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Analytica Chimica Acta (v.581, #2)

Editorial Board (pp. co1).

Contents (pp. iii-iv).

Calendar of forthcoming meetings (pp. n3).

Contents (pp. iii-iv).

Editorial Board (pp. co1).

Calendar of forthcoming meetings (pp. n3).

Towards multi-colour strategies for the detection of oligonucleotide hybridization using quantum dots as energy donors in fluorescence resonance energy transfer (FRET) by W. Russ Algar; Ulrich J. Krull (pp. 193-201).

The potential for a simultaneous two-colour diagnostic scheme for nucleic acids operating on the basis of fluorescence resonance energy transfer (FRET) has been demonstrated. Upon ultraviolet excitation, two-colours of CdSe/ZnS quantum dots with conjugated oligonucleotide probes act as energy donors yielding FRET-sensitized acceptor emission upon hybridization with fluorophore (Cy3 and Alexa647) labeled target oligonucleotides. Energy transfer efficiencies, Förster distances, changes in quantum yield and lifetime, and signal-to-noise with respect to non-specific adsorption have been investigated. The dynamic range and limit-of-detection are tunable with the concentration of QD–DNA conjugate. The Cy3 and Alexa647 acceptor schemes can detect target from 4 to 100% or 10 to 100% of the QD–DNA conjugate concentration, respectively. Nanomolar limits of detection have been demonstrated in this paper, however, results indicate that picomolar detection limits can be achieved with standard instrumentation. The use of an intercalating dye (ethidium bromide) as an acceptor to alleviate non-specific adsorption is also described and increases signal-to-noise from S/N<2 to S/N=9–10. The ethidium bromide system had a dynamic range from 8 to 100% of the QD–DNA conjugate concentration and could detect target in a matrix containing an excess of non-complementary nucleic acid.

Keywords: Quantum dots; Energy transfer; Deoxyribonucleic acid; Ethidium bromide; Biosensor

Luminescent sensing of organophosphates using europium(III) containing imprinted polymers prepared by RAFT polymerization by Glen E. Southard; Kelly A. Van Houten; Edward W. Ott Jr.; George M. Murray (pp. 202-207).

Molecularly imprinted polymers capable of sensing organophosphorous compounds by luminescence have been prepared by reversible addition fragmentation chain transfer (RAFT) polymerization. The polymer contained a dithiobenzoate substituted tris(β-diketonate) europium(III) complex which served as a polymerization substrate and as a luminescent binding site for pinacolyl methylphosphonate (PMP), the hydrolysis product of the nerve agent Soman. The resultant polymer allowed quantitation of PMP in the low ppb range with minimal interference from similar compounds. Polymers were characterized by luminescence spectroscopy and scanning electron microscopy.

Keywords: Molecular imprinting; Luminescence; Organophosphates; Controlled polymerization

Imprinted polymer particles for selenium uptake: Synthesis, characterization and analytical applications by Mostafa Khajeh; Yadollah Yamini; Ensieh Ghasemi; Javad Fasihi; Mojtaba Shamsipur (pp. 208-213).

This work reports the preparation of molecularly imprinted polymer (MIP) particles for selective extraction and determination of selenium ions from aqueous media. Polymerization was achieved in a glass tube containing SeO₂, o-phenylenediamine, 2-vinylpyridine (VP), ethyleneglycoldimethacrylate (EDMA), 2,2′-azobisisobutyronitrile (AIBN). The polymer block obtained was ground and sieved (55–75μm) and the Se- o-phenylenediamine complex was removed from polymer particles by leaching with 2M of HCl, which leaves a cavity in the polymer particles. The polymer particles both prior to and after leaching have been characterized by IR and thermogravimetric (TG) studies. The effect of different parameters, such as pH, extraction time, type and least amount of eluent for elution of complex from polymer were evaluated. Extraction efficiencies >99% were obtained by elution of the polymers with 15mL of methanol–acetonitrile mixture (1:2, v/v). The limit of detection of the proposed method followed by hydride generation atomic absorption spectroscopy (HG-AAS) was found to be 3.3μgL⁻¹ and a dynamic linear range (DLR) of 10–200μgL⁻¹ was obtained. The relative standard deviations (R.S.D.s) at 30.0μgL⁻¹ of Se were below than 8.1%. The influence of various cationic interferences on percent recovery of complex was studied. The method was applied to the recovery and determination of selenium in different real samples.

Keywords: Selenium; Molecular imprinted polymer; o; -Phenylenediamine; Serum; Elution

Functionalization of chitosan with 3,4-dihydroxybenzoic acid for the adsorption/collection of uranium in water samples and its determination by inductively coupled plasma-mass spectrometry by Akhmad Sabarudin; Mitsuko Oshima; Toshio Takayanagi; Lukman Hakim; Koji Oshita; Yun Hua Gao; Shoji Motomizu (pp. 214-220).

A chitosan resin derivatized with 3,4-dihydroxybenzoic acid moiety (CCTS-DHBA resin) was newly synthesized for the collection/concentration of trace uranium by using cross-linked chitosan (CCTS) as base material, and the adsorption behavior of uranium as well as 60 elements on the resin was examined by passing the sample solutions through a mini-column packed with the resin. After the elution of the collected elements on the resin with 1M HNO₃, the eluates were measured by inductively coupled plasma-mass spectrometry (ICP-MS).The CCTS-DHBA resin can adsorb several metal cations and several oxoanionic elements at appropriate pH. Among these metal ions, uranium shows an excellent adsorption behavior on this resin. Uranium as UO₂²⁺ species can be adsorbed on the resin by chelating mechanism with adsorption capacity of 330mgg⁻¹ resin. Through the column treatment, the complete removal of large amounts of alkali and alkaline earth matrices without any loss of adsorption efficiency over prolonged usage were achieved with this resin.The CCTS-DHBA resin was applied to the adsorption/collection of uranium in tap water, river water and seawater samples with satisfactory results. The validation of the proposed method was carried out by analyzing uranium in the standard reference materials of SLRS-4, CASS-4, and NASS-5 after passing through the CCTS-DHBA resin, and the results showed good agreement with the certified values.

Keywords: Chitosan resin; 3,4-Dihydroxybenzoic acid; Uranium; Adsorption; Water; Inductively coupled plasma-mass spectrometry

Solid-phase microextraction–gas chromatography–time-of-flight mass spectrometry utilized for the evaluation of the new-generation super elastic fiber assemblies by Lucie Setkova; Sanja Risticevic; Christopher M. Linton; Gangfeng Ouyang; Leslie M. Bragg; Janusz Pawliszyn (pp. 221-231).

The aim of this study was to evaluate the performance characteristics of the recently developed super elastic solid-phase microextraction (SPME) fibers. The fiber needle, plunger and fiber core are manufactured with a special type of flexible alloy that exhibits excellent shape memory and tensile strength. This material makes the assemblies more robust, permitting several hundreds of analyses in a sequence, which is one of the ways to improve the robustness and sample throughput of automated SPME methods. The design and size of the needle utilized in the new fiber assemblies is discussed here, as well as the use of a septum-free injector replacement and a low-volume direct injection glass liner placed in the GC inlet. Deionized water and pump oil samples spiked with target volatile compounds (McReynold's probes and toluene) were used for the purposes of the presented study. A fully automated SPME sample preparation technique was combined with the GC–TOFMS system for the chromatographic separation and identification/quantification of the target analytes.

Keywords: Abbreviations; 1-N; 1-nitropropane; 2-P; 2-pentanone; B; benzene; BTEX; a mixture of benzene, toluene, ethylbenzene and; o; -xylene; CAR; carboxen; CE; capillary electrophoresis; DI; direct immersion; DIL; direct injection liner; DVB; divinylbenzene; GC; gas chromatography; HS; headspace; LC; liquid chromatography; M; metal fiber; n; statistically non-significant difference; P; pyridine; PDMS; polydimethylsiloxane; s; statistically significant difference; S; silica fiber; PA; polyacrylate; RT; retention time; SFC; supercritical fluid chromatography; SPME; solid-phase microextraction; T; toluene; TOFMS; time-of-flight mass spectrometerSolid-phase microextraction; Automation; High-throughput chemical analysis; Gas chromatography–time-of-flight mass spectrometry

Optical determination of Cr(VI) using regenerable, functionalized sol–gel monoliths by Nathan A. Carrington; George H. Thomas; D. Lynn Rodman; David B. Beach; Zi-Ling Xue (pp. 232-240).

Transparent, pyridine-functionalized sol–gel monoliths have been formed and their use in Cr(VI) sensing applications is demonstrated. The monoliths were immersed in acidic Cr(VI)-containing solutions, and the Cr(VI) uptake was monitored using UV–vis and atomic absorption spectroscopies. At concentrations at the ppm level, the monoliths exhibit a yellow color change characteristic of Cr(VI) uptake, and this can be measured by monitoring the absorption change at about 350nm using UV–vis spectroscopy. Concentrations at the ppb level are below the limit of detection using this wavelength of 350nm for measurement. However, by adding a diphenylcarbazide solution to monoliths that have been previously immersed in ppb-level Cr(VI) solutions, a distinct color change takes place within the gels that can be measured at about 540nm using UV–vis spectroscopy. Concentrations as low as 10ppb Cr(VI) can be measured using this method. The monoliths can then be regenerated for subsequent sensing cycles by thorough washing with 6.0M HCl. The factors affecting monolith uptake of Cr(VI) have been explored. In addition, the gels have been characterized using X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and Brunauer–Emmett–Teller (BET) measurements.

Keywords: Sol–gel; Chromium(VI); Monolith; Diphenylcarbazide; Pyridine

Optical determination of Cr(VI) using regenerable, functionalized sol–gel monoliths by Nathan A. Carrington; George H. Thomas; D. Lynn Rodman; David B. Beach; Zi-Ling Xue (pp. 232-240).

Keywords: Sol–gel; Chromium(VI); Monolith; Diphenylcarbazide; Pyridine

Biosorption of copper(II), lead(II), iron(III) and cobalt(II) on Bacillus sphaericus-loaded Diaion SP-850 resin by Mustafa Tuzen; Ozgur Dogan Uluozlu; Canan Usta; Mustafa Soylak (pp. 241-246).

The biosorption of copper(II), lead(II), iron(III) and cobalt(II) on Bacillus sphaericus-loaded Diaion SP-850 resin for preconcentration–separation of them have been investigated. The sorbed analytes on biosorbent were eluted by using 1molL⁻¹ HCl and analytes were determined by flame atomic absorption spectrometry. The influences of analytical parameters including amounts of pH, B. sphaericus, sample volume etc. on the quantitative recoveries of analytes were investigated. The effects of alkaline, earth alkaline ions and some metal ions on the retentions of the analytes on the biosorbent were also examined. Separation and preconcentration of Cu, Pb, Fe and Co ions from real samples was achieved quantitatively. The detection limits by 3 sigma for analyte ions were in the range of 0.20–0.75μgL⁻¹ for aqueous samples and in the range of 2.5–9.4ngg⁻¹ for solid samples. The validation of the procedure was performed by the analysis of the certified standard reference materials (NRCC-SLRS 4 Riverine Water, SRM 2711 Montana soil and GBW 07605 Tea). The presented method was applied to the determination of analyte ions in green tea, black tea, cultivated mushroom, boiled wheat, rice and soil samples with successfully results.

Keywords: Bacillus sphaericus; Diaion SP-850; Biosorption; Preconcentration; Trace metal; Atomic absorption spectrometry

Biosorption of copper(II), lead(II), iron(III) and cobalt(II) on Bacillus sphaericus-loaded Diaion SP-850 resin by Mustafa Tuzen; Ozgur Dogan Uluozlu; Canan Usta; Mustafa Soylak (pp. 241-246).

Keywords: Bacillus sphaericus; Diaion SP-850; Biosorption; Preconcentration; Trace metal; Atomic absorption spectrometry

Microwave-assisted extraction of rare earth elements from petroleum refining catalysts and ambient fine aerosols prior to inductively coupled plasma-mass spectrometry by Pranav Kulkarni; Shankararaman Chellam; David W. Mittlefehldt (pp. 247-259).

A robust microwave-assisted acid digestion procedure followed by inductively coupled plasma-mass spectrometry (ICP-MS) was developed to quantify rare earth elements (REEs) in fluidized-bed catalytic cracking (FCC) catalysts and atmospheric fine particulate matter (PM_2.5). High temperature (200°C), high pressure (200psig), acid digestion (HNO₃, HF and H₃BO₃) with 20min dwell time effectively solubilized REEs from six fresh catalysts, a spent catalyst and PM_2.5. This method was also employed to measure 27 non-REEs including Na, Mg, Al, Si, K, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, As, Se, Rb, Sr, Zr, Mo, Cd, Cs, Ba, Pb and U. Complete extraction of several REEs (Y, La, Ce, Pr, Nd, Tb, Dy and Er) required HF indicating that they were closely associated with the aluminosilicate structure of the zeolite FCC catalysts. Internal standardization using¹¹⁵In quantitatively corrected non-spectral interferences in the catalyst digestate matrix. Inter-laboratory comparison using ICP-optical emission spectroscopy (ICP-OES) and instrumental neutron activation analysis (INAA) demonstrated the applicability of the newly developed analytical method for accurate analysis of REEs in FCC catalysts. The method developed for FCC catalysts was also successfully implemented to measure trace to ultra-trace concentrations of La, Ce, Pr, Nd, Sm, Gd, Eu and Dy in ambient PM_2.5 in an industrial area of Houston, TX.

Keywords: Microwave digestion; Fluidized-bed catalytic cracking (FCC) catalysts; Inductively coupled plasma-mass spectrometry (ICP-MS); Instrumental neutron activation analysis (INAA); Rare earth elements; Lanthanides; Particulate matter (PM; _2.5; )

Determination of photoformation rates and scavenging rate constants of hydroxyl radicals in natural waters using an automatic light irradiation and injection system by Nobutake Nakatani; Norichika Hashimoto; Hirotaka Shindo; Masatoshi Yamamoto; Megumi Kikkawa; Hiroshi Sakugawa (pp. 260-267).

Photoformation rates and scavenging rate constants of hydroxyl radicals (OH) in natural water samples were determined by an automatic determination system. After addition of benzene as a chemical probe to a water sample in a reaction cell, light irradiation and injection of irradiated water samples into an HPLC as a function of time were performed automatically. Phenol produced by the reaction betweenOH and the benzene added to the water sample was determined to quantify theOH formation rate. The rate constants ofOH formation from the photolysis of nitrate ions, nitrite ions and hydrogen peroxide were comparable with those obtained in previous studies. The percent of expectedOH photoformation rate from added nitrate ion were high in drinking water (97.4%) and river water (99.3%). On the other hand, the low percent (65.0%) was observed in seawater due to the reaction ofOH with the high concentrations of chloride and bromide ions. For the automatic system, the coefficient of variance for the determination of theOH formation rate was less than 5.0%, which is smaller than that in the previous report. When the complete time sequence of analytical cycle was 40min for one sample, the detection limit of the photoformation rate and the sample throughput were 8×10⁻¹³Ms⁻¹ and 20 samples per day, respectively. The automatic system successfully determined the photoformation rates and scavenging rate constants ofOH in commercial drinking water and the major source and sink ofOH were identified as nitrate and bicarbonate ions, respectively.

Keywords: Automatic determination system; Hydroxyl radical; Natural water; Photoformation rate; Scavenging rate constant; Source and sink

An integrated procedure of selective injection, sample stacking and fractionation of phosphopeptides for MALDI MS analysis by Haixia Zhang; Graeme K. Hunter; Harvey A. Goldberg; Gilles A. Lajoie; Ken K.-C. Yeung (pp. 268-280).

Protein phosphorylation is one of the most important post-translational modifications (PTM), however, the detection of phosphorylation in proteins using mass spectrometry (MS) remains challenging. This is because many phosphorylated proteins are only present in low abundance, and the ionization of the phosphorylated components in MS is very inefficient compared to the non-phosphorylated counterparts. Recently, we have reported a selective injection technique that can separate phosphopeptides from non-phosphorylated peptides due to the differences in their isoelectric points (p I) [1]. Phosphorylated peptides from α-casein were clearly observed at low femtomole level using MALDI MS. In this work, further developments on selective injection of phosphopeptides are presented to enhance its capability in handling higher sample complexity. The approach is to integrate selective injection with a sample stacking technique used in capillary electrophoresis to enrich the sample concentration, followed by electrophoresis to fractionate the components in preparation for MALDI MS analysis. The effectiveness of the selective injection and stacking was evaluated quantitatively using a synthetic phosphopeptide as sample, with an enrichment factor of up to 600 being recorded. Next, a tryptic digest of α-casein was used to evaluate the separation and fractionation of peptides for MALDI MS analysis. The elution order of phosphopeptides essentially followed the order of decreasing number of phosphates on the peptides. Finally, to illustrate the applicability, the integrated procedure was applied to evaluate the phosphorylation of a highly phosphorylated protein, osteopontin. Up to 41 phosphopeptides were observed, which allowed us to examine the phosphorylation of all 29 possible sites previously reported [2]. A high level of heterogeneity in the phosphorylation of OPN was evident by the multiple-forms of variable phosphorylation detected for a large number of peptides.

Keywords: Protein phosphorylation; Phosphopeptide purification; Peptide enrichment; Sample stacking; Capillary electrophoresis; MALDI MS

Molar mass of main-chain bile acid-based oligo-esters measured by SEC, MALDI-TOF spectrometry and NMR spectroscopy: A comparative study by Julien E. Gautrot; X.X. Zhu (pp. 281-286).

Bile acid-based polymers are promising new materials for biomedical applications. The determination of their molar mass, as for other novel polymers, has been difficult, due to the lack of suitable standards for size exclusion chromatography (SEC). In order to solve this problem, a family of main-chain bile acid-based oligo-esters has been synthesized by acyclic diene metathesis to be used as analogues in such analysis. These oligomers have been characterized by SEC, MALDI-TOF mass spectrometry and NMR spectroscopy. The results show that SEC with polystyrene standards tends to overestimate the molar mass of these materials and that a correction factor between 0.50 and 0.60 should be used for more accuracy.

Keywords: Chromatography; Bile acids; Biodegradable; Polymers

Molar mass of main-chain bile acid-based oligo-esters measured by SEC, MALDI-TOF spectrometry and NMR spectroscopy: A comparative study by Julien E. Gautrot; X.X. Zhu (pp. 281-286).

Keywords: Chromatography; Bile acids; Biodegradable; Polymers

Development and validation of a liquid chromatographic method for the determination of hydroxymethylfurfural and alpha-ketoglutaric acid in human plasma by K. Michail; H. Juan; A. Maier; V. Matzi; J. Greilberger; R. Wintersteiger (pp. 287-297).

Hydroxymethylfurfural (HMF) and alpha-ketoglutaric acid (KG) have been recently investigated as potential cancer cell damaging agents. We herein report for the first time a validated quantitative assay for their simultaneous determination in human plasma which is amenable to be applied in the future screening of the target compounds in human probands in order to properly design a targeted chemotherapeutic regimen for certain types of malignant tumors.A simple liquid chromatographic method in conjunction to derivatization after a two-step optimized solid phase clean-up procedure is described. The method is based on the reaction of HMF and KG with 2-nitrophenylhydrazine or 2,4-dinitrophenylhydrazine in an aqueous environment. Reaction conditions were studied with respect to pH, reagent volume, reaction temperature and time. Exact testing of such parameters beside careful selection of the mobile phase composition rendered feasible the quantification of the chemically significantly differing analytes along a single chromatographic run. The formed derivatives could be separated isocratically by reversed-phase LC on a C₈-column. Detection in the UV and in the visible range is possible. Results showed good recovery and reproducibility with detection limits ( S/ N=3) down to 2 picomoles analyte on column. Resolution of the syn and anti geometric isomers of the HMF and KG derivatives is possible. The isomeric ratio in relation to the reaction pH is discussed.

Keywords: High-performance liquid chromatography (HPLC); Derivatization; Hydroxymethylfurfural and alpha-ketoglutaric acid; 2-Nitrophenylhydrazine; 2,4-Dinitrophenylhydrazine; Plasma

An effective method for fast determination of artemisinin in Artemisia annua L. by high performance liquid chromatography with evaporative light scattering detection by Chun-Zhao Liu; Hua-Ying Zhou; Yan Zhao (pp. 298-302).

Artemisinin isolated from the aerial parts of Artemisia annua L., is a promising and potent antimalarial drug, which meets the dual challenge posed by drug-resistant parasites and rapid progression of malarial illness. The aim of the current study was to develop a reliable and fast analytical procedure for the determination of artemisinin in A. annua using high performance liquid chromatography (HPLC) with evaporative light scattering detection (ELSD) in couple with microwave-assisted extraction (MAE) as an efficient sample preparation technique. The HPLC conditions were Agilent C18 column using water:acetonitrile (40:60 v/v) mixture as mobile phase at a flow rate of 1mLmin⁻¹. ELSD conditions were optimized at nebulizer-gas flow rate of 2.0Lmin⁻¹ and drift tube temperature of 70°C under the impactor off-mode, and the gain was set at 2. Afterwards, method validation system for HPLC–ELSD analysis was developed. Calibration range was 0.2–1.0mgmL⁻¹ and correlation coefficient r was above 0.9990. Precision experiments showed relative standard deviation (R.S.D.) of retention time was less than 0.5% and R.S.D. of peak area was less than 1.30%. Inter-day and intra-day variabilities showed that R.S.D. was ranged from 1.01% to 4.66%. Limit of detection was less than 40μgmL⁻¹ and limit of quantification was less than 100μgmL⁻¹. Accuracy validation showed that average recovery was between 98.23% and 104.97%. The developed analytical procedure was successfully applied to determine the contents of artemisinin in the different parts of A. annua plants.

Keywords: Evaporative light scattering detection; High performance liquid chromatography; Microwave-assisted extraction; Artemisinin; Artemisia annua; L

Laser-induced breakdown spectroscopy in analysis of Al³⁺ liquid droplets: On-line preconcentration by use of flow-injection manifold by Jer-Shing Huang; Hsiao-Tsui Liu; King-Chuen Lin (pp. 303-308).

Laser-induced breakdown spectroscopy (LIBS), combined with a flow-injection system, is demonstrated to analyze liquid droplets of aluminum salt, as generated with an electrospray ionization device. The spray needle also serves as the anode, through which the analyte solution is spread toward the other metal base as the cathode. Along the passage of the FI manifold, the Al-sample loading speed is controlled at 0.15mLmin⁻¹, restricted to the small diameter of the spray needle, and the loading volume amounts to 0.1mL. The metal ion is retained in a cation-exchange resin microcolumn immobilized with Chromotrope 2B chelating agent, followed by elution with a 0.5M HCl solution into LIBS. Upon laser irradiation at the preconcentrated liquid droplets, the time-resolved laser-induced breakdown (LIB) emission and plasma-induced current signals are acquired concurrently on a single-shot basis. The area under the LIB/current distribution increases in linear proportion as the concentration of the sample solution increases. The detection limit thus obtained can reach 1.5mgL⁻¹, about an order of magnitude lower than those achieved previously using single-laser ablation without involvement of preconcentration. The linear dynamic range is more than two orders of magnitude.

Keywords: Laser-induced breakdown spectroscopy; Preconcentration; Flow-injection: Liquid analysis

Quantitative detection of aqueous arsenic and other oxoanions using attenuated total reflectance infrared spectroscopy utilizing iron oxide coated internal reflection elements to enhance the limits of detection by B. McAuley; S.E. Cabaniss (pp. 309-317).

An attenuated total reflectance Fourier transform infrared spectroscopy technique has been developed utilizing an oxide coated internal reflection element to quantitatively evaluate the concentrations of three inorganic oxoanions, arsenate, sulfate, and selenate, at environmentally significant levels. Two iron oxide coatings, goethite and an iron sol–gel, were used and compared to an uncoated internal reflection element which typically has a limit of detection around 1.0mM. The goethite coating improved the limits of detection by factors of 45.6 and 137.0 for arsenate and sulfate as compared to an uncoated cell. The iron sol coating improved the limits of detection by factors of 481.2, 156.2, and 114.0 for arsenate, sulfate, and selenate, respectively.

Keywords: Atennuated total reflectance; Infrared spectroscopy; Iron; Arsenate; Selenate; Sulfate

Determination of low analyte concentrations by near-infrared spectroscopy: Effect of spectral pretreatments and estimation of multivariate detection limits by Marcel Blanco; Miguel Castillo; Antonio Peinado; Rafael Beneyto (pp. 318-323).

Near infrared spectroscopy (NIRS) was used in combination with partial least squares (PLS) calibration to determine low concentrated analytes. The effect of the orthogonal signal correction (OSC) and net analyte signal (NAS) pretreatments on the models obtained at concentrations of analyte near its detection limit was studied. Both pretreatments were found to accurately resolve the analyte signal and allow the construction of PLS models from a reduced number of factors; however, they provided no substantial advantage in terms of %RSE for the prediction samples. Multiple methodologies for the estimation of detection limits could be found in the bibliography. Nevertheless, detection limits were determined by a multivariate method based on the sample-specific standard error for PLS regression, and compared with the univariate method endorsed by ISO 11483. The two methods gave similar results, both being effective for the intended purpose of estimating detection limits for PLS models. Although OSC and NAS allow isolating the analyte signal from the matrix signal, they provide no substantial improvement in terms of detection limits. The proposed method was used to the determine 2-ethylhexanol at concentrations from 20 to 1600ppm in an industrial ester. The detection limit obtained, round 100ppm, testifies to the ability of NIR spectroscopy to detect low concentrated analytes.

Keywords: Near infrared spectroscopy; Detection limit; Orthogonal signal correction; Net analyte signal; Low concentration analytes

How to construct a multiple regression model for data with missing elements and outlying objects by Ivana Stanimirova; Sven Serneels; Pierre J. Van Espen; Beata Walczak (pp. 324-332).

The aim of this study is to show the usefulness of robust multiple regression techniques implemented in the expectation maximization framework in order to model successfully data containing missing elements and outlying objects. In particular, results from a comparative study of partial least squares and partial robust M-regression models implemented in the expectation maximization algorithm are presented. The performances of the proposed approaches are illustrated on simulated data with and without outliers, containing different percentages of missing elements and on a real data set. The obtained results suggest that the proposed methodology can be used for constructing satisfactory regression models in terms of their trimmed root mean squared errors.

Keywords: Modelling; Chemometrics; Robust regression; Outliers; Missing data; Partial least squares (PLS); Partial robust M-regression (PRM)

How to construct a multiple regression model for data with missing elements and outlying objects by Ivana Stanimirova; Sven Serneels; Pierre J. Van Espen; Beata Walczak (pp. 324-332).

Keywords: Modelling; Chemometrics; Robust regression; Outliers; Missing data; Partial least squares (PLS); Partial robust M-regression (PRM)

Structure–activity relationship study of oxindole-based inhibitors of cyclin-dependent kinases based on least-squares support vector machines by Jiazhong Li; Huanxiang Liu; Xiaojun Yao; Mancang Liu; Zhide Hu; Botao Fan (pp. 333-342).

The least-squares support vector machines (LS-SVMs), as an effective modified algorithm of support vector machine, was used to build structure–activity relationship (SAR) models to classify the oxindole-based inhibitors of cyclin-dependent kinases (CDKs) based on their activity. Each compound was depicted by the structural descriptors that encode constitutional, topological, geometrical, electrostatic and quantum-chemical features. The forward-step-wise linear discriminate analysis method was used to search the descriptor space and select the structural descriptors responsible for activity. The linear discriminant analysis (LDA) and nonlinear LS-SVMs method were employed to build classification models, and the best results were obtained by the LS-SVMs method with prediction accuracy of 100% on the test set and 90.91% for CDK1 and CDK2, respectively, as well as that of LDA models 95.45% and 86.36%. This paper provides an effective method to screen CDKs inhibitors.

Keywords: Structure–activity relationship (SAR); Cyclin-dependent kinases (CDKs); Inhibitor; Linear discriminant analysis (LDA); Least-squares support vector machines (LS-SVMs); Oxindole

Modelling of analytical peaks by S.V. Romanenko; A.G. Stromberg (pp. 343-354).

The basic principles of symmetric peaks modifications are considered in this work. Four types of modifications—two symmetric and two asymmetric are considered in detail. Double sequent peak modification was taken as example. The dependences of peak shape parameters on modification parameters were obtained for considered examples of modifications of three basic peaks. The methods of obtaining of common sequent modifications and techniques of suitable result function choice for adequate description of analytical signal series are developed. The approximation of groups of stripping voltammetry and chromatographic peaks with some single, double and triple modifications of elementary peaks has been get. The appreciable increasing of adequacy in description of more complicated modifications was shown.

Keywords: Chemometrics; Analytical peak modelling

Modelling of analytical peaks by S.V. Romanenko; A.G. Stromberg (pp. 343-354).

Keywords: Chemometrics; Analytical peak modelling

Nonionic surfactant-selective electrode and its application for determination in real solutions by Milan Sak-Bosnar; Dubravka Madunic-Cacic; Ruzica Matesic-Puac; Zorana Grabaric (pp. 355-363).

A liquid membrane nonionic surfactant sensitive electrode has been prepared, based on a new barium pseudocationic complex of a highly ethoxylated fatty alcohol polyglycol ether and tetraphenylborate as sensing material. The complex has been incorporated into the plasticized PVC-membrane and used as sensing material.The electrode exhibited positive linear non-Nernstian response toward different nonionic surfactants and sub-Nernstian response toward tetraphenylborate with the lower detection limit of 3.3×10⁻⁷moldm⁻³ in barium chloride solution.The interfering effect of some alkaline, alkaline earth, and heavy metal cations, has been demonstrated by displaying their calibration curves compared with that of Triton X-100.The electrode has been used as an end-point indicator for potentiometric titration of analytical and technical grade polyethoxylated nonionic surfactants, modelled detergent products, and commercial detergents.

Keywords: Surfactant electrode; Poly(vinyl chloride) membrane; Polyethoxylated nonionic surfactant; Potentiometric titration; Detergent products

Nonionic surfactant-selective electrode and its application for determination in real solutions by Milan Sak-Bosnar; Dubravka Madunic-Cacic; Ruzica Matesic-Puac; Zorana Grabaric (pp. 355-363).

Keywords: Surfactant electrode; Poly(vinyl chloride) membrane; Polyethoxylated nonionic surfactant; Potentiometric titration; Detergent products

An electrochemical on-field sensor system for the detection of compost maturity by Miyuki Chikae; Kagan Kerman; Naoki Nagatani; Yuzuru Takamura; Eiichi Tamiya (pp. 364-369).

A maturity sensor system was developed, based on the combination of three electrically measured parameters, pH, NH₄⁺ concentration, and phosphatase activity in the water extracts of compost samples. One of these parameters, the apparent phosphatase activity in crude test solutions was determined using screen-printed carbon strips (SPCSs) coated with α-naphthyl phosphate (α-NP) in Nafion film. The phosphatase activity was monitored in connection with differential pulse voltammetry (DPV) with an aliquot (30μL) of the test solution on SPCS. The phosphatase activity sensor was validated using alkaline phosphatase (ALP) in Tris–HCl buffer (pH 8.0) and acid phosphatase (ACP) in citric acid buffer (pH 5.0). The activity of the spiked enzymes in the water extract of the compost sample could be confirmed with the change of corresponding oxidation peak current signal of the product, α-naphthol. The water extracts of compost samples ( n=24) collected in various composting days were applied to our compost maturity sensor system, and the conventional germination tests. Using multiple regression analysis, the germination index (GI) was expressed by the multi-linear regression equation consisting of pH, NH₄⁺ concentration, and the phosphatase activity. The calculated GI from the regression equation had a good correlation with the measured GI of the corresponding composts ( r=0.873). As a result, we have determined an equation for the determination of the compost stability using our portable sensor system rapidly at the composting site.

Keywords: Compost; Maturity; Phosphatase activity; Germination index (GI); Screen-printed carbon electrode

An electrochemical on-field sensor system for the detection of compost maturity by Miyuki Chikae; Kagan Kerman; Naoki Nagatani; Yuzuru Takamura; Eiichi Tamiya (pp. 364-369).

Keywords: Compost; Maturity; Phosphatase activity; Germination index (GI); Screen-printed carbon electrode

Optimization of an analytical method for determining organotin compounds in fish tissue by base-hydrolysis pretreatment and simultaneous ethylation–extraction procedures by Chuan-Ho Tang; Wei-Hsien Wang (pp. 370-376).

To determine butyl- and phenyl-tins in fish muscle, a method including base digestion pretreatment, followed by a simultaneous ethylation–extraction procedure and gas chromatograph-flame photometric detector (GC-FPD) analysis is outlined. Key parameters that influence analyte recovery were investigated and optimized. A solution of 3% (w/v) potassium hydroxide (KOH) and 1h digestion time at 60°C were chosen in the base digestion step, to ensure complete solubilization of fish muscle and the decomposition of organotins was found to be insignificant. We found that the ratio of fish muscle/reaction solution should not exceed 0.2g (dry weight) per 100mL in order to avoid the matrix effect caused by the binding of hydrolyzed fish tissue with organotin ions. Ethylation of organotins were conducted at pH 6–7 with a 1% (w/v) sodium tetraethylborate (NaBEt₄) solution for 1h. This simple and timesaving procedure should be able to be applied to the routine analysis of organotins in other bio-tissues.

Keywords: Organotin compound; Ethylation; Matrix effect; Base-hydrolysis

A stereochemical examination of the equine metabolism of 17α-methyltestosterone by Andrew R. McKinney; Craig J. Suann; Allen M. Stenhouse (pp. 377-387).

An investigation was conducted into the stereochemistry of the equine urinary metabolites of 17α-methyltestosterone observed after oral administration. Standards of the complete range of C3/C5/C16 stereoisomeric 17α-methylandrostane-3,17β-diols, 17α-methylandrostane-3,16,17β-triols and 17α-hydroxymethylandrostane-3,17β-diols were purchased or synthesised, and were used to unequivocally identify the absolute structures of the metabolites. Phase I metabolism was found to involve combinations of Δ⁴-3-ketone reduction with both 5α,3β- and 5β,3α-stereochemistry, hydroxylation at C16 with both 16α- and 16β-stereochemistry and hydroxylation of the 17α-methyl substituent. Phase II metabolism involved mainly sulfation with a lesser degree of β-glucuronidation.

Keywords: 17α-Methyltestosterone; 17-Methylandrostane-3,17-diol; 17-Methylandrostane-3,16,17-triol; 17-Hydroxymethylandrostane-3,17-diol; 17-Methylandrostane-3,17,20-triol; Anabolic-androgenic steroid; Horse; Stereochemistry; GC–MS

A stereochemical examination of the equine metabolism of 17α-methyltestosterone by Andrew R. McKinney; Craig J. Suann; Allen M. Stenhouse (pp. 377-387).

Erratum to “Risk assessment, remedial decisions and the challenge to protect public health: The perchlorate case study�? [Anal. Chim. Acta 567 (2006) 13–19] by C. Baier-Anderson (pp. 388-388).

Erratum to “Risk assessment, remedial decisions and the challenge to protect public health: The perchlorate case study” [Anal. Chim. Acta 567 (2006) 13–19] by C. Baier-Anderson (pp. 388-388).

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Analytica Chimica Acta (v.581, #2)