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Analytica Chimica Acta (v.704, #1-2)
Fast and simple methods for the optimization of kurtosis used as a projection pursuit index by S. Hou; P.D. Wentzell (pp. 1-15).
Display Omitted► Algorithms allow maximization or minimization of kurtosis. ► Adaptable to univariate or multivariate kurtosis. ► Fast and simple iterative procedure based on the power method. ► Improved class separation demonstrated for three experimental data sets.As a powerful method for exploratory data analysis, projection pursuit (PP) often outperforms principal component analysis (PCA) to discover important data structure. PP was proposed in 1970s but has not been widely used in chemistry largely because of the difficulty in the optimization of projection indices. In this work, new algorithms, referred as “quasi-power methods”, are proposed to optimize kurtosis as a projection index. The new algorithms are simple, fast, and stable, which makes the search for the global optimum more efficient in the presence of multiple local optima. Maximization of kurtosis is helpful in the detection of outliers, while minimization tends to reveal clusters in the data, so the ability to search separately for the maximum and minimum of kurtosis is desirable. The proposed algorithms can search for either with only minor changes. Unlike other methods, no optimization of step size is required and sphering or whitening of the data is not necessary. Both univariate and multivariate kurtosis can be optimized by the proposed algorithms. The performance of the algorithms is evaluated using three simulated data sets and its utility is demonstrated with three experimental data sets relevant to analytical chemistry.
Keywords: Optimization; Quasi-power method; Univariate kurtosis; Multivariate kurtosis; Projection pursuit; Independent component analysis
Analytical applications of the electrochemiluminescence of tris(2,2′-bipyridyl)ruthenium(II) coupled to capillary/microchip electrophoresis: A review by Ming Su; Wei Wei; Songqin Liu (pp. 16-32).
The mechanism of Ru(bpy)32+ electrochemiluminescence, addition mode of Ru(bpy)32+, recent applications of capillary electrophoresis coupled with electrochemiluminescent detection in drug and other substrates analysis are reviewed.A comprehensive review on the development of analytical methods, by coupling electrochemiluminescence (ECL) detection with capillary electrophoresis (CE) and microchip electrophoresis (ME), is presented. After the description of the basic mechanism of ECL, the addition mode of luminescence reagent in CE–ECL system has been discussed. The analytical applications of the CE–ECL technique in terms of different analytes are also given. Due to the importance of ME as a separation method for the present and future, the ME detection methods based on ECL are considered in a relatively detailed way. Finally, possible trends for CE/ME-ECL in the near future are discussed.
Keywords: Abbreviations; ECL; electrochemiluminescence; CE; capillary electrophoresis; ME; microchip electrophoresis; DPA; 9,10-diphenylanthracene; PAHs; polycyclic aromatic hydrocarbons; NPs; nanoparticles; Ru(bpy); 3; 2+; tris(2,2′-bipyridyl)ruthenium(II); FIA; flow-injection analysis; HPLC; high performance liquid chromatography; (TAS; micro total analysis system; TPA; tripropylamine; LOD; limit of detection; PMT; photomultiplier tube; ITO; indium-tin oxide; DC; direct current; pHPP; p-hydroxyphenylpyruvic acid; RSDs; relative standard deviations; DMEA; N,N-dimethyl ethanolamine; HSA; human serum albumin; EOF; electro-osmotic flow; AEMP; 2-(2-aminoethyl)-1-methylpyrrolidine; ILs; ionic liquids; EMIMBF; 4; 1-ethyl-3-methylimidazolium tetrafluoroborate; PDMS; poly(dimethylsiloxane); MEKC; micellar electrokinetic chromatography; BV; benzyl viologenKeyword; Capillary electrophoresis; Electrochemiluminescence; Microchip electrophoresis; Tris(2,2′-bipyridyl) ruthenium; Analytical application
Determination of steroid hormones in biological and environmental samples using green microextraction techniques: An overview by Jana Aufartová; Cristina Mahugo-Santana; Zoraida Sosa-Ferrera; José Juan Santana-Rodríguez; Lucie Nováková; Petr Solich (pp. 33-46).
Display Omitted► Green methodologies for the determination of hormones in environmental samples. ► Applications in MIPs, in-tube SPME, SBSE and MEPS. ► Liquid-phase microextraction approaches like HFME and SD-LPME are also included. ► Automation, use of experimental designs and new solvents should be introduced.Residues of steroid hormones have become a cause for concern because they can affect the biological activity of non-target organisms. Steroid hormones are a potential risk for wildlife and humans through the consumption of contaminated food or water. Their determination requires extraction and clean-up steps, prior to detection, to reach low concentration levels. In recent years, a great effort has been made to develop new analytical methodologies, such as microextraction techniques, that reduce environmental pollution. Researchers have modified old methods to incorporate procedures that use less-hazardous chemicals or that use smaller amounts of them. They are able to do direct analysis using miniaturised equipment and reduced amounts of solvents and wastes. These accomplishments are the main objectives of green analytical chemistry. In this overview, we focus on microextraction techniques for the determination of steroid hormones in biological (e.g., human urine, human serum, fish, shrimp and prawn tissue and milk) and environmental (e.g., wastewaters, surface waters, tap waters, river waters, sewage sludges, marine sediments and river sediments) samples. We comment on the most recent applications in sorptive-microextraction modes, such as solid phase microextraction (SPME) with molecularly imprinted polymers (MIPs), in-tube solid-phase microextraction (IT-SPME), stir-bar sorptive extraction (SBSE) and microextraction in packed sorbent (MEPS). We also describe liquid-phase microextraction (LPME) approaches reported in the literature that are applied to the determination of steroid hormones.
Keywords: Green analytical chemistry; Microextraction; Liquid-phase microextraction; Micellar media; Steroid hormones; Biological samples; Water samples
How to pre-process Raman spectra for reliable and stable models? by Thomas Bocklitz; Angela Walter; Katharina Hartmann; Petra Rösch; Jürgen Popp (pp. 47-56).
► The pre-processing was arranged in a hierarchical manner. ► A library of pre-processing methods for Raman spectra was set together. ► The influence of pre-processing was checked for calibration and classification task. ► A genetic optimization was introduced in order to enhance the pre-processing.Raman spectroscopy in combination with chemometrics is gaining more and more importance for answering biological questions. This results from the fact that Raman spectroscopy is non-invasive, marker-free and water is not corrupting Raman spectra significantly. However, Raman spectra contain despite Raman fingerprint information other contributions like fluorescence background, Gaussian noise, cosmic spikes and other effects dependent on experimental parameters, which have to be removed prior to the analysis, in order to ensure that the analysis is based on the Raman measurements and not on other effects.Here we present a comprehensive study of the influence of pre-processing procedures on statistical models. We will show that a large amount of possible and physically meaningful pre-processing procedures leads to bad results. Furthermore a method based on genetic algorithms (GAs) is introduced, which chooses the spectral pre-processing according to the carried out analysis task without trying all possible pre-processing approaches (grid-search). This was demonstrated for the two most common tasks, namely for a multivariate calibration model and for two classification models. However, the presented approach can be applied in general, if there is a computational measure, which can be optimized. The suggested GA procedure results in models, which have a higher precision and are more stable against corrupting effects.
Keywords: Raman spectroscopy; Quantitative analysis; Calibration; Pre-processing; Classification; Genetic algorithm
Building optimal regression tree by ant colony system–genetic algorithm: Application to modeling of melting points by Bahram Hemmateenejad; Mojtaba Shamsipur; Vali Zare-Shahabadi; Morteza Akhond (pp. 57-62).
.Display Omitted► Ant colony systems help to build optimum classification and regression trees. ► Using of genetic algorithm operators in ant colony systems resulted in more appropriate models. ► Variable selection in each terminal node of the tree gives promising results. ► CART–ACS–GA could model the melting point of organic materials with prediction errors lower than previous models.The classification and regression trees (CART) possess the advantage of being able to handle large data sets and yield readily interpretable models. A conventional method of building a regression tree is recursive partitioning, which results in a good but not optimal tree. Ant colony system (ACS), which is a meta-heuristic algorithm and derived from the observation of real ants, can be used to overcome this problem. The purpose of this study was to explore the use of CART and its combination with ACS for modeling of melting points of a large variety of chemical compounds. Genetic algorithm (GA) operators (e.g., cross averring and mutation operators) were combined with ACS algorithm to select the best solution model. In addition, at each terminal node of the resulted tree, variable selection was done by ACS–GA algorithm to build an appropriate partial least squares (PLS) model. To test the ability of the resulted tree, a set of approximately 4173 structures and their melting points were used (3000 compounds as training set and 1173 as validation set). Further, an external test set containing of 277 drugs was used to validate the prediction ability of the tree. Comparison of the results obtained from both trees showed that the tree constructed by ACS–GA algorithm performs better than that produced by recursive partitioning procedure.
Keywords: Ant colony system; Classification and regression tree; Genetic algorithm; Melting points; Quantitative structure–property relationship
Electrochemical quantification of 2,6-diisopropylphenol (propofol) by Jan Langmaier; Fernando Garay; Francine Kivlehan; Edward Chaum; Ernő Lindner (pp. 63-67).
Display Omitted► Target-controlled infusion anesthesia (TCIA) requires feedback controlled monitoring. ► Propofol is a potent anesthetic drug widely used in TCIA but its measurement in blood is difficult. ► Voltammetric methods have been developed for the determination of propofol in acidic solutions. ► Detection limits (DLs) of 5.5μM (cathodic stripping) and 3.2μM (linear sweep) have been achieved. ► The selectivity and the DL can be improved by organic film coated planar electrochemical cells.2,6-Diisopropylphenol (propofol) is a potent anesthetic drug with fast onset of the anesthetic effect and short recovery time for the patients. Outside of the United States, propofol is widely used in performing target controlled infusion anesthesia. With the long term vision of an electrochemical sensor for in vivo monitoring and feedback controlled dosing of propofol in blood, different alternatives for the electrochemical quantification of propofol using diverse working electrodes and experimental conditions are presented in this contribution.When the electrochemical oxidation of propofol takes place on a glassy carbon working electrode, an electrochemically active film grows on the electrode surface. The reduction current of the film is proportional to the propofol concentration and the accumulation time. Based on these findings a stripping analytical method was developed for the detection of propofol in acidic solutions between 0 and 30μM, with a detection limit of 5.5±0.4μM.By restricting the scanned potential window between 0.5V and 1.0V in cyclic voltammetric experiments, the formation of the electrochemically active polymer can be prevented. This allowed the development of a direct voltammetric method for assessing propofol in acidic solutions between 0 and 30μM, with a 3.2±0.1μM ( n=3) detection limit.The stripping method has a better sensitivity but somewhat worse reproducibility because the electrode surface has to be renewed between each experiment. The direct method does not require the renewal of the electrode surface between measurements but has no adequate selectivity towards the common interfering compounds.
Keywords: 2,6-Diisopropylphenol; Propofol; Anesthesia; Target-controlled infusion anesthesia; Electrochemistry; Cyclic voltammetry
Potentiometric flow injection system for determination of reductants using a polymeric membrane permanganate ion-selective electrode based on current-controlled reagent delivery by Wenjing Song; Jiawang Ding; Rongning Liang; Wei Qin (pp. 68-72).
A polymeric membrane permanganate-selective electrode has been developed as a current-controlled reagent release system for potentiometric detection of reductants in flow injection analysis. By applying an external current, diffusion of permanganate ions across the polymeric membrane can be controlled precisely. The permanganate ions released at the sample-membrane interface from the inner filling solution of the electrode are consumed by reaction with a reductant in the sample solution thus changing the measured membrane potential, by which the reductant can be sensed potentiometrically.Display Omitted► A novel reagentless sensor is developed for consecutive detection of reductants in FIA. ► The ion-selective electrode is used as a permanganate controlled-release system. ► The amount of permanganate released at the membrane surface can be controlled precisely by an external current. ► The recovery of the sensor is rapid.A polymeric membrane permanganate-selective electrode has been developed as a current-controlled reagent release system for potentiometric detection of reductants in flow injection analysis. By applying an external current, diffusion of permanganate ions across the polymeric membrane can be controlled precisely. The permanganate ions released at the sample-membrane interface from the inner filling solution of the electrode are consumed by reaction with a reductant in the sample solution thus changing the measured membrane potential, by which the reductant can be sensed potentiometrically. Ascorbate, dopamine and norepinephrine have been employed as the model reductants. Under the optimized conditions, the potential peak heights are proportional to the reductant concentrations in the ranges of 1.0×10−5 to 2.5×10−7M for ascorbate, of 1.0×10−5 to 5.0×10−7M for dopamine, and of 1.0×10−5 to 5.0×10−7M for norepinephrine, respectively with the corresponding detection limits of 7.8×10−8, 1.0×10−7 and 1.0×10−7M. The proposed system has been successfully applied to the determination of reductants in pharmaceutical preparations and vegetables, and the results agree well with those of iodimetric analysis.
Keywords: Potentiometry; Flow injection analysis; Ion-selective electrodes; Reductants; Current-controlled release
New polymeric membrane cadmium(II)-selective electrodes using tripodal amine based ionophores by Utisawadee Khamjumphol; Sarayut Watchasit; Chomchai Suksai; Wanwisa Janrungroatsakul; Suthasinee Boonchiangma; Thawatchai Tuntulani; Wittaya Ngeontae (pp. 73-86).
Display Omitted► New four ionophores having tripodal amine (TPA) unit on anthracene and calixarene. ► Synthesis and characterization data were reported. ► Incorporated to the plasticized PVC membranes to prepare Cd-ISEs. ► Two TPA units on calixarene showed the best selectivity toward Cd2+. ► Applied for sensing Cd2+ from the oxidation of CdS QDs solution.Fabrication of PVC membrane electrodes incorporating selective neutral carriers for Cd2+ was reported. The ionophores were designed to have different topologies, donor atoms and lipophilicity by attaching tripodal amine (TPA) units to the lipophilic anthracene (ionophoreI) and p-tert-butylcalix[4]arene (ionophoresII,III andIV). The synthesized ionophores were incorporated to the plasticized PVC membranes to prepare Cd(II) ion selective electrodes (ISEs). The membrane electrodes were optimized by changing types and amounts of ionic sites and plasticizers. The selectivity of the membranes fabricated from the synthesized ionophores was evaluated, the relationship between structures of ionophores and membrane characteristics were explored. The ionophoreIV which composed of two opposites TPA units on the calix[4]arene compartment showed the best selectivity toward Cd2+. The best membrane electrode was fabricated from ionophoreIV (10.2mmolkg−1) with KTpClPB (50.1mol% related to the ionophore) as an ion exchanger incorporated in the DOS plasticized PVC membrane (1:2; PVC:DOS). The Cd-ISE fabricated from ionophoreIV exhibited good properties with a Nernstian response of 29.4±0.6mVdecade−1 of activity for Cd2+ ions and a working concentration range of 1.6×10−6–1.0×10−2M. The sensor has a fast response time of 10s and can be used for at least 1 week without any divergence in potential. The electrode can be used in the pH range of 6.0–9.0. The proposed electrodes using ionophoresIII andIV were employed as a probe for determining Cd2+ from the oxidation of CdS QDs solution and the real treatment waste water sample with excellent results.
Keywords: Cadmium; Poly(vinylchloride) membrane; Ion selective electrode; Tripodal amine; Calix[4]arene; Ionophore
Determination of volatile organic compounds in water by headspace solid-phase microextraction gas chromatography coupled to tandem mass spectrometry with triple quadrupole analyzer by M.I. Cervera; J. Beltran; F.J. Lopez; F. Hernandez (pp. 87-97).
Display Omitted► Employing a statistical optimization improves results reducing experiments. ► Use of MS (QqQ) allows high sensitivity determination and improves identification capabilities. ► Using Q/ q intensity ratios is a powerful tool to ensure compound identification. ► HS SPME GC–MS/MS method allows determination of VOCs in complex matrix water samples.In the present work, a rapid method with little sample handling has been developed for determination of 23 selected volatile organic compounds in environmental and wastewater samples. The method is based on headspace solid-phase microextraction (SPME) followed by gas chromatography coupled to tandem mass spectrometry (GC–MS/MS) determination using triple quadrupole analyzer (QqQ) in electron ionization mode. The best conditions for extraction were optimised with a factorial design taking into account the interaction between different parameters and not only individual effects of variables. In the optimized procedure, 4mL of water sample were extracted using a 10mL vial and adding 0.4g NaCl (final NaCl content of 10%). An SPME extraction with carboxen/polydimethylsiloxane 75μm fiber for 30min at 50°C (with 5min of previous equilibration time) with magnetic stirring was applied. Chromatographic determination was carried out by GC–MS/MS working in Selected Reaction Monitoring (SRM) mode. For most analytes, two MS/MS transitions were acquired, although for a few compounds it was difficult to obtain characteristic abundant fragments. In those cases, a pseudo selected reaction monitoring (pseudo-SRM) with three ions was used instead. The intensity ratio between quantitation ( Q) and confirmation ( q) signals was used as a confirmatory parameter.The method was validated by means of recovery experiments ( n=6) spiking mineral water samples at three concentration levels (0.1, 5 and 50μgL−1). Recoveries between 70% and 120% were generally obtained with relative standard deviations (RSDs) lower than 20%.The developed method was applied to surface water and wastewater from a wastewater treatment plant and from a municipal solid-waste treatment plant. Several compounds, like chloroform, benzene, trichloroethylene, toluene, tetrachloroethylene, dibromochloromethane, xylenes and bromoform were detected and confirmed in all the samples analyzed.
Keywords: Volatile organic compounds; Gas chromatography tandem mass spectrometry; Triple quadrupole; Environmental water; Wastewater; Headspace solid-phase microextraction
Ionic liquid foam floatation coupled with solid phase extraction for separation and determination of hormones by high-performance liquid chromatography by Rui Zhang; Na Li; Chuanliu Wang; Yuping Bai; Ruibing Ren; Shiqian Gao; Wenzhi Yu; Tianqi Zhao; Hanqi Zhang (pp. 98-109).
Display Omitted► The foaming property of ionic liquids (ILs) was found. ► The factors that can influence foamability of the ILs were investigated. ► On foamability of ILs, the foam floatation-solid phase extraction was developed. ► IL-FF-SPE was applied to the extraction and concentration of steroid hormones. ► The extraction and concentration were performed synchronously in 10min.The foaming property of ionic liquids (ILs) was found and the factors that can influence foamability of the ILs were investigated. Based on the property of the ILs, the foam floatation-solid phase extraction (FF-SPE) was developed. The IL-based FF-SPE was applied to the extraction and concentration of steroid hormones, including corticosterone, 17-β-estadiol, 17-α-estradiol, 19-nortestosterone, estrone, testosterone, 17-α-hydroxyprogesterone, medroxyprogesterone, chloromadinon 17-acetate, norethisterone acetate, medroxyprogesterone-17-acetate, progesterone, 17-β-estradiol 3-benzoate and testosteron 17-propionate in water samples and then the steroid hormones were determined by high-performance liquid chromatography. The extraction and concentration were performed synchronously in 10min. Some experimental conditions were examined and optimized. The recoveries ranged from 50.6% to 95.2% for lake water sample and from 53.4% to 98.7% for rain water sample. The precision ranged from 2.43% to 7.43% for the lake water sample and 2.07–7.01% for rain water sample. Based on the foaming property of ILs, the application of foam floatation should be widened.
Keywords: Ionic liquid; Foam floatation-solid phase extraction; Steroid hormones; Liquid chromatography
Comparison of 24-h volume and creatinine-corrected total urinary polyphenol as a biomarker of total dietary polyphenols in the Invecchiare InCHIANTI study by Raul Zamora-Ros; Montserrat Rabassa; Antonio Cherubini; Mireia Urpi-Sarda; Rafael Llorach; Stefania Bandinelli; Luigi Ferrucci; Cristina Andres-Lacueva (pp. 110-115).
Display Omitted► Twenty-four hour urine volume and urinary creatinine are compared to normalize urinary total polyphenols. ► Urinary total polyphenols by 24-h volume is better biomarker of polyphenol intake than by urinary creatinine normalization. ► After covariate adjustment, urinary total polyphenols by creatinine can also used as biomarker of polyphenol intake.Polyphenols have beneficial effects on several chronic diseases but assessing polyphenols intake from self-reported dietary questionnaires tends to be inaccurate and not very reliable. A promising alternative is to use urinary excretion of polyphenols as a proxy measure of intake. The best method to assess urinary excretion is to collect 24-h urine. However, since collecting 24-h urine method is expensive, time consuming and may be difficult to implement in large population-based studies, measures obtained from spot urine normalized by creatinine are commonly used. The purpose of the study was to evaluate the correlation between polyphenols dietary intake and total urinary polyphenol excretion (TPE), expressed by both 24-h volume and urinary creatinine normalization in 928 participants from the InCHIANTI study. Dietary intake data were collected using a validated food frequency questionnaire. Urinary TPE was analyzed by Folin–Ciocalteau assay. Both urinary TPE expression models were statistically correlated ( r=0.580), and the partial correlation coefficient improved (pr=0.722) after adjusting for the variables that modify the urinary creatinine excretion (i.e. gender, age, BMI, physical activity and renal function). In crude models, polyphenol intake was associated with TPE corrected by 24-h volume ( r=0.211; P<0.001), but not with creatinine normalization ( r=0.014; P=0.692). However, urinary TPE expressed by creatinine correction was significantly correlated with dietary polyphenols after adjusting for covariates (pr=0.113; P=0.002). We conclude that urinary TPE expressed by 24-h volume is a better biomarker of polyphenol dietary intake than by urinary creatinine normalization. After covariate adjustment, both can be used for studying the relationships between polyphenol intake and health in large-scale epidemiological studies.
Keywords: Abbreviations; TPE; total polyphenol excretion; F–C; Folin–Ciocalteau; GAE; gallic acid equivalents; EPIC; European Prospective Investigation into Cancer and Nutrition; FFQ; food frequency questionnairePolyphenols; Urine 24-h; Creatinine normalization; Biomarker; InCHIANTI study
Flow analysis methods for the direct ultra-violet spectrophotometric measurement of nitrate and total nitrogen in freshwaters by Brady S. Gentle; Peter S. Ellis; Michael R. Grace; Ian D. McKelvie (pp. 116-122).
Display Omitted► Second derivative UV spectrophotometry has been used to determine nitrate and total N using flow analysis techniques. ► A simple flow system with a single-reflection flow-through cell was used for the UV measurement of nitrate. ► Total N was determined after on-line UV photooxidation with alkaline peroxodisulfate. ► Analyses carried out using the developed flow systems show a high degree of agreement with comparative analyses. ► This method requires no colorimetric reagents and eliminates the requirement for a toxic cadmium reduction column.Second derivative ultra-violet spectrophotometric methods are described for the measurement of nitrate and total nitrogen in freshwaters using flow analysis techniques. A simple flow system consisting of a peristaltic pump and a single-reflection flow-through cell was used for the measurement of nitrate. Quantification of total nitrogen using alkaline peroxodisulfate photo-digestion was achieved by incorporating an ultra-violet photo-reactor, a hollow-fibre filter and a debubbler into the flow system. The nitrate system featured a limit of detection of 0.04mgNL−1, 0.4%RSD (1mgNL−1 as nitrate, n=10), a coefficient of determination ( R2) of 0.9995 over the calibration range 0.0–2.0mgNL−1, and a data acquisition time of 1.5s per spectrum. The total nitrogen system featured a limit of detection of 0.05mgNL−1, 1%RSD (1mgNL−1 as ammonium chloride, n=10), a coefficient of determination of 0.9989 over the calibration range 0.0–2.0mgNL−1, and a throughput of 5sampleh−1 measured in triplicate. Digestions of five model nitrogen compounds returned recoveries of >88%. Determinations carried out using the developed systems show a high degree of agreement with data obtained using reference methods. These methods require no colorimetric reagents and eliminate the requirement for a toxic cadmium reduction column. The overlap of chloride and nitrate spectra in seawater is not eliminated entirely by the use of second derivative spectrophotometry, and consequently the methods are restricted to the analysis of freshwaters.
Keywords: Nitrate; Total nitrogen; Flow analysis; Derivative spectrophotometry; Fresh waters
Electrospray ionization tandem mass spectrometry for the simultaneous determination of opiates and cocaine in human hair by Martha Míguez-Framil; Antonio Moreda-Piñeiro; Pilar Bermejo-Barrera; José Ángel Cocho; María Jesús Tabernero; Ana María Bermejo (pp. 123-132).
Display Omitted► Direct ESI-MS/MS can be used for abuse drugs determination in human hair. ► Interference-free measurement is possible because specific precursor ion→product ion transitions. ► USEH and MSPD allow a fast target isolation from hair. ► The developed method is an appealing methodology for routine analysis.A fast and highly sensitive electrospray ionization tandem mass spectrometry (ESI-MS/MS) method has been developed for the simultaneous determination of morphine, 6-methylacetylmorphine (6-MAM), codeine, cocaine and benzoylecgonine (BZE) in hair from drug abusers. Pulverized hair samples were subjected to an optimized matrix solid phase dispersion (MSPD) procedure with alumina, followed by diluted hydrochloric acid elution on column solid-phase extraction (SPE) clean-up/pre-concentration. Alternatively, samples were also subjected to an optimized ultrasound assisted enzymatic hydrolysis (USEH) with Pronase E, followed by an off-line SPE clean up/pre-concentration procedure. Positive electrospray ionization and multiple reaction monitoring (MRM) with one precursor ion/product ion transition were used for the identification and quantification (deuterated analogues of each target as internal standards) of each analyte. The chromatographic pump and the autosampler were used for injecting the standards and the hair extracts (20μL) as a flow injection analysis mode. The highest sensitivity was achieved when delivering the targets with an acetonitrile/water/formic acid (80/19.875/0.125) mixture. The limits of detection of the method were 39.2, 4.4, 6.8, 7.0 and 7.4ngg−1 for morphine, 6-MAM, codeine, cocaine and BZE, respectively. Relative standard deviations of intra- and inter-day precision were lower than 9 and 12%, respectively; whereas, analytical recoveries ranged from 96±5 to 106±4%. The developed method (MSPD–ESI-MS/MS) was applied to different hair samples from polydrug abusers, and results were statistically compared to those obtained after a conventional gas chromatography–mass spectrometry (GC–MS) analysis and also after USEH and ESI-MS/MS or GC–MS determinations.
Keywords: Mass spectrometry; Drugs of abuse; Human hair; Matrix solid phase dispersion; Ultrasound assisted enzymatic hydrolysis
Electrochemical deoxyribonucleic acid biosensor based on the self-assembly film with nanogold decorated on ionic liquid modified carbon paste electrode by Hongwei Gao; Xiaowei Qi; Ying Chen; Wei Sun (pp. 133-138).
.Display Omitted► Nanogold decorated on ionic liquid modified carbon paste electrode was fabricated by electrodeposition to get a new substrate electrode. ► The ssDNA probe was further covalently-linked with self-assembled mercaptoacetic acid film on the electrode surface to prepare the electrochemical DNA biosensor. ► The polymerase chain reaction product of arachis Arabinose operon D gene was successfully detected by the proposed method.An electrochemical DNA biosensor was fabricated by self-assembling probe single-stranded DNA (ssDNA) with a nanogold decorated on ionic liquid modified carbon paste electrode (IL-CPE). IL-CPE was fabricated using 1-butylpyridinium hexafluorophosphate as the binder and the gold nanoparticles were electrodeposited on the surface of IL-CPE (Au/IL-CPE). Then mercaptoacetic acid was self-assembled on the Au/IL-CPE to obtain a layer of modified film, and the ssDNA probe was further covalently-linked with mercaptoacetic acid by the formation of carboxylate ester with the help of N-(3-dimethylamino-propyl)-N′-ethylcarbodiimide hydrochloride and N-hydroxysuccinimide. The hybridization reaction with the target ssDNA was monitored with methylene blue (MB) as the electrochemical indicator. Under the optimal conditions, differential pulse voltammetric responses of MB was proportional to the specific ssDNA arachis sequences in the concentration range from 1.0×10−11 to 1.0×10−6molL−1 with the detection limit as 1.5×10−12molL−1 (3 σ). This electrochemical DNA sensor exhibited good stability and selectivity with the discrimination ability of the one-base and three-base mismatched ssDNA sequences. The polymerase chain reaction product of arachis Arabinose operon D gene was successfully detected by the proposed method, which indicated that the electrochemical DNA sensor designed in this paper could be further used for the detection of specific ssDNA sequence.
Keywords: Carbon paste electrode; Ionic liquid; 1-butylpyridinium hexafluorophosphate; Self-assemble; Electrochemical DNA biosensor; Gold nanoparticle
Plasmophore sensitized imaging of ammonia release from biological tissues using optodes by Niklas Strömberg; Aron Hakonen (pp. 139-145).
Display Omitted► A plasmophore sensitized optode for imaging ammonia (NH3) concentrations in muscle tissues was developed. ► Ammonia concentrations ranging from 10nM and upwards can be quantified reversibly with an optical resolution of 127μm. ► The general sensing scheme offers new possibilities for the development of artificial optical noses and tongues.A plasmophore sensitized optode was developed for imaging ammonia (NH3) concentrations in muscle tissues. The developed ammonia sensor and an equivalent non plasmophore version of the sensor were tested side by side to compare their limit of detection, dynamic range, reversibility and overall imaging quality. Bio-degradation patterns of ammonia release from lean porcine skeletal muscle were studied over a period of 11 days. We demonstrate that ammonia concentrations ranging from 10nM can be quantified reversibly with an optical resolution of 127μm in a sample area of 25mm×35mm. The plasmophore ammonia optode showed improved reversibility, less false pixels and a 2nM ammonia detection limit compared to 200nM for the non-plasmophore sensor. Main principles of the sensing mechanism include ammonia transfer over a gas permeable film, ammonia protonation, nonactin facilitated merocyanine-ammonium coextraction and plasmophore enhancement. The vast signal improvement is suggested to rely on solvatochroism, nanoparticle scattering and plasmonic interactions that are utilized constructively in a fluorescence ratio. In addition to fundamental medicinal and biological research applications in tissue physiology, reversible ammonia quantification will be possible for a majority of demanding imaging and non imaging applications such as monitoring of low ammonia background concentrations in air and non-invasive medicinal diagnosis through medical breath or saliva analysis. The nanoparticle doped sensor constitutes a highly competitive technique for ammonia sensing in complex matrixes and the general sensing scheme offers new possibilities for the development of artificial optical noses and tongues.
Keywords: Ammonia; Nanoparticles; Plasmonics; Optode; Fluorosensor; Imaging
Dodecylbenzene sulfonate-coated magnetite nanoparticles as a new adsorbent for solid phase extraction-spectrophotometric determination of ultra trace amounts of ammonium in water samples by Habibollah Eskandari; Mohammad Reza Shariati (pp. 146-153).
. Zero- (A: analyte and B: blank) and first-derivative (C: analyte and D: blank) spectra of the back-extracted solution against water for the proposed ammonium determination method.Display Omitted► We introduce dodecylbenzene sulfonate modified magnetite nanoparticles as an adsorbent. ► Ammonium was preconcentrated and determined by forming an azo dye. ► Drying of the sorbent phase was performed after extraction prior to back-extraction. ► A low volume of sodium hydroxide solution was used for back-extraction of the formed azo dye.A new method was proposed for the determination of ammonium based on the preconcentration with dodecylbenzene sulfonate modified magnetite nanoparticles. Ammonium was oxidized to nitrite by hypobromite and then the nitrite produced was determined spectrophotometrically, using sulfabenzamide and N-(1-naphthyl) ethylenediamine after solid phase extraction. The azo dye produced was desorbed by an appropriate small volume of sodium hydroxide prior to the absorbance measurement. The linear calibration graphs were obtained in the concentration range of 0.03–6.00ngmL−1 ammonium. The relative standard deviation and recovery percents were 1.0 and 99.0, respectively, for 1.0ngmL−1 ammonium, and the limit of detection was 3.2ngL−1 ammonium. The interfering effects of a large number of diverse ions on the determination of ammonium were studied. The method was applied to the determination of ammonium in various types of water resources. The results revealed a high efficiency for the recommended ammonium determination method.
Keywords: Spectrophotometric determination; Magnetite nanoparticles; Ammonium; Sulfabenzamide
A robust method for speciation, separation and photometric characterization of all [PtCl6− nBr n]2− ( n=0–6) and [PtCl4− nBr n]2− ( n=0–4) complex anions by means of ion-pairing RP-HPLC coupled to ICP-MS/OES, validated by high resolution195Pt NMR spectroscopy by Pieter-Hugo van Wyk; Wilhelmus J. Gerber; Klaus R. Koch (pp. 154-161).
Display Omitted► Ion-pairing RP-HPLC separation of all homoleptic and heteroleptic [PtCl6− nBr n]2− ( n=0–6) and [PtCl4− nBr n]2− ( n=0–4). ► High resolution195Pt NMR validation of chromatographic peak assignments, including stereo-isomers of PtII/IV complexes. ► IP-RP-HPLC coupled to ICP-MS/OES gives accurate concentrations of all PtII/IV species in aqueous acidic solutions. ► UV/Vis photometric properties ( λmax and ɛ) of all [PtCl6− nBr n]2− and [PtCl4− nBr n]2− complexes determined for future use.A robust reversed phase ion-pairing RP-HPLC method has been developed for the unambiguous speciation and quantification of all possible homoleptic and heteroleptic octahedral platinumIV [PtCl6− nBr n]2− ( n=0–6) as well as the corresponding platinumII [PtCl4− nBr n]2− ( n=0–4) complex anions using UV/Vis detection. High resolution195Pt NMR in more concentrated solutions of these PtII/IV complexes (≥50mM) served to validate the chromatographic peak assignments, particularly in the case of the possible stereoisomers of PtII/IV complex anions. By means of IP-RP-HPLC coupled to ICP-MS or ICP-OES it is possible to accurately determine the relative concentrations of all possible PtII/IV species in these solutions, which allows for the accurate determination of the photometric characteristics ( λmax and ɛ) of all the species in this series, by recording of the UV/Vis absorption spectra of all eluted species, using photo-diode array, and quantification with ICP-MS or ICP-OES. With this method it is readily possible to separate and estimate the concentrations of the various stereoisomers which are present in these solutions at sub-millimolar concentrations, such as cis- and trans-[PtCl4Br2]2−, fac- and mer-[PtCl3Br3]2− and cis- and trans-[PtCl2Br4]2− for PtIV, and cis- and trans-[PtCl2Br2]2− in the case of PtII. All mixed halide PtII and PtIV species can be separated and quantified in a single IP-RP-HPLC experiment, using the newly obtained photometric molar absorptivities, ɛ, determined herein at given wavelengths.
Keywords: Speciation of [PtCl; 6−; n; Br; n; ]; 2−; (; n; =; 0–6) and [PtCl; 4−; n; Br; n; ]; 2−; (; n; =; 0–4) complex anions; Ion-pair Reversed Phase-HPLC coupled Inductively Coupled Plasma-Mass Spectrometry/Optical Emission Spectroscopy; 195; Pt Nuclear Magnetic Resonance; molar absorptivities of [PtCl; 6−; n; Br; n; ]; 2−; (; n; =; 0–6) and [PtCl; 4−; n; Br; n; ]; 2−; (; n; =; 0–4) complexes
Sensitive determination of glyoxal, methylglyoxal and hydroxyacetaldehyde in environmental water samples by using dansylacetamidooxyamine derivatization and liquid chromatography/fluorescence by Stéphan Houdier; Manuel Barret; Florent Dominé; Tiffany Charbouillot; Laurent Deguillaume; Didier Voisin (pp. 162-173).
Display Omitted► Dansylacetamidooxyamine (DNSAOA) in acidic media is used to derivatize dicarbonyls and hydro-aldehydes. ► Method is simple of use. ► Derivatization of dicarbonyls follows kinetics of consecutive reactions. ► High sensitivities were achieved (nM level) and no preconcentration of the sample is needed. ► First measurement of glyoxal and methylglyoxal in polar snow samples.In this study we improved the dansylacetamidooxyamine (DNSAOA)–LC–fluorescence method for the determination of aqueous-phase glyoxal (GL), methylglyoxal (MG) and hydroxyacetaldehyde (HA). As derivatization of dicarbonyls can potentially lead to complex mixtures, a thorough study of the reaction patterns of GL and MG with DNSAOA was carried out. Derivatization of GL and MG was shown to follow the kinetics of successive reactions, yielding predominantly doubly derivatized compounds. We verified that the bis-DNSAOA structure of these adducts exerted only minor influence on their fluorescence properties. Contrary to observations made with formaldehyde, derivatization of GL, MG and, to a lesser extent of HA, was shown to be faster in acidic (H2SO4) medium with a maximum of efficiency for acid concentrations of ca. 2.5mM. Concomitant separation of GL, MG, HA and of single carbonyls was achieved within 20min by using C18 chromatography and a gradient of CH3CN in water. Detection limits of 0.27, 0.17 and 0.12nM were determined for GL, MG and HA, respectively. Consequently, low sample volumes are sufficient and, unlike numerous published methods, neither preconcentration nor large injection volumes are necessary to monitor trace-level samples. The method shows relative measurement uncertainties better than ±15% at the 95% level of confidence and good dynamic ranges ( R2>0.99) from 0.01 to 1.5μM for all carbonyls. GL, MG and HA were identified for the first time in polar snow samples, but also in saline frost flowers for which unexpected levels of 0.1–0.6μM were measured. Concentrations in the 0.02–2.3μM range were also measured in cloud water. In most samples, a predominance of HA over GL and MG was observed.
Keywords: HPLC; Fluorescence; Dicarbonyl compounds; Hydroxyaldehydes; Water samples; Environment
Polypyrrole/hexagonally ordered silica nanocomposite as a novel fiber coating for solid-phase microextraction by Mohammad Bagher Gholivand; Mir Mahdi Abolghasemi; Peyman Fattahpour (pp. 174-179).
Display Omitted► The polypyrrole/SBA15) nanocomposite was used as a novel coating for SPME fiber. ► The proposed fiber was used for the extraction of polycyclic aromatic hydrocarbons. ► The proposed SPME fiber is thermal stable, and it has a low limit of detection. ► The SPME fiber was applied in polluted river water and wastewater samples.A highly porous fiber coated polypyrrole/hexagonally ordered silica (PPy/SBA15) materials were prepared for solid-phase microextraction (SPME). The PPy/SBA15 nanocomposite was synthesized by an in situ polymerization technique. The resulting material was characterized by the scanning electron microscopy, thermogravimetric analysis and differential thermal analysis. The prepared nanomaterial was immobilized onto a stainless steel wire for fabrication of the SPME fiber. The fiber was evaluated for the extraction of some polycyclic aromatic hydrocarbons (PAHs) from aqueous sample solutions in combination with gas chromatography–mass spectrometry (GC–MS). A one at-the-time optimization strategy was applied for optimizing the important extraction parameters such as extraction temperature, extraction time, ionic strength, stirring rate, desorption time and desorption temperature. In optimum conditions (extraction temperature 70°C, extraction time 20min, ionic strength 20% (WV−1), stirring rate 500rpm, desorption temperature 270°C, desorption time 5min) the repeatability for one fiber ( n=3), expressed as relative standard deviation (R.S.D. %), was between 5.0% and 9.3% for the tested compounds. The quantitation limit for the studied compounds were between 13.3 and 66.6pgmL−1. The life span and stability of the PPy/SBA15 fiber are good, and it can be used more than 50 times at 260°C without any significant change in sorption properties. The developed method offers the advantage of being simple to use, with shorter analysis times, lower cost of equipment, thermal stability of fiber and high relative recovery in comparison to conventional methods of analysis.
Keywords: Polycyclic aromatic hydrocarbons; Polypyrrole; Nanocomposite; Solid phase microextraction; Gas chromatography–mass spectrometry
Combined use of algorithms for peak picking, peak tracking and retention modelling to optimize the chromatographic conditions for liquid chromatography–mass spectrometry analysis of fluocinolone acetonide and its degradation products by Mattias J. Fredriksson; Patrik Petersson; Bengt-Olof Axelsson; Dan Bylund (pp. 180-188).
Display Omitted► Highly automated algorithms for peak detection, peak tracking, and retention modelling have been combined. ► The strategy was exemplified with a typical application of LC–MS method development for stability studies of drug substances. ► Fast and efficient generation of accurate results was obtained at levels relevant for pharmaceutical products.A strategy for rapid optimization of liquid chromatography column temperature and gradient shape is presented. The optimization as such is based on the well established retention and peak width models implemented in software like e.g. DryLab and LC simulator. The novel part of the strategy is a highly automated processing algorithm for detection and tracking of chromatographic peaks in noisy liquid chromatography–mass spectrometry (LC–MS) data. The strategy is presented and visualized by the optimization of the separation of two degradants present in ultraviolet (UV) exposed fluocinolone acetonide. It should be stressed, however, that it can be utilized for LC–MS analysis of any sample and application where several runs are conducted on the same sample. In the application presented, 30 components that were difficult or impossible to detect in the UV data could be automatically detected and tracked in the MS data by using the proposed strategy. The number of correctly tracked components was above 95%. Using the parameters from the reconstructed data sets to the model gave good agreement between predicted and observed retention times at optimal conditions. The area of the smallest tracked component was estimated to 0.08% compared to the main component, a level relevant for the characterization of impurities in the pharmaceutical industry.
Keywords: Liquid chromatography; Mass spectrometry; Method development; Peak tracking