Analytica Chimica Acta (v.527, #2)

Contents (iii-iv).

Analytical chemistry of freshwater humic substances by Suzanne McDonald; Andrea G. Bishop; Paul D. Prenzler; Kevin Robards (105-124).
Dissolved organic carbon (DOC) in aquatic environments represents one of the largest active organic carbon reservoirs in the biosphere. Current ideologies concerning the sources of DOC, how it is formed and utilized, and what determines the quality of DOC are examined. Humic substances can comprise a significant fraction of the DOC and developments in methods of analysis including the isolation and characterization of this fraction are reviewed.
Keywords: Dissolved organic carbon; Freshwater humic substance; Aquatic environment;

Determination of Cr(III) and Cr(VI) in industrial and environmental liquid samples by EDXRF method by Visnja Orescanin; Luka Mikelic; Stipe Lulic; Mirta Rubcic (125-129).
A rapid, sensitive and selective procedure for determination of Cr(III) and Cr(VI) in environmental and industrial liquid samples via preconcentration with ammonium pyrrolidine dithiocarbamate (APDC) and determination by means of the EDXRF was described. The effect of pH in the range of 3–11 on the recovery of Cr(III) and Cr(VI) has been investigated separately and in combination of these two species. The influence of organic matter, carbonate species and elements V, Mn and Fe on the recovery of each chromium specie (separately/in combination) over whole pH range was also tested in order to simulate condition occurring in natural waters that usually contain certain amount of dissolved organic matter and carbonate ions. Cr(VI) and Cr(III) have shown different behaviors in reaction with APDC at different pH ranges and therefore it is possible to separate those two species. It was found that Cr(VI) creates complex with APDC only in the pH range from 3 to 5 with quantitative recovery (app. 98%) at pH 3, but there was no recovery of Cr(III) at that pH. On the contrary, in pH range from 6 to 11, reaction with Cr(III) and APDC reviled that the only reaction product is Cr(OH)3 instead of the expected Cr(III)–APDC complex. All reaction products were characterized by IR spectroscopy.
Keywords: Cr(VI); Cr(III); APDC; EDXRF; Preconcentration; IR spectroscopy;

Highly sensitive colour change system within slight differences in metal ion concentrations based on homo–binuclear complex formation equilibrium for visual threshold detection of trace metal ions by Hitoshi Mizuguchi; Hiroshi Atsumi; Keigo Hashimoto; Yasuhiro Shimada; Yuki Kudo; Masatoshi Endo; Fumihiko Yokota; Junichi Shida; Takao Yotsuyanagi (131-138).
A new technique of expressing slight differences in metal ion concentrations by clear difference in colour was established for visual threshold detection of trace metal ions. The proposed method is based on rapid change of the mole fraction of the homo–binuclear complex (M2L) about a ligand in a narrow range of the total metal ion concentration (M T) in a small excess, in case the second metal ion is bound to the reagent molecule which can bind two metal ions. Theoretical simulations showed that the highly sensitive colour change within slight differences in metal ion concentrations would be realized under the following conditions: (i) both of the stepwise formation constants of complex species are sufficiently large; (ii) the stepwise formation constant of the 1:1 complex (ML) is larger than that of M2L; and (iii) the absorption spectrum of M2L is far apart from the other species in the visible region. Furthermore, the boundary of the colour region in M T would be readily controlled by the total ligand concentration (L T). Based on this theory, the proposed model was verified with the 3,3′-bis[bis(carboxymethyl)amino]methyl derivatives of sulphonephthalein dyes such as xylenol orange (XO), methylthymol blue (MTB), and methylxylenol blue (MXB), which can bind two metal ions at both ends of a π-electron conjugated system. The above-mentioned model was proved with the iron(III)–XO system at pH 2. In addition, MTB and MXB were suitable reagents for the visual threshold detection of trivalent metal ions such as iron(III), aluminium(III), gallium(III) and indium(III) ion in slightly acidic media. The proposed method has been applied successfully as a screening test for aluminium(III) ion in river water sampled at the downstream area of an old mine.
Keywords: Highly sensitive colour change; Homo–binuclear complex; Slight differences in metal ion concentrations; Visual threshold detection; XO analogues;

Use of polystyrene nanoparticles to enhance enantiomeric separation of propranolol by capillary electrophoresis with Hp-beta-CD as chiral selector by Na Na; Yuping Hu; Jin Ouyang; Willy R.G. Baeyens; Joris R. Delanghe; Thomas De Beer (139-147).
We describe the use of polystyrene (PS) nanoparticles to manipulate chiral selectivity of propranolol analysis by capillary electrophoresis, by dispersing PS nanoparticles into the run buffer employing hydroxypropyl-β-cyclodextrin (HP-β-CD) as chiral selector. Distinct separational differences are observed between the buffer containing PS nanoparticles and buffer without, when changing separating conditions including PS nanoparticles concentration, pH, buffer concentration, HP-β-CD concentration and when adding an organic additive. Selectivity improvements are reflected by changes in the observed mobility as a result of interactions between the propranolol enantiomers and HP-β-CD governing the absorption process on the PS particles surface. The presence of PS nanoparticles increases the enantioseparation at low particle concentration in the presence of HP-β-CD as a chiral selector.
Keywords: Polystyrene nanoparticles; Capillary electrophoresis; Enantiomer separation; Propranolol;

Determination of psilocin in magic mushrooms and rat plasma by liquid chromatography with fluorimetry and electrospray ionization mass spectrometry by Kimie Saito; Toshimasa Toyo’oka; Takeshi Fukushima; Masaru Kato; Osamu Shirota; Yukihiro Goda (149-156).
The sensitive determination of psilocin was carried out by reversed-phase liquid chromatography (HPLC) coupled with fluorimetry (FL) and electrospray ionization mass spectrometry (ESI–MS). Psilocin and bufotenine, used as an internal standard (IS), were labeled with excess amounts of 4-(N,N-dimethylaminosulfonyl)-7-(2-chloroformylpyrrolidin-1-yl)-2,1,3-benzoxadiazole (DBD-Pro-COCl) at 60 °C for 10 min in the presence of pyridine as the scavenger of HCl produced in the solution. The resulting derivatives were separated by a Mightysil RP-18 GP column (150 mm × 4.6 mm, i.d., 3 μm) with an acidic mobile-phase containing 0.1% trifluoroacetic acid (TFA) and detected at 560 nm (excitation at 440 nm). Under the conditions for derivatization, separation and detection, a good linearity of the calibration curve of psilocin was observed by the HPLC–FL method. On the other hand, the derivative, separated by a Mightysil RP-18 GP (100 mm × 2.0 mm, i.d., 3 μm) using 50 mM AcONH4–CH3CN (73:27), was also determined by HPLC–ESI–MS. The mass spectrometer was operated in the selected-ion monitoring (SIM) mode for the protonated-molecular ion [M + H]+ (m/z = 527). The calibration curve in the SIM mode was also linear in the range of 0.16–4.08 ng psilocin, similar to the HPLC–FL method. The coefficient of variation (CV) was 5.15% (0.16 ng injection, n = 6). The quantitation limit was 0.64 ng/mg dried mushroom. The amounts of psilocin in six magic mushrooms using HPLC–MS were lower than 12.67 ng/mg samples. The developed method was also successfully applied to the determination of psilocin in rat plasma after a single i.p. administration of psilocybin. The proposed method provides good precision and trace detection of psilocin in actual samples, suggesting that these analytical techniques are usable for the determination of psilocin in various specimens.
Keywords: Psilocin; Magic mushroom; Rat plasma; HPLC–FL; HPLC–ESI–MS; Selective-ion monitoring;

A new headspace solid-phase microextraction (HS-SPME) system was designed with a cooling device on the upper part of the sample vial and a heating and ultrasonic activating device for the analysis of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) in soil samples. A 100 μm polydimethylsiloxane (PDMS) fiber was applied to the analysis of all the chloro congeners. In order to improve the extraction efficiency, the soil sample was heated and ultrasonically activated and the fiber coating was cooled by chilled alcohol during the extraction procedure. Gas chromatography/ion-trap tandem mass spectrometry (GC/MS/MS) was then used for the determination of PCDDs/PCDFs with multiple reaction monitoring (MRM). 13C12-labelled PCDDs/PCDFs were used as an internal standard to calibrate the data by calculation of relative response factor (RRF). The detection limits were in the range 2.2–77.2 ng g−1, and the RSDs (%) were less than 15.8% (concentrations in the range 50–250 ng g−1, n  = 7). The solid-phase microextraction method developed was shown to be a fast, efficient and economical technique for the rapid screening of PCDDs/PCDFs in soil samples.
Keywords: Solid-phase microextraction; Polychlorinated dibenzo-p-dioxins; Soil; Ion-trap tandem mass spectrometry;

The extraction of 75 elements by N,N,N′,N′-tetraoctyl-3-oxapentanediamide (TODGA) from nitric acid to n-dodecane was investigated and discussed concerning distribution ratios (D) of metal ions and their ionic radii. The extractability for elements depends strongly on their oxidation state. Monovalent and pentavalent ions were not extractable. In divalent metal extraction, Ca(II) (ionic radius: 100 pm) showed the highest D-value and the D decreased with increase or decrease of the ionic radius. Trivalent and tetravalent ions with ionic radii of 87–113 and 83–94 pm, respectively, showed the D over 1000, and the extracted chemical forms were determined to be M(TODGA)3(NO3) n or M(TODGA)4(NO3) n (n  = 3 or 4). The oxonium ions with higher oxidation states than tetravalent one forms the complicated metal-complex with TODGA, and the number of TODGA associated in those extraction reactions was confirmed to be two at most.
Keywords: TODGA; Extraction; Diamide; Nitric acid; n-Dodecane;

Polymeric membrane sensor for potentiometric determination of vanadyl ions by M. Moghimi; M.A. Bagherinia; M. Arvand; M.A. Zanjanchi (169-175).
In this research, new electrodes were prepared by incorporating a new calix[4]arene derivative into a plasticized poly(vinyl chloride) matrix. Calibration plots with Nernstian slopes (29.9 ± 1.1 mV/decade) for vanadyl ion were observed over a linear range of about four decades of concentration (1.0 × 10−5 to 1.0 × 10−1  mol dm−3, at 25 °C). This electrode revealed a lower limit of detection of 3.9 × 10−6  mol dm−3. Conductometric data showed the relatively strong interaction between calix[4]arene and vanadyl ions. The results show that this electrode can be used in acetonitril and methanol media until 10% (v/v) concentration without interference. It has a short response time and can be used for more than two months without any considerable divergence in the potentials. The influence of membrane composition, the pH of the test solution, and the interfering ions on the electrode performance was investigated. The effect of temperature on the electrode response showed that the temperature higher than 50 °C deteriorates the electrode performance. The isothermal temperature coefficient of this electrode amounted to 0.0015 V °C−1. The results of application show that the electrode can be used successfully in present Cr3+ and Fe3+.
Keywords: Vanadyl ions; Calix[4]arene; Non-aqueous media; Isothermal temperature coefficient;

Theoretical prediction of the chemiluminescence behaviour of the ergot alkaloids by E. Polo Martí; M. Catalá Icardo; L. Lahuerta Zamora; G.M. Antón Fos; J. Martínez Calatayud (177-186).
The present manuscript is dealing with the application of molecular connectivity calculations to predict the chemiluminescent behaviour of ergot alkaloids when they react with common strong oxidants in liquid phase. Twenty compounds were theoretically studied by means of a discriminant equation formerly published, being 19 of them predicted as chemiluminescent with a high probability. Empirical confirmation of the chemiluminometric behaviour is performed with the few soluble and commercially available ergot alkaloids.On the basis of these results, a new FIA-direct chemiluminescent method is proposed for the determination of the ergot presenting the higher light emission, the pharmaceutical ergotamine. The method is based on the oxidation of the drug by K3[Fe(CN)6] in sodium hydroxide medium, at seventy degrees and enhanced by the presence of dioxane. The studied calibration up to 5.0 mg l−1, revealed a linear dynamic graph up to 0.5 mg l−1. The reproducibility between days resulted in a rsd (in slope %) of 8.9 (n, 5) and the repeatability with a %R.S.D. (n = 20) of 1.9 and 0.6 for 0.3 and 4.0 mg l−1, respectively. LOD (s/n = 3) of 6 × 10−7  mg l−1 and sample throughput of 73 h−1. The influence of foreign compounds is also tested and the optimised flow-assembly is applied to other compounds of the ergot alkaloids family.
Keywords: Chemiluminescence; FIA; Ergotamine; Ergot alkaloids; Molecular connectivity;

Flow injection renewable drops spectrofluorimetry for sequential determinations of Vitamins B1, B2 and B6 by Feng Feng; Kemin Wang; Zezhong Chen; Qiting Chen; Jiediao Lin; Shasheng Huang (187-193).
A novel optical chemical sensor based on the dynamic liquid drops combined with flow injection-solid phase has been developed for continuous and sequential determinations of the mixture of Vitamin B1, Vitamin B2 and Vitamin B6. The design and characteristics of the sensor system are described. The dynamically growing and falling drops serve as windowless optical cells. The adsorption, desorption and quantitative determinations of VB1, VB2 and VB6 were carried out based on selective adsorption of Sephadex CMC-25 and different fluorescence characteristics of VB2, VB6 in the basic solutions. The optimum analytical conditions for compound Vitamin B assay have been established. Under these conditions, linear calibration curves were obtained over the range of 0.01–8.00, 0.01–10.00 and 0.01–3.00 μg/ml for VB1, VB2 and VB6 with the limits of determination of 0.008, 0.005 and 0.006 μg/ml, respectively. This method has been applied in the determination of synthetic mixture of VB1, VB2, VB6 and Vitamin B compound tablets with satisfactory results. The technique, which has been described, provides a simple, effective and sensitive method to assay the biological samples.
Keywords: Flow injection; Droplet sensor; Sephadex; Vitamin B; Spectrofluorimetry;

The charge state of Fe in iron-gall inks was studied by 57Fe Mössbauer spectroscopy. Three ancient manuscripts from the 16th century and a set of model samples were characterized. The chemical fingerprint was found to be well defined for the ancient manuscripts whereas the model samples show a larger spread of chemical states. Two different modes of Mössbauer spectroscopy were used in this work: (1) the detection of γ-quanta in the usual transmission mode and (2) the detection of conversion electrons in backscattering geometry in a special parallel plate avalanche counter. The use of these two measuring modes allowed to reveal differences between the chemical features of the core and the surface of the iron-gall ink structures.

Rank annihilation factor analysis combined with the optimization of kinetic parameter is adopted to resolve the two-way kinetic-spectral data measured online from chemical reactions. To a multi-step reaction whose intermediate process is complicated and reaction order is fractional, the reaction order and rate constant of the first step can be determined without the knowledge of the kinetic model of the reaction. Taken a three-step reaction as an example, the synthetic data has been resolved and its effectiveness was proved. When the approach is applied to the analysis of practical reaction systems such as alkaline hydrolysis of phenyl benzoate, oxidization of sodium bromide by potassium permanganate and electro-degradation of sunset yellow, reliable results are obtained.
Keywords: Rank annihilation factor analysis (RAFA); Optimization; Kinetic-spectral data; Reaction order; Rate constant;

Author Index (211-212).