Analytical and Bioanalytical Chemistry (v.389, #5)
Bad blood in the laboratory-conflicts and how to avoid or resolve them by J. Fetzer (1293-1295).
is the author or coauthor of over 130 research articles, reviews, and book chapters. He is a member of the International Advisory Board of Analytical and Bioanalytical Chemistry. He has worked for over 20 years as an analytical chemist for the Chevron Corporation and now runs his own consulting company, Fetzpahs Consulting, in Hercules, CA, USA. His book Career management for chemists-a guide to success in a chemistry career was published by Springer.
Spectroscopy challenge 12 by Reinhard Meusinger (1297-1299).
Solution to half-titration challenge by Juris Meija; Janis Bisenieks (1301-1302).
Wilfried M.A. Niessen: Liquid chromatography–mass spectrometry (Third edition) by Uwe Karst (1303-1304).
Dwayne E. Heard (Ed.): Analytical techniques for atmospheric measurement by Thorsten Hoffmann (1305-1306).
Michael Webb and Richard Smith (Eds.): Analysis of drug impurities by Jun Haginaka (1307-1308).
Ultrahigh resolution mass spectrometry by Philippe Schmitt-Kopplin; Norbert Hertkorn (1309-1310).
is leader of the molecular BioGeonomics Group at the GSF Institute for Ecological Chemistry in Neuherberg, Germany. He has a long experience in the field of capillary separation sciences with a more recent emphasis on the coupling to mass spectrometry. Other research efforts are directed at the development of novel powerful research tools enabling the targeted and non targeted analysis of complex mixtures such as in metabolomics, and the structural investigation of non-repetitive structures from different environments. is member of the molecular BioGeonomics Group at the GSF Institute for Ecological Chemistry in Neuherberg, Germany. His current research interests are focused on molecular-level structural characterization of natural organic matter and other complex, non-repetitive systems by a combination of NMR spectroscopy, mass spectrometry, separation and combined mathematical data evaluation; the investigation of molecular mechanisms of the interaction of NOM with organic and inorganic pollutants, mineral surfaces and living systems; plant and microbial metabolism; authentification of the origin of natural compounds with isotope-specific methods and biotic and abiotic enantioselectivity.
High-precision frequency measurements: indispensable tools at the core of the molecular-level analysis of complex systems by N. Hertkorn; C. Ruecker; M. Meringer; R. Gugisch; M. Frommberger; E. M. Perdue; M. Witt; P. Schmitt-Kopplin (1311-1327).
This perspective article provides an assessment of the state-of-the-art in the molecular-resolution analysis of complex organic materials. These materials can be divided into biomolecules in complex mixtures (which are amenable to successful separation into unambiguously defined molecular fractions) and complex nonrepetitive materials (which cannot be purified in the conventional sense because they are even more intricate). Molecular-level analyses of these complex systems critically depend on the integrated use of high-performance separation, high-resolution organic structural spectroscopy and mathematical data treatment. At present, only high-precision frequency-derived data exhibit sufficient resolution to overcome the otherwise common and detrimental effects of intrinsic averaging, which deteriorate spectral resolution to the degree of bulk-level rather than molecular-resolution analysis. High-precision frequency measurements are integral to the two most influential organic structural spectroscopic methods for the investigation of complex materials—NMR spectroscopy (which provides unsurpassed detail on close-range molecular order) and FTICR mass spectrometry (which provides unrivalled resolution)—and they can be translated into isotope-specific molecular-resolution data of unprecedented significance and richness. The quality of this standalone de novo molecular-level resolution data is of unparalleled mechanistic relevance and is sufficient to fundamentally advance our understanding of the structures and functions of complex biomolecular mixtures and nonrepetitive complex materials, such as natural organic matter (NOM), aerosols, and soil, plant and microbial extracts, all of which are currently poorly amenable to meaningful target analysis. The discrete analytical volumetric pixel space that is presently available to describe complex systems (defined by NMR, FT mass spectrometry and separation technologies) is in the range of 108–14 voxels, and is therefore capable of providing the necessary detail for a meaningful molecular-level analysis of very complex mixtures. Nonrepetitive complex materials exhibit mass spectral signatures in which the signal intensity often follows the number of chemically feasible isomers. This suggests that even the most strongly resolved FTICR mass spectra of complex materials represent simplified (e.g. isomer-filtered) projections of structural space.
Keywords: NMR; FT mass spectrometry; Compositional space; Separation; Intrinsic averaging; Isomers; Resolution; Complexity; Complex systems
Mass-spectrometric analysis of complex volatile and nonvolatile crude oil components: a challenge by Saroj K. Panda; Jan T. Andersson; Wolfgang Schrader (1329-1339).
Crude oil analysis has long been an inspiration for the development of analytical techniques. Especially mass spectrometry has flourished as a result of the challenge these extremely complex problems offer. Here an overview of different analytical methods is presented that shows different ways to analyze volatile and nonvolatile crude oil components. Focus has been placed on the use of mass spectrometry and especially the new developments that have been introduced using the emerging technique of Fourier transform ion cyclotron resonance mass spectrometry. These studies are examples of how far the development of analytical methods has come for the task of studying such complex problems.
Keywords: Fourier transform ion cyclotron resonance mass spectrometry; Petroleum; Crude oil; Mass spectrometry
FTICR-MS applications for the structure determination of natural products by Xidong Feng; Marshall M. Siegel (1341-1363).
Natural products are a source of unique chemical entities with specific biological activities of great value to the pharmaceutical industry. However, the determination of unknown structures is usually time consuming and often becomes a bottleneck in the effort to develop natural products into effective drugs. The high-performance features of high magnetic field FTMS have greatly alleviated the structural elucidation bottleneck to meet increasingly shorter discovery timelines for drug candidates based on natural products. The high-performance features of high field FTMS include unsurpassed mass measurement accuracy for elemental formula determination, ultra-high mass resolution for component separation, the ability to perform multiple levels of tandem mass spectrometry for structural elucidation, and moderate sensitivity for limited supply of isolates. A number of applications utilizing these properties of FTMS have been reported recently for the structural elucidation of novel natural product structures originating from terrestrial and marine microorganisms. In this review, FTMS methods and their applications for the structural elucidation and characterization of natural products will be reviewed. Figure Molecular structure and positive ion mode nanoelectrospray FTICR mass spectrum of methylspirastrellolide A (3). The inset shows the isotopic distribution with high abundance of the A + 2 peak, but less than the abundance of the A + 1 peak. The resolved isotopic fine structure of the A + 2 peak reveals the presence of one chlorine atom based on accurate mass assignment and the measured abundance ratio between the resolved 37Cl peak and the monoisotopic peak
Keywords: FTICR-MS; Natural products; Structure elucidation; High resolution; Accurate mass
Application of FT-ICR-MS for the study of proton-transfer reactions involving biomolecules by E. D. Raczyńska; J.-F. Gal; P.-C. Maria; K. Zientara; M. Szelag (1365-1380).
Fourier transform ion cyclotron resonance mass spectrometry, combined with modern ionization (fast atom bombardment , electrospray ionization, matrix-assisted laser desorption–ionization), fragmentation (collision-induced dissociation, surface-induced dissociation, one-photon ultraviolet photodissociation, infrared multiphoton dissociation, blackbody infrared radiative dissociation, electron-capture dissociation), and separation (high-performance liquid chromatography, liquid chromatography, capillary electrophoresis) techniques is now becoming one of the most attractive and frequently used instrumental platforms for gas-phase studies of biomolecules such as amino acids, bioamines, peptides, polypeptides, proteins, nucleobases, nucleosides, nucleotides, polynucleotides, nucleic acids, saccharides, polysaccharides, etc. Since it gives the possibilities to trap the ions from a few seconds up to thousands of seconds, it is often applied to study ion/molecule reactions in the gas phase, particularly proton-transfer reactions which provide important information on acid–base properties. These properties determine in part the three-dimensional structure of biomolecules, most of their intramolecular and intermolecular interactions, and consequently their biological activity. They also indicate the form (unionized, zwitterionic, protonated, or deprotonated) which the biomolecule may take in a nonpolar environment. Figure Biomolecules in the gas-phase acidity-basicity scale
Keywords: Fourier transform ion cyclotron resonance mass spectrometry; Biomolecules; Gas-phase; Acidity–basicity; Zwitterions
Laser-induced Fourier transform ion cyclotron resonance mass spectrometry of organic and inorganic compounds: methodologies and applications by Frédéric Aubriet (1381-1396).
The combination of a laser with a Fourier transform ion cyclotron resonance mass spectrometer (FTICRMS) enables a variety of MS experiments to be conducted. The laser can be used either as an intense photonic source for the photoionization of neutral species introduced in a variety of ways into the FTICR cell, or it can be made to directly interact with a solid, generating gas-phase ions. Depending on the experimental conditions used, various laser-matter interactions can occur. When high laser energy (also referred to as power density or irradiance) is used, laser ablation (LA) processes lead to the release of species into the gas phase, a significant fraction of which are ionic. The number of ions decreases with the irradiance. For low irradiance values, the so-called laser desorption (LD) regime applies, where the expelled species are mainly neutrals. LA–FTICRMS and LD–FTICRMS can be used to study a wide range of materials, including mineral, organic, hybrid and biological compounds (although matrix-assisted laser desorption ionization, MALDI, which is not reviewed in this paper, is more commonly applied to biological compounds). This paper will review a selection of methodological developments and applications in the field of laser ionization FTICRMS, LD–FTICRMS, and LA–FTICRMS for the analysis of organics and inorganics in complex mixtures, emphasizing insoluble materials. Specifically, silicate- and carbon-based complex materials as well as organic compounds will be examined due to their relevance to natural environmental and anthropogenic matrices.
Keywords: Laser desorption; Laser ablation; FTICRMS; Complex mixtures; Pollutants; Laser microprobe
Analysis of O-glycan heterogeneity in IgA1 myeloma proteins by Fourier transform ion cyclotron resonance mass spectrometry: implications for IgA nephropathy by Matthew B. Renfrow; C. Logan Mackay; Michael J. Chalmers; Bruce A. Julian; Jiri Mestecky; Mogens Kilian; Knud Poulsen; Mark R. Emmett; Alan G. Marshall; Jan Novak (1397-1407).
IgA nephropathy (IgAN) is the most common form of primary glomerulonephritis. In IgAN, IgA1 molecules with incompletely galactosylated O-linked glycans in the hinge region (HR) are present in mesangial immunodeposits and in circulating immune complexes. It is not known whether the galactose deficiency in IgA1 proteins occurs randomly or preferentially at specific sites. We have previously demonstrated the first direct localization of multiple O-glycosylation sites on a single IgA1 myeloma protein by use of activated ion-electron capture dissociation (AI-ECD) Fourier transform ion cyclotron resonance (FT-ICR) tandem mass spectrometry. Here, we report the analysis of IgA1 O-glycan heterogeneity by use of FT-ICR MS and liquid chromatography FT-ICR MS to obtain unbiased accurate mass profiles of IgA1 HR glycopeptides from three different IgA1 myeloma proteins. Additionally, we report the first AI-ECD fragmentation on an individual IgA1 O-glycopeptide from an IgA1 HR preparation that is reproducible for each IgA1 myeloma protein. These results suggest that future analysis of IgA1 HR from IgAN patients and normal healthy controls should be feasible.
Keywords: ICR; FT-ICR; FTMS; O-Glycosylation; Electron capture dissociation
The effects of mass accuracy, data acquisition speed, and search algorithm choice on peptide identification rates in phosphoproteomics by Corey E. Bakalarski; Wilhelm Haas; Noah E. Dephoure; Steven P. Gygi (1409-1419).
Proteomic analyses via tandem mass spectrometry have been greatly enhanced by the recent development of fast, highly accurate instrumentation. However, successful application of these developments to high-throughput experiments requires careful optimization of many variables which adversely affect each other, such as mass accuracy and data collection speed. We examined the performance of three shotgun-style acquisition methods ranging in their data collection speed and use of mass accuracy in identifying proteins from yeast-derived complex peptide and phosphopeptide-enriched mixtures. We find that the combination of highly accurate precursor masses generated from one survey scan in the FT-ICR cell, coupled with ten data-dependent tandem MS scans in a lower-resolution linear ion trap, provides more identifications in both mixtures than the other examined methods. For phosphopeptide identifications in particular, this method identified over twice as many unique phosphopeptides as the second-ranked, lower-resolution method from triplicate 90-min analyses (744 ± 50 vs. 308 ± 50, respectively). We also examined the performance of four popular peptide assignment algorithms (Mascot, Sequest, OMSSA, and Tandem) in analyzing the results from both high-and low-resolution data. When compared in the context of a false positive rate of approximately 1%, the performance differences between algorithms were much larger for phosphopeptide analyses than for an unenriched, complex mixture. Based upon these findings, acquisition speed, mass accuracy, and the choice of assignment algorithm all largely affect the number of peptides and proteins identified in high-throughput studies.
Keywords: Mass accuracy; Phosphorylation analysis; Database searching; Shotgun sequencing; High-throughput proteomics
Fourier transform ion cyclotron resonance mass spectrometry of covalent adducts of proteins and 4-hydroxy-2-nonenal, a reactive end-product of lipid peroxidation by Navin Rauniyar; Stanley M. Stevens Jr; Laszlo Prokai (1421-1428).
Covalent adduction of the model protein apomyoglobin by 4-hydroxy-2-nonenal, a reactive end-product of lipid peroxidation, was characterized by nanoelectrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (FTICR). The high mass resolving power and mass measurement accuracy of the instrument facilitated a detailed compositional analysis of the complex reaction product without the need for deconvolution and transformation to clearly show the pattern of adduction and component molecular weights. Our study has also demonstrated the value of electron capture dissociation over collision-induced dissociation for the tandem mass spectrometric determination of site modification for the 4-hydroxy-2-nonenal adduct of oxidized insulin B chain as an example. Figure FTICR allowed characterization of 4-hydroxy-2-nonenal (HNE)-modified apomyoglobin (an expanded spectrum of the +15 charge state is shown)
Keywords: Fourier transform ion cyclotron resonance mass spectrometry; Electrospray ionization; Protein carbonylation; 4-Hydroxy-2-nonenal; Electron capture dissociation
Comparison of collision-induced dissociation and electron-induced dissociation of singly protonated aromatic amino acids, cystine and related simple peptides using a hybrid linear ion trap–FT-ICR mass spectrometer by Hadi Lioe; Richard A. J. O’Hair (1429-1437).
The gas-phase fragmentation reactions of singly protonated aromatic amino acids, their simple peptides as well as simple models for intermolecular disulfide bonds have been examined using a commercially available hybrid linear ion trap–Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer. Low-energy collision-induced dissociation (CID) reactions within the linear ion trap are compared with electron-induced dissociation (EID) reactions within the FT-ICR cell. Dramatic differences are observed between low-energy CID (which occurs via vibrational excitation) and EID. For example, the aromatic amino acids mainly fragment via competitive losses of NH3 and (H2O+CO) under CID conditions, while side-chain benzyl cations are major fragment ions under EID conditions. EID also appears to be superior in cleaving the S–S and S–C bonds of models of peptides containing an intermolecular disulfide bond. Systematic studies involving fragmentation as a function of electron energy reveal that the fragmentation efficiency for EID occurs at high electron energy (more than 10 eV) compared with the low-electron energy (less than 0.2 eV) typically observed for electron capture dissociation fragmentation. Finally, owing to similarities between the types of fragment ions observed under EID conditions and those previously reported in ultraviolet photodissociation experiments and the electron-ionization mass spectra, we propose that EID results in fragmentation via electronic excitation and vibrational excitation. EID may find applications in analyzing singly charged molecular ions formed by matrix-assisted laser desorption ionization. Figure Fragmentation of singly protonated aromatic amino acids and peptide models under electron induced dissociation (EID) conditions is observed to yield complementary fragmentation to collision induced dissociation (CID), with abundant product ions are formed from bond cleavages from the sidechain
Keywords: Fourier transform ion cyclotron resonance mass spectrometer; Linear ion trap; Collision-induced dissociation; Electron-induced dissociation; Protonated peptide fragmentation
At-line coupling of UPLC to chip-electrospray-FTICR-MS by Xiaojing Li; Agnes Fekete; Matthias Englmann; Moritz Frommberger; Shuiyuan Lv; Guonan Chen; Philippe Schmitt-Kopplin (1439-1446).
Since highly sensitive on-line coupling of UPLC with FTICR-MS is technically infeasible due to their different scan rates, at-line coupling of these techniques was developed for rapid analysis. To enable cutting of one peak of the chromatogram into one fraction, several conditions and relationships were investigated, e.g. the optimum volume of the inserted delay loop, the relationship between retention time, loop outlet drop speed, individual drop volume versus mobile phase composition under constant speed, and linear solvent strength gradient elution modes. Good and reproducible results were achieved applying UPLC as an efficient separation and fast fractionation tool before the FTICR-MS measurements. A chip-based nanoelectrospray ionization system was employed which was perfectly suited to handling the small-volume fractions and was thus chosen for the at-line coupling. The method was initially applied to spiked extracts of cell-free bacterial culture supernatants in which bacterial signalling compounds, namely N-acyl homoserine lactones (AHL), were detected. Good reproducibility and high recovery was observed. Afterwards, a culture supernatant of Erwinia sp. JX3.2, a putative AHL producer, was investigated and N-hexanoyl-homoserine lactone was determined as a possible signalling molecule. More reliable assignments were achieved by use of at-line coupling of UPLC and FTICR-MS compared with off-line measurements.
Keywords: At-line coupling; Fractionation; UPLC; FTICR-MS; N-Acylhomoserine lactones
Uptake, degradation and chiral discrimination of N-acyl-D/L-homoserine lactones by barley (Hordeum vulgare) and yam bean (Pachyrhizus erosus) plants by Christine Götz; Agnes Fekete; Istvan Gebefuegi; Sándor T. Forczek; Květoslava Fuksová; Xiaojing Li; Matthias Englmann; Milan Gryndler; Anton Hartmann; Miroslav Matucha; Philippe Schmitt-Kopplin; Peter Schröder (1447-1457).
Bacterial intraspecies and interspecies communication in the rhizosphere is mediated by diffusible signal molecules. Many Gram-negative bacteria use N-acyl-homoserine lactones (AHLs) as autoinducers in the quorum sensing response. While bacterial signalling is well described, the fate of AHLs in contact with plants is much less known. Thus, adsorption, uptake and translocation of N-hexanoyl- (C6-HSL), N-octanoyl- (C8-HSL) and N-decanoyl-homoserine lactone (C10-HSL) were studied in axenic systems with barley (Hordeum vulgare L.) and the legume yam bean (Pachyrhizus erosus (L.) Urban) as model plants using ultra-performance liquid chromatography (UPLC), Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) and tritium-labelled AHLs. Decreases in AHL concentration due to abiotic adsorption or degradation were tolerable under the experimental conditions. The presence of plants enhanced AHL decline in media depending on the compounds’ lipophilicity, whereby the legume caused stronger AHL decrease than barley. All tested AHLs were traceable in root extracts of both plants. While all AHLs except C10-HSL were detectable in barley shoots, only C6-HSL was found in shoots of yam bean. Furthermore, tritium-labelled AHLs were used to determine short-term uptake kinetics. Chiral separation by GC-MS revealed that both plants discriminated D-AHL stereoisomers to different extents. These results indicate substantial differences in uptake and degradation of different AHLs in the plants tested.
Keywords: UPLC; FTICR-MS; Tritium autoradiography; Chiral separation; Hordeum vulgare ; Pachyrhizus erosus
Characterization of imazamox degradation by-products by using liquid chromatography mass spectrometry and high-resolution Fourier transform ion cyclotron resonance mass spectrometry by M. Harir; M. Frommberger; A. Gaspar; D. Martens; A. Kettrup; M. El Azzouzi; Ph. Schmitt-Kopplin (1459-1467).
The photodecomposition of imazamox, a herbicide of the imidazolinone family, was investigated in pure water. The main photoproducts from the photolysis were followed over time by liquid chromatography mass spectrometry and structures were proposed from exact mass determinations obtained by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry. The method comprised exact mass determination with better than 0.2 ppm mass accuracy and a corresponding structural visualization taking care of respective isotopes with an adapted van Krevelen diagram that enabled a systematic approach to the characterisation of the elementary composition of each photoproduct. By taking advantage of the high resolving power of FT-ICR MS to make precise formula assignments, the derived 2D van Krevelen diagram (O/C; H/C; m/z) enabled one to structurally differentiate the formed photoproducts and to propose a degradation pathway for imazamox. Figure Overview of applied method to analyse the photolysis process of imazamox herbicide
Keywords: Photolysis; Imazamox; LC/MS; FT-ICR MS; Photoproducts
Metabolic profiling using Fourier-transform ion-cyclotron-resonance mass spectrometry by Daisaku Ohta; Daisuke Shibata; Shigehiko Kanaya (1469-1475).
With the aid of the extreme resolving power of Fourier-transform ion-cyclotron-resonance mass spectrometry (FT-ICR/MS), we have developed a metabolomics platform for high-throughput metabolic profiling and metabolite candidate identification integrating a data-processing system, the Dr.DMASS program ( http://kanaya.naist.jp/DrDMASS/ ), and a metabolite-species database, KNApSAcK ( http://kanaya.aist-nara.ac.jp/KNApSAcK/ ). We discuss the potential of this FT-ICR/MS-based metabolic profiling scheme as a general metabolomics tool by clarification of plant metabolic disorders and specific metabolite accumulation patterns caused by herbicidal enzyme inhibitors.
Keywords: Fourier-transform ion-cyclotron-resonance mass spectrometry; Metabolomics; Data processing
Retention behavior of ginsenosides on a poly(vinyl alcohol)-bonded stationary phase in hydrophilic interaction chromatography by Noel S. Quiming; Nerissa L. Denola; Azamjon B. Soliev; Yoshihiro Saito; Kiyokatsu Jinno (1477-1488).
The influences of the organic component of the mobile phase and the column temperature on the retention of ginsenosides on a poly(vinyl alcohol) (PVA) bonded stationary phase operated under hydrophilic interaction chromatographic mode were investigated. The retention of the ginsenosides was found to increase with increasing amount of acetonitrile (MeCN) in the mobile phase, which is typical of hydrophilic interaction chromatographic behavior. It was also found that the retention of the analytes was highly affected by the type of the organic modifier used. Aqueous MeCN (75–90%) gave the most satisfactory retention and separation of ginsenosides Rf, Rg1, Rd, Re, Rc, Rb2 and Rb1 compared with aqueous methanol, isopropyl alcohol or tetrahydrofuran at the same composition levels. The effects of the different types of organic modifiers on the retention of the analytes were attributed to their solvent strength and hydrogen-bond accepting/donating properties. The effect of temperature on the retention of ginsenoside on the PVA-bonded phase was assessed by constructing van’t Hoff plots for two temperature ranges: subambient (273–293 K) and ambient-elevated (298–333 K) temperatures. van’t Hoff plots for all analytes were linear at the two temperature intervals; however, the slopes of the lines corresponding to ginsenosides Rg1 and Re were completely different from those for the rest of the analytes especially in the subambient temperature range. Enthalpy-entropy compensation (EEC) studies were conducted to verify the difference in thermodynamics observed for ginsenosides Rg1 and Re compared with the other analytes. EEC plots showed that Rf, Rd, Rc, Rb2 and Rb1 were possibly retained by the same retention mechanism, which was completely different from that of Rg1 and Re at subambient temperatures. Retention prediction models were derived using multiple linear regression to identify solute attributes that affected the retention of the analytes on the PVA-bonded phase. The mathematical models derived revealed that the number of hydrogen-bond donors and the ovality of the molecules are important molecular properties that govern the retention of the compounds on the chromatographic system.
Keywords: Ginsenosides; Enthalpy-entropy compensation; Hydrophilic interaction chromatography; Poly(vinyl alcohol)-bonded phase; Van’t Hoff plot
Microstructural and chemical transformation of thin Ti/Pd and TiD y /Pd bilayer films induced by vacuum annealing by W. Lisowski; E. G. Keim; Z. Kaszkur; A. H. J. van den Berg; M. A. Smithers (1489-1498).
Using a combination of scanning electron microscopy, transmission electron microscopy (TEM), X-ray diffraction and X-ray photoelectron spectroscopy (XPS), we made a comparative study of the high-temperature annealing impact on thin titanium deuteride (TiD y ) films covered by an ultrathin Pd layer, and on Ti/Pd bilayer films. The bilayer films were prepared under ultrahigh vacuum conditions and were in situ annealed using the same annealing procedure. It was found that the surface and the bulk morphology of both films undergo different annealing-induced transformations, leading to an extensive intermixing between the Ti and Pd layers and the formation of a new PdTi2 bimetallic phase. Energy-filtered TEM imaging and energy-dispersive X-ray spectrometry analysis, as well as XPS depth profiling all provided evidence of a different distribution of Pd and Ti in the annealed TiD y /Pd film compared with the annealed Ti/Pd film. Our results show that thermal decomposition of TiD y , as a consequence of annealing the TiD y /Pd film, modifies the intermixing process, thereby promoting Ti diffusion into the Pd-rich top layer of the TiD y film and thus providing a more likely path for the formation of the PdTi2 phase than in an annealed Ti/Pd film. Figure Figure Microstructural and chemical characterisation of thin TiDy/Pd film after annealing
Keywords: Annealing; Titanium deuteride; Microstructure; X-ray photoelectron spectroscopy
Optimization of direct whole blood PCR amplification with applications on a static thermostat chip by Bai-Yan Qu; Zhi-Yong Wu; Xiao-Xi Tian; Kun Chen; Fang Fang (1499-1504).
In this paper, direct whole blood PCR amplifications on a static chip thermostat without sample purifications are demonstrated; in these amplifications, problems such as cross-interferences and contaminations could be avoided. The amplification conditions, such as the compositions of reagents and thermal programs, were investigated systematically by a GeneAmp PCR system with a native p53 gene segment (about543 bp) of human genome and an exterior lambda DNA segment (about 500 bp) as targets. Direct amplifications of p53 and K-ras (about 157 bp) gene segments from 0.5 μL blood samples were successfully demonstrated by a static PCR chip with an indium tin oxide glass substrate. The chip thermostat has a typical size of 25 mm × 25 mm, and a polyethylene tube was used as the PCR vial on the glass surface of the chip. Fuzzy proportional integration–differentiation algorithms were adopted in temperature controls of the chip with an aid of a micro-Pt100 sensor. In the direct PCR with the thermostat chip, the whole process only involves automatic thermal programs. This work demonstrated that a chip PCR for field test without desktop facilities is possible either for a point of care test or for forensic analysis. Figure Photo of the glass static thermostat chip with 2 PCR reaction vials
Keywords: Direct PCR; Whole blood; Static thermostat chip
A liquid chromatography/tandem mass spectrometric multi-mycotoxin method for the quantification of 87 analytes and its application to semi-quantitative screening of moldy food samples by Michael Sulyok; Rudolf Krska; Rainer Schuhmacher (1505-1523).
This paper describes the extension of a previously published method based on liquid chromatography/electrospray ionization tandem mass spectrometry (HPLC/ESI-MS/MS) from 39 to currently 87 analytes. Besides the mycotoxins for which regulated concentrations exist, the method now comprises not only almost all mycotoxins for which standards are commercially available, but also a number of other important metabolites produced by fungi involved in food spoilage. The method is based on a single extraction step using an acidified acetonitrile/water mixture followed by analysis of the diluted crude extract. Method performance characteristics were determined after spiking breadcrumbs as model matrix at multiple concentration levels. With very few exceptions, coefficients of variation of the whole procedure of <5% and repeatabilities at the highest spiking level of <7% were obtained. Limits of detection ranged between 0.02 and 225 μg kg−1. The quantitative determination of ergopeptides was disturbed by epimerization due to the acidic conditions. From the remaining 77 analytes, the apparent recoveries of nine substances deviated significantly from the CEN target range of 70–110% due to incomplete extraction and/or matrix effects. In principle, the latter can be compensated for by the application of matrix-matched calibration. The developed method was applied to 18 moldy samples (including bread, fruits, vegetables, jam, cheese, chestnuts and red wine) from private households. This study revealed the great value of the described method: 37 different fungal metabolites were identified at concentrations of up to 33 mg kg−1, and some of these have never been reported before in the context of moldy food products. Figure ESI (+) MS/MS chromatogram (total ion current of all MRMs) of a sample of moldy dark bread
Keywords: Liquid chromatography; Tandem mass spectrometry; Mycotoxins; Multi-target analysis; Food analysis; Molds
Characterization of genuine and fake artesunate anti-malarial tablets using Fourier transform infrared imaging and spatially offset Raman spectroscopy through blister packs by Camilla Ricci; Charlotte Eliasson; Neil A. Macleod; Paul N. Newton; Pavel Matousek; Sergei G. Kazarian (1525-1532).
In support of the efforts to combat the illegal sale and distribution of counterfeit anti-malarial drugs, we evaluated a new analytical approach for the characterization and fast screening of fake and genuine artesunate tablets using a combination of Raman spectroscopy, Spatially Offset Raman Spectroscopy (SORS) and Attenuated Total Reflection-Fourier Transform Infrared (ATR-FTIR) imaging. Vibrational spectroscopy provided chemically specific information on the composition of the tablets; the complementary nature of Raman scattering and FTIR imaging allowed the characterization of both the overall and surface composition of the tablets. The depth-resolving power of the SORS approach provided chemically specific information on the overall composition of the tablets, non-invasively, through a variety of packaging types. Spatial imaging of the tablet surface (using ATR-FTIR) identified the location of domains of excipients and active ingredients with high sensitivity and enhanced spatial resolution. The advantages provided by a combination of SORS and ATR-FTIR imaging in this context confirm its potential for inclusion in the analytical protocol for forensic investigation of counterfeit medicines.
Keywords: FT-IR spectroscopy; Fake drugs; Malaria; Chemical imaging; SORS; Turbid; Artesunate
pH-sensitive holograms for continuous monitoring in plasma by Kathryn Medlock; Hazel Harmer; Graham Worsley; Adrian Horgan; John Pritchard (1533-1539).
Conventional electrochemical methods of determining the pH of body fluids have drawbacks. Newer optical methods offer the promise of miniaturisation and continuous in vivo measurements without drift. This report examines the ability of a holographic sensor based on a thin-film, biocompatible hydrogel (approximately 10 μm) of poly(2-hydroxyethyl methacrylate) and ionisable 2-(dimethylaminoethyl) methacrylate to accurately measure the pH of blood plasma ex vivo. It is found that the sensors behave in a fully reversible manner. After an initial calibration with buffers, they can measure pH over extended periods (more than 40 h).
Keywords: Biosensors; Hologram; Polymer; Hydrogel; pH; Continuous
Integrated sorption–energy-dispersive X-ray fluorescence detection for automatic determination of lead and cadmium in low-concentration solutions by J. A. Pérez-Serradilla; M. D. Luque de Castro (1541-1547).
Sorbent material packed in a PTFE laboratory-made flow cell located in the specimen holder of an energy-dispersive X-ray fluorescence (EDXRF) detector has been used for in situ solid-phase extraction (SPE) preconcentration–detection of metals. The flow cell was connected to a single-channel flow-injection (FI) manifold (for full automation of the steps and proper development of the method) by two PTFE tubes of 0.5-mm inner diameter introduced into the spectrometer specimen holder by a small orifice without distortion or modification of the instrument. The optical window open in the PTFE flow cell was adjusted to the X-ray irradiation zone of the spectrometer and fixed to it. The approach was tested by using both Pb and Cd aqueous solutions and a Dowex 50 cation-exchange resin as a sorbent, and flushing the sample through the flow cell for EDXRF measurements after removal of the sample matrix. The limits of detection and the limits of quantification (LOQs) thus obtained were 0.15 and 0.5 μg for Pb and 0.3 and 0.8 μg for Cd, respectively, values that allow the approach to be used for the analysis of drinking water by injecting a 100-mL sample into the FI manifold, taking into account the EC drinking water directives. The linear dynamic ranges are between the LOQ and 600 μg for both analytes. The method was validated by the standard addition method using tap-water samples. In addition, the integrated SPE–EDXRF approach enables the study of the variables influencing the sorption step–namely the effects of the volume of sample flushed through the column, concentrations of the analytes in the sample, breakthrough volume of the resin, elution profiles, sample pH and retention and elution flow rates–in an automatic, cheap, fast and precise way.
Keywords: Solid-phase extraction; Energy-dispersive X-ray fluorescence; Lead; Cadmium; Flow injection; Ion-exchange resin
A new highly specific and robust yeast androgen bioassay for the detection of agonists and antagonists by Toine F. H. Bovee; Richard J. R. Helsdingen; Astrid R. M. Hamers; Majorie B. M. van Duursen; Michel W. F. Nielen; Ron L. A. P. Hoogenboom (1549-1558).
Public concern about the presence of natural and anthropogenic compounds which affect human health by modulating normal endocrine functions is continuously growing. Fast and simple high-throughput screening methods for the detection of hormone activities are thus indispensable. During the last two decades, a panel of different in vitro assays has been developed, mainly for compounds with an estrogenic mode of action. Here we describe the development of an androgen transcription activation assay that is easy to use in routine screening. Recombinant yeast cells were constructed that express the human androgen receptor and yeast enhanced green fluorescent protein (yEGFP), the latter in response to androgens. Compared with other reporters, the yEGFP reporter protein is very convenient because it is directly measurable in intact living cells, i.e., cell wall disruption and the addition of a substrate are not needed. When yeast was exposed to 17β-testosterone, the concentration where half-maximal activation is reached (EC50) was 50 nM. The relative androgenic potencies, defined as the ratio between the EC50 of 17β-testosterone and the EC50 of the compound, of 5α-dihydrotestosterone, methyltrienolone, and 17β-boldenone are 2.3, 1.4, and 0.15 respectively. The results presented in this paper demonstrate that this new yeast androgen bioassay is fast, sensitive, and very specific and also suited to detect compounds that have an antiandrogenic mode of action.
Keywords: Antagonists; Brominated flame retardants; Crosstalk; Metabolism; Receptor; Saccharomyces cerevisiae
ESI-MS analyses of lake dissolved organic matter in light of supramolecular assembly by J. Peuravuori; P. Bursáková; K. Pihlaja (1559-1568).
A high-performance size-exclusion chromatography (SEC) system was coupled on-line to an electrospray ionization (ESI) interface to detect gas-phase ions by an API 365 LC/MS/MS triple quadrupole analyzer. The SEC fractions of a strongly coloured freshwater solution containing dissolved organic matter-humic substances (DOM-HS) were screened both by UV254 and by ESI mass spectrometry (ESI-MS) in the full-scan mode within the m/z range of 100–2,900 amu in negative and positive polarities. The ESI-MS spectra were also collected by direct infusion of the DOM-HS solution in both polarities. ESI-MS spectra did not primarily favour low mass compounds, and negative and positive total ion chromatograms were parallel to the SEC elution profile obtained by UV254 detection from DOM-HS solution. The UV254 detection overestimated the SEC portion of higher size/mass solutes and underestimated that of solutes of smaller sizes/masses as compared with the total ion chromatogram intensities in negative or positive polarities. The change of mass-weighted and number-weighted average sizes/masses (M w and M n) of different SEC fractions was fairly small, in contrast to UV254 detection, with increasing elution volume. A reasonable explanation for the great differences between M w and M n values, obtained by UV254 and ESI-MS detections for eight different SEC fractions, seems to be a supramolecular-type association of relatively small components through weak dispersive forces. M n values obtained by vapour-pressure osmometry for different SEC fractions were to some extent analogous with those of negative and positive ESI-MS. The shapes obtained by either negative or positive polarities and calculated M w and M n values indicated a close structural similarity between each SEC fraction. Positive ion and negative ion spectra of different humic fractions represented quite similar components, and there was no evidence for noteworthy occurrence of multiply charged ions being able to lower mass distributions of negative ion spectra. The effect of nitrogen on the mass spectra seemed to be unimportant, and the weak ions observed at even m/z values correspond most likely to the 13C counterparts of the more abundant 12C odd ions. No uncontrolled ESI fragmentation was observable and humic solutes seemed to be quite heat-resistant. Direct infusion of the untreated DOM-HS solution and statistical calculation verified that the SEC-separated different fractions really represent distinct entities of the original DOM-HS mixture. ESI-MS results support the opinion that the structural composition of humic solutes in their original combined mixture resembles supramolecular-type associations of smaller molecular size entities possessing similar structural functionalities.
Keywords: Electrospray ionization mass spectrometry; Molecular sizes; Humic substances; Molecular mixtures; Aquatic; Supramolecular associations
Semi-quantitative chemical analysis of hard coatings by Raman micro-spectroscopy: the aluminium chromium nitride system as an example by R. Kaindl; B. Sartory; J. Neidhardt; R. Franz; A. Reiter; P. Polcik; R. Tessadri; C. Mitterer (1569-1576).
A new method for chemical analyses of nitride-based hard coatings is presented. Raman band shifts in the spectra of Al x Cr1−x N coatings, deposited by physical vapour deposition from Al x Cr1−x targets with x T,Al = 0, 0.25, 0.50, 0.70 and 0.85, are calibrated using compositional data of the coatings derived by elastic recoil detection analysis (ERDA) and electron probe micro-analysis (EPMA). Inserting the composition-dependent Raman shift of a combinatorial acoustic-optic lattice mode into an empirically derived equation allows the determination of Al/Cr ratios of the coating with an accuracy of about ±2%. Spot, line and area analyses of coated cemented carbide and cold work steel samples by using a computer-controlled, motorized x,y-stage are demonstrated and the most important errors influencing precision and accuracy are discussed. Figure Raman map of a coated cold-work steel sample
Keywords: IR spectroscopy/Raman spectroscopy; Instrumentation; Thin films; Chemometrics/Statistics; Electron/ion microprobe; Inorganic compounds/Trace inorganic compounds; Metals/Heavy metals
Quality control of cosmetic mixtures by NIR spectroscopy by Marcelo Blanco; Manel Alcalá; Joaquim Planells; Rufí Mulero (1577-1583).
Cosmetic preparations typically consist of mixtures of various compounds of natural origin or their derivatives. Their analysis is made rather difficult by their usually high complexity and is utterly impossible with a single analytical method; also, there is usually little to be gained by determining every individual component of the mixture. Rather, analyses are aimed at ensuring a proper balance between the contents of each component and thus require the use of methods capable of delivering global information. The combined use of near-infrared (NIR) spectroscopy and multivariate spectral processing chemometric techniques has enabled the development of effective methods for establishing the composition of complex samples with acceptable levels of analytical properties, such as accuracy, precision and throughput. In this work, we developed partial least squares calibration models for the determination of each component in a cosmetic mixture, and global indices (viz. the hydroxyl value), simply from the NIR spectrum of the sample. The models thus obtained are accurate enough for use in quality control analyses of cosmetic preparations and provide an effective alternative to existing conventional global methods. Experimental setup for measurement
Keywords: Cosmetics; Near-infrared spectroscopy; Quality control; Multivariate calibration
Analyses of the temperature and pH effects on the complexation of magnesium and calcium in human blood plasma: an approach using artificial neural networks by J. C. D. Conway; A. Liparini; J. R. de Oliveira Jr; J. C. Belchior (1585-1594).
The temperature and pH effects on the equilibrium of a blood plasma model have been studied on the basis of artificial neural networks. The proposed blood plasma was modeled considering two important metals, calcium and magnesium, and six ligands, namely, alanate, carbonate, citrate, glycinate, histidinate and succinate. A large data set has been used to simulate different concentrations of magnesium and calcium as a function of temperature and pH and these data were used for training the neural network. The proposed model allowed different types of analyses, such as the effects of pH on calcium and magnesium concentrations, the competition between calcium and magnesium for ligands and the effects of temperature on calcium and magnesium concentrations. The model developed was also used to predict how the variation of calcium concentration can affect magnesium concentrations. A comparison of neural network predictions against experimental data produced errors of about 3%. Moreover, in agreement with experimental measurements (Wang et al. in Arch. Pathol. 126:947–950, 2002; Heining et al. in Scand. J. Clin. Lab. Invest. 43:709–714, 1983), the artificial neural network predicted that calcium and magnesium concentrations decrease when pH increases. Similarly, the magnesium concentrations are less sensitive than calcium concentrations to pH changes. It is also found that both calcium and magnesium concentrations decrease when the temperature increases. Finally, the theoretical model also predicted that an increase of calcium concentrations will lead to an increase of magnesium concentration almost at the same rate. These results suggest that artificial neural networks can be efficiently applied as a complementary tool for studying metal ion complexation, with especial attention to the blood plasma analysis. Figure Artificial neural networks for predicting the behavior of calcium and magnesium as a function of pH and temperature in human blood plasma
Keywords: Artificial neural networks; Metal ions; Calcium; Magnesium; Blood plasma
On-line solid-phase extraction and multisyringe flow injection analysis of Al(III) and Fe(III) in drinking water by Pierre Vanloot; Catherine Branger; André Margaillan; Christophe Brach-Papa; Jean-Luc Boudenne; Bruno Coulomb (1595-1602).
A new analytical method was developed for on-line monitoring of residual coagulants (aluminium and iron salts) in potable water. The determination was based on a sequential procedure coupling an extraction/enrichment step of the analytes onto a modified resin and a spectrophotometric measurement of a surfactant-sensitized binary complex formed between eluted analytes and Chrome Azurol S. The optimization of the solid phase extraction was performed using factorial design and a Doehlert matrix considering six variables: sample percolation rate, sample metal concentration, flow-through sample volume (all three directly linked to the extraction step), elution flow rate, concentration and volume of eluent (all three directly linked to the elution step). A specific reagent was elaborated for sensitive and specific spectrophotometric determination of Al(III) and Fe(III), by optimizing surfactant and ligand concentrations and buffer composition. The whole procedure was automated by a multisyringe flow injection analysis (MSFIA) system. Detection limits of 4.9 and 5.6 μg L−1 were obtained for Al(III) and Fe(III) determination , respectively, and the linear calibration graph up to 300 μg L−1 (both for Al(III) and Fe(III)) was well adapted to the monitoring of drinking water quality. The system was successfully applied to the on-site determination of Al(III) and Fe(III) at the outlet of two water treatment units during two periods of the year (winter and summer conditions).
Keywords: Solid-phase extraction; Multisyringe flow injection analysis; Al(III); Fe(III); Sensitization of complexes
Optimisation of the on-fibre derivatisation of volatile fatty acids in the simultaneous determination together with phenols and indoles in cow slurries by J. Larreta; A. Usobiaga; N. Etxebarria; G. Arana; O. Zuloaga (1603-1609).
The on-fibre derivatisation of volatile fatty acids (VFAs) using N-(tert-butyldimethylsilyl)-N-methyltrifluoroacetamide (MTBSTFA) was optimised in the simultaneous determination of VFAs together with phenols and indoles by headspace solid-phase microextraction (SPME)–gas chromatography–mass spectrometry. Firstly, the nature of the SPME fibre was optimised and four different fibres were studied (100 μm polydimethylsiloxane, 85 μm Carboxen/polydimethylsiloxane, 5/30 μm divinylbenzene/Carboxen/polydimethylsiloxane and 85 μm polyacrylate). The optimum fibre (50/30 μm divinylbenzene/Carboxen/polydimethylsiloxane) was used to study the exposure time of the fibre to the derivatisation agent and the desorption time and temperature. Firstly, a factorial design was built but since the three variables had a significant effect, a central composite design was used to build the response surfaces. The best signals were obtained after the exposure of the fibre in the headspace of the MTBSTFA derivatisation reagent for 1 h and desorption at 300 °C for 9 min. The determination of underivatised phenols and indoles was not affected by the presence of the derivatisation reagent in the fibre.
Keywords: Solid-phase microextraction; Volatile fatty acids; Phenols; Indoles; Derivatisation; N-(tert-Butyldimethylsilyl)-N-methyltrifluoroacetamide
A method for identification of diastereomers of 2-decarboxy-betacyanins and 2,17-bidecarboxy-betacyanins in reversed-phase HPLC by Sławomir Wybraniec (1611-1621).
A method was developed for identification of diastereomers of 2-decarboxy-betacyanins and 2,17-bidecarboxy-betacyanins chromatographed in reversed-phase high-performance liquid chromatography (HPLC) as pairs of unknown elution order. The method was based on alkaline hydrolysis of selected betacyanin and decarboxylated betacyanin mixtures and subsequent cross-recondensation of the hydrolysates. The arising intermediate derivatives of decarboxylated betalamic acid and cyclo-dopa were stable enough for subsequent recondensation. Generated diagnostic pigments as the recondensation products were monitored by HPLC–diode-array detection–electrospray ionisation mass spectrometry. The isoforms (15R) of 2-decarboxy-betacyanins and 2,17-bidecarboxy-betacyanins were eluted earlier than the 15S forms, in contrast to betacyanins and 17-decarboxy-betacyanins, but in accordance with betaxanthins. 2,17-Bidecarboxy-betanin/2,17-bidecarboxy-isobetanin, being not resolved in reversed-phase HPLC, were partially separated by ion-pair chromatography and under these conditions their order of elution was the same as that of acylated 2,17-bidecarboxy-betacyanins. The method allows complete identification of all the decarboxylated groups of betanin, phyllocactin and hylocerenin as well as other betacyanins in biological or pharmaceutical material.
Keywords: Betanin; Phyllocactin; Hylocerenin; Decarboxy-betacyanins; High-performance liquid chromatography
Reduction of the interferences of biochemicals and hematocrit ratio on the determination of whole blood glucose using multiple screen-printed carbon electrode test strips by Yueh-Hui Lin; Thomas Y. Shen; C. Allen Chang (1623-1631).
A practical approach to reduce the interferences of biochemicals and hematocrit ratio (Hct%) in the determination of whole blood glucose using multiple screen-printed carbon electrode (SPCE) test strips is described. SPCE test strips with and without glucose oxidase [i.e., GOD(+)-SPCEs and GOD(-)-SPCEs] were used and the chronoamperometric currents of test glucose solutions with various spiked uric acid concentrations and Hct% were measured. By establishing the interference relationships between glucose concentrations and uric acid concentrations as well as Hct% values and with appropriate corrections, the whole blood glucose determinations could be made to be more accurate and comparable to those determined by the reference YSI method. Specifically, the use of the ΔI value, i.e., the current difference between GOD(+)-SPCE and GOD(-)-SPCE measurements, would reduce most of the uric acid/biochemical interferences. An interpolation method was also established to correct for the glucose determinations with Hct% interferences. The Hct% corrections using the interpolation method are especially important and necessary for those blood samples with glucose concentrations higher than 110 mg dL-1 and Hct% values lower than 35%. This approach should also be applicable to other biochemical determinations using similar electrochemical techniques.
Keywords: Screen-printed carbon electrodes; Electrochemical biosensor; Glucose; Interference; Hematocrit ratio; Uric acid
Discrimination between wild-type and ampicillin-resistant Escherichia coli by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry by Johanna E. Camara; Faith A. Hays (1633-1638).
Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) was optimized to discriminate between wild-type and ampicillin-resistant Escherichia coli. Only ampicillin-resistant E. coli displayed an m/z ≈ 29,000 peak, which was confirmed as β-lactamase by in-gel digestion followed by peptide mass fingerprinting. Rapid MALDI-TOF MS detection of antibiotic-resistance could fulfill an important clinical need, providing critical phenotypic information beyond genus–species identification.
Keywords: Antibiotic resistance; β-Lactamase; Escherichia coli; Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry
Relative quantitation of proteins fractionated by the ProteomeLab™ PF 2D system using isobaric tags for relative and absolute quantitation (iTRAQ) by Helena Skalnikova; Pavel Rehulka; Josef Chmelik; Jirina Martinkova; Michaela Zilvarova; Suresh Jivan Gadher; Hana Kovarova (1639-1645).
We describe an optimised protocol for application of isobaric tags for relative and absolute quantitation (iTRAQ) and tandem mass spectrometry to obtain relative quantitative data from peptides derived from tryptic digestions of proteins fractionated by using the 2D liquid-phase ProteomeLab™ PF 2D technique. This methodology is suitable for the quantitation of proteins from a pool of co-eluting proteins which are often difficult to identify for the purpose of candidate protein selection for biologically relevant qualitative/quantitative changes under experimental conditions or in disease states. iTRAQ quantitation also facilitates the possibility of result to result comparison using other methodologies such as UV protein quantitation via the ProteomeLab™ PF 2D technique. The optimised protocol outlined here allows relative quantitation by MALDI-TOF/TOF mass spectrometry with high sensitivity and without the need to perform 2D HPLC separation of labelled peptides. The overall outcome is the simplification in the data complexity and the ease of use of the labelling protocol.
Keywords: 2D liquid chromatography; Human T-lymphoblastic leukemia cell proteins; iTRAQ; ProteomeLab™ PF 2D; Relative quantitation
Flow cell within an LED: a proposal for an optical absorption detector by Cássia Ugucione; Arnaldo Alves Cardoso (1647-1650).
Droplets formed at the tip of a tube under the same conditions possess extreme uniformity of form, volume and weight. These properties of liquid drop formation have been known for a long time and consequently many applications for the drop have been found in instrumentation and chemical analysis methods. In the present paper, we report on the analytical use of a dynamic LED-based flow-through optical absorption detector with optical path length controlled by continuous dropping of a solution. This arrangement consists of a flow cell built within a high-intensity red LED (λ max = 630 nm). The feasibility of the detector is demonstrated by colorimetric determination of methylene blue, and ammonium by Berthelot’s reaction, in a flow-injection system. For ammonium, the reaction forms a blue dye (indophenol) with a maximum absorption at 630–650 nm. The detection limit, considered as 3 times the signal of the blank, is better than 125 μg l-1. The small flow cell represents a good combination of optical path length, low volume and fast washout. This detector can be used advantageously in automated methods and can represent a solution to problems of optical detection involving gas bubbles and precipitation of particles in turbidimetric applications.
Keywords: LED-based detector; Optical absorption detector; Flow cell; Ammonium determination