Analytica Chimica Acta (v.603, #2)

Contents (iii).

This is a comparison of the latest developments in the emerging field of surface acoustic wave (SAW) sensors. Progress has been made particularly with regard to (sub-) microstructure technology and material sciences. Improvements are displayed based on the impact on a new generation of SAW sensors working efficiently in liquid media, from modeling to the fabrication steps of the individual components. It is explained, which obstacles have to be overcome for applications to the bioanalytical field. SAW sensors are shown to be extremely useful for the analysis of both small and large molecules as well as whole cells interacting with an immobilized binding partner. The output signal gives information about the pure mass loading, intrinsic properties of bound materials, or viscoelastic effects like structural rearrangements. Different setups are shown that minimize the influence of physical bulk effects on the sensor signal, e.g. salt content and viscosity. The choice of materials which can be used for sensible surfaces are presented, enabling the development of completely new coupling chemistries. Finally, the advantages compared to other biosensor technologies are pointed out.
Keywords: Surface acoustic wave sensor; Developments; Sensor chip; Applications; Biosensing techniques;

A simple and precise determination method for platinum group elements (PGEs) and Re in rock samples was developed using isotope dilution coupled with inductively coupled plasma mass spectrometry (ID-ICP-MS). Cation exchange separation was employed for simplicity, because it is applicable to group separation and simultaneous isotopic measurement in contrast with the widely used anion exchange separation which entails separate elution. However, its application to ID-ICP-MS has been limited due to spectral interferences from impurities retained in the PGE fraction even after ion chromatography. To overcome this limitation, solvent extraction using N-benzoyl-N-phenylhydroxylamine (BPHA) in chloroform was successfully applied for further purification.After the examination of optimum experimental parameters in cation exchange separation and solvent extraction using synthetic PGE solution, the established procedure was applied to the determination of PGEs and Re in some geochemical reference materials. The obtained results agreed well with the literature data determined using the different digestion methods (NiS fire assay and the use of a high-pressure asher) within the analytical uncertainties of each other. Significant difference in reproducibility between Ru, Ir, Pt and Os group, and Pd and Re group was observed in the results for BHVO-2 and JA-2. By considering the error factors affecting analytical reproducibility, we concluded that the difference is ascribed to the sample heterogeneity of minor minerals enriched in Ru, Ir, Pt and Os.
Keywords: Isotope dilution analysis; Platinum group elements; Inductively coupled plasma mass spectrometry; N-Benzoyl-N-phenylhydroxylamine; Cation exchange chromatography;

The kinetic methodology based on the difference of reaction rates, is based on the reaction between a common oxidizing agents such as tris(1,10-phenanthroline) and iron(III) complex (ferriin, [Fe (phen)3]3+) in the presence of citrate and spectrophotometrically, monitoring the changes of absorbance at the maximum wavelength of 511 nm. Experimental conditions such as pH, reagents and citrate concentrations were optimized, and the data obtained from the experiments were processed by several chemometric approaches, such as artificial neural network (ANN) and partial least squares (PLS). A set of synthetic mixtures of carbidopa (CD), levodopa (LD) and methyldopa (MD) was evaluated and the results obtained by the applications of these chemometric approaches were discussed and compared. It was found that the back propagation artificial neural network (BP-ANN) method afforded better precision relatively than those of radial basis function artificial neural networks (RBF-ANN) and PLS. The proposed method was also applied satisfactorily to the determination of carbidopa, levodopa and methyldopa in real samples.
Keywords: Carbidopa; Levodopa; Methyldopa; Simultaneous determination; Orthogonal design; Chemometric;

Application of the ANOVA-PCA method to stability studies of reference materials by Julien Sarembaud; Rui Pinto; Douglas N. Rutledge; Max Feinberg (147-154).
Near infrared spectroscopy (NIRS) is an analytical technique that can be very useful for stability studies in particular because of its non destructive analytical capability. However, the spectral interpretation and treatment of this kind of multivariate data remains difficult without the use of chemometrics. In this article, a recent chemometrics method, analysis of variance – principal component analysis (ANOVA-PCA), was used for NIRS stability studies of sunflower and bread wheat external reference materials (ERM). It provided a practical tool for the study of the significance of various storage conditions according to an experimental design. Thus, the effect of the temperature, the nature of the atmosphere in the packaging and the storage duration were tested. ANOVA-PCA highlighted the influence of temperature and storage duration on the stability of the sunflower materials. For the bread wheat materials, the storage conditions did not have a significant effect on stability. Consequently, by applying ANOVA-PCA to near infrared spectral data, the sunflower materials were found to be considered stable for the time length of the study, i.e. 18 months stored in a cold room, while the bread wheat materials were found to be considered stable for the time length of the study, i.e. 12 months under the same conditions.
Keywords: Near infrared spectroscopy; Stability study; External reference materials; ANOVA-PCA;

The jack-knife is a resampling method that is increasingly used for assessing the uncertainty in regression coefficient estimates, even when the predictor variables (X) are designed. Application of the jack-knife to designed data, however, violates a basic assumption underlying all resampling methods, namely that the resampled units should constitute a random sample from some distribution; the idea is to ‘resample the sample.’ This paper advances the view that the jack-knife should not be applied to estimate the uncertainty in regression coefficient estimates obtained from designed data, since a sound alternative is available. A literature data set is re-analyzed to lend support to this view.
Keywords: Resampling; Jack-knife; Design; Regression coefficient; Uncertainty estimate;

Construction and evaluation of a flow injection micro-analyser based on urethane–acrylate resin by Alexandre Fonseca; Ivo M. Raimundo; Jarbas J.R. Rohwedder; Luiz Otávio S. Ferreira (159-166).
A flow injection micro-analyser with an integrated injection device and photometric detection is described. Channels measuring 205–295 μm depth by 265–290 μm maximum width were manufactured by deep UV lithography on two layers of urethane–acrylate oligomers-based photoresist. Hypodermic syringe needles (450 μm diameter) were connected to the channels for introduction of solutions into the system. Plastic optical fibres were connected to the ends of a 5.0 mm long channel, in order to conduct the light from and to a homemade photometer. The device has a total volume of 7.0 μL and three different sample volumes (0.09, 0.22 and 0.30 μL) can be inserted into the system by choosing the appropriate loop of the hydrodynamic injection approach. The micro-analyser, designed as a single line manifold, was evaluated by determining chloride in waters (mercuric thiocyanate method), and chromium (VI) in wastewater and total chromium in metallic alloys (diphenylcarbazide method). For chloride determination two micro-pumps were employed to impel the solutions, while for chromium determination this task was performed by a conventional peristaltic pump. The results obtained in all determinations did not differ significantly from the reference methods at a confidence level of 95%. In the chloride determination, a flow rate of 50 μL min−1 was used, providing a sample frequency of 45 injection h−1, generating ca. 0.7 mg of Hg(II) after an 8-h working day (ca. 20 mL of solution). This result suggests the potential of the micro-analyser towards the reduction of waste, following the philosophy of Green Chemistry.
Keywords: Micro-FIA; Microfluidic devices; Lab-on-a-chip; Flow analysis; Deep ultraviolet lithography;

Methods for extracting biochemical information from bacterial Raman spectra: Focus on a group of structurally similar biomolecules—Fatty acids by Joke De Gelder; Kris De Gussem; Peter Vandenabeele; Marc Vancanneyt; Paul De Vos; Luc Moens (167-175).
In this paper we explore the possibilities of Raman spectroscopy in order to deduce information on the fatty acid composition of bacterial cells. Therefore, representative strains of two bacterial taxa were each cultured in different conditions and in parallel analyzed by Raman spectroscopy and gaschromatographic FAME analysis. Raman spectra of pure fatty acids were recorded and used as reference spectra. The culturing conditions for each strain could be easily distinguished by the fatty acid information retrieved from bacterial Raman spectra. Chemometric techniques such as EMSC and PCA allowed to extract information about groups of fatty acids, that was consistent with the results from FAME analysis. Although the information retrieved from Raman spectroscopy is not as refined as that from FAME analysis, the presented methods could be useful to obtain basic information on the fatty acid present in bacteria when performing Raman spectroscopic analysis for fast whole cell profiling, which provides information for different types of cell components (fatty acids, amino acids, primary metabolites, etc.).
Keywords: Raman spectroscopy; Bacteria; Fatty acids; FAME; EMSC;

Chemical screening of olive biophenol extracts by hyphenated liquid chromatography by Hassan K. Obied; Danny R. Bedgood; Paul D. Prenzler; Kevin Robards (176-189).
Chemical screening using reversed phase HPLC–photodiode array detection (RPLC–DAD) and RPLC–electrospray ionisation mass spectrometry (RPLC–ESI-MS) is widely applied as an approach to streamline natural products research. The full potential of this approach is demonstrated in this paper by application to the chemical screening of olive products including olive mill waste (OMW). Out of 100 biophenols previously reported in olive products, the on-line RPLC–DAD–ESI-MS was able to confirm the presence of 52 compounds in OMW. This included a number of simple phenols, flavonoids and secoiridoids. By careful examination of the combined DAD and ESI-MS data, extra information was elucidated including: the site of glycosidation on the phenol ring of hydroxytyrosol; the identity of the other luteolin-glucoside isomer as luteolin-4′-O-glucoside; identifying rutin rather than the previously reported hesperidin (and the reasons for possible mis-assignment); and the detection of diastereomers of 4-hydroxyphenylethyl alcohol-deacetoxy elenolic acid dialdehyde (4-HPEA-DEDA) and 3,4-dihydroxyphenylethyl alcohol-deacetoxy elenolic acid dialdehyde (3,4-DHPEA-DEDA).
Keywords: Liquid chromatography–electrospray ionisation-mass spectrometry; Photodiode array detection; Fluorimetry; Olive mill waste; Oil; Fruit; Secoiridoids; Polyphenols;

An improved flow analysis–ion chromatography method for determination of cationic and anionic species at trace levels in Antarctic ice cores by Andrea Morganti; Silvia Becagli; Emiliano Castellano; Mirko Severi; Rita Traversi; Roberto Udisti (190-198).
A method was developed for the quantitative determination of cations and anions in Antarctic ice cores at μg L−1 and sub-μg L−1 levels by ion chromatography (IC), after ultra-clean decontamination procedures. Strict manipulation and decontamination procedures were used in sub-sampling, in order to minimise sample contamination. Na+, NH4 +, K+, Mg2+ and Ca2+ were determined by 12-min isocratic elution (H2SO4 eluent). Contemporaneously, in a parallel device, F, MSA (methanesulfonic acid), Cl, NO3 and SO4 2− were analysed in a single 12-min run with multiple-step elution using Na2CO3/NaHCO3 as eluent. Melted ice samples were pumped from their still-closed containers (polystyrene accuvettes with polyethylene caps), shared between the two ion chromatographic systems, online filtered (0.45 μm Teflon membrane) and pre-concentrated (anions and cations pre-concentration columns) using a flow analysis system, thus avoiding uptake of contaminants from the laboratory atmosphere. Sensitivity, linear range, reproducibility and detection limit were evaluated for each chemical species. Anion or cation detection limits ranged from 0.01 to 0.15 μg L−1 by using a relatively small sample volume (1.5 mL). Such values are significantly lower than those reported in literature for almost all the components. These methods were successfully applied to the analysis of cations and anions at trace levels in the Dome C ice core. The composition of the atmospheric aerosol for the last 850 kyr was reconstructed by high-resolution continuous chemical stratigraphies. Concentration trends in the last nine glacial-interglacial climatic cycles were shown and briefly discussed.
Keywords: Ion chromatography; Anions; Cations; Antarctic ice core; Sample handling;

Allele-specific extension on microarray for DNA methylation analysis by Zhixiang Wu; Junfeng Luo; Qinyu Ge; Dingdong Zhang; Yan Wang; Chao Jia; Zuhong Lu (199-204).
Aberrant DNA methylation of CpG site in the gene promoter region has been confirmed to be closely associated with carcinogenesis. In this present study, a new method based on the allele-specific extension on microarray technique for detecting changes of DNA methylation in cancer was developed. The target gene regions were amplified from the bisulfite treated genomic DNA (gDNA) with modified primers and treated with exonuclease to generate single-strand targets. Allele-specific extension of the immobilized primers took place along a stretch of target sequence with the presence of DNA polymerase and Cy5-labeled dGTP. To control the false positive signals, the hybridization condition, DNA polymerase, extension time and primers design were optimized. Two breast tumor-related genes (P16 and E-cadherin) were analyzed with this present method successfully and all the results were compatible with that of traditional methylation-specific PCR. The experiments results demonstrated that this DNA microarray-based method could be applied as a high throughput tool for methylation status analysis of the cancer-related genes, which could be widely used in cancer diagnosis or the detection of recurrence.
Keywords: Methylation; Microarray; Allele-specific extension; Methylation-specific PCR;

A highly sensitive and label-free amperometric immunosensor has been developed for the detection of carcinoembryonic antigen (CEA) based on layer-by-layer (LBL) assembly of gold nanoparticles (GNPs), multi-walled carbon nanotubes-thionine (MWNTs-THI) and chitosan (CHIT) on 3-mercaptopropanesulfonic, sodium salt (MPS)-modified gold electrode surface by electrostatic adsorption. The stepwise LBL assembly process of electroactive species on electrode surface was characterized by means of cyclic voltammetry (CV) in PBS. The factors influencing the performance of the resulting immunosensor were studied in detail. The morphologies of MWNTs, MWNTs-THI and GNPs–MWNTs-THI–CHIT were further characterized by transmission electron microscopy (TEM). The immunosensor was highly sensitive to CEA with a detection limit of 0.01 ng mL−1 (signal/noise ratio of 3) and the linear range with two concentration intermittences was from 0.5 to 15.0 ng mL−1 and from 15.0 to 200.0 ng mL−1, respectively. In addition, the prepared immunosensor could be regenerated 10 times with 5 M urea solution. When the immunosensor was stored at 4 °C and measured intermittently (every 4–6 days), no apparent change was found over 3 months. The immunosensor system showed an excellent reproducibility and stability.
Keywords: Immunosensor; Layer-by-layer; Gold nanoparticles; Carcinoembryonic antigen; Multi-walled carbon nanotubes;