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Analytica Chimica Acta (v.616, #1)

Contents (pp. v-vi).

Editorial Board (pp. iii).

Sorbent preconcentration procedures coupled to capillary electrophoresis for environmental and biological applications by Patricia Puig; Francesc Borrull; Marta Calull; Carme Aguilar (pp. 1-18).

Sorbent preconcentration offers good strategies to overcome the poor detection limits of capillary electrophoresis (CE). The present review focuses on the recent trends of the coupling between sorbent preconcentration techniques, namely solid-phase extraction (SPE) and solid-phase microextraction (SPME), to capillary electrophoresis (CE). Special attention is given to their environmental and biological application. We also discuss the most important advantages and disadvantages of the different methodologies and briefly outline the new trends of the coupling between sorbent preconcentration and CE.

Keywords: At-line; Capillary electrophoresis; In-line; Off-line; On-line; Preconcentration technique; Solid-phase extraction; SPE; Solid-phase microextraction; SPME

Fingerprinting of complex mixtures with the use of high performance liquid chromatography, inductively coupled plasma atomic emission spectroscopy and chemometrics by Yongnian Ni; Yunyan Peng; Serge Kokot (pp. 19-27).

The molecular and metal profile fingerprints were obtained from a complex substance, Atractylis chinensis DC—a traditional Chinese medicine (TCM), with the use of the high performance liquid chromatography (HPLC) and inductively coupled plasma atomic emission spectroscopy (ICP-AES) techniques. This substance was used in this work as an example of a complex biological material, which has found application as a TCM. Such TCM samples are traditionally processed by the Bran, Cut, Fried and Swill methods, and were collected from five provinces in China. The data matrices obtained from the two types of analysis produced two principal component biplots, which showed that the HPLC fingerprint data were discriminated on the basis of the methods for processing the raw TCM, while the metal analysis grouped according to the geographical origin. When the two data matrices were combined into a one two-way matrix, the resulting biplot showed a clear separation on the basis of the HPLC fingerprints. Importantly, within each different grouping the objects separated according to their geographical origin, and they ranked approximately in the same order in each group. This result suggested that by using such an approach, it is possible to derive improved characterisation of the complex TCM materials on the basis of the two kinds of analytical data.In addition, two supervised pattern recognition methods, K-nearest neighbors (KNNs) method, and linear discriminant analysis (LDA), were successfully applied to the individual data matrices—thus, supporting the PCA approach.

Keywords: Two-way fingerprint; High performance liquid chromatography; Inductively coupled plasma atomic emission spectroscopy; Complex mixtures; Traditional Chinese medicine (; Atractylis chinensis; DC); Chemometrics

Chemically surface-modified carbon nanoparticle carrier for phenolic pollutants: Extraction and electrochemical determination of benzophenone-3 and triclosan by Lorena Vidal; Alberto Chisvert; Antonio Canals; Elefteria Psillakis; Alexei Lapkin; Fernando Acosta; Karen J. Edler; James A. Holdaway; Frank Marken (pp. 28-35).

Chemically surface-modified (tosyl-functionalized) carbon nanoparticles (Emperor 2000 from Cabot Corp.) are employed for the extraction and electrochemical determination of phenolic impurities such as benzophenone-3 (2-hydroxy-4-methoxybenzophenone) or triclosan (5-chloro-2-(2,4-dichlorophenoxy)phenol). The hydrophilic carbon nanoparticles are readily suspended and separated by centrifugation prior to deposition onto suitable electrode surfaces and voltammetric analysis. Voltammetric peaks provide concentration information over a 10–100μM range and an estimated limit of detection of ca. 10μM (or 2.3ppm) for benzophenone-3 and ca. 20μM (or 5.8ppm) for triclosan.Alternatively, analyte-free carbon nanoparticles immobilized at a graphite or glassy carbon electrode surface and directly immersed in analyte solution bind benzophenone-3 and triclosan (both with an estimated Langmuirian binding constants of K≈6000mol⁻¹dm³ at pH 9.5) and they also give characteristic voltammetric responses (anodic for triclosan and cathodic for benzophenone-3) with a linear range of ca. 1–120μM. The estimated limit of detection is improved to ca.5μM (or 1.2ppm) for benzophenone-3 and ca. 10μM (or 2.3ppm) for triclosan. Surface functionalization is discussed as the key to further improvements in extraction and detection efficiency.

Keywords: Carbon nanoparticle; Voltammetry; Sensor; Extraction; Benzophenone-3; UV filter; Triclosan; Fungicide; Biocide

Development of low-cost metal oxide pH electrodes based on the polymeric precursor method by G.M. da Silva; S.G. Lemos; L.A. Pocrifka; P.D. Marreto; A.V. Rosario; E.C. Pereira (pp. 36-41).

In this work, the polymeric precursor method was used to prepare low-cost solid-state sensors for pH determination based on iridium oxide as the main pH sensitive material. The iridium content was reduced with addition of TiO₂, forming the binary system IrO_x–TiO₂, whose electroanalytical properties were evaluated in comparison with a commercial glass pH electrode. The minimum iridium content which gave suitable results was 30mol%, and the electrode presented Nernstian and fast response in the pH range from 1 to 13, with no hysteresis effect observed. Besides, the electrode showed high selectivity in the presence of alkali ions as Li⁺, Na⁺ or K⁺. The amount of iridium in the prepared electrodes was very small (<0.1mg), supporting the efficiency of this method on the simple preparation of functional low-cost pH electrodes.

Keywords: pH electrode; Metal oxide; Iridium; Titanium; Polymeric precursor method

A novel liquid-phase microextraction method combined with high performance liquid chromatography for analysis of phthalate esters in landfill leachates by Jinrong Yao; Hui Xu; Lili Lv; Dandan Song; Yangfang Cui; Taozhi Zhang; Yu-Qi Feng (pp. 42-48).

A novel liquid-phase microextraction (LPME) method was presented in this paper. The most attractive feature of this method is using a polychloroprene rubber tube (PCR tube) instead of a microsyringe to load organic solvent. The PCR tube and sample vial were horizontally placed so that the selection of organic solvent was not affected by the density of extractant. Therefore, the stability of organic solvent increased and the available organic solvent was extended greatly. In this work, three phthalate esters (PAEs) (dimethyl phthalate (DMP), diethyl phthalate (DEP), and di- n-butyl phthalate (DnBP)) were chosen as model analytes to testify the feasibility of the new method. A series of extraction parameters have been investigated systematically. Under the optimized condition, the method showed linear response over four orders of magnitude, ranged from 0.005mgL⁻¹ to 50mgL⁻¹. The correlation coefficients ( r) were better than 0.997 and the limits of detection (LOD) were 0.0012mgL⁻¹ for DMP, 0.0014mgL⁻¹ for DEP and 0.0022mgL⁻¹ for DnBP. Good reproducibility of extraction was acquired, the inter-day and intra-day relative standard deviation (R.S.D.) were below 7.9% and 7.4%, respectively. Recoveries that ranged from 82.7% to 116.9% were gained when the new method was used to determine three phthalate esters in landfill leachates. The enrichment factors were 5–26 for the three PAEs. The novel LPME is promising to be an alternative sample preparation method for extracting target analytes in complex sample matrices because of the simplicity, low cost and short sample preparation time.

Keywords: Liquid-phase microextraction; High performance liquid chromatography; Phthalate esters; Polychloroprene rubber tube; Landfill leachates

A novel sol–gel-based amino-functionalized fiber for headspace solid-phase microextraction of phenol and chlorophenols from environmental samples by Habib Bagheri; Esmaeil Babanezhad; Faezeh Khalilian (pp. 49-55).

A novel amino-functionalized polymer was synthesized using 3-(trimethoxysilyl) propyl amine (TMSPA) as precursor and hydroxy-terminated polydimethylsiloxane (OH-PDMS) by sol–gel technology and coated on fused-silica fiber. The synthesis was designed in a way to impart polar moiety into the coating network. The scanning electron microscopy (SEM) images of this new coating showed the homogeneity and the porous surface structure of the film. The efficiency of new coating was investigated for headspace solid-phase microextraction (SPME) of some environmentally important chlorophenols from aqueous samples followed by gas chromatography–mass spectrometry (GC–MS) analysis. Effect of different parameters influencing the extraction efficiency such as extraction temperature, extraction time, ionic strength and pH was investigated and optimized. In order to improve the separation efficiency of phenolic compounds on chromatography column all the analytes were derivatized prior to extraction using acetic anhydride at alkaline condition. The detection limits of the method under optimized conditions were in the range of 0.02–0.05ngmL⁻¹. The relative standard deviations (R.S.D.) ( n=6) at a concentration level of 0.5ngmL⁻¹ were obtained between 6.8 and 10%. The calibration curves of chlorophenols showed linearity in the range of 0.5–200ngmL⁻¹. The proposed method was successfully applied to the extraction from spiked tap water samples and relative recoveries were higher than 90% for all the analytes.

Keywords: Solid-phase microextraction; Sol–gel; Chlorophenols; Gas chromatography–mass spectrometry; Water analysis

An improved procedure for flow-based turbidimetric sulphate determination based on a liquid core waveguide and pulsed flows by Wanessa R. Melchert; Fábio R.P. Rocha (pp. 56-62).

An improved flow-based procedure is proposed for turbidimetric sulphate determination in waters. The flow system was designed with solenoid micro-pumps in order to improve mixing conditions and minimize reagent consumption as well as waste generation. Stable baselines were observed in view of the pulsed flow characteristic of the systems designed with solenoid micro-pumps, thus making the use of washing solutions unnecessary. The nucleation process was improved by stopping the flow prior to the measurement, thus avoiding the need of sulphate addition. When a 1-cm optical path flow cell was employed, linear response was achieved within 20–200mgL⁻¹, described by the equation S=−0.0767+0.00438 C (mgL⁻¹), r=0.999. The detection limit was estimated as 3mgL⁻¹ at the 99.7% confidence level and the coefficient of variation was 2.4% ( n=20). The sampling rate was estimated as 33 determinations per hour. A long pathlength (100-cm) flow cell based on a liquid core waveguide was exploited to increase sensitivity in turbidimetry. Baseline drifts were avoided by a periodical washing step with EDTA in alkaline medium. Linear response was observed within 7–16mgL⁻¹, described by the equation S=−0.865+0.132 C (mgL⁻¹), r=0.999. The detection limit was estimated as 150μgL⁻¹ at the 99.7% confidence level and the coefficient of variation was 3.0% ( n=20). The sampling rate was estimated as 25 determinations per hour. The results obtained for freshwater and rain water samples were in agreement with those achieved by batch turbidimetry at the 95% confidence level.

Keywords: Flow analysis; Liquid-core waveguides; Pulsed flows; Solenoid micro-pumps; Sulphate; Turbidimetry

A time-gated fluorescence detector using a tuning fork chopper by Qingyang Li; Purnendu K. Dasgupta; Henryk Temkin (pp. 63-68).

We describe an affordable gated fluorescence detection system to measure fluorescent compounds with long-lifetimes that uses a tuning fork chopper to block the intense excitation pulse from a flash lamp or short-lived fluorescence. A conventional non-gated inexpensive photosensor module is used to collect the luminescence signal. Using the long-lived luminescence from the terbium(III)–dipicolinic acid (DPA) chelate, we demonstrate a limit of detection (LOD) of 120pM for DPA. This system is not only an order of magnitude less expensive than an electronically gateable phototomultiplier tube (GPMT), it exhibits no evidence of gradual loss of sensitivity, due likely to photocathode fatigue and deterioration, observed with a GPMT.

Keywords: Time-gated detection; Lanthanide; Afterpulsing

Surface-enhanced Raman and fluorescence joint analysis of soil humic acids by G. Corrado; S. Sanchez-Cortes; O. Francioso; J.V. Garcia-Ramos (pp. 69-77).

Surface-enhanced Raman scattering (SERS) and surface-enhanced fluorescence (SEF) combined emissions were used in this work to the analysis of humic acids (HA). This study examined HA structure at different pH and HA concentrations and assessed the structural differences taking place in HA as a result of various amendment trials. Raman and fluorescence emissions behave in opposite ways due to the effect of the metal surface on the aromatic groups responsible for these emissions. The information afforded by these techniques can be successfully employed in the structural and dynamic analysis of these important macromolecules. The surface-enhanced emission (SEE) spectra, that is the sum of the Raman and the fluorescence emissions, were acquired by using both macro- and micro-experimental configurations in order to apply imaging and confocal Raman and fluorescence spectroscopy techniques on the analysis of HA.

Keywords: Surface-emhanced Raman Scattering; Surface-enhanced Fluorescence; Humic acids; Spectroscopic imaging

Modifications and insights into a method for the analysis of the nitrogen mustard mechlorethamine by high-performance liquid chromatography by John C. Reepmeyer; Wei Ye; Wolfgang A. Ritschel (pp. 78-84).

Previously, a method was presented for the analysis of mechlorethamine by derivatization of this unstable nitrogen mustard to bis(2-phenylthioethyl)methylamine (PTEMA), a stable compound suitable for analysis by HPLC with UV detection [J.C. Reepmeyer, J. Chromatogr. A, 1085 (2005) 262]. Mechlorethamine HCl served as a reference standard and it was derivatized in situ simultaneously with samples of mechlorethamine HCl in ointment preparations. This paper presents the synthesis of PTEMA on a gram scale, synthesis of its picrate salt, bis(2-phenylthioethyl)methylamine picrate (PTEMAP), and isolation of the picrate as a crystalline solid. PTEMAP may serve as a reference standard replacing the toxic mechlorethamine HCl. Insights into the handling, storage, drying, and hygroscopic properties of mechlorethamine HCl and PTEMAP are discussed. In addition, one step following the derivatization procedure in the original method is recognized as a potential for error, and a procedure relating to the order of addition of reagents is presented to avoid this error. The method has been extended to the analysis of mechlorethamine in aqueous solutions.

Keywords: Nitrogen mustard; Mechlorethamine; Analysis; Derivatization; High-performance liquid chromatography

Reversed-phase liquid chromatographic method with spectrophotometric detection for the determination of antiretroviral drugs by Antonio Checa; Ramon Oliver; Santiago Hernández-Cassou; Javier Saurina (pp. 85-94).

In the present paper, a new chromatographic method for the determination of acquired immune deficiency syndrome (AIDS) drugs in plasma samples is proposed. The method consists of solid-phase extraction for sample pretreatment and further chromatographic analysis. Drugs have been separated on a C₁₈ column using an elution gradient based on an increase in the acetonitrile percentage. Analytes have been detected spectrophotometrically at 240, 250, 260 and 280nm. Chromatographic conditions have been thoroughly optimized using experimental design and multicriteria functions. Analytical parameters of the method have been established for both synthetic and plasma samples. Limits of detection are around 5ngmL⁻¹ for reverse transcriptase inhibitors (nucleoside and non-nucleoside) and 20ngmL⁻¹ for protease inhibitors. The method has been validated through a spiking/recovery procedure at three concentration levels. Results obtained are highly satisfactory, with recovery values around 100% for all drugs. The method has been applied to the determination of various drug mixtures of medical interest in plasma samples.

Keywords: Antiretroviral drugs; Plasma; Reversed-phase liquid chromatography; UV detection; Solid-phase extraction; Validation

Determination of Ni²⁺ using an equilibrium ion exchange technique: Important chemical factors and applicability to environmental samples by Isabelle A.M. Worms; Kevin J. Wilkinson (pp. 95-102).

In natural waters, the determination of free metal concentrations is a key parameter for studying bioavailability. Unfortunately, few analytical tools are available for determining Ni speciation at the low concentrations found in natural waters. In this paper, an ion exchange technique (IET) that employs a Dowex resin is evaluated for its applicability to measure [Ni²⁺] in freshwaters. The presence of major cations ( e.g. Na, Ca and Mg) reduced both the times that were required for equilibration and the partition coefficient to the resin(λ′Ni). IET measurements of [Ni²⁺] in the presence of known ligands (citrate, diglycolate, sulfoxine, oxine and diethyldithiocarbamate) were verified by thermodynamic speciation models (MINEQL⁺ and VisualMINTEQ). Results indicated that the presence of hydrophobic complexes ( e.g. Ni(DDC)₂⁰) lead to an overestimation of the Ni²⁺ fraction. On the other hand, [Ni²⁺] measurements that were made in the presence of amphiphilic complexes formed with humic substances (standard aquatic humic acid (SRHA) and standard aquatic fulvic acid (SRFA)) were well correlated to free ion concentrations that were calculated using a NICA-DONNAN model. An analytical method is also presented here to reduce the complexity of the calibration (due to the presence of many other cations) for the use of Dowex equilibrium ion exchange technique in natural waters.

Keywords: Nickel speciation; Ion exchange; Natural organic matter; Stability constant

Noncontact analysis of the fiber weight per unit area in prepreg by near-infrared spectroscopy by B. Jiang; Y.D. Huang (pp. 103-108).

The fiber weight per unit area in prepreg is an important factor to ensure the quality of the composite products. Near-infrared spectroscopy (NIRS) technology together with a noncontact reflectance sources has been applied for quality analysis of the fiber weight per unit area. The range of the unit area fiber weight was 13.39–14.14mgcm⁻². The regression method was employed by partial least squares (PLS) and principal components regression (PCR). The calibration model was developed by 55 samples to determine the fiber weight per unit area in prepreg. The determination coefficient ( R²), root mean square error of calibration ( RMSEC) and root mean square error of prediction ( RMSEP) were 0.82, 0.092, 0.099, respectively. The predicted values of the fiber weight per unit area in prepreg measured by NIRS technology were comparable to the values obtained by the reference method. For this technology, the noncontact reflectance sources focused directly on the sample with neither previous treatment nor manipulation. The results of the paired t-test revealed that there was no significant difference between the NIR method and the reference method. Besides, the prepreg could be analyzed one time within 20s without sample destruction.

Keywords: Fiber weight per unit area; Near-infrared spectroscopy; Partial least squares; Principal components regression

An enzyme-linked immunosorbent assay for aconitine-type alkaloids using an anti-aconitine monoclonal antibody by Katsumi Kido; Kyoko Edakuni; Osamu Morinaga; Hiroyuki Tanaka; Yukihiro Shoyama (pp. 109-114).

3-Succinylaconitine was conjugated with bovine serum albumin (BSA) for use as an immunogen for the preparation of a monoclonal antibody (MAb) against aconitine (Aco). Splenocytes from mice immunized with the Aco-BSA conjugate were fused with an aminopterin-sensitive mouse myeloma cell line, P3-X63-Ag8-653, and a hybridoma secreting a MAb against Aco was successfully obtained. The MAb cross-reacted with mesaconitine, hypaconitine and jesaconitine, which are Aco-type alkaloids, but not with any other compounds examined. The full measurement range of an enzyme-linked immunosorbent assay (ELISA) developed using the new MAb extended from 100ngmL⁻¹ to 1.5μgmL⁻¹ of Aco. The concentrations of Aco-type alkaloids in various Aconiti radixes assayed using the new ELISA method showed good agreement with previous reports.

Keywords: Aconitine-type alkaloid; Monoclonal antibody; Enzyme-linked immunosorbent assay; Aconiti radix

Ultraviolet absorbance titration for determining stability constants of humic substances with Cu(II) and Hg(II) by Y.C. Bai; F.C. Wu; C.Q. Liu; W. Li; J.Y. Guo; P.Q. Fu; B.S. Xing; J. Zheng (pp. 115-121).

We describe an ultraviolet (UV) absorbance titration method that can be used to determine complexing capacities ( C_L) and conditional stability constants (log K) of humic substances (HSs) with metal ions such as Cu(II) and Hg(II). Two fulvic acids (FA) and one humic acid (HA) were used for this study. UV absorbance of HSs gradually increased with the addition of Cu(II) or Hg(II) after blank correction, and these increases followed the theoretical 1:1 (ligand:metal ion) binding model. The results from the absorbance titration calculation for HSs with Cu(II) and Hg(II) compared well with those from fluorescence quenching titration. The titration of the model compoundl-tyrosine with Cu(II) proved the validity of this method, and the K and C_L were within 2.3% and 7.4% of the fluorescence quenching titration. The results suggest that the UV absorbance titration can be used to study the binding capacities of HSs and/or dissolved organic matter (DOM) with trace metals. The advantages and disadvantages of the absorbance titration method were also discussed.

Keywords: UV absorbance; Fluorescence; Binding; Humic substance; Metal ion

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Analytica Chimica Acta (v.616, #1)