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Analytica Chimica Acta (v.648, #2)
Flow/sequential injection sample treatment coupled to capillary electrophoresis. A review by Petr Kubáň; Bo Karlberg (pp. 129-145).
Various flow sample handling approaches coupled to capillary electrophoresis (CE) are reviewed, covering the research in this field in the 12 years since the milestone year of 1997, when practical interfaces to on-line couple flow injection (FI) and capillary electrophoresis were first developed independently by two research groups. Some previous attempts are also presented. Since 1997 a plethora of ingenious coupled systems have been developed. Although several reviews are available on various aspects of the topic, we have opted for a comprehensive overview of all FI–CE systems, as well as related and similar systems. This coupling has thus also led to the development of systems based on hybrids between the classical and microchip approaches. Truly microchip FI–CE systems are also included in this review.The developed systems have been used for various sample treatments, including on-line membrane-assisted sample treatment, column-based preconcentration, on-line derivatization and monitoring, to name just a few. The utility of coupling flow sampling to CE has been demonstrated in various practical applications that are discussed in detail. The current state-of-the-art and foreseeable future developments are also discussed.
Keywords: Flow injection analysis; Sequential injection analysis; Capillary electrophoresis; On-line coupling; Flow injection–capillary electrophoresis (FI–CE); Sequential injection analysis–capillary electrophoresis (SIA–CE); Sample pretreatment
Geographical origin of Sauvignon Blanc wines predicted by mass spectrometry and metal oxide based electronic nose by Amalia Z. Berna; Stephen Trowell; David Clifford; Wies Cynkar; Daniel Cozzolino (pp. 146-152).
Analysis of 34 Sauvignon Blanc wine samples from three different countries and six regions was performed by gas chromatography–mass spectrometry (GC–MS). Linear discriminant analysis (LDA) showed that there were three distinct clusters or classes of wines with different aroma profiles. Wines from the Loire region in France and Australian wines from Tasmania and Western Australia were found to have similar aroma patterns. New Zealand wines from the Marlborough region as well as the Australian ones from Victoria were grouped together based on the volatile composition. Wines from South Australia region formed one discrete class. Seven analytes, most of them esters, were found to be the relevant chemical compounds that characterized the classes. The grouping information obtained by GC–MS, was used to train metal oxide based electronic (MOS-Enose) and mass spectrometry based electronic (MS-Enose) noses. The combined use of solid phase microextraction (SPME) and ethanol removal prior to MOS-Enose analysis, allowed an average error of prediction of the regional origins of Sauvignon Blanc wines of 6.5% compared to 24% when static headspace (SHS) was employed. For MS-Enose, the misclassification rate was higher probably due to the requirement to delimit the m/ z range considered.
Keywords: Sauvignon Blanc; Electronic nose; Gas chromatography–mass spectrometry; Prediction
Systematic error arising from ‘sequential’ standard addition calibrations. 2. Determination of analyte mass fraction in blank solutions by Richard J.C. Brown (pp. 153-156).
The use of a sequential standard addition calibration (S-SAC) can introduce systematic errors into measurements results. Whilst this error for the determination of blank-corrected solutions has previously been described, no similar treatment has been available for the quantification of analyte mass fraction in blank solutions – a crucial first step in any analytical procedure. This paper presents the theory describing the measurement of blank solutions using S-SAC, derives the correction that needs to be applied following analysis, and demonstrates the systematic error that occurs if this correction is not applied. The relative magnitudes of this bias and the precision of extrapolated measurements values are also considered.
Keywords: Calibration; Standard addition; Systematic error; Blank determination
Comparison of two experimental speciation methods with a theoretical approach to monitor free and labile Cd fractions in soil solutions by C. Parat; J.-Y. Cornu; A. Schneider; L. Authier; V. Sapin-Didier; L. Denaix; M. Potin-Gautier (pp. 157-161).
This work focused on the suitability of two techniques to monitor cadmium speciation in soil solutions collected during a 7-day incubation of a contaminated soil. Anodic stripping voltammetry (ASV) and ion exchange were performed on soil solutions collected daily and results were compared with calculations obtained with the speciation software Visual MINTEQ. The electrochemically labile Cd fraction was greater than the exchange-estimated free Cd fraction during the first 6 days, after which it decreased sharply during the last 2 days to reach values close to the exchange-estimated free Cd fraction. Further investigations showed that the increase in pH was mainly responsible for the reduction. However, calculations performed with Visual MINTEQ software clearly demonstrated that a change in the nature of organic matter and/or its complexing capacity also needed to be taken into consideration.
Keywords: Labile Cd complexes; Free Cd; Speciation; Anodic stripping voltammetry; Visual MINTEQ
Voltammetric determination of Se(IV) and Se(VI) in saline samples—Studies with seawater, hydrothermal and hemodialysis fluids by Paulo C. do Nascimento; Cristiane L. Jost; Leandro M. de Carvalho; Denise Bohrer; Andrea Koschinsky (pp. 162-166).
Determination of Se(IV) and Se(VI) in high saline media was investigated by cathodic stripping voltammetry (CSV). The voltammetric method was applied to assay selenium in seawater, hydrothermal and hemodialysis fluids. The influence of ionic strength on selenium determination is discussed. The CSV method was based on the co-electrodeposition of Se(IV) with Cu(II) ions and Se(VI) determined by difference after sample UV-irradiation for photolytic selenium reduction. UV-irradiation was also used as sample pre-treatment for organic matter decomposition. Detection limit of 0.030μgL−1 (240s deposition time) and relative standard deviation (RSD) of 6.19% ( n=5) for 5.0μgL−1 of Se(IV) were calculated. Linear calibration range for selenium was observed from 1.0 to 100.0μgL−1. Concerning the pre-treatment step, best results were obtained by using 60min UV-irradiation interval in H2O2/HCl medium. Se(VI) was reduced to the Se(IV) electroactive species with recoveries between 91.7% and 112.9%. Interferents were also investigated.
Keywords: Selenium; Ionic strength; Speciation analysis; Cathodic stripping voltammetry; UV-irradiation
Micro-Winkler titration method for dissolved oxygen concentration measurement by Irja Helm; Lauri Jalukse; Martin Vilbaste; Ivo Leito (pp. 167-173).
In this report a gravimetric micro-Winkler titration method for determination of dissolved oxygen concentration in water is presented. Mathematical model of the method taking into account all influence factors is derived and an uncertainty analysis is carried out to determine the uncertainty contributions of all influence factors. The method is highly accurate: the relative expanded uncertainties ( k=2) are around 1% in the case of small (9–10g) water samples. The uncertainty analysis carried out in characterizing the uncertainty of the method is the most comprehensive published for a micro-Winkler method, resulting in experimentally obtained estimates for all uncertainty sources of practical significance (around 20 uncertainty sources altogether).
Keywords: Micro-Winkler titration; Gravimetric titration; Primary method; Dissolved oxygen; Measurement uncertainty; Uncertainty budget
Determination of itopride hydrochloride by high-performance liquid chromatography with Ru(bpy)32+ electrogenerated chemiluminescence detection by Yonghua Sun; Zhujun Zhang; Zhijun Xi; Zuolong Shi; Wei Tian (pp. 174-177).
In this work, a stable electrogenerated chemiluminescence (ECL) detector was developed. The detector was prepared by packing cation-exchanged resin particles in a glass tube, followed by inserting Pt wires (working electrode) in this tube and sealing. The leakage of Ru(bpy)32+ can be compensated by adding a small amount of Ru(bpy)32+ into solution phase. Coupled with high-performance liquid chromatography separation, the detector has been used for determination of itopride hydrochloride in human serum. Under the optimal conditions, the ECL intensity has a linear relationship with the concentration of itopride hydrochloride in the range of 1.0×10−8gmL−1 to 1.0×10−6gmL−1 and the detection limit was 3×10−9gmL−1 (S/N=3). The as-prepared ECL detector displayed good sensitivity and stability.
Keywords: Electrogenerated chemiluminescence detector; Ru(bpy); 3; 2+; High-performance liquid chromatography; Cation-exchanged resin; Itopride hydrochloride
Development of a focused ultrasonic-assisted extraction of polycyclic aromatic hydrocarbons in marine sediment and mussel samples by Patricia Navarro; Nestor Etxebarria; Gorka Arana (pp. 178-182).
Focused ultrasonic-assisted extraction (FUSE) is a new and particular technique based on the cavitation effect. In this work, the focused ultrasound assisted extraction was studied and developed for the extraction of polycyclic aromatic hydrocarbons from marine sediments and mussel tissues. The variables influencing the extraction (amplitude of the ultrasound pulse, the extraction time and the solvent) were studied by a full factorial design and a central composite design. As a result, flat response surfaces were obtained and the most convenient conditions were 45% of ultrasound amplitude, 120s of extraction time and 5mL of acetone. Both accuracy and precision of the method were evaluated by means of two certified reference materials (marine sediment and mussel tissue) and the results were also compared to those obtained by microwave assisted extraction.
Keywords: Focused ultrasonic-assisted extraction; Microwave assisted extraction; Polycyclic aromatic hydrocarbons; Sediment; Mussel tissue
Liquid-phase microextraction and fibre-optics-based cuvetteless CCD-array micro-spectrophotometry for trace analysis by Nisha Sharma; Aradhana K.K.V. Pillai; Neeraj Pathak; Archana Jain; Krishna K. Verma (pp. 183-193).
Liquid-phase microextraction (LPME) has been investigated for trace analysis in the present work in conjunction with fibre-optic-based micro-spectrophotometry which accommodates sample volume of 1μL placed between the two ends of optical fibres. Methods have been evolved for the determination of (i) 1–100μM and 0.5–20μM of thiols by single drop microextraction (SDME) and LPME in 25μL of the organic solvent, respectively, involving their reaction with the Ellman reagent and ion pair microextraction of thiolate ion formed; (ii) 70μg to 7mgL−1 of chlorine/chlorine dioxide by headspace in-drop reaction with alternative reagents, viz., mixed phenylhydrazine-4-sulphonic acid and N-(1-naphthyl)ethylenediamine dihydrochloride, o-dianisidine, o-tolidine, and N, N-diethyl- p-phenylenediamine; (iii) 0.2–4mgL−1 of ammonia by reaction with 2,4-dinitro-1-fluorobenzene to give 2,4-dinitroaniline which was diazotized and coupled with 1-naphthylamine, the resulting dye was subjected to preconcentration by solid-phase extraction and LPME; and (iv) 25–750μgL−1 of iodide/total iodine by oxidation of iodide by 2-iodosobenzoate, microextraction of iodine in organic solvent, and re-extraction into aqueous starch-iodide reagent drop held in the organic phase. LPME using 25–30μL of organic solvent was found to produce more sensitive results than SDME. The cuvetteless spectrophotometry as used in combination with sample handling techniques produced limits of detection of analytes which were better than obtained by previously reported spectrophotometry.
Keywords: Micro-spectrophotometry; Fibre optics; Charged couple device-array; Liquid-phase microextraction; Thiols; Chlorine; Ammonia; Iodine
The extraction performance of methacrylic acid–trimethylolpropanetrimethacrylate solid-phase microextraction fibers in aqueous solutions by Jingbin Zeng; Jinmei Chen; Liangbi Chen; Yiru Wang; Wenfeng Chen; Xiaoli Huang; Xi Chen (pp. 194-199).
The extraction performance of solid-phase microextraction fibers, based on methacrylic acid–trimethylolpropanetrimethacrylate (MAA/TRIM) copolymers, was investigated in aqueous solutions using triazines as target analytes and 2-bromobiphenyl as a reference compound. The results revealed that the combination of electrostatic forces and hydrophobicity was the primary interaction between the MAA/TRIM coating and the triazines. To improve the selectivity of the MAA/TRIM-coated fiber for the triazines, several experimental parameters including pH of the sample solution, washing step, organic modifier, and salt concentration were optimized so as to amplify electrostatic interaction and suppress the hydrophobic effect. To evaluate the practicability of the proposed method, samples with complex matrixes, including corn extract and sewage sludge, were extracted with a MAA/TRIM-coated fiber under the optimized conditions chosen. The results showed that the extraction efficiency for target analytes was not enhanced, but the matrix effect of the interfering compounds in the samples was effectively restrained and thus the selectivity was obviously improved.
Keywords: Methacrylic acid–trimethylolpropanetrimethacrylate-coated fibers; Solid-phase microextraction; Aqueous solutions; Electrostatic interaction
On-line coupling of dynamic microwave-assisted extraction to solid-phase extraction for the determination of sulfonamide antibiotics in soil by Ligang Chen; Qinglei Zeng; Hui Wang; Rui Su; Yang Xu; Xiaopan Zhang; Aimin Yu; Hanqi Zhang; Lan Ding (pp. 200-206).
A rapid technique based on dynamic microwave-assisted extraction (DMAE) coupled on-line with solid-phase extraction (SPE) was developed for the determination of sulfonamides (SAs) including sulfadiazine, sulfameter, sulfamonomethoxine and sulfaquinoxaline in soil. The SAs were first extracted with acetonitrile under the action of microwave energy, and then directly introduced into the SPE column which was packed with neutral alumina for preconcentration of analytes and clean-up of sample matrix. Subsequently, the SAs trapped on the alumina were eluted with 0.3% acetic acid aqueous solution and determined by liquid chromatography–tandem mass spectrometry. The DMAE parameters were optimized by the Box–Behnken design. Maximum extraction efficiency was achieved using 320W of microwave power; 12mL of extraction solvent and 0.8mLmin−1 of extraction solvent flow rate. The limits of detection and quantification obtained are in the range of 1.4–4.8ngg−1 and 4.6–16.0ngg−1 for the SAs, respectively. The mean values of relative standard deviation of intra- and inter-day ranging from 2.7% to 5.3% and from 5.6% to 6.7% are obtained, respectively. The recoveries of SAs obtained by analyzing four spiked soil samples at three fortified levels (20ngg−1, 100ngg−1 and 500ngg−1) were from 82.6±6.0% to 93.7±5.5%. The effect of standing time of spiked soil sample on the SAs recoveries was examined. The recoveries of SAs decreased from (86.3–101.9)% to (37.6–47.5)% when the standing time changed from one day to four weeks.
Keywords: Sulfonamide antibiotics; Soil; Dynamic microwave-assisted extraction; Solid-phase extraction; Liquid chromatography–tandem mass spectrometry
Analysis of MALDI FT-ICR mass spectrometry data: A time series approach by Donald A. Barkauskas; Scott R. Kronewitter; Carlito B. Lebrilla; David M. Rocke (pp. 207-214).
Matrix-assisted laser desorption/ionization Fourier transform ion cyclotron resonance mass spectrometry is a technique for high mass-resolution analysis of substances that is rapidly gaining popularity as an analytic tool. Extracting signal from the background noise, however, poses significant challenges. In this article, we model the noise part of a spectrum as an autoregressive, moving average (ARMA) time series with innovations given by a generalized gamma distribution with varying scale parameter but constant shape parameter and exponent. This enables us to classify peaks found in actual spectra as either noise or signal using a reasonable criterion that outperforms a standard threshold criterion.
Keywords: Fourier transform ion cyclotron resonance; Generalized gamma distribution; Matrix-assisted laser desorption/ionization
Development of a method for comprehensive and quantitative analysis of plant hormones by highly sensitive nanoflow liquid chromatography–electrospray ionization-ion trap mass spectrometry by Yoshihiro Izumi; Atsushi Okazawa; Takeshi Bamba; Akio Kobayashi; Eiichiro Fukusaki (pp. 215-225).
In recent plant hormone research, there is an increased demand for a highly sensitive and comprehensive analytical approach to elucidate the hormonal signaling networks, functions, and dynamics. We have demonstrated the high sensitivity of a comprehensive and quantitative analytical method developed with nanoflow liquid chromatography–electrospray ionization-ion trap mass spectrometry (LC–ESI-IT-MS/MS) under multiple-reaction monitoring (MRM) in plant hormone profiling. Unlabeled and deuterium-labeled isotopomers of four classes of plant hormones and their derivatives, auxins, cytokinins (CK), abscisic acid (ABA), and gibberellins (GA), were analyzed by this method. The optimized nanoflow-LC–ESI-IT-MS/MS method showed ca. 5–10-fold greater sensitivity than capillary-LC–ESI-IT-MS/MS, and the detection limits (S/N=3) of several plant hormones were in the sub-fmol range. The results showed excellent linearity ( R2 values of 0.9937–1.0000) and reproducibility of elution times (relative standard deviations, RSDs, <1.1%) and peak areas (RSDs, <10.7%) for all target compounds. Further, sample purification using Oasis HLB and Oasis MCX cartridges significantly decreased the ion-suppressing effects of biological matrix as compared to the purification using only Oasis HLB cartridge. The optimized nanoflow-LC–ESI-IT-MS/MS method was successfully used to analyze endogenous plant hormones in Arabidopsis and tobacco samples. The samples used in this analysis were extracted from only 17 tobacco dry seeds (1mg DW), indicating that the efficiency of analysis of endogenous plant hormones strongly depends on the detection sensitivity of the method. Our analytical approach will be useful for in-depth studies on complex plant hormonal metabolism.
Keywords: Nanoflow liquid chromatography–electrospray ionization-ion trap mass spectrometry; Comprehensive plant hormone analysis; Standard isotope-dilution; Arabidopsis thaliana; Nicotiana tabacum
Exploitation of phosphorescent labelling reagent of fullerol-fluorescein isothiocyanate and new method for the determination of trace alkaline phosphatase as well as forecast of human diseases by Jia-Ming Liu; Xiao-Mei Huang; Zhen-Bo Liu; Shao-Qin Lin; Fei-Ming Li; Fei Gao; Zhi-Ming Li; Li-Qing Zeng; Lian-Ying Li; Ying Ouyang (pp. 226-234).
A new phosphorescent labelling reagent consisting of fullerol, fluorescein isothiocyanate and N,N-dimethylaniline (F-ol-(FITC) n-DMA) was developed. The mode of action is based on the reactivity of the active –OH group in F-ol with the –COOH group of FITC to form an F-ol-(FITC) n-DMA complex containing several FITC molecules. F-ol-(FITC) n-DMA increased the number of luminescent molecules in the biological target of WGA-AP-WGA-F-ol-(FITC) n-DMA (WGA and AP are wheat germ agglutinin and alkaline phosphatase, respectively) which improved the sensitivity using solid substrate room temperature phosphorimetry (SSRTP) detection. The proposed method provided high sensitivity and strong specificity for WGA-AP. The limit of detection (LD) was 0.15 ag AP spot−1 for F-ol and 0.097 ag AP spot−1 for FITC in F-ol-(FITC) n-DMA, which was lower than the method using single luminescent molecules of F-ol-DMA and FITC-DMA to label WGA (0.20 ag AP spot−1 for F-ol-DMA and 0.22 ag AP spot−1 for FITC-DMA). Results for the determination of AP in human serum were in good agreement with those obtained by enzyme-linked immunosorbent assay. The mechanism of F-ol-(FITC) n-DMA labelling of WGA was discussed.
Keywords: Alkaline phosphatase; Fullerol-fluorescein isothiocyanate; Wheat germ agglutinin; Affinity adsorption solid substrate room temperature phosphorimetry
A comparison study on Raman scattering properties of α- and β-MnO2 by Tao Gao; Helmer Fjellvåg; Poul Norby (pp. 235-239).
In this comment to a recent paper [Anal. Chim. Acta 585 (2007) 241–245], we report a comparison study on Mn oxide-related compounds with different crystallographic forms, which distinguish between β-MnO2 and α-MnO2 type materials via Raman scattering (RS) spectroscopy. The tetragonal rutile-type β-MnO2 is characterized by a RS band at ∼667cm−1 of symmetry A1g, whereas the α-MnO2 type materials feature two main RS contributions at about 574 and 634cm−1, belonging to Ag spectroscopic species of a tetragonal hollandite-type framework. These data represent a clear signature for identifying β-MnO2 and α-MnO2 type materials via RS spectroscopy.
Keywords: Raman scattering spectroscopy; β-MnO; 2; α-MnO; 2; type materials
Measurement of total calcium by flash chronopotentiometry at polymer membrane ion-selective electrodes by Kebede L. Gemene; Eric Bakker (pp. 240-245).
Ionophore-based ion-selective electrodes are widely used for potentiometric electrolyte measurements, in which case they are known to detect the free ion activity. Total ion concentrations cannot be directly assessed by this methodology if the ion is predominantly present in a complexed form. We present here the direct measurement of total calcium using a calcium ion-selective electrode interrogated in a flash chronopotentiometric transduction mode. A high magnitude of cathodic current pulse is applied across a calcium ion-selective membrane containing the ionophore ETH 5234 but void of ion-exchanger to prevent spontaneous extraction. This induces a defined flux of calcium ions from the sample side to the membrane and results in the release of labile bound calcium and a concomitant depletion at the membrane surface at a critical current or time. This is observed as an inflection point on the potential–time curve and the square root of the transition time is linearly related to the total concentration in the sample. It is shown that the responses to solutions of labile calcium complexes of nitrilotriacetic acid (NTA) are in a good agreement with that of the same concentration of calcium chloride in saline solution with this protocol. Initial applications are aimed towards assaying extracellular calcium. Calcium binding to albumin is shown to be inconsequential with sample dilutions typical for clinical assays. Calcium calibration curves in real and artificial dilute serum are finally shown to correspond to that of calcium chloride, suggesting that the methodology is indeed capable of detecting total calcium under these conditions. The present membrane materials allow detection of up to over 0.5mM total calcium in serum, currently requiring such samples to be diluted about 5-fold. The slopes of the square root of time–concentration dependence for the calibrations of free calcium in a background of NaCl and total serum calcium were found to be 3.857 and 3.717s1/2mM−1, respectively, deviating by just 3.6%. The lower detection limit (3× SD) was calculated as 12μM.
Keywords: Ion-selective electrodes; Total calcium sensor; Clinical analysis; Flash chronopotentiometry; Solvent polymeric membrane
Erratum to “Ultrasound extracted flavonoids from four varieties of Portuguese red grape skins determined by reverse-phase high-performance liquid chromatography with electrochemical detection” [Anal. Chim. Acta 630 (2008) 107–115]
by Ivana Novak; Patricia Janeiro; Marijan Seruga; Ana Maria Oliveira-Brett (pp. 246-246).