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Analytica Chimica Acta (v.775, #)

Editorial Board (pp. iii).

Recent advances in high resolution scanning electrochemical microscopy of living cells – A review by Stefan Bergner; Preety Vatsyayan; Frank-Michael Matysik (pp. 1-13).

High resolution scanning electrochemical microscopy (SECM) is a rapidly developing tool for studies of living cells. Various methodical approaches of SECM imaging can be used to gain detailed information concerning the morphology and function of single cell and cell assemblies.Display Omitted► We discuss recent advances in high resolution SECM of living cells. ► Advantages and disadvantages of the various imaging techniques are compared. ► New horizons in high resolution SECM studies of cellular processes are discussed.This review discusses advances in the field of high resolution scanning electrochemical microscopy (HR-SECM) and scanning ion conductance microscopy (SICM) to study living cells. Relevant references from the advent of this technique in the late 1980s to most recent contributions in 2012 are presented with special discussion on high resolution images. A clear progress especially within the last 5 years can be seen in the field of HR-SECM. Furthermore, we also concentrate on the intrinsic properties of SECM imaging techniques e.g. different modes of image acquisition, their advantages and disadvantages in imaging living cells and strategies for further enhancement of image resolution, etc. Some of the recent advances of SECM in nanoimaging have also been discussed which may have potential applications in high resolution imaging of cellular processes.

Keywords: Scanning electrochemical microscopy; High resolution imaging; Living cells

The challenge of identifying non-intentionally added substances from food packaging materials: A review by C. Nerin; P. Alfaro; M. Aznar; C. Domeño (pp. 14-24).

Display Omitted► Non intentionally added substances (NIAS) are frequently present in packaged food. ► In-depth review about the different NIAS origin is described. ► An analytical approach for sample treatment and NIAS identification is suggested. ► The analytical approach selected dictates which NIAS are identified. ► A risk assessment protocol for identified NIAS is presented.Packaged food can contain non-intentionally added substances (NIAS) as a result of reaction and degradation processes or the presence of impurities in the raw materials used for the packaging production. This manuscript reviews the evidence of NIAS and their possible origin. One of the most challenging and difficult tasks when a sample of packaging materials arrives at the laboratory is knowing the procedure to apply for identifying the unknown compounds. This work proposes an analytical procedure for sample treatment, applicable to polymers as well as to migration samples, and for NIAS identification. The identification protocol comprises the determination of both volatile and non-volatile compounds. A review is presented of the most novel analytical techniques used for identification purposes, particularly high resolution mass spectrometry (HRMS).

Keywords: NIAS; HRMS; TOF; Packaging; Migration; Identification; Unknowns

Monolithic column in gas chromatography by A. Kurganov (pp. 25-40).

•Review covers recent achievements in preparation of efficient monolithic columns for GC.•Monolithic columns may perform high speed separations.•Increased column pressure in GC may increase column performance.•Monolithic columns may be a right choice of column second dimension in comprehensive GC×GC.Monolithic columns invented in chromatographic praxis almost 40 years ago gained nowadays a lot of popularity in separations by liquid chromatographic technique. At the same time, application of monolithic columns in gas chromatography is less common and only a single review published by Svec et al. [1] covers this field of research. Since that time a lot of new findings on application and properties of monolithic columns in gas chromatography have been published in the literature deserving consideration and discussion. This review considers preparation of monolithic columns for GC, an impact of preparation conditions on column performance, optimization of separation conditions for GC analysis on monolithic columns and other important aspects of preparation and usage of monolithic capillary columns in GC. A final part of the review discusses the modern trends and possible applications in the future of capillary monolithic columns in GC.

Keywords: Monolith; Gas chromatography; High pressure; GC; ×; GC analysis, Capillary column

Potential of visible-near infrared spectroscopy combined with chemometrics for analysis of some constituents of coffee and banana residues by M.K.D. Rambo; E.P. Amorim; M.M.C. Ferreira (pp. 41-49).

•Cemometrics and NIR used for biomass characterization.•Characterization of second generation biomasses.•Lignin, moisture and extractive contents in coffee husks and leaves.•Lignin, moisture and extractive contents in banana stalk, steam and leaves.Banana (stalk, leaf, rhizome, rachis and stem) and coffee (leaf and husks) residues are promising feedstock for fuel and chemical production. In this work we show the potential of near-infrared spectroscopy (NIR) and multivariate analysis to replace reference methods in the characterization of some constituents of coffee and banana residues. The evaluated parameters were Klason lignin (KL), acid soluble lignin (ASL), total lignin (TL), extractives, moisture, ash and acid insoluble residue (AIR) contents of 104 banana residues (B) and102 coffee (C) residues from Brazil. PLS models were built for banana (B), coffee (C) and pooled samples (B+C). The precision of NIR methodology was better ( p<0.05) than the reference method for almost all the parameters, being worse for moisture. With the exception of ash (B and C) and ASL (C) content, which was predicted poorly ( R²<0.80), the models for all the analytes exhibited R²>0.80. The range error ratios varied from 4.5 to 16.0. Based on the results of external validation, the statistical tests and figures of merit, NIR spectroscopy proved to be useful for chemical prediction of banana and coffee residues and can be used as a faster and more economical alternative to the standard methodologies.

Keywords: Chemical composition; Lignin; Extractives; Moisture; Multivariate calibration; Figures of merit

Simultaneous derivatization and air-assisted liquid–liquid microextraction of some aliphatic amines in different aqueous samples followed by gas chromatography-flame ionization detection by Mir Ali Farajzadeh; Nina Nouri (pp. 50-57).

Display Omitted•Simultaneous derivatization/AALLME was proposed for extraction of aliphatic amines.•The new method avoided using disperser solvent.•This method was easy to use and derivatization and extraction were performed simultaneously.•The method was applied to determine some aliphatic amines in water samples.•Additional peaks resulting hydrolysis of derivatization agent were observed.The paper presents a new method based on simultaneous derivatization and air-assisted liquid–liquid microextraction (AALLME) for the extraction and preconcentration of some aliphatic amines prior to gas chromatography-flame ionization detection (GC-FID). Primary aliphatic amines are derivatized and extracted simultaneously by a fast reaction with butylchloroformate (derivatization agent/extraction solvent) under mild conditions. The mixture of butylchloroformate and aqueous sample solution is rapidly sucked into a 10-mL glass syringe and then is injected into a test tube with conical bottom and the procedure is repeated seven times. After centrifuging the resulted cloudy solution, the derivatized analytes in the sedimented phase are determined by GC-FID. The influence of main factors on the efficiency of derivatization/extraction procedure is studied. Under the optimal conditions, the enrichment factors (EFs) for aliphatic amines are obtained in the range of 248–360 and limits of detection (LODs) are between 0.30 and 2.6μgL⁻¹. The obtained extraction recoveries ranged from 50 to 72% and the relative standard deviation (RSD) was less than 4.8% for intra-day ( n=6) and inter-days ( n=4) precision. The method is successfully applied to determine some aliphatic amines in environmental water samples.

Keywords: Abbreviations; AALLME; Air-assisted liquid–liquid microextraction; CE; Capillary electrophoresis; C; _sed; Concentration in sedimented phase; DLLME; Dispersive liquid–liquid microextraction; EF; Enrichment factor; FID; Flame ionization detection; GC; Gas chromatography; HPLC; High performance liquid chromatography; LLE; Liquid–liquid extraction; LPME; Liquid phase microextration; LOQ; Limit of quantification; LOD; Limit of detection; LR; Linear range; MS; Mass spectrometry; n; ₀; The total analyte amount; n; _sed; The amount of analyte wich is extracted into the sedimented phase; RSD; Relative starndard deviation; SPE; Solid phase extraction; SDME; Single drop microextration; SPME; Solid phase microextration; TIC; Total ion chromatogram; USAEME; Ultrasound-assisted emulsification microextraction; VALLME; Vortex-assisted liquid–liquid microextraction; V; _sed; Volume of sedimented phase; V; _aq; Volume of aqueous solutionAir-assisted liquid–liquid microextraction; Derivatization; Primary aliphatic amines; Gas chromatography

Highly sensitive and selective organophosphate screening in twelve commodities of fruits, vegetables and herbal medicines by dispersive liquid–liquid microextraction by Yee-Man Ho; Yeuk-Ki Tsoi; Kelvin Sze-Yin Leung (pp. 58-66).

Display Omitted•A rapid, high throughput single DLLME analysis for 10 organophosphorus pesticides in foods or herbs.•Optimization dealt with unique chemistry in 3 sample types: fruit, vegetable, dried herb.•Rapid, micro-scale sample clean-up completes <9min using about 1mL solvent.•100-fold enrichment achieved sub-ppt LOD for trace residues based on 0.1g sample.•High throughput method effectively deals with a wide array of routine samples.The article describes a simple sample pretreatment procedure for the analysis of ten organophosphorus pesticides using dispersive liquid–liquid microextraction (DLLME) followed by gas chromatography–mass spectrometry (GC–MS) in three distinctively different types of matrices: fresh fruits, fresh vegetables and dried herbs. The method was carefully developed, focusing on the chemistry of various dispersive solvents, to achieve simultaneous, comprehensive extraction and preconcentration in a great span of selected matrices. According to matrix-matched validation study, the set of optimized DLLME conditions has been proven robust to determine target OPPs within a wide linear range from 0.1 to 1000μgL⁻¹. With limited usage of organic extractants, remarkable enrichment factors up to 100-fold were obtained, enabling ultra-trace pesticide quantification down to sub-ppt levels at 0.12–4.92ngkg⁻¹. Practical application of the method was illustrated by quantitative recovery (70–119%) and good precision (2.6–10% R.S.D.) in a representative range of three fruits and four vegetable commodities featured by the CODEX Alimentarius classification as well as their unique matrix compositions. A careful selection of dried herbs was further classified based on their morphological structures to validate analytical ruggedness of the method. Compared with existing methods for food analysis vis-à-vis OPPs, the present method is superior in terms of high sample throughput, minimal solvent consumption, and small sample size requirement. An additional, significant aspect of this universal DLLME method is that it models sample pretreatment methods with wide coverage of analytical matrices that are more effective, more comprehensive, and more flexible than those currently being used.

Keywords: Organophosphorus pesticides; Dispersive liquid–liquid microextraction; Preconcentration; Fruits; Vegetables; Herbs

Automated thermochemolysis reactor for detection of Bacillus anthracis endospores by gas chromatography–mass spectrometry by Dan Li; Anthony D. Rands; Scott C. Losee; Brian C. Holt; John R. Williams; Stephen A. Lammert; Richard A. Robison; H. Dennis Tolley; Milton L. Lee (pp. 67-74).

•An automated sample preparation system for Bacillus anthracis endospores was developed. •A thermochemolysis method was applied to produce and derivatize biomarkers for Bacillus anthracis detection. •The autoreactor controlled the precise delivery of reagents, and TCM reaction times and temperatures. •Solid phase microextraction was used to extract biomarkers, and GC–MS was used for final identification.•This autoreactor was successfully applied to the identification of Bacillus anthracis endospores.An automated sample preparation system was developed and tested for the rapid detection of Bacillus anthracis endospores by gas chromatography–mass spectrometry (GC–MS) for eventual use in the field. This reactor is capable of automatically processing suspected bio-threat agents to release and derivatize unique chemical biomarkers by thermochemolysis (TCM). The system automatically controls the movement of sample vials from one position to another, crimping of septum caps onto the vials, precise delivery of reagents, and TCM reaction times and temperatures. The specific operations of introduction of sample vials, solid phase microextraction (SPME) sampling, injection into the GC–MS system, and ejection of used vials from the system were performed manually in this study, although they can be integrated into the automated system. Manual SPME sampling is performed by following visual and audible signal prompts for inserting the fiber into and retracting it from the sampling port. A rotating carousel design allows for simultaneous sample collection, reaction, biomarker extraction and analysis of sequential samples. Dipicolinic acid methyl ester (DPAME), 3-methyl-2-butenoic acid methyl ester (a fragment of anthrose) and two methylated sugars were used to compare the performance of the autoreactor with manual TCM. Statistical algorithms were used to construct reliable bacterial endospore signatures, and 24 out of 25 (96%) endospore-forming Bacillus species were correctly identified in a statistically designed test.

Keywords: Thermochemolysis; Automated reactor; Bacillus anthracis; endospores; GC–MS

Functionalized diamond nanopowder for phosphopeptides enrichment from complex biological fluids by Dilshad Hussain; Muhammad Najam-ul-Haq; Fahmida Jabeen; Muhammad N. Ashiq; Muhammad Athar; Matthias Rainer; Christian W. Huck; Guenther K. Bonn (pp. 75-84).

•Derivatization of diamond nanopowder as IMAC and RP.•Characterization with SEM, EDX and FT-IR.•Phosphopeptide enrichment from standard as well as real samples.•Desalting and human serum profiling with reproducible results.•MALDI-MS analysis with database identification.Diamond is known for its high affinity and biocompatibility towards biomolecules and is used exclusively in separation sciences and life science research. In present study, diamond nanopowder is derivatized as Immobilized Metal Ion Affinity Chromatographic (IMAC) material for the phosphopeptides enrichment and as Reversed Phase (C-18) media for the desalting of complex mixtures and human serum profiling through MALDI-TOF-MS. Functionalized diamond nanopowder is characterized by Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) spectroscopy. Diamond-IMAC is applied to the standard protein (β-casein), spiked human serum, egg yolk and non-fat milk for the phosphopeptides enrichment. Results show the selectivity of synthesized IMAC-diamond immobilized with Fe³⁺ and La³⁺ ions. To comprehend the elaborated use, diamond-IMAC is also applied to the serum samples from gall bladder carcinoma for the potential biomarkers. Database search is carried out by the Mascot program (www.matrixscience.com) for the assignment of phosphorylation sites. Diamond nanopowder is thus a separation media with multifunctional use and can be applied to cancer protein profiling for the diagnosis and biomarker identification.

Keywords: Diamond nanopowder; Immobilized metal ion affinity chromatography; Reversed phase; Phosphopeptide enrichment; Desalting; Serum profiling

Ultrasensitive electrochemical immunoassay for carcinoembryonic antigen based on three-dimensional macroporous gold nanoparticles/graphene composite platform and multienzyme functionalized nanoporous silver label by Guoqiang Sun; Juanjuan Lu; Shenguang Ge; Xianrang Song; Jinghua Yu; Mei Yan; Jiadong Huang (pp. 85-92).

Three-dimensional macroporous AuNPs/graphene complex (3D-AuNPs/GN) and functionalized NPS were prepared to immobilize Ab₁ and Ab₂ respectively and combined to fabricate a sandwich-type ultrasensitive electro-chemical immunosensor for detecting CEA.•Ultrasensitive electrochemical immunoassay for detecting CEA was developed.•3D-AuNPs/GN was employed as the carrier of primary antibodies.•Multienzyme functionalized nanoporous silver was used as signal enhancer.Three-dimensional macroporous gold nanoparticles/graphene composites (3D-AuNPs/GN) were synthesized through a simple two-step process, and were used to modify working electrode sensing platform, based on which a facile electrochemical immunoassay for sensitive detection of carcinoembryonic antigen (CEA) in human serum was developed. In the proposed 3D-AuNPs/GN, AuNPs were distributed not just on the surface, but also on the inside of graphene. And this distribution property increased the area of sensing surface, resulting in capturing more primary antibodies as well as improving the electronic transmission rate. In the presence of CEA, a sandwich-type immune composite was formed on the sensing platform, and the horseradish peroxidase-labeled anti-CEA antibody (HRP-Ab₂)/thionine/nanoporous silver (HRP-Ab₂/TH/NPS) signal label was captured. Under optimal conditions, the electrochemical immunosensor exhibited excellent analytical performance: the detection range of CEA is from 0.001 to 10ngmL⁻¹ with low detection limit of 0.35pgmL⁻¹ and low limit of quantitation (LOQ) of 0.85pgmL⁻¹. The electrochemical immunosensor showed good precision, acceptable stability and reproducibility, and could be used for the detection of CEA in real samples. The proposed method provides a promising platform of clinical immunoassay for other biomolecules

Keywords: Three-dimensional gold nanoparticles/graphene composite; Nanoporous silver; Carcinoembryonic antigen; Electrochemical immunosensor

BODIPY-based fluorometric sensor array for the highly sensitive identification of heavy-metal ions by Li-Ya Niu; Hui Li; Liang Feng; Ying-Shi Guan; Yu-Zhe Chen; Chun-Feng Duan; Li-Zhu Wu; Ya-Feng Guan; Chen-Ho Tung; Qing-Zheng Yang (pp. 93-99).

A BODIPY-based fluorometric sensor array has been developed for the highly sensitive detection of eight heavy metal ions at micromolar concentration. 12 cross-reactive BODIPY fluorescent indicators provide facile identification of the heavy metal ions using a standard chemometric approach (hierarchical clustering analysis); no misclassifications were found over 45 trials. Clear differentiation among heavy metal ions as a function of concentration was also achieved, even down to 10⁻⁷M.•Indicators based on BODIPY and di-2-picolyamine derivatives were designed.•12 cross-reactive BODIPY indicators provide facile identification of the heavy metal ions.•The collected images were digitized for the semi-quantitative discriminations.•Array technologies and pattern-recognition were combined.A BODIPY(4,4-difluoro-4-bora-3a,4a-diaza-s-indacene)-based fluorometric sensor array has been developed for the highly sensitive detection of eight heavy-metal ions at micromolar concentration. The di-2-picolyamine (DPA) derivatives combine high affinities for a variety of heavy-metal ions with the capacity to perturb the fluorescence properties of BODIPY, making them perfectly suitable for the design of fluorometric sensor arrays for heavy-metal ions. 12 cross-reactive BODIPY fluorescent indicators provide facile identification of the heavy-metal ions using a standard chemometric approach (hierarchical clustering analysis); no misclassifications were found over 45 trials. Clear differentiation among heavy-metal ions as a function of concentration was also achieved, even down to 10⁻⁷M. A semi-quantitative interpolation of the heavy-metal concentration is obtained by comparing the total Euclidean distance of the measurement with a set of known concentrations in the library.

Keywords: 4,4-Difluoro-4-bora-3a,4a-diaza-s-indacene; Multipyridyl ligand; Fluorescent indicator; Sensor array; Heavy-metal ions

A fluorescence ratiometric sensor for hypochlorite based on a novel dual-fluorophore response approach by Lingliang Long; Dongdong Zhang; Xiufen Li; Jinfang Zhang; Chi Zhang; Liping Zhou (pp. 100-105).

Display Omitted•A fluorescence ratiometric sensor for hypochlorite has been developed.•The sensor was designed based on novel dual-fluorophore response approach.•The sensor contains two fluorophores that responded simultaneously to hypochlorite at two separate optical windows.•Upon treatment with hypochlorite, fluorescence ratio ( I₅₇₈/ I₅₀₁) of the sensor displayed significant changes.•The sensor can also be applied in real samples.A fluorescence ratiometric sensor for OCl⁻ has been developed based on a novel dual fluorophore response approach. The sensor molecule contains a coumarin fluorophore and a rhodamine fluorophore, and the two fluorophores are directly linked to an OCl⁻ recognition group. The structure of the sensor was characterized by ESI-MS, NMR, and X-ray crystallographic analysis. Upon treatment with OCl⁻, both fluorophores in the sensor responded simultaneously at two separate optical windows, with large enhancement of the fluorescence ratio ( I₅₇₈/ I₅₀₁) from 0.01 to 39.55. The fluorescence ratios for the sensor showed a good linearity with the concentration of OCl⁻ in the range of 0.2–40μM and the detection limits is 0.024μM ( S N⁻¹=3). Investigation of reaction products indicated that the sensor reaction with OCl⁻ produced two new fluorescent molecules, which were responsible for the fluorescence changes in two optical windows. In addition, the sensor showed high selectivity to OCl⁻ over other reactive oxygen species, reactive nitrogen species, cations, and anions. The sensor has also been successfully applied to detection of OCl⁻ in natural water samples with satisfactory recovery.

Keywords: Fluorescent sensors; Fluorescence; Dyes/pigments; Ratiometric; Hypochlorite

A solvent extraction technique for the isotopic measurement of dissolved copper in seawater by Claire M. Thompson; Michael J. Ellwood; Martin Wille (pp. 106-113).

•A new sample preparation method for seawater copper isotopic analysis (δ⁶⁵Cu).•Solvent-extraction was used to pre-concentrate metals from seawater samples.•Anion-exchange was used to purify copper from the metal-rich extract.•δ⁶⁵Cu was measured in the north Tasman Sea.•Seawater δ⁶⁵Cu may be linked to marine biological activity.Stable copper (Cu) isotope geochemistry provides a new perspective for investigating and understanding Cu speciation and biogeochemical Cu cycling in seawater. In this work, sample preparation for isotopic analysis employed solvent-extraction with amino pyrollidine dithiocarbamate/diethyl dithiocarbamate (APDC/DDC), coupled with a nitric acid back-extraction, to concentrate Cu from seawater. This was followed by Cu-purification using anion-exchange. This straightforward technique is high yielding and fractionation free for Cu and allows precise measurement of the seawater Cu isotopic composition using multi-collector inductively coupled plasma mass-spectrometry. A deep-sea profile measured in the oligotrophic north Tasman Sea shows fractionation in the Cu isotopic signature in the photic zone but is relatively homogenised at depth. A minima in the Cu isotopic profile correlates with the chlorophyll a maximum at the site. These results indicate that a range of processes are likely to fractionate stable Cu isotopes in seawater.

Keywords: Copper; Isotope; Speciation; Solvent-extraction; MC ICP-MS; Seawater

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Analytica Chimica Acta (v.775, #)