Analytical and Bioanalytical Chemistry (v.400, #2)

Analytical and bioanalytical luminescence by Petr Solich (311-312).
is currently Professor and Head of the Analytical Chemistry Department at the Faculty of Pharmacy, Charles University in Hradec Kralové, Czech Republic. His research interests are automation of analytical procedures, flow methods (flow-injection analysis, sequential injection analysis, and sequential injection chromatography), chromatographic methods (mainly UHPLC with sub-2-micron columns or use of monolithic columns) applied to environmental analysis of low concentrations of pharmaceuticals or bioanalytical analysis for determination of biomarkers, and, finally, modern sample-preparation methods used in environmental and bioanalytical applications. He has published more than 140 research papers and has been responsible for more than 20 research grants from different disciplines (pharmaceutical, environmental, health care).

A quantitative chemiluminescent assay for analysis of peroxide-based explosives by S. Girotti; E. Ferri; E. Maiolini; L. Bolelli; M. D’Elia; D. Coppe; F. S. Romolo (313-320).
A quantitative chemiluminescent method, enabling indirect identification of the peroxide-based explosives TATP (triacetone triperoxide) and HMTD (hexamethylene triperoxide diamine) has been developed. Treatment of these compounds with acidic solutions produced peroxides, which were transformed into radical derivatives by horseradish peroxidase (HRP) and then quantified by measuring the light emitted during their oxidation of luminol. The method was first developed in the microplate format and later optimized for a portable luminometer, to enable rapid application of the assay directly on site. When the portable luminometer was used each analysis took only 5–10 min. The method had good selectivity, sensitivity, and reproducibility; in the microplate format the limits of detection (LOD) and quantification (LOQ) were 40 and 50 ng mL−1, respectively, for both TATP and HMTD. When the portable luminometer was used the LOD and LOQ were 50 and 100 ng mL−1, respectively, for both compounds. Introduction of light emission-enhancing compounds did not improve the analytical performance of the assay. Imprecision (CV values) was always below 10%. Recovery varied rapidly with time, with an average value of 78% after 5 min. No false-positive result was detected on measurement of a variety of samples; this is an important feature for analysis on site. The method was applied both to contaminated materials and to fortified soil samples, simulating operational conditions.
Keywords: Triacetone triperoxide (TATP); Hexamethylene triperoxide diamine (HMTD); Chemiluminescence; Peroxide-based explosives; Forensic chemistry; Portable luminometer

Study of non-covalent interactions of luotonin A derivatives and the DNA minor groove as a first step in the study of their analytical potential as DNA probes by Pierluigi Mussardo; Elisa Corda; Víctor González-Ruiz; Jegathalaprathaban Rajesh; Stefano Girotti; M. Antonia Martín; Ana I. Olives (321-327).
The interaction between DNA and several newly synthesized derivatives of the natural anticancer compound luotonin A has been studied. The results from our work reveal an effective and selective alkaloid/double-stranded DNA (ds-DNA) interaction. In the presence of increasing amounts of ds-DNA, a noticeable fluorescence quenching of the luotonin A derivatives under study was observed. However, this effect did not take place when single-stranded DNA (ss-DNA) was employed. The association constant alkaloids/ds-DNA was calculated by quantitation of such a quenching effect. The influence of other quenchers, namely Co2+ and Br on the native fluorescence of luotonin A and derivatives was also studied, and a remarkable quenching effect was observed for both ions. We have also investigated how by binding DNA the alkaloids could get protected from the external Co2+ and Br quenchers. The Stern–Volmer constants (K SV) for Co2+ and Br quenching effect on the studied alkaloids were considerably reduced (10–50%) after incubation of the compounds in the presence of DNA with regard to the K SV values in absence of DNA. An increase in the fluorescence anisotropy values of luotonins was also produced only in the presence of ds-DNA but not in the case of ss-DNA. To better characterize the nature of that interaction, viscosimetry assays and ethidium bromide displacement studies were conducted. With regard to DNA reference solutions, the viscosity of solutions containing DNA and luotonin A derivatives was reduced or not significantly increased. It was also observed that the studied compounds were unable to displace the intercalating agent ethidium bromide. All of these results, together with the obtained association constants values (K ass = 2.2 × 102 – 1.3 × 103), support that neither covalent nor intercalating interactions luotonin A derivatives/ds-DNA are produced, leading to the conclusion that these alkaloids bind ds-DNA through the minor groove. The specific changes in the fluorescence behavior of luotonin A and derivatives distinguishing between ss-DNA and ds-DNA binding, lead us to propose these compounds as attractive turn-off probes to detect DNA hybridization.
Keywords: Drug–DNA interactions; DNA hybridization; Fluorescence quenching; Luotonin A; Viscosimetry

Detoxification of AM-241 solutions by humic substances: bioluminescent monitoring by Tatiana Rozhko; Lidia Bondareva; Olga Mogilnaya; Galina Vydryakova; Alexander Bolsunovsky; Devard Stom; Nadezhda Kudryasheva (329-334).
The study addresses the effect of humic substances on marine luminous bacteria Photobacterium phosphoreum exposed to Am-241 (3,000 Bq L−1, water solution). Luminescent intensity of the bacteria was applied as a marker of their physiological activity. Humic substances have been found to reduce the effect of Am-241 on luminescence, decrease damage to cells, and change distribution of Am-241 between bacterial cells and intercellular media. It was shown that water-soluble humic substances, being products of natural transformation of organic substances in soil and bottom sediments, can serve as protecting agents for water microorganisms exposed to alpha radionuclides.
Keywords: Luminous bacteria; Ionizing radiation; Detoxification; Humic substances

Lie group study of Raman spectra of the Gurken gradient in Drosophila oogenesis by Jen-Cheng Wang; Pei-Yu Wang; Ruo-Rung Huang; Wei-Chieh Lin; Chia-Hui Fang; Li-Mei Pai; Tzer-En Nee (335-341).
We carried out a Lie group study of the micro-Raman tissue spectra of the Gurken gradients of Drosophila oogenesis. Matrix representations (2 × 2) resulting from the polarized Raman scattering were employed to assess the roles of the ligand-receptor complexes in follicle cell. It was found that the Gurken expansion caused by overexpressing Dally-like protein (Dlp) revealed an X 1 Lie point symmetry, while the Gurken distribution in the wild-type egg showed an X 23 Lie point symmetry. The correlation between the corresponding continuous symmetry operations and the observed Gurken localization were a corroboration of the significance of the Lie group analysis by means of the reaction–diffusion equation in a prolate spheroidal coordinate system. These investigations suggested that the group-theoretical approach can be applied to characterize the fluctuating asymmetry and the developmental stability in a wide variety of organisms.
Keywords: Lie group; Raman spectra; Gurken; Drosophila

Effect of halogenated fluorescent compounds on bioluminescent reactions by Tamara N. Kirillova; Marina A. Gerasimova; Elena V. Nemtseva; Nadezhda S. Kudryasheva (343-351).
The paper investigates an application of luminescent bioassays to monitor the toxicity of organic halides. Effects of xanthene dyes (fluorescein, eosin Y, and erythrosin B), used as model compounds, on bioluminescent reactions of firefly Luciola mingrelica, marine bacteria Photobacterium leiognathi, and hydroid polyp Obelia longissima were studied. Dependence of bioluminescence quenching constants on the atomic weight of halogen substituents in dye molecules was demonstrated. Bacterial bioluminescence was shown to be most sensitive to heavy halogen atoms involved in molecular structure; hence, it is suitable for construction of sensors to monitor toxicity of halogenated compounds. Mechanisms of bioluminescence quenching—energy transfer processes, collisional interactions, and enzyme–dye binding—were considered. Changes of bioluminescence (BL) spectra in the presence of the dyes were analyzed. Interactions of the dyes with enzymes were studied using fluorescence characteristics of the dyes in steady-state and time-resolved experiments. The dependences of fluorescence anisotropy of enzyme-bound dyes, the average fluorescence lifetime, and the number of exponential components in fluorescence decay on the atomic weight of halogen substituents were demonstrated. The results are discussed in terms of “dark effect of heavy halogen atom” in the process of enzyme–dye binding; hydrophobic interactions were assumed to be responsible for the effect. Figure Bioluminescent quenching constants vs. atomic weight of substituents in xanthene dyes.
Keywords: Bioluminescent assay; Xanthene dyes; Effect of heavy halogen atom; Bioluminescent enzymes; Fluorescence; Lifetime; Anisotropy

Sulfamethoxazole (SMX) is a synthetic antibiotic widely applied as a bacteriostatic drug to treat a number of diseases. SMX can persist in the environment for long periods of time because of its low biodegradability, which may result in various, direct and indirect, toxicological effects on the environment and on human health. Therefore, we have developed the electrochemical advanced oxidation process (AOP) “electro-Fenton” to degrade SMX in aqueous media. In this work, a detailed study of the evolution of toxicity of SMX and its degradation products in aqueous solutions, during treatment by the electro-Fenton AOP, is described, using the bioluminescence Microtox® method, based on the inhibition of luminescence of marine bacteria Vibrio fischeri. Samples were collected at various electrolysis times and analyzed by HPLC for quantifying the evolution of the degradation products, and their toxicity was measured by the Microtox® method. Our results demonstrated that the toxicity of SMX aqueous solutions varied considerably with the electrolysis time and the applied current intensity. This phenomenon could be explained by the formation and disappearance of several degradation products, including cyclic and/or aromatic intermediates, and short-chain acid carboxylic acids, having a toxicity different of the initial antibiotic. The curves of the % of bacterial luminescence inhibition vs. electrolysis time, corresponding to the evolution of the toxicity of the formed degradation products, were investigated and tentatively interpreted. Figure Effect of the applied electrolysis current intensity on the evolution of the V. fischeri bacteria luminescence inhibition with time during the electro-Fenton process of SMX aqueous solutions, after an exposure time of 15 min
Keywords: Sulfamethoxazole; Electro-Fenton; Toxicity; Bioluminescence; Microtox® method

We investigated the chemisorption of self-assembled monolayers of sulfur-functionalized 4-amino-7-nitrobenzofurazan on gold and silver nanoisland films (NIFs) by means of surface-enhanced fluorescence (SEF) and surface-enhanced Raman scattering (SERS). The ligand is a push–pull molecule, where an intramolecular charge transfer occurs between an electron-donor and an electron-acceptor group, thus exhibiting nonlinear optical properties that are related to both SERS and SEF effects. The presence of different heteroatoms in the molecule ensures the possibility of chemical interaction with both silver and gold substrates. The SERS spectra suggest that furazan is bound to silver via lone pairs of the nitrogen atoms, whereas the ligand is linked to gold via a sulfur atom. Silver NIFs provide more efficient enhancement of both fluorescence and Raman scattering in comparison with gold NIFs. The present SEF and SERS investigation could provide useful information for foreseeing changes in the nonlinear responses of this push–pull molecule. Figure Surface-enhanced fluorescence on Ag and Au substrates
Keywords: Surface-enhanced fluorescence; Surface-enhanced Raman scattering; Silver; Gold; Nanoparticle

Conjugation reactions in the preparations of quantum dot-based immunoluminescent probes for analysis of proteins by capillary electrophoresis by M. Lišková; I. Voráčová; K. Klepárník; V. Hezinová; J. Přikryl; F. Foret (369-379).
A number of biologically important molecules, such as DNA, proteins, and antibodies, are routinely conjugated with fluorescent tags for high-sensitivity analyses. Here, the application of quantum dots in the place of bright and size-tunable luminophores is studied. Several selected bioconjugation reactions via zero-length cross-linkers, long-chain linkers, and oriented methods for linking of quantum dots with proteins were tested. Anti-ovalbumin, anti-proliferating cell nuclear antigen, anti-hemagglutinin, and anti-CD3 membrane protein as model antibodies and annexin V were used as high-specificity selectors. The reaction yield and efficiency of the prepared immunoluminescent probes were tested by capillary zone electrophoresis with laser-induced fluorescence detection. Figure Scheme of antibody-quantum dot conjugate
Keywords: CdTe quantum dots; Luminescent probe; Capillary zone electrophoresis; Bioconjugation reactions

Selective determination of ubiquinone in human plasma by HPLC with chemiluminescence reaction based on the redox cycle of quinone by Naoya Kishikawa; Nobuhiro Ohkubo; Kaname Ohyama; Kenichiro Nakashima; Naotaka Kuroda (381-385).
Ubiquinone is an important biologically active compound in the living body. The determination of ubiquinone in human plasma is useful for the investigation of bioavailability of ubiquinone and for early diagnosis of several diseases. Therefore, we developed a high-performance liquid chromatography (HPLC) with chemiluminescence detection method for the analysis of ubiquinone in plasma samples. The method is based on luminol chemiluminescence detection of super oxide anion that is generated by the redox cycle reaction between ubiquinone and dithiothreitol. The HPLC system involved an octyl column with a mobile phase of methanol. Ubiquinone eluted from the column was mixed with dithiothreitol and luminol solutions simultaneously, and generated chemiluminescence was monitored by chemiluminescence detector. The calibration curve for standard ubiquinone solution was linear from 0.09 to 43.2 μg/mL (0.45–216 ng on column) with the correlation coefficient of 0.999, and the detection limit (S/N = 3) was 26 ng/mL (130 pg on column). Using the proposed HPLC method, the peak of ubiquinone in human plasma could be clearly detected on the chromatogram without any interference from plasma components.
Keywords: Ubiquinone; Human plasma; Chemiluminescence; Redox cycle; HPLC

HPLC determination of methylphenidate and its metabolite, ritalinic acid, by high-performance liquid chromatography with peroxyoxalate chemiluminescence detection by Mitsuhiro Wada; Keisuke Abe; Rie Ikeda; Ruri Kikura-Hanajiri; Naotaka Kuroda; Kenichiro Nakashima (387-393).
An HPLC–peroxyoxalate chemiluminescence (PO-CL) method for simultaneous determination of methylphenidate (MPH) and ritalinic acid (RA) was developed. The method was used to monitor MPH and RA after administration of MPH to rats. Deproteinized plasma spiked with 1-(3-trifluoromethylphenyl)piperazine (IS) was dried and labeled with 4-(N,N-dimethylaminosulfonyl)-7-fluoro-2,1,3-benzoxadiazole (DBD-F). The labeled sample was cleaned with two kinds of solid-phase extraction cartridge, and the DBD-labels were separated on an ODS column with gradient elution using a mixture of CH3CN and imidazole–HNO3 buffer. Separation of MPH and RA can be achieved within 33 min. The LODs of MPH and RA at a signal-to-noise ratio of 3 were 2.2 and 0.4 ng mL−1, respectively. Moreover, monitoring of MPH and RA after MPH administration (10 mg kg−1) to rat could be performed. The concentration of RA 480 min after administration was eight times higher than that of MPH. The proposed HPLC–PO-CL method was useful for determination of MPH and RA in rat plasma and was successfully used to monitor these substances after MPH administration.
Keywords: Methylphenidate; Ritalinic acid; HPLC; Peroxyoxalate chemiluminescence; 4-(N,N-dimethylaminosulfonyl)-7-fluoro-2,1,3-benzoxadiazole

The analysis of beta-carboline alkaloids presents a renewed interest due to their biological relevance and their increasing popularity as recreational drugs. In the present work, a novel chromatographic reverse-phase high-performance liquid chromatography (RP-HPLC) method with fluorimetric detection has been applied to the determination of beta-carbolines spiked in human serum samples. The chromatographic procedure involves the use of less retentive, unusual C1 columns combined with hydro-alcoholic mobile phases and the use of beta-cyclodextrin or (2-hydroxypropyl)-beta-cyclodextrin as mobile-phase additives. The effective combination of C1 columns and the modified mobile phases with cyclodextrins leads to a considerable reduction in the organic proportion in the mobile phase (up to 50%) with good resolution and efficiency. Besides, the presence of cyclodextrins allows the use of ethanol, a green solvent, as the organic component in the mobile phase. Traditional RP-HPLC thus becomes an attractive eco-separation technique using conventional stationary phases under simple and user-friendly experimental conditions. Solid-phase extraction was employed as sample clean-up protocol with attractive features, i.e., a low consumption of organic solvents, time and step economy and diminished need for sample handling. The analytical procedure was completely validated showing satisfactory figures of merit. Limits of detection of 10−9–10−10 M can be achieved. The recoveries obtained for the total methodology (sample pre-treatment and chromatographic determination in the case of the mobile phases containing cyclodextrins) were very satisfactory (95–107%) as well as the intraday (2–3%) and interday precision values (3–7%). The use of 3-hydroxymethyl-beta-carboline as an internal standard allows the comparison of the goodness of response of the analytical methodology in the presence or absence of cyclodextrins.
Keywords: Cyclodextrins; Eco-friendly mobile phases; β-carboline derivatives; HPLC

Flow injection analysis combined with photo-induced fluorescence (FIA-PIF) has been applied for the determination of α-cypermethrin pesticide residues in Senegalese natural waters, using organic solutions and cyclodextrin (β-cyclodextrin and 2-hydroxypropyl-β-cyclodextrin) aqueous media. The α-cypermethrin insecticide has a very weak natural fluorescence, but it is converted into strongly fluorescent photoproduct(s) by UV irradiation. Cyclodextrins were found to enhance the PIF signal. FIA parameters, including mobile phase flow rate, injected volume, and reactor length, were optimized. Analytical performances of the FIA-PIF method for the determination of α-cypermethrin were satisfactory, with concentration linear dynamic ranges over one to two orders of magnitude and with rather low limits of detection and limits of quantification, in the ng mL−1 range, and relative standard deviations comprised between 1.2% and 3.8%. Application of FIA-PIF for the analysis of fortified natural water samples collected from Senegal yielded good recovery values (84–112%). Because of its high sampling rate, the FIA-PIF method constitutes a rapid analytical tool, useful for quantification of α-cypermethrin residues in natural waters.
Keywords: Flow injection analysis (FIA); Photo-induced fluorescence (PIF); α-Cypermethrin; Cyclodextrin; Pesticides; Water analysis

Methods developed for use in emergency toxicology have to be fast and simple. Additionally, such methods should be multi-analyte procedures because they allow monitoring of analytes of different drug classes in one single body sample. This is important because often only a limited amount of sample is available and the results have to be reported as fast as possible. Therefore, we describe the improvement of an existing method published by van Hee at al. The new method is fast and simple and designed for the simultaneous determination of ethylene glycol, 1,2-propylene glycol, lactic acid, glycolic acid, gamma-hydroxybutyric acid (GHB), diethylene glycol, triethylene glycol, and tetraethylene glycol in human plasma or urine. A 50-μL aliquot of sample was deproteinized and 20 μl of the diluted specimen were derivatized using bis-N,O-trimethylsilyl trifluoroacetamide and the catalyst dimethylformamide. After microwave-assisted derivatization, an aliquot was injected into the gas chromatograph and analyzed with electron ionization mass spectrometry in selective ion monitoring mode. All compounds are separated within 12 min and detected with a limit of quantification of 0.05 and 0.01 g/L for glycols and GHB, respectively. Calibration was linear from 0.05 to 1.0 g/L for glycols and 0.01 to 0.2 g/L for GHB. Validation criteria were shown to be in the required limits with exception of lactic acid. Average analysis time from starting sample preparation until quantitative plasma results of approximately 35 min was achieved. This turnaround time is considered most appropriate for emergency cases.
Keywords: Ethylene glycol; GHB; Glycolic acid; Toxicology; Validated

Combination of acid labile detergent and C18 Empore™ disks for improved identification and sequence coverage of in-gel digested proteins by Henning Koehn; Benjamin Lau; Stefan Clerens; Jeffrey E. Plowman; Jolon M. Dyer; Umi Salamah Ramli; Santanu Deb-Choudhury (415-421).
A protocol for improved extraction of peptides from in-gel protein digests, using a combination of the acid labile surfactant, sodium deoxycholate (SDC) and C18 Empore™ membranes, is presented. This approach results in better mass spectrum quality, higher numbers of identified peptide peaks and improved identification scores compared to standard tryptic digestion protocols, or protocols using only SDC or only C18 Empore™ disks. The advantages of the new protocol are demonstrated for two different types of samples: Merino wool intermediate filament proteins and Elaeis guineensis (oil palm) mesocarp proteins.
Keywords: 2-D electrophoresis; MALDI-TOF; In-gel digestion

The aim of the proposed work was to develop and validate a simple and sensitive assay for the analysis of atorvastatin (ATV) acid, ortho- and para-hydroxy-ATV, ATV lactone, and ortho- and para-hydroxy-ATV lactone in human plasma using liquid chromatography-tandem mass spectrometry. All six analytes and corresponding deuterium (d5)-labeled internal standards were extracted from 50 μL of human plasma by protein precipitation. The chromatographic separation of analytes was achieved using a Zorbax-SB Phenyl column (2.1 mm × 100 mm, 3.5 μm). The mobile phase consisted of a gradient mixture of 0.1% v/v glacial acetic acid in 10% v/v methanol in water (solvent A) and 40% v/v methanol in acetonitrile (solvent B). All analytes including ortho- and para-hydroxy metabolites were baseline-separated within 7.0 min using a flow rate of 0.35 mL/min. Mass spectrometry detection was carried out in positive electrospray ionization mode, with multiple-reaction monitoring scan. The calibration curves for all analytes were linear (R 2 ≥ 0.9975, n = 3) over the concentration range of 0.05–100 ng/mL and with lower limit of quantitation of 0.05 ng/mL. Mean extraction recoveries ranged between 88.6–111%. Intra- and inter-run mean percent accuracy were between 85–115% and percent imprecision was ≤ 15%. Stability studies revealed that ATV acid and lactone forms were stable in plasma during bench top (6 h on ice-water slurry), at the end of three successive freeze and thaw cycles and at −80 °C for 3 months. The method was successfully applied in a clinical study to determine concentrations of ATV and its metabolites over 12 h post-dose in patients receiving atorvastatin. Figure Chromatogram of atorvastatin and metabolites obtained with postcolumn infusion shows no matrix effect at the retention times of analytes and IS. Arrow indicates region where the signal of compounds infused post-column is suppressed during the elution of endogenous matrix components
Keywords: Assay; Atorvastatin; Concentration; Lactones; LC-MS/MS; Metabolites; Pharmacokinetics

A class of stationary phases for packed column supercritical fluid chromatography (SFC), referred to as immobilized ionic liquids (IILs), is evaluated with a two-part study: (1) a cation effect study and (2) an anion effect study. The former study compares six different IILs (tripropylphosphonium, tributylphosphonium, methyl-imidazolium, benzyl-imidazolium, triphenylphosphonium, and 4,4′-bipyridyl) on silica gel, evaluating their performance in SFC with all the counter anions as trifluoroacetate (TFA). In the latter study, the stationary phase consisted of a bonded tributylphosphonium cation and varying counter anions (acetate, TFA, chloride, NTf 2 , and perchlorate). An order of retentivity was established for the cation effect study, and the favorable behavior of phosphonium-based stationary phases is reported for the first time in SFC. It was not possible to always assign a retentivity order for the anion effect study, but wide variations in selectivity are noted for different anions showing the tunable nature of this class of stationary phases.
Keywords: SFC (supercritical fluid chromatography); Separations/instrumentation; Ionic liquids

The monitoring of radioactive xenon isotopes is one of the principal methods for the detection of nuclear explosions in order to identify clandestine nuclear testing. In this work, a miniaturized, multiple-oven, six-column, preparative gas chromatograph was constructed in order to isolate trace quantities of radioactive xenon isotopes from ambient air, utilizing nitrogen as the carrier gas. The multidimensional chromatograph comprised preparative stainless steel columns packed with molecular sieves, activated carbon, and synthetic carbon adsorbents (e.g., Anasorb®-747 and Carbosphere®). A combination of purification techniques—ambient adsorption, thermal desorption, back-flushing, thermal focusing, and heart cutting—was selectively optimized to produce a well-defined xenon peak that facilitated reproducible heart cutting and accurate quantification. The chromatographic purification of a sample requires approximately 4 h and provides complete separation of xenon from potentially interfering components (such as water vapor, methane, carbon dioxide, and radon) with recovery and accuracy close to 100%. The preparative enrichment process isolates and concentrates a highly purified xenon gas fraction that is suitable for subsequent ultra-low-level γ-, ß/γ-spectroscopic or high-resolution mass spectrometric measurement (e.g., to monitor the gaseous fission products of nuclear explosions at remote locations). The Xenon Processing Unit is a free-standing, relatively lightweight, and transportable system that can be interfaced to a variety of sampling and detection systems. It has a relatively inexpensive, rugged, and compact modular (19-inch rack) design that provides easy access to all parts for maintenance and has a low power requirement.
Keywords: Preparative enrichment of xenon; Noble gas; Radioxenon; Stable xenon; Radon separation; Carbon adsorbents; CTBT; IMS; Nuclear safeguards

Hexylacrylate-based mixed-mode monolith, a stationary phase for the nano-HPLC separation of structurally related enkephalins by Ayat Abbood; Christine Herrenknecht; Gaëlle Proczek; Stéphanie Descroix; Jordi Rodrigo; Myriam Taverna; Claire Smadja (459-468).
The potential of an in situ photopolymerized hexylacrylate-based monolithic stationary phase-bearing sulfonic acid groups was investigated by studying the chromatographic retention of small structurally related peptides (enkephalins) by nano-LC. Several retention mechanisms were highlighted. First, a reverse-phase chromatographic behavior toward neutral solutes due to hexylacrylate-moieties was demonstrated. Second, an evaluation of the influences of buffer pH suggested the involvement of a cation-exchange mechanism due to the presence of 2-acrylamido-2-methyl-1-propanesulfonic acid. This cation-exchange phenomenon was confirmed by the clear influence of Na+ concentration in the mobile phase on peptide retention.
Keywords: Monolith; Enkephalin; Peptides; Chromatography; Retention; Cation-exchange

Chromatographic profiles of Phyllanthus aqueous extracts samples: a proposition of classification using chemometric models by Lucia Regina Rocha Martins; Edenir Rodrigues Pereira-Filho; Quezia Bezerra Cass (469-481).
Taking in consideration the global analysis of complex samples, proposed by the metabolomic approach, the chromatographic fingerprint encompasses an attractive chemical characterization of herbal medicines. Thus, it can be used as a tool in quality control analysis of phytomedicines. The generated multivariate data are better evaluated by chemometric analyses, and they can be modeled by classification methods. “Stone breaker” is a popular Brazilian plant of Phyllanthus genus, used worldwide to treat renal calculus, hepatitis, and many other diseases. In this study, gradient elution at reversed-phase conditions with detection at ultraviolet region were used to obtain chemical profiles (fingerprints) of botanically identified samples of six Phyllanthus species. The obtained chromatograms, at 275 nm, were organized in data matrices, and the time shifts of peaks were adjusted using the Correlation Optimized Warping algorithm. Principal Component Analyses were performed to evaluate similarities among cultivated and uncultivated samples and the discrimination among the species and, after that, the samples were used to compose three classification models using Soft Independent Modeling of Class analogy, K-Nearest Neighbor, and Partial Least Squares for Discriminant Analysis. The ability of classification models were discussed after their successful application for authenticity evaluation of 25 commercial samples of “stone breaker.” Figure Chromatographic profile of Phyllanthus cultivated samples, a young seedling of Phyllanthus niruri and exploratory analysis (PCA) of cultivated samples (below)
Keywords: Phyllanthus ; Chromatographic fingerprint; Chemometric analysis; Classification models

Supramolecular complexes of quantum dots and a polyamidoamine (PAMAM)-folate derivative for molecular imaging of cancer cells by Daniela A. Geraldo; Esteban F. Duran-Lara; Daniel Aguayo; Raul E. Cachau; Jaime Tapia; Rodrigo Esparza; Miguel J. Yacaman; Fernando Danilo Gonzalez-Nilo; Leonardo S. Santos (483-492).
Polyamidoamine (PAMAM) dendrimers and water-soluble 3-mercaptopropionic acid (MPA)-capped CdSe quantum dots (QDs) were combined to produce a new gel containing supramolecular complexes of QDs/PAMAM dendrimers. The formation of the QDs/PAMAM supramolecular complexes was confirmed by high resolution electron microscopy and Fourier transform infrared (FTIR) analyses. Molecular dynamics simulations corroborated the structure of the new QDs/PAMAM-based supramolecular compound. Finally, on the basis of the prominent fluorescent properties of the supramolecular complexes, PAMAM dendrimer was functionalized with folic acid to produce a new QDs/PAMAM-folate derivative that showed an efficient and selective performance as a marker for gastric cancer cells. Figure The new QDs/PAMAM-folate derivative (left) is a selective marker for imaging of cancer cells as illustrated by the fluorescence image of human stomach adenocarcinoma (AGS) cells with internalized marker (right)
Keywords: Quantum dots; PAMAM dendrimers; Supramolecular complexes; Transmission electron microscopy (TEM); Molecular dynamics (MD) simulations; Gastric cancer cells

Agricultural workers are exposed to folpet, but biomonitoring data are limited. Phthalimide (PI), phthalamic acid (PAA), and phthalic acid (PA) are the ring metabolites of this fungicide according to animal studies, but they have not yet been measured in human urine as metabolites of folpet, only PA as a metabolite of phthalates. The objective of this study was thus to develop a reliable gas chromatography–tandem mass spectrometry (GC–MS) method to quantify the sum of PI, PAA, and PA ring-metabolites of folpet in human urine. Briefly, the method consisted of adding p-methylhippuric acid as an internal standard, performing an acid hydrolysis at 100 °C to convert ring-metabolites into PA, purifying samples by ethyl acetate extraction, and derivatizing with N,O-bis(trimethylsilyl)trifluoro acetamide prior to GC–MS analysis. The method had a detection limit of 60.2 nmol/L (10 ng/mL); it was found to be accurate (mean recovery, 97%), precise (inter- and intra-day percentage relative standard deviations <13%), and with a good linearity (R 2 > 0.98). Validation was conducted using unexposed peoples urine spiked at concentrations ranging from 4.0 to 16.1 μmol/L, along with urine samples of volunteers dosed with folpet, and of exposed workers. The method proved to be (1) suitable and accurate to determine the kinetic profile of PA equivalents in the urine of volunteers orally and dermally administered folpet and (2) relevant for the biomonitoring of exposure in workers. Figure Representative chromatograms of PA equivalents (trimethylsilyl phthalic acid or TMS-PA) in the urine of a volunteer orally dosed with folpet (a) and of a worker following folpet spraying (b; TMS-IS is the derivatized internal standard)
Keywords: Phthalic acid; Phthalamic acid; Folpet; Human urine; Biological monitoring

Quantification of glucuronidated and sulfated steroids in human urine by ultra-high pressure liquid chromatography quadrupole time-of-flight mass spectrometry by Flavia Badoud; Elia Grata; Julien Boccard; Davy Guillarme; Jean-Luc Veuthey; Serge Rudaz; Martial Saugy (503-516).
The urinary steroid profile is constituted by anabolic androgenic steroids, including testosterone and its relatives, that are extensively metabolized into phase II sulfated or glucuronidated steroids. The use of liquid chromatography coupled to mass spectrometry (LC-MS) is an issue for the direct analysis of conjugated steroids, which can be used as urinary markers of exogenous steroid administration in doping analysis, without hydrolysis of the conjugated moiety. In this study, a sensitive and selective ultra high-pressure liquid chromatography coupled to quadrupole time-of-flight mass spectrometer (UHPLC-QTOF-MS) method was developed to quantify major urinary metabolites simultaneously after testosterone intake. The sample preparation of the urine (1 mL) was performed by solid-phase extraction on Oasis HLB sorbent using a 96-well plate format. The conjugated steroids were analyzed by UHPLC-QTOF-MSE with a single-gradient elution of 36 min (including re-equilibration time) in the negative electrospray ionization mode. MSE analysis involved parallel alternating acquisitions of both low- and high-collision energy functions. The method was validated and applied to samples collected from a clinical study performed with a group of healthy human volunteers who had taken testosterone, which were compared with samples from a placebo group. Quantitative results were also compared to GC-MS and LC-MS/MS measurements, and the correlations between data were found appropriate. The acquisition of full mass spectra over the entire mass range with QTOF mass analyzers gives promise of the opportunity to extend the steroid profile to a higher number of conjugated steroids. Figure UHPLC-QTOF-MSE acquisition mode for DHEAG in urine sample
Keywords: Testosterone; Steroids; Glucuronide and sulfate conjugates; Ultra high-pressure liquid chromatography; Quadrupole time-of-flight; Quantification; MSE

Fast and selective extraction of nicotine from human plasma based on magnetic strong cation exchange resin followed by liquid chromatography–tandem mass spectrometry by Yang Xu; Changjia Wang; Xiaopan Zhang; Haiyan Chen; Qi Zhao; Weitao Song; Hui Wang; Qinglei Zeng; Lan Ding (517-526).
In the study, a fast and selective method based on magnetic separation has been developed for the extraction of nicotine from human plasma using magnetic strong cation exchange (MSCX) resins as adsorbent. MSCX resins were prepared using hydrophobic Fe3O4 magnetite as magnetically susceptible component, styrene and acrylic acid as polymeric matrix components, and acetyl sulfonate as the sulfonation agent. The extraction procedure was carried out in a single step by stirring the mixture of diluted plasma sample and MSCX resins in the vortex for 5 min. Then, the resins with adsorbed nicotine were separated from the sample matrix by applying an appropriate magnetic field. Main factors affecting the extraction of nicotine such as the amount of MSCX resins, pH value of the extraction solvent, extraction time, and washing and eluting conditions were optimized. The nicotine eluted from the resins was determined by liquid chromatography–tandem mass spectrometry. The calibration curve obtained by analyzing matrix-matched standards shows excellent linear relationship (r 2 = 0.9998) in the concentration range of 10–2,500 ng mL−1. The limit of detection and quantification obtained are 2.9 and 9.7 ng mL−1, respectively. The relative standard deviations of intra- and inter-day obtained are in the range of 1.9–6.9% and 2.5–7.8% with the recoveries ranging from 78.7% to 99.1%. The proposed method was successfully applied to determine nicotine in human plasma phlebotomized from ten male smokers. Nicotine was detectable with the contents ranging from 44.4 to 221.9 ng mL−1 in five samples. Figure Preparation and application process of magnetic strong cation exchange resins
Keywords: Magnetic strong cation exchange resin; Nicotine; Human plasma; Liquid chromatography–tandem mass spectrometry

A rapid method for the simultaneous determination of several non-steroidal anti-inflammatory drugs (NSAIDs) in human plasma and urine was developed using transient pseudo-isotachophoresis (ITP) in capillary zone electrophoresis (CZE). The influence of different parameters on resolution and preconcentration efficiency, such as background electrolyte (BGE) composition, sample injection, sample matrix composition, and pH, were studied to optimize the transient pseudo-ITP performance. Optimized conditions were a BGE consisting of 100 mM Na2B4O7 in 10% aqueous MeOH solution and hydrodynamic injection of the sample at 50 mbar for 90 s. The sample was prepared in a solution mixture of 1% NaCl/ethanol (30:70 v/v) at pH 10. Our results show that this simple strategy offers improved sensitivity compared to conventional CZE analysis, reaching a 45-fold preconcentration factor. The detection limits (LODs) were as low as 0.07 mg/L for standard samples with good repeatability (values of relative standard deviation, %RSD < 11%). The method was applied to the analysis of NSAIDs in biological samples. Validation for human plasma and urine samples demonstrated good linearity, low detection limits, and satisfactory repeatability values.
Keywords: Capillary electrophoresis; Non-steroidal anti-inflammatory drugs; Plasma samples; Transient pseudo-isotachophoresis; Urine samples

PEGylated polyethyleneimine grafted silica nanoparticles: enhanced cellular uptake and efficient siRNA delivery by Haisung Lee; Dongkyung Sung; Murugan Veerapandian; Kyusik Yun; Soo-Won Seo (535-545).
The present paper reports the utilization of hybrid nanocomposite particles consisting of PEI25k-PEG5k copolymer grafted silica nanoparticles (SiO2NPs) for enhanced cellular uptake and siRNA delivery. High-resolution transmission electron microscopy and dynamic light scattering measurements ensured the average particle size of the final hybrid component as 45 nm (core SiO2, 28–30 nm and shell PEI25k-PEG5k, 12–15 nm). Surface morphology from atomic force microscopy analysis showed the significant relationship between the particle size and shape. 29Si and 13C cross-polarization–magic angle spinning solid state nuclear magnetic resonance (NMR), 1H-NMR, and Fourier transform infrared spectroscopy were used to obtain the relevant structural information (such as Q3, silanol; Q4, siloxane functional groups of SiO2NPs; resonance shifts and bending vibrations of PEI25k, –CH2–CH2–NH–; and PEG5k, –CH2–CH2–O–) from copolymer nanoparticle. Stable complexation of siRNA and nanocomposite particle (wt.%:wt.%) was achieved from 1:5 to 1:15 ratio. Nanocomposite particle (N/P) ratio and siRNA concentration determine the stability and knockdown efficiency of the PEI25k-PEG5k-graft-SiO2NPs–siRNA complexes. It was shown that highly positively charged (zeta potential, +66 mV) PEI25k-PEG5k-graft-SiO2NPs result in strong affinity with negatively charged siRNA. Confocal microscopy showed intensified cellular uptake of siRNA into cytoplasm of A549 cancer cell utilized for in vitro study. In conclusion, the coherence, graft density of copolymer-SiO2NPs, and siRNA concentration were found to strongly influence the stability, and hence determine the knockdown efficiency, of PEI25k-PEG5k-graft-SiO2NPs–siRNA complexes. Figure PEI25k-PEG5k-graft-SiO2NPs: enhanced cellular uptake and efficient siRNA delivery
Keywords: siRNA; PEI25k-PEG5k-graft-SiO2NPs; Cellular transfection; Low cytotoxicity

Structural and biological evaluation of a multifunctional SWCNT-AgNPs-DNA/PVA bio-nanofilm by Ramesh P. Subbiah; Haisung Lee; Murugan Veerapandian; Sathya Sadhasivam; Soo-won Seo; Kyusik Yun (547-560).
A bio-nanofilm consisting of a tetrad nanomaterial (nanotubes, nanoparticles, DNA, polymer) was fabricated utilizing in situ reduction and noncovalent interactions and it displayed effective antibacterial activity and biocompatibility. This bio-nanofilm was composed of homogenous silver nanoparticles (AgNPs) coated on single-walled carbon nanotubes (SWCNTs), which were later hybridized with DNA and stabilized in poly(vinyl alcohol) (PVA) in the presence of a surfactant with the aid of ultrasonication. Electron microscopy and bio-AFM (atomic force microscopy) images were used to assess the morphology of the nanocomposite (NC) structure. Functionalization and fabrication were examined using FT–Raman spectroscopy by analyzing the functional changes in the bio-nanofilm before and after fabrication. UV–visible spectroscopy and X-ray powder diffraction (XRD) confirmed that AgNPs were present in the final NC on the basis of its surface plasmon resonance (370 nm) and crystal planes. Thermal gravimetric analysis was used to measure the percentage weight loss of SWCNT (17.5%) and final SWCNT-AgNPs-DNA/PVA (47.7%). The antimicrobial efficiency of the bio-nanofilm was evaluated against major pathogenic organisms. Bactericidal ratios, zone of inhibition, and minimum inhibitory concentration were examined against gram positive and gram negative bacteria. A preliminary cytotoxicity analysis was conducted using A549 lung cancer cells and IMR-90 fibroblast cells. Confocal laser microscopy, bio-AFM, and field emission scanning electron microscopy (FE-SEM) images demonstrated that the NCs were successfully taken up by the cells. These combined results indicate that this bio-nanofilm was biocompatible and displayed antimicrobial activity. Thus, this novel bio-nanofilm holds great promise for use as a multifunctional tool in burn therapy, tissue engineering, and other biomedical applications. Schematic representation of the fabrication of bio-nanofilm, and it's photographic images and applications.
Keywords: Hybrid; Characterization; Antibacterial; Cytotoxicity; Cellular uptake; Skin film

Electronic coupling and scaling effects during dielectric barrier electrospray ionization by A. K. Stark; C. Meyer; T. Kraehling; G. Jestel; U. Marggraf; M. Schilling; D. Janasek; J. Franzke (561-569).
The mechanism of the previously published technique of dielectric barrier electrospray ionization (DB-ESI) was investigated in more detail. Two independent current signals occurring during the DB-ESI could be explained and allocated to sub-processes. The modulated shape of the HV signal, the applied frequency as well as the inner diameter of the emitter capillary have a big impact on the spray. Furthermore, there exists a cut-off frequency which depends on the electronic properties of the DB-ESI interface. Comparable mass spectra for lysine employing both conventional ESI and DB-ESI show a good analytical potential of the new technique.
Keywords: Dielectric barrier electrospray ionization; DB-ESI; Displacement current

Membrane distillation (MD) is presented for the first time as a real-time, online concentration technique, where the aqueous matrix is removed from the sample to enhance analyte enrichment. Therefore, MD is a universal method for a wide range of compounds and is unlike conventional membrane extractions that rely on the permeation of the solute into an extractant phase. The MD process showed excellent precision with relative standard deviation between 3% and 5%, linear calibration, and the detection limits for pharmaceutical compounds in the range of 0.01 to 20 mg L−1 by HPLC-UV analysis. The temperature and flow rate of the feed solution were found to be important variables. Figure
Keywords: Membrane distillation; Hollow fiber membrane; Enrichment factor; Solvent reduction

Screening for multiple classes of marine biotoxins by liquid chromatography–high-resolution mass spectrometry by Pearl Blay; Joseph P. M. Hui; James Chang; Jeremy E. Melanson (577-585).
Marine biotoxins pose a significant food safety risk when bioaccumulated in shellfish, and adequate testing for biotoxins in shellfish is required to ensure public safety and long-term viability of commercial shellfish markets. This report describes the use of a benchtop Orbitrap system for liquid chromatography–mass spectrometry (LC-MS) screening of multiple classes of biotoxins commonly found in shellfish. Lipophilic toxins such as dinophysistoxins, pectenotoxins, and azaspiracids were separated by reversed phase LC in less than 7 min prior to MS data acquisition at 2 Hz with alternating positive and negative scans. This approach resulted in mass accuracy for analytes detected in positive mode (gymnodimine, 13-desmethyl spirolide C, pectenotoxin-2, and azaspiracid-1, -2, and -3) of less than 1 ppm, while those analytes detected in negative mode (yessotoxin, okadaic acid, and dinophysistoxin-1 and -2) exhibited mass errors between 2 and 4 ppm. Hydrophilic toxins such as domoic acid, saxitoxin, and gonyautoxins were separated by hydrophilic interaction LC (HILIC) in less than 4 min, and MS data was collected at 1 Hz in positive mode, yielding mass accuracy of less than 1 ppm error at a resolving power of 100,000 for the analytes studied (m/z 300–500). Data were processed by extracting 5 ppm mass windows centered around the calculated masses of the analytes. Limits of detection (LOD) for the lipophilic toxins ranged from 0.041 to 0.10 μg/L (parts per billion) for the positive ions, 1.6–5.1 μg/L for those detected in negative mode, while the domoic acid and paralytic shellfish toxins yielded LODs ranging from 3.4 to 14 μg/L. Toxins were detected in mussel tissue extracts free of interference in all cases.
Keywords: Marine biotoxins; Paralytic shellfish toxins; High-resolution mass spectrometry; Accurate mass screening; LC-MS; HILIC

Semi-automated liquid chromatography–mass spectrometry (LC–MS/MS) method for basic pesticides in wastewater effluents by Michael G. Cahill; Giovanni Caprioli; Mary Stack; Sauro Vittori; Kevin J. James (587-594).
Effluent from wastewater treatment plants have been identified as an important source of micro-organic contaminants in the environment. An online high-performance liquid chromatography–heated electrospray ionization tandem mass spectrometric method was developed and validated for the determination of basic pesticides in effluent wastewaters. Most available methods for pesticide analysis of wastewater samples are time-consuming, require complex clean-up steps and are difficult to automate. The method developed used a simple solid-phase extraction clean-up for salt and lipid reduction. On-line sample pre-concentration was performed using a reversed phase (C18) column, and analytes were separated by back-flushing onto an analytical column (C8) with detection using QqQ MS. An option to increase MS resolution was exploited to minimize interference from endogenous compounds in the matrix. A better than unit mass resolution was used (Q1 full width half maximum (FWHM) = 0.2 Da and Q3 FWHM = 0.7 Da), which was as rugged as a unit resolution method, and improved signal/noise and better detection limits were achieved for the targeted basic pesticides. This method was applied to the determination of 11 pesticides, including methoxytriazine, chlorotriazines, chloroacetanilides, phenylurea and carbamate pesticides. The percentage recovery values for these pesticides using the online trapping column were within the range, 73–95%, with relative standard deviation (RSD) values <8.9%. The highest concentrations of these pesticides in wastewater effluents in County Cork, Ireland, were simazine (0.51 μg/L), prometon (0.14 μg/L), diuron (0.21 μg/L) and atrazine (0.19 μg/L). Online Abstract Figure Effect of mass resolution change on signal/noise in the ion chromatograms for simazine at a) resolution setting, FWHM = 0.6 Da, b) resolution setting, FWHM = 0.2 Da.
Keywords: Priority pollutants; Online solid-phase extraction; Triple quadrupole mass analyzer

A novel and simple device for membrane-assisted liquid-phase microextraction is used for the first time in a three-phase system. The device consists of a glass vial containing the aqueous acceptor phase, whose septum of its screw stopper has been replaced by a sized piece of polytetrafluoroethylene membrane impregnated with n-decane. The vial is assembled to a volumetric flask containing the aqueous donor phase, and the membrane comes in contact alternatively with both donor and acceptor aqueous phases by orbital agitation. The device has been tested for the determination of nitrite in tap water samples, which is extensively carried out in routine analysis, as model analytical application. Experimental variables, such as the organic solvent used to form the supported liquid membrane, the volumes of both donor and acceptor phases, the orbital agitation rate, and the extraction time were studied and optimized in terms of enrichment factor. Under the selected working conditions, the analytical figures of merit for nitrite determination were a linearity range up to 50 ng mL−1, limits of detection and quantification of 0.15 and 0.50 ng mL−1, respectively, and a good repeatability (RSD < 10%). The method has been applied to four tap water samples of different origins, and accurate and precise results were achieved. Besides, the very low volume of organic solvent used, its low cost and the no-risk of cross-contamination are significant operational advantages.
Keywords: Membrane-assisted liquid-phase microextraction; Nitrite; Supported liquid membrane; Tap water; Three-phase microextraction system

This work describes an effective, low solvent consumption and affordable sample preparation approach for the determination of eight UV filters in surface and wastewater samples. It involves sorptive extraction of target analytes in a disposable, technical grade silicone disc (5 mm diameter × 0.6 mm thickness) followed by organic solvent desorption, large volume injection (LVI), and gas chromatography-mass spectrometry determination. Final working conditions involved overnight extraction of 100-mL samples, containing 10% of methanol, followed by analytes desorption with 0.2 mL of ethyl acetate. The method provides linear responses between the limits of quantification (from 0.003 to 0.040 ng mL−1) and 10 ng mL−1, an intra-day precision below 13%, and low matrix effects for surface, swimming pool, and treated sewage water samples. Moreover, the extraction yields provided by silicone discs were in excellent agreement with those achieved using polydimethylsiloxane-covered stir bars. Several UV filters were found in surface and sewage water samples, with the maximum concentrations corresponding to octocrylene.
Keywords: Sample preparation; Sorptive extraction; Silicone sorbents; UV filters; Water analysis

Comprehensive study of condensed tannins by ESI mass spectrometry: average degree of polymerisation and polymer distribution determination from mass spectra by Laetitia Mouls; Jean-Paul Mazauric; Nicolas Sommerer; Hélène Fulcrand; Gérard Mazerolles (613-623).
The determination of the molecular mass distribution of tannins is still a challenge. To elucidate it, mass spectrometry is potentially interesting, but many previous studies have highlighted that the mass spectra of a tannin fraction do not always reflect the actual abundance of different chain lengths. To clarify the potentialities offered by the MS approach, a comprehensive study involving different tannin fractions analysed under different conditions was conducted with an electrospray ionization (ESI) source. This study allowed optimised ESI-MS conditions to be established for analysing tannins but also it outlines the limits of detection encountered. If the detection of high molecular weight tannins seems difficult or even impossible, the spectral distortions brought about by this limitation are not totally related to the sole average degree of polymerisation of the tannin fraction studied but greatly depend on its polymer distribution. However, ESI-MS used under optimised conditions is a suitable method to study tannin composition of vegetable extracts which contain degree of polymerisations below 26.
Keywords: Tannins; Polyphenols; Electrospray ionisation–mass spectrometry (ESI-MS); Degree of polymerisation; Polymer distribution; Chemometrics

Discrete wavelet transform (DWT) provides a well-established means for spectral denoising and baseline elimination to enhance resolution and improve the performance of calibration and classification models. However, the limitation of a fixed filter bank can prevent the optimal application of conventional DWT for the multiresolution analysis of spectra of arbitrarily varying noise and background. This paper presents a novel methodology based on an improved, second-generation adaptive wavelet transform (AWT) algorithm. This AWT methodology uses a spectrally adapted lifting scheme to generate an infinite basis of wavelet filters from a single conventional wavelet, and then finds the optimal one. Such pretreatment combined with a multivariate calibration approach such as partial least squares can greatly enhance the utility of Raman spectroscopy for quantitative analysis. The present work demonstrates this methodology using two dispersive Raman spectral data sets, incorporating lactic acid and melamine in pure water and in milk solutions. The results indicate that AWT can separate spectral background and noise from signals of interest more efficiently than conventional DWT, thus improving the effectiveness of Raman spectroscopy for quantitative analysis and classification. Figure The Raman spectrum of trace melamine in water through an adaptive wavelet prism
Keywords: Adaptive wavelet transform; Multivariate quantitative analysis; Wavelet regression; Baseline compensation; Denoising; Raman spectroscopy

Erratum to: Towards an unbiased metabolic profiling of protozoan parasites: optimisation of a Leishmania sampling protocol for HILIC-orbitrap analysis by Ruben t’Kindt; Andris Jankevics; Richard A. Scheltema; Liang Zheng; David G. Watson; Jean-Claude Dujardin; Rainer Breitling; Graham H. Coombs; Saskia Decuypere (635-635).