Analytica Chimica Acta (v.605, #1)

Contents (v-vi).

In this work, a novel sol–gel coating of N-(2-aminoethyl)-3-aminopropyltrimethoxysilane (AAPTS)-silica was prepared for capillary microextraction (CME) of trace Cu, Zn, Ni, Hg and Cd followed by on-line ICP-MS detection. This organic–inorganic hybrid coating was in situ created on the inner walls of fused silica capillary using a sol solution containing tetramethoxysilane (TMOS) as a precursor, AAPTS as a co-precursor, ethanol as the solvent and cetyltrimethylammonium bromide (CTAB) as the template. The structure of the capillary coating was characterized by IR, SEM and TEM. Various experimental parameters affecting capillary microextraction of the target analytes have been investigated carefully, and the optimized extraction conditions were established. It was found that the AAPTS-silica coating with a terminal functional group of –NH–CH2–CH2–NH2 exhibited a high selectivity towards the selected metal ions. With a consumption of 1.0 mL sample solution and 80 μL eluent, the detection limits (3σ) were found to be 1.8, 11.8, 1.1, 3.3 and 1.4 pg mL−1 for Cu, Zn, Ni, Hg and Cd, respectively. A sampling frequency of 14 h−1 and an enrichment factor of 12.5 were obtained under the optimized experimental conditions. The relative standard deviations (RSDs) for the target analytes were less than 3.6% (C  = 1 ng mL−1, n  = 7, sample volume = 1 mL). Two certified reference materials of NIES No.10-c rice flour and BCR-CRM 278 mussel flesh were analyzed to validate the proposed method, and the determined values were in good agreement with the certified values. The developed method had also been applied to the determination of trace target elements in human hair, serum and urine, and the recoveries for the spiked samples were in the range of 89.2–101.8%. The AAPTS-silica coated capillary showed an excellent pH resistance and could be used for more than 120 times without decreasing adsorption efficiency.
Keywords: N-(2-Aminoethyl)-3-aminopropyltrimethoxysilane-silica coating; Capillary microextraction; Inductively coupled plasma mass spectrometry; Cu, Zn, Ni, Hg and Cd; Biological samples;

The reversed-phase high-performance liquid chromatographic (RP-HPLC) behavior of some newly synthesized hydroxythioxanthone derivatives using binary acetonitrile–water mixtures as mobile phase has been examined. First, the variation in the retention time of each molecule as a function of mobile phase properties was studied by Kamlet–Taft solvatochromic equations. Then, the influences of molecular structure of the hydroxythioxanthone derivatives on their retention time in various mobile phase mixtures were investigated by quantitative structure–property relationship (QSPR) analysis. Finally, a unified model containing both the molecular structure parameters and mobile phase properties was developed to describe the chromatographic behavior of the systems studied. Among the solvent properties, polarity/polarizability parameter (π *) and hydrogen-bond basicity (β), and among the solute properties, the most positive local charge (MPC), the sum of positive charges on hydrogen atoms contributing in hydrogen bonding (SPCH) and lipophilicity index (log  P) were identified as controlling factors in the RP-HPLC behavior of hydroxythioxanthone derivatives in actonitrile–water binary solvents.
Keywords: Reversed-phase high-performance liquid chromatography; Hydroxythioxanthones; Acetonitrile–water; Quantitative structure–property relationship/quantitative structure–retention relationship;

Differentiation of opium and poppy straw using capillary electrophoresis and pattern recognition techniques by Raymond G. Reid; David G. Durham; Susanne P. Boyle; Ann S. Low; Jinda Wangboonskul (20-27).
Opium samples from four different locations and poppy straw from different plant varieties have been assayed using micellar capillary electrophoresis incorporating a sweeping technique. Individual alkaloids (morphine, codeine, papaverine, noscapine, thebaine, oripavine, reticuline and narceine) were quantitatively determined in the different samples by a validated capillary electrophoresis method. Unsupervised pattern recognition of the opium samples and the poppy straw samples using hierarchical cluster analysis (HCA) and principal component analysis (PCA), showed distinct clusters. Supervised pattern recognition using soft independent modelling of class analogy (SIMCA) was performed to show individual groupings and allow unknown samples to be classified according to the models built using the CZE assay results.
Keywords: Capillary electrophoresis; Sweeping; Opium; Poppy straw; Quantitative analysis; Hierarchical cluster analysis; Principal component analysis; Soft independent modelling of class analogy;

Preparation and characterization of Prussian blue nanowire array and bioapplication for glucose biosensing by Fengli Qu; Aiwu Shi; Minghui Yang; Jianhui Jiang; Guoli Shen; Ruqin Yu (28-33).
Prussian blue nanowire array (PBNWA) was prepared via electrochemical deposition with polycarbonate membrane template for effective modification of glassy carbon electrode. The PBNWA electrode thus obtained was demonstrated to have high-catalytic activity for the electrochemical reduction of hydrogen peroxide in neutral media. This enabled the PBNWA electrode to show rapid response to H2O2 at a low potential of −0.1 V over a wide range of concentrations from 1 × 10−7  M to 5 × 10−2  M with a high sensitivity of 183 μA mM−1  cm−2. Such a low-working potential also substantially improved the selectivity of the PBNWA electrode against most electroactive species such as ascorbic acid and uric acid in physiological media. A detection limit of 5 × 10−8  M was obtained using the PBNWA electrode for H2O2, which compared favorably with most electroanalysis procedures for H2O2. A biosensor toward glucose was then constructed with the PBNWA electrode as the basic electrode by crosslinking glucose oxidase (GOx). The glucose biosensor allowed rapid, selective and sensitive determination of glucose at −0.1 V. The amperometric response exhibited a linear correlation to glucose concentration through an expanded range from 2 × 10−6  M to 1 × 10−2  M, and the response time and detection limit were determined to be 3 s and 1 μM, respectively.
Keywords: Prussian blue nanowire; Polycarbonate membrane; Nanowire array electrode; Glucose biosensor; Glucose oxidase;

Differential pulse voltammetric determination of methylprednisolone in pharmaceuticals and human biological fluids by Rajendra N. Goyal; Neeta Bachheti; Anuradha Tyagi; Ashish K. Pandey (34-40).
Electrochemical behaviour of methylprednisolone (MP) at the fullerene-C60-modified glassy carbon electrode has been investigated using differential pulse voltammetry. The experimental results suggest that the modified electrode exhibits electrocatalytic effect on the oxidation of MP resulting in a marked enhancement of the peak current response. Under the selected conditions, the oxidation peak current was linearly dependent on the concentration of MP in the range 5.0 nM–1.0 μM with a sensitivity of 0.0107 μA μM−1. The detection limit was estimated to be 5.6 nM. The electrode showed good sensitivity, selectivity, stability and reproducibility. In addition, the developed method was satisfactorily applied to the determination of MP in pharmaceutical formulations and human serum and urine samples without any necessity for sample treatment or time-consuming extraction steps prior to the analysis. GC–MS method was used to cross-validate the results obtained for the quantitative estimation of MP in biological fluids and the results showed ∼2% deviation to those obtained using the proposed method.
Keywords: Methylprednisolone; Fullerene-C60-modified glassy carbon electrode; Differential pulse voltammetry; Pharmaceutical formulations; Human body fluids;

A CPE-HPLC (UV) method was developed for the determination of Sudan (I–IV) dyes, non-ionic surfactant Triton X-100 was used to extract and preconcentrate Sudan dyes from chilli powder prior to their determination by HPLC-UV. The separation and determination of Sudan dyes was then carried out in the HPLC-UV system with isocratic elution, and the detector was set at 500 nm. The parameters and variables that affect the extraction were investigated. Under optimum conditions: 3% of Triton X-100 (W/V), 10% of Na2CO3 (W/V), heat-assisted at 70 °C for 30 min. Recoveries of the Sudan dyes ranged from 80.70% to 85.45% in chilli powder by CPE method, with all the relative standard deviations of less than 3%. Limit of detection (LOD) and limit of quantification (LOQ) were in the range of 2.0–4.0 and 7.0–12.0 μg kg−1 in chilli powder, respectively.
Keywords: Cloud point extraction; Sudan dyes; High performance liquid chromatography; Chilli powder;

Protons on water molecules are strongly affected by paramagnetic ions. Since the acid–base properties of water facilitate rapid proton exchange, a single proton nuclear magnetic resonance (NMR) signal is seen in aqueous solutions of paramagnetic ions. Proton relaxation times are significantly affected by paramagnetic species and the readily detectable single signal serves as a powerful amplifier of the information contained concerning the protons in the paramagnetic environment. Where water molecules coordinated to free paramagnetic ions and to metal complexes of ligands that form non-labile (on the NMR time scale) complexes, the effects on water in the two environments can be distinguished. This can provide information on the nature of the ligand binding sites. The example of Cu2+ bound to the Laurentian humic acid mixture reported here using convenient low field NMR relaxometers shows that the information can enrich our understanding of complexation and speciation in the presence of complex mixture ligands characteristic of natural water systems. In this case, the data underline the role of aggregation and conformation in defining the complexation sites.
Keywords: Nuclear magnetic resonance; Relaxometry; Humic acid; Copper complexation; Humic complexes;

Development of a new method for the enantiomer specific determination of HBCD using an ion trap mass spectrometer by Belén Gómara; Rosa Lebrón-Aguilar; Jesús Eduardo Quintanilla-López; María José González (53-60).
An alternative method for the enantiomer specific determination of hexabromocyclododecanes (HBCD) by LC–ESI-MS/MS using an ion trap analyser is proposed. The method is based on the formation of a chlorine adduct (m/z 676.6) of the (±)α-, (±)β-, and (±)γ-HBCD enantiomers and their further fragmentation into their stable quasi-molecular ion (m/z 640.6). In this way, problems related to the ion trap low mass cutoff and variable amounts of other adduct peaks in the samples are solved. Parameters affecting separation, ionisation and MS/MS detection were studied. Method performance was also evaluated: calibration curves were found linear from 20 to 400 pg μL−1 for each enantiomer; detection limits ranged between 1.5 and 4.3 pg μL−1; repeatability and reproducibility, expressed as relative standard deviation, were lower than 6% and 13%, respectively. The application to different types of spiked samples (pork meat, lean fish, and butter) pointed out the occurrence of matrix effects that could be solved by using labelled standards.
Keywords: Hexabromocyclododecane; Liquid chromatography; Tandem mass spectrometry; Enantioselective method;

Carboxylic acid functional group analysis using constant neutral loss scanning-mass spectrometry by Julien Dron; Gregory Eyglunent; Brice Temime-Roussel; Nicolas Marchand; Henri Wortham (61-69).
The present study describes the development of a new analytical technique for the functional group determination of the carboxylic moiety using atmospheric pressure chemical ionization-mass spectrometry (APCI-MS/MS) operated in the constant neutral loss scanning (CNLS) mode. Carboxylic groups were first derivatized into their corresponding methyl esters by reacting with BF3/methanol mix and the reaction mixture was then directly injected into the APCI chamber. The loss of methanol (m/z  = 32 amu) resulting from the fragmentation of the protonated methyl esters was then monitored. Applying this method together with a statistical approach to reference mixtures containing 31 different carboxylic acids at randomly calculated concentrations demonstrated its suitability for quantitative functional group measurements with relative standard deviations below 15% and a detection limit of 0.005 mmol L−1. Its applicability to environmental matrices was also shown through the determination of carboxylic acid concentrations inside atmospheric aerosol samples. To the best of our knowledge, it is the first time that the tandem mass spectrometry was successfully applied to functional group analysis, offering great perspectives in the characterization of complex mixtures which are prevailing in the field of environmental analysis as well as in the understanding of the chemical processes occurring in these matrices.
Keywords: Functional group analysis; Carboxylic acid; Organic aerosol; Neutral loss; Mass spectrometry;

An immunoaffinity tandem mass spectrometry (iMALDI) assay for detection of Francisella tularensis by Jian Jiang; Carol E. Parker; James R. Fuller; Thomas H. Kawula; Christoph H. Borchers (70-79).
Francisella tularensis (F. tularensis) has been designated by the CDC as 1 of the 10 organisms most likely to be engineered for bioterrorism. Symptoms of tularemia in humans are non-specific, thus making the disease difficult to diagnose. If not quickly diagnosed and treated, the disease has a high mortality rate – thus methods for early and specific diagnosis are of critical importance.This immunoaffinity MALDI MS/MS (iMALDI) assay provides unambiguous detection of F. tularensis peptides at attomole levels from peptide solutions, and at low CFU levels from bacteria. The addition of stable-labeled versions of the peptide as internal standards allows absolute quantitation of F. tularensis peptides with a linear dynamic range spanning two orders of magnitude. The ability of mass spectrometry to obtain amino acid sequence data on affinity-captured peptides provides absolute specificity and avoids “false positives” from the non-specific binding. The F. tularensis iMALDI assay has been applied to different samples, such as nasal swabs.This novel quantitative diagnostic F. tularensis iMALDI assay allows the safe, sensitive, and specific detection of F. tularensis. The assay can be easily adapted to other target peptides and therefore has broad application potential in clinical diagnosis of other pathogens and diseases.
Keywords: Francisella tularensis; Immunoaffinity tandem mass spectrometry; Matrix-assisted laser desorption/ionization; Quantitation;

Techniques for rapid screening of uranium in environmental samples are needed, and this study entails the development of surface-enhanced Raman scattering (SERS) for analyzing uranium in aqueous media with improved sensitivity and reproducibility. A new SERS substrate based on (aminomethyl)phosphonic acid (APA)-modified gold nanoparticles was found to give greater than three orders of magnitude SERS enhancement compared with unmodified bare gold nanoparticles. Intensities of uranyl band at about 830 cm−1 were proportional to the concentrations of uranium in solution, especially at relatively low concentrations (<10−5  M). A detection limit of ∼8 × 10−7  M was achieved with a good reproducibility since the measurement was performed directly in dispersed aqueous suspension. Without pretreatment, the technique was successfully employed for detecting uranium in a highly contaminated groundwater with a low pH, high dissolved salts (e.g., nitrate, sulfate, calcium and aluminum) and total organic carbon.
Keywords: Surface-enhanced Raman spectroscopy; Uranium detection; Groundwater; Gold nanoparticles;

An enzyme sensor for the electrochemical detection of the marine toxin okadaic acid (OA) has been developed. The strategy was based on the inhibition of immobilised protein phosphatase (PP2A) by this toxin and the electrochemical measurement of the enzyme activity by the use of appropriate enzyme substrates, electrochemically active after dephosphorylation by the enzyme. Colorimetric inhibition assays have demonstrated the PP2A from human red blood cells to be more sensitive and to provide a wider linear range than the one produced by genetic engineering. Catechyl monophosphate (CMP) and p-aminophenyl phosphate (p-APP) have been tested as enzyme substrates, the former providing higher electrochemical currents at convenient working potentials (+450 mV vs. Ag/AgCl). Biosensors with 19.1 and 5.0 U of immobilised enzyme have been applied to the OA detection. Whereas the 19.1-U biosensor has provided higher electrochemical currents and more reliable determinations, the 5.0-U one has attained a lower 50% inhibition coefficient (IC50) value (22.19 in front of 154.84 μg L−1) and a larger working range (2.69–171.87 in front of 42.97–171.87 μg L−1). The analysis of toxicogenic dinoflagellate extracts with both biosensors and the comparison with the colorimetric assay and liquid chromatography coupled to tandem mass spectrometry (LC–MS/MS) have demonstrated the applicability of the developed electrochemical devices as screening biotools for the assessment of the toxicity of a sample.
Keywords: Okadaic acid (OA); Protein phosphatase 2A (PP2A); Inhibition; Catechyl monophosphate (CMP); Electrochemical biosensor;

Quantitative analysis of total retronecine esters-type pyrrolizidine alkaloids in plant by high performance liquid chromatography by Fang Zhang; Chang-hong Wang; Ai-zhen Xiong; Wan Wang; Li Yang; Christopher J. Branford-White; Zheng-tao Wang; S.W. Annie Bligh (94-101).
Pyrrolizidine alkaloids (PAs) are alkaloids which typically contain a necine (7-hydroxy-1-hydroxymethyl-6,7-dihydro-5H-pyrrolizidine) base unit, and they can be found in one third of the higher plants around the world. They are hepatotoxic, mutagenic and carcinogenic and pose a threat to human health and safety. A specific, quick and sensitive method is therefore needed to detect and quantify the PAs sometimes in trace amount in herbs, tea or food products. Based on high performance liquid chromatography with prior derivatization of the alkaloids using o-chloranil and Ehrlich's reagent, we report an improved method for quantitative analysis of the total amount of retronecine esters-type pyrrolizidine alkaloids (RET-PAs) in a plant extract. The total quantitation of RET-PAs is achieved because of a common colored retronecine marker, a 7-ethoxy-1-ethoxylmethyl retronecine derivative, is produced with all the different RET-PAs during the derivatization reaction. The chemical identity of the common retronecine marker was characterized on-line by positive mode electrospray ionization mass spectrometry and nuclear magnetic resonance spectroscopy. The limit of detection using the improved method is 0.26 nmol mL−1 and the limit of quantitation is 0.79 nmol mL−1. The advantages of this method are much enhanced sensitivity in detection and quantitation, and, no restriction on the choice of RET-PA as a calibration standard. Application of the developed method to the quantitation of total RET esters-type PAs in Senecio scandens from different regions of China is also reported.
Keywords: Retronecine; Pyrrolizidine alkaloids; Dimethylaminobenzaldehyde; High performance liquid chromatography–mass spectrometry; Senecio scandens;

Linear alkylbenzene sulphonates (LAS) and polycyclic aromatics hydrocarbons (PAH) are organic pollutants in sewage sludge which will have to be monitored in the European Union according to the third draft of a future sludge directive. In the present work, an analytical method for the simultaneous extraction of 4 LAS homologues and 16 PAH congeners in sludge from wastewater treatment plants is proposed to improve the routine analysis of these compounds in sludge samples. The method involves sonication assisted extraction, clean-up and preconcentration by solid phase extraction, and determination by high-performance liquid chromatography with ultraviolet diode array (UV-DAD) and fluorescence (FLD) detectors. Average recoveries were 87% for LAS and 76% for PAH, with relative standard deviations below 13%. Limits of quantification of LAS and PAH were in the range from 13 to 56 mg kg−1 and from 80 to 650 μg kg−1, respectively, when using UV-DAD. Limits of quantification of LAS and PAH were in the range 5–18 mg kg−1 and from 1 to 150 μg kg−1, respectively, when using FLD. The applicability of the proposed method was evaluated by the determination of these compounds in sludge from wastewater treatment plants in Seville (South Spain).
Keywords: Linear alkylbenzene sulphonates; Polycyclic aromatic hydrocarbons; Sewage sludge; Sonication-assisted extraction; Liquid chromatography;