap, effective, rugged, and safe) method was used, which was initially developed for pesticide residue analysis. For cleanup procedure, low-temperature cleanup method was combined with multiplug filtration cleanup (m-PFC) method based on multi-walled carbon nanotubes (MWCNTs). The volume of water, extraction solvent, cleanup sorbents, and m-PFC procedure were optimized for carp, striped bass, and giant salamander matrices. It was validated by analyzing four residues in each matrix spiked at three concentration levels of 0.5, 5, and 50 μg/kg (n = 5). The method was successfully validated according to the 2002/657/EC guidelines. After optimization, spike recoveries were within 73–106 % and <15 % relative standard deviations (RSDs) for all analytes in the tested matrices. Limits of quantification (LOQs) for the proposed method ranged from 0.10 to 0.50 μg/kg. Matrix-matched calibrations were performed with the coefficients of determination >0.998 between concentration levels of 0.5 and 200 μg/kg. The developed method was successfully applied to the determination of residues in market samples. Graphical abstract Flow chart of multi-plug filtration cleanup combined with low-temperature cleanup method
Keywords: Multiple-walled carbon nanotubes; Multiplug filtration cleanup; Aquaculture; Residue analysis
A fluorescent aptasensor based on a DNA pyramid nanostructure for ultrasensitive detection of ochratoxin A by Morteza Alinezhad Nameghi; Noor Mohammad Danesh; Mohammad Ramezani; Faezeh Vahdati Hassani; Khalil Abnous; Seyed Mohammad Taghdisi (5811-5818).
Analytical techniques for detection of ochratoxin A (OTA) in food products and blood serum are of great significance. In this study, a fluorescent aptasensor was developed for sensitive and specific detection of OTA, based on a DNA pyramid nanostructure (DPN) and PicoGreen (PG) dye. The designed aptasensor inherits characteristics of DPN, such as high stability and capacity for PG loading. PG, as a fluorescent dye, could bind to double-stranded DNA (dsDNA). In the absence of OTA, the pyramid structure of DPN remains intact, leading to a very strong fluorescence emission. Because of higher affinity of aptamer for its target relative to its complementary strand, upon addition of target, the pyramid structure of DPN is disassembled, leading to a weak fluorescence emission. The presented aptasensor showed high specificity toward OTA with a limit of detection (LOD) as low as 0.135 nM. Besides, the designed sensing strategy was successfully utilized to recognize OTA in serum and grape juice with LODs of 0.184 and 0.149 nM, respectively.
Keywords: DNA pyramid nanostructure; Fluorescent aptasensor; PicoGreen; Ochratoxin A
A nano-silver enzyme electrode for organophosphorus pesticide detection by Qiqi Zheng; Yonghua Yu; Kai Fan; Feng Ji; Jian Wu; Yibin Ying (5819-5827).
A nano-silver electrode immobilizing acetylcholinesterase (AChE) for the detection of organophosphorus (OPPs) pesticides is reported. Scanning electron microscopy (SEM) was used to characterize the surface structure of two kinds of electrodes fabricated with different sizes of silver powders and the interface between chitosan layer and nano-silver powder layer. Cyclic voltammetry was carried out to characterize the response of silver/chitosan electrode in the absence and in the presence of thiocholine (TCh). It was also used to evaluate the insulativity of the chitosan layer. An amperometric method was performed to measure the response of the electrode to TCh, which is the product of the enzymatic reaction for detecting organophosphorus pesticides indirectly. Although there are many kinds of nanoparticles, silver was chosen for its internal advantage in detecting TCh at low potential without further modification. The result shows nano-silver powder has better performance than usual silver powder, and the limit of detection of paraoxon is 4 ppb under optimized conditions. One percent (w/v) chitosan solution was used as binder for the immobilization of nano-silver powder and AChE, which made it possible for independent electrode fabrication at room temperature, whereas 3% (w/v) chitosan solution was used as insulating compound for controlling the electrode area. Unlike traditional organic insulating ink, chitosan is safe and environmentally friendly, and it is used as insulating material for the first time. The flexible nano-silver/AChE/chitosan electrode was evaluated in Chinese chives and cabbage, and the recoveries of standard addition were 105.11 and 96.41%, respectively. Owing to the antibacterial property of nano-silver and the biocompatibility, safety, and biodegradability of chitosan, the proposed method is safe, facile, environmentally friendly, and has great potential in organophosphorus pesticide detection for food safety. Graphical Abstract Current response of nano-silver electrode (a) and silver electrode (b) to thiocholine in 0.02 M PBS + KCl at 0.15 V; addition of thiocholine (0.09 mM) every 50 s (↓); inset: calibration curve of nano-silver (▲) and silver (◆) electrode
Keywords: Nano-silver; Chitosan; Electrochemistry; Acetylcholinesterase; Organophosphorus pesticide
Assessment of the effects of As(III) treatment on cyanobacteria lipidomic profiles by LC-MS and MCR-ALS by Aline S. Marques; Carmen Bedia; Kássio M. G. Lima; Romà Tauler (5829-5841).
Cyanobacteria are a group of photosynthetic, nitrogen-fixing bacteria present in a wide variety of habitats such as freshwater, marine, and terrestrial ecosystems. In this work, the effects of As(III), a major toxic environmental pollutant, on the lipidomic profiles of two cyanobacteria species (Anabaena and Planktothrix agardhii) were assessed by means of a recently proposed method based on the concept of regions of interest (ROI) in liquid chromatography mass spectroscopy (LC-MS) together with multivariate curve resolution alternating least squares (MCR-ALS). Cyanobacteria were exposed to two concentrations of As(III) for a week, and lipid extracts were analyzed by ultrahigh-performance liquid chromatography/time-of-flight mass spectrometry in full scan mode. The data obtained were compressed by means of the ROI strategy, and the resulting LC-MS data sets were analyzed by the MCR-ALS method. Comparison of profile peak areas resolved by MCR-ALS in control and exposed samples allowed the discrimination of lipids whose concentrations were changed due to As(III) treatment. The tentative identification of these lipids revealed an important reduction of the levels of some galactolipids such as monogalactosyldiacylglycerol, the pigment chlorophyll a and its degradation product, pheophytin a, as well as carotene compounds such as 3-hydroxycarotene and carotene-3,3′-dione, all of these compounds being essential in the photosynthetic process. These results suggested that As(III) induced important changes in the composition of lipids of cyanobacteria, which were able to compromise their energy production processes. Graphical abstract Steps of the proposed LC-MS + MCR-ALS procedure
Keywords: LC-MS; MCR-ALS; Cyanobacteria; As(III)
Investigations on the cell metabolomics basis of multidrug resistance from tumor cells by ultra-performance liquid chromatography–mass spectrometry by Ruixing Zhang; Xiaoyu Zhuang; Li Zong; Shu Liu; Zhiqiang Liu; Fengrui Song (5843-5854).
Although anticancer drug resistance has been linked to high expression of P-glycoprotein and the enhanced DNA repair ability, the biochemical process and the underlying mechanisms of drug resistance are not clear. In order to clarify the biochemical mechanisms of drug resistance during anticancer drug treatment, we studied the metabolomics of MCF-7/S and MCF-7/Adr cell lines, the COC1 and COC1/DDP cell lines, including the metabolic pathways of multidrug-resistant tumor cells and the changes of endogenous substances in cells. The intracellular metabolites were profiled using ultra-performance liquid chromatography–tandem mass spectrometry (UPLC–MS/MS). In this study, 24 biomarkers in MCF-7/Adr cells and 15 biomarkers in COC1/DDP cells that are involved in some important metabolic pathways were putatively identified. Several metabolic pathways are changed in tumor cells showing drug resistance, such as protein synthesis pathways, cysteine synthesis, the glutamine metabolic pathway, and the ammonia cycle; the first of these are involved in the synthesis of some important proteins including membrane proteins, multidrug resistance-associated proteins, and P-glycoprotein (P-gp). Proteins related to drug resistance were overexpressed in multidrug-resistant tumor cells. These proteins depended on energy and play important roles in the emergence of drug resistance. The changes in glutathione and cysteine metabolic pathways showed that the cells can activate related metabolic pathways and reduce the cell apoptosis when they encounter oxidative damage. These findings indicate that drug resistance is likely associated with increased P-gp synthesis and reduced apoptosis of tumor cells. Graphical Abstract Drug resistance was charactered in the changing of genomics and proteomics. Like enhancing DNA repair, reducing uptake, high P-g protein expression. Here, we studied the changes of metabolite pathway which could be also play an imported role in drug resistance
Keywords: Ultra-performance liquid chromatography–mass spectrometry; Multidrug resistance; Cell metabolomics; Tumor
Evaluation of chromatographic conditions in reversed phase liquid chromatography-mass spectrometry systems for fingerprinting of polar and amphiphilic plant metabolites by Nikoline J. Nielsen; Giorgio Tomasi; Jan H. Christensen (5855-5865).
Metabolic fingerprinting is a relatively young scientific discipline requiring robust, yet flexible and fit-for-purpose analytical methods. Here, we introduce a simple approach to select reversed phase LC systems with electrospray MS detection for fingerprinting of polar and amphiphilic plant metabolites. The approach does not rely on isotopic labeling or biological origin of sample constituent and can also be used for non-biological matrices (e.g., oil or sewage sludge) or for other optimization purposes (e.g., mass spectrometric source parameterization). The LC systems varied in column chemistry and temperature, mobile phase pH/additive, gradient steepness/eluotropic strength, and electrospray mode of operation. The systems were evaluated based on the number of features detected using the matchedFilter algorithm from XCMS and the repeatability of this detection across analytical replicates. For negative ion mode detection, the best performances were obtained with an HSS T3 column operated at low pH, which produced a 3-fold increase in the number of reliable features extracted compared with the worst system. The best system for positive ion mode (i.e., the BEH C18 column operated at intermediate pH) only produced a 50 % increase in the number of reliable features. The data also indicate that baseline removal is unavoidable for reliable intensity estimations using peak areas, and that peak heights may be a more robust measure of intensity when baselines cannot be completely removed or in case of coelution, fronting or tailing.
Keywords: LC-MS; Metabolomics; Fingerprinting; Feature detection
Highly sensitive detection of M.SssI DNA methyltransferase activity using a personal glucose meter by Huimin Deng; Si Ying Peng; Zhiqiang Gao (5867-5872).
We should like to call your attention to the fact that Si Ying Png’s name was misspelled in the original publication: it should be Si Ying Png.A simple method for highly sensitive and selective detection of M.SssI CpG methyltransferase (M.SssI MTase) activity is developed, leveraging on the portability and ease of use of a personal glucose meter (PGM). Briefly, DNA-invertase conjugates are hybridized with their complementary DNA strands pre-immobilized on magnetic beads. The 5′-CCGG-3′ sequence present in the DNA duplexes serves as the recognition site for both Hpa II restriction enzyme and M.SssI MTase (5′-CG-3′). Hpa II restriction enzyme specifically cleaves at unmethylated 5′-CCGG-3′ sequence, and the invertase that remains on the methylated DNA catalyzes the hydrolysis of sucrose to glucose and fructose. It is found that the amount of glucose is proportional to the M.SssI MTase methylation activity in the range of 0.5 to 80 U/mL with a detection limit of 0.37 U/mL. Due to the specific recognition sequence present in the DNA strands, this method also shows high selectivity for M.SssI MTase. In addition, inhibition studies with 5′-azacytidine demonstrate the capability of inhibition screening using this method. Graphical abstractDeteciton of M.SssI DNA methyltransferase activity by a personal glucose meter
Keywords: DNA Methyltransferase; Invertase; Electrochemical biosensor; M.SssI MTase
A liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the human biomonitoring of non-occupational exposure to the fragrance 2-(4-tert-butylbenzyl)propionaldehyde (lysmeral) by Nikola Pluym; Dusan Krnac; Gerhard Gilch; Max Scherer; Edgar Leibold; Gerhard Scherer (5873-5882).
2-(4-tert-Butylbenzyl)propionaldehyde also known as lysmeral, lilial, or lily aldehyde (CAS No. 80-54-6) is a synthetic odorant mainly used as a fragrance in a variety of consumer products like cleaning agents, fine fragrances, cosmetics, and air fresheners. Due to its broad application in various fields, lysmeral was selected for the development of a biomonitoring method for the quantitative exposure assessment within the frame of the cooperation project of the Federal Ministry for the Environment, Nature Conservation, Building and Nuclear Safety (BMUB) and the German Chemical Industry Association (VCI). A method based on ultra-high pressure liquid chromatography combined with tandem mass spectrometry (UPLC-MS/MS) was developed for the simultaneous determination of potential biomarkers of lysmeral in human urine samples. Sample cleanup was performed by liquid-liquid extraction (LLE). Quantification was achieved by standard addition using stable isotope-labeled, authentic reference standards. The method is characterized by its robustness, reliability, and excellent sensitivity as proven during method validation according to approved standard guidelines. The following five lysmeral metabolites were identified as potential biomarkers of exposure for lysmeral in human urine samples: lysmerol, lysmerylic acid, hydroxylated lysmerylic acid, tert-butylbenzoic acid (TBBA), and tert-butylhippuric acid (TBHA). The determination of lysmerol required derivatization with 3-nitrophthalic acid anhydride and showed the lowest limit of detection (LOD) and limit of quantification (LOQ) in urine (0.035 and 0.10 μg/L, respectively). LOD and LOQ for the other metabolites were in the range of 0.12–0.15 and 0.36–0.45 μg/L, respectively. Accuracy for all analytes was in the range of 90–110 %. Intra- and inter-day precision was in the range of 5–10 %, except for TBHA, for which the coefficient of variation was unacceptably high (>20 %) and therefore excluded from the method. The method was applied to urine samples of 40 adult volunteers. The four remaining lysmeral metabolites were detectable in most of the 40 urine samples in the following order according to quantity excreted: TBBA >> lysmerol ≈ lysmerylic acid > hydroxy-lysmerylic acid. In conclusion, we successfully developed a biomonitoring method for the assessment of the exposure to lysmeral in the general population. The method is characterized by its precision, robustness, and accuracy. The metabolites lysmerol, lysmerylic acid, hydroxylated lysmerylic acid, and TBBA turned out to be suitable biomarkers of exposure to lysmeral, either alone or in combination with one or more of the other metabolites. Sensitivity was found to be sufficient for assessing the background exposure to this chemical in the general population.
Keywords: 2-(4-tert-Butylbenzyl)propionaldehyde; Lysmeral; Urine; UPLC-MS/MS; Human biomonitoring (HBM)
A fast and sensitive method for the separation of carotenoids using ultra-high performance supercritical fluid chromatography-mass spectrometry by Firas Jumaah; Merichel Plaza; Victor Abrahamsson; Charlotta Turner; Margareta Sandahl (5883-5894).
In this study, a rapid and sensitive ultra-high performance supercritical fluid chromatography-mass spectrometry (UHPSFC-MS) method has been developed and partially validated for the separation of carotenoids within less than 6 min. Six columns of orthogonal selectivity were examined, and the best separation was obtained by using a 1-aminoanthracene (1-AA) column. The length of polyene chain as well as the number of hydroxyl groups in the structure of the studied carotenoids determines their differences in the physiochemical properties and thus the separation that is achieved on this column. All of the investigated carotenoids were baseline separated with resolution values greater than 1.5. The effects of gradient program, back pressure, and column temperature were studied with respect to chromatographic properties such as retention and selectivity. Electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) were compared in both positive and negative mode, using both direct infusion and hyphenated with UHPSFC. The ESI in positive mode provided the highest response. The coefficient of determination (R 2) for all calibration curves were greater than 0.998. Limit of detection (LOD) was in the range of 2.6 and 25.2 ng/mL for α-carotene and astaxanthin, respectively, whereas limit of quantification (LOQ) was in the range of 7.8 and 58.0 ng/mL for α-carotene and astaxanthin, respectively. Repeatability and intermediate precision of the developed UHPSFC-MS method were determined and found to be RSD < 3 % and RSD < 6 %, respectively. The method was applied in order to determine carotenoids in supercritical fluid extracts of microalgae and rosehip. Graphical Abstract Ultra-high performance supercritical fluid chromatography-a rapid separation method for the analysis of carotenoids in rosehip and microalgae samples
Keywords: Carotene; Xanthophyll; Orthogonal column screening; Method development; Supercritical fluid; Mass spectrometry
Evaluation of the degradation of acetaminophen by the filamentous fungus Scedosporium dehoogii using carbon-based modified electrodes by Serge Foukmeniok Mbokou; Maxime Pontié; Bienvenue Razafimandimby; Jean-Philippe Bouchara; Evangéline Njanja; Ignas Tonle Kenfack (5895-5903).
The nonpathogenic filamentous fungus Scedosporium dehoogii was used for the first time to study the electrochemical biodegradation of acetaminophen (APAP). A carbon fiber microelectrode (CFME) modified by nickel tetrasulfonated phthalocyanine (p-NiTSPc) and a carbon paste electrode (CPE) modified with coffee husks (CH) were prepared to follow the kinetics of APAP biodegradation. The electrochemical response of APAP at both electrodes was studied by cyclic voltammetry and square wave voltammetry. p-NiTSPc-CFME was suitable to measure high concentrations of APAP, whereas CH–CPE gave rise to high current densities but was subject to the passivation phenomenon. p-NiTSPc–CFME was then successfully applied as a sensor to describe the kinetics of APAP biodegradation: this was found to be of first order with a kinetics constant of 0.11 day−1 (at 25 °C) and a half-life of 6.30 days. APAP biodegradation by the fungus did not lead to the formation of p-aminophenol (PAP) and hydroquinone (HQ) that are carcinogenic, mutagenic, and reprotoxic (CMR). Graphical Abstract The kinetics of APAP biodegradation, followed by a poly-nickel tetrasulfonated phtalocyanine modified carbon fiber microelectrode
Keywords: Acetaminophen; Biodegradation; Kinetics; Scedosporium dehoogii ; Carbon-based electrodes
Extraction of cocoa proanthocyanidins and their fractionation by sequential centrifugal partition chromatography and gel permeation chromatography by Vasilisa Pedan; Norbert Fischer; Sascha Rohn (5905-5914).
Cocoa beans contain secondary metabolites ranging from simple alkaloids to complex polyphenols with most of them believed to possess significant health benefits. The increasing interest in these health effects has prompted the need to develop techniques for their extraction, fractionation, separation, and analysis. This work provides an update on analytical procedures with a focus on establishing a gentle extraction technique. Cocoa beans were finely ground to an average particle size of <100 μm, defatted at 20 °C using n-hexane, and extracted three times with 50 % aqueous acetone at 50 °C. Determination of the total phenolic content was done using the Folin-Ciocalteu assay, the concentration of individual polyphenols was analyzed by electrospray ionization high performance liquid chromatography-mass spectrometry (ESI-HPLC/MS). Fractions of bioactive compounds were separated by combining sequential centrifugal partition chromatography (SCPC) and gel permeation column chromatography using Sephadex LH-20. For SCPC, a two-phase solvent system consisting of ethyl acetate/n-butanol/water (4:1:5, v/v/v) was successfully applied for the separation of theobromine, caffeine, and representatives of the two main phenolic compound classes flavan-3-ols and flavonols. Gel permeation chromatography on Sephadex LH-20 using a stepwise elution sequence with aqueous acetone has been shown for effectively separating individual flavan-3-ols. Separation was obtained for (−)-epicatechin, proanthocyanidin dimer B2, trimer C1, and tetramer cinnamtannin A2. The purity of alkaloids and phenolic compounds was determined by HPLC analysis and their chemical identity was confirmed by mass spectrometry.
Keywords: Cocoa proanthocyanidins; Sequential centrifugal partition chromatography; Gel permeation chromatography; Total phenolic content
High-throughput identification of monoclonal antibodies after compounding by UV spectroscopy coupled to chemometrics analysis by Emmanuel Jaccoulet; Julien Boccard; Myriam Taverna; Andrea Santos Azevedos; Serge Rudaz; Claire Smadja (5915-5924).
Monoclonal antibodies (mAbs) compounded into the hospital pharmacy are widely used nowadays. Their fast identification after compounding and just before administration to the patient is of paramount importance for quality control at the hospital. This remains challenging due to the high similarity of the structure between mAbs. Analysis of the ultraviolet spectral data of four monoclonal antibodies (cetuximab, rituximab, bevacizumab, and trastuzumab) using unsupervised principal component analysis led us to focus exclusively on the second-derivative spectra. Partial least squares-discriminant analysis (PLS-DA) applied to these data allowed us to build models for predicting which monoclonal antibody was present in a given infusion bag. The calibration of the models was obtained from a k-fold validation. A prediction set from another batch was used to demonstrate the ability of the models to predict well. PLS-DA models performed on the spectra of the region of aromatic amino acid residues presented high ability to predict mAb identity. The region corresponding to the tyrosine residue reached the highest score of good classification with 89 %. To improve the score, standard normal variate (SNV) preprocessing was applied to the spectral data. The quality of the optimized PLS-DA models was enhanced and the region from the tyrosine/tryptophan residues allowed us excellent classification (100 %) of the four mAbs according to the matrix of confusion. The sensitivity and specificity performance parameters assessed this excellent classification. The usefulness of the combination of UV second-derivative spectroscopy to multivariate analysis with SNV preprocessing demonstrated the unambiguous identification of commercially available monoclonal antibodies. Graphical abstract PLS-DA models on the spectra of the region of aromatic amino acid residues allows mAb identification with high prediction
Keywords: Excipients; Multivariate analysis; Pharmacy hospital; Quality control; Therapeutic monoclonal antibody; UV spectroscopy; mAb discrimination
ATP and autophosphorylation driven conformational changes of HipA kinase revealed by ion mobility and crosslinking mass spectrometry by Yurong Wen; Frank Sobott; Bart Devreese (5925-5933).
Toxin-antitoxin systems are genetic modules involved in a broad range of bacterial cellular processes including persistence, multidrug resistance and tolerance, biofilm formation, and pathogenesis. In type II toxin-antitoxin systems, both the toxin and antitoxin are proteins. In the prototypic Escherichia coli HipA-HipB module, the antitoxin HipB forms a complex with the protein kinase HipA and sequesters it in the nucleoid. HipA is then no longer able to phosphorylate glutamyl-tRNA-synthetase and this prevents the initiation of the forthcoming stringent response. Here we investigated the assembly of the Shewanella oneidensis MR-1 HipA-HipB complex using native electrospray ion mobility-mass spectrometry and chemical crosslinking combined with mass spectrometry. We revealed that the HipA autophosphorylation was accompanied by a large conformational change, and confirmed structural evidence that S. oneidensis MR-1 HipA-HipB assembly was distinct from the prototypic E. coli HipA-HipB complex. Graphical abstract Ion mobility mass spectrometry shows a two phase transition from unstructured HipA to a compact folded phosphorylated protein
Keywords: Toxin-antitoxin system; HipAB; Ion mobility; Chemical crosslinking; Mass spectrometry
The interaction of an amino-modified ZrO2 nanomaterial with macrophages—an in situ investigation by Raman microspectroscopy by Anja Silge; Thomas Bocklitz; Rainer Ossig; Jürgen Schnekenburger; Petra Rösch; Jürgen Popp (5935-5943).
Metal oxide nanoparticles (NP) are applied in the fields of biomedicine, pharmaceutics, and in consumer products as textiles, cosmetics, paints, or fuels. In this context, the functionalization of the NP surface is a common method to modify and modulate the product performance. A chemical surface modification of NP such as an amino-functionalization can be used to achieve a positively charged and hydrophobic surface. Surface functionalization is known to affect the interaction of nanomaterials (NM) with cellular macromolecules and the responses of tissues or cells, like the uptake of particles by phagocytic cells. Therefore, it is important to assess the possible risk of those modified NP for human health and environment. By applying Raman microspectroscopy, we verified in situ the interaction of amino-modified ZrO2 NP with cultivated macrophages. The results demonstrated strong adhesion properties of the NP to the cell membrane and internalization into the cells. The intracellular localization of the NP was visualized via Raman depth scans of single cells. After the cells were treated with sodium azide (NaN3) and 2-deoxy-glucose to inhibit the phagocytic activity, NP were still detected inside cells to comparable percentages. The observed tendency of amino-modified ZrO2 NP to interact with the cultivated macrophages may influence membrane integrity and cellular functions of alveolar macrophages in the respiratory system. Graphical abstract Detection of ZrO2 NM at subcellular level
Keywords: Raman microspectroscopy; ZrO2 nanoparticles; Surface functionalization; Cellular uptake
Improved procedure for dendrimer-based mass calibration in matrix-assisted laser desorption/ionization-time-of-flight-mass spectrometry by Jürgen H. Gross (5945-5951).
A procedure is described that results in a substantial increase in signal intensity and in improved accuracy of positive-ion mass calibration when using commercially available kits of monodisperse dendrimers (SpheriCal®) in matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MS). The peak intensities are amplified by an admixture of 2-[(2E)-3-(4-tert-butylphenyl)-2-methylprop-2-enylidene] malononitrile (DCTB) matrix to the kits comprising of 9-nitroanthracene matrix, sodium trifluoroacetate, and four dendrimers. Boosted ion formation then permits lower laser fluence to be used and thus yields enhanced mass resolution. Further, the number of reference peaks is doubled by doping the sample preparation with cesium ions. This results in four [M+Cs]+ ion signals in addition to four [M+Na]+ ion signals provided by the standard kit. Overall, the modified procedure notably reduces the consumption of the expensive calibration standard kits, while it increases mass resolution and enables the use of an advanced calibration algorithm requiring at least six reference peaks. Graphical abstract A dendrimer-based mass calibration for MALDI-TOF-MS can be improved by adding a DCTB matrix and doping the sample preparation with Cs+ ions. Having eight rather than just four reference peaks reduces the average mass error of the calibration curve about fivefold.
Keywords: Dendrimer; Matrix-assisted laser desorption/ionization (MALDI); Time-of-flight (TOF); Mass calibration; Mass spectrometry; Mass accuracy; Mass resolution