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Analytica Chimica Acta (v.703, #2)

Editorial Board (pp. i).

Method ruggedness studies incorporating a risk based approach: A tutorial by Phil J. Borman; Marion J. Chatfield; Ivana Damjanov; Patrick Jackson (pp. 101-113).

Display Omitted► Design and analysis of method ruggedness studies using a risk based approach. ► Experimental evaluation of noise factors. ► Identification of special and common cause variability. ► Identification of method controls following ruggedness assessment. ► Assessment of overall analytical method precision.This tutorial explains how well thought-out application of design and analysis methodology, combined with risk assessment, leads to improved assessment of method ruggedness. The authors define analytical method ruggedness as an experimental evaluation of noise factors such as analyst, instrument or stationary phase batch. Ruggedness testing is usually performed upon transfer of a method to another laboratory, however, it can also be employed during method development when an assessment of the method's inherent variability is required. The use of a ruggedness study provides a more rigorous method for assessing method precision than a simple comparative intermediate precision study which is typically performed as part of method validation. Prior to designing a ruggedness study, factors that are likely to have a significant effect on the performance of the method should be identified (via a risk assessment) and controlled where appropriate. Noise factors that are not controlled are considered for inclusion in the study. The purpose of the study should be to challenge the method and identify whether any noise factors significantly affect the method's precision. The results from the study are firstly used to identify any special cause variability due to specific attributable circumstances. Secondly, common cause variability is apportioned to determine which factors are responsible for most of the variability. The total common cause variability can then be used to assess whether the method's precision requirements are achievable. The approach used to design and analyse method ruggedness studies will be covered in this tutorial using a real example.

Keywords: Precision; Variance; Components; Noise; Variability; Ruggedness

A review of recent, unconventional applications of ion mobility spectrometry (IMS) by Sergio Armenta; Manel Alcala; Marcelo Blanco (pp. 114-123).

Display Omitted► Contributions of IMS as fast and sensitive analytical tool. ► Instrumental developments including drift tube materials and ionization sources. ► Analytical applications of IMS in pharmaceutical, food, clinical, environmental and polymer areas.The applications of ion mobility spectrometry (IMS) have grown exponentially beyond its uses for explosive, illicit drug and chemical warfare agent monitoring in recent years. Instrumental developments including new drift tube materials and ionization sources have enabled the manufacturing of more sophisticated and affordable IMS equipment for the advantageous analysis of samples with no pretreatment. The most recent applications of IMS include quality control and cleaning validation procedures in the pharmaceutical industry; determinations of contaminants in food samples; clinical analyses of biological fluids; environmental analyses of contaminants in gaseous, liquid and solid samples; and (bio)process quality control monitoring. Coupling IMS with MSⁿ has enabled the analysis of very complex samples and the extraction of knowledge unavailable from isolated MS measurements, especially in the polymer and petroleomic industries.

Keywords: Ion mobility spectrometry; Pharmaceuticals; Food analysis; Environmental analysis; Clinical analysis; Process control

Technology behind commercial devices for blood glucose monitoring in diabetes management: A review by Sandeep Kumar Vashist; Dan Zheng; Khalid Al-Rubeaan; John H.T. Luong; Fwu-Shan Sheu (pp. 124-136).

The expanded views of Abbott's FreeStyle Navigator sensor chip for blood glucose monitoring .Display Omitted► In this review article, we provide critical views on the technology behind commercial glucose sensor. ► We express opinion regarding the relative merits of designed sensors for monitoring serum glucose. ► We also comment as on the pros and cons of recently reported glucose biosensors in the literature.The blood glucose monitoring devices (BGMDs) are an integral part of diabetes management now-a-days. They have evolved tremendously within the last four decades in terms of miniaturization, rapid response, greater specificity, simplicity, minute sample requirement, painless sample uptake, sophisticated software and data management. This article aims to review the developments in the technologies behind commercial BGMD, especially those in the areas of chemistries, mediators and other components. The technology concerns, on-going developments and future trends in blood glucose monitoring (BGM) are also discussed.

Keywords: Blood glucose monitoring devices; Electron mediators; Glucose limiting membranes; Interferences; Glucose strips

Determination of ultra trace arsenic species in water samples by hydride generation atomic absorption spectrometry after cloud point extraction by Halil İbrahim Ulusoy; Mehmet Akçay; Songül Ulusoy; Ramazan Gürkan (pp. 137-144).

The possible complex formation mechanism for ultra-trace As determination.Display Omitted► CPE/HGAAS system for arsenic determination and speciation in real samples has been applied first time until now. ► The proposed method has the lowest detection limit when compared with those of similar CPE studies present in literature. ► The linear range of the method is highly wide and suitable for its application to real samples.Cloud point extraction (CPE) methodology has successfully been employed for the preconcentration of ultra-trace arsenic species in aqueous samples prior to hydride generation atomic absorption spectrometry (HGAAS). As(III) has formed an ion-pairing complex with Pyronine B in presence of sodium dodecyl sulfate (SDS) at pH 10.0 and extracted into the non-ionic surfactant, polyethylene glycol tert-octylphenyl ether (Triton X-114). After phase separation, the surfactant-rich phase was diluted with 2mL of 1M HCl and 0.5mL of 3.0% (w/v) Antifoam A. Under the optimized conditions, a preconcentration factor of 60 and a detection limit of 0.008μgL⁻¹ with a correlation coefficient of 0.9918 was obtained with a calibration curve in the range of 0.03–4.00μgL⁻¹. The proposed preconcentration procedure was successfully applied to the determination of As(III) ions in certified standard water samples (TMDA-53.3 and NIST 1643e, a low level fortified standard for trace elements) and some real samples including natural drinking water and tap water samples.

Keywords: Arsenic speciation; Pyronine B; Cloud point extraction; Hydride generation atomic absorption spectrometry

Synthesis and application of imprinted polyvinylimidazole-silica hybrid copolymer for Pb²⁺ determination by flow-injection thermospray flame furnace atomic absorption spectrometry by César Ricardo Teixeira Tarley; Felipe Nascimento Andrade; Fernanda Midori de Oliveira; Marcela Zanetti Corazza; Luiz Fernando Mendes de Azevedo; Mariana Gava Segatelli (pp. 145-151).

Display Omitted► Ion imprinted hybrid copolymer as selective sorbent for Pb²⁺ ions. ► The sorbent was at least 10 times more selective than non imprinted copolymer. ► A method for Pb²⁺ determination by TS-FF-AAS in different samples was developed. ► High reusability and chemical stability of ion imprinted hybrid copolymer were observed.A novel ion imprinted polyvinylimidazole-silica hybrid copolymer (IIHC) was synthesized and used as a selective solid sorbent for Pb²⁺ ions preconcentration using an on-line solid phase extraction (SPE) system coupled to TS-FF-AAS. The ionic hybrid sorbent was prepared using 1-vinylimidazole and 3-(trimethoxysilyl)propylmethacrylate as monomers, Pb²⁺ ions as template, tetraethoxysilane as reticulating agent and 2,2′-azobis-isobutyronitrile as initiator. The best on-line SPE conditions concerning sorption behavior, including sample pH (6.46), buffer concentration (9.0mmolL⁻¹), eluent (HNO₃) concentration (0.5molL⁻¹) and preconcentration flow rate (4.0mLmin⁻¹), were optimized by means of full factorial design and Doehlert matrix. The analytical curve ranged from 2.5 to 65.0μgL⁻¹ ( r=0.999) with limit of detection of 0.75μgL⁻¹; the precision (repeatability) calculated as relative standard deviation ( n=10) was 5.0 and 3.6% for Pb²⁺ concentration of 10.0 and 60.0μgL⁻¹, respectively. From on-line breakthrough curve, column capacity was 3.5mgg⁻¹. Preconcentration factor (PF), consumptive index (CI) and concentration efficiency (CE) were 128.0, 0.16mL and 25.6min⁻¹, respectively. The selective performance of the sorbent, based on relative selectivity coefficient, was compared to NIC ( non imprinted copolymer) for the binary mixture Pb²⁺/Cd²⁺, Pb²⁺/Cu²⁺ and Pb²⁺/Zn²⁺. The results showed that ion imprinted polyvinylimidazole-silica hybrid polymer had higher selectivity for Pb²⁺ than NIC at 64.9, 16.0 and 8.8 folds. The developed method was successfully applied for highly sensitive and selective Pb²⁺ determination in different kinds of water samples, parenteral solutions and urine. Accuracy was also assessed by analyzing certified reference fish protein (DORM-3) and marine sediment (MESS-3 and PACS-2) with satisfactory results.

Keywords: Lead; Ion imprinted polyvinylimidazole-silica hybrid; Thermospray flame furnace atomic absorption spectrometry; Solid phase preconcentration

Support vector machines in water quality management by Kunwar P. Singh; Nikita Basant; Shikha Gupta (pp. 152-162).

The SVM model is tested in the current study to predict the surface water BOD using set of selected directly measurable parameters. This figure shows a good correlation between the predicted and measured BOD values.Display Omitted► SVM classification and regression models applied to a large surface water quality data set to optimize monitoring program. ► SVM classification (spatial and temporal) model grouping similar sampling sites and months rendered 92.5% data reduction. ► SVM regression model using a set of six directly measurable variables predicted water BOD precisely ( R>0.90). ► Performances of SVM, KDA, KPLS comparable, and relatively better than DA and PLS. ► SVM based modeling has helped in redesigning the water quality monitoring program.Support vector classification (SVC) and regression (SVR) models were constructed and applied to the surface water quality data to optimize the monitoring program. The data set comprised of 1500 water samples representing 10 different sites monitored for 15 years. The objectives of the study were to classify the sampling sites (spatial) and months (temporal) to group the similar ones in terms of water quality with a view to reduce their number; and to develop a suitable SVR model for predicting the biochemical oxygen demand (BOD) of water using a set of variables. The spatial and temporal SVC models rendered grouping of 10 monitoring sites and 12 sampling months into the clusters of 3 each with misclassification rates of 12.39% and 17.61% in training, 17.70% and 26.38% in validation, and 14.86% and 31.41% in test sets, respectively. The SVR model predicted water BOD values in training, validation, and test sets with reasonably high correlation (0.952, 0.909, and 0.907) with the measured values, and low root mean squared errors of 1.53, 1.44, and 1.32, respectively. The values of the performance criteria parameters suggested for the adequacy of the constructed models and their good predictive capabilities. The SVC model achieved a data reduction of 92.5% for redesigning the future monitoring program and the SVR model provided a tool for the prediction of the water BOD using set of a few measurable variables. The performance of the nonlinear models (SVM, KDA, KPLS) was comparable and these performed relatively better than the corresponding linear methods (DA, PLS) of classification and regression modeling.

Keywords: Support vector classification; Support vector regression; Kernel discriminant analysis; Kernel partial least squares; Water quality; Biochemical oxygen demand

Identification of protein methylation sites by coupling improved ant colony optimization algorithm and support vector machine by Zhan-Chao Li; Xuan Zhou; Zong Dai; Xiao-Yong Zou (pp. 163-171).

.Display Omitted► The proposed predictor of Methy_SVMIACO achieves good accuracies. ► Methylation of lysine and arginine is likely to occur at helix region of protein. ► Improved ant colony algorithm is utilized to find the optimal feature subset. ► Some upstream and downstream residues play important role in methylation.Protein methylation is involved in dozens of biological processes and plays an important role in adjusting protein physicochemical properties, conformation and function. However, with the rapid increase of protein sequence entering into databanks, the gap between the number of known sequence and the number of known methylation annotation is widening rapidly. Therefore, it is vitally significant to develop a computational method for quick and accurate identification of methylation sites. In this study, a novel predictor (Methy_SVMIACO) based on support vector machine (SVM) and improved ant colony optimization algorithm (IACO) is developed to identify methylation sites. The IACO is utilized to find the optimal feature subset and parameter of SVM, while SVM is employed to perform the identification of methylation sites. Comparison of the IACO with conventional ACO shows that the IACO converges quickly toward the global optimal solution and it is more useful tool for feature selection and SVM parameter optimization. The performance of Methy_SVMIACO is evaluated with a sensitivity of 85.71%, a specificity of 86.67%, an accuracy of 86.19% and a Matthew's correlation coefficient ( MCC) of 0.7238 for lysine as well as a sensitivity of 89.08%, a specificity of 94.07%, an accuracy of 91.56% and a MCC of 0.8323 for arginine in 10-fold cross-validation test. It is shown through the analysis of the optimal feature subset that some upstream and downstream residues play important role in the methylation of arginine and lysine. Compared with other existing methods, the Methy_SVMIACO provides higher Acc, Sen and Spe, indicating that the current method may serve as a powerful complementary tool to other existing approaches in this area. The Methy_SVMIACO can be acquired freely on request from the authors.

Keywords: Methylation; Support vector machine; Ant colony optimization algorithm; Feature selection

A three-dimensional hierarchical nanoporous PdCu alloy for enhanced electrocatalysis and biosensing by Aihua Liu; Haoran Geng; Caixia Xu; Huajun Qiu (pp. 172-178).

Display Omitted► Nanotubular mesoporous PdCu (NM-PdCu) alloy is facilely fabricated via one-step metal replacement reaction between nanoporous Cu and H₂PdCl₄. ► The NM-PdCu exhibits remarkably improved structure stability and electrocatalytic activity towards formic acid and hydrogen peroxide oxidation compared with NP-Pd. ► When coupled with GOx, the GOx/NM-PdCu electrode can be used for sensitive detection of glucose over a wide concentration range.Nanoporous copper (NPC) obtained by dealloying CuAl alloy is used as both three-dimensional template and reducing agent for the fabrication of nanoporous PdCu alloy with hollow ligaments by a simple galvanic replacement reaction with H₂PdCl₄ aqueous solution. Electron microscopy and X-ray diffraction characterizations demonstrate that after the replacement reaction, the ligaments become hollow tubular structure and the ligament shell is also comprised of small pores and nanoparticles with a typical size of ∼4nm (third order porosity). The as-prepared nanotubular mesoporous PdCu alloy (NM-PdCu) structure exhibits remarkably improved electrocatalytic activity towards the oxidation of formic acid and H₂O₂ compared with nanoporous Pd (NP-Pd), and can be used for sensitive electrochemical sensing applications. After coupled with glucose oxidase (GOx), the enzyme modified NM-PdCu electrode can sensitively detect glucose over a wide linear range (0.5–20mM).

Keywords: Dealloying; Galvanic replacement; Formic acid; Hollow nanostructure; Glucose biosensor

Pre-analytical method for NMR-based grape metabolic fingerprinting and chemometrics by Kashif Ali; Federica Maltese; Ana Margarida Fortes; Maria Salomé Pais; Robert Verpoorte; Young Hae Choi (pp. 179-186).

Pre-analytical method for NMR-based grape metabolic fingerprinting and chemometrics.Display Omitted► Different pre-analytical methods were used for metabolic profiling of grapevine. ► We define own range of metabolites detected in each method. ► Extraction with deuterated solvents shows higher efficiency of primary metabolites. ► Solid phase extraction with C18 improves extraction efficiency of minor phenolics.Although metabolomics aims at profiling all the metabolites in organisms, data quality is quite dependent on the pre-analytical methods employed. In order to evaluate current methods, different pre-analytical methods were compared and used for the metabolic profiling of grapevine as a model plant. Five grape cultivars from Portugal in combination with chemometrics were analyzed in this study. A common extraction method with deuterated water and methanol was found effective in the case of amino acids, organic acids, and sugars. For secondary metabolites like phenolics, solid phase extraction with C-18 cartridges showed good results. Principal component analysis, in combination with NMR spectroscopy, was applied and showed clear distinction among the cultivars. Primary metabolites such as choline, sucrose, and leucine were found discriminating for ‘Alvarinho’, while elevated levels of alanine, valine, and acetate were found in ‘Arinto’ (white varieties). Among the red cultivars, higher signals for citrate and GABA in ‘Touriga Nacional’, succinate and fumarate in ‘Aragonês’, and malate, ascorbate, fructose and glucose in ‘Trincadeira’, were observed. Based on the phenolic profile, ‘Arinto’ was found with higher levels of phenolics as compared to ‘Alvarinho’. ‘Trincadeira’ showed lowest phenolics content while higher levels of flavonoids and phenylpropanoids were found in ‘Aragonês’ and ‘Touriga Nacional’, respectively. It is shown that the metabolite composition of the extract is highly affected by the extraction procedure and this consideration has to be taken in account for metabolomics studies.

Keywords: NMR spectroscopy; Grapes; Pre-analytical method; Solid phase extraction; Phenolics; Metabolomics

Optimized cleanup method for the determination of short chain polychlorinated n-alkanes in sediments by high resolution gas chromatography/electron capture negative ion–low resolution mass spectrometry by Yuan Gao; Haijun Zhang; Jiping Chen; Qing Zhang; Yuzeng Tian; Peipei Qi; Zhengkun Yu (pp. 187-193).

The sediment sample could be purified by the optimized cleanup method, and satisfying cleanup efficiency was obtained.Display Omitted► The elution characters of sPCAs and interfering substances were evaluated on three adsorbents. ► An optimized cleanup method was developed for sPCAs with satisfying cleanup efficiency. ► The cleanup method combined with HRGC/ECNI–LRMS was applied for sPCAs analysis. ► The sPCAs levels range from 53.6ngg⁻¹ to 289.3ngg⁻¹ in tested sediment samples.The performances of three adsorbents, i.e. silica gel, neutral and basic alumina, in the separation of short chain polychlorinated n-alkanes (sPCAs) from potential interfering substances such as polychlorinated biphenyls (PCBs) and organochlorine pesticides were evaluated. To increase the cleanup efficiency, a two-step cleanup method using silica gel column and subsequent basic alumina column was developed. All the PCB and organochlorine pesticides could be removed by this cleanup method. The very satisfying cleanup efficiency of sPCAs has been achieved and the recovery in the cleanup method reached 92.7%. The method detection limit (MDL) for sPCAs in sediments was determined to be 14ngg⁻¹. Relative standard deviation (R.S.D.) of 5.3% was obtained for the mass fraction of sPCAs by analyzing four replicates of a spiked sediment sample. High resolution gas chromatography/electron capture negative ion–low resolution mass spectrometry (HRGC/ECNI–LRMS) was used for sPCAs quantification by monitoring [M−HCl]⁻ ions. When applied to the sediment samples from the mouth of the Daliao River, the optimized cleanup method in conjunction with HRGC/ECNI–LRMS allowed for highly selective identifications for sPCAs. The sPCAs levels in sediment samples are reported to range from 53.6ngg⁻¹ to 289.3ngg⁻¹. C₁₀- and C₁₁-PCAs are the dominant residue in most of investigated sediment samples.

Keywords: Abbreviations; HRGC/ECNI–LRMS; high resolution gas chromatography/electron capture negative ion–low resolution mass spectrometry; sPCAs; short chain polychlorinated; n; -alkanes; PCBs; polychlorinated biphenyls; GPC; gel permeation chromatography; SIM; selected ion monitoringShort chain polychlorinated; n; -alkanes; Silica gel; Alumina; Column chromatography; Cleanup

Implications of partial tryptic digestion in organic–aqueous solvent systems for bottom-up proteome analysis by Mark J. Wall; Andrew M.J. Crowell; Gordon A. Simms; Fang Liu; Alan A. Doucette (pp. 194-203).

. While solvent-assisted digestion can rapidly produce high quality protein digestion maps, trypsin digestion efficiency under these conditions is shown to be significantly reduced. High sequence coverage is explain through detection of a large diversity of peptides, though the absolute quantity of these products is far less than a conventional (overnight aqueous) digestion. If a complete (or near complete) protein digestion is desired, solvent-assisted digestion is therefore not recommended.Display Omitted► LC/MS, SDS PAGE and BAEE assay are used to assess trypsin activity in 80% acetonitrile ► Above 40% acetonitrile, (unmodified) trypsin activity is lower at 37°C than at 22°C ► Low enzyme activity results in poor protein digestion in high organic solvent ► Incomplete digestion can result in higher protein sequence coverage ► High sequence coverage should not be taken as indication of high digestion efficiencyFor bottom-up MS, the digestion step is critical and is typically performed with trypsin. Solvent-assisted digestion in 80% acetonitrile has previously been shown to improve protein sequence coverage at shorter digestion times. This has been attributed to enhanced enzyme digestion efficiency in this solvent. However, our results demonstrate that tryptic digestion in 80% acetonitrile is less efficient than that of conventional (aqueous) digestion. This is a consequence of decreased enzyme activity beyond ∼40% acetonitrile, increased enzyme autolysis and lower protein solubility in 80% acetonitrile. We observe multiple missed cleavages and reduced concentration of fully cleaved digestion products. Nonetheless we confirm, through room temperature solvent-assisted digestion, a consistent improvement in protein sequence coverage when analyzed by mass spectrometry. These results are explained through the increased number of unique digestion products available for detection. Thus, while solvent-assisted digestion has clear merits for proteome analysis, one should be aware of the inefficiency of protein digestion though this protocol, particularly with absolute protein quantitation experiments.

Keywords: Solvent-assisted digestion; Trypsin; Acetonitrile; Rapid digestion; Enzyme activity; Bottom-up mass spectrometry; Shotgun proteomics

Metabolomic approach for determination of key volatile compounds related to beef flavor in glutathione-Maillard reaction products by Sang Mi Lee; Goo Young Kwon; Kwang-Ok Kim; Young-Suk Kim (pp. 204-211).

Display Omitted► The non-targeted analysis, combining GC–TOF/MS and sensory evaluation, was applied. ► Volatile compounds correlating to beef flavor attribute were then determined. ► This approach allowed the identification of key volatiles in Maillard model systems.The non-targeted analysis, combining gas chromatography coupled with time-of-flight mass spectrometry (GC–TOF/MS) and sensory evaluation, was applied to investigate the relationship between volatile compounds and the sensory attributes of glutathione-Maillard reaction products (GSH-MRPs) prepared under different reaction conditions. Volatile compounds in GSH-MRPs correlating to the sensory attributes were determined using partial least-squares (PLS) regression. Volatile compounds such as 2-methylfuran-3-thiol, 3-sulfanylpentan-2-one, furan-2-ylmethanethiol, 2-propylpyrazine, 1-furan-2-ylpropan-2-one, 1 H-pyrrole, 2-methylthiophene, and 2-(furan-2-ylmethyldisulfanylmethyl)furan could be identified as possible key contributors to the beef-related attributes of GSH-MRPs. In this study, we demonstrated that the unbiased non-targeted analysis based on metabolomic approach allows the identification of key volatile compounds related to beef flavor in GSH-MRPs.

Keywords: Glutathione-Maillard reaction products; Non-targeted analysis; Beef flavor; Sensory attributes; Gas-chromatography coupled with time-of-flight mass spectrometry; Partial least-squares regression

Determination of amines based on their interaction with QDs: Effect of the formation QD-assemblies by Carolina Carrillo-Carrión; Bartolomé M. Simonet; Miguel Valcárcel (pp. 212-218).

Display Omitted► Formation of quantum dots-nanochains assisted by the covalent linking through bifunctional dithiol molecules. ► With time, the extent of chain assembly and network formation became enhanced and interconnectivity between chains was observed. ► The optical properties changed as a function of the total length of the structure. ► Fluorescence response of QDs towards amines was enhanced after the formation of QD-assemblies induced by the presence of dithiol molecules.Assemblies of closed nanoparticles have focused interest because they exhibit new optical and chemical properties. The use of a 1D covalent strategy for quantum dots-assemblies has been proposed in this work as novelty. It was studied the effect of use different dithiols, including aromatic and aliphatic dithiol compounds, on the formation of QDs-assemblies in order to establish the influence of the linker's structure on the geometry of the assemblies, and hence on their properties. As a second part of the work, the changes on analytical response to analytes thanks to the formation of QDs-assemblies when dithiols are added were studied for firs time. For this study, some biogenic amines were selected as target analytes. We observed an improvement of 2.7–4 times in the sensitivity, expressed as slope of the calibration graph, when the dithiols were added to the system obtaining QDs-assemblies.

Keywords: CdSe/ZnS quantum dots; Quantum dot-assemblies; Nanochains; Dithiol linker; Amplified fluorescence quenching

A carbohydrate modified fluoride ion sensor and its applications by Guohua Wei; Junxia Yin; Xing Ma; Shouyi Yu; Dongbin Wei; Yuguo Du (pp. 219-225).

A new fluorescent probe which exhibits excellent F⁻ ion selectivity as well as significant color changes visible to the naked eye has been developed. This new carbohydrate modified probe can be used directly for water samples and in bioimaging without using organic co-solvents.Display Omitted► We provide a carbohydrate modified fluorescent probe with excellent F⁻ selectivity. ► The probe shows visible color change at WHO recommended F⁻ level in drinking water. ► F⁻ detection is processed in aqueous medium without using any organic co-solvents. ► The probe presents high sensitivity and selectivity for F⁻ imaging in HepG2 cells.A new fluorescent probe for the detection of F⁻ (TBA⁺ and Na⁺ salts) has been developed, which is based on a desilylation triggered chromogenic reaction in water. This probe exhibits excellent F⁻ ion selectivity as well as significant color changes visible to the naked eye at the concentration of 1.5mgL⁻¹, the WHO recommended level of F⁻ ions in drinking water. This new carbohydrate modified probe can be used directly in aqueous medium without using organic co-solvents. Furthermore, the probe presents high sensitivity and selectivity for the imaging of F⁻ ions in HepG2 cells.

Keywords: Fluorescent probes; Fluoride ions; Carbohydrates; Sensors; Imaging agents

Molecularly imprinted polymers as optical sensing receptors: Correlation between analytical signals and binding isotherms by Ng Sing Muk; R. Narayanaswamy (pp. 226-233).

Display Omitted► We studied the parameters involved in the binding of molecularly imprinted polymers with the template using binding isotherm models. ► We model the correlation between the binding isotherm parameters with the optical signals. ► Good correlation was found between binding affinity, sites density and the shift of optical signal. ► The correlation between the parameters was used to construct an analytical model to represent the sensor analytical capability.Despite the increasing number of usage of molecularly imprinted polymers (MIPs) in optical sensor application, the correlation between the analytical signals and the binding isotherms has yet to be fully understood. This work investigates the relationship between the signals generated from MIPs sensors to its respective binding affinity variables generated using binding isotherm models. Two different systems based on the imprinting of metal ion and organic compound have been selected for the study, which employed reflectance and fluorescence sensing schemes, respectively. Batch binding analysis using the standard binding isotherm models was employed to evaluate the affinity of the binding sites. Evaluation using the discrete bi-Langmuir isotherm model found both the MIPs studied have generally two classes of binding sites that was of low and high affinities, while the continuous Freundlich isotherm model has successfully generated a distribution of affinities within the investigated analytical window. When the MIPs were incorporated as sensing receptors, the changes in the analytical signal due to different analyte concentrations were found to have direct correlation with the binding isotherm variables. Further data analyses based on this observation have generated robust models representing the analytical performance of the optical sensors. The best constructed model describing the sensing trend for each of the sensor has been tested and demonstrated to give accurate prediction of concentration for a series of spiked analytes.

Keywords: Molecularly imprinted polymer; Optical sensors; Binding isotherms; Fluorescence; Reflectance; Multi-regressions analysis

Surface-enhanced Raman scattering detection of cholinesterase inhibitors by Zvi Liron; Adi Zifman; Vered Heleg-Shabtai (pp. 234-238).

Display Omitted► A new sensitive surface-enhanced Raman scattering (SERS) assay for detection of cholinesterase inhibitors such as organophosphorous pesticides using silver colloidal nanoparticles was developed and optimized. ► Acetylcholinesterase (AChE) mediated the hydrolysis of acetylthiocholine to produce thiocholine, which interacted with the silver nanoparticles to give a specific SERS spectrum. ► The method was demonstrated for the detection of paraoxon as reference AChE inhibitor, and limit of detection for 5min incubation at 25°C was 1.8×10⁻⁸M. ► This assay can be utilized for the detection of trace amounts of any AChE inhibitor.A new sensitive surface-enhanced Raman scattering (SERS) assay for detection of cholinesterase inhibitors such as organophosphorous pesticides using silver colloidal nanoparticles was developed and optimized. Acetylcholinesterase (AChE) mediated the hydrolysis of acetylthiocholine to produce thiocholine, which interacted with the silver nanoparticles to give a specific SERS spectrum. Variation in enzyme activity due to inhibition was measured from changes in intensity of a characteristic peak (772cm⁻¹) of the SERS spectrum that was directly correlated with the concentration of produced thiocholine. The method was demonstrated for the detection of paraoxon as reference AChE inhibitor. Limit of detection of paraoxon for 5min incubation at 25°C was 1.8×10⁻⁸M. This assay can be utilized for the detection of trace amounts of any AChE inhibitor.

Keywords: Acetylcholinesterase; Paraoxon; Silver nanoparticles; Surface-enhanced Raman scattering; Thiocholine

Comparison of molecular imprinted particles prepared using precipitation polymerization in water and chloroform for fluorescent detection of nitroaromatics by R. Cody Stringer; Shubhra Gangopadhyay; Sheila A. Grant (pp. 239-244).

Display Omitted► Imprinted polymers prepared using precipitation polymerization. ► Comparison of chloroform and water as polymerization solvent. ► Imprinted polymer doped with quantum dots for fluorescent sensor. ► Fluorescent imprinted polymer used to detect nitroaromatic explosives. ► Chloroform is ideal solvent for molecular imprinting of nitroaromatics.A comparative study was conducted to study the effects that two different polymerization solvents would have on the properties of imprinted polymer microparticles prepared using precipitation polymerization. Microparticles prepared in chloroform, which previous results indicated was the optimal solvent for molecular imprinting of nitroaromatic explosive compounds, were compared to water, which was hypothesized to decrease water swelling of the polymer and allow enhanced rebinding of aqueous template. The microparticles were characterized and were integrated into a fluorescence sensing mechanism for detection of nitroaromatic explosive compounds. The performance of the sensing mechanisms was compared to illustrate which polymerization solvent produced optimal imprinted polymer microparticles for detection of nitroaromatic molecules. Results indicated that the structures of microparticles synthesized in chloroform versus water varied greatly. Sensor performance studies showed that the microparticles prepared in chloroform had greater imprinting efficiency and higher template rebinding than those prepared in water. For detection of 2,4,6-trinitrotoluene, the chloroform-based fluorescent microparticles achieved a lower limit of detection of 0.1μM, as compared to 100μM for the water-based fluorescent microparticles. Detection limits for 2,4-dinitrotoluene, as well as time response studies, also demonstrated that the chloroform-based particles are more effective for detection of nitroaromatic compounds than water-based particles. These results illustrate that the enhanced chemical properties of using the experimentally determined optimal polymerization solvent overcome deformation of imprinted binding sites by water swelling and benefits of using the polymerization solvent for rebinding of the template.

Keywords: Imprinted polymer; Nitroaromatic; Explosive; Precipitation polymerization

Anomalies in evaporative light scattering detection by D. Shock; G.R. Dennis; G. Guiochon; P.K. Dasgupta; R.A. Shalliker (pp. 245-249).

Comparative difference in detection response between UV and ELS detectors in the analysis of oligostyrene diastereomers.Display Omitted► Power transforms might be imbedded in ELS detector firmware. ► Power transforms alter chromatographic peak moments. ► Power transforms can lead to selective detection.A two-dimensional (2-D) “heart-cutting” HPLC system was used to fractionate oligostyrenes into the respective diastereoisomers. For samples of known composition, the response of an ultraviolet (UV) absorbance detector followed the anticipated pattern. The response of an evaporative light-scattering (ELSD) detector on the other hand indicated quite different concentrations for the two diastereoisomers, relative to what was anticipated and what was indicated by the UV detector. Whereas approximately the same concentration was indicated by UV, ELSD in some cases indicated no detection of the later eluting isomer. The magnitude of the errors depended on both the molecular weight and the tacticity of the diastereomers. These anomalies appear to be an artifact of power transform functions imbedded within the firmware processor of the ELSD, invisible to the user.

Keywords: Evaporative light scattering detection; Power transforms; Polymer analysis; HPLC

Weak affinity ligands selection using quartz crystal microbalance biosensor: Multi-hydroxyl amine ligands for protein separation by Qing Cao; Yueyan Yin; Li Quan; Na Li; Kean Li; Feng Liu (pp. 250-256).

Display Omitted► A QCM biosensor was fabricated to develop novel weak affinity ligands. ► Three multi-hydroxyl amines were selected as weak affinity chromatographic ligands. ► Two proteins were separated on one single column modified the affinity ligands.Multi-hydroxyl amines including tris(hydroxymethyl)aminomethane (Tris), serinol and ethanolamine were selected as weak affinity ligands using a rapid screening by quartz crystal microbalance (QCM) biosensor. Based on the specific recognition between the ligands and two proteins, lysozyme (LZM) and cytochrome c (Cyt c), a weak affinity chromatography method was developed for specific separation of the two proteins. The frontal analysis results showed that the apparent dissociation constants ( K_D) of ligand–protein complexes were all in the order of weak affinity (10⁻⁴M). By weak affinity columns modified with the three multi-hydroxyl amines individually, LZM and Cyt c were baseline separated as retarded peaks from non-specific protein and each other in a single cycle of loading and eluting. Moreover, the Tris-modified column typically showed the satisfactory repeatability and stability as a new type of weak affinity columns. The present strategy composed of QCM selecting and affinity chromatography separating was promising to extend the variety of weak affinity ligands and develop inexpensive specific affinity methods for separation and purification of multiple proteins on one single column.

Keywords: Weak affinity chromatography; Quartz crystal microbalance; Tris(hydroxymethyl)aminomethane; Serinol; Ethanolamine; Protein separation

One-pot labeling-based capillary zone electrophoresis for separation of amino acid mixture and assay of biofluids by Lijuan Song; Zhenpeng Guo; Yi Chen (pp. 257-263).

.Display Omitted► One-pot labeling for amino acid analysis. ► Simplified derivatization procedure with cost-effective reagents. ► Speed of reaction at mild conditions. ► Efficient separation of nineteen amino acids using capillary zone electrophoresis without any additive. ► Successful analysis of human serum, saliva and urine.A fast, simple and cost-effective one-pot labeling strategy coupled with capillary zone electrophoresis was developed for the complete separation of amino acid mixture. The strategy includes two steps of reactions: Cyanuric chloride was made to react first with 7-amino-1,3-naphthalenedisulfonic acid monopotassium salt at 0°C for 10min, and then with amino acids at 55°C for 6min. The resulted products, after diluted with water, were injected into capillary zone electrophoresis system for separation. Using a running buffer of 20mM sodium tetraborate decahydrate at pH 10.1, nineteen amino acids were efficiently separated in 25min, with relative standard deviation of 0.36–1.6% and 0.96–2.1% (within and between days, respectively) for migration time and 0.030–1.6% and 0.22–2.4% (within and between days, respectively) for peak area. The proposed method has been successfully applied to the determination of free amino acids in biofluids, including human serum, urine, and saliva. The linearity of quantification was over two orders of magnitude for most amino acids, with a correlation coefficient larger than 0.999. The average recovery, determined by spiking a known amount of amino acid standards into real samples, was in a range from 91.6% to 105.9%. This method can be a noninvasive means since it could directly assay the urine and saliva samples.

Keywords: One-pot labeling; Amino acids; Biofluids; Capillary electrophoresis

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Analytica Chimica Acta (v.703, #2)

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Analytica Chimica Acta (v.703, #2)