Analytica Chimica Acta (v.653, #2)

The use of near infrared (NIR) hyperspectral imaging and hyperspectral image analysis for distinguishing between hard, intermediate and soft maize kernels from inbred lines was evaluated. NIR hyperspectral images of two sets (12 and 24 kernels) of whole maize kernels were acquired using a Spectral Dimensions MatrixNIR camera with a spectral range of 960–1662 nm and a sisuChema SWIR (short wave infrared) hyperspectral pushbroom imaging system with a spectral range of 1000–2498 nm. Exploratory principal component analysis (PCA) was used on absorbance images to remove background, bad pixels and shading. On the cleaned images, PCA could be used effectively to find histological classes including glassy (hard) and floury (soft) endosperm. PCA illustrated a distinct difference between glassy and floury endosperm along principal component (PC) three on the MatrixNIR and PC two on the sisuChema with two distinguishable clusters. Subsequently partial least squares discriminant analysis (PLS-DA) was applied to build a classification model. The PLS-DA model from the MatrixNIR image (12 kernels) resulted in root mean square error of prediction (RMSEP) value of 0.18. This was repeated on the MatrixNIR image of the 24 kernels which resulted in RMSEP of 0.18. The sisuChema image yielded RMSEP value of 0.29. The reproducible results obtained with the different data sets indicate that the method proposed in this paper has a real potential for future classification uses.
Keywords: Near infrared hyperspectral imaging; Hyperspectral image analysis; Maize hardness; Principal component analysis; Partial least squares discriminant analysis;

Improving the detection of significant factors using ANOVA-PCA by selective reduction of residual variability by R. Climaco-Pinto; A.S. Barros; N. Locquet; L. Schmidtke; D.N. Rutledge (131-142).
Selective elimination of residual error can be used when applying Harrington's ANOVA-PCA in order to improve the capabilities of the method. ANOVA-PCA is sometimes unable to discriminate between levels of a factor when sources of high residual variability are present. In some cases this variability is not random, possesses some structure and is large enough to be responsible for the first principal components calculated by the PCA step in the ANOVA-PCA. This fact sometimes makes it impossible for the interesting variance to be in the first two PCA components. By using the proposed selective residuals elimination procedure, one may improve the ability of the method to detect significant factors as well as have an understanding of the different kinds of residual variance present in the data.Two datasets are used to show how the method is used in order to iteratively detect variance associated with the factors even when it is not initially visible. A permutation method is used to confirm that the observed significance of the factors was not accidental.
Keywords: ANOVA-PCA; ASCA; Error removal; Discrimination;

Sparse component analysis (SCA) is demonstrated for blind extraction of three pure component spectra from only two measured mixed spectra in 13C and 1H nuclear magnetic resonance (NMR) spectroscopy. This appears to be the first time to report such results and that is the first novelty of the paper. Presented concept is general and directly applicable to experimental scenarios that possibly would require use of more than two mixtures. However, it is important to emphasize that number of required mixtures is always less than number of components present in these mixtures. The second novelty is formulation of blind NMR spectra decomposition exploiting sparseness of the pure components in the wavelet basis defined by either Morlet or Mexican hat wavelet. This enabled accurate estimation of the concentration matrix and number of pure components by means of data clustering algorithm and pure components spectra by means of linear programming with constraints from both 1H and 13C NMR experimental data. The third novelty is capability of proposed method to estimate number of pure components in demanding underdetermined blind source separation (uBSS) scenario. This is in contrast to majority of the BSS algorithms that assume this information to be known in advance. Presented results are important for the NMR spectroscopy-associated data analysis in pharmaceutical industry, medicine diagnostics and natural products research.
Keywords: Chemometrics; Nuclear magnetic resonance spectroscopy; Underdetermined blind source separation; Sparse component analysis; Wavelet transform;

A novel electrochemical methods namely standard free anodic stripping voltammetry and anodic stripping voltammetric titration are proposed for determination of dissolved sulfide concentration. 2Ag+  + S2−  → Ag2S reaction is used to provide the information. The anodic stripping voltammetric response of unreacted silver-ions at the glassy carbon electrode is used as analytical signal. Results reliability and accuracy are confirmed by analysis of model solutions, spiked natural and tap waters and recovery study, with a recovery of 100 ± 5% (n  = 7) obtained. The approaches show the detection limit (3σ blank) of 2–5 × 10−10  mol L−1 and the relative standard deviation of 2–5% for repeated measurements.
Keywords: Anodic stripping voltammetry; Anodic stripping voltammetric titration; Glassy carbon electrode; Sulfide; Water analysis;

Comparative studies of praseodymium(III) selective sensors based on newly synthesized Schiff's bases by Vinod K. Gupta; Rajendra N. Goyal; Manoj K. Pal; Ram A. Sharma (161-166).
Praseodymium ion selective polyvinyl chloride (PVC) membrane sensors, based on two new Schiff's bases 1,3-diphenylpropane-1,3-diylidenebis(azan-1-ylidene)diphenol (M 1 ) and N,N′-bis(pyridoxylideneiminato) ethylene (M 2 ) have been developed and studied. The sensor having membrane composition of PVC: o-NPOE: ionophore (M 1 ): NaTPB (w/w; mg) of 150: 300: 8: 5 showed best performances in comparison to M 2 based membranes. The sensor based on (M 1 ) exhibits the working concentration range 1.0 × 10−8 to 1.0 × 10−2  M with a detection limit of 5.0 × 10−9  M and a Nernstian slope 20.0 ± 0.3 mV decade−1 of activity. It exhibited a quick response time as <8 s and its potential responses were pH independent across the range of 3.5–8.5.The influence of the membrane composition and possible interfering ions have also been investigated on the response properties of the electrode. The sensor has been found to work satisfactorily in partially non-aqueous media up to 15% (v/v) content of methanol, ethanol or acetonitrile and could be used for a period of 3 months. The selectivity coefficients determined by using fixed interference method (FIM) indicate high selectivity for praseodymium(III) ions over wide variety of other cations. To asses its analytical applicability the prepared sensor was successfully applied for determination of praseodymium(III) in spiked water samples.
Keywords: Ion selective electrode; Praseodymium ion; Schiff base; Polyvinyl chloride membranes;

In this work, electrochemical immunoassay involving magnetic beads to determine zearalenone in selected food samples has been developed. The immunoassay scheme has been based on a direct competitive immunoassay method in which antibody-coated magnetic beads were employed as the immobilisation support and horseradish peroxidase (HRP) was used as enzymatic label. Amperometric detection has been achieved through the addition of hydrogen peroxide substrate and hydroquinone as mediator.Analytical performance of the electrochemical immunoassay has been evaluated by analysis of maize certified reference material (CRM) and selected baby food samples. A detection limit (LOD) of 0.011 μg L−1 and EC50 0.079 μg L−1 were obtained allowing the assessment of the detection of zearalenone mycotoxin. In addition, an excellent accuracy with a high recovery yield ranging between 95 and 108% has been obtained. The analytical features have shown the proposed electrochemical immunoassay to be a very powerful and timely screening tool for the food safety scene.
Keywords: Electrochemical immunoassay; Magnetic beads; Zearalenone; Food safety;

Ligandless-dispersive liquid–liquid microextraction of trace amount of copper ions by Sayed Zia Mohammadi; Daryoush Afzali; Yar Mohammad Baghelani (173-177).
In the present work, a new ligandless-dispersive liquid–liquid microextraction (LL-DLLME) method has been developed for preconcentration trace amounts of copper as a prior step to its determination by flame atomic absorption spectrometry. In the proposed approach 1,2-dicholorobenzene and ethanol were used as extraction and dispersive solvents, respectively. Some factors influencing on the extraction efficiency of copper and its subsequent determination were studied and optimized, such as the extraction and dispersive solvent type and volume, pH of sample solution, extraction time and salting out effect. Under the optimal conditions, the calibration curve was linear in the range of 1.0 ng mL−1–0.6 μg mL−1 of copper with R 2  = 0.9985. Detection limit was 0.5 ng mL−1 in original solution (3S b/m) and the relative standard deviation for seven replicate determination of 0.2 μg mL−1 copper was ±1.4%. The proposed method has been applied for determination of copper in standard and water samples with satisfactory results.
Keywords: Dispersive liquid–liquid microextraction; Copper determination; Preconcentration; Ligandless;

Extraction and mechanism investigation of trace roxithromycin in real water samples by use of ionic liquid–salt aqueous two-phase system by Chun-Xiang Li; Juan Han; Yun Wang; Yong-Sheng Yan; Xiao-Hui Xu; Jian-Ming Pan (178-183).
The ionic liquid, as a green solvent, has several advantages over the organic solvents in traditional liquid–liquid extraction. Aqueous two-phase system (ATPS) consisting of a hydrophilic ionic liquid (1-butyl-3-methylimidazolium tetrafluoraborate, [Bmim]BF4) and Na2CO3, which is a novel, simple, non-toxic and effective sample pretreatment technique coupled with molecular fluorescence spectrophotometry, was developed for the simultaneous separation, enrichment and rapid analysis of roxithromycin. The extraction yield of roxithromycin in [Bmim]BF4–Na2CO3 aqueous two-phase system is influenced by the types of salts, concentrations of Na2CO3 and [Bmim]BF4, as well as the extracting temperature. Under the optimum conditions, the average extraction efficiency is up to 90.7%. The mechanism of ionic liquid–salt ATPS formation was discussed by hydration theory, and the extraction mechanism of the [Bmim]BF4–salt ATPS was investigated by FT-IR spectroscopy and UV–vis spectroscopy. The results demonstrate that no chemical (bonding) interactions are observed between ionic liquid and roxithromycin, while the nature properties of the roxithromycin are not altered. This method was practical when applied to the analysis of roxithromycin in real water samples with the detection limit of 0.03 μg mL−1, relative standard deviation (RSD) of 1.9% (n  = 13), and linear ranges of 1.00–20.00 μg mL−1. The proposed extraction technique will be promising in the separation of other small biomolecules.
Keywords: [Bmim]BF4–salt aqueous two-phase system; Roxithromycin; Extraction; Real water samples;

HPLC determination of ibuprofen, diclofenac and salicylic acid using hollow fiber-based liquid phase microextraction (HF-LPME) by María Ramos Payán; Miguel Ángel Bello López; Rut Fernández-Torres; Juan Luis Pérez Bernal; Manuel Callejón Mochón (184-190).
This paper describes an extraction method using a polypropylene membrane supporting dihexyl ether (three-phase hollow fiber-based liquid phase microextraction (HF-LPME)) for the analysis of several pharmaceuticals (salicylic acid (SAC), ibuprofen (IBU) and diclofenac (DIC)) followed by a HPLC determination using a monolithic silica type HPLC column, that allows lower retention times than the usual packed columns with adequate resolution. Detection was realized by means of a coupled in series diode array (DAD) and fluorescence (FLD) detectors. HF-LPME is a relatively new technique employed in analytical chemistry for sample pretreatment which offers more selectivity and sensitivity than any traditional extraction technique. Detection limits by DAD are 12, 53 and 40 ng mL−1 for salicylic acid, diclofenac and ibuprofen, respectively and by FLD 7 and 2 ng mL−1 for salicylic acid, and ibuprofen. The method has been successfully applied to their direct determination in human urine and the results obtained demonstrated that could be also applied to the determination of the corresponding metabolites.
Keywords: Hollow fiber liquid phase microextraction; Salicylic acid; Diclofenac; Ibuprofen; Urine;

Comparison of digestion methods for ICP-MS determination of trace elements in fish tissues by Shailini Ashoka; Barrie M. Peake; Graeme Bremner; Kimberly J. Hageman; Malcolm R. Reid (191-199).
A comparison is presented of six methods involving nitric acid in conjunction with other reagents to digest three certified marine biological samples (DOLT-3, DORM-3, IAEA-407) and a fish bone homogenate (prepared from Merluccius australis). An inductively coupled plasma-mass spectrometer with an octopole collision cell was used to determine up to 40 elements (Li, B, Na, Mg, Al, K, Ca, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Rb, Sr, Y, Ag, Cd, Cs, Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, Lu, Pb, Th, U) in the digests. These results were assessed in terms of their accuracy and precision, and a flow chart was developed to aid the selection of the optimal digestion method. Although none of the methods was found to give accurate determinations for all elements in the different reference materials, a relatively simple method involving nitric acid and hydrogen peroxide heated in a domestic microwave oven gave the most acceptable results.
Keywords: Acid digestion; Microwave digestion; Certified reference materials; Inductively coupled plasma-mass spectrometry; Fish tissue;

Raman spectroscopy has been used for the quantitative determination of the conversion efficiency at each step in the production of ethanol from biomass. The method requires little sample preparation; therefore, it is suitable for screening large numbers of biomass samples and reaction conditions in a complex sample matrix. Dilute acid or ammonia-pretreated corn stover was used as a model biomass for these studies. Ammonia pretreatment was suitable for subsequent measurements with Raman spectroscopy, but dilute acid-pretreated corn stover generated a large background signal that surpassed the Raman signal. The background signal is attributed to lignin, which remains in the plant tissue after dilute acid pretreatment. A commercial enzyme mixture was used for the enzymatic hydrolysis of corn stover, and glucose levels were measured with a dispersive 785 nm Raman spectrometer. The glucose detection limit in hydrolysis liquor by Raman spectroscopy was 8 g L−1. The mean hydrolysis efficiency for three replicate measurements obtained with Raman spectroscopy (86 ± 4%) was compared to the result obtained using an enzymatic reaction with UV–vis spectrophotometry detection (78 ± 8%). The results indicate good accuracy, as determined using a Student's t-test, and better precision for the Raman spectroscopy measurement relative to the enzymatic detection assay. The detection of glucose in hydrolysis broth by Raman spectroscopy showed no spectral interference, provided the sample was filtered to remove insoluble cellulose prior to analysis. The hydrolysate was further subjected to fermentation to yield ethanol. The detection limit for ethanol in fermentation broth by Raman spectroscopy was found to be 6 g L−1. Comparison of the fermentation efficiencies measured by Raman spectroscopy (80 ± 10%) and gas chromatrography–mass spectrometry (87 ± 9%) were statistically the same. The work demonstrates the utility of Raman spectroscopy for screening the entire conversion process to generate lignocellulosic ethanol.
Keywords: Raman Spectroscopy; Biofuels/biomass; Glucose; Ethanol; Enzymatic hydrolysis; Fermentation;

A new resonance light scattering (RLS) spectrometric method for mercury ions (Hg2+) in aqueous solutions with sulfur ion (S2−) modified gold nanoparticles (Au-NPs-S) has been developed in this contribution. It was found that S2− at the surface of Au-NPs resulting from the surface modification can interact with Hg2+ to form very stable S–Hg–S bonds when Hg2+ concentration is lower than that of S2−, resulting in the aggregation of Au-NPs-S and causing enhanced RLS signals. The enhanced RLS intensities (ΔI RLS) characterized at 392 nm were found to be proportional to the concentration of Hg2+ in the range of 0.025–0.25 μmol L−1 with a detection limit (3σ) of 0.013 μmol L−1. Our results showed that this approach has excellent selectivity for Hg2+ over other substances in aqueous solutions.
Keywords: Gold nanoparticles; Sulfide; Mercury; Resonance light scattering spectrometry;

Zinc oxide–potassium ferricyanide composite thin film matrix for biosensing applications by Shibu Saha; Sunil K. Arya; S.P. Singh; K. Sreenivas; B.D. Malhotra; Vinay Gupta (212-216).
Thin film of zinc oxide–potassium ferricyanide (ZnO–KFCN) composite has been deposited on indium tin oxide (ITO) coated corning glass using pulsed laser deposition (PLD). The composite thin film electrode has been exploited for amperometric biosensing in a mediator-free electrolyte. The composite matrix has the advantages of high iso-electric point of ZnO along with enhanced electron communication due to the presence of a redox species in the matrix itself. Glucose oxidase (GOx) has been chosen as the model enzyme for studying the application of the developed matrix to biosensing. The sensing response of the bio-electrode, GOx/ZnO–KFCN/ITO/glass, towards glucose was studied using cylic voltammetry (CV) and photometric assay. The bio-electrode exhibits good linearity from 2.78 mM to 11.11 mM glucose concentration. The low value of Michaelis–Menten constant (1.69 mM) indicates an enhanced affinity of the immobilized enzyme towards its substrate. A quassireversible system is obtained with the composite matrix. The results confirm promising application of the ZnO–KFCN composite matrix for amperometric biosensing applications in a mediator-less electrolyte that could lead to the realization of an integrated lab-on-chip device.
Keywords: Biosensor; Pulsed laser deposition; Potassium ferricyanide; Zinc oxide; Composite matrix;

Chiral salen Mn(III) complex-based enantioselective potentiometric sensor for l-mandelic acid by Lan Xu; Yuanyuan Yang; Yaqiong Wang; Jiuzhi Gao (217-221).
A new enantioselective potentiometric sensor containing chiral salen Mn(III) as the chiral selector was designed for the assay of l-mandelic acid (l-MA). Optimized membrane electrodes displayed linear dynamic range from 1 × 10−5 to 1 × 10−1  mol L−1 with a detection limit of 7.2 × 10−6  mol L−1 and a Nernstian response of −58.1 ± 0.5 mV decade−1 towards l-MA within pH range 7.0–10.2. The potentiometric enantioselectivity coefficient ( log K L,D Pot ) of this sensor was −4.0, indicating that the chiral salen Mn(III) complex-based electrode exhibited fairly good discrimination toward l-MA over counter isomer d-MA. The mechanism of chiral recognition for l-MA is discussed by using HF/STO-3G calculation method simulation.
Keywords: Chiral salen Mn(III) complex; Enantioselective recognition; Potentiometric sensors; Poly(vinyl chloride) membranes; l-Mandelic acid;

Simultaneous evaluation of toxicities using a mammalian cell array chip prepared by photocatalytic lithography by Kikuo Komori; Jun Nada; Masaki Nishikawa; Hideo Notsu; Tetsu Tatsuma; Yasuyuki Sakai (222-227).
A prototype of a mammalian cell array chip was developed on a flat glass surface. A superhydrophilic (water contact angle = 5°)/highly hydrophobic (120°) pattern was prepared on a fluorinated polymer-coated glass surface by means of photocatalytic lithography, and A549 (a human alveolar epithelial cell line), Hep G2 (a human hepatoma cell line) and mouse fibroblast 3T3 cells were inoculated onto the superhydrophilic regions. The cell populations were confined in the superhydrophilic regions for at least 24 h and separated from each other for at least one week. Organ-specific toxicity of aflatoxin B1 and non-specific toxicity of adriamycin were successfully detected by using the cell array chip.
Keywords: Mammalian cell array chip; Photocatalytic lithography; Toxicity evaluation; Biosensing; Hydrophilic/hydrophobic patterning;

A fast separation of alkali and alkaline earth metal cations and ammonium was carried out by capillary electrochromatography on monolithic octadecylsilica columns of 15 cm length and 100 μm inner diameter using water/methanol mixtures containing acetic acid as mobile phase. On-column contactless conductivity detection was used for quantification of these non-UV-absorbing species. The method was also extended successfully to the determination of small amines as well as of amino acids, and the separation selectivity was optimized by varying the composition of the mobile phase. Detection limits of about 1 μM were possible for the inorganic cations as well as for the small amines, while the amino acids could be quantified down to about 10 μM. The separation of 12 amino acids was achieved in the relatively short time of 10 min.
Keywords: Capacitively coupled contactless conductivity detection; Capillary electrochromatography; Inorganic cations; Amines; Amino acids;

Eight reversed-phase columns intended for rapid HPLC were assessed for the separation of thirteen microcystins and nodularins, cyclic peptidic hepatotoxins. The instrumentation consisted of an Agilent Technologies 1200 Rapid Resolution high performance liquid chromatography system coupled to a mass spectrometer, Bruker Daltonics Ultra Performance High Capacity Ion Trap MS (HCT Ultra) with electrospray ionisation (RRLC-ESI-IT-MS). The columns tested were 2–2.1 mm × 50 mm in diameter and length, and contained small particles (1.8–2.7 μm), or monolithic silica supports for fast performance. The shortest total run time achieved was 3 min 15 s including equilibration and injection. Critical microcystin pairs were still resolved. Several columns showed excellent performance.
Keywords: Ultra-high performance liquid chromatography systems; Liquid chromatography – mass spectrometry; Microcystins; Nodularins; Cyclic peptides; Toxins;