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Analytica Chimica Acta (v.687, #2)

Editorial Board (pp. i).

Fabrication of nanostructured silicon by metal-assisted etching and its effects on matrix-free laser desorption/ionization mass spectrometry by W.Y. Chen; J.T. Huang; Y.C. Cheng; C.C. Chien; C.W. Tsao (pp. 97-104).

A matrix-free, high sensitivity, nanostructured silicon surface assisted laser desorption/ionization mass spectrometry (LDI-MS) method fabricated by metal-assisted etching was investigated. Effects of key process parameters, such as etching time, substrate resistance and etchant composition, on the nanostructured silicon formation and its LDI-MS efficiency were studied. The results show that the nanostructured silicon pore depth and size increase with etching time, while MS ion intensity increases with etching time to 300s then decreases until 600s for both low resistance (0.001–0.02Ωcm) and high resistance (1–100Ωcm) silicon substrates. The nanostructured silicon surface morphologies were found to directly affect the LDI-MS signal ion intensity. By characterizing the nanostructured silicon surface roughness using atomic force microscopy (AFM) and sample absorption efficiency using fluorescence microscopy, it was further demonstrated that the nanostructured silicon surface roughness was highly correlated to the LDI-MS performance.

Keywords: Abbreviations; LDI; laser desorption/ionization; MS; mass spectrometry; ESI; electrospray ionization; MALDI; matrix-assisted laser desorption/ionization; DIOS; desorption/ionization on silicon; D/I; desorption/ionization; FE-SEM; field emission scanning electron microscope; AFM; atomic force microscopeMass spectrometry; Nanostructured silicon; Metal-assisted etching; Matrix-free laser desorption/ionization; Desorption/ionization on silicon

Chemiresistors based on conducting polymers: A review on measurement techniques by Ulrich Lange; Vladimir M. Mirsky (pp. 105-113).

This review covers the development of measurement configurations for chemiresistors based on conducting polymers. The simplest chemiresistors are based on application of a two-electrode technique. Artifacts caused by contact resistance can be overcome by application of a four-electrode technique. Simultaneous application of the two- and four-electrode measurement configurations provides an internal control of sensor integrity. An incorporation of two additional electrodes controlling the redox state of chemosensitive polymers and connecting to the measurement electrodes through liquid or (quasi)solid electrolyte results in a six-electrode technique; an electrically driven regeneration of such sensors allows one to perform fast and completely reversible measurements.

Keywords: Chemiresistor; Chemotransistor; Conducting polymer; Chemosensor; Contact resistance; s24-Technique

A review of monolithic multichannel quartz crystal microbalance: A review by Adisorn Tuantranont; Anurat Wisitsora-at; Pornpimol Sritongkham; Kata Jaruwongrungsee (pp. 114-128).

Monolithic multichannel quartz crystal microbalance (MQCM) is an emerging technology for advanced sensing and measurement applications. In this report, a comprehensive review of MQCM technology is presented. Firstly, basic MQCM's design, simulation and characterization with emphasis on acoustic interference are described. Next, various MQCM schemes to minimize interference and enhance sensitivity of conventional MQCM devices based on modification of quartz substrate structure are digested. These include mesa, convex and x-axis inversion structures. Three important MQCM sensing platforms and their application areas are then discussed. These comprise MQCM as a static multichannel detector, series MQCM as a multichannel detector for the flow injection analysis and multi-frequency QCM for multi-sensitivity/multi-dynamic range detection. Finally, potential MQCM applications including electronic noses, bio-sensor arrays, and photocatatalytic measurement are illustrated and prospective MQCM applications including electronic tongues and electrochemical measurement are suggested.

Keywords: Monolithic multichannel quartz crystal microbalance; QCM array; Sensor array

Improving the visualization of the Pareto-optimal front for the multi-response optimization of chromatographic determinations by M.C. Ortiz; L.A. Sarabia; M.S. Sánchez; D. Arroyo (pp. 129-136).

The paper shows tools to visualize and more easily interpret the effect that some experimental factors may exert on analytical responses of interest when optimization of several responses is needed.It is based on an adaptation of the parallel coordinate plot, a tool for graphical representation of points in multidimensional spaces that, theoretically and contrary to the usual Cartesian plots, does not have limits in the dimension of the points being depicted.The joint use of the Pareto-optimal solutions and their visualization allows a deeper knowledge about the problem at hand as well as the wise selection of the conditions of experimental factors for achieving specific goals about the responses.Although the methodology is for a general use, the procedure, its interpretation and usefulness is shown with several analytical cases in chromatography. The first one refers to the experimental conditions to obtain simultaneously the maximum allowable area for both the peak of the malachite green and its metabolite leucomalachite green in fish by liquid chromatography with tandem mass spectrometry detection (LC–MS/MS). The second one is about the simultaneous determination of steroid hormones estrone and 17-α-ethinylestradiol by gas chromatography–mass spectrometry (GC/MS). In the last case, the chromatographic separation by GC/MS of the diastereoisomers, α- and β-estradiol is needed taking into account that these hormones have the same mass fragments.

Keywords: Chromatography; Pareto-optimal front; Multiresponse optimization; Parallel coordinate plot; Hormones; Fungicides

Electrochemical determination of iodide by poly(3-aminophenylboronic acid) film electrode at moderately low pH ranges by Hakan Çiftçi; Uğur Tamer (pp. 137-140).

A new potentiometric sensor for the determination of iodide based on poly(3-aminophenylboronic acid) (PAPBA) film electrode was constructed. Poly(3-Aminophenylboronic acid) films were synthesized electrochemically on platinum electrode by cyclic voltammetry. The effect of film thickness, pH, and preconditioning parameters on the electrode performance were examined. The analytical performance was evaluated and linear calibration graphs were obtained in the concentration range of 10⁻⁶ to 10⁻¹M iodide ion. The limit of detection was found to be 8×10⁻⁷M. The response time of the sensor was 5s and its lifetime is about one week. To check the selectivity of the PAPBA film for iodide ion, potential interferences such as Cl⁻, Br⁻, F⁻, CN⁻, IO₃⁻, Ca²⁺, and Mg²⁺ were tested. The PAPBA electrode was also employed as a sensing platform for the determination of iodide ions in commercial table salt.

Keywords: Poly(3-Aminophenylboronic acid); Iodide-selective electrode; Open circuit potential; Conducting polymer electrode

Role of counteranions in polymeric ionic liquid-based solid-phase microextraction coatings for the selective extraction of polar compounds by Yunjing Meng; Verónica Pino; Jared L. Anderson (pp. 141-149).

A polymeric ionic liquid (PIL) poly(1-vinyl-3-hexylimidazolium chloride) (poly(ViHIm⁺Cl⁻)) was designed as a coating material for solid phase microextraction (SPME) to extract polar compounds including volatile fatty acids (VFAs) and alcohols. The extracted analytes were analyzed by using gas chromatography (GC) coupled with flame ionization detection (FID). Extraction parameters of the HS–SPME–GC–FID method, such as ionic strength, extraction temperature, pH and extraction time were optimized. Calibration studies were carried out under the optimized conditions to further evaluate the performance of the PIL-based SPME coating. For comparison purposes, the PIL poly(1-vinyl-3-hexylimidazolium bis[(trifluoromethyl)sulfonyl]imide) (poly(ViHIm⁺NTf₂⁻)) was also used as the SPME coating to extract the same analytes. The results showed that the poly(ViHIm⁺Cl⁻) PIL coating had higher selectivity towards more polar analytes due to the presence of the Cl⁻ anion which provides higher hydrogen bond basicity than the NTf₂⁻ anion. The limits of detection (LODs) determined by the designed poly(ViHIm⁺Cl⁻) PIL coating ranged from 0.02μgL⁻¹ for octanoic acid and decanoic acid and 7.5μgL⁻¹ for 2-nitrophenol, with precision values (as relative standard deviation) lower than 14%. The observed performance of the poly(ViHIm⁺Cl⁻) PIL coating was comparable to previously reported work in which commercial or novel materials were used as SPME coatings. The selectivity of the developed PIL coatings was also evaluated using heptane as the matrix solvent. This work demonstrates that the selectivity of PIL-based SPME coatings can be simply tuned by incorporating different counteranions to the sorbent coating.

Keywords: Ionic liquids; Polymeric ionic liquids; Solid-phase microextraction; Volatile compounds; Gas chromatography

A modular microfluidic system for deoxyribonucleic acid identification by short tandem repeat analysis by Carmen R. Reedy; Kristin A. Hagan; Daniel J. Marchiarullo; Alison H. Dewald; Annalise Barron; Joan M. Bienvenue; James P. Landers (pp. 150-158).

Microfluidic technology has been utilized in the development of a modular system for DNA identification through STR (short tandem repeat) analysis, reducing the total analysis time from the ∼6h required with conventional approaches to less than 3h. Results demonstrate the utilization of microfluidic devices for the purification, amplification, separation and detection of 9 loci associated with a commercially-available miniSTR amplification kit commonly used in the forensic community. First, DNA from buccal swabs purified in a microdevice was proven amplifiable for the 9 miniSTR loci via infrared (IR)-mediated PCR (polymerase chain reaction) on a microdevice. Microchip electrophoresis (ME) was then demonstrated as an effective method for the separation and detection of the chip-purified and chip-amplified DNA with results equivalent to those obtained using conventional separation methods on an ABI 310 Genetic Analyzer. The 3-chip system presented here demonstrates development of a modular, microfluidic system for STR analysis, allowing for user-discretion as to how to proceed after each process during the analysis of forensic casework samples.

Keywords: Microfluidics; Short tandem repeat analysis; Deoxyribonucleic acid identification; Forensics

Determination of the nucleosides and nucleobases in Tuber samples by dispersive solid-phase extraction combined with liquid chromatography–mass spectrometry by Ping Liu; Yuan-Yuan Li; Hong-Mei Li; Duan-Ji Wan; Ya-Jie Tang (pp. 159-167).

A simple, fast and inexpensive method based on dispersive solid phase extraction (DSPE) combined with LC–MS was developed for simultaneous determination of 7 nucleosides and nucleobases (i.e., adenine, hypoxanthine, uridine, adenosine, guanine, guanosine, and inosine) in Tuber fruiting-bodies and fermentation mycelia. The DSPE procedure was firstly introduced to remove the protein interference from sample solutions, and D3520 macroporous resin was chosen as the DSPE sorbent because of its high removal capability on protein interferences, but low adsorption rate on analytes. Besides, key parameters on DSPE procedure (i.e., macroporous resin type, macroporous resin amount, methanol concentration, and vortex time) were optimized, and the protein removal efficacy could achieve about 95% after the process optimization. Though the method validation test, the DSPE-LC–MS method was confirmed to be precise, accurate and sensitive, and the column blinding problem was solved successfully. By using this established method, the total amount of nucleosides and nucleobases in the fermentation mycelia was determined to range from 4881.5 to 12,592.9μgg⁻¹, which was about 2–25 times higher than the fruiting-bodies (from 498.1 to 2274.1μgg⁻¹). The formulation of nucleosides and nucleobases in the fermentation mycelia maintained relatively constant, while the formulation in Tuber fruiting-bodies varied significantly with their species. Hierarchical cluster analysis (HCA) showed the formulation similarity of nucleosides and nucleobases between Tuber fermentation mycelia and the fruiting-bodies of Tuber indicum and Tuber himalayense. From the viewpoint of nucleosides and nucleobases, this work confirms the potentiality of Tuber fermentation mycelia as the alternative resource for its fruiting-bodies.

Keywords: Truffle; Nucleosides; Nucleobases; Protein removal; Dispersive solid-phase extraction; Liquid chromatography–mass spectrometry (LC–MS)

Performance evaluation of fast Fourier-transform continuous cyclic-voltammetry pesticide biosensor by Bahman Ebrahimi; Seyed Abbas Shojaosadati; Parandis Daneshgar; Parviz Norouzi; Seyyed Mohammad Mousavi (pp. 168-176).

In this work, a method for the fast monitoring of OPs in flow-injection systems was evaluated. The fast Fourier transform continuous cyclic-voltammetry (FFTCCV) at the carbon-paste electrode in a flowing solution system was used for determination of OPs. In this method the S/N ratio is enhanced by using of fast Fourier transform of the analyte and signal integration. FFTCCV can be considered as a new sensitive, accurate and fast method for determination of drugs and some pesticides. However, in order to obtain better sensitivity for a specific target, experimental parameters should be optimized. Response surface methodology (RSM) was applied to optimize three effective parameters (enzyme activity, multiwall carbon nanotube quantity and acidic sol–gel quantity). The optimum values for the tested parameters were enzyme amount H0.169Ucm⁻², multiwall carbon nanotube (MWCNT) 0.607mL and acidic sol–gel 1.012mL. The optimum feed pH, feed flow rate, ATChCl concentration and sweeping-rate were found to be 7.4, 0.34mLmin⁻¹, 0.750mM and 10Vs⁻¹, respectively. The long-term stability of this flow-through system was 80% of its initial response after 120 days. Based on an incubation time of 12min, it was found that the detection limit for paraoxon was equal to 1.7×10⁻⁷mgL⁻¹ (6.2×10⁻¹³M). The developed biosensor exhibited good repeatability and reproducibility. This study provides a new, modern, sensitive tool for the analysis of organophosphate pesticides.

Keywords: Continuous cyclic voltammetry; Fast Fourier transform; Flow-through system; Acetylcholinesterase; Multiwall carbon nanotube; Optimization

Development of glucose amperometric biosensor based on a novel attractive enzyme immobilization matrix: Amino derivative of thiacalix[4]arene by Ming Chen; Wang Zhang; Ruimiao Jiang; Guowang Diao (pp. 177-183).

Calixarenes and their derivatives may be a promising material for enzyme immobilization owing to their particular configuration, unique molecule recognition function and aggregation properties. In this paper, p-tert-butylthiacalix[4]arene tetra-amine (TC4TA) was first used as enzyme immobilization material. This attractive material was exploited for the mild immobilization of glucose oxidase (GOD) to develop glucose amperometric biosensor. GOD was strongly adsorbed on the TC4TA modified electrode to form TC4TA/GOD composite membrane. The adsorption mechanism was driven from the covalent bond between amino-group of TC4TA and carboxyl group of GOD and molecule recognition function of TC4TA. Amperometric detection of glucose was evaluated by holding the modified electrode at 0.60V (versus SCE) to oxidize the hydrogen peroxide generated by the enzymatic reaction. The sensor (TC4TA/GOD) showed a relative fast response (response time was about 5s), low detection limit (20μM, S/N=3), and high sensitivity (ca. 10.2mAM⁻¹cm⁻²) with a linear range of 0.08–10mM of glucose, as well as a good operational and storage stability. In addition, optimization of the biosensor construction, the effects of the applied potential as well as common interfering compounds on the amperometric response of the sensor were investigated and discussed herein.

Keywords: p-Tert-butylthiacalix[4]arene tetra-amine; Glucose oxidase; Biosensor; Immobilization materials; Composite membrane

Development of a rubber elongation factor, surface-imprinted polymer–quartz crystal microbalance sensor, for quantitative determination of Hev b1 rubber latex allergens present in natural rubber latex products by Chonlatid Sontimuang; Roongnapa Suedee; Bhutorn Canyuk; Narubodee Phadoongsombut; Franz L. Dickert (pp. 184-192).

Molecularly imprinted polymers (MIPs) for screening to detect rubber latex allergens (Hev b1) in natural rubber based products were designed as artificial recognition polymeric materials coated onto a quartz crystal microbalance (QCM). The polymers were prepared using a stamp imprinting procedure after mixing optimum amounts of methacrylic acid–vinylpyrrolidone–dihydroxyethylene bisacrylamide and Hev b1 latex allergen proteins, obtained from rubber gloves. QCM measurements showed that the resulting polymer layers after removal of the proteins used in their preparation could incorporate structures and features down to nanometer scale of protein templates into the imprinted polymer much better than a non-specific control polymer under controlled sensor conditions and an optimized polymerization process. This selective polymer but not the non-selective polymer clearly distinguished between the latex allergen Hev b1 and proteins such as lysozyme, ovalbumin and bovine serum albumin, with a selectivity factor of from 2 to 4, and the response of the rubber elongation factors by an astonishing factor of 12. The imprinted cavities recognized specific binding sites and could distinguish among related hevein latex allergenic proteins isolated from fresh natural rubber latex; Hev b1, Hev b2, and Hev b3 with a selectivity factor of from 4 to 6. The different QCM measurements obtained presumably reflected slightly different conformations and affinities to the MIP binding sites. The sensor layers selectively adsorbed Hev b1 within minutes in amounts ranging from 10 to 1500μgL⁻¹ and with a detection limit of 1μgL⁻¹. This work has demonstrated that this new sensor provides a fast and reliable response to natural rubber latex protein, even after being extracted from the matrix of rubber gloves.

Keywords: Molecularly imprinted polymers; Surface imprinting; Quartz crystal microbalance; Biosensor; Latex allergy

Chitosan- g-poly(acrylic acid) hydrogel with crosslinked polymeric networks for Ni²⁺ recovery by Yian Zheng; Dajian Huang; Aiqin Wang (pp. 193-200).

In this study, chitosan- g-poly(acrylic acid) (CTS- g-PAA) hydrogel with crosslinked polymeric networks was prepared from an aqueous dispersion polymerization and then used as the adsorbent to recover a valuable metal, Ni²⁺. The adsorption capacity of CTS- g-PAA for Ni²⁺ was evaluated and the adsorption kinetics was investigated using Voigt-based model and pseudo-second-order model. In addition, the effects of pH values and coexisting heavy metal ions such as Cu²⁺ and Pb²⁺ on the adsorption capacity were studied. The results indicate that the as-prepared adsorbent has faster adsorption rate and higher adsorption capacity for Ni²⁺ recovery, with the maximum adsorption capacity of 161.80mgg⁻¹. In a wide pH range of 3–7, the adsorption capacity keeps almost the same, and even under competitive conditions, the adsorption capacity of CTS- g-PAA for Ni²⁺ is observed to be as high as 54.47mgg⁻¹. Finally, the adsorption performance of CTS- g-PAA for Ni²⁺ in real water sample and the reusability of the as-prepared adsorbent were evaluated, and also the controlled adsorption mechanism was proposed.

Keywords: Hydrogel; Adsorption; Nickel; Recovery; Mechanism

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Analytica Chimica Acta (v.687, #2)