Linear Modulated Stochastic Resonance Algorithm Applied to Determination of Thidiazuron Residue in Water Using Stochastic Resonance

Abstract

The newly proposed linear modulated stochastic resonance algorithm (LSRA) was used to amplify and detect the weak chromatographic peaks of thidiazuron. The output chromatographic peak is often distorted when using the traditional stochastic resonance algorithm because of the existence of strong noise. In LSRA, the distortion of the output peak can be corrected by introducing a linear force into the nonlinear system. A two‐step optimization method was proposed to give attention to both the signal‐to‐noise ratio and the peak shape of output signal. The weak chromatographic peaks of thidiazuron can be amplified significantly and the distortion of the output peaks can be corrected using LSRA. The algorithm was used to detect thidiazuron residue in water with solid phase extraction‐high performance liquid chromatography. The limit of detection and limit of quantification were improved to 2.5 ng/l and 10 ng/l, respectively.     

31P NMR study on the autophosphorylation of insulin receptors in the plasma membrane

A nonradioactive ³¹P nuclear magnetic resonance (NMR) spectroscopy protocol has been developed and used to investigate in vitro autophosphorylation of insulin receptors. Optimum experimental conditions have been explored, and the effects of Mn²⁺ and phosphocreatine (PCr) on the determination of the phosphorylation reaction have been assayed. The method was used to monitor the time courses of the phosphorylation reaction in solution. The results from this NMR study were in agreement with observations of insulin receptor phosphorylation made by using Western blotting.      

A binary matrix for background suppression in MALDI-MS of small molecules

Application of matrix-assisted laser-desorption ionization mass spectrometry (MALDI-MS) to small-molecule detection is often limited, because of high matrix background signals in the low-mass region. We report here an approach in which a mixture of two conventional MALDI matrices with different proton affinity was used to suppress the formation of matrix clusters and fragments. Specifically, when acidic α-cyano-4-hydroxycinnamic acid (CHCA) and basic 9-aminoacridine (9-AA) were used as the binary matrix, fewer background matrix peaks were observed in both positive and negative-mode detection of small molecules. In addition, the presence of CHCA substantially reduced the laser fluence needed for analyte desorption and ionization; thus better signal-to-background ratios were observed for negatively charged inositol phosphates in complex plant extracts. The mixing of MALDI matrices of different protonaffinities leads to suppression of matrix clusterformation and subsequently yields cleaner MS spectraof fewer background peaks in both positive andnegative detection of small molecules     

H-point standard addition method applied to solid-state stripping voltammetry: quantitation of lead and tin in archaeological glazes

A solid-state electrochemical application of the H-point standard addition method to the quantification of two depositable metals A and B, which produce strongly overlapped stripping peaks, is described. The method is based on the mechanical transference of mixtures of the solid sample plus a selected compound, of a reference depositable metal R, and of known amounts of a reference material containing A or B, to paraffin-impregnated graphite electrodes. After a reductive deposition step, voltammograms recorded for those modified electrodes immersed into a suitable electrolyte produce stripping peaks for the oxidation of all of the metals deposited. Measurement of the currents at selected potentials in overlapping peaks corresponding to the stripping of A and B permits the quantitation of these metals in the solid sample, while avoiding matrix effects. The method was applied to the simultaneous determination of Pb and Sn in archaeological glazes using PbCO₃ and SnO₂ as standards and ZnO as a reference material.      

Application of anodized aluminum in fluorescence detection of biological species

Thin nanoporous alumina obtained by anodization of aluminum films offers promising advantages for application in fluorescence-based biological sensors including convenient preparation, increased density of binding sites, and improved collection efficiency of fluorescence. These advantages are illustrated in the detection of streptavidin using biotin covalently bound to the surface of alumina nanopores. Fluorescence intensity enhancement as high as 7 times is observed in nanopores in comparison to flat glass surface.      

Determination of the titanium content of human transferrin by inductively-coupled plasma-atomic-emission spectroscopy

We report a simple method that combines dialysis, as a purification method, with the multielement capability of ICP to determine the titanium-to-transferrin mole ratio at physiological pH, under buffer conditions. The method, by means of which titanium and transferrin are determined simultaneously, enabled us to assess the binding capacities of different titanocene complexes. Figure Titanocene dichloride     

Recent advances in capillary electrophoretic analysis of individual cells

Because variability exists within populations of cells, single-cell analysis has become increasingly important for probing complex cellular environments. Capillary electrophoresis (CE) is an excellent technique for identifying and quantifying the contents of single cells owing to its small volume requirements and fast, efficient separations with highly sensitive detection. Recent progress in both whole-cell and subcellular sampling has allowed researchers to study cellular function in the areas of neuroscience, oncology, enzymology, immunology, and gene expression.      

Headspace mass spectrometry methodology: application to oil spill identification in soils

In the present work we report the results obtained with a methodology based on direct coupling of a headspace generator to a mass spectrometer for the identification of different types of petroleum crudes in polluted soils. With no prior treatment, the samples are subjected to the headspace generation process and the volatiles generated are introduced directly into the mass spectrometer, thereby obtaining a fingerprint of volatiles in the sample analysed. The mass spectrum corresponding to the mass/charge ratios (m/z) contains the information related to the composition of the headspace and is used as the analytical signal for the characterization of the samples. The signals obtained for the different samples were treated by chemometric techniques to obtain the desired information. The main advantage of the proposed methodology is that no prior chromatographic separation and no sample manipulation are required. The method is rapid, simple and, in view of the results, highly promising for the implementation of a new approach for oil spill identification in soils. Figure PCA score plots illustrate clear discrimination of types of crude oil in polluted soil samples (e.g. results are shown for vertisol)     

SPME in environmental analysis

Recent advances in the use of solid-phase microextraction (SPME) in environmental analysis, including fiber coatings, derivatization techniques, and in-tube SPME, are reviewed in this article. Several calibration methods for SPME, including traditional calibration methods, the equilibrium extraction method, the exhaustive extraction method, and several diffusion-based calibration methods, are presented. Recent developed SPME devices for on-site sampling and several applications of SPME in environmental analysis are also introduced.      

Impedimetric genosensors for the detection of DNA hybridization

Impedance spectroscopy is proposed as the transduction principle for detecting the hybridization of DNA complementary strands. In our experiments, different DNA oligonucleotides were used as model gene substances. The gene probe is first immobilized on a graphite-epoxy composite working electrode based genosensor. Detection principle is based on changes of impedance spectra of a redox marker, the ferro/ferricyanide couple, after hybridization with target DNA. Resistance offered to the electrochemical reaction serves as the working signal, allowing for an unlabelled gene assay.      

A solution to the 1D NMR alignment problem using an extended generalized fuzzy Hough transform and mode support

This paper approaches the problem of intersample peak correspondence in the context of later applying statistical data analysis techniques to 1D ¹H-nuclear magnetic resonance (NMR) data. Any data analysis methodology will fail to produce meaningful results if the analyzed data table is not synchronized, i.e., each analyzed variable frequency (Hz) does not originate from the same chemical source throughout the entire dataset. This is typically the case when dealing with NMR data from biological samples. In this paper, we present a new state of the art for solving this problem using the generalized fuzzy Hough transform (GFHT). This paper describes significant improvements since the method was introduced for NMR datasets of plasma in Csenki et al. (Anal Bioanal Chem 389:875-885, 15) and is now capable of synchronizing peaks from more complex datasets such as urine as well as plasma data. We present a novel way of globally modeling peak shifts using principal component analysis, a new algorithm for calculating the transform and an effective peak detection algorithm. The algorithm is applied to two real metabonomic ¹H-NMR datasets and the properties of the method are compared to bucketing. We implicitly prove that GFHT establishes the objectively true correspondence. Desirable features of the GFHT are: (1) intersample peak correspondence even if peaks change order on the frequency axis and (2) the method is symmetric with respect to the samples. Figure From chaos to order: heatmaps of a H-NMR spectral segment prior and post sorting on one peak position. Post sorting sample order reveals that peak positions exhibits distinctive patterns which are modeled by the GFHT to establish correspondence. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

A simple electroanalytical methodology for the simultaneous determination of dopamine,serotonin and ascorbic acid using an unmodified edge plane pyrolytic graphite electrode

A simple method using an unmodified edge plane pyrolytic graphite electrode (EPPGE) is reported for the simultaneous determination of dopamine (DA), serotonin (ST) and ascorbic acid (AA). The performance of this electrode is superior to other unmodified carbon-based electrodes and also to many modified electrodes in terms of detection limit, sensitivity and peak separation for determination of DA, ST and AA. Using this method, detection limits of 90 nM, 60 nM and 200 nM were obtained for DA, ST and AA respectively. No electrode fouling is observed during a set of experiments and good sensitivity is obtained for the simultaneous determination of DA, ST and AA. The peaks for the three species are well resolved from each other and the electrode is successfully utilised for their determination in standard and real samples.      

Diagonal chromatographic selection of cysteinyl peptides modified with benzoquinones

The derivatization of cysteine-containing peptides with benzoquinone compounds is rapid, quantitative and specific in acidic media. The conversion of cysteines into hydrophobic benzoquinone-adducted residues in peptides is used here to alter the chromatographic properties of cysteinyl peptides during liquid chromatography separation. The benzoquinone derivatization is shown to allow the accurate selection of cysteine-containing peptides of bovine serum albumin tryptic digest by diagonal reversed-phase chromatography, which consists of one primary and a series of secondary identical liquid chromatographic separations, before and after a cysteinyl-targeted modification of the peptides by benzoquinone compounds. Figure Diagonal chromatographic selection of cysteinyl peptides modified with benzoquinones Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Modì: a new mobile instrument for in situ double-pulse LIBS analysis

Laser-induced breakdown spectroscopy (LIBS) is a promising technique for in situ elemental analysis. A new mobile instrument for LIBS analysis, developed in a collaboration between Marwan Technology s.r.l. and the Applied Laser Spectroscopy Laboratory in Pisa, is presented, and some applications of it and results from it are outlined. The innovative experimental set-up, based on the use of two suitably retarded laser pulses and a standardless analysis procedure, which overcomes problems related to matrix effects, greatly improves the potential of this technique for accurate quantitative analysis.      

Arsine and selenium hydride trapping in a novel quartz device for atomic-absorption spectrometry

A novel quartz device has been designed to trap arsine and selenium hydride and subsequently to volatilize the collected analyte and atomize it for atomic-absorption spectrometric detection. The device is actually the multiple microflame quartz-tube atomizer (multiatomizer) with inlet arm modified to serve as the trap and to accommodate the oxygen-delivery capillary used to combust hydrogen during the trapping step. The effect of relevant experimental conditions (trap temperature during trapping and hydrogen flow rate and trap temperature during volatilization) on collection and volatilization efficiency was investigated. Under the optimum conditions collection and volatilization efficiency for arsenic and selenium were 50 and 70%, respectively.      

Proof of principle of a generalized fuzzy Hough transform approach to peak alignment of one-dimensional <Superscript>1</Superscript>H NMR data

In metabolic profiling, multivariate data analysis techniques are used to interpret one-dimensional (1D) ¹H NMR data. Multivariate data analysis techniques require that peaks are characterised by the same variables in every spectrum. This location constraint is essential for correct comparison of the intensities of several NMR spectra. However, variations in physicochemical factors can cause the locations of the peaks to shift. The location prerequisite may thus not be met, and so, to solve this problem, alignment methods have been developed. However, current state-of-the-art algorithms for data alignment cannot resolve the inherent problems encountered when analysing NMR data of biological origin, because they are unable to align peaks when the spatial order of the peaks changes—a commonly occurring phenomenon. In this paper a new algorithm is proposed, based on the Hough transform operating on an image representation of the NMR dataset that is capable of correctly aligning peaks when existing methods fail. The proposed algorithm was compared with current state-of-the-art algorithms operating on a selected plasma dataset to demonstrate its potential. A urine dataset was also processed using the algorithm as a further demonstration. The method is capable of successfully aligning the plasma data but further development is needed to address more challenging applications, for example urine data. Figure Traces of NMR peaks visualizing the Generalized Fuzzy Hough Transform (GFHT) method for elucidating peak correspondence between samples. The spectra are sorted according to one shift sensitive peak and reveals that other peaks exhibit a similar shift pattern. This pattern(s) can now be searched for using the GFHT. The red and black spectra in the figure are the most shifting spectra (top and bottom), by following the GFHT traces peak correspondence is easily established although peaks change spatial location Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Critical evaluation of sample pretreatment techniques

Sample preparation before chromatographic separation is the most time-consuming and error-prone part of the analytical procedure. Therefore, selecting and optimizing an appropriate sample preparation scheme is a key factor in the final success of the analysis, and the judicious choice of an appropriate procedure greatly influences the reliability and accuracy of a given analysis. The main objective of this review is to critically evaluate the applicability, disadvantages, and advantages of various sample preparation techniques. Particular emphasis is placed on extraction techniques suitable for both liquid and solid samples. Figure Miniaturised extraction techniques allow sensitive analysis of also small sample volumes.     

Determination of vancomycin in human plasma using high-performance liquid chromatography with fluorescence detection

A high-performance liquid chromatographic (HPLC) method with fluorescence detection for the quantification of vancomycin in human plasma was developed and validated. The method includes an extraction of vancomycin by deproteinization with acetonitrile. The analyses were carried out at 258 nm as the emission wavelength while exciting at 225 nm on a reversed-phase column (30 cm × 4 mm i.d. × 10 μm Waters Associates μBondapak C18) using a mobile phase composed of methanol and phosphate buffer at pH 6.3. Vancomycin was quantitatively recovered from human plasma samples (>96%) with high values of precision. The separation was completed within 27 min. The calibration curve was linear over the range from 5 to 1,000 ng/mL with the detection and quantification limits of 2 ng/mL and 5 ng/mL, respectively. This method is suitable for the routine assay of plasma samples. Figure The effect of the deproteinization solvent on the signal of the interference peak at retention time of 15.0 min. The peak which interferes with the peaks of Erythromycin and Vancomycin has been disappeared by using 2 mL acetonitrile as the deproteinization solvent.